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Time-Dependent ATR-FTIR Spectroscopic Studies on Solvent Diffusion and Film Swelling in Oil Paint Model Systems
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  • Lambert Baij*
    Lambert Baij
    Van‘t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090GD Amsterdam, The Netherlands
    Conservation and Restoration, Rijksmuseum Amsterdam, PO Box 74888, 1070DN Amsterdam, The Netherlands
    *E-mail: [email protected] (L.B.).
    More by Lambert Baij
    Orcidhttp://orcid.org/0000-0002-9196-2955
  • Joen J. Hermans*
    Joen J. Hermans
    Van‘t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090GD Amsterdam, The Netherlands
    Conservation and Restoration, Rijksmuseum Amsterdam, PO Box 74888, 1070DN Amsterdam, The Netherlands
    *E-mail: [email protected] (J.J.H.).
    More by Joen J. Hermans
    Orcidhttp://orcid.org/0000-0002-9446-9904
  • Katrien Keune
    Katrien Keune
    Conservation and Restoration, Rijksmuseum Amsterdam, PO Box 74888, 1070DN Amsterdam, The Netherlands
    More by Katrien Keune
  • Piet D. Iedema
    Piet D. Iedema
    Van‘t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090GD Amsterdam, The Netherlands
    More by Piet D. Iedema
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Macromolecules

Cite this: Macromolecules 2018, 51, 18, 7134–7144
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https://doi.org/10.1021/acs.macromol.8b00890
Published September 7, 2018

Copyright © 2018 American Chemical Society. This publication is licensed under CC-BY-NC-ND.

Abstract

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In the restoration of paintings, solvent diffusion and swelling of polymeric oil paint binding media are important factors to consider. Common cleaning methods with organic solvents or aqueous solutions could lead to undesirable physicochemical changes in the paint in the long term, though the extent of this effect is not yet clear. We used tailored nonporous model systems for aged oil paint to measure paint swelling and solvent diffusion for a wide range of relevant solvents. Using dynamic mechanical analysis (DMA), the glass transition temperature of our model systems was found to be close to room temperature. Subsequently, with a custom sample cell and time-dependent attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, we were able to accurately track swelling and diffusion processes in the polymer films. To quantify the spectroscopic data, we developed a model that completely describes the solvent migration process, including significant film swelling and non-Fickian solvent diffusion. The relation between solvent properties, the diffusion coefficient, and the swelling capacity proved to be rather complex and could not be explained using a single solvent parameter. However, it was found that strongly swelling solvents generally diffuse faster than weakly swelling solvents and that pigmentation does not significantly influence solvent diffusion. These results contribute to a better understanding of transport phenomena in paintings and support the development of improved paint restoration strategies.

Copyright © 2018 American Chemical Society

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Introduction

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Paintings are exposed to organic solvents or aqueous solutions during restoration or cleaning procedures. These cleaning actions may induce many types of undesirable chemical changes, (1−4) which are often not immediately visible to the restorer. At present, our understanding of the influence of solvent treatment on fundamental chemical processes is too limited to make a reliable estimate of the long-term effects of common restoration procedures. For example, it is unclear to which depth solvents typically penetrate during cleaning and to what degree soluble components are transported between paint layers. Although the rate of transport processes of soluble components can vary considerably between paintings and cleaning methods, (5) the degree of paint swelling and the rate of solvent diffusion are both important factors.
The binding medium in oil paint consists of triacylglycerides (TAGs) that have a high degree of unsaturation on their fatty acid chains. As it dries through autoxidation, the oil forms a strongly cross-linked polymer network. (6−17) The presence of potentially reactive metal-containing pigments and a variety of additives further adds to the complexity of aged oil paint. Oil paints can be considered metastable polymers, subject to slow chemical and physical deterioration processes that affect the appearance and structural integrity of oil paintings.

Scheme 1

Scheme 1. Formation of Ionomers by Copolymerization of Linseed Oil with Metal Sorbatea
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aLinseed oil is represented by a typical structure of a triacyl glycerol (TAG) Unit. The depicted carboxylate coordination geometry does not reflect the real (unknown) geometry.

We have previously demonstrated that mixtures of oil binding media and ZnO or PbO gradually form an ionomer-like structure. (18,19) In such an ionomer structure, metal ions originating from pigments or driers are distributed throughout the polymerized oil network and associated with carboxylic acid groups. An ionomer-like structure has been detected in many oil paint layers that contain lead or zinc ions. We have developed ionomer model systems for aged oil paint to study the molecular structure and dynamic processes in paintings. These models consist of linseed oil copolymerized with lead or zinc sorbate (2,4-hexanedieneoate) complexes, as illustrated in Figure 1. In previous work, small-angle X-ray scattering (SAXS) measurements on these ionomer systems indicated that metal carboxylates form clusters in oil polymers, (19) and we showed that the reaction of saturated fatty acids with network-bound metal carboxylates is a rapid process that is accelerated by solvent swelling. (1) In this study of solvent behavior, we have employed the same model systems for aged oil paint (Pbpol and Znpol) and included films of pure polymerized linseed oil (pLO) and films pigmented with ZnO (ZnO-LO) for comparison. The pigmented system has the same ionomeric structure in the polymer binding medium as Znpol (19) and differs from the pure ionomer system only in the presence of ZnO pigment particles.

Figure 1

Figure 1. Illustration of the measurement cell used for time-dependent ATR-FTIR measurements of polymer films in contact with solvents. The spring provides a small pressure to keep a constant contact between the sample and the ATR crystal as solvents swell the sample, while the porosity of the metal disk ensures unhindered diffusion of the solvent through the sample film.

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When investigating the solvent diffusion and swelling behavior of a polymer, it is important to know whether the system is studied above or below the glass transition temperature (Tg). It is well-known that the Tg of polymers can strongly influence solvent diffusion behavior. Above the Tg (in the rubbery region), polymers generally show Fickian (ideal) sorption, whereas polymers can show strong deviations from ideal behavior below their Tg (glassy regime). (20) Therefore, we have studied the viscoelastic properties of our model systems and used dynamic mechanical analysis (DMA) to determine their Tg.
Time-dependent attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to follow swelling and diffusion processes in our ionomeric model systems. (21) This approach has been applied before to study single- or multicomponent solvent diffusion, (22−24) solute diffusion from an external medium into a polymer, (25,26) polymer chain interdiffusion, (27,28) and metal ion diffusion in ionomers. (27) Diffusion and swelling by organic solvents (29−32) and water (33−37) in polymer blends based on linseed oil has been measured before using a variety of methods. For ionomers, data on diffusion and swelling are mainly limited to water and alcohols for fuel cell applications. (38−42) In most of these studies, polymer films are cast from solution (e.g., by spin-coating or dip-coating) directly onto the ATR elements as thin films to ensure a good contact. However, polymer films based on drying oils are insoluble due to their high degree of cross-linking, and our model systems did not adhere well to ATR elements. To meet the challenge of maintaining a reproducible and constant contact between polymerized oil films and the ATR crystal during solvent swelling, we developed a measurement setup that can be combined with a standard diamond ATR module in which a very small constant pressure is applied on the sample during solvent exposure. The method allows the measurement of dynamic processes in unsupported film-like materials with at least one smooth surface (e.g., paints, polymers, gels, or skin). Finally, to fully describe the process of solvent sorption in oil-based polymers, we have developed a combined diffusion/swelling model based on a polymer fraction dependent diffusion coefficient.
Combining new insights into the viscoelastic properties of oil paint model systems and the swelling and diffusion behavior of water and other solvents, this work aims to provide a better understanding of solvent action on oil paints to support the development of improved conservation and restoration strategies.

Experimental Section

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Sample Preparation

Metal sorbate complexes were synthesized by dissolving 550 mg of sorbic acid (Aldrich, 99+%) with 1 mL of triethylamine (Sigma-Aldrich, >99%) in 20 mL of demineralized water at 50 °C. The addition of 1.0 g of Zn(NO3)2·6H2O (Sigma-Aldrich p.a.) or 1.1 g of Pb(NO3)2 (Sigma-Aldrich, >99%) dissolved in 5 mL of water resulted in immediate precipitation of the white product. After stirring for 20 min, the product was separated by vacuum filtration, washed with water followed by acetone, and dried overnight at reduced pressure. The metal sorbate salts were stored under an inert atmosphere to prevent oxidation.
Binding medium model systems for diffusion studies Znpol-std and Pbpol-std were made by grinding 250 mg of zinc sorbate or an equivalent molar amount of lead sorbate with 1750 mg of cold-pressed untreated linseed oil (LO, Kremer Pigmente) to a smooth paste with mortar and pestle. This concentration of metal ions is equivalent to a molar metal carboxylate to ester ratio (COOM/COOR) of 0.29 and corresponds to roughly 420 mM Zn2+/Pb2+ in the uncured sample mixture. For DMA analysis, Znpol and Pbpol samples with constant total acid group concentration and increasing metal neutralization were made according to Table S1. The mixtures were applied to 50 × 75 mm2 glass slides and spread with a draw-down bar to achieve a wet thickness of 190 μm. The layers were cured overnight in an air-circulated oven at 150 °C, resulting in transparent homogeneous dark orange films with a thickness around 140 μm. Films of pure polymerized LO (pLO) were prepared in a similar fashion. Model paint samples for zinc (ZnO-LO) were made by grinding ZnO with cold-pressed untreated LO in a 1:1 (w/w) ratio to a smooth paste with mortar and pestle. The wet sample thickness was 190 μm, and the samples were dried at 60 °C in air for 7 days. For all measurements, 5 × 5 mm2 squares of the films were cut and lifted off the glass support. The thickness of each sample was measured with a digital micrometer accurate to 1 μm prior to diffusion measurements.

Experimental Setup

DMA analysis was performed on a PerkinElmer Pyris Diamond DMA in tensile mode using a temperature range from −50 to 150 °C and a heating rate of 2 °C/min under a N2 atmosphere. For all samples, an amplitude of 10 μm, a minimum tension/compression force of 10 mN, a minimum tension/compression force gain of 1.1 mN, and a force amplitude default value of 500 mN were used. The glass transition temperature (Tg) was obtained from the maximum value of tan δ. For Pbpol, two Gaussian functions and a baseline were fitted to determine both Tg and Tc (see Figure S1).
ATR-FTIR spectra were measured on a PerkinElmer Frontier FT-IR spectrometer fitted with a Pike GladiATR module with a diamond ATR crystal (ø = 3 mm). Spectra were recorded at the bottom of the sample every 10, 30, or 60 s (depending on the diffusion rate of the solvent) at 4 cm–1 resolution and averaged over four scans. To measure spectra of polymer samples during exposure to solvents or solutions, a custom-built stainless steel cylinder was used as illustrated in Figure 1. The cell volume was sealed with two solvent-resistant O-rings between the top plate and the pressure clamp of the ATR module. The polymer sample was covered by a ø = 10 mm porous sintered metal disk, and a small but constant pressure was applied to the polymer sample by a spring placed between the pressure clamp of the ATR module and the porous disk. An inlet in the cylinder allowed for the addition of liquids to the sample chamber with a syringe. The inlet was kept sealed with parafilm during measurements to avoid solvent evaporation. In all experiments, analytical grade solvents were used. Automated spectrum collection was started as soon as solvent was injected into the measurement cell.

Data Processing

Diffusion curves in polymer films were measured of cyclohexane (904 cm–1), ethanol (879 cm–1), acetone (529 cm–1), D2O (2510 cm–1), methanol-d4 (2485 cm–1), DCM (1265 cm–1), and toluene-d8 (541 cm–1). The wavenumbers in parentheses for each solvent refer to the positions of a characteristic solvent band that was sufficiently isolated for accurate band integration. The time-dependent band areas were calculated with PerkinElmer TimeBase software using a baseline anchored to the spectrum to either side of a band and required no further processing before model fitting. FTIR spectra of Znpol at maximum solvent swelling for all solvents are shown in Figure S2. The reproducibility of the diffusion curves was investigated by repeating the acetone diffusion experiment eight times on Znpol films with thicknesses varying between 124 and 159 μm. The standard deviation in the thickness measurement, caused by uneven sample surfaces, was ∼10%. The standard deviation in the swelling factor was determined by repeating the experiment for acetone nine times and was found to be 0.13. We have applied a method to calculate the 95% confidence intervals of the fitting parameters using a least-squares procedure (43) (see the Supporting Information). The 95% confidence interval in DFick resulting from the parameter estimation procedure was below 4%, whereas for Deq the interval was between 27% and 34%.

Results and Discussion

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DMA Analysis of Model Paint Films

The viscoelastic properties of the model ionomer and paint systems were characterized by DMA. Figure 2 and Table 1 present glass transition temperature and cross-link density data for ionomer films with increasing metal content (from 0% neutralization to 100%) as well as pure polymerized linseed oil (pLO) and ZnO-based paint (ZnO-LO). The Tg values were obtained from the maximum of the tan δ plots (note that tan δ = E″/E′, where E″ and E′ are the loss and storage modulus values, respectively).

Figure 2

Figure 2. DMA thermograms showing (a) Mpol-0, pLO, and ZnO-LO and (b) Znpol and (c) Pbpol ionomer systems with increasing metal content.

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Table 1. Tg, Tc, and νe Values for pLO, ZnO-LO, Mpol-0, Znpol, and Pbpol Ionomer Systems with Increasing Metal Contenta
sampleCOOM/COOHTg (°C)Tc (°C)νe (mol/cm3)
pLO08 2.1 × 10–5
Mpol-0010 3.5 × 10 –4
Pbpol-320.3233318.5 × 10–4
Pbpol-640.6420531.2 × 10–3
Pbpol-100117614.0 × 10–3
Pbpol-std111674.8 × 10–3
Znpol-320.3211 6.3 × 10–4
Znpol-640.6410 6.8 × 10–4
Znpol-10019 8.6 × 10–4
Znpol-std116 2.2 × 10–3
ZnO-LO 21 5.6 × 10–4
a

COOM/COOH refers to the proportion of sorbic acid groups that is coordinated to a metal ion (Zn2+ or Pb2+).

At present, there is some uncertainty in the literature on the Tg of linseed oil-based paint films. Previous studies reported values between 0 and 10 °C, (44−47) while Ploeger et al. (48) observed an increase to around 40 °C upon aging of the paint films. LO polymers modified with styrene (49) or epoxy groups (50) tend to have a higher Tg. We found a Tg for pLO at 8 °C. The Tg is raised slightly to 10 °C upon copolymerization with sorbic acid (Mpol-0, essentially an “empty” ionomer), suggesting possible hydrogen bonding between adjacent acid groups. (51)
For the lead ionomers (Pbpol), the characteristic behavior of a two-phase system was observed. It is known that in a relatively apolar polymer matrix the introduction of ionic groups can lead to the formation of ionic aggregates, (52,53) giving rise to ion-poor (i.e., polymer matrix) and ion-rich (i.e., metal carboxylate cluster region) phases. The tan δ peak at low temperature is attributed to the bulk Tg, while the peak at higher temperatures corresponds to the glass transition in the ion-rich regions (Tc). This Tc peak grows at the expense of the main glass transition peak and shifts to higher temperatures as the ion content increases. In contrast to Tc, the “matrix” Tg for Pbpol shifts to lower temperatures when the ion content is increased. The shifts in Tg and Tc suggest that there are changes in the structure or composition of the ion-poor and ion-rich phases in Pbpol with increasing lead content, not just in the concentration of ion-rich clusters. In previous research, SAXS analysis on Pbpol samples showed that long-range inhomogeneity in lead concentration exists at low neutralization levels, while lead ions tended to be grouped in smaller and more defined ion-rich clusters at high neutralization. (19) In line with these observations, to explain the trends in Tg and Tc we propose that the lead carboxylate concentration (and therefore also the cross-link density) decreases in the bulk polymer with increasing neutralization leading to lower Tg values, while at the same time the ion-rich phases become more enriched in lead, leading to a rise in Tc.
Considering Znpol, it was observed that increasing the zinc content has no significant effect on the Tg values. No Tc was observed for Znpol in the measured temperature range, though Figure 2b seems to suggest there could be a transition (>150 °C) that is related to ion cluster relaxation. A very high Tc would be in agreement with the fact that the formation of crystalline zinc soaps in ionomeric polymer systems is much slower than the formation of lead soaps. (1,54) The tan δ peaks close to room temperature decreased strongly in height with increasing zinc content, which is thought to reflect a decreasing mobility of the polymer chain segments. (55) While decreasing chain mobility seems plausible with increasing zinc carboxylate content, SAXS measurements on Znpol systems showed no clear trend in either the concentration or the size of ionic domains with increasing zinc neutralization. (19) Clearly, more DMA and SAXS experiments on systems with a wide neutralization range are necessary to clarify the structural details of linseed oil-based ionomers.
The Tg of ZnO-LO was measured at 21 °C, even though Phenix et al. (46) could only detect “progressive, general thermal softening” in 16 year old ZnO paint. The slightly higher Tg for ZnO-LO might be explained by the lower degree of curing for ZnO-LO (1 week at 60 °C) compared to Znpol (17 h at 150 °C).
The elasticity modulus E′ in rubbery plateau region at 140 °C (see Figure S3) was used to calculate cross-link densities (νe) according to (56)
(1)
The calculated values for νe as a function of metal carboxylate concentration (COOM/COOR) are shown in Figure 3. For both Znpol and Pbpol, νe increases significantly with metal content. Ionic cross-links thus contribute significantly to the measured storage modulus and calculated cross-link densities, despite the fact that the unbound carboxylic acids in the not fully neutralized ionomers can also form “cross-links” by hydrogen bonding. In analogy with Weiss et al., (57) we also calculated a cross-link density by assuming that every metal sorbate unit forms an additional cross-link (νc) on top of the cross-link density of Mpol-0 and compared this with νe calculated from eq 1. It was found that νe was consistently higher than νc by approximately 5–20%. In the paper by Weiss et al., (57) two possible explanations are given for this high contribution of metal neutralization to νe: (1) Synergism exists between the ionic cross-links and molecular entanglements that yield a higher effective cross-link density than that based on a linear combination of the two effects. (2) Ionic clusters have a lower molar mass between cross-links than that calculated from the average chain length between simple contact ion-pair associations. Because we are currently primarily concerned with solvent behavior in these oil-based ionomers, the in-depth investigation of these hypotheses is beyond the scope of this paper.

Figure 3

Figure 3. Relation between ion content and νe as calculated by eq 1.

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Concluding, we established that our model systems have bulk Tg values close to room temperature. Therefore, it is expected that both Znpol and Pbpol will show Fickian-type solvent diffusion behavior. The effect of the Tc on solvent diffusion remains to be investigated.

Solvent Diffusion and Swelling in Model Paint Films

The diffusion and swelling behavior of seven solvents was investigated in Znpol, Pbpol, and ZnO-LO model systems. Solvent concentration profiles were obtained by integration of characteristic solvent IR bands. The maximum swelling capacity of each solvent was determined by monitoring the IR absorption bands corresponding to the linseed oil polymer. As solvent diffused into the volume probed by the IR beam, the concentration of polymer chains in that volume decreased according to a profile that mirrored the solvent diffusion profiles. Because it was shown previously (58) that FTIR spectroscopy can be used to measure swelling factors that are equivalent to those obtained from size measurements using a CCD camera, the relative difference in absorbance of the ester carbonyl band (1740 cm–1) at saturation and at t = (i.e., ΔA/A0) was used as a measure for the maximum degree of swelling (feq). Values for feq for all solvents and samples are given in Table 2.
Table 2. Values of Diffusion Coefficient at Equilibrium Swelling According to the Diffusion-Swelling Model (Deq) and Those with the Assumption of Fickian Diffusion (DFick)a
 ZnpolPbpolZnO-LO
solventDeq (10–11 m2/s)DFick (10–11 m2/s)feqDeq (10–11 m2/s)DFick (10–11 m2/s)feqDeq (10–11 m2/s)DFick (10–11 m2/s)feq
DCM57141.248141.146160.66
acetone154.90.73276.10.89167.50.47
toluene-d87.92.50.717.93.10.813.82.20.26
methanol-d43.71.00.601.80.720.562.31.50.24
ethanol1.60.430.891.20.400.871.10.500.41
cyclohexane0.280.140.240.26b0.11b0.45b0.0860.0520.18
D2O0.0590.0610.050.0640.0530.130.0380.0350.05
a

Diffusion parameters have been estimated at a 95% confidence interval and were found to vary between 27% and 34% for Deq and below 4% for DFick (see the Supporting Information). The standard deviation in the swelling factor is 0.13.

b

Measured at 40 °C.

A significant variation in the solvent swelling capacity was observed. DCM swelled the investigated model systems by more than a factor of 2, while water hardly swelled the oil polymer at all (approximately 5–10% volume increase for zinc and lead). The FTIR spectroscopic method for measuring equilibrium swelling accurately reproduced trends reported in the literature for solvent swelling of oil paints and confirms the low swelling capacity of water. (59,60) The trends in feq for different solvents are consistent between all three investigated polymers. It is noted that for low-swelling solvents such as cyclohexane and water the differences between Znpol and Pbpol are larger. In the case of cyclohexane in Pbpol, it was not possible to carry out the diffusion experiment at room temperature due to detachment of the rather stiff polymer film from the ATR crystal during solvent exposure. Therefore, this measurement was conducted at 40 °C. Despite the differences in viscoelastic properties that were measured with DMA, no significant differences in feq between Znpol and Pbpol were found (standard deviation in feq of ±0.13, see Experimental Section). However, ZnO-LO did exhibit consistently lower values for feq than the unpigmented ionomer films. This result is explained by the fact that the pigment particles do not contribute to the swelling of the system upon solvent absorption.

Fickian Diffusion Model

A Fickian diffusion model for ATR-FTIR has been developed by Fieldson and Barbari, (21) which allows for the calculation of diffusion parameters using the recorded IR spectra. Having established that the model systems under investigation have Tg values close to room temperature, we investigated the applicability of this Fickian diffusion model. A typical concentration profile of acetone in Znpol is shown in Figure 4. For ideal diffusion with a constant diffusion coefficient, Fick’s second law states
(2)
where C is the concentration of penetrant in the medium and D is the diffusion coefficient. A solution to this differential equation has been derived by Fieldson and Barbari (21) using appropriate boundary conditions for the geometry of an ATR-FTIR setup, making use of the exponential decay of the evanescent field of the IR beam into the sample and the Beer–Lambert law
(3)
in which
and
(4)
In this relation, γ is the inverse of the penetration depth dp of the IR beam into the sample. dp varies from 0.5 to 3.5 μm from 3500 to 500 cm–1 in our experiments, so with a typical film thickness around 150 μm the recorded spectra are representative for the bottom side of the film. Parameters n1 and n2 are the refractive indices of the polymer sample and ATR crystal, respectively, δ is the thickness of the film, θ is the angle of incidence of the IR beam (45°), and λ is the wavelength corresponding to the maximum of the characteristic IR band of the penetrant. For the experimental conditions described in this paper, the shape of the diffusion profile is very insensitive to the exact value of γ. Therefore, a single measured value for the refractive index of a Znpol film was assumed as a constant for all calculations. This model represents an ideal case of penetrant transport (i.e., negligible preferential interaction between the polymer and solvent), corresponding to a diffusion of penetrant that is on a much slower time scale than polymer chain relaxation. (20)

Figure 4

Figure 4. Diffusion profile for acetone in Znpol (square symbols) and fits of a standard (blue) and adapted (red) Fickian diffusion model to the data.

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Fitting eq 3 to the diffusion curve of acetone in Znpol, it is immediately clear that the ideal model is not capable of describing simultaneously the long delay until solvent signal is first detected as well as the sharp increase in solvent concentration that follows (see Figure 4, blue curve). Similar results were found for all investigated solvents and films (for instance, see Figure S4). While eq 3 is frequently applied to describe penetrant diffusion in polymers, our use of relatively thick films enhances the effect of potential polymer swelling during diffusion, and it causes a significant delay time (τd, the time necessary for solvent to reach the sampling volume). Therefore, using thick polymer films, it becomes easier to investigate deviations from ideal diffusion behavior.
To allow for the considerable delay time, τd, eq 3 was adapted such that
(5)
With this procedure, the swelling between 0 < t < τd is neglected, while Fickian diffusion is assumed at t > τd. The shifted Fickian model of eq 5 provided a near-perfect fit to the experimental concentration profiles, as shown in Figure 4. Corresponding diffusion coefficients DFick are listed in Table 2.
From the excellent match between the ideal diffusion model and the experimental concentration profiles at t > τd, it can be concluded that once the polymer is nearly completely swollen (i.e., only minor changes in polymer fraction), (near) Fickian diffusion behavior is observed in the measurement volume at the bottom of the film. However, film swelling does cause an significant increase in τd. This effect is easily observed by comparing the experimental τd values with values calculated with the common relation between δ and D, . The relation yields consistently lower τd values than observed experimentally, demonstrating that the ideal diffusion model needs to be replaced with a diffusion model that accounts for film swelling.
In paint restoration, the swelling of paintings is an important phenomenon. It is well-known that aged oil paint can swell significantly during cleaning and varnish removal. (61) Especially with the relatively short solvent application times typical for restoration work, one might argue that equilibrium swelling (feq) is never reached, except in the areas of the paint closest to the surface. The initial stages of solvent diffusion are therefore especially relevant to understand the potential effects of restoration treatments on paintings, adding to the importance of developing a model that describes the entire swelling and diffusion process.

Diffusion-Swelling Model

Construction of the Diffusion-Swelling Model

In the model paint systems, sample swelling to more than twice the original dry volume occurred in the most extreme cases, corresponding to a polymer fraction decreasing from 1 to 0.5. Solvent swelling and diffusion in polymers is widely discussed in the literature. (62−66) The most comprehensive models are those based on the free-volume theory originally developed by Vrentas and Duda. (67,68) However, free-volume models contain many parameters that despite having physical meaning, are largely unknown. Therefore, we decided to employ the simplest model that accounts for a decreasing polymer volume fraction during swelling, using a variable diffusion coefficient. The functional form of this model is inspired on Cukier’s formula for diffusion in hydrogels (64) and describes a diffusion coefficient that is an exponential function of the polymer volume fraction ϕ as
(6)
Because D = D0 at ϕ = 0 (pure solvent), for hydrogels D0 has been interpreted as the diffusion coefficient of solvent molecules in their own environment (65) or at infinite dilution. (64) However, for systems swelling much less than hydrogels, the pre-exponential factor D0 should be considered as a fitting parameter. Parameter α has been correlated to the radius of solvent molecules. (64) For parameter β, values of 0.5 and 0.75 are mentioned by Amsden. (64) Given the limited range in polymer fraction ϕ for our samples, it was expected that one parameter describing its effect of diffusion would be sufficient, and we assumed β = 1, yielding a diffusion coefficient dependent only on D0 and α. As the diffusion coefficient at equilibrium swelling, Deq, is most relevant in the present case, eq 6 is rewritten as
(7)
Here, ϕeq is the polymer fraction at equilibrium (complete) swelling feq. Next, the swelling factor F is defined as
(8)
Here, υs is volume of solvent, υp is volume of polymer, and υtot is the total volume. The total polymer mass is assumed to occupy the same (partial) volume, υp, during swelling, while υs and υtot do increase. If cs is the molar solvent concentration, then υtot contains υtotcs moles of solvent of volume υs. Given the solvent density ρs and the solvent molar mass Ms, we know that υs contains υsρs/Ms moles of of solvent. Therefore
(9)
Combining eqs 8 and 9 gives the relation between swelling factor and molar solvent concentration
(10)
A method-of-lines numerical method was applied to solve the convective diffusion problem, as illustrated in Figure 5. We have followed a similar procedure as Bisschops et al. (69) where diffusion of solvent caused by a gradient in solvent concentration is described on a moving grid. The initial thickness of the pure polymer film at t = 0 is δ(0). As solvent is penetrating from the surface into the polymer, the polymer starts to swell, causing the polymer/solvent interface to move in opposite direction. The initial polymer slab is divided in a number of layers of equal thickness, Δx0, at t = 0; hence, the grid points are at equal distance. During swelling, at 0 < t < tend, these grid points move with the same velocity as the polymer moves outward (the moving grid) until solvent saturation at t = tend. During swelling, the total film thickness, δ, increases at a velocity equal to that of the interface. At t = 0, diffusion of solvent starts to occur under the influence of a concentration gradient, with an equilibrium concentration cs* at interface, and cs = 0 everywhere else, as depicted in Figure 5, left pane. This equilibrium concentration is calculated from the final swelling factor using eq 10. At 0 < t < tend, a solvent concentration gradient exists as schematically shown in the center pane of Figure 5. Note that eq 10 implies that a higher solvent concentration corresponds to a higher swelling coefficient. Therefore, the different polymer layers are expanding at different rates as long as a concentration gradient is present.

Figure 5

Figure 5. Illustration of the method-of-lines model with elements that increase in thickness during swelling. The concentration cs* is the concentration of solvent at equilibrium or maximum swelling.

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The convective diffusion equation to be solved differs from the usual form, as it has to account for simultaneous swelling. Consider a volume element at time t and solvent concentration c (we drop the subscript s for the remainder of this derivation) of volume V = aΔx, where Δx is its thickness (Δx0 at t = 0) and a is its cross-sectional area. This volume element contains cV moles of solvent. At time t + dt, the solvent concentration is c + Δc, the thickness is x + Δx′, and the amount of solvent is cV + Δ(cV). By evaluating this change in amount of solvent to the difference in influx and outflux at both sides of the volume element, during Δt through surface a, we can write the finite difference equation
(11)
With Δt → 0 and substituting V, we obtain the first order differential equation
(12)
In the absence of swelling, Δx remains constant during the diffusion process and equal to Δx0. With an infinite number of lines, (i.e., letting Δx0 → 0), eq 12 reduces to the usual second-order differential equation for convective diffusion of eq 2.
In the presence of swelling, we can make use of the relation between the swelling factor and thickness
(13)
The relation between swelling factor and solvent concentration in eq 10 allows writing cΔx as a function of c only. After differentiation, the left-hand side of eq 12 then becomes
Thus, letting Δx0 → 0, eq 12 can be written as the second-order partial differential equation
(14)
Note that both the diffusion coefficient D (eq 7) and the swelling factor F (eq 10) are functions of t and x. This formulation of the convective diffusion equation accounts for two effects of swelling: (1) the stretching of the polymer layers that reduces the solvent concentration gradient; (2) the dilution of penetrant in the polymer by an increase in volume. The new diffusion-swelling model is more general than eq 3 and includes both non-Fickian and Fickian diffusion. For Fickian diffusion, one would assume constant D and film thickness, which yields results identical to eq 2.
The partial differential equation in eq 14 was solved using the method-of-lines as illustrated in Figure 5 with the following boundary conditions
It is important to note that similar to what was assumed by Bisschops et al., (69) the concentration gradient is defined with respect to a moving grid. Thus, the finite difference version of eq 14 is solved for each layer of increasing thickness, and at each integration step the thickness of the slabs is updated.
Finally, we derive a relation between the concentration of solvent and the measured IR absorbance, as an alternative to eq 3, which assumes a constant diffusion coefficient and no sample swelling. The starting point for this derivation is eq 15, relating the absorbance of the IR band of the penetrating solvent over time, A(t), to the changing concentration profile in the film, c(t,x). This relation is based on the decay of the evanescent electric field strength associated with the IR beam (21)
(15)
Using an expression for the relative IR absorbance and concentration allows us to use a simplified representation (eq 15) instead of the full equation used by Fieldson and Barbari. (21) In eq 15, the factor K is determined by several optical properties like the extinction coefficient and refractive indices. Using the ratio A(t)/A∞, factor K vanishes, while the parameter γ is still defined as in eq 4. Because of the fast exponential decay of the evanescent wave (e–2γx), the concentration at the bottom of the film c(t, x = 0) accounts for the measured absorbance A(t). The relative change of solvent concentration over time can now be expressed as
(16)
In this model, A(t) is the area of an IR band of the penetrant at time t, and A(∞) is the band area when the sample is completely saturated with penetrant.

Application of the Diffusion-Swelling Model

Figure 6 shows the experimental solvent profiles and fitted curves according to the diffusion-swelling model with nonconstant diffusion coefficients. In all cases, an excellent agreement was found between the experimental and fitted curves. The values obtained for Deq are listed in Table 2. The trend in the values of solvent diffusion coefficients is similar to those determined by measurements of paint swelling on polymerized linseed oil films reported by Stolow. (70) For water, the measured diffusion coefficients are of the same order of magnitude as the values reported for water diffusion in pigmented alkyd paints (37) and vapor diffusion in historical samples of Prussian blue and basic lead carbonate paints (33) (in the range (1.2–7.7) × 10–13 m2/s).

Figure 6

Figure 6. Diffusion profiles of seven solvents in Pbpol, Znpol, and ZnO-LO films of 135–160 μm thickness and a metal ion concentration in the polymer films of roughly 420 mM. Solid black lines represent best fits of the two-parameter diffusion-swelling model (eq 7) as employed in the convective diffusion equation (eq 14).

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An important achievement of the diffusion-swelling model is that unlike the (adapted) Fickian model, it gives an adequate prediction of τd. The values for α obtained are listed in Table S4 and range between 0 and −19. The fact that α ≤ 0 indicates that the diffusion rate increases with decreasing polymer fraction ϕ during the transition from dry to swollen polymer. The relation between D and ϕ for solvent diffusion in Znpol is shown in Figure 7 (for Pbpol and ZnO-LO, see Figure S5), which also highlights the significant differences in the equilibrium swelling factor, with feq ranging between 0.05 for D2O and 1.2 for DCM. The minimal values for D (Dmin), in the dry state, are in the order of 10–13 m2 s–1, which is still higher than typical diffusion coefficients found for glassy polymers. (71) This finding is in agreement with the Tg values close to room temperature that we measured for dry Znpol, Pbpol, and ZnO-LO. In general, similar diffusion coefficients (varying less than a factor of 2) were found for all three investigated model paint systems, indicating that small differences in chemical composition do not significantly affect the diffusivity. It is especially noteworthy that the introduction of 50 wt % of pigment in ZnO-LO does not lead to strongly altered diffusion behavior. This result indicates that in intact oil paint films (i.e., paint films without cracks) solvent diffusion around pigment particles is relatively fast, and the rate of diffusion is mostly determined by the properties of the organic polymer matrix.

Figure 7

Figure 7. Diffusion coefficient in Znpol film versus polymer fraction ϕ, calculated using the diffusion-swelling model, eq 8, using parameters in Tables S3 and S4.

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Figure S6 compares the diffusion coefficients obtained using the adapted ideal model DFick and those at equilibrium swelling obtained using the diffusion-swelling model (Deq). In the adapted ideal model (eq 5), swelling effects above or inside the measurement volume after the first detection of solvent signal that slow down solvent migration are not taken into account. The diffusion-swelling model does incorporate this swelling, and therefore one expects Deq > DFick. Indeed, Deq is consistenly larger than DFick, with the difference being largest for the most swelling solvent (DCM) and very small for the least swelling solvent (D2O). These observations show that even though only minor swelling occurs after solvent signal is first detected, a variable diffusion coefficient is necessary to accurately model the solvent diffusion process close to equilibrium swelling. However, the simple adapted ideal model can still be used to calculate a reasonable approximation of the solvent diffusion coefficient. Tables S3 and S4 list the obtained diffusion parameters Deq and α from eq 7 values with their 95% confidence intervals for all paint models.
Having established that the swelling-diffusion model accurately describes solvent transport in oil paint systems, we can now compare diffusion parameters of the different solvents. The complexity of the solvent diffusion process is illustrated by the fact that some of the faster diffusing solvents like DCM and toluene have the highest molecular weight and that toluene and cyclohexane have very different diffusion rates despite having a similar structure. Moreover, the two slowest diffusing solvents—water and cyclohexane—are the most and least polar solvents and have the smallest and largest molecular radius in the set.
According to Amsden, (64) the parameter α of eq 6, which determines how strongly the solvent diffusion coefficient changes with polymer fraction, is related to the molecular radius of the diffusing molecule. The fitted values of α are plotted versus the molecular radius of the solvent molecules in Figure S7. With this solvent set, we did not find a significant correlation between molecular radius and α. Because our set of solvent consists of a limited range of molecular radii and very diverse solvent properties, it is necessary to consider different solvent properties to explain the differences in diffusion behavior. Stolow (70) correlated kinematic viscosity ν (absolute viscosity η divided by density ρ) and the diffusion coefficient. As illustrated in Figure S8, our findings confirm this correlation, with the more slowly flowing solvents having the lowest diffusion coefficients. Water deviates from this trend with a diffusion rate that is much slower than what is expected based on its kinematic viscosity.
Historically, equilibrium swelling data have been used to quantify diffusion behavior in paints. (70) Additionally, a high degree of swelling is associated with an increased risk of pigment loss during oil paint cleaning treatments. (30)Figure 8 shows a logarithmic plot of Deq versus feq, showing that solvents with a high swelling capacity are indeed generally diffusing faster. Alcohols exhibit relatively strong swelling compared to their moderately fast diffusion. These results confirm that swelling studies can be a useful indication of diffusion behavior of solvents in linseed oil-based paints. However, it is important to emphasize that accurately describing diffusion phenomena in paint is not straightforward.

Figure 8

Figure 8. Correlation of equilibrium swelling factor, feq, with Deq. Lower swelling generally leads to slower diffusion. Error bars calculated as described in the Supporting Information.

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The experiments described in this work have practical implications for paintings restoration. Disregarding potential reactivity between the solvent and paint components, it is often desired to minimize mechanical stress and limit the volume of paint material that is affected by a solvent during cleaning. In this light, both water and aliphatic hydrocarbons like cyclohexane offer a combination of two useful properties: low swelling power and slow diffusion. As water and aliphatic hydrocarbons are at opposite ends of the polarity scale, it should be possible to remove a broad range of soiling materials from the surface of oil paintings with these two solvents. The risk of mechanical damage can be further reduced by making use of tailored gel systems for oil paint cleaning. (72,73) To this end, we would encourage the development of gel systems that can be loaded with aliphatic solvents, solvent mixtures, or even microemulsions that allow precise tuning of solvent polarity. Finally, the methods described here can be extended to study paint swelling and solvent diffusion for porous paint and mixtures of solvents.

Conclusion

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Paintings are exposed to organic solvents and aqueous solutions during restoration treatments, which may lead to chemical alterations within the paint layers and altered viscoelastic properties of the paint. We have characterized linseed oil based binding medium models with DMA and found viscoelastic properties similar to classical ionomers. Ionomers containing zinc show gradual broadening of tan δ with increasing metal content whereas lead ionomers show characteristic behavior of matrix- and ion-cluster relaxation. In all cases, Tg is only weakly influenced by metal content.
Accurate concentration profiles of solvents and water in model paint samples were measured successfully using ATR-FTIR spectroscopy. Both an adapted Fickian diffusion model and a diffusion-swelling model incorporating the effect of film swelling on diffusion were used to describe the experimental data. In contrast to the adapted Fickian diffusion model, the considerable delay time observed for the relatively thick films was successfully predicted by the diffusion-swelling model. With the diffusion-swelling model, it was found that the solvent diffusion coefficients of solvents increase during paint swelling. No single solvent parameter was sufficient to explain the measured trend in solvent swelling or diffusion rate. However, strongly swelling solvents (e.g., acetone) generally diffuse faster than weakly swelling solvents (e.g., water).

Supporting Information

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b00890.

  • Details on the composition of samples, the analysis of DMA and FTIR spectroscopy data and the procedure for error estimation; additional data tables with fit parameters and figures showing the correlation between fit parameters and solvent/polymer properties (PDF)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Authors
    • Lambert Baij - Van‘t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090GD Amsterdam, The Netherlands;  Conservation and Restoration, Rijksmuseum Amsterdam, PO Box 74888, 1070DN Amsterdam, The Netherlands;  Orcidhttp://orcid.org/0000-0002-9196-2955;  Email: [email protected]
    • Joen J. Hermans - Van‘t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090GD Amsterdam, The Netherlands;  Conservation and Restoration, Rijksmuseum Amsterdam, PO Box 74888, 1070DN Amsterdam, The Netherlands;  Orcidhttp://orcid.org/0000-0002-9446-9904;  Email: [email protected]
  • Authors
    • Katrien Keune - Conservation and Restoration, Rijksmuseum Amsterdam, PO Box 74888, 1070DN Amsterdam, The Netherlands
    • Piet D. Iedema - Van‘t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090GD Amsterdam, The Netherlands
  • Author Contributions

    L.B. and J.J.H. contributed equally.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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The authors thank Dr. Hans Poulis, Lijing Xue, and Frans van Oostrum for use of the DMA equipment and Prof. Kim McAuley for useful discussions. This research was carried out within the framework of the NANORESTART project funded by the European Union’s Horizon 2020 research and innovation program under Agreement No. 646063.

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    The formation of metal soaps is a major problem for oil paintings conservators. The complexes of either lead or zinc and fatty acids are the product of reactions between common pigments and the oil binder, and they are assocd. with many types of degrdn. that affect the appearance and stability of oil paint layers. Fourier transform IR spectroscopy (FTIR) reveals that a paint sample from The Woodcutter (after Millet) by Vincent van Gogh contains two distinct zinc carboxylate species, one similar to cryst. zinc palmitate and one that is characterized by a broadened asym. stretch COO- band shifted to 1570-1590 cm-1. This observation has been made in many paintings. Although several hypotheses exist to explain the shifted broad carboxylate band, these were not supported by exptl. evidence. In this paper, expts. were carried out to characterize the second zinc carboxylate type. It is shown that neither variations in the compn. of zinc soaps (i.e. zinc soaps contg. mixts. of fatty acids or metals) nor fatty acids adsorbed on pigment surfaces are responsible for the second zinc carboxylate species. X-Ray diffraction (XRD) and FTIR anal. indicate that the broad COO- band represents amorphous zinc carboxylates. These species can be interpreted as either non-cryst. zinc soaps or zinc ions bound to carboxylate moieties on the polymd. oil network, a system similar to ionomers. These findings uncover an intermediate stage of metal soap-related degrdn. of oil paintings, and lead the way to improved methods for the prevention and treatment of oil paint degrdn.
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    Hermans, J. J.; Keune, K.; van Loon, A.; Corkery, R. W.; Iedema, P. D. Ionomer-like structure in mature oil paint binding media. RSC Adv. 2016, 6, 93363– 93369,  DOI: 10.1039/C6RA18267D
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    Ionomer-like structure in mature oil paint binding media
    Hermans, Joen J.; Keune, Katrien; van Loon, Annelies; Corkery, Robert W.; Iedema, Piet D.
    RSC Advances (2016), 6 (96), 93363-93369CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
    IR spectra of samples from oil paintings often show metal carboxylate bands that are broader and shifted compared to those of cryst. metal soap stds. (metal complexes of long-chain satd. fatty acids). Using quant. attenuated total reflection Fourier transform IR spectroscopy (ATR-FTIR), it is demonstrated that the broad metal carboxylate band is typically too intense to be explained by carboxylates adsorbed on the surface of pigment particles or disordered metal complexes of satd. fatty acids. The metal carboxylate species assocd. with the broad bands must therefore be an integral part of the polymd. binding medium. Small-angle X-ray scattering (SAXS) measurements on model ionomer systems based on linseed oil revealed that the medium contains ionic clusters similar to more classical ionomers. These structural similarities are very helpful in understanding the chem. of mature oil paint binding media and the potential degrdn. mechanisms that affect oil paintings.
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    Van Der Wel, G. K.; Adan, O. C. G. Moisture in organic coatings - a review. Prog. Org. Coat. 1999, 37, 1– 14,  DOI: 10.1016/S0300-9440(99)00058-2
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    Moisture in organic coatings - a review
    van der Wel, G. K.; Adan, O. C. G.
    Progress in Organic Coatings (1999), 37 (1-2), 1-14CODEN: POGCAT; ISSN:0300-9440. (Elsevier Science S.A.)
    A review, with 71 refs., is given on transport and equil. sorption of moisture in polymer films and org. coatings. Polymeric material forms the continuous phase of a coating and is therefore important for transport properties. Besides polymer, coatings consist of pigments and fillers and various additives, each of them affecting moisture transport. Firstly, in this paper typical transport and equil. characteristics of pure polymer films are covered, and secondly those of coatings, assimilating the impact of pigments, fillers and additives. Discrimination between Fickian and non-Fickian effects is usually based on the appearance of kinetic absorption curves. Several types of curve are dealt with, and models that describe these curves are discussed. These include "two-stage" sorption, "sigmoidal" sorption and "Case II" sorption. The common practice of fitting Fick's law to kinetic data by means of relaxation parameters is criticized. Transport kinetics are modelled on the basis of kinetic plots, thereby introducing relaxation parameters in Fick's diffusion law. Although these models describe moisture transport in polymers reasonably, these models imply a lot of "curve-fitting" without a clear mechanistic foundation. Equil. sorption of moisture in polymeric systems is reflected by their sorption isotherms. Type II and III isotherms of the BET classification are commonly encountered, together with linear isotherms according to Henry's law. The suitability of porous media adsorption models for polymeric systems is discussed. These models are treated in relation to interactions of water in polymers, since localized binding of water to specific groups may justify the use of these models. Pigments may lower moisture permeation, but non-ideality of pigmentation reduces this effect. Coating additives increase moisture soly., but only little is known in detail.
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    Fieldson, G. T.; Barbari, T. A. The use of FTi.r.-a.t.r. spectroscopy to characterize penetrant diffusion in polymers. Polymer 1993, 34, 1146– 1153,  DOI: 10.1016/0032-3861(93)90765-3
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    The use of attenuated total reflection FTIR spectroscopy to characterize penetrant diffusion in polymers
    Fieldson, G. T.; Barbari, T. A.
    Polymer (1993), 34 (6), 1146-53CODEN: POLMAG; ISSN:0032-3861.
    The diffusion of liq. water in polyacrylonitrile (I) was measured using FTIR attenuated total reflection spectroscopy. The measured diffusion coeffs. agreed well with those reported in the literature for high-activity water vapor in I. The test also demonstrated both the reproducibility and accuracy of FTIR expts. for measuring the diffusion coeff. The diffusion coeff. and the amt. of water sorbed at equil. were dependent on the temp. at which the films were treated.
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    Hong, S. U.; Barbari, T. A.; Sloan, J. M. Multicomponent diffusion of methyl ethyl ketone and toluene in polyisobutylene from vapor sorption FTIR-ATR spectroscopy. J. Polym. Sci., Part B: Polym. Phys. 1998, 36, 337– 344,  DOI: 10.1002/(SICI)1099-0488(19980130)36:2<337::AID-POLB12>3.0.CO;2-I
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    Multicomponent diffusion of methyl ethyl ketone and toluene in polyisobutylene from vapor sorption FTIR-ATR spectroscopy
    Hong, S. U.; Barbari, T. A.; Sloan, J. M.
    Journal of Polymer Science, Part B: Polymer Physics (1998), 36 (2), 337-344CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
    Diffusion coeffs. of toluene/methyl Et ketone (MEK) mixts. in polyisobutylene were measured at 50°C using vapor sorption FTIR-ATR (Fourier Transform IR Attenuated Total Reflectance) spectroscopy. For three mixt. compns., the diffusion coeffs. were detd. using a diffusion framework for ternary systems. The "crossterm" diffusion coeff. for MEK was found to be very small under the exptl. conditions studied here, while that for toluene was found to increase with increasing MEK concn. On the basis of this finding, a binary diffusion model was used to det. diffusion coeffs. for MEK over a wide range of mixt. compns. and the results compared well with those detd. from pure MEK transport data. Relative transport rates during integral sorption expts. with mixts. were used to explain the results.
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    Sammon, C.; Yarwood, J.; Everall, N. A FTIR-ATR study of liquid diffusion processes in PET films: Comparison of water with simple alcohols. Polymer 2000, 41, 2521– 2534,  DOI: 10.1016/S0032-3861(99)00405-X
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    A FTIR-ATR study of liquid diffusion processes in PET films: comparison of water with simple alcohols
    Sammon, C.; Yarwood, J.; Everall, N.
    Polymer (1999), 41 (7), 2521-2534CODEN: POLMAG; ISSN:0032-3861. (Elsevier Science Ltd.)
    An in-situ FTIR-ATR method for simultaneously obtaining both kinetic and structural information during liq. sorption into polymers was presented. The kinetics and diffusion profile of the sorption of liq. water and liq. methanol into poly(ethylene terephthalate) (PET) were compared and contrasted. The diffusion of water into PET was shown to follow Fickian kinetics, without significant swelling and the calcd. diffusion coeffs. (D) varied between 8.57 and 0.52 × 10-9 cm2 s-1 for a crystallinity range of 4-25%. The D values decreased non-linearly with the increase in crystallinity. The av. spherulitic crystal size was thought to play a significant role in detg. the rate of water sorption. Conversely, the sorption of liq. methanol was accompanied by significant swelling and crystn. and hence showed non-Fickian or anomalous kinetics. The sorption data were fitted to a dual-sorption model which indicated that the rate of diffusion of liq. methanol was faster than that of liq. water, probably due to the accompanying swelling. Increasing the level of crystallinity was shown to decrease the capacity for the polymer to swell and reduced the calcd. diffusion coeffs.
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    Guo, J.; Barbari, T. A. Unified dual mode description of small molecule sorption and desorption kinetics in a glassy polymer. Macromolecules 2009, 42, 5700– 5708,  DOI: 10.1021/ma9007576
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    Unified Dual Mode Description of Small Molecule Sorption and Desorption Kinetics in a Glassy Polymer
    Guo, Juchen; Barbari, Timothy A.
    Macromolecules (Washington, DC, United States) (2009), 42 (15), 5700-5708CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    FTIR-ATR (Fourier transform IR-attenuated total reflectance) spectroscopy and a conventional gravimetric sorption balance were used to study sorption and desorption kinetics of vapor phase acetonitrile in glassy cellulose acetate. A time delay was obsd. in the measured concn. at the polymer-crystal interface from the FTIR-ATR expts. that was longer than expected from applying the simple Fickian diffusion model used to fit the gravimetric data for this system. By using the dual mode sorption model with total immobilization of the hole population rather than a simple Fickian framework, the time behavior at the boundary was readily captured. This model in turn was used to fit the FTIR-ATR data for desorption kinetics. The desorption diffusion coeffs. were considerably higher than those obtained for sorption owing to the necessary redistribution between the dissolved and hole populations when the classic dual mode sorption model is applied to the desorption isotherm. To resolve this inconsistency and remove the discontinuity in concn. at the penetrant-polymer boundary between sorption and desorption, a unified dual mode model to describe both sorption and desorption is proposed. In this model, a fraction of the dissolved population creates holes during the sorption process at each activity. The new model was applied to the sorption and desorption kinetics data in this study, resulting in unifying dual mode parameters and comparable diffusion coeffs.
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    Farinas, K. C.; Doh, L.; Venkatraman, S.; Potts, R. O. Characterization of solute diffusion in a polymer using ATR-FTIR spectroscopy and bulk transport techniques. Macromolecules 1994, 27, 5220– 5222,  DOI: 10.1021/ma00096a055
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    Dias, M.; Hadgraft, J.; Raghavan, S. L.; Tetteh, J. The effect of solvent on permeant diffusion through membranes studied using ATR-FTIR and chemometric data analysis. J. Pharm. Sci. 2004, 93, 186– 196,  DOI: 10.1002/jps.10530
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    Van Alsten, J. G. Ionic and Chain Interdiffusion and Interfacial Strength Development in Ionomers of Poly(ethylene- co -methacrylic acid). Macromolecules 1996, 29, 2163– 2168,  DOI: 10.1021/ma950431f
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    Fleming, O. S.; Chan, K. L. A.; Kazarian, S. G. High-pressure CO2-enhanced polymer interdiffusion and dissolution studied with in situ ATR-FTIR spectroscopic imaging. Polymer 2006, 47, 4649– 4658,  DOI: 10.1016/j.polymer.2006.04.059
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    High-pressure CO2-enhanced polymer interdiffusion and dissolution studied with in situ ATR-FTIR spectroscopic imaging
    Fleming, Oliver S.; Chan, K. L. Andrew; Kazarian, Sergei G.
    Polymer (2006), 47 (13), 4649-4658CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
    A novel application of attenuated total reflection Fourier transform IR (ATR-FTIR) spectroscopic imaging to study polymer interdiffusion and dissoln. under high-pressure or supercrit. carbon dioxide environments has been demonstrated. Miscible systems of polyvinylpyrrolidone (PVP) and poly(ethylene glycol) (PEG) of different mol. wts. have been chosen for this investigation. These systems were subjected to a controlled pressure of CO2 and the interfacial area of contact between the two polymers was studied by ATR-FTIR imaging in situ. Using this spectroscopic imaging approach, the phenomenon of polymer interdiffusion enhanced by CO2 dissolved in both polymers was investigated as a function of time. The evolution of spatially resolved images as a function of time was studied with FTIR imaging and the corresponding concn. profiles for both polymers were obtained. The chem. specificity of FTIR imaging also allowed us to measure the amt. of CO2 dissolved in each domain of the polymer system. Effects of PEG mol. wt. and pressure of CO2 on the mechanism and the rate of polymer interdiffusion was investigated. This approach has not only shown the ability to visualize the process of interdiffusion but also demonstrated the ability of high-pressure CO2 to 'tune' the rate of interdiffusion, this information is important for a better understanding of CO2-induced mixing of polymeric materials.
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    Stolow, N. Action of Solvents on Dried Linseed Oil Films. Nature 1957, 179, 579– 580,  DOI: 10.1038/179579b0
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    Action of solvents on dried linseed-oil films
    Stolow, N.
    Nature (London, United Kingdom) (1957), 179 (), 579-80CODEN: NATUAS; ISSN:0028-0836.
    Action of a range of org. solvents on aged linseed-oil films, pigmented and unpigmented, was investigated. A specially designed app. based on the parallel-plate viscometer was used to make precise measurements of changes in thickness of films coated on a rigid substrate, while free films were observed under a microscope. Random, amorphous structure concepts for linseed-oil films were given support from the results of tests made. The result of leaching and swelling was a film of greater d. with altered swelling characteristics. Degree of swelling depends on the solvent used. Method of measurement enabled rates of swelling or diffusion to be investigated and it was found that Fick's law of diffusion for a semi-infinite solid applied up to 0.6 to 0.8 of the swelling max. By raising the temp. the rate of diffusion of solvent was markedly increased. It was found that pigmentation slowed down the progress of diffusion owing to the impedance of the pigment particles.
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    Phenix, A. The Swelling of Artists’ Paints in Organic Solvents. Part 1, a Simple Method for Measuring the In-Plane Swelling of Unsupported Paint Films. J. Am. Inst. Conserv. 2002, 41, 43,  DOI: 10.2307/3179896
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    Ward, S. A.; Pethrick, R. A. Positron annihilation lifetime spectroscopy and diffusion studies of large molecule penetrants into alkyd resins. Prog. Org. Coat. 2012, 75, 509– 526,  DOI: 10.1016/j.porgcoat.2012.06.002
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    Positron annihilation lifetime spectroscopy and diffusion studies of large molecule penetrants into alkyd resins
    Ward, Shelia A.; Pethrick, Richard A.
    Progress in Organic Coatings (2012), 75 (4), 509-526CODEN: POGCAT; ISSN:0300-9440. (Elsevier B.V.)
    Alkyd resins can be used to create transparent films and their characteristics depend on the method used in their cure. Changing the catalysts can have profound effects on the phys. properties of the films formed. Positron annihilation lifetime spectroscopy (PALS) measurements are used to explore how changes in catalyst influence the free vol. for an alkyd resin system. Diffusion measurements are reported for large mol. permeants; dioctyl phthalate, 2-Et hexylbenzyl phthalate, nonyl phenol ethoxylate, iso-Pr myristate and oleic acid into these alkyd resins. The diffusion behavior changes as the temp. is raised through the glass transition temp. of the resin but is also sensitive to the chem. structure of the permeant. The diffusion deviates from simple Fickian behavior in a no. of cases and is indicative of plasticization influencing diffusion. Comparison of the av. mol. size with the available free vol. indicates that diffusion involves a complex co-operative motion in which the matrix plays an important role. Increasing the crosslink d. by post cure of the alkyd resin at elevated temps., reduces the free vol. and decreases the ability for the large mols. to permeate in to the matrix. Oleic acid exhibits a two stage diffusion process; the second stage being assocd. with opening up of the resin structure as a result of acid catalyzed degrdn. The unusual behavior of iso-Pr myristate is attributed to a combination of its ability to adopt favorable conformations and a high degree of compatibility with the matrix. This study highlights the importance of the chem. structure of the permeant on its ability to enter and diffuse through the coating.
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    Sharma, V.; Banait, J. S.; Kundu, P. P. Swelling kinetics of linseed oil-based polymers. J. Appl. Polym. Sci. 2009, 111, 1816– 1827,  DOI: 10.1002/app.29006
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    Swelling kinetics of linseed oil-based polymers
    Sharma, Vinay; Banait, J. S.; Kundu, P. P.
    Journal of Applied Polymer Science (2009), 111 (4), 1816-1827CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
    Kinetics of swelling and sorption behavior of copolymers based on linseed oil, styrene, divinylbenzene, and acrylic acid obtained by cationic and thermal polymn. is studied in THF at different temps. The values of n in the transport equation are found to be below 0.4, showing non-Fickian or pseudo-Fickian transport in the polymers. The dependence of diffusion coeff. on the compn. and temp. has also been studied for the linseed oil-based polymers. The diffusion coeff. in cationic samples decreases with an increase in the oil contents in the samples. In case of thermal samples, the diffusion coeff. first increases up to 30% oil contents and then decreases. The diffusion coeff. decreases with an increase in temp. for all of the linseed oil polymer samples. The sorption coeff. increases with an increase in the oil contents for all samples. The crosslink d. (calcd. from the THF swelling) ranges from 20.16 to 92.34 × 106 mol/cm3 for cationic samples and 20.62 to 86.01 × 106 mol/cm3 for thermal samples.
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    Chan, T. Y. A.; Odlyha, M. The effect of relative humidity and pigment type on paint films. Thermochim. Acta 1995, 269–270, 755– 767,  DOI: 10.1016/0040-6031(95)02669-X
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    The effect of relative humidity and pigment type on paint films
    Chan, T. Y. A.; Odlyha, M.
    Thermochimica Acta (1995), 269/270 (), 755-67CODEN: THACAS; ISSN:0040-6031. (Elsevier)
    Thermogravimetry was used to continuously monitor the moisture uptake of paint film at given temp. and relative humidity as a function of time. The elec. properties of the paint films were studied by low frequency dielec. spectroscopy over the frequency range 10-4 to 105. The crit. frequency increased with increasing relative humidity and moisture content. The adsorbed water layers were formed on the surfaces of the pigment grains. A model was presented to describe the "charge hopping" process in the adsorbed water layers which gave rise to the low frequency dispersion.
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    Nguyen, T.; Bentz, D.; Byrd, E. Method for measuring water diffusion in a coating applied to a substrate. J. Coat. Technol. 1995, 67, 37– 46
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    Method for measuring water diffusion in a coating applied to a substrate
    Nguyen, T.; Bentz, D.; Byrd, E.
    Journal of Coatings Technology (1995), 67 (844), 37-46CODEN: JCTEDL; ISSN:0361-8773. (Federation of Societies for Coatings Technology)
    A method based on Fourier-transform IR-multiple internal reflection (FTIR-MIR) spectroscopy was developed for measuring the apparent diffusion coeff. of water in a coating applied to a substrate. The method requires an application of a coating of any thickness on an internal reflection element, which serves as the substrate, with the attachment of a water chamber to the coated specimen. Water is introduced to the chamber and FTIR-MIR spectra are collected automatically without disturbing the specimen or the instrument. The amt. of water at the coating/substrate interface was detd. using a model based on the theory of internal reflection spectroscopy. A mass-time curve for water at the interface is established, which provides the time-lag value, the time required for water to diffuse through the coating film and reach the interface. The diffusion coeff. (D) is then detd. by the time-lag equation. For thick coating films (>25 μm), D may be estd. from the FTIR-MIR in situ intensity data only. The sensitivity of FTIR-MIR spectroscopy and the strong FTIR absorption of water mols. make this an ideal method for measuring the diffusivity of liq. water through a coating applied to a substrate.
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    Liu, B.; Li, Y.; Lin, H.; Cao, C.-n. Effect of PVC on the diffusion behaviour of water through alkyd coatings. Corros. Sci. 2002, 44, 2657– 2664,  DOI: 10.1016/S0010-938X(02)00061-6
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    Effect of PVC on the diffusion behaviour of water through alkyd coatings
    Liu, Bin; Li, Ying; Lin, Haichao; Cao, Chu-nan
    Corrosion Science (2002), 44 (12), 2657-2664CODEN: CRRSAA; ISSN:0010-938X. (Elsevier Science Ltd.)
    The diffusion behavior of water through alkyd coatings with micaceous iron oxide pigment at different pigment vol. concn. (PVC) was studied by EIS and SEM techniques. The diffusion coeffs. of water through the coatings were also calcd. The exptl. results showed that, in the initial diffusion period, the diffusion processes of water through alkyd coatings immersed in 0.5 M NaCl followed the Fick's second law. Within the PVC values which have been studied, the diffusion coeffs. of water diffusing through alkyd coatings initially decreased with increasing PVC, reaching a min. value at 60%, and then increased with increasing PVC. When PVC was less than 60%, the barrier property of pigment was the main factor affecting the water diffusion behavior. However, the coatings' microstructure played an important role when PVC was greater than 60%.
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    Xu, Y.; Yan, C.; Ding, J.; Gao, Y.; Cao, C. Water vapour in the coatings of alkyd and polyurethane varnish. Prog. Org. Coat. 2002, 45, 331– 339,  DOI: 10.1016/S0300-9440(02)00069-3
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    Water vapor in the coatings of alkyd and polyurethane varnish
    Xu, Yongxiang; Yan, Chuanwei; Ding, Jie; Gao, Yanmin; Cao, Chunan
    Progress in Organic Coatings (2002), 45 (4), 331-339CODEN: POGCAT; ISSN:0300-9440. (Elsevier Science B.V.)
    Absorption and desorption of water vapor in alkyd and polyurethane varnish were studied by a quartz crystal microbalance. The absorption and desorption kinetics curves were Fickian in nature when the relative humidity is higher than 30%, while the soly. followed Henry's law. The av. diffusion coeff. was calcd. A residual amt. of water was found to remain in the coatings after extended exposure to dry air. FTIR anal. showed that the mol. structure of the coatings changed after the absorption and desorption of water vapor. The results showed that the residual water reacted with the coatings mol.
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    van der Zanden, A.; Goossens, E. The measurement of the diffusion coefficient and the sorption isotherm of water in paint films. Chem. Eng. Sci. 2003, 58, 1521– 1530,  DOI: 10.1016/S0009-2509(02)00674-7
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    The measurement of the diffusion coefficient and the sorption isotherm of water in paint films
    Van Der Zanden, A. J. J.; Goossens, E. L. J.
    Chemical Engineering Science (2003), 58 (8), 1521-1530CODEN: CESCAC; ISSN:0009-2509. (Elsevier Science Ltd.)
    An exptl. technique together with a numerical model is proposed with which the diffusion coeff. and the sorption isotherm of water in paint can be measured. Inside a closed vessel, paint films are on stainless-steel plates. Water is present as water vapor in the air and in the paint. After blowing dry or wet air through the vessel for some time, the situation moves to a new equil. The relative humidity of the air inside the vessel is measured as a function of time. From fitting the theor./numerical model against the exptl. values, follow the diffusion coeff. and the sorption isotherm of water in the paint. The results show large scattering. When the independently measured sorption isotherm is used as an input parameter in the model, the fitting procedure gives much smaller scattering for the diffusion coeff.
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    Saarinen, V.; Kreuer, K. D.; Schuster, M.; Merkle, R.; Maier, J. On the swelling properties of proton conducting membranes for direct methanol fuel cells. Solid State Ionics 2007, 178, 533– 537,  DOI: 10.1016/j.ssi.2006.12.001
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    On the swelling properties of proton conducting membranes for direct methanol fuel cells
    Saarinen, V.; Kreuer, K. D.; Schuster, M.; Merkle, R.; Maier, J.
    Solid State Ionics (2007), 178 (7-10), 533-537CODEN: SSIOD3; ISSN:0167-2738. (Elsevier B.V.)
    The swelling properties of different fluorinated (Nafion 117, poly(ethylene-alt-tetrafluoroethylene) and poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid)) and hydrocarbon (sulfonated poly(phenylene sulfone)) proton conducting ionomers were studied in alc. (MeOH, EtOH, 2-propanol, tBuOH)-water and H2SO4-water mixts. Solvent uptake and its water/alc. selectivity were detd. by thermal desorption using combined thermogravimetry (TGA) and mass spectrometry (MS). Clear trends are obsd. for the selectivity: preferential water uptake (alc. rejection) correlates with high IEC (ion exchange capacity) and low solvent uptake (swelling) indicating a preferred interaction of the ionic groups (-SO3-, H+) and the groups on the polymerbackbone carrying partial charges (e.g. sulfone units (-SO2-) in the sulfonated poly(phenylene sulfone)) with water. The total swelling significantly decreases in the presence of H2SO4 indicating osmosis being a major driving force in the swelling process. This is particularly low for ETFE-SA, which is highlighting its supreme mech. properties and its high selectivity for water uptake (selectivity coeffs. ≤10 for λ =7). Unlike Nafion, which shows high swelling in alc.-water mixts. and almost no selectivity, high selectivity coeffs. (≤8) are obsd. for sulfonated poly(phenylene sulfone) even at medium solvent uptake (λ = 12). The total solvent uptake in these highly polar ionomers even decreases with methanol mole fraction and is virtually independent of temp. (T ≤120°). Together with the high proton cond. and high hydrolytic stability reported in the literature, the swelling properties presented in this work are making sulfonated poly(phenylene sulfone) interesting membrane materials for DMFC applications.
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    Hallinan, D. T.; De Angelis, M. G.; Giacinti Baschetti, M.; Sarti, G. C.; Elabd, Y. A. Non-Fickian Diffusion of Water in Nafion. Macromolecules 2010, 43, 4667– 4678,  DOI: 10.1021/ma100047z
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    Non-Fickian Diffusion of Water in Nafion
    Hallinan, Daniel T., Jr.; Grazia De Angelis, Maria; Giacinti Baschetti, Marco; Sarti, Giulio C.; Elabd, Yossef A.
    Macromolecules (Washington, DC, United States) (2010), 43 (10), 4667-4678CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Understanding the dynamics of water in solid-state polymer electrolytes (e.g., Nafion) is important for a variety of applications ranging from membrane-based water purifn. to hydrogen fuel cells. In this study, the dynamics of water in Nafion was investigated at both low and high humidities with time-resolved Fourier transform IR-attenuated total reflectance (FTIR-ATR) spectroscopy; a technique that provides a mol. fingerprint of both the diffusant and the polymer simultaneously in real time. At low humidities (0-22% RH), an extended initial time lag resulted in non-Fickian behavior, where dynamic IR data provided evidence for a reaction between water and sulfonic acid. A diffusion-reaction model was developed and predicted this anomalous behavior, where the time lag was a function of water content. At high humidities (0-100% RH), a slow approach to steady state resulted in non-Fickian behavior, where dynamic IR data provided evidence of water-induced relaxation in the polymer backbone. A diffusion-relaxation model was developed and regressed well to both the polymer relaxation and water diffusion data, where only one fitting parameter was used for each data set to det. both a relaxation time const. and diffusion coeff. This approach differs significantly from previous work on non-Fickian behavior in glassy polymers, which, consisted of regressing gravimetric data to models with a min. of six fitting parameters. Not only do the diffusion coeffs. from these two models compare well with Fickian diffusion coeffs. from expts. with small water concn. gradients, but also the results in this study provide phys. insight into the transport mechanisms of water and relaxation phenomena in solid-state polymer electrolytes.
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    Hickner, M. A. Water-mediated transport in ion-containing polymers. J. Polym. Sci., Part B: Polym. Phys. 2012, 50, 9– 20,  DOI: 10.1002/polb.22381
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    Water-mediated transport in ion-containing polymers
    Hickner, Michael A.
    Journal of Polymer Science, Part B: Polymer Physics (2012), 50 (1), 9-20CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
    A review. Water-mediated ion conduction enables high cond. in hydrated polymer membranes commonly used in electrochem. devices. Understanding the coupling of the absorbed water with the polymer matrix and the dynamics of water inside the polymer network across the full range of length scales in the membrane is important for unraveling the structure-property relationships in these materials. By considering the water behavior in ion-contg. polymers, next-generation fuel cell membranes are being designed that exceed the cond. of the state-of-the-art materials and have optimized cond. and permeability that may be useful in other types of devices such as redox flow batteries. Water-polymer assocns. can be exploited to tune the transport and mech. property tradeoffs in these polymers. Measurements of water motion provide important criteria for assessing the factors that control the performance of these types of materials. This review article discusses current understanding of water behavior in ion-contg. polymers and the relation between water motion and ion and mol. transport. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011.
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    Dishari, S. K.; Hickner, M. A. Antiplasticization and water uptake of nafion thin films. ACS Macro Lett. 2012, 1, 291– 295,  DOI: 10.1021/mz200169a
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    Antiplasticization and Water Uptake of Nafion Thin Films
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    ACS Macro Letters (2012), 1 (2), 291-295CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    Fluorescence of 9-(2-carboxy-2-cyanovinyl)julolidine (CCVJ) was measured to probe the local motion within 70-600 nm thick Nafion films at controlled levels of hydration. Thinner films showed increased confinement under dry conditions as evidenced by their high fluorescence intensity values per unit thickness. Antiplasticization, or a stiffening of the film, was obsd. as an increase in fluorescence intensity when the sample was exposed to low water activity (≤30% RH) and the extent of antiplasticization changed with film thickness. At higher relative humidities, the films became plasticized with water and the fluorescence of CCVJ declined. Quartz crystal microbalance (QCM) expts. revealed higher hydration nos. (λ = nH2O/nSO3H) in thinner films on SiO2 surfaces. The higher water uptake in thin films was explained by considering the polymer order at the Nafion-SiO2 interface and the influence of this interfacial layer on the swelling properties of thin films.
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    Davis, E. M.; Stafford, C. M.; Page, K. A. Elucidating water transport mechanisms in Nafion thin films. ACS Macro Lett. 2014, 3, 1029– 1035,  DOI: 10.1021/mz500515b
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    Elucidating Water Transport Mechanisms in Nafion Thin Films
    Davis, Eric M.; Stafford, Christopher M.; Page, Kirt A.
    ACS Macro Letters (2014), 3 (10), 1029-1035CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
    Ion-exchange membranes are crit. components of hydrogen fuel cells, where these ionomers can be confined to nanoscale thicknesses, altering the phys. properties of these films from that of bulk membranes. Therefore, it is important to develop methods capable of measuring and elucidating the transport mechanisms under thin film confinement compared to bulk Nafion. In this study, water sorption and diffusion in a Nafion thin film were measured using time-resolved in situ polarization modulation IR reflection absorption spectroscopy (PM-IRRAS). Interfacial mass transport limitations were confirmed to be minimal, while restricted water diffusion was obsd., where the effective diffusion coeff. of water in the thin Nafion film was many orders of magnitude lower (between 4 and 5 orders of magnitude) than those reported for bulk membranes and was dependent on the initial hydration state of the Nafion. Furthermore, the response of the hydrophobic domains (Teflon backbone) to the swelling of the hydrophilic domains (ionic clusters) was shown to be orders of magnitude slower than that of bulk Nafion.
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    Yao, K. Z.; Shaw, B. M.; Kou, B.; McAuley, K. B.; Bacon, D. W. Modeling Ethylene/Butene Copolymerization with Multi-site Catalysts: Parameter Estimability and Experimental Design. Polym. React. Eng. 2003, 11, 563– 588,  DOI: 10.1081/PRE-120024426
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    Modeling ethylene/butene copolymerization with multi-site catalysts: parameter estimability and experimental design
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    Mechanistic models for ethylene-1-butene copolymn. with Ziegler-Natta catalysts contain many kinetic rate consts. Precise ests. of key parameters are required if the models are to be used to obtain reliable predictions of copolymer properties for a specified catalyst over a range of polymn. conditions. In this paper, a novel method is developed to assist modelers in assessing whether their model parameters will be estimable from existing or proposed exptl. data, and in detg. subsets of influential parameters that can be estd. from the data when the complete set of model parameters cannot be estd. The effects of using different types of data, varying the no. of observations per exptl. run, and increasing the no. of exptl. runs on the no. of estimable parameters are considered. A method for comparison of the relative effectiveness of different exptl. designs for estg. key parameters in gas-phase ethylene copolymn. is also presented.
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    Podgorski, L.; Merlin, A.; Saiter, J. Natural and artificial ageing of an alkyd based wood finish: Calorimetric investigations. J. Therm. Anal. 1994, 41, 1319– 1324,  DOI: 10.1007/BF02549926
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    Journal of Thermal Analysis (1994), 41 (6), 1319-24CODEN: JTHEA9; ISSN:0368-4466.
    Wood protection in exterior use is generally achieved with a stain. This protective product is often obtained from an alkyl resin. A natural and artificial aging were studied by measuring the glass transition temp. (Tg) of the finish variations in terms of time. In both agings, the Tg variations are the same; there is an increase in Tg during the first steps of ageing and then a stabilization. A behavior equation is proposed and is perfectly suitable to both agings. Time consts. are calcd.
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    Hedley, G.; Odlyha, M.; Burnstock, A.; Tillinghast, J.; Husband, C. A study of the mechanical and surface properties of oil paint films treated with organic solvents and water. J. Therm. Anal. 1991, 37, 2067– 2088,  DOI: 10.1007/BF01905579
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    A study of the mechanical and surface properties of oil paint films treated with organic solvents and water
    Hedley, G.; Odlyha, M.; Burnstock, A.; Tillinghast, J.; Husband, C.
    Journal of Thermal Analysis (1991), 37 (9), 2067-88CODEN: JTHEA9; ISSN:0368-4466.
    The mech. and surface properties of naturally aged 12-yr-old samples of Pb white-linseed oil and burnt sienna-linseed oil paints treated with org. solvents and water were studied using thermomech. and dielec. techniques together with FTIR spectroscopy and SEM. Changes in the nature of the surfaces after treatment were obsd. The effects of water, iso-PrOH, and acetone immersion for 24 h and swabbing for a few min on the surfaces were measured directly in terms of the change in the shear modulus of the paint films together with the accompanying change in the ratio of viscous to elastic components present in each system. Generally, the solvent-treated films became harder and showed reduced viscous components, whereas the water-treated samples became softer. There was a change in the dielec. properties of the leached films which pointed to the polar nature of the leachings. FTIR diffuse reflectance spectra supported this conclusion.
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    Phenix, A.; Mechanical, T.; Paints, O.; Phenix, A. Thermal Mechanical Transitions in Artists’ Oil Paints and Selected Conservation Materials: a Study by Dynamic Mechanical Analysis (DMA). AIC Paintings Specialty Group Postprints 2009, 22, 72– 89
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    Sanches, D.; Ramos, A. M.; Coelho, J. F. J.; Costa, C. S. M. F.; Vilarigues, M.; Melo, M. J. Correlating thermophysical properties with the molecular composition of 19th century chrome yellow oil paints. Polym. Degrad. Stab. 2017, 138, 201– 211,  DOI: 10.1016/j.polymdegradstab.2017.02.010
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    Correlating thermophysical properties with the molecular composition of 19th century chrome yellow oil paints
    Sanches, Diogo; Ramos, Ana Maria; Coelho, Jorge F. J.; Costa, Catia S. M. F.; Vilarigues, Marcia; Melo, Maria Joao
    Polymer Degradation and Stability (2017), 138 (), 201-211CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
    In the present study, we explore Dynamic Mech. Thermal Anal. (DMTA) as a tool for assessing the phys. performance in 19th century paints and to evaluate the parameters that influence the mech. properties of the paint films. This data is particularly important for accurate life-time predictions as well as better conservation treatments. DMTA is used to study the thermophys. properties of chrome yellow (PbCrO4) oil paints under the influence of common fillers found in 19th century chrome yellow oil paints: calcium carbonate (CaCO3), barium sulfate (BaSO4) and gypsum (CaSO4·2H2O). Oil paint mock-ups were dry to touch and included oil plus the single paint components (chrome yellow pigment and the three fillers) that were compared with 19th c. Winsor & Newton historic paint formulations. The fillers selected were applied with a ratio to pigment ranging from 10 to 40% in wt. DMTA data revealed that the addn. of solids (pigment and/or fillers) reduces the flexibility of the oil paint films, confirmed by the increase of the storage modulus (E') and glass transition temp. (Tg). DMTA provided a clear differentiation between the thermo-mech. behavior of the oil film and oil with inorg. compds. and, more importantly, pigment oil system vs. oil with fillers. The data revealed that the pigment and filler system oil is modulated essentially by the presence of the filler irresp. of the individual filler behavior (as a single component) and its percentage (within the proportions used by Winsor & Newton in their 19th c. chrome yellow paints).
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    Ploeger, R.; Scalarone, D.; Chiantore, O. Thermal analytical study of the oxidative stability of artists’ alkyd paints. Polym. Degrad. Stab. 2009, 94, 2036– 2041,  DOI: 10.1016/j.polymdegradstab.2009.07.018
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    Thermal analytical study of the oxidative stability of artists' alkyd paints
    Ploeger, Rebecca; Scalarone, Dominique; Chiantore, Oscar
    Polymer Degradation and Stability (2009), 94 (11), 2036-2041CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
    Artists' alkyd paints are relatively new in the art world and were introduced in the 1970s. Since they are so new, little is known about their aging properties and behavior in the conservation field. Thermal analyses, specifically, differential scanning calorimetry (DSC) and thermogravimetric anal. (TGA), were used in this work to study the changes in properties of artists' alkyd paint films with age. Both techniques revealed changes in the thermal properties as the films increased in age. The crosslinking rate during accelerated photo-aging was obsd. with DSC by monitoring the exothermic reaction after the decompn. of peroxide groups, which form during auto-oxidn. of the alkyd resin. The investigation of naturally aged films, some up to 28 years, revealed an increase in the glass transition temp. with age. TGA studies of naturally aged films indicated an increase in film d. with age, probably due to crosslinking at first and then the possible formation of oxidative degrdn. products over time, such as carboxylate salts.
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    Mosiewicki, M. A.; Rojas, O.; Sibaja, M. R.; Borrajo, J.; Aranguren, M. I. Aging study of linseed oil resin/styrene thermosets and their composites with wood flour. Polym. Int. 2007, 56, 875– 881,  DOI: 10.1002/pi.2218
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    Aging study of linseed oil resin/styrene thermosets and their composites with wood flour
    Mosiewicki, Mirna A.; Rojas, Oscar; Sibaja, Maria R.; Borrajo, Julio; Aranguren, Mirta I.
    Polymer International (2007), 56 (7), 875-881CODEN: PLYIEI; ISSN:0959-8103. (John Wiley & Sons Ltd.)
    The changes in the properties of new crosslinked polymers based on renewable resources and their derived composites have been monitored as a function of time; this knowledge is necessary to est. their behavior in final applications. Rigid thermoset polymers prepd. by free radical polymn. of resins obtained from linseed oil and styrene and composites reinforced with wood flour were evaluated in different environmental conditions and at different times after their prepn. The action of atm. oxygen on the unsatd. groups in fatty acids produces chem. changes in these polymers, which affect the properties of the cured materials. These changes were analyzed using Fourier transform IR spectroscopy, dynamic mech. anal. and mech. testing. An increase in the modulus with time was obsd. during exposure of the samples to dry conditions, or humid environments (60% relative humidity), with or without UV irradn. The reaction with oxygen appears to be accelerated when the materials are subjected to UV irradn., showing a large effect on the glass transition temp.
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    Boquillon, N.; Fringant, C. Polymer networks derived from curing of epoxidisedlinseed oil: influence of different catalysts and anhydride hardeners. Polymer 2000, 41, 8603– 8613,  DOI: 10.1016/S0032-3861(00)00256-1
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    Polymer networks derived from curing of epoxidised linseed oil: influence of different catalysts and anhydride hardeners
    Boquillon, N.; Fringant, C.
    Polymer (2000), 41 (24), 8603-8613CODEN: POLMAG; ISSN:0032-3861. (Elsevier Science Ltd.)
    Epoxidized linseed oil was cured with anhydrides. The reactions were catalyzed with different types of tertiary amines and imidazoles. 2-Methylimidazole leads to very interesting properties. The effects of steric factors and of the rigidity of the diester segment formed due to the extent of conversion of anhydride groups and on the network's properties were obsd. Thus, the thermosets obtained with phthalic anhydride and methyl-endo-methylenetetrahydrophthalic anhydride hardeners have a lower crosslink d. than those obtained with cis-1,2,3,6-tetrahydrophthalic anhydride. The effects of the epoxidized triglyceride structure, made of aliph. chains, on the network's properties were also examd.
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    Earnest, T. R.; MacKnight, W. J. Infrared Studies of Hydrogen Bonding in Ethylene-Methacrylic Acid Copolymers and Ionomers. Macromolecules 1980, 13, 844– 849,  DOI: 10.1021/ma60076a014
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    Eisenberg, A.; Hird, B.; Moore, R. B. A new multiplet-cluster model for the morphology of random ionomers. Macromolecules 1990, 23, 4098– 4107,  DOI: 10.1021/ma00220a012
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    A new multiplet-cluster model for the morphology of random ionomers
    Eisenberg, A.; Hird, B.; Moore, R. B.
    Macromolecules (1990), 23 (18), 4098-107CODEN: MAMOBX; ISSN:0024-9297.
    A morphol. model for random ionomers is proposed which incorporates the findings of recent dynamic mech. and x-ray scattering studies. The model is based on the existence of multiplets, which reduce the mobility of the polymer chains in their vicinity. The thickness of the restricted mobility layer surrounding each multiplet is postulated to be of the order of the persistence length of the polymer. Isolated multiplets act as large crosslinks, thus increasing the glass temp. of the material. As the ion content is increased, the regions of restricted mobility surrounding each multiplet overlap to form larger contiguous regions of restricted mobility. When these regions become sufficiently large, they exhibit phase-sepd. behavior and are termed clusters. The model is in good agreement with a very wide range of exptl. obsd. phenomena, esp. those based on dynamic mech. and x-ray scattering techniques.
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    Hermans, J. J.; Keune, K.; van Loon, A.; Iedema, P. D.; van Loon, A.; Iedema, P. D. The crystallization of metal soaps and fatty acids in oil paint model systems. Phys. Chem. Chem. Phys. 2016, 18, 10896– 10905,  DOI: 10.1039/C6CP00487C
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    The crystallization of metal soaps and fatty acids in oil paint model systems
    Hermans, Joen J.; Keune, Katrien; Loon, Annelies van; Iedema, Piet D.
    Physical Chemistry Chemical Physics (2016), 18 (16), 10896-10905CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    The formation and crystn. of metal soaps in oil paint layers is an important issue in the conservation of oil paintings. The chem. reactions and phys. processes that are involved in releasing metal ions from pigments and fatty acids from the oil binder to form cryst. metal soap deposits have so far remained poorly understood. We have used a combination of differential scanning calorimetry (DSC) and attenuated total reflection Fourier transform IR spectroscopy (ATR-FTIR) on model mixts. of palmitic acid, lead palmitate or zinc palmitate and linseed oil to study the transition from amorphous material to cryst. fatty acid or metal soap. This transition forms the final stage in the cascade of processes leading to metal soap-related oil paint degrdn. Palmitic acid as well as the metal soaps showed nearly ideal soly. behavior. However, it was found that, near room temp., both lead and zinc palmitate are practically insol. in both liq. and partially polymd. linseed oil. Interestingly, the rate of metal soap and fatty acid crystn. decreased rapidly with the degree of linseed oil polymn., possibly leading to systems where metal soaps are kinetically trapped in a semi-cryst. state. To explain the various morphologies of metal soap aggregates obsd. in oil paint layers, it is proposed that factors affecting the probability of crystal nucleation and the rate of crystal growth play a crucial role, like exposure to heat or cleaning solvents and the presence of microcracks.
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    Park, J.; Eslick, J.; Ye, Q.; Misra, A.; Spencer, P. The influence of chemical structure on the properties in methacrylate-based dentin adhesives. Dent. Mater. 2011, 27, 1086– 1093,  DOI: 10.1016/j.dental.2011.07.011
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    The influence of chemical structure on the properties in methacrylate-based dentin adhesives
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    Dental Materials (2011), 27 (11), 1086-1093CODEN: DEMAEP; ISSN:0109-5641. (Elsevier Ltd.)
    Objectives: The objective of this study was to investigate the influence of the chem. structure of methacrylate monomers used in dentin adhesives on degree of conversion (DC), water sorption, and dynamic mech. properties. Materials and methods: Exptl. adhesives contg. 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy) phenyl]-propane (BisGMA), 2-hydroxyethyl methacrylate (HEMA), and co-monomer, 30/45/25 (wt./wt.) were photo-polymd. Ethyleneglycol dimethacrylate (EGDM), diethyleneglycol dimethacrylate (DEGDM), triethyleneglycol dimethacrylate (TEGDMA), 1,3-glycerol dimethacrylate (GDM), and glycerol trimethacrylate (GTM) were used as a co-monomer. The adhesives were characterized with regard to DC, water sorption, and dynamic mech. anal. and compared to control adhesive [HEMA/BisGMA, 45/55 (wt./wt.)]. Results: DC and water sorption increased with an increase in the no. of ethylene glycol units in the monomer. Exptl. adhesive contg. GDM showed significantly higher storage moduli (p < 0.05) in both dry and wet samples than exptl. adhesives contg. EGDM or DEGDM. The rubbery moduli of adhesives contg. GDM and GTM were found to be significantly greater (p < 0.05) than that of the control. Adhesives contg. GTM exhibited the widest tan δ curves, indicating the greatest structural heterogeneity. Significance: The hydrophilicity, functionality and size of monomers in dentin adhesives affected the water sorption, soly., crosslink d. and heterogeneity of the polymer network. The exptl. adhesives contg. GDM and GTM showed higher rubbery moduli, indicating higher crosslink d. accompanied by a decrease in the homogeneity of the polymer network structure.
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    Simple, new equations are provided for calcg. the crosslink d. of networks prepd. from low-mol.-wt., multi-functional reactants. The equations apply to stoichiometric mixts. at incomplete conversion and are obtained by modification of the Scanlan equation. Examples are selected to represent network forming reactions frequently encountered in thermoset industrial coatings. The rather complex Miller and Macosko calcns. are applied to the same examples. At extent of conversion 0.75-1.00, both calcns. give the same results. Clarifications are provided to explain inconsistencies in published values of no. av. mol. wt. of network chains.
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    Two different approaches for modifying the linear viscoelastic behavior of the title ionomer were described. Adding a backbone plasticizer (DOP) affected that part of the relaxation behavior ascribed to the backbone polymer. DOP lowered the primary glass transition temp. without affecting the relaxation time spectrum assocd. with the ionic clusters. However, an ionic plasticizer (glycerol) affected the relaxation of the ionic clusters and had little or no effect on the viscoelastic response of the nonpolar phase. For the ionomer, the addn. of glycerol shifted the long-time relaxations assocd. with the ionic clusters to shorter times, thus decreasing the melt viscosity and reducing the networklike response due to the phys. assocns. of the ionic groups.
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    The equil. swelling behavior of hydrogels sensitive to pH or ionic strength changes of the swelling medium was studied using structural models which are based on the Flory-Huggins thermodn. theory, the rubber elasticity theory, and the ionic interaction deviations therefrom. The no. av. mol. wt. between crosslinks was related to equil. swelling characteristics, the thermodn. compatibility of the polymer-swelling agent system, the ionic charges, the pKa of the ionizable polymer moieties, and the pH and ionic strength of the surrounding medium. The models have predictive correlative and design capabilities.
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    Edwards, D. A. Non-Fickian Diffusion in Thin Polymer Films. J. Polym. Sci., Part B: Polym. Phys. 1996, 34, 981– 997,  DOI: 10.1002/(SICI)1099-0488(19960415)34:5<981::AID-POLB16>3.0.CO;2-7
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    Diffusion of penetrants through polymers often does not follow the std. Fickian model. Such anomalous behavior can cause difficulty when designing polymer networks for specific uses. One type of non-Fickian behavior that results is so-called case II diffusion, where Fickian-like fronts initially move like √t with a transition to a non-Fickian concn. profile and front speed for moderate time. A math. model is presented that replicates this behavior in thin polymer films, and an anal. is performed that yields relevant dimensionless groups for study. An unusual result is derived: In certain parameter ranges, the concn. profile can change concavity, reflecting Fickian behavior for short times and non-Dickian behavior for moderate times. Asymptotic and numerical results are then obtained to characterize the dependence of such relevant quantities as failure time, front speed, and mass transport on these dimensionless groups. This information can aid in the design of effective polymer protectant films.
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    Solute diffusion in hydrogels is important in many biotechnol. fields. Solute behavior in hydrogels has been explained in terms of redn. in hydrogel free vol., enhanced hydrodynamic drag on the solute, increased path length due to obstruction, and a combination of hydrodynamic drag and obstruction effects. In this article the various math. models derived to explain and predict solute diffusion in hydrogels are discussed and tested against literature data. These models can be divided into those applicable to hydrogels composed of flexible polymer chains (i.e., homogeneous hydrogels) and those composed of rigid polymer chains (i.e., heterogeneous hydrogels). For homogeneous hydrogels it was detd. that a scaling hydrodynamic model provided the best explanation for solute diffusion, while for heterogeneous hydrogels obstruction models were more consistent with the exptl. data. Both the scaling hydrodynamic model and the most appropriate obstruction model contain undefined parameters which must be clarified in order for these models to gain widespread acceptance.
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    A review with refs.; diffusion in polymer solns. and gels has been studied by various techniques such as gravimetry, membrane permeation, fluorescence and radioactive labeling. These studies have led to a better knowledge of polymer morphol., transport phenomena, polymer melt and controlled release of drugs from polymer carriers. Various theor. descriptions of the diffusion processes have been proposed. The theor. models are based on different phys. concepts such as obstruction effects, free-vol. effects and hydrodynamic interactions. With the availability of pulsed-field gradient NMR techniques and other modern exptl. methods, the study of diffusion has become much easier and data on diffusion in polymers have become more available. This review article summarizes the different phys. models and theories of diffusion and their uses in describing the diffusion in polymer solns., gels and even solids. Comparisons of the models and theories are made in an attempt to illustrate the applicability of the phys. concepts. Examples in the literature are used to illustrate the application and applicability of the models in the treatment of diffusion data in various systems.
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    Canadian Journal of Chemical Engineering (2005), 83 (6), 913-929CODEN: CJCEA7; ISSN:0008-4034. (Canadian Society for Chemical Engineering)
    A review. This review paper deals with mass transport in macromol. materials. The study of mass transport through polymeric composite materials for example has applications in a variety of areas such as coatings, packaging and gas sepns., to name just a few. Here we discuss several models for diffusion as well as several exptl. techniques. In particular, we discuss models for case II diffusion, from a continuum mechanics point of view as well as via a mesoscopic theory. Variables such as temp., mol. structure and mech. deformation, affecting mass transport are also discussed.
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    Soft, Peelable Organogels from Partially Hydrolyzed Poly(vinyl acetate) and Benzene-1,4-diboronic Acid: Applications to Clean Works of Art
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    ACS Applied Materials & Interfaces (2017), 9 (33), 28069-28078CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    We have developed soft, peelable organogels from 40% hydrolyzed poly(vinyl acetate) (40PVAc) and benzene-1,4-diboronic acid (BDBA). The org. liqs. gelated include DMSO, DMF, THF, 2-ethoxyethanol, and methanol. The rheol. of these soft materials can be tuned by altering the concn. of the polymer and/or crosslinker. Insights into the mechanisms leading to gelation were obtained from 1H NMR expts., fluorescence measurements, and studies comparing properties of materials made from BDBA and phenylboronic acid, a mol. incapable of forming covalent crosslinks between the polymer chains. These organogels can be easily peeled off a surface, leaving no residue detectable by UV-vis spectroscopy. They are demonstrated to be effective at softening and removing deteriorated coatings from water-sensitive works of art and delicate surfaces. They have the needed characteristics to clean topog. complex surfaces: good contact with the surface, easy removal, and little to no residue after removal. A 2-ethoxyethanol organogel was used to remove oxidized varnish from a 16th century reliquary decorated with painted gold leaf, and an ethanol gel was used to remove solvent-resistant coatings from 16th and 18th century oil paintings.
  73. 73
    Baglioni, M.; Domingues, J. A. L.; Carretti, E.; Fratini, E.; Chelazzi, D.; Giorgi, R.; Baglioni, P. Complex Fluids Confined into Semi-interpenetrated Chemical Hydrogels for the Cleaning of Classic Art: A Rheological and SAXS Study. ACS Appl. Mater. Interfaces 2018, 10, 19162– 19172,  DOI: 10.1021/acsami.8b01841
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    Complex Fluids Confined into Semi-interpenetrated Chemical Hydrogels for the Cleaning of Classic Art: A Rheological and SAXS Study
    Baglioni, Michele; Domingues, Joana A. L.; Carretti, Emiliano; Fratini, Emiliano; Chelazzi, David; Giorgi, Rodorico; Baglioni, Piero
    ACS Applied Materials & Interfaces (2018), 10 (22), 19162-19172CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    The removal of aged varnishes from the surface of easel paintings using the common conservation practice (i.e by means of org. solvents) often causes pigment leaching, paint loss and varnish re-deposition. Recently, we proposed an innovative cleaning system based on semi-interpenetrated polymer networks (SIPN), where a covalently cross-linked poly(hydroxyethyl methacrylate), pHEMA, network is interpenetrated by linear chains of poly(vinylpyrrolidone), PVP. This chem. gel, simply loaded with water, was designed to safely remove surface dirt from water-sensitive artifacts. Here, we modified the SIPN to confine complex cleaning fluids, able to remove aged varnishes. These complex fluids are 5-components water-based nanostructured systems, where solvents are partially dispersed as nano-sized droplets in a continuous aq. phase, using surfactants. The rheol. behavior of the SIPN and the nanostructure of the fluids loaded into the gel were investigated, and the mech. behavior of the gel was optimized by varying both the crosslinking d. and the polymer concn. Once loaded with the complex fluids, the hydrogels maintained their structural and mech. features, while the complex fluids showed a decrease in the size of the dispersed solvent droplets. Two challenging case studies have been selected to evaluate the applicability of the SIPN hydrogels loaded with the complex fluids. The first case study concerns the removal of a surface layer composed by an aged brown resinous patina from a wood panel, the second case study concerns the removal of a homogeneous layer of a yellowed varnish from a watercolor on paper. The results show that the confinement of complex fluids into gels allowed unprecedented removal of varnishes from artifacts, overcoming the limitations of traditional cleaning methods.

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Cite this: Macromolecules 2018, 51, 18, 7134–7144
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Published September 7, 2018

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  • Abstract

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    Scheme 1

    Scheme 1. Formation of Ionomers by Copolymerization of Linseed Oil with Metal Sorbatea
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    aLinseed oil is represented by a typical structure of a triacyl glycerol (TAG) Unit. The depicted carboxylate coordination geometry does not reflect the real (unknown) geometry.

    Figure 1

    Figure 1. Illustration of the measurement cell used for time-dependent ATR-FTIR measurements of polymer films in contact with solvents. The spring provides a small pressure to keep a constant contact between the sample and the ATR crystal as solvents swell the sample, while the porosity of the metal disk ensures unhindered diffusion of the solvent through the sample film.

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    Figure 2

    Figure 2. DMA thermograms showing (a) Mpol-0, pLO, and ZnO-LO and (b) Znpol and (c) Pbpol ionomer systems with increasing metal content.

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    Figure 3

    Figure 3. Relation between ion content and νe as calculated by eq 1.

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    Figure 4

    Figure 4. Diffusion profile for acetone in Znpol (square symbols) and fits of a standard (blue) and adapted (red) Fickian diffusion model to the data.

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    Figure 5

    Figure 5. Illustration of the method-of-lines model with elements that increase in thickness during swelling. The concentration cs* is the concentration of solvent at equilibrium or maximum swelling.

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    Figure 6

    Figure 6. Diffusion profiles of seven solvents in Pbpol, Znpol, and ZnO-LO films of 135–160 μm thickness and a metal ion concentration in the polymer films of roughly 420 mM. Solid black lines represent best fits of the two-parameter diffusion-swelling model (eq 7) as employed in the convective diffusion equation (eq 14).

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    Figure 7

    Figure 7. Diffusion coefficient in Znpol film versus polymer fraction ϕ, calculated using the diffusion-swelling model, eq 8, using parameters in Tables S3 and S4.

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    Figure 8

    Figure 8. Correlation of equilibrium swelling factor, feq, with Deq. Lower swelling generally leads to slower diffusion. Error bars calculated as described in the Supporting Information.

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      A review with 97 refs. The primary products formed from the autoxidn. of lipids can be understood based upon a mechanism that involves five different reaction types. These reactions are: reaction of a carbon radical and mol. oxygen, atom transfer of a hydrogen from substrate to the chain carrying peroxyl, fragmentation of the chain carrying peroxyl to give oxygen and a carbon radical, rearrangement of the peroxyl, and cyclization of the peroxyl. The mechanism of these primary reaction steps has been the focus of extensive research over the past fifty years, and the current level of understanding of these transformations is the subject of this review.
    7. 7
      Porter, N. A.; Weber, B. A.; Weenen, H.; Khan, J. A. Autoxidation of polyunsaturated lipids. Factors controlling the stereochemistry of product hydroperoxides. J. Am. Chem. Soc. 1980, 102, 5597– 5601,  DOI: 10.1021/ja00537a032
      There is no corresponding record for this reference.
    8. 8
      Yin, H.; Porter, N. A. New insights regarding the autoxidation of polyunsaturated fatty acids. Antioxid. Redox Signaling 2005, 7, 170– 184,  DOI: 10.1089/ars.2005.7.170
      8
      New insights regarding the autoxidation of polyunsaturated fatty acids
      Yin, Huiyong; Porter, Ned A.
      Antioxidants & Redox Signaling (2005), 7 (1 & 2), 170-184CODEN: ARSIF2; ISSN:1523-0864. (Mary Ann Liebert, Inc.)
      A review. Free radical-initiated autoxidn. of polyunsatd. fatty acids (PUFAs) has been implicated in numerous human diseases, including atherosclerosis and cancer. This review covers the free radical mechanisms of lipid oxidn. and recent developments of anal. techniques to analyze the lipid oxidn. products. Autoxidn. of PUFAs generates hydroperoxides as primary oxidn. products, and further oxidn. leads to cyclic peroxides as secondary oxidn. products. Characterization of these oxidn. products is accomplished by several mass spectrometric techniques. Ag+ coordination ion spray mass spectrometry has proven to be a powerful tool to analyze the intact lipid peroxides. Monocyclic peroxides, bicyclic endoperoxides, serial cyclic peroxides, and a novel class of endoperoxides (dioxolane-isoprostane peroxides) have been identified from the oxidn. of arachidonate. Electron capture atm. pressure chem. ionization mass spectrometry has been applied to study lipid oxidn. products after derivatization. All 8 possible diastereomeric isoprostanes are obsd. from the oxidn. of a single hydroperoxide precursor. 5- And 15-series isoprostanes are more abundant than the 8- and 12-series because the precursors that lead to 8- and 12-series compds. can undergo further oxidn. and form dioxolane-isoprostane peroxides. Furthermore, formation of isoprostanes from 15-hydroperoxyeicosatetraenoate occurs from β-fragmentation of the corresponding peroxyl radical to generate a pentadienyl radical rather than a "dioxetane" intermediate, as previously suggested.
    9. 9
      Yin, H.; Xu, L.; Porter, N. A. Free radical lipid peroxidation: mechanisms and analysis. Chem. Rev. 2011, 111, 5944– 5972,  DOI: 10.1021/cr200084z
      9
      Free Radical Lipid Peroxidation: Mechanisms and Analysis
      Yin, Huiyong; Xu, Libin; Porter, Ned A.
      Chemical Reviews (Washington, DC, United States) (2011), 111 (10), 5944-5972CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. It is the aim of this Review to discuss the chem. assocd. with each of the steps of the free radical chain sequence in the reaction of lipids and mol. oxygen. The primary reactions of lipid peroxidn. include hydrogen-atom abstraction by peroxyl or alkoxyl radicals; oxygen addn. to carbon radicals; peroxyl radical fragmentation or rearrangement; peroxyl radical addn. to carbon-carbon double bonds or cyclization; and peroxylperoxyl termination. There are a no. of reviews of lipid peroxidn. that have appeared in recent years, particularly related to the biol. of lipid oxidn. products. We focus here principally on the basic free radical chem. of lipid peroxidn. and recent developments for the detection and anal. of free radical lipid peroxidn. products and their biol. relevance. The anal. of lipid peroxidn. products has been particularly important in the advancement of research in this field because of the complexity of product mixts.
    10. 10
      Gardner, H. W. Oxygen radical chemistry of polyunsaturated fatty acids. Free Radical Biol. Med. 1989, 7, 65– 86,  DOI: 10.1016/0891-5849(89)90102-0
      10
      Oxygen radical chemistry of polyunsaturated fatty acids
      Gardner, Harold W.
      Free Radical Biology & Medicine (1989), 7 (1), 65-86CODEN: FRBMEH; ISSN:0891-5849.
      A review with 109 refs. covering peroxyl radicals in polyunsatd. fatty acid autoxidn., cleavage of hydrperoxides to give either a peroxyl or alkoxy radical, intramol. rearrangement of peroxyl to give cyclic peroxides or bicyclic endoperoxides, epoxide formation from alkoxyl radicals, and rearrangement of hydroperoxides.
    11. 11
      Soucek, M. D.; Khattab, T.; Wu, J. Review of autoxidation and driers. Prog. Org. Coat. 2012, 73, 435– 454,  DOI: 10.1016/j.porgcoat.2011.08.021
      11
      Review of autoxidation and driers
      Soucek, M. D.; Khattab, T.; Wu, J.
      Progress in Organic Coatings (2012), 73 (4), 435-454CODEN: POGCAT; ISSN:0300-9440. (Elsevier B.V.)
      A review. This article is an overview of the chem. and driers used in autoxidatively cured coatings and in particular alkyds. The drying process for alkyds and other unsatd. fatty acid materials is based on a series of chem. reactions known as autoxidn. The autoxidative process is usually catalyzed by metal salts known as driers. Numerous of investigations have elucidated the catalytic activity and reaction mechanism of the drying process. Spectroscopic techniques, esp. mass spectrometry, have been used to study the autoxidn. process and its products. Recent investigations on the oxidative drying of alkyd coating films are presented with a focus on both metal based and more environmental friendly means of catalysis.
    12. 12
      Lazzari, M.; Chiantore, O. Drying and oxidative degradation of linseed oil. Polym. Degrad. Stab. 1999, 65, 303– 313,  DOI: 10.1016/S0141-3910(99)00020-8
      12
      Drying and oxidative degradation of linseed oil
      Lazzari, Massimo; Chiantore, Oscar
      Polymer Degradation and Stability (1999), 65 (2), 303-313CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Science Ltd.)
      The drying and oxidative degrdn. of linseed oil have been investigated through exposition of samples in form of thin films to indoor lab. conditions, or treated at a const. temp. of 80°C, or with irradn. at wavelengths > 295 mm. Structure and property changes resulted almost independent of the different treatments and were followed by FTIR spectra, TGA, DSC, insols. detn.- and size-exclusion chromatog. The initial phase of drying consists of the autoxidn. phenomenon of the unsatd. fatty acid components with the development of extensive crosslinking, together with formation of conjugated unsatns. The following stage of slow consumption of labile crosslinks gives rise to a highly stable network, which contains small amts. of low mol. wt. mols., either formed by fragmentation or still present as unreacted triglycerides. The oxidative degrdn. of linseed oil consists of the continuation of the hardening process, and only after long periods of artificial ageing, corresponding to years of natural ageing, the oxidn. also takes place on the alkyl segments, leading to partial fragmentation of the structure.
    13. 13
      Mallégol, J.; Lemaire, J.; Gardette, J. L. Drier influence on the curing of linseed oil. Prog. Org. Coat. 2000, 39, 107– 113,  DOI: 10.1016/S0300-9440(00)00126-0
      13
      Drier influence on the curing of linseed oil
      Mallegol, J.; Lemaire, J.; Gardette, J.-L.
      Progress in Organic Coatings (2000), 39 (2-4), 107-113CODEN: POGCAT; ISSN:0300-9440. (Elsevier Science S.A.)
      Fourier transform IR spectroscopy has been used to investigate the oxidative polymn. of linseed oil in presence of cobalt 2-ethylhexanoate drier. Cobalt drier addn. provokes the acceleration of all reactions involved in oxidn. and the formation of surface solid film. Quantification of oxidn. products using SF4 and NO treatments show lower concns. in carboxylic acids, ketones and alcs., for films cured with cobalt drier. Photoacoustic spectroscopy has been used to analyze oxidn. profiles at the surface of the solid film formed in presence of cobalt drier. Efficiency as peroxides decomposers of cobalt, zirconium and calcium/zirconium drier, alone and in combination, were compared, by measuring variations of the peroxide value as a function of oxidn. time. Indeed, peroxide value detn. in oxidized drying oils can be considered as a measure of the extent of curing. It was shown that the activity of primary drier (Co) was modified by addn. of secondary drier such as Zr or Ca/Zr.
    14. 14
      Van Gorkum, R.; Bouwman, E. The oxidative drying of alkyd paint catalysed by metal complexes. Coord. Chem. Rev. 2005, 249, 1709– 1728,  DOI: 10.1016/j.ccr.2005.02.002
      14
      The oxidative drying of alkyd paint catalysed by metal complexes
      van Gorkum, Remy; Bouwman, Elisabeth
      Coordination Chemistry Reviews (2005), 249 (17-18), 1709-1728CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
      The focus of this review paper is the transition metal chem. involved in alkyd (paint) drying. A general introduction is given on the compn. of a common alkyd paint and the latest insights in the structure of the dried alkyd film are discussed. The drying of an alkyd paint is an autoxidn. process catalyzed by transition metal salts. Thorough investigations have shed light on the role of the transition metals as catalysts in the drying process and a wealth of spectroscopic techniques have been used to monitor the autoxidn. process and to analyze the autoxidn. products. More recently, these techniques have been used to develop a test reaction for the rapid screening of new manganese and iron based drier catalysts. Promising new driers based on simple manganese complexes have been proposed as replacements for the environmentally unfriendly cobalt driers that are presently used in alkyd paints.
    15. 15
      Hubert, J. C.; Venderbosch, R. A. M.; Muizebelt, W. J.; Klaasen, R. P.; Zabel, K. H. Mechanistic study of drying of alkyd resins using (Z, Z)-and (E, E)-3, 6-nonadiene as model substances. Prog. Org. Coat. 1997, 31, 331– 340,  DOI: 10.1016/S0300-9440(97)00091-X
      15
      Mechanistic study of drying of alkyd resins using (Z,Z)- and (E,E)-3,6-nonadiene as model substances
      Hubert, J. C.; Venderbosch, R. A. M.; Muizbelt, W. J.; Klaasen, R. P.; Zabel, K. H.
      Progress in Organic Coatings (1997), 31 (4), 331-340CODEN: POGCAT; ISSN:0300-9440. (Elsevier Science S.A.)
      The cobalt-catalyzed autoxidative drying of alkyd resins was studied using (Z,Z)-3,6-nonadiene and (E,E)-3,6-nonadiene as model compds. A large no. of reaction products were isolated from the autoxidn. mixt. using HPLC and preparative size exclusion chromatog. and identified with 1H- and 13C-NMR. The identified compds. comprised C9 hydroperoxides, endoperoxides, epoxides, aldehydes and ketones and some other oxidn. products. Their chem. structures pointed to three different types of oxidn. processes taking place. Besides the main radical autoxidn. reaction, evidence was found for photo-sensitized oxidn. involving singlet oxygen. Thirdly, epoxidn. occurs via peracids or hydroperoxides formed as intermediates. Because of the large no. of possible isomers having similar phys. properties, isolation of dimers required considerable effort. Nevertheless, two dimers were isolated and characterized. Their structures indicate crosslinking to occur by recombination of radicals as termination reaction.
    16. 16
      Oyman, Z. O.; Ming, W.; Micciche, F.; Oostveen, E.; Van Haveren, J.; van Der Linde, R. A promising environmentally-friendly manganese-based catalyst for alkyd emulsion coatings. Polymer 2004, 45, 7431– 7436,  DOI: 10.1016/j.polymer.2004.08.052
      16
      A promising environmentally-friendly manganese-based catalyst for alkyd emulsion coatings
      Oyman, Z. O.; Ming, W.; Micciche, F.; Oostveen, E.; van Haveren, J.; van der Linde, R.
      Polymer (2004), 45 (22), 7431-7436CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      A manganese(IV) complex (MnMeTACN) contg. 1,4,7-trimethyl-1,4,7-triazacyclononane (MeTACN), in the presence of polyamines, significantly accelerated the oxidn. of Et linoleate (EL) emulsions, and appeared to be a potential environmentally-friendly alternative for Co-based driers that are currently widely used for alkyd emulsion coatings. The polyamines greatly enhanced the catalytic activity of MnMeTACN in decompg. the formed hydroperoxides during the oxidn. of EL.
    17. 17
      Oakley, L.; Casadio, F.; Shull, K.; Broadbelt, L. Microkinetic modeling of the autoxidative curing of an alkyd and oil-based paint model system. Appl. Phys. A: Mater. Sci. Process. 2015, 121, 869,  DOI: 10.1007/s00339-015-9363-1
      17
      Microkinetic modeling of the autoxidative curing of an alkyd and oil-based paint model system
      Oakley, Lindsay H.; Casadio, Francesca; Shull, Kenneth R.; Broadbelt, Linda J.
      Applied Physics A: Materials Science & Processing (2015), 121 (3), 869-878CODEN: APAMFC; ISSN:0947-8396. (Springer)
      Elucidating the curing and aging mechanisms of alkyd and other oil-based paints is valuable for the fields of conservation and bio-based coatings. Recent research has demonstrated the limitations of artificial aging in predicting the actual properties of paints that are hundreds of years old. Kinetic modeling offers pathways to develop a realistic and dynamic description of the compn. of these oil-based paint coatings and facilitates the exploration of the effects of various environmental conditions on their long-term chem. stability. This work presents the construction of a kinetic Monte Carlo framework from elementary steps for the cobalt-catalyzed autoxidative curing of an Et linoleate model system up to the formation of single cross-links. Kinetic correlations for reaction families of similar chem. are employed to reduce the no. of parameters required to calc. rate consts. in Arrhenius form. The model, developed from mechanisms proposed in the literature, shows good agreement with expt. for the formation of primary products in the early stages of curing. The model has also revealed that the mechanisms proposed in the literature for the formation of secondary products, such as volatile aldehydes, are still not well established, and alternative routes are under evaluation.
    18. 18
      Hermans, J. J.; Keune, K.; van Loon, A.; Iedema, P. D. An infrared spectroscopic study of the nature of zinc carboxylates in oil paintings. J. Anal. At. Spectrom. 2015, 30, 1600– 1608,  DOI: 10.1039/C5JA00120J
      18
      An infrared spectroscopic study of the nature of zinc carboxylates in oil paintings
      Hermans, Joen J.; Keune, Katrien; van Loon, Annelies; Iedema, Piet D.
      Journal of Analytical Atomic Spectrometry (2015), 30 (7), 1600-1608CODEN: JASPE2; ISSN:0267-9477. (Royal Society of Chemistry)
      The formation of metal soaps is a major problem for oil paintings conservators. The complexes of either lead or zinc and fatty acids are the product of reactions between common pigments and the oil binder, and they are assocd. with many types of degrdn. that affect the appearance and stability of oil paint layers. Fourier transform IR spectroscopy (FTIR) reveals that a paint sample from The Woodcutter (after Millet) by Vincent van Gogh contains two distinct zinc carboxylate species, one similar to cryst. zinc palmitate and one that is characterized by a broadened asym. stretch COO- band shifted to 1570-1590 cm-1. This observation has been made in many paintings. Although several hypotheses exist to explain the shifted broad carboxylate band, these were not supported by exptl. evidence. In this paper, expts. were carried out to characterize the second zinc carboxylate type. It is shown that neither variations in the compn. of zinc soaps (i.e. zinc soaps contg. mixts. of fatty acids or metals) nor fatty acids adsorbed on pigment surfaces are responsible for the second zinc carboxylate species. X-Ray diffraction (XRD) and FTIR anal. indicate that the broad COO- band represents amorphous zinc carboxylates. These species can be interpreted as either non-cryst. zinc soaps or zinc ions bound to carboxylate moieties on the polymd. oil network, a system similar to ionomers. These findings uncover an intermediate stage of metal soap-related degrdn. of oil paintings, and lead the way to improved methods for the prevention and treatment of oil paint degrdn.
    19. 19
      Hermans, J. J.; Keune, K.; van Loon, A.; Corkery, R. W.; Iedema, P. D. Ionomer-like structure in mature oil paint binding media. RSC Adv. 2016, 6, 93363– 93369,  DOI: 10.1039/C6RA18267D
      19
      Ionomer-like structure in mature oil paint binding media
      Hermans, Joen J.; Keune, Katrien; van Loon, Annelies; Corkery, Robert W.; Iedema, Piet D.
      RSC Advances (2016), 6 (96), 93363-93369CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
      IR spectra of samples from oil paintings often show metal carboxylate bands that are broader and shifted compared to those of cryst. metal soap stds. (metal complexes of long-chain satd. fatty acids). Using quant. attenuated total reflection Fourier transform IR spectroscopy (ATR-FTIR), it is demonstrated that the broad metal carboxylate band is typically too intense to be explained by carboxylates adsorbed on the surface of pigment particles or disordered metal complexes of satd. fatty acids. The metal carboxylate species assocd. with the broad bands must therefore be an integral part of the polymd. binding medium. Small-angle X-ray scattering (SAXS) measurements on model ionomer systems based on linseed oil revealed that the medium contains ionic clusters similar to more classical ionomers. These structural similarities are very helpful in understanding the chem. of mature oil paint binding media and the potential degrdn. mechanisms that affect oil paintings.
    20. 20
      Van Der Wel, G. K.; Adan, O. C. G. Moisture in organic coatings - a review. Prog. Org. Coat. 1999, 37, 1– 14,  DOI: 10.1016/S0300-9440(99)00058-2
      20
      Moisture in organic coatings - a review
      van der Wel, G. K.; Adan, O. C. G.
      Progress in Organic Coatings (1999), 37 (1-2), 1-14CODEN: POGCAT; ISSN:0300-9440. (Elsevier Science S.A.)
      A review, with 71 refs., is given on transport and equil. sorption of moisture in polymer films and org. coatings. Polymeric material forms the continuous phase of a coating and is therefore important for transport properties. Besides polymer, coatings consist of pigments and fillers and various additives, each of them affecting moisture transport. Firstly, in this paper typical transport and equil. characteristics of pure polymer films are covered, and secondly those of coatings, assimilating the impact of pigments, fillers and additives. Discrimination between Fickian and non-Fickian effects is usually based on the appearance of kinetic absorption curves. Several types of curve are dealt with, and models that describe these curves are discussed. These include "two-stage" sorption, "sigmoidal" sorption and "Case II" sorption. The common practice of fitting Fick's law to kinetic data by means of relaxation parameters is criticized. Transport kinetics are modelled on the basis of kinetic plots, thereby introducing relaxation parameters in Fick's diffusion law. Although these models describe moisture transport in polymers reasonably, these models imply a lot of "curve-fitting" without a clear mechanistic foundation. Equil. sorption of moisture in polymeric systems is reflected by their sorption isotherms. Type II and III isotherms of the BET classification are commonly encountered, together with linear isotherms according to Henry's law. The suitability of porous media adsorption models for polymeric systems is discussed. These models are treated in relation to interactions of water in polymers, since localized binding of water to specific groups may justify the use of these models. Pigments may lower moisture permeation, but non-ideality of pigmentation reduces this effect. Coating additives increase moisture soly., but only little is known in detail.
    21. 21
      Fieldson, G. T.; Barbari, T. A. The use of FTi.r.-a.t.r. spectroscopy to characterize penetrant diffusion in polymers. Polymer 1993, 34, 1146– 1153,  DOI: 10.1016/0032-3861(93)90765-3
      21
      The use of attenuated total reflection FTIR spectroscopy to characterize penetrant diffusion in polymers
      Fieldson, G. T.; Barbari, T. A.
      Polymer (1993), 34 (6), 1146-53CODEN: POLMAG; ISSN:0032-3861.
      The diffusion of liq. water in polyacrylonitrile (I) was measured using FTIR attenuated total reflection spectroscopy. The measured diffusion coeffs. agreed well with those reported in the literature for high-activity water vapor in I. The test also demonstrated both the reproducibility and accuracy of FTIR expts. for measuring the diffusion coeff. The diffusion coeff. and the amt. of water sorbed at equil. were dependent on the temp. at which the films were treated.
    22. 22
      Hong, S. U.; Barbari, T. A.; Sloan, J. M. Multicomponent diffusion of methyl ethyl ketone and toluene in polyisobutylene from vapor sorption FTIR-ATR spectroscopy. J. Polym. Sci., Part B: Polym. Phys. 1998, 36, 337– 344,  DOI: 10.1002/(SICI)1099-0488(19980130)36:2<337::AID-POLB12>3.0.CO;2-I
      22
      Multicomponent diffusion of methyl ethyl ketone and toluene in polyisobutylene from vapor sorption FTIR-ATR spectroscopy
      Hong, S. U.; Barbari, T. A.; Sloan, J. M.
      Journal of Polymer Science, Part B: Polymer Physics (1998), 36 (2), 337-344CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
      Diffusion coeffs. of toluene/methyl Et ketone (MEK) mixts. in polyisobutylene were measured at 50°C using vapor sorption FTIR-ATR (Fourier Transform IR Attenuated Total Reflectance) spectroscopy. For three mixt. compns., the diffusion coeffs. were detd. using a diffusion framework for ternary systems. The "crossterm" diffusion coeff. for MEK was found to be very small under the exptl. conditions studied here, while that for toluene was found to increase with increasing MEK concn. On the basis of this finding, a binary diffusion model was used to det. diffusion coeffs. for MEK over a wide range of mixt. compns. and the results compared well with those detd. from pure MEK transport data. Relative transport rates during integral sorption expts. with mixts. were used to explain the results.
    23. 23
      Sammon, C.; Yarwood, J.; Everall, N. A FTIR-ATR study of liquid diffusion processes in PET films: Comparison of water with simple alcohols. Polymer 2000, 41, 2521– 2534,  DOI: 10.1016/S0032-3861(99)00405-X
      23
      A FTIR-ATR study of liquid diffusion processes in PET films: comparison of water with simple alcohols
      Sammon, C.; Yarwood, J.; Everall, N.
      Polymer (1999), 41 (7), 2521-2534CODEN: POLMAG; ISSN:0032-3861. (Elsevier Science Ltd.)
      An in-situ FTIR-ATR method for simultaneously obtaining both kinetic and structural information during liq. sorption into polymers was presented. The kinetics and diffusion profile of the sorption of liq. water and liq. methanol into poly(ethylene terephthalate) (PET) were compared and contrasted. The diffusion of water into PET was shown to follow Fickian kinetics, without significant swelling and the calcd. diffusion coeffs. (D) varied between 8.57 and 0.52 × 10-9 cm2 s-1 for a crystallinity range of 4-25%. The D values decreased non-linearly with the increase in crystallinity. The av. spherulitic crystal size was thought to play a significant role in detg. the rate of water sorption. Conversely, the sorption of liq. methanol was accompanied by significant swelling and crystn. and hence showed non-Fickian or anomalous kinetics. The sorption data were fitted to a dual-sorption model which indicated that the rate of diffusion of liq. methanol was faster than that of liq. water, probably due to the accompanying swelling. Increasing the level of crystallinity was shown to decrease the capacity for the polymer to swell and reduced the calcd. diffusion coeffs.
    24. 24
      Guo, J.; Barbari, T. A. Unified dual mode description of small molecule sorption and desorption kinetics in a glassy polymer. Macromolecules 2009, 42, 5700– 5708,  DOI: 10.1021/ma9007576
      24
      Unified Dual Mode Description of Small Molecule Sorption and Desorption Kinetics in a Glassy Polymer
      Guo, Juchen; Barbari, Timothy A.
      Macromolecules (Washington, DC, United States) (2009), 42 (15), 5700-5708CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      FTIR-ATR (Fourier transform IR-attenuated total reflectance) spectroscopy and a conventional gravimetric sorption balance were used to study sorption and desorption kinetics of vapor phase acetonitrile in glassy cellulose acetate. A time delay was obsd. in the measured concn. at the polymer-crystal interface from the FTIR-ATR expts. that was longer than expected from applying the simple Fickian diffusion model used to fit the gravimetric data for this system. By using the dual mode sorption model with total immobilization of the hole population rather than a simple Fickian framework, the time behavior at the boundary was readily captured. This model in turn was used to fit the FTIR-ATR data for desorption kinetics. The desorption diffusion coeffs. were considerably higher than those obtained for sorption owing to the necessary redistribution between the dissolved and hole populations when the classic dual mode sorption model is applied to the desorption isotherm. To resolve this inconsistency and remove the discontinuity in concn. at the penetrant-polymer boundary between sorption and desorption, a unified dual mode model to describe both sorption and desorption is proposed. In this model, a fraction of the dissolved population creates holes during the sorption process at each activity. The new model was applied to the sorption and desorption kinetics data in this study, resulting in unifying dual mode parameters and comparable diffusion coeffs.
    25. 25
      Farinas, K. C.; Doh, L.; Venkatraman, S.; Potts, R. O. Characterization of solute diffusion in a polymer using ATR-FTIR spectroscopy and bulk transport techniques. Macromolecules 1994, 27, 5220– 5222,  DOI: 10.1021/ma00096a055
      There is no corresponding record for this reference.
    26. 26
      Dias, M.; Hadgraft, J.; Raghavan, S. L.; Tetteh, J. The effect of solvent on permeant diffusion through membranes studied using ATR-FTIR and chemometric data analysis. J. Pharm. Sci. 2004, 93, 186– 196,  DOI: 10.1002/jps.10530
      There is no corresponding record for this reference.
    27. 27
      Van Alsten, J. G. Ionic and Chain Interdiffusion and Interfacial Strength Development in Ionomers of Poly(ethylene- co -methacrylic acid). Macromolecules 1996, 29, 2163– 2168,  DOI: 10.1021/ma950431f
      There is no corresponding record for this reference.
    28. 28
      Fleming, O. S.; Chan, K. L. A.; Kazarian, S. G. High-pressure CO2-enhanced polymer interdiffusion and dissolution studied with in situ ATR-FTIR spectroscopic imaging. Polymer 2006, 47, 4649– 4658,  DOI: 10.1016/j.polymer.2006.04.059
      28
      High-pressure CO2-enhanced polymer interdiffusion and dissolution studied with in situ ATR-FTIR spectroscopic imaging
      Fleming, Oliver S.; Chan, K. L. Andrew; Kazarian, Sergei G.
      Polymer (2006), 47 (13), 4649-4658CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      A novel application of attenuated total reflection Fourier transform IR (ATR-FTIR) spectroscopic imaging to study polymer interdiffusion and dissoln. under high-pressure or supercrit. carbon dioxide environments has been demonstrated. Miscible systems of polyvinylpyrrolidone (PVP) and poly(ethylene glycol) (PEG) of different mol. wts. have been chosen for this investigation. These systems were subjected to a controlled pressure of CO2 and the interfacial area of contact between the two polymers was studied by ATR-FTIR imaging in situ. Using this spectroscopic imaging approach, the phenomenon of polymer interdiffusion enhanced by CO2 dissolved in both polymers was investigated as a function of time. The evolution of spatially resolved images as a function of time was studied with FTIR imaging and the corresponding concn. profiles for both polymers were obtained. The chem. specificity of FTIR imaging also allowed us to measure the amt. of CO2 dissolved in each domain of the polymer system. Effects of PEG mol. wt. and pressure of CO2 on the mechanism and the rate of polymer interdiffusion was investigated. This approach has not only shown the ability to visualize the process of interdiffusion but also demonstrated the ability of high-pressure CO2 to 'tune' the rate of interdiffusion, this information is important for a better understanding of CO2-induced mixing of polymeric materials.
    29. 29
      Stolow, N. Action of Solvents on Dried Linseed Oil Films. Nature 1957, 179, 579– 580,  DOI: 10.1038/179579b0
      29
      Action of solvents on dried linseed-oil films
      Stolow, N.
      Nature (London, United Kingdom) (1957), 179 (), 579-80CODEN: NATUAS; ISSN:0028-0836.
      Action of a range of org. solvents on aged linseed-oil films, pigmented and unpigmented, was investigated. A specially designed app. based on the parallel-plate viscometer was used to make precise measurements of changes in thickness of films coated on a rigid substrate, while free films were observed under a microscope. Random, amorphous structure concepts for linseed-oil films were given support from the results of tests made. The result of leaching and swelling was a film of greater d. with altered swelling characteristics. Degree of swelling depends on the solvent used. Method of measurement enabled rates of swelling or diffusion to be investigated and it was found that Fick's law of diffusion for a semi-infinite solid applied up to 0.6 to 0.8 of the swelling max. By raising the temp. the rate of diffusion of solvent was markedly increased. It was found that pigmentation slowed down the progress of diffusion owing to the impedance of the pigment particles.
    30. 30
      Phenix, A. The Swelling of Artists’ Paints in Organic Solvents. Part 1, a Simple Method for Measuring the In-Plane Swelling of Unsupported Paint Films. J. Am. Inst. Conserv. 2002, 41, 43,  DOI: 10.2307/3179896
      There is no corresponding record for this reference.
    31. 31
      Ward, S. A.; Pethrick, R. A. Positron annihilation lifetime spectroscopy and diffusion studies of large molecule penetrants into alkyd resins. Prog. Org. Coat. 2012, 75, 509– 526,  DOI: 10.1016/j.porgcoat.2012.06.002
      31
      Positron annihilation lifetime spectroscopy and diffusion studies of large molecule penetrants into alkyd resins
      Ward, Shelia A.; Pethrick, Richard A.
      Progress in Organic Coatings (2012), 75 (4), 509-526CODEN: POGCAT; ISSN:0300-9440. (Elsevier B.V.)
      Alkyd resins can be used to create transparent films and their characteristics depend on the method used in their cure. Changing the catalysts can have profound effects on the phys. properties of the films formed. Positron annihilation lifetime spectroscopy (PALS) measurements are used to explore how changes in catalyst influence the free vol. for an alkyd resin system. Diffusion measurements are reported for large mol. permeants; dioctyl phthalate, 2-Et hexylbenzyl phthalate, nonyl phenol ethoxylate, iso-Pr myristate and oleic acid into these alkyd resins. The diffusion behavior changes as the temp. is raised through the glass transition temp. of the resin but is also sensitive to the chem. structure of the permeant. The diffusion deviates from simple Fickian behavior in a no. of cases and is indicative of plasticization influencing diffusion. Comparison of the av. mol. size with the available free vol. indicates that diffusion involves a complex co-operative motion in which the matrix plays an important role. Increasing the crosslink d. by post cure of the alkyd resin at elevated temps., reduces the free vol. and decreases the ability for the large mols. to permeate in to the matrix. Oleic acid exhibits a two stage diffusion process; the second stage being assocd. with opening up of the resin structure as a result of acid catalyzed degrdn. The unusual behavior of iso-Pr myristate is attributed to a combination of its ability to adopt favorable conformations and a high degree of compatibility with the matrix. This study highlights the importance of the chem. structure of the permeant on its ability to enter and diffuse through the coating.
    32. 32
      Sharma, V.; Banait, J. S.; Kundu, P. P. Swelling kinetics of linseed oil-based polymers. J. Appl. Polym. Sci. 2009, 111, 1816– 1827,  DOI: 10.1002/app.29006
      32
      Swelling kinetics of linseed oil-based polymers
      Sharma, Vinay; Banait, J. S.; Kundu, P. P.
      Journal of Applied Polymer Science (2009), 111 (4), 1816-1827CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
      Kinetics of swelling and sorption behavior of copolymers based on linseed oil, styrene, divinylbenzene, and acrylic acid obtained by cationic and thermal polymn. is studied in THF at different temps. The values of n in the transport equation are found to be below 0.4, showing non-Fickian or pseudo-Fickian transport in the polymers. The dependence of diffusion coeff. on the compn. and temp. has also been studied for the linseed oil-based polymers. The diffusion coeff. in cationic samples decreases with an increase in the oil contents in the samples. In case of thermal samples, the diffusion coeff. first increases up to 30% oil contents and then decreases. The diffusion coeff. decreases with an increase in temp. for all of the linseed oil polymer samples. The sorption coeff. increases with an increase in the oil contents for all samples. The crosslink d. (calcd. from the THF swelling) ranges from 20.16 to 92.34 × 106 mol/cm3 for cationic samples and 20.62 to 86.01 × 106 mol/cm3 for thermal samples.
    33. 33
      Chan, T. Y. A.; Odlyha, M. The effect of relative humidity and pigment type on paint films. Thermochim. Acta 1995, 269–270, 755– 767,  DOI: 10.1016/0040-6031(95)02669-X
      33
      The effect of relative humidity and pigment type on paint films
      Chan, T. Y. A.; Odlyha, M.
      Thermochimica Acta (1995), 269/270 (), 755-67CODEN: THACAS; ISSN:0040-6031. (Elsevier)
      Thermogravimetry was used to continuously monitor the moisture uptake of paint film at given temp. and relative humidity as a function of time. The elec. properties of the paint films were studied by low frequency dielec. spectroscopy over the frequency range 10-4 to 105. The crit. frequency increased with increasing relative humidity and moisture content. The adsorbed water layers were formed on the surfaces of the pigment grains. A model was presented to describe the "charge hopping" process in the adsorbed water layers which gave rise to the low frequency dispersion.
    34. 34
      Nguyen, T.; Bentz, D.; Byrd, E. Method for measuring water diffusion in a coating applied to a substrate. J. Coat. Technol. 1995, 67, 37– 46
      34
      Method for measuring water diffusion in a coating applied to a substrate
      Nguyen, T.; Bentz, D.; Byrd, E.
      Journal of Coatings Technology (1995), 67 (844), 37-46CODEN: JCTEDL; ISSN:0361-8773. (Federation of Societies for Coatings Technology)
      A method based on Fourier-transform IR-multiple internal reflection (FTIR-MIR) spectroscopy was developed for measuring the apparent diffusion coeff. of water in a coating applied to a substrate. The method requires an application of a coating of any thickness on an internal reflection element, which serves as the substrate, with the attachment of a water chamber to the coated specimen. Water is introduced to the chamber and FTIR-MIR spectra are collected automatically without disturbing the specimen or the instrument. The amt. of water at the coating/substrate interface was detd. using a model based on the theory of internal reflection spectroscopy. A mass-time curve for water at the interface is established, which provides the time-lag value, the time required for water to diffuse through the coating film and reach the interface. The diffusion coeff. (D) is then detd. by the time-lag equation. For thick coating films (>25 μm), D may be estd. from the FTIR-MIR in situ intensity data only. The sensitivity of FTIR-MIR spectroscopy and the strong FTIR absorption of water mols. make this an ideal method for measuring the diffusivity of liq. water through a coating applied to a substrate.
    35. 35
      Liu, B.; Li, Y.; Lin, H.; Cao, C.-n. Effect of PVC on the diffusion behaviour of water through alkyd coatings. Corros. Sci. 2002, 44, 2657– 2664,  DOI: 10.1016/S0010-938X(02)00061-6
      35
      Effect of PVC on the diffusion behaviour of water through alkyd coatings
      Liu, Bin; Li, Ying; Lin, Haichao; Cao, Chu-nan
      Corrosion Science (2002), 44 (12), 2657-2664CODEN: CRRSAA; ISSN:0010-938X. (Elsevier Science Ltd.)
      The diffusion behavior of water through alkyd coatings with micaceous iron oxide pigment at different pigment vol. concn. (PVC) was studied by EIS and SEM techniques. The diffusion coeffs. of water through the coatings were also calcd. The exptl. results showed that, in the initial diffusion period, the diffusion processes of water through alkyd coatings immersed in 0.5 M NaCl followed the Fick's second law. Within the PVC values which have been studied, the diffusion coeffs. of water diffusing through alkyd coatings initially decreased with increasing PVC, reaching a min. value at 60%, and then increased with increasing PVC. When PVC was less than 60%, the barrier property of pigment was the main factor affecting the water diffusion behavior. However, the coatings' microstructure played an important role when PVC was greater than 60%.
    36. 36
      Xu, Y.; Yan, C.; Ding, J.; Gao, Y.; Cao, C. Water vapour in the coatings of alkyd and polyurethane varnish. Prog. Org. Coat. 2002, 45, 331– 339,  DOI: 10.1016/S0300-9440(02)00069-3
      36
      Water vapor in the coatings of alkyd and polyurethane varnish
      Xu, Yongxiang; Yan, Chuanwei; Ding, Jie; Gao, Yanmin; Cao, Chunan
      Progress in Organic Coatings (2002), 45 (4), 331-339CODEN: POGCAT; ISSN:0300-9440. (Elsevier Science B.V.)
      Absorption and desorption of water vapor in alkyd and polyurethane varnish were studied by a quartz crystal microbalance. The absorption and desorption kinetics curves were Fickian in nature when the relative humidity is higher than 30%, while the soly. followed Henry's law. The av. diffusion coeff. was calcd. A residual amt. of water was found to remain in the coatings after extended exposure to dry air. FTIR anal. showed that the mol. structure of the coatings changed after the absorption and desorption of water vapor. The results showed that the residual water reacted with the coatings mol.
    37. 37
      van der Zanden, A.; Goossens, E. The measurement of the diffusion coefficient and the sorption isotherm of water in paint films. Chem. Eng. Sci. 2003, 58, 1521– 1530,  DOI: 10.1016/S0009-2509(02)00674-7
      37
      The measurement of the diffusion coefficient and the sorption isotherm of water in paint films
      Van Der Zanden, A. J. J.; Goossens, E. L. J.
      Chemical Engineering Science (2003), 58 (8), 1521-1530CODEN: CESCAC; ISSN:0009-2509. (Elsevier Science Ltd.)
      An exptl. technique together with a numerical model is proposed with which the diffusion coeff. and the sorption isotherm of water in paint can be measured. Inside a closed vessel, paint films are on stainless-steel plates. Water is present as water vapor in the air and in the paint. After blowing dry or wet air through the vessel for some time, the situation moves to a new equil. The relative humidity of the air inside the vessel is measured as a function of time. From fitting the theor./numerical model against the exptl. values, follow the diffusion coeff. and the sorption isotherm of water in the paint. The results show large scattering. When the independently measured sorption isotherm is used as an input parameter in the model, the fitting procedure gives much smaller scattering for the diffusion coeff.
    38. 38
      Saarinen, V.; Kreuer, K. D.; Schuster, M.; Merkle, R.; Maier, J. On the swelling properties of proton conducting membranes for direct methanol fuel cells. Solid State Ionics 2007, 178, 533– 537,  DOI: 10.1016/j.ssi.2006.12.001
      38
      On the swelling properties of proton conducting membranes for direct methanol fuel cells
      Saarinen, V.; Kreuer, K. D.; Schuster, M.; Merkle, R.; Maier, J.
      Solid State Ionics (2007), 178 (7-10), 533-537CODEN: SSIOD3; ISSN:0167-2738. (Elsevier B.V.)
      The swelling properties of different fluorinated (Nafion 117, poly(ethylene-alt-tetrafluoroethylene) and poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid)) and hydrocarbon (sulfonated poly(phenylene sulfone)) proton conducting ionomers were studied in alc. (MeOH, EtOH, 2-propanol, tBuOH)-water and H2SO4-water mixts. Solvent uptake and its water/alc. selectivity were detd. by thermal desorption using combined thermogravimetry (TGA) and mass spectrometry (MS). Clear trends are obsd. for the selectivity: preferential water uptake (alc. rejection) correlates with high IEC (ion exchange capacity) and low solvent uptake (swelling) indicating a preferred interaction of the ionic groups (-SO3-, H+) and the groups on the polymerbackbone carrying partial charges (e.g. sulfone units (-SO2-) in the sulfonated poly(phenylene sulfone)) with water. The total swelling significantly decreases in the presence of H2SO4 indicating osmosis being a major driving force in the swelling process. This is particularly low for ETFE-SA, which is highlighting its supreme mech. properties and its high selectivity for water uptake (selectivity coeffs. ≤10 for λ =7). Unlike Nafion, which shows high swelling in alc.-water mixts. and almost no selectivity, high selectivity coeffs. (≤8) are obsd. for sulfonated poly(phenylene sulfone) even at medium solvent uptake (λ = 12). The total solvent uptake in these highly polar ionomers even decreases with methanol mole fraction and is virtually independent of temp. (T ≤120°). Together with the high proton cond. and high hydrolytic stability reported in the literature, the swelling properties presented in this work are making sulfonated poly(phenylene sulfone) interesting membrane materials for DMFC applications.
    39. 39
      Hallinan, D. T.; De Angelis, M. G.; Giacinti Baschetti, M.; Sarti, G. C.; Elabd, Y. A. Non-Fickian Diffusion of Water in Nafion. Macromolecules 2010, 43, 4667– 4678,  DOI: 10.1021/ma100047z
      39
      Non-Fickian Diffusion of Water in Nafion
      Hallinan, Daniel T., Jr.; Grazia De Angelis, Maria; Giacinti Baschetti, Marco; Sarti, Giulio C.; Elabd, Yossef A.
      Macromolecules (Washington, DC, United States) (2010), 43 (10), 4667-4678CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Understanding the dynamics of water in solid-state polymer electrolytes (e.g., Nafion) is important for a variety of applications ranging from membrane-based water purifn. to hydrogen fuel cells. In this study, the dynamics of water in Nafion was investigated at both low and high humidities with time-resolved Fourier transform IR-attenuated total reflectance (FTIR-ATR) spectroscopy; a technique that provides a mol. fingerprint of both the diffusant and the polymer simultaneously in real time. At low humidities (0-22% RH), an extended initial time lag resulted in non-Fickian behavior, where dynamic IR data provided evidence for a reaction between water and sulfonic acid. A diffusion-reaction model was developed and predicted this anomalous behavior, where the time lag was a function of water content. At high humidities (0-100% RH), a slow approach to steady state resulted in non-Fickian behavior, where dynamic IR data provided evidence of water-induced relaxation in the polymer backbone. A diffusion-relaxation model was developed and regressed well to both the polymer relaxation and water diffusion data, where only one fitting parameter was used for each data set to det. both a relaxation time const. and diffusion coeff. This approach differs significantly from previous work on non-Fickian behavior in glassy polymers, which, consisted of regressing gravimetric data to models with a min. of six fitting parameters. Not only do the diffusion coeffs. from these two models compare well with Fickian diffusion coeffs. from expts. with small water concn. gradients, but also the results in this study provide phys. insight into the transport mechanisms of water and relaxation phenomena in solid-state polymer electrolytes.
    40. 40
      Hickner, M. A. Water-mediated transport in ion-containing polymers. J. Polym. Sci., Part B: Polym. Phys. 2012, 50, 9– 20,  DOI: 10.1002/polb.22381
      40
      Water-mediated transport in ion-containing polymers
      Hickner, Michael A.
      Journal of Polymer Science, Part B: Polymer Physics (2012), 50 (1), 9-20CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
      A review. Water-mediated ion conduction enables high cond. in hydrated polymer membranes commonly used in electrochem. devices. Understanding the coupling of the absorbed water with the polymer matrix and the dynamics of water inside the polymer network across the full range of length scales in the membrane is important for unraveling the structure-property relationships in these materials. By considering the water behavior in ion-contg. polymers, next-generation fuel cell membranes are being designed that exceed the cond. of the state-of-the-art materials and have optimized cond. and permeability that may be useful in other types of devices such as redox flow batteries. Water-polymer assocns. can be exploited to tune the transport and mech. property tradeoffs in these polymers. Measurements of water motion provide important criteria for assessing the factors that control the performance of these types of materials. This review article discusses current understanding of water behavior in ion-contg. polymers and the relation between water motion and ion and mol. transport. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011.
    41. 41
      Dishari, S. K.; Hickner, M. A. Antiplasticization and water uptake of nafion thin films. ACS Macro Lett. 2012, 1, 291– 295,  DOI: 10.1021/mz200169a
      41
      Antiplasticization and Water Uptake of Nafion Thin Films
      Dishari, Shudipto K.; Hickner, Michael A.
      ACS Macro Letters (2012), 1 (2), 291-295CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      Fluorescence of 9-(2-carboxy-2-cyanovinyl)julolidine (CCVJ) was measured to probe the local motion within 70-600 nm thick Nafion films at controlled levels of hydration. Thinner films showed increased confinement under dry conditions as evidenced by their high fluorescence intensity values per unit thickness. Antiplasticization, or a stiffening of the film, was obsd. as an increase in fluorescence intensity when the sample was exposed to low water activity (≤30% RH) and the extent of antiplasticization changed with film thickness. At higher relative humidities, the films became plasticized with water and the fluorescence of CCVJ declined. Quartz crystal microbalance (QCM) expts. revealed higher hydration nos. (λ = nH2O/nSO3H) in thinner films on SiO2 surfaces. The higher water uptake in thin films was explained by considering the polymer order at the Nafion-SiO2 interface and the influence of this interfacial layer on the swelling properties of thin films.
    42. 42
      Davis, E. M.; Stafford, C. M.; Page, K. A. Elucidating water transport mechanisms in Nafion thin films. ACS Macro Lett. 2014, 3, 1029– 1035,  DOI: 10.1021/mz500515b
      42
      Elucidating Water Transport Mechanisms in Nafion Thin Films
      Davis, Eric M.; Stafford, Christopher M.; Page, Kirt A.
      ACS Macro Letters (2014), 3 (10), 1029-1035CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
      Ion-exchange membranes are crit. components of hydrogen fuel cells, where these ionomers can be confined to nanoscale thicknesses, altering the phys. properties of these films from that of bulk membranes. Therefore, it is important to develop methods capable of measuring and elucidating the transport mechanisms under thin film confinement compared to bulk Nafion. In this study, water sorption and diffusion in a Nafion thin film were measured using time-resolved in situ polarization modulation IR reflection absorption spectroscopy (PM-IRRAS). Interfacial mass transport limitations were confirmed to be minimal, while restricted water diffusion was obsd., where the effective diffusion coeff. of water in the thin Nafion film was many orders of magnitude lower (between 4 and 5 orders of magnitude) than those reported for bulk membranes and was dependent on the initial hydration state of the Nafion. Furthermore, the response of the hydrophobic domains (Teflon backbone) to the swelling of the hydrophilic domains (ionic clusters) was shown to be orders of magnitude slower than that of bulk Nafion.
    43. 43
      Yao, K. Z.; Shaw, B. M.; Kou, B.; McAuley, K. B.; Bacon, D. W. Modeling Ethylene/Butene Copolymerization with Multi-site Catalysts: Parameter Estimability and Experimental Design. Polym. React. Eng. 2003, 11, 563– 588,  DOI: 10.1081/PRE-120024426
      43
      Modeling ethylene/butene copolymerization with multi-site catalysts: parameter estimability and experimental design
      Yao, K. Zhen; Shaw, Benjamin M.; Kou, Bo; McAuley, Kim B.; Bacon, D. W.
      Polymer Reaction Engineering (2003), 11 (3), 563-588CODEN: PREEEG; ISSN:1054-3414. (Marcel Dekker, Inc.)
      Mechanistic models for ethylene-1-butene copolymn. with Ziegler-Natta catalysts contain many kinetic rate consts. Precise ests. of key parameters are required if the models are to be used to obtain reliable predictions of copolymer properties for a specified catalyst over a range of polymn. conditions. In this paper, a novel method is developed to assist modelers in assessing whether their model parameters will be estimable from existing or proposed exptl. data, and in detg. subsets of influential parameters that can be estd. from the data when the complete set of model parameters cannot be estd. The effects of using different types of data, varying the no. of observations per exptl. run, and increasing the no. of exptl. runs on the no. of estimable parameters are considered. A method for comparison of the relative effectiveness of different exptl. designs for estg. key parameters in gas-phase ethylene copolymn. is also presented.
    44. 44
      Podgorski, L.; Merlin, A.; Saiter, J. Natural and artificial ageing of an alkyd based wood finish: Calorimetric investigations. J. Therm. Anal. 1994, 41, 1319– 1324,  DOI: 10.1007/BF02549926
      44
      Natural and artificial aging of an alkyd based wood finish. Calorimetric investigations
      Podgorski, L.; Merlin, A.; Saiter, J. M.
      Journal of Thermal Analysis (1994), 41 (6), 1319-24CODEN: JTHEA9; ISSN:0368-4466.
      Wood protection in exterior use is generally achieved with a stain. This protective product is often obtained from an alkyl resin. A natural and artificial aging were studied by measuring the glass transition temp. (Tg) of the finish variations in terms of time. In both agings, the Tg variations are the same; there is an increase in Tg during the first steps of ageing and then a stabilization. A behavior equation is proposed and is perfectly suitable to both agings. Time consts. are calcd.
    45. 45
      Hedley, G.; Odlyha, M.; Burnstock, A.; Tillinghast, J.; Husband, C. A study of the mechanical and surface properties of oil paint films treated with organic solvents and water. J. Therm. Anal. 1991, 37, 2067– 2088,  DOI: 10.1007/BF01905579
      45
      A study of the mechanical and surface properties of oil paint films treated with organic solvents and water
      Hedley, G.; Odlyha, M.; Burnstock, A.; Tillinghast, J.; Husband, C.
      Journal of Thermal Analysis (1991), 37 (9), 2067-88CODEN: JTHEA9; ISSN:0368-4466.
      The mech. and surface properties of naturally aged 12-yr-old samples of Pb white-linseed oil and burnt sienna-linseed oil paints treated with org. solvents and water were studied using thermomech. and dielec. techniques together with FTIR spectroscopy and SEM. Changes in the nature of the surfaces after treatment were obsd. The effects of water, iso-PrOH, and acetone immersion for 24 h and swabbing for a few min on the surfaces were measured directly in terms of the change in the shear modulus of the paint films together with the accompanying change in the ratio of viscous to elastic components present in each system. Generally, the solvent-treated films became harder and showed reduced viscous components, whereas the water-treated samples became softer. There was a change in the dielec. properties of the leached films which pointed to the polar nature of the leachings. FTIR diffuse reflectance spectra supported this conclusion.
    46. 46
      Phenix, A.; Mechanical, T.; Paints, O.; Phenix, A. Thermal Mechanical Transitions in Artists’ Oil Paints and Selected Conservation Materials: a Study by Dynamic Mechanical Analysis (DMA). AIC Paintings Specialty Group Postprints 2009, 22, 72– 89
      There is no corresponding record for this reference.
    47. 47
      Sanches, D.; Ramos, A. M.; Coelho, J. F. J.; Costa, C. S. M. F.; Vilarigues, M.; Melo, M. J. Correlating thermophysical properties with the molecular composition of 19th century chrome yellow oil paints. Polym. Degrad. Stab. 2017, 138, 201– 211,  DOI: 10.1016/j.polymdegradstab.2017.02.010
      47
      Correlating thermophysical properties with the molecular composition of 19th century chrome yellow oil paints
      Sanches, Diogo; Ramos, Ana Maria; Coelho, Jorge F. J.; Costa, Catia S. M. F.; Vilarigues, Marcia; Melo, Maria Joao
      Polymer Degradation and Stability (2017), 138 (), 201-211CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
      In the present study, we explore Dynamic Mech. Thermal Anal. (DMTA) as a tool for assessing the phys. performance in 19th century paints and to evaluate the parameters that influence the mech. properties of the paint films. This data is particularly important for accurate life-time predictions as well as better conservation treatments. DMTA is used to study the thermophys. properties of chrome yellow (PbCrO4) oil paints under the influence of common fillers found in 19th century chrome yellow oil paints: calcium carbonate (CaCO3), barium sulfate (BaSO4) and gypsum (CaSO4·2H2O). Oil paint mock-ups were dry to touch and included oil plus the single paint components (chrome yellow pigment and the three fillers) that were compared with 19th c. Winsor & Newton historic paint formulations. The fillers selected were applied with a ratio to pigment ranging from 10 to 40% in wt. DMTA data revealed that the addn. of solids (pigment and/or fillers) reduces the flexibility of the oil paint films, confirmed by the increase of the storage modulus (E') and glass transition temp. (Tg). DMTA provided a clear differentiation between the thermo-mech. behavior of the oil film and oil with inorg. compds. and, more importantly, pigment oil system vs. oil with fillers. The data revealed that the pigment and filler system oil is modulated essentially by the presence of the filler irresp. of the individual filler behavior (as a single component) and its percentage (within the proportions used by Winsor & Newton in their 19th c. chrome yellow paints).
    48. 48
      Ploeger, R.; Scalarone, D.; Chiantore, O. Thermal analytical study of the oxidative stability of artists’ alkyd paints. Polym. Degrad. Stab. 2009, 94, 2036– 2041,  DOI: 10.1016/j.polymdegradstab.2009.07.018
      48
      Thermal analytical study of the oxidative stability of artists' alkyd paints
      Ploeger, Rebecca; Scalarone, Dominique; Chiantore, Oscar
      Polymer Degradation and Stability (2009), 94 (11), 2036-2041CODEN: PDSTDW; ISSN:0141-3910. (Elsevier Ltd.)
      Artists' alkyd paints are relatively new in the art world and were introduced in the 1970s. Since they are so new, little is known about their aging properties and behavior in the conservation field. Thermal analyses, specifically, differential scanning calorimetry (DSC) and thermogravimetric anal. (TGA), were used in this work to study the changes in properties of artists' alkyd paint films with age. Both techniques revealed changes in the thermal properties as the films increased in age. The crosslinking rate during accelerated photo-aging was obsd. with DSC by monitoring the exothermic reaction after the decompn. of peroxide groups, which form during auto-oxidn. of the alkyd resin. The investigation of naturally aged films, some up to 28 years, revealed an increase in the glass transition temp. with age. TGA studies of naturally aged films indicated an increase in film d. with age, probably due to crosslinking at first and then the possible formation of oxidative degrdn. products over time, such as carboxylate salts.
    49. 49
      Mosiewicki, M. A.; Rojas, O.; Sibaja, M. R.; Borrajo, J.; Aranguren, M. I. Aging study of linseed oil resin/styrene thermosets and their composites with wood flour. Polym. Int. 2007, 56, 875– 881,  DOI: 10.1002/pi.2218
      49
      Aging study of linseed oil resin/styrene thermosets and their composites with wood flour
      Mosiewicki, Mirna A.; Rojas, Oscar; Sibaja, Maria R.; Borrajo, Julio; Aranguren, Mirta I.
      Polymer International (2007), 56 (7), 875-881CODEN: PLYIEI; ISSN:0959-8103. (John Wiley & Sons Ltd.)
      The changes in the properties of new crosslinked polymers based on renewable resources and their derived composites have been monitored as a function of time; this knowledge is necessary to est. their behavior in final applications. Rigid thermoset polymers prepd. by free radical polymn. of resins obtained from linseed oil and styrene and composites reinforced with wood flour were evaluated in different environmental conditions and at different times after their prepn. The action of atm. oxygen on the unsatd. groups in fatty acids produces chem. changes in these polymers, which affect the properties of the cured materials. These changes were analyzed using Fourier transform IR spectroscopy, dynamic mech. anal. and mech. testing. An increase in the modulus with time was obsd. during exposure of the samples to dry conditions, or humid environments (60% relative humidity), with or without UV irradn. The reaction with oxygen appears to be accelerated when the materials are subjected to UV irradn., showing a large effect on the glass transition temp.
    50. 50
      Boquillon, N.; Fringant, C. Polymer networks derived from curing of epoxidisedlinseed oil: influence of different catalysts and anhydride hardeners. Polymer 2000, 41, 8603– 8613,  DOI: 10.1016/S0032-3861(00)00256-1
      50
      Polymer networks derived from curing of epoxidised linseed oil: influence of different catalysts and anhydride hardeners
      Boquillon, N.; Fringant, C.
      Polymer (2000), 41 (24), 8603-8613CODEN: POLMAG; ISSN:0032-3861. (Elsevier Science Ltd.)
      Epoxidized linseed oil was cured with anhydrides. The reactions were catalyzed with different types of tertiary amines and imidazoles. 2-Methylimidazole leads to very interesting properties. The effects of steric factors and of the rigidity of the diester segment formed due to the extent of conversion of anhydride groups and on the network's properties were obsd. Thus, the thermosets obtained with phthalic anhydride and methyl-endo-methylenetetrahydrophthalic anhydride hardeners have a lower crosslink d. than those obtained with cis-1,2,3,6-tetrahydrophthalic anhydride. The effects of the epoxidized triglyceride structure, made of aliph. chains, on the network's properties were also examd.
    51. 51
      Earnest, T. R.; MacKnight, W. J. Infrared Studies of Hydrogen Bonding in Ethylene-Methacrylic Acid Copolymers and Ionomers. Macromolecules 1980, 13, 844– 849,  DOI: 10.1021/ma60076a014
      There is no corresponding record for this reference.
    52. 52
      Eisenberg, A. Clustering of Ions in Organic Polymers. A Theoretical Approach. Macromolecules 1970, 3, 147– 154,  DOI: 10.1021/ma60014a006
      52
      Clustering of ions in organic polymers. A theoretical approach
      Eisenberg, Adi
      Macromolecules (1970), 3 (2), 147-54CODEN: MAMOBX; ISSN:0024-9297.
      See CA 72: 22055k.
    53. 53
      Eisenberg, A.; Hird, B.; Moore, R. B. A new multiplet-cluster model for the morphology of random ionomers. Macromolecules 1990, 23, 4098– 4107,  DOI: 10.1021/ma00220a012
      53
      A new multiplet-cluster model for the morphology of random ionomers
      Eisenberg, A.; Hird, B.; Moore, R. B.
      Macromolecules (1990), 23 (18), 4098-107CODEN: MAMOBX; ISSN:0024-9297.
      A morphol. model for random ionomers is proposed which incorporates the findings of recent dynamic mech. and x-ray scattering studies. The model is based on the existence of multiplets, which reduce the mobility of the polymer chains in their vicinity. The thickness of the restricted mobility layer surrounding each multiplet is postulated to be of the order of the persistence length of the polymer. Isolated multiplets act as large crosslinks, thus increasing the glass temp. of the material. As the ion content is increased, the regions of restricted mobility surrounding each multiplet overlap to form larger contiguous regions of restricted mobility. When these regions become sufficiently large, they exhibit phase-sepd. behavior and are termed clusters. The model is in good agreement with a very wide range of exptl. obsd. phenomena, esp. those based on dynamic mech. and x-ray scattering techniques.
    54. 54
      Hermans, J. J.; Keune, K.; van Loon, A.; Iedema, P. D.; van Loon, A.; Iedema, P. D. The crystallization of metal soaps and fatty acids in oil paint model systems. Phys. Chem. Chem. Phys. 2016, 18, 10896– 10905,  DOI: 10.1039/C6CP00487C
      54
      The crystallization of metal soaps and fatty acids in oil paint model systems
      Hermans, Joen J.; Keune, Katrien; Loon, Annelies van; Iedema, Piet D.
      Physical Chemistry Chemical Physics (2016), 18 (16), 10896-10905CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      The formation and crystn. of metal soaps in oil paint layers is an important issue in the conservation of oil paintings. The chem. reactions and phys. processes that are involved in releasing metal ions from pigments and fatty acids from the oil binder to form cryst. metal soap deposits have so far remained poorly understood. We have used a combination of differential scanning calorimetry (DSC) and attenuated total reflection Fourier transform IR spectroscopy (ATR-FTIR) on model mixts. of palmitic acid, lead palmitate or zinc palmitate and linseed oil to study the transition from amorphous material to cryst. fatty acid or metal soap. This transition forms the final stage in the cascade of processes leading to metal soap-related oil paint degrdn. Palmitic acid as well as the metal soaps showed nearly ideal soly. behavior. However, it was found that, near room temp., both lead and zinc palmitate are practically insol. in both liq. and partially polymd. linseed oil. Interestingly, the rate of metal soap and fatty acid crystn. decreased rapidly with the degree of linseed oil polymn., possibly leading to systems where metal soaps are kinetically trapped in a semi-cryst. state. To explain the various morphologies of metal soap aggregates obsd. in oil paint layers, it is proposed that factors affecting the probability of crystal nucleation and the rate of crystal growth play a crucial role, like exposure to heat or cleaning solvents and the presence of microcracks.
    55. 55
      Park, J.; Eslick, J.; Ye, Q.; Misra, A.; Spencer, P. The influence of chemical structure on the properties in methacrylate-based dentin adhesives. Dent. Mater. 2011, 27, 1086– 1093,  DOI: 10.1016/j.dental.2011.07.011
      55
      The influence of chemical structure on the properties in methacrylate-based dentin adhesives
      Park, Jonggu; Eslick, John; Ye, Qiang; Misra, Anil; Spencer, Paulette
      Dental Materials (2011), 27 (11), 1086-1093CODEN: DEMAEP; ISSN:0109-5641. (Elsevier Ltd.)
      Objectives: The objective of this study was to investigate the influence of the chem. structure of methacrylate monomers used in dentin adhesives on degree of conversion (DC), water sorption, and dynamic mech. properties. Materials and methods: Exptl. adhesives contg. 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy) phenyl]-propane (BisGMA), 2-hydroxyethyl methacrylate (HEMA), and co-monomer, 30/45/25 (wt./wt.) were photo-polymd. Ethyleneglycol dimethacrylate (EGDM), diethyleneglycol dimethacrylate (DEGDM), triethyleneglycol dimethacrylate (TEGDMA), 1,3-glycerol dimethacrylate (GDM), and glycerol trimethacrylate (GTM) were used as a co-monomer. The adhesives were characterized with regard to DC, water sorption, and dynamic mech. anal. and compared to control adhesive [HEMA/BisGMA, 45/55 (wt./wt.)]. Results: DC and water sorption increased with an increase in the no. of ethylene glycol units in the monomer. Exptl. adhesive contg. GDM showed significantly higher storage moduli (p < 0.05) in both dry and wet samples than exptl. adhesives contg. EGDM or DEGDM. The rubbery moduli of adhesives contg. GDM and GTM were found to be significantly greater (p < 0.05) than that of the control. Adhesives contg. GTM exhibited the widest tan δ curves, indicating the greatest structural heterogeneity. Significance: The hydrophilicity, functionality and size of monomers in dentin adhesives affected the water sorption, soly., crosslink d. and heterogeneity of the polymer network. The exptl. adhesives contg. GDM and GTM showed higher rubbery moduli, indicating higher crosslink d. accompanied by a decrease in the homogeneity of the polymer network structure.
    56. 56
      Hill, L. W. Calculation of crosslink density in short chain networks. Prog. Org. Coat. 1997, 31, 235– 243,  DOI: 10.1016/S0300-9440(97)00081-7
      56
      Calculation of crosslink density in short chain networks
      Hill, Loren W.
      Progress in Organic Coatings (1997), 31 (3), 235-243CODEN: POGCAT; ISSN:0300-9440. (Elsevier Science S.A.)
      Simple, new equations are provided for calcg. the crosslink d. of networks prepd. from low-mol.-wt., multi-functional reactants. The equations apply to stoichiometric mixts. at incomplete conversion and are obtained by modification of the Scanlan equation. Examples are selected to represent network forming reactions frequently encountered in thermoset industrial coatings. The rather complex Miller and Macosko calcns. are applied to the same examples. At extent of conversion 0.75-1.00, both calcns. give the same results. Clarifications are provided to explain inconsistencies in published values of no. av. mol. wt. of network chains.
    57. 57
      Weiss, R. A.; Fitzgerald, J. J.; Kim, D. Viscoelastic behavior of plasticized sulfonated polystyrene ionomers. Macromolecules 1991, 24, 1064– 1070,  DOI: 10.1021/ma00005a014
      57
      Viscoelastic behavior of plasticized sulfonated polystyrene ionomers
      Weiss, R. A.; Fitzgerald, J. J.; Kim, D.
      Macromolecules (1991), 24 (5), 1064-70CODEN: MAMOBX; ISSN:0024-9297.
      Two different approaches for modifying the linear viscoelastic behavior of the title ionomer were described. Adding a backbone plasticizer (DOP) affected that part of the relaxation behavior ascribed to the backbone polymer. DOP lowered the primary glass transition temp. without affecting the relaxation time spectrum assocd. with the ionic clusters. However, an ionic plasticizer (glycerol) affected the relaxation of the ionic clusters and had little or no effect on the viscoelastic response of the nonpolar phase. For the ionomer, the addn. of glycerol shifted the long-time relaxations assocd. with the ionic clusters to shorter times, thus decreasing the melt viscosity and reducing the networklike response due to the phys. assocns. of the ionic groups.
    58. 58
      Giacinti Baschetti, M.; Piccinini, E.; Barbari, T. A.; Sarti, G. C. Quantitative Analysis of Polymer Dilation during Sorption Using FTIR-ATR Spectroscopy. Macromolecules 2003, 36, 9574– 9584,  DOI: 10.1021/ma0302457
      There is no corresponding record for this reference.
    59. 59
      Browne, F. Swelling of paint-films in water VII: Swelling of Linseed Oil Paints in Water and Organic Liquids. Forest Products Journal 1956, 5, 312– 318
      There is no corresponding record for this reference.
    60. 60
      Zumbühl, S. Parametrization of the solvent action on modern artists’ paint systems. Stud. Conserv. 2014, 59, 24– 37,  DOI: 10.1179/2047058413Y.0000000099
      There is no corresponding record for this reference.
    61. 61
      Phenix, A. Effects of organic solvents on artists’ oil paint films: swelling. Smithsonian Contributions to Museum Conservation 2013, 3, 69– 76
      There is no corresponding record for this reference.
    62. 62
      Brannon-Peppas, L.; Peppas, N. A. Equilibrium swelling behavior of pH-sensitive hydrogels. Chem. Eng. Sci. 1991, 46, 715– 722,  DOI: 10.1016/0009-2509(91)80177-Z
      62
      Equilibrium swelling behavior of pH-sensitive hydrogels
      Brannon-Peppas, Lisa; Peppas, Nikolaos A.
      Chemical Engineering Science (1991), 46 (3), 715-22CODEN: CESCAC; ISSN:0009-2509.
      The equil. swelling behavior of hydrogels sensitive to pH or ionic strength changes of the swelling medium was studied using structural models which are based on the Flory-Huggins thermodn. theory, the rubber elasticity theory, and the ionic interaction deviations therefrom. The no. av. mol. wt. between crosslinks was related to equil. swelling characteristics, the thermodn. compatibility of the polymer-swelling agent system, the ionic charges, the pKa of the ionizable polymer moieties, and the pH and ionic strength of the surrounding medium. The models have predictive correlative and design capabilities.
    63. 63
      Edwards, D. A. Non-Fickian Diffusion in Thin Polymer Films. J. Polym. Sci., Part B: Polym. Phys. 1996, 34, 981– 997,  DOI: 10.1002/(SICI)1099-0488(19960415)34:5<981::AID-POLB16>3.0.CO;2-7
      63
      Non-Fickian diffusion in thin polymer films
      Edwards, D. A.
      Journal of Polymer Science, Part B: Polymer Physics (1996), 34 (5), 981-97CODEN: JPBPEM; ISSN:0887-6266. (Wiley)
      Diffusion of penetrants through polymers often does not follow the std. Fickian model. Such anomalous behavior can cause difficulty when designing polymer networks for specific uses. One type of non-Fickian behavior that results is so-called case II diffusion, where Fickian-like fronts initially move like √t with a transition to a non-Fickian concn. profile and front speed for moderate time. A math. model is presented that replicates this behavior in thin polymer films, and an anal. is performed that yields relevant dimensionless groups for study. An unusual result is derived: In certain parameter ranges, the concn. profile can change concavity, reflecting Fickian behavior for short times and non-Dickian behavior for moderate times. Asymptotic and numerical results are then obtained to characterize the dependence of such relevant quantities as failure time, front speed, and mass transport on these dimensionless groups. This information can aid in the design of effective polymer protectant films.
    64. 64
      Amsden, B. Solute Diffusion within Hydrogels. Mechanisms and Models. Macromolecules 1998, 31, 8382– 8395,  DOI: 10.1021/ma980765f
      64
      Solute Diffusion within Hydrogels. Mechanisms and Models
      Amsden, Brian
      Macromolecules (1998), 31 (23), 8382-8395CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Solute diffusion in hydrogels is important in many biotechnol. fields. Solute behavior in hydrogels has been explained in terms of redn. in hydrogel free vol., enhanced hydrodynamic drag on the solute, increased path length due to obstruction, and a combination of hydrodynamic drag and obstruction effects. In this article the various math. models derived to explain and predict solute diffusion in hydrogels are discussed and tested against literature data. These models can be divided into those applicable to hydrogels composed of flexible polymer chains (i.e., homogeneous hydrogels) and those composed of rigid polymer chains (i.e., heterogeneous hydrogels). For homogeneous hydrogels it was detd. that a scaling hydrodynamic model provided the best explanation for solute diffusion, while for heterogeneous hydrogels obstruction models were more consistent with the exptl. data. Both the scaling hydrodynamic model and the most appropriate obstruction model contain undefined parameters which must be clarified in order for these models to gain widespread acceptance.
    65. 65
      Masaro, L.; Zhu, X. X. Physical models of diffusion for polymer solutions, gels and solids. Progress in Polymer Science; Elsevier: 1999; Vol. 24, pp 731– 775.
      65
      Physical models of diffusion for polymer solutions, gels and solids
      Masaro, L.; Zhu, X. X.
      Progress in Polymer Science (1999), 24 (5), 731-775CODEN: PRPSB8; ISSN:0079-6700. (Elsevier Science Ltd.)
      A review with refs.; diffusion in polymer solns. and gels has been studied by various techniques such as gravimetry, membrane permeation, fluorescence and radioactive labeling. These studies have led to a better knowledge of polymer morphol., transport phenomena, polymer melt and controlled release of drugs from polymer carriers. Various theor. descriptions of the diffusion processes have been proposed. The theor. models are based on different phys. concepts such as obstruction effects, free-vol. effects and hydrodynamic interactions. With the availability of pulsed-field gradient NMR techniques and other modern exptl. methods, the study of diffusion has become much easier and data on diffusion in polymers have become more available. This review article summarizes the different phys. models and theories of diffusion and their uses in describing the diffusion in polymer solns., gels and even solids. Comparisons of the models and theories are made in an attempt to illustrate the applicability of the phys. concepts. Examples in the literature are used to illustrate the application and applicability of the models in the treatment of diffusion data in various systems.
    66. 66
      De Kee, D.; Liu, Q.; Hinestroza, J. Viscoelastic (Non-Fickian) Diffusion. Can. J. Chem. Eng. 2005, 83, 913– 929,  DOI: 10.1002/cjce.5450830601
      66
      Viscoelastic (non-Fickian) diffusion
      De Kee, D.; Liu, Q.; Hinestroza, J.
      Canadian Journal of Chemical Engineering (2005), 83 (6), 913-929CODEN: CJCEA7; ISSN:0008-4034. (Canadian Society for Chemical Engineering)
      A review. This review paper deals with mass transport in macromol. materials. The study of mass transport through polymeric composite materials for example has applications in a variety of areas such as coatings, packaging and gas sepns., to name just a few. Here we discuss several models for diffusion as well as several exptl. techniques. In particular, we discuss models for case II diffusion, from a continuum mechanics point of view as well as via a mesoscopic theory. Variables such as temp., mol. structure and mech. deformation, affecting mass transport are also discussed.
    67. 67
      Vrentas, J. S.; Duda, J. L. Diffusion in polymer-solvent systems. I. Reexamination of the free-volume theory. J. Polym. Sci., Polym. Phys. Ed. 1977, 15, 403– 416,  DOI: 10.1002/pol.1977.180150302
      67
      Diffusion in polymer-solvent systems. I. Reexamination of the free-volume theory
      Vrentas, J. S.; Duda, J. L.
      Journal of Polymer Science, Polymer Physics Edition (1977), 15 (3), 403-16CODEN: JPLPAY; ISSN:0098-1273.
      The calcn. of specific free vol. for diffusion in polymer-solvent system was discussed, and equations were developed for the detn. of the self-diffusion coeff. of the polymer and solvent. Conditions under which the mutual diffusion coeff. could be deduced solely from free-vol. considerations are clarified, and a more general version of the free-vol. diffusion theory of H. Fugita (1961) was presented. The further restrictions needed for the Fujita theory were discussed and these addnl. restrictions were considered responsible for failures of the theory. The diffusion of 0.1-1.0 mass fraction of EtPh [100-41-4] in polystyrene [9003-53-6] was analyzed based on expressions involving self-diffusion coeffs., and free vol.
    68. 68
      Vrentas, J. S.; Duda, J. L. Diffusion in polymer-solvent systems. II. A predictive theory for the dependence of diffusion coefficients on temperature, concentration, and molecular weight. J. Polym. Sci., Polym. Phys. Ed. 1977, 15, 417– 439,  DOI: 10.1002/pol.1977.180150303
      68
      Diffusion in polymer-solvent systems. II. A predictive theory for the dependence of diffusion coefficients on temperature, concentration, and molecular weight
      Vrentas, J. S.; Duda, J. L.
      Journal of Polymer Science, Polymer Physics Edition (1977), 15 (3), 417-39CODEN: JPLPAY; ISSN:0098-1273.
      A new free-vol. theory was combined with the thermodn. theory of P. J. Flory (1970) and the entanglement theory of F. Bueche (1962) to provide a means of predicting the temp., concn., and mol. wt. dependence of mutual-diffusion coeffs. in amorphous polymer-solvent systems. The theor. predictions were compared with exptl. diffusion data for EtPh [100-41-4] diffusion in polystyrene [9003-53-6].
    69. 69
      Bisschops, M. a. T.; Luyben, K. C. a. M.; van der Wielen, L. A. M. Generalized Maxwell-Stefan Approach for Swelling Kinetics of Dextran Gels. Ind. Eng. Chem. Res. 1998, 37, 3312– 3322,  DOI: 10.1021/ie9800389
      There is no corresponding record for this reference.
    70. 70
      Stolow, N. The action of solvents on drying-oil films: parts I and II. J. Oil Colour Chemists’ Assoc. 1957, 40, 377– 402
      70
      The action of solvents on drying-oil films. I
      Stolow, N.
      Journal of the Oil and Colour Chemists' Association (1957), 40 (), 377-402CODEN: JOCCAB; ISSN:0030-1337.
      The soly. and leaching effects of org. solvents on linseed-oil films is studied. The oils used are raw linseed, alkali-refined linseed, open-pot stand oil, and vacuum-bodied stand oil. Pb naphthenate drier (0.5% Pb by wt. of oil) is added to some oils. Some oils also contain basic Pb carbonate (4:1 salt to oil by wt.). The films are cast on flat plate glass and dried for periods of 48 hrs. to 2 years. Film d. is measured in a pycnometer or by a flotation method. The solvents used are ketones, alcs., hydrocarbons, and chlorinated hydrocarbons. Swelling and shrinkage of the supported films are measured in an app. similar to a parallel-plate viscometer, in which one of the parallel surfaces is the film itself. As the solvent swells the film, a back-pressure is built up, and this is recorded manometrically. Swelling of the unsupported films is measured by a traveling microscope, or by a gravimetric method. Leaching depends on time, age of the film, and the solvent used. Swelling increases the rate of leaching of the lower mol. wt. film components. Swelling curves, both for the pigmented and unpigmented films, show the combined leaching and swelling effects. As solvent action progresses, the d. of the film increases, and the film has a lower swelling potential. The equil. degree of swelling and the d. can be correlated mathematically by empirical equations. The limiting, nonswelling structure approaches a d. of 1.2. Mol.-vol. analysis and detn. of crit. energy ds. are helpful in correlating the data. The soly. parameter for leached-linseed-oil films is 9.3 units. Linseed-oil films are considered to have a felt-like structure. The bulk of the film is composed of highly branched triglyceride polymers whose mols. have become intertwined during film formation. The spaces in-between are occupied by the nonpolymerizing portions of the oil and by oxidative-breakdown products. These diffuse out of the structure during swelling and leaching.
    71. 71
      Guo, J.; Barbari, T. A. A Dual Mode, Local Equilibrium Relaxation Model for Small Molecule Diffusion in a Glassy Polymer. Macromolecules 2008, 41, 238– 245,  DOI: 10.1021/ma071662c
      There is no corresponding record for this reference.
    72. 72
      Duncan, T. T.; Berrie, B. H.; Weiss, R. G. Soft, Peelable Organogels from Partially Hydrolyzed Poly(vinyl acetate) and Benzene-1,4-diboronic Acid: Applications to Clean Works of Art. ACS Appl. Mater. Interfaces 2017, 9, 28069– 28078,  DOI: 10.1021/acsami.7b09473
      72
      Soft, Peelable Organogels from Partially Hydrolyzed Poly(vinyl acetate) and Benzene-1,4-diboronic Acid: Applications to Clean Works of Art
      Duncan, Teresa T.; Berrie, Barbara H.; Weiss, Richard G.
      ACS Applied Materials & Interfaces (2017), 9 (33), 28069-28078CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      We have developed soft, peelable organogels from 40% hydrolyzed poly(vinyl acetate) (40PVAc) and benzene-1,4-diboronic acid (BDBA). The org. liqs. gelated include DMSO, DMF, THF, 2-ethoxyethanol, and methanol. The rheol. of these soft materials can be tuned by altering the concn. of the polymer and/or crosslinker. Insights into the mechanisms leading to gelation were obtained from 1H NMR expts., fluorescence measurements, and studies comparing properties of materials made from BDBA and phenylboronic acid, a mol. incapable of forming covalent crosslinks between the polymer chains. These organogels can be easily peeled off a surface, leaving no residue detectable by UV-vis spectroscopy. They are demonstrated to be effective at softening and removing deteriorated coatings from water-sensitive works of art and delicate surfaces. They have the needed characteristics to clean topog. complex surfaces: good contact with the surface, easy removal, and little to no residue after removal. A 2-ethoxyethanol organogel was used to remove oxidized varnish from a 16th century reliquary decorated with painted gold leaf, and an ethanol gel was used to remove solvent-resistant coatings from 16th and 18th century oil paintings.
    73. 73
      Baglioni, M.; Domingues, J. A. L.; Carretti, E.; Fratini, E.; Chelazzi, D.; Giorgi, R.; Baglioni, P. Complex Fluids Confined into Semi-interpenetrated Chemical Hydrogels for the Cleaning of Classic Art: A Rheological and SAXS Study. ACS Appl. Mater. Interfaces 2018, 10, 19162– 19172,  DOI: 10.1021/acsami.8b01841
      73
      Complex Fluids Confined into Semi-interpenetrated Chemical Hydrogels for the Cleaning of Classic Art: A Rheological and SAXS Study
      Baglioni, Michele; Domingues, Joana A. L.; Carretti, Emiliano; Fratini, Emiliano; Chelazzi, David; Giorgi, Rodorico; Baglioni, Piero
      ACS Applied Materials & Interfaces (2018), 10 (22), 19162-19172CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      The removal of aged varnishes from the surface of easel paintings using the common conservation practice (i.e by means of org. solvents) often causes pigment leaching, paint loss and varnish re-deposition. Recently, we proposed an innovative cleaning system based on semi-interpenetrated polymer networks (SIPN), where a covalently cross-linked poly(hydroxyethyl methacrylate), pHEMA, network is interpenetrated by linear chains of poly(vinylpyrrolidone), PVP. This chem. gel, simply loaded with water, was designed to safely remove surface dirt from water-sensitive artifacts. Here, we modified the SIPN to confine complex cleaning fluids, able to remove aged varnishes. These complex fluids are 5-components water-based nanostructured systems, where solvents are partially dispersed as nano-sized droplets in a continuous aq. phase, using surfactants. The rheol. behavior of the SIPN and the nanostructure of the fluids loaded into the gel were investigated, and the mech. behavior of the gel was optimized by varying both the crosslinking d. and the polymer concn. Once loaded with the complex fluids, the hydrogels maintained their structural and mech. features, while the complex fluids showed a decrease in the size of the dispersed solvent droplets. Two challenging case studies have been selected to evaluate the applicability of the SIPN hydrogels loaded with the complex fluids. The first case study concerns the removal of a surface layer composed by an aged brown resinous patina from a wood panel, the second case study concerns the removal of a homogeneous layer of a yellowed varnish from a watercolor on paper. The results show that the confinement of complex fluids into gels allowed unprecedented removal of varnishes from artifacts, overcoming the limitations of traditional cleaning methods.

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