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Amphiphilic Self-Assembly of Alkanols in Protic Ionic Liquids
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† School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia
‡ Centre for Advanced Particle Processing and Transport, Chemistry Building, The University of Newcastle, Callaghan, NSW 2308, Australia
*E-mail [email protected]; Tel (+61 2) 9351 2106 (G.G.W.).
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The Journal of Physical Chemistry B

Cite this: J. Phys. Chem. B 2014, 118, 33, 9983–9990
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https://doi.org/10.1021/jp504998t
Published July 28, 2014

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Abstract

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Strong cohesive forces in protic ionic liquids (PILs) can induce a liquid nanostructure consisting of segregated polar and apolar domains. Small-angle X-ray scattering has shown that these forces can also induce medium chain length n-alkanols to self-assemble into micelle- and microemulsion-like structures in ethylammonium (EA+) and propylammonium (PA+) PILs, in contrast to their immiscibility with both water and ethanolammonium (EtA+) PILs. These binary mixtures are structured on two distinct length scales: one associated with the self-assembled n-alkanol aggregates and the other with the underlying liquid nanostructure. This suggests that EA+ and PA+ enable n-alkanol aggregation by acting as cosurfactants, which EtA+ cannot do because its terminating hydroxyl renders the cation nonamphiphilic. The primary determining factor for miscibility and self-assembly is the ratio of alkyl chain lengths of the alkanol and PIL cation, modulated by the anion type. These results show how ILs can support the self-assembly of nontraditional amphiphiles and enable the creation of new forms of soft matter.

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Introduction

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Salts that are molten at or near room temperature, or ionic liquids (ILs), are remarkable liquids. (1-4) They are typically formed from an organic cation and an organic or inorganic anion with delocalized charges or some other structural feature that destabilizes the crystal. In many ILs H-bonding is an important secondary interaction that influences both physical properties and miscibility with other liquids. Thus, ILs may be broadly classified as hydrophilic or hydrophobic according to their miscibility with water. (5, 6) Many ionic liquids have been found to be good solvents for self-assembly of surfactants and amphiphilic polymers into micelles, (7-10) liquid crystals, (11-13) and microemulsions. (14-16)
Research interest in protic ILs (PILs) is increasing due to their ease of synthesis (by Brønsted acid–base neutralization), low cost, and the simplicity, stability, and low toxicity of their constituent ions. (17-21) PILs are overwhelmingly water-miscible, and like their aprotic cousins, many have been shown to be excellent solvents for amphiphilic self-assembly. (22-30)
H-bonding in PILs has been shown to be a key feature in controlling self-assembly behavior. (31, 32) Simple ILs with identifiable polar and nonpolar moieties, exemplified by ethylammonium nitrate (EAN), exhibit an inherent amphiphilic nanostructure in the pure liquid state, (33) the extent and nature of which depend on cation and anion structure and H-bond capacity. (32, 34-36) This is also critical in determining the nanostructures that form in mixtures of PILs with water. (37, 38)
Both protic and aprotic ILs exhibit a complex set of miscibility behavior with aliphatic alcohols. EAN + methanol exhibit many characteristics of ideal mixtures (39) but do exhibit some structural complexities. (40) However, EAN and n-octanol are only partially miscible at room temperature and exhibit an UCST at 47 °C, (41, 42) above which EAN and n-octanol are miscible. Hydrophobic aprotic ILs also show partial miscibility with short-chain alcohols; butylmethylimidazolium hexafluorophosphate (bmimPF6) has a UCST with ethanol at 71 °C and with n-propanol at 87 °C, (43) and mixtures of ethylmethylimidazolium NTf2 and n-butanol have a UCST at 47 °C. (44)
Here we examine the miscibility of protic ILs and aliphatic alcohols through a systematic variation of cation (ethyl-, propyl-, and 2-hydroxyethylammonium) and anion (nitrate and formate) structure and aliphatic chain length from ethanol through dodecanol. The ILs examined are shown in Figure 1. Using small-angle X-ray scattering, we demonstrate amphiphilic self-assembly of the alkanols, which in turn reveals the connections between amphiphilicity, structure, and miscibility in these systems. The miscibility of a number of protic ILs with aliphatic alcohols has been examined recently, and we will also discuss some discrepancies between ours and these previously reported results. (45)

Figure 1

Figure 1. Structures of the ILs used in this work.

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Experimental Section

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Materials and Methods

Analytical-grade n-alcohols were dried, and their purity was confirmed by melting point, TLC, and mass spectrometry prior to use. Ionic liquids were prepared from ethylamine (Aldrich), propylamine (Acros), and ethanolamine (Merck) bases and either nitric acid (AJAX) or formic acid (Aldrich). All of the ionic liquids were synthesized by slow acid neutralization of the relevant alkylamine base with the relevant dilute acid as reported previously. (24) The reaction was kept below 10 °C in an ice bath. The nitrate ionic liquids (EAN, PAN, EtAN) were dried first to less than 10 wt % water content on a rotary evaporator and then to less than 0.2 wt % water content under nitrogen at 110 °C for at least 16 h. Note that formate PILs have a tendency to form amides and could not be heated during the synthesis or the drying process. Instead, they were dried under vacuum while the amide content was monitored by NMR on regularly collected samples. Aqueous EtAF could not be dried below 2 wt % water content without heating, so dry EtAF was made in THF. THF (AJAX) was dried over molecular sieves (to <0.01 wt % water), ethanolamine was dried by vacuum distillation (to 0.03 wt % water), and formic acid was dried over boric anhydride (B2O3) and then distilled (to 0.18 wt % water). After the EtAF synthesis the THF was removed under vacuum. Water contents were measured by Karl Fischer titration to be less than 0.2 wt % (typically much lower) for all ILs after drying.

Small- and Wide-Angle X-ray Scattering

Small- and wide-angle scattering (SAXS/WAXS) was performed on a point collimated Anton Paar SAXSess on a single image plate which was radially averaged and normalized to a direct beam intensity of 1 before subtraction of the empty cell scattering. Scattering was measured at 25 °C from 1 mm quartz capillaries for 10 min per sample.

Miscibility Measurements

Samples for miscibility measurements were prepared by mass in 1 mL glass vials at approximately 10 wt % intervals. The samples were mixed by mechanical agitation on a Vortex mixer for between 1 and 5 min, followed by bath sonication for 30 s, and then left to equilibrate in a water bath thermostated at 25 °C. Miscibility or otherwise was determined after 30 min equilibration and confirmed after 1 week. Immiscible samples were identified by the formation of a meniscus and by optical turbidity when mechanically agitated after having equilibrated. Note that some of the EAF samples initially appear opaque or two phase when first made (probably from slow mixing due to the high viscosity of the ionic liquid) but are miscible at equilibrium. Small amounts of adventitious water were also found to decrease miscibility in some systems examined (e.g., PAN + dodecanol). Hence, dryness was reconfirmed by Karl Fischer titration for any mixed systems exhibiting such ambiguities. These difficulties are probably responsible for previously published results (45) that are inconsistent with our results.
Partially miscible samples were examined as a function of warming in 5 °C increments, allowing us to determine or confirm the phase boundaries in, for example, EAN + n-octanol. (41)

Results and Discussion

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Table 1 summarizes the observed liquid–liquid miscibilities of protic ILs with aliphatic alcohols at 25 °C. This includes the behavior of long-lived, metastable but subcooled EtAN. An immediate distinction can be drawn between ILs with the ethanolammonium cation, which only mix with ethanol, and the ethylammonium and propylammonium salts, which are miscible with much longer alkanol chain lengths. Mixtures of between 20 and 80 wt % butanol in EtAN remained mutually immiscible between 5 and 70 °C, well above its equilibrium melting point. This and the absence of any precipitation confirms that the observed immiscibility is not a consequence of EtAN being a metastable liquid at room temperature. The temperature dependence of EtAF miscibilities was not pursued due to the risk of amide formation.
Table 1. Miscibility of n-Alkanols with PILsa
 EANPANEtANEAFPAFEtAF
mp =13 °C (22)6 °C (20)51 °C (20)–15 °C (20)48 °C (46)–82 °C (47)
ethanolmisciblemisciblemisciblemiscible–miscible
butanolmisciblemiscibleimmisciblemiscible–immiscible
hexanolmisciblemiscibleimmisciblemiscible<10 wt %cimmiscible
octanolpartialbmiscibleimmisciblemiscible<6.4 wt %cimmiscible
decanolimmisciblemiscible–miscible––
dodecanolimmisciblemiscible–partial––
a

Data are for liquid mixtures at 25 °C, except for PAF which melts at 48 °C. Note that EtAN is a metastable liquid at this temperature. “–” denotes mixtures not examined in this study.

b

Partly miscible at room temperature. Octanol becomes fully miscible with EAN above its UCST. (41)

c

Solubility of solid PAF in alcohol at 25 °C. PAF is fully miscible with both alcohols above 48 °C.

EAN is miscible with all (even-chained) alcohols up to hexanol, and partially miscible with octanol, becoming fully miscible above its UCST. (41) EAF is miscible with all the alcohols examined up to decanol and PAN up to dodecanol at 25 °C. PAF is a solid at room temperature where its solubility in hexanol and octanol is below 10% w/w. Above its melting point PAF is completely miscible with both alkanols. Our results show miscibility of much longer alkanols with some of these PILS than previously reported. (45) As discussed in the Experimental Section, we attribute this to two factors: many of these mixtures become immiscible in the presence of small amounts of water, and mixing is sometimes quite slow due to the high viscosity of some PILs.
Previous studies of IL structure by neutron (34) and X-ray (36) diffraction have shown that EtAN and EtAF both lack the characteristic amphiphilic nanostructure exhibited by EAN, PAN, and EAF, generated by a solvophobic effect. Ethanolammonium ILs are among the most water-like as judged by surface tension and surface structure (48) and by comparison of critical micelle concentrations and solubility behavior of representative nonionic surfactants. (49, 50) Indeed, EAN behaves as a surfactant at both the EtAN/air and water/air interfaces. (51)
Primary alkylammonium ILs form pronounced, bicontinuous, sponge-like nanostructures composed of interpenetrating domains of polar, charged, and H-bonding groups, with nonpolar domains. These are reminiscent of surfactant microemulsions or sponge phases, even to the extent that water dissolves into the H-bonding regions of such ILs. (37) The degree of this amphiphilic structuring depends slightly on anion (nitrate > formate) (32) and more on alkyl chain length (butyl- > propyl- > ethylammonium). (34, 35) A signature of this is the presence of a low-angle peak or shoulder in the neutron (33) or X-ray (36) scattering patterns of these ILs. This is sometimes referred to as a prepeak, which we denote q1. Figure 2 shows the increasing prominence of this peak in the SAXS patterns of pure EAF, EAN, and PAN, and that the periodicity or repeat spacing of the amphiphilic nanostructure (2π/qpeak) increases with cation alkyl chain length from 10 Å for ethylammonium to 12 Å for propylammonium salts, and is relatively insensitive to anion. (Note that peak intensity depends on the contrast conditions for the radiation used, so that quantitative structural comparison between formate and nitrate is not possible based on this single contrast condition. (32))
The second peak in IL scattering patterns (q2) observed near 20 nm–1 has been shown to arise from a combination of multiple shorter-range correlations (cation–cation, anion–anion, and anion cation or polar–polar, polar–nonpolar, and nonpolar–nonpolar depending on the contrast conditions and ion structures) between nearest neighbors. (52) This peak is also observed in many nonamphiphilic ILs, including EtAN. (34, 53)
Figure 2 also shows that aliphatic alcohols exhibit similar scattering patterns, as has been documented many times previously. (54-57) The inherent amphiphilicity of primary n-alkanols with alkyl chain lengths from 2 to 10 gives rise to a low-angle (q1) peak with a repeat spacing that increases from around 8 Å to 20 Å. From the earliest studies this was identified with a nanosegregation of polar and nonpolar moieties into a locally bilayer-like structure, (54) and concentrated ethanol–water mixtures have been shown, like EAN and water, to exhibit molecular segregation. (58)

Figure 2

Figure 2. SAXS/WAXS patterns of pure ionic liquids and aliphatic alcohols at 25 °C.

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Figure 3 shows a matrix of the room temperature SAXS/WAXS patterns of mixtures of EAF, EAN, and PAN with various 1-alkanols. Each mixture is shown over the composition ranges where they are miscible. Only in very few cases can the SAXS patterns of IL–alkanol mixtures be interpreted as an “average” liquid structure in which the two peaks shift smoothly and monotonically between the two pure liquids as a function of composition. Instead, the low-angle scattering increases and the position of q1 develops nonmonotonically as composition changes. In some cases q1 disappears completely at intermediate compositions. This provides clear evidence of large changes in liquid nanostructure and the presence in the mixtures of aggregates or domains much larger than in either pure liquid.

Figure 3

Figure 3. SAXS/WAXS of amphiphilic ionic liquid + aliphatic n-alcohol mixtures of various compositions at 25 °C: yellow, IL; brown, 10 wt % alkanol; green, 20 wt %; light blue, 40 wt %; blue, 60 wt %; purple, 80 wt %; red, 90 wt %; black, alkanol.

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In contrast, q2 shifts smoothly and monotonically with varying composition between the pure liquid components in all systems studied. This confirms that the two components are indeed intimately mixed and that nearest-neighbor distances can be interpreted as simple averages.
The closest approximation to simple mixing of components occurs with EAF + ethanol (Figure 3, top right). Even here, addition of ethanol causes q1 of EAF to gradually become more prominent and move toward lower wave vector (larger spacing) and through a minimum at around 50 wt %, before moving back to the higher wave vector of pure ethanol. This peak also broadens, and the low angle scattering increases at all intermediate compositions well above the baseline of either pure liquid. This indicates disruption of the pure IL structure; peak broadening is consistent with a less regular arrangement of polar and nonpolar domains, and the increased low-q scattering suggests formation of larger and possibly polydisperse nanostructures.
These changes in longer-range nanostructure become more evident upon changing either component. As the alkanol length is increased to 1-butanol, the minimum in q1 versus composition becomes more pronounced and shifts toward lower alkanol concentration. This trend continues upon further increasing chain length to 1-hexanol and beyond. The increase in low-angle scattering also becomes clearer, itself adopting a pronounced structure. In all systems examined q2 continues to shift smoothly and monotonically from pure IL to pure alkanol with changing composition.
At some concentrations of 1-hexanol (20–40 wt %), 1-octanol (20–40 wt %), and 1-decanol (10–40 wt %) in EAF, the q1 peak is completely absent, exhibiting instead the intense small-angle scattering profile expected from micelles or dilute microemulsions. This suggests that, while the amphiphilic nanostructure inherent in EAF can be altered to accommodate short alkyl chains, longer alkyl chains cannot. Instead, the solvent drives the amphiphilic self-assembly of the alkanols on a distinct and larger length scale than in either of the pure components. In EAF this occurs once the chain length of the alkanol exceeds twice that of the PIL cation. The pronounced low-angle scattering shifts toward progressively lower angles, indicating larger alkanol aggregates, as the chain length increases up to dodecanol, which is only partially miscible with EAF.
The same pattern of behavior occurs in mixtures of alkanols with both EAN and PAN. Ethanol/EAN mixtures behave similarly to ethanol and EAF; nonmonotonic changes in q1 and increase in low-angle scattering signal modification of the inherent PIL nanostructure, while monotonic changes in q2 show that the components are well-mixed. Increasing alkanol chain length to 1-butanol and 1-hexanol shows the emergence of a distinct new structural length scale, which is both more pronounced and becomes evident at shorter alkanol chains than in EAF. In EAN, this new structure seems to arise in butanol rather than hexanol—but still at approximately twice the cation alkyl group length. Partial miscibility is also encountered earlier for EAN, with octanol rather than dodecanol at 25 °C. Longer alkanols are almost completely immiscible with EAN.
Although similar in many respects, the amphiphilic nanostructure of pure EAN has previously been shown to be stronger than that in EAF. (32) This has been attributed to a greater density of H-bond donors and acceptors and to their more efficient arrangement into a dense H-bond network. It is thus unsurprising that EAN has a lower “tolerance” for long alkanols and the disruption of the underlying domain structure that accompanies their dissolution. EAN/butanol mixtures already display the small-angle scattering features attributed to small micelles or microemulsions that only emerge in EAF with hexanol or longer chains. The partial miscibility of EAN and octanol is also consistent with its reduced tolerance for disruption of the existing PIL structure.
In their groundbreaking study of the miscibility behavior of the EAN + octanol system, Weingärtner et al. (41, 59) incorporated hydrogen-bonded ion pairs and triple ions into their model of mixtures and their conductivity. While they also considered the possibility of “solvophobic” demixing, the results presented here constitute the first direct evidence of such long-range structural effects.
The same general pattern of behavior is seen again in PAN/alkanol mixtures. Short alkanols disrupt the nanostructure and regular periodicity of the PIL just as they do in EAN and EAF. However, PAN has both a more pronounced underlying amphiphilic nanostructure than either EAN or EAF, (35) but also longer propyl chains which lead to larger nonpolar domains. This gives PAN a greater tolerance for incorporating longer alkanol chains before it drives their amphiphilic assembly. This greater solubility is also reflected in, for example, the lower surfactant efficiencies of nonionic surfactants in PAN than in EAN (60) and the smaller free energies of transfer of alkyl groups from alkanes into PAN versus EAN. (61)
PAN is miscible with alkanols from ethanol through to at least dodecanol at 25 °C. Figure 3 shows that mixtures with hexanol and shorter alkanols exhibit the same nonmonotonic evolution of nanostructure as reflected in the position of q1, accompanied by an increase in low angle scattering. Mixtures with 1-octanol and longer alkanols yield characteristically micellar small-angle scattering patterns with no q1 peak over at least part of their composition ranges. As with the two ethylammonium PILs, a distinct nanostructure only arises when the alkanol length reaches at least twice the cation alkyl chain length.
The emergence of larger (but still nanoscale) structures within these PIL/alkanol mixtures is most clearly seen in systems with large alkyl chain length differences between cation and alcohol, which lie near the miscibility limit. The low-angle scattering component of these systems can be treated approximately by a continuum or small-angle scattering approach, in which the background is treated as constant over the angular or q-range of interest. The low-angle scattering patterns from low concentrations of alkanols can be fit to conventional models of polydisperse spherical or spheroidal micelles. (62) Such fits do yield physically plausible micelle radii that are slightly smaller than the fully extended lengths of the alkanol chains and which increase with alkanol chain length. However, it is not possible to determine the aggregate structures unambiguously, as the best-fit dimensions are sensitive to the solvent scattering, which is itself structured.
At higher concentrations of alkanol, the peak in the scattering reveals long-range order different from that present in either pure liquid. This may arise due to correlations between micelle-like aggregates (likely for dilute alkanol-in-PIL systems) or from percolation of aggregates into a bicontinuous structure. (26, 63) Again, physically plausible dimensions can be obtained assuming a variety of models ranging from bicontinuous (e.g., Teubner–Strey) (63-66) to discrete micelle model with (e.g., excluded volume) interactions. However, the reliability of the quantitative results of either discrete or bicontinuous models is again compromised by the structured scattering of the underlying liquid components, which itself changes with composition. Unlike micelles formed from conventional surfactants, (25) the separation of length scales between n-alkanol aggregates and the alkylammonium ionic liquid nanostructure is too small to apply the small-angle scattering approximation.
The progression of the small-angle scattering component of these mixtures is also highly reminiscent of that seen in binary poly(oxyethylene)-n-alkyl ether/water mixtures. (67) We conclude, therefore, that the low-angle component of the scattering is due to self-assembly structures formed by medium to long-chained aliphatic alcohols, driven by the solvophobic effect in these PILs. Multiple isotopically labeled contrast variation neutron scattering is expected to resolve the structure in greater detail.
The formation of discrete micelles and/or bicontinuous microemulsions by primary alkanols in these PILs is itself remarkable. Although surface active, alkanols are not normally regarded as surfactants and do not self-assemble in aqueous solution. The SAXS patterns presented in Figure 3 reveal trends in behavior consistent with the sequestering of alkyl groups and amphiphilic self-assembly in these PILs. Addition of 10 wt % hexanol to EAN causes a small increase in low-angle scattering, but at 20 wt % the presence of a population of aggregates is clearly signaled by the low-angle scattering. Octanol behaves similarly in both PAN and EAF, but increasing alkanol chain length to 10 or 12 lowers the amount of alkanol required to generate such structures. This mimics the well-known trends in the critical micelle concentrations of surfactants in water as a function of alkyl chain length.
Laughlin (68) has reported that, while a single hydroxy group is insufficiently hydrophilic to cause self-assembly in water, alkane-1,2-diols can exhibit lyotropic surfactant phase behavior in aqueous systems. This is consistent with the observed immiscibility of the n-alkanols examined in this study with both EtAF and EtAN, clearly pointing at the amphiphilicity of the EA+ and PA+ cations as a critical contributor to miscibility and self-assembly structure. This suggests that the micelles, and other structures at higher alkanol contents, include some alkylammonium cations on their surface, oriented such that the alkyl chains are solubilized into the hydrophobic regions of the alkanol tails. These PILs (cations) may thus be acting as cosurfactants or hydrotropes as well as solvents that promote self-assembly. Alkanol self-assembly does not occur in EtAN and EtAF because the PIL cation alcohol group renders the cation nonamphilic, (48) preventing it from acting as a cosurfactant.
Indeed, these mixtures are highly reminiscent of “surfactant-free microemulsions” and structures reported in the so-called pre-Ouzo regime of ternary mixtures such as water, with short- and long-chained alcohols near their miscibility limit. (69, 70) Here, however, the PIL is a single component that plays the same role as the water/hydrotrope mixture.
The formation of these hierarchical amphiphilic nanostructures in alkanol–PIL mixtures rests on several conditions being met. The solubility of the alkanol in the PIL at low concentrations is favored by the presence of a pre-existing amphiphilic domain nanostructure, as in EAF, EAN, and PAN, but not EtAN or EtAF. Dissolution of short alkanols disrupts the periodicity of this structure while retaining its domain-like character. The tolerance of a given PIL for this disruption depends on the Coulombic and H-bonding driving force for solvophobic segregation, and hence cation and anion structure, but also on nonpolar domain size. In these PILs this is determined solely by cation alkyl chain length. When the alkanol chain length or concentration is increased, the PILs capacity to incorporate the alkanol into its nanostructure is compromised which drives the separation of the alkanols into larger amphiphilic aggregates. These aggregates are not simply alkanol micelles existing in a PIL solvent (like conventional surfactant micelles in water) but also include the inherently amphiphilic PIL cations in their surface. From the perspective of a pseudophase model of self-assembly (71) these liquid mixtures are composed of regions that are alcohol-rich and PIL-poor, and vice versa, but no regions or aggregates that are either pure alcohol or pure PIL. Although the solution structures give well-defined scattering patterns, they are in this sense weakly segregated. (72) Importantly, these mixtures can in no way be interpreted as molecularly homogeneous and exhibit structure on two distinct length scales.
ILs, and in the present context particularly PILs, have dramatically expanded the number of solvents known to support self-assembly by traditional surfactants. (30, 73-76) The results presented here show that the potential of PILs is in fact much broader, enabling self-assembly by solutes outside the current, “water-centric” definition of surfactants, leading to the formation of new kinds of soft, self-assembled matter.

Conclusions

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We have shown that mixtures of aliphatic alcohols with protic ionic liquids exhibit complex miscibility behavior and solution structure, but one which follows an internally consistent pattern. While EtAN and EtAF mix only with ethanol, ethyl- and propylammonium ILs are completely miscible with much longer alkanols.
Both the miscibility and the solution structure of these mixtures are primarily sensitive to the ratio of alkyl chain lengths of the alkanol and the ammonium cation. Alkanols shorter than twice the alkylammonium cation disrupt the inherent amphiphilic nanostructure of the PIL, reducing its periodic order, but do not generate a qualitatively different solution structure. Longer alkanols cannot be accommodated within the PIL nanostructure to any significant extent and instead are expelled into larger amphiphilic aggregates. The self-assembled structures thus formed depend on composition: globular micelles form at low concentrations, and it is likely that these percolate into bicontinuous structures at higher concentrations. These larger aggregates are alkanol-rich but contain some PIL cations acting as cosurfactants or hydrotropes. For ethanolammonium PILs, which cannot act as cosurfactants, no self-assembly of alkanols is possible, and immiscibility results once the alkanol exceeds twice the cation chain length.
The transition to alkanol immiscibility with alkylammonium PILs only occurs at much larger alcohol:cation chain length ratios (near 4–5). Both transitions are affected by the anion and its H-bonding capacity, so it is expected that replacing the alcohol with other similar solutes would also affect the boundaries between the domains described above, i.e., disruptive nonideal mixing, amphiphilic self-assembly, and partial miscibility. Understanding solution structure in these systems is an important step toward understanding how ILs function effectively as solvents and reaction media for a diverse range of solutes and how they can be used to assemble new forms of soft matter.

Author Information

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  • Corresponding Author
    • Gregory G. Warr - School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia;  Email: [email protected]
  • Authors
    • Haihui Joy Jiang - School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia
    • Paul A. FitzGerald - School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia
    • Andrew Dolan - School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia
    • Rob Atkin - Centre for Advanced Particle Processing and Transport, Chemistry Building, The University of Newcastle, Callaghan, NSW 2308, Australia
  • Notes
    The authors declare no competing financial interest.

Acknowledgment

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This work was supported by the Australian Research Council and the University of Sydney.

References

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    Green Chemistry (2001), 3 (4), 156-164CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
    A series of hydrophilic and hydrophobic 1-alkyl-3-methylimidazolium room temp. ionic liqs. (RTILs) have been prepd. and characterized to det. how water content, d., viscosity, surface tension, m.p., and thermal stability are affected by changes in alkyl chain length and anion. In the series of RTILs studied here, the choice of anion dets. water miscibility and has the most dramatic effect on the properties. Hydrophilic anions (e.g., chloride and iodide) produce ionic liqs. that are miscible in any proportion with water but, upon the removal of some water from the soln., illustrate how sensitive the phys. properties are to a change in water content. In comparison, for ionic liqs. contg. more hydrophobic anions (e.g., PF6- and N(SO2CF3)2-), the removal of water has a smaller affect on the resulting properties. For a series of 1-alkyl-3-methylimidazolium cations, increasing the alkyl chain length from Bu to hexyl to octyl increases the hydrophobicity and the viscosities of the ionic liqs. increase, whereas densities and surface tension values decrease. Thermal analyses indicate high temps. are attainable prior to decompn. and DSC studies reveal a glass transition for several samples. ILs incorporating PF6- have been used in liq./liq. partitioning of org. mols. from water and the results for two of these are also discussed here. On a cautionary note, the chem. of the individual cations and anions of the ILs should not be overlooked as, in the case of certain conditions for PF6- ILs, contact with an aq. phase may result in slow hydrolysis of the PF6- with the concomitant release of HF and other species.
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  7. 7
    Anderson, J. L.; Pino, V.; Hagberg, E. C.; Sheares, V. V.; Armstrong, D. W. Surfactant Solvation Effects and Micelle Formation in Ionic Liquids Chem. Commun. (Cambridge, U. K.) 2003, 2444– 2445
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    Surfactant solvation effects and micelle formation in ionic liquids
    Anderson, Jared L.; Pino, Veronica; Hagberg, Erik C.; Sheares, Valerie V.; Armstrong, Daniel W.
    Chemical Communications (Cambridge, United Kingdom) (2003), (19), 2444-2445CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    The formation of micelles in 1-butyl-3-Me imidazolium chloride (BMIM-Cl) and hexafluorophosphate (BMIM-PF6) were explored using different surfactants and the solvation behavior of the new micellar-ionic liq. solns. examd. using inverse gas chromatog.
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  8. 8
    Li, N.; Zhang, S.; Ma, H.; Zheng, L. Role of Solubilized Water in Micelles Formed by Triton X-100 in 1-Butyl-3-methylimidazolium Ionic Liquids Langmuir 2010, 26, 9315– 9320
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    He, Y.; Li, Z.; Simone, P.; Lodge, T. P. Self-Assembly of Block Copolymer Micelles in an Ionic Liquid J. Am. Chem. Soc. 2006, 128, 2745– 2750
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    Self-Assembly of Block Copolymer Micelles in an Ionic Liquid
    He, Yiyong; Li, Zhibo; Simone, Peter; Lodge, Timothy P.
    Journal of the American Chemical Society (2006), 128 (8), 2745-2750CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Four amphiphilic poly((1,2-butadiene)-block-ethylene oxide) (PB-PEO) diblock copolymers were shown to aggregate strongly and form micelles in an ionic liq., 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). The universal micellar structures (spherical micelle, wormlike micelle, and bilayered vesicle) were all accessed by varying the length of the corona block while holding the core block const. The nanostructures of the PB-PEO micelles formed in an ionic liq. were directly visualized by cryogenic transmission electron microscopy (cryo-TEM). Detailed micelle structural information was extd. from both cryo-TEM and dynamic light scattering measurements, with excellent agreement between the two techniques. Compared to aq. solns. of the same copolymers, [BMIM][PF6] solns. exhibit some distinct features, such as temp.-independent micellar morphologies between 25° and 100°. As in aq. solns., significant nonergodicity effects were also obsd. This work demonstrates the flexibility of amphiphilic block copolymers for controlling nanostructure in an ionic liq., with potential applications in many arenas.
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    Sharma, S. C.; Atkin, R.; Warr, G. G. The Effect of Ionic Liquid Hydrophobicity and Solvent Miscibility on Pluronic Amphiphile Self-Assembly J. Phys. Chem. B 2013, 117, 14568– 14575
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    Yue, X.; Chen, X.; Wang, X.; Li, Z. Lyotropic Liquid Crystalline Phases Formed by Phyosterol Ethoxylates in Room-Temperature Ionic Liquids Colloids Surf., A 2011, 392, 225– 232
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    11
    Lyotropic liquid crystalline phases formed by phyosterol ethoxylates in room-temperature ionic liquids
    Yue, Xiu; Chen, Xiao; Wang, Xudong; Li, Zhihong
    Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2011), 392 (1), 225-232CODEN: CPEAEH; ISSN:0927-7757. (Elsevier B.V.)
    The phase behaviors of four phytosterol ethoxylates surfactants (BPS-n, n = 5, 10, 20, and 30) with different oxyethylene units in room temp. ionic liq., 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), have been studied. The polarized optical microscopy and small-angle X-ray scattering techniques are used to characterize the phase structures of these binary systems at 25 °C. The structure and ordering of the liq. cryst. (LC) phases in such BPS-n/[Bmim]BF4 systems are found to be influenced by BPS-n concn. and the temp. Due to the bulky and rigid cholesterol group, the phytosterol ethoxylates surfactants exhibit different properties and interaction mechanism from the conventional CnEOm type nonionic surfactant systems. The rheol. measurements indicate a highly viscoelastic nature of these lyotropic LC phases and disclose a lamellar phase characteristic with a rather strong rigidity at high surfactant concns. The control expt. with Brij 97(polyoxyethylene (10) oleyl ether)/[Bmim]BF4 system and the FTIR measurements help to recognize that the solvophobic interaction combining with the hydrogen bonding are the main driving forces for the LC phases formation.
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  12. 12
    Sakai, H.; Saitoh, T.; Misono, T.; Tsuchiya, K.; Sakai, K.; Abe, M. Phase Behavior of Phytosterol Ethoxylates in an Imidazolium-Type Room-Temperature Ionic Liquid J. Oleo Sci. 2012, 61, 135– 141
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    12
    Phase behavior of phytosterol ethoxylates in an imidazolium-type room-temperature ionic liquid
    Sakai, Hideki; Saitoh, Takanori; Misono, Takeshi; Tsuchiya, Koji; Sakai, Kenichi; Abe, Masahiko
    Journal of Oleo Science (2012), 61 (3), 135-141CODEN: JOSOAP; ISSN:1345-8957. (Japan Oil ChemistsÏ Society)
    The temp.-concn. phase behavior of nonionic surfactants in an aprotic imidazolium-type room-temp. ionic liq. (RT-IL) was evaluated on the basis of a combination of visual appearance, polarized optical microscopy, and small angle X-ray scattering data. Phytosterol ethoxylates (BPS-n, where n denotes oxyethylene chain lengths of 5, 10, 20, and 30) were used as surfactants in the RT-IL, 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6). The two component mixts. yielded various phases such as discontinuous cubic, hexagonal, and lamellar phases. An increased tendency toward formation of lesser-curved mol. assemblies was obsd. at higher BPS-n concns., at lower temps., and for shorter oxyethylene chain surfactants. These trends are similar to those obsd. in aq. BPS-n systems; however, notable differences in the phase states of the aq. system vs. the BmimPF6 system were evident. Comparison with the water system showed that the BmimPF6 system yielded fewer phases and generally required higher BPS-n concns. to induce phase transitions. Evaluation of the effects of addn. of a third component (e.g., 1-dodecanol and dodecane) to the binary system on the phase behavior showed that at a given compn. ratio of BPS-20 to BmimPF6, the addn. of 1-dodecanol generally results in the phase transition to lesser-curved assemblies whereas dodecane generated no significant effects. The obsd. phase change is satisfactorily rationalized by localized solubilization of the third component into the binary surfactant assemblies.
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  13. 13
    Wang, L. Y.; Chen, X.; Chai, Y. C.; Hao, J. C.; Sui, Z. M.; Zhuang, W. C.; Sun, Z. W. Lyotropic Liquid Crystalline Phases Formed in an Ionic Liquid Chem. Commun. (Cambridge, U. K.) 2004, 24, 2840– 2841
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    Anjum, N.; Guedeau-Boudeville, M.-A.; Stubenrauch, C.; Mourchid, A. Phase Behavior and Microstructure of Microemulsions Containing the Hydrophobic Ionic Liquid 1-Butyl-3-methylimidazolium Hexafluorophosphate J. Phys. Chem. B 2009, 113, 239– 244
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    Gao, H. X.; Li, J. C.; Han, B. X.; Chen, W. N.; Zhang, J. L.; Zhang, R.; Yan, D. D. Microemulsions with Ionic Liquid Polar Domains Phys. Chem. Chem. Phys. 2004, 6, 2914– 2916
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    Microemulsions with ionic liquid polar domains
    Gao, Haixiang; Li, Junchun; Han, Buxing; Chen, Wenna; Zhang, Jianling; Zhang, Rui; Yan, Dadong
    Physical Chemistry Chemical Physics (2004), 6 (11), 2914-2916CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    In this work 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4], an ionic liq.)/Triton X-100 (TX-100)/cyclohexane microemulsions have been prepd. and characterized by phase behavior, cond. measurement, dynamic light scattering, freeze-fracturing electron microscopy, and UV-vis techniques, and our attention is concd. on the microemulsions with the ionic liq. as the nano-sized polar domains.
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  16. 16
    Gao, Y. N.; Han, S. B.; Han, B. X.; Li, G. Z.; Shen, D.; Li, Z. H.; Du, J. M.; Hou, W. G.; Zhang, G. Y. TX-100/water/1-butyl-3-methylimidazolium Hexafluorophosphate Microemulsions Langmuir 2005, 21, 5681– 5684
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    Walden, P. Über die Molekulargröβe und elektrische Leitfähigkeit Einiger Geschmolzener Salze Bull. Acad. Imp. Sci. St.-Petersbourg 1914, 8, 405– 422
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    Belieres, J. P.; Angell, C. A. Protic Ionic Liquids: Preparation, Characterization, and Proton Free Energy Level Representation J. Phys. Chem. B 2007, 111, 4926– 4937
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    Protic ionic liquids: preparation, characterization, and proton free energy level representation
    Belieres, Jean-Philippe; Angell, C. Austen
    Journal of Physical Chemistry B (2007), 111 (18), 4926-4937CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
    The authors give a perspective on the relations between inorg. and org. cation ionic liqs. (ILs), including members with m.ps. that overlap around the borderline 100 °C. The paper presents the synthesis and properties (melting, boiling, glass temps., etc.) of a large no. of an intermediate group of liqs. that cover the ground between equimolar mol. mixts. and ILs, depending on the energetics of transfer of a proton from one member of the pair to the other. These proton-transfer ILs have interesting properties, including the ability to serve as electrolytes in solvent-free fuel cell systems. This work provides a basis for assessing their relation to aprotic ILs by means of a Gurney-type proton-transfer free energy level diagram, with approx. values of the energy levels based on free energy of formation and pKa data. The energy level scheme allows verifying the relation between solvent-free acidic and basic electrolytes, and the familiar aq. variety, and to identify neutral protic electrolytes that are unavailable in the case of aq. systems.
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    Yoshizawa, M.; Xu, W.; Angell, C. A. Ionic Liquids by Proton Transfer: Vapor Pressure, Conductivity, and the Relevance of Delta pKa from Aqueous Solutions J. Am. Chem. Soc. 2003, 125, 15411– 15419
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    Greaves, T. L.; Drummond, C. J. Protic Ionic Liquids: Properties and Applications Chem. Rev. 2008, 108, 206– 237
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    Protic Ionic Liquids: Properties and Applications
    Greaves, Tamar L.; Drummond, Calum J.
    Chemical Reviews (Washington, DC, United States) (2008), 108 (1), 206-237CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    This review covers the ionicity, physicochem. and thermal properties of protic ionic liqs., along with a description of their applications, and where they have been used, including org. synthesis, chromatog., biol. applications, fuel cells, explosives, and, very recently, industrial lubricants.
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    Angell, C. A.; Byrne, N.; Belieres, J.-P. Parallel Developments in Aprotic and Protic Ionic Liquids: Physical Chemistry and Applications Acc. Chem. Res. 2007, 40, 1228– 1236
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    Parallel Developments in Aprotic and Protic Ionic Liquids: Physical Chemistry and Applications
    Angell, C. Austen; Byrne, Nolene; Belieres, Jean-Philippe
    Accounts of Chemical Research (2007), 40 (11), 1228-1236CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review. This account covers research dating from the early 1960s in the field of low-melting molten salts and hydrates, which has recently become popular under the rubric of "ionic liqs.". It covers understanding gained in the principal author's labs. (initially in Australia, but mostly in the U.S.A.) from spectroscopic, dynamic, and thermodn. studies and includes recent applications of this understanding in the fields of energy conversion and biopreservation. Both protic and aprotic varieties of ionic liqs. are included, but recent studies have focused on the protic class because of the special applications made possible by the highly variable proton activities available in these liqs.
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  22. 22
    Evans, D. F.; Yamauchi, A.; Roman, R.; Casassa, E. Z. Micelle Formation in Ethylammonium Nitrate, a Low-Melting Fused Salt J. Colloid Interface Sci. 1982, 88, 89– 96
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    Micelle formation in ethylammonium nitrate, a low-melting fused salt
    Evans, D. Fennell; Yamauchi, Akira; Roman, Ronald; Casassa, Ethel Z.
    Journal of Colloid and Interface Science (1982), 88 (1), 89-96CODEN: JCISA5; ISSN:0021-9797.
    Crit. micelle concns. (CMC) were detd. from surface tension measurements for alkyltrimethylammonium bromides and alkylpyridinium bromides at 50° and for Triton X-100 at 20 and 50° in ethylammonium nitrate, a low-melting anhyd. fused salt. The CMC's are ∼5 to 10 times larger than those obsd. in water. From the change of CMC with surfactant chain length, the free energy of transfer of a methylene group from the fused salt to the micelle interior is calcd. to be -370 cal/mol compared to -680 cal/mol for a similar transfer from water to the micelle. With respect to solvophobic behavior, ethylammonium nitrate and water show a no. of similarities.
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    Evans, D. F.; Yamauchi, A.; Wei, G. J.; Bloomfield, V. A. Micelle Size in Ethylammonium Nitrate as Determined by Classical and Quasi-Elastic Light Scattering J. Phys. Chem. 1983, 87, 3537– 3541
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    Micelle size in ethylammonium nitrate as determined by classical and quasi-elastic light scattering
    Evans, D. Fennell; Yamauchi, A.; Wei, G. Jason; Bloomfield, Victor A.
    Journal of Physical Chemistry (1983), 87 (18), 3537-41CODEN: JPCHAX; ISSN:0022-3654.
    The aggregation of surfactants to form micelles in ethylammonium nitrate, a low melting fused salt, was investigated by classical and quasi-elastic light scattering. For tetradecylpyridinium bromide and hexadecylpyridinium bromide, the following data are obtained: crit. micelle concns., 8.0 × 10-2 and 2.0 × 10-2 mol kg-1; micellar aggregation nos., 17 and 26; 2nd virial coeffs., 1.64 × 10-3 and 1.30 × 10-3 mol3 g-2; and hydrodynamic radii, 14 and 22 Å, resp. The results are consistent with either a small classical spherical micelle contg. only surfactant or a spherical mixed micelle contg. surfactant and ethylammonium ions as a cosurfactant. The 2nd virial coeffs. are almost equal to those calcd. for hard spheres and reflect highly screened electrostatic interactions in the totally ionized solvent.
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    Araos, M. U.; Warr, G. G. Self-Assembly of Nonionic Surfactants into Lyotropic Liquid Crystals in Ethylammonium Nitrate, a Room-Temperature Ionic Liquid J. Phys. Chem. B 2005, 109, 14275– 14277
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    Self-Assembly of Nonionic Surfactants into Lyotropic Liquid Crystals in Ethylammonium Nitrate, a Room-Temperature Ionic Liquid
    Araos, Miguel U.; Warr, Gregory G.
    Journal of Physical Chemistry B (2005), 109 (30), 14275-14277CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
    The stability of a variety of lyotropic liq. crystals formed by a no. of polyoxyethylene nonionic surfactants in the room-temp. ionic liq. ethylammonium nitrate (EAN) is surveyed and reported. The pattern of self-assembly behavior and mesophase formation is strikingly similar to that obsd. in water, even including the existence of a lower consolute boundary or cloud point. The only quant. difference from water is that longer alkyl chains are necessary to drive the formation of liq. cryst. mesophases in EAN, suggesting that a rich pattern of "solvophobic" self-assembly should exist in this solvent.
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    Araos, M. U.; Warr, G. G. Structure of Nonionic Surfactant Micelles in the Ionic Liquid Ethylammonium Nitrate Langmuir 2008, 24, 9354– 9360
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    Structure of Nonionic Surfactant Micelles in the Ionic Liquid Ethylammonium Nitrate
    Araos, Miguel U.; Warr, Gregory G.
    Langmuir (2008), 24 (17), 9354-9360CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    The structure of micelles formed by nonionic polyoxyethylene alkyl ether nonionic surfactants, CnEm, in room-temp. ionic liq., ethylammonium nitrate (EAN), was detd. by small-angle neutron scattering (SANS) as a function of alkyl and ethoxy chain length, concn., and temp. Micelles form for all surfactant alkyl chain lengths from dodecyl through to octadecyl. The dodecyl-chain surfactants have high crit. micelle concn., around 1%, and form weakly structured micelles. Surfactants with longer alkyl chains readily form micelles in EAN. The obsd. micelle structure changes systematically with alkyl and ethoxy chain length, in parallel with observations in aq. solns. Decreasing ethoxy chain length at const. alkyl chain length leads to a sphere to rod transition. These micelles also grow into rods with increasing temp. as their cloud point is approached in EAN.
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    Atkin, R.; Warr, G. G. Phase Behavior and Microstructure of Microemulsions with a Room-Temperature Ionic Liquid as the Polar Phase J. Phys. Chem. B 2007, 111, 9309– 9316
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    Phase Behavior and Microstructure of Microemulsions with a Room-Temperature Ionic Liquid as the Polar Phase
    Atkin, Rob; Warr, Gregory G.
    Journal of Physical Chemistry B (2007), 111 (31), 9309-9316CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
    Microemulsions of nonionic alkyl oligoethyleneoxide (CiEj) surfactants, alkanes, and ethylammonium nitrate (EAN), a room-temp. ionic liq., have been prepd. and characterized. Studies of phase behavior reveal that EAN microemulsions have many features in common with corresponding aq. systems, the primary difference being that higher surfactant concns. and longer surfactant tailgroups are required to offset the decreased solvophobicity the surfactant mols. in EAN compared with water. The response of the EAN microemulsions to variation in the length of the alkane, surfactant headgroup, and surfactant tailgroup has been found to parallel that obsd. in aq. systems in most instances. EAN microemulsions exhibit a single broad small-angle X-ray scattering peak, like aq. systems. These are well described by the Teubner-Strey model. A lamellar phase was also obsd. for surfactants with longer tails at lower temps. The scattering peaks of both microemulsion and lamellar phases move to lower wave vector on increasing temp. This is ascribed to a decrease in the interfacial area of the surfactant layer. Phase behavior, small-angle X-ray scattering, and cond. expts. have allowed the weakly to strongly structured transition to be identified for EAN systems.
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    Atkin, R.; De Fina, L.-M.; Kiederling, U.; Warr, G. G. Structure and Self Assembly of Pluronic Amphiphiles in Ethylammonium Nitrate and at the Silica Surface J. Phys. Chem. B 2009, 113, 12201– 12213
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    Velasco, S. B.; Turmine, M.; Di Caprio, D.; Letellier, P. Micelle Formation in Ethyl-ammonium Nitrate (an Ionic Liquid) Colloids Surf., A 2006, 275, 50– 54
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    Evans, D. F.; Kaler, E. W.; Benton, W. J. Liquid Crystals in a Fused Salt: β,γ-Distearoylphosphatidylcholine in N-Ethylammonium Nitrate J. Phys. Chem. 1983, 87, 533– 535
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    Greaves, T. L.; Weerawardena, A.; Fong, C.; Drummond, C. J. Many Protic Ionic Liquids Mediate Hydrocarbon-Solvent Interactions and Promote Amphiphile Self-Assembly Langmuir 2007, 23, 402– 404
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    Many Protic Ionic Liquids Mediate Hydrocarbon-Solvent Interactions and Promote Amphiphile Self-Assembly
    Greaves, Tamar L.; Weerawardena, Asoka; Fong, Celesta; Drummond, Calum J.
    Langmuir (2007), 23 (2), 402-404CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    A large no. of protic ionic liqs. (PILs) have been found to mediate solvent-hydrocarbon interactions and promote amphiphile self-assembly. Hexagonal, cubic, and lamellar lyotropic liq. cryst. phases were obsd. in PIL-hexadecyltrimethylammonium bromide systems. The driving force for the formation of the self-assembled aggregate structures has been attributed to an entropic contribution to the free energy of assocn., analogous to the hydrophobic effect in water. The specific aggregate structures formed depend upon the cationic and anionic components of the PIL and their interactions with the amphiphiles.
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    Evans, D. F.; Chen, S.-H.; Schriver, G. W.; Arnett, E. M. Thermodynamics of Solution of Nonpolar Gases in a Fused Salt. Hydrophobic Bonding Behavior in a Nonaqueous System J. Am. Chem. Soc. 1981, 103, 481– 482
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    Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. The Nature of Hydrogen Bonding in Protic Ionic Liquids Angew. Chem., Int. Ed. 2013, 52, 4623– 4627
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    The Nature of Hydrogen Bonding in Protic Ionic Liquids
    Hayes, Robert; Imberti, Silvia; Warr, Gregory G.; Atkin, Rob
    Angewandte Chemie, International Edition (2013), 52 (17), 4623-4627CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The ion arrangements in protic ionic liqs. (PILs) are a consequence of the balance between intermol. forces and the phys. dimensions of the ions. While similar bicontinuous sponge-like nanostructures form in all systems, there is significant variation in the H-bonding. The PIL nanostructure controls the H-bond strength and structure by dictating the relative orientations of the cations and anions to each other. The distribution of H-bond geometries is related to the ability of each PIL to accommodate H-bonds in the bicontinuous arrangement rather than inducing a different bulk structure. When the nanostructures have a relatively high proportion of H-bonds are linear (RX:HN ≈ 1), attractions between ions increase and phys. properties become more solid-like. At higher RX:HN ratios, bi-or trifurcated H-bonding results, leading to weaker, bent- H-bonds, decreasing cation-anion attractions and leading to a more fluid-like material.
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    Atkin, R.; Warr, G. G. The Smallest Amphiphiles: Nanostructure in Protic Room-Temperature Ionic Liquids with Short Alkyl Groups J. Phys. Chem. B 2008, 112, 4164– 4166
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    The Smallest Amphiphiles: Nanostructure in Protic Room-Temperature Ionic Liquids with Short Alkyl Groups
    Atkin, Rob; Warr, Gregory G.
    Journal of Physical Chemistry B (2008), 112 (14), 4164-4166CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
    Room-temp. ionic liqs. (ILs) are low-melting-point org. salts that, until recently, were thought to have homogeneous microstructure. In this work, we investigate nanoscale segregation of short (<C4) alkyl chain ILs using propylammonium nitrate (PAN) and ethylammonium nitrate (EAN). Structure peaks at q = 0.54 Å-1 for PAN and at q = 0.66 Å-1 for EAN, corresponding to Bragg spacings (D* = 2π/qmax) of 11.6 and 9.7 Å resp., provide the first exptl. evidence of nanoscale heterogeneity for ILs with alkyl chains less than C4. The observation that these ILs are not optically birefringent and the fits obtained suggest a disordered, locally smectic or sponge-like structure. Solvophobic interaction between alkyl groups is the most important factor for the prodn. of nanoscale heterogeneities, but electrostatic and hydrogen bonding attractions between the amine nitrogen and the nitrate anion will also play a role.
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    Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Amphiphilicity Determines Nanostructure in Protic Ionic Liquids Phys. Chem. Chem. Phys. 2011, 13, 3237– 3247
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    Amphiphilicity determines nanostructure in protic ionic liquids
    Hayes, Robert; Imberti, Silvia; Warr, Gregory G.; Atkin, Rob
    Physical Chemistry Chemical Physics (2011), 13 (8), 3237-3247CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    The bulk structure of the two oldest ionic liqs. (ILs), ethylammonium nitrate (EAN) and ethanolammonium nitrate (EtAN), is elucidated using neutron diffraction. The spectra were modelled using empirical potential structure refinement (EPSR). EAN exhibits a long-range structure of solvophobic origin, similar to a bicontinuous microemulsion or disordered L3-sponge phase, but with a domain size of only 1 nm. The alc. (-OH) moiety in EtAN interferes with solvophobic assocn. between cation alkyl chains resulting in small clusters of ions, rather than an extended network.
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    Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Pronounced Sponge-like Nanostructure in Propylammonium Nitrate Phys. Chem. Chem. Phys. 2011, 13, 13544– 13551
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    Pronounced sponge-like nanostructure in propylammonium nitrate
    Hayes, Robert; Imberti, Silvia; Warr, Gregory G.; Atkin, Rob
    Physical Chemistry Chemical Physics (2011), 13 (30), 13544-13551CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    The bulk structure of the ionic liq. propylammonium nitrate (PAN) was detd. using neutron diffraction. Empirical potential structure refinement (EPSR) fits to the data show that PAN self-assembles into a quasi-periodic bicontinuous nanostructure reminiscent of an amphiphile L3-sponge phase. Atomic detail on the ion arrangements around the propylammonium cation and nitrate anion yields evidence of hydrogen bonding between ammonium and nitrate groups and of strong alkyl chain aggregation and interdigitation. The resultant amphiphilic PAN nanostructure is more pronounced than that previously detd. for ethylammonium nitrate (EAN) or ethanolammonium nitrate (EtAN).
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    Greaves, T. L.; Kennedy, D. F.; Mudie, S. T.; Drummond, C. J. Diversity Observed in the Nanostructure of Protic Ionic Liquids J. Phys. Chem. B 2010, 114, 10022– 10031
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    Diversity Observed in the Nanostructure of Protic Ionic Liquids
    Greaves, Tamar L.; Kennedy, Danielle F.; Mudie, Stephen T.; Drummond, Calum J.
    Journal of Physical Chemistry B (2010), 114 (31), 10022-10031CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
    The nanostructure of a series of 20 protic ionic liqs. (PILs) has been investigated using small- and wide-angle X-ray scattering (SAXS and WAXS). The PILs contained alkylammonium, dialkylammonium, trialkylammonium, and cyclic ammonium cations combined with org. or inorg. anions. The presence of hydroxyl and methoxy substituents on the alkyl chains of the cations was also explored. Many of the PILs showed a nanostructure resulting from segregation of the polar and nonpolar components of the ionic liq. It was found that this segregation was enhanced for longer alkyl chains, with a corresponding increase in the length scale, whereas the presence of hydroxyl groups on the alkyl chains led to much less ordered liqs. The broad range of protic ionic liqs. studied allowed several structure-property relationships to be established. The solvophobic effect was shown to be dependent on the nanostructure of the PILs. These PILs support amphiphile self-assembly, and it was shown that the less structured PILs had more "water-like" behavior in the diversity of lyotropic liq.-crystal phases supported, and the thermal stability ranges for these phases.
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    Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. How Water Dissolves in Protic Ionic Liquids Angew. Chem., Int. Ed. 2012, 51, 7468– 7471
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    How Water Dissolves in Protic Ionic Liquids
    Hayes, Robert; Imberti, Silvia; Warr, Gregory G.; Atkin, Rob
    Angewandte Chemie, International Edition (2012), 51 (30), 7468-7471, S7468/1-S7468/13CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    When equal masses of water and the protic ionic liq. ethylammonium nitrate are mixed a bicontinuous nanostructure results. This nanostructure resembles aq. surfactant mesophases but has length scales at least an order of magnitude smaller. The local structure of both the water and the ionic liq. are strikingly similar to that found in the pure liqs.
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    Greaves, T. L.; Kennedy, D. F.; Weerawardena, A.; Tse, N. M. K.; Kirby, N.; Drummond, C. J. Nanostructured Protic Ionic Liquids Retain Nanoscale Features in Aqueous Solution While Precursor Bronsted Acids and Bases Exhibit Different Behavior J. Phys. Chem. B 2011, 115, 2055– 2066
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    Hadded, M.; Mayaffre, A.; Letellier, P. Surface-Tension Of Ideal Solutions - Application To Binary-Mixtures Of Methanol And Molten Ethylammonium Nitrate At 298-K J. Chim. Phys. Phys.-Chim. Biol. 1989, 86, 525– 537
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    Surface tension of ideal solutions: application to binary mixtures of methanol and molten ethylammonium nitrate at 298 K
    Hadded, M.; Mayaffre, A.; Letellier, P.
    Journal de Chimie Physique et de Physico-Chimie Biologique (1989), 86 (3), 525-37CODEN: JCPBAN; ISSN:0021-7689.
    Surface tension and excess vols. measurements of MeOH-molten EtNH2.HNO3 mixts. were detd. at 298 K. In terms of excess vols., the behavior of these solns. can be described approx. by the laws of ideal solns. For the surface tensions, an unusual formalism of the Gibbs equation, which involves concns. of the soln. components and a distance parameter, Δh, is proposed. The parameter Δh does not depend on the choice of surface location. This formalism is able to define the behavior of the surface for an ideal mixt. Surface tensions of MeOH-EtNH2.HNO3 mixts. are described accurately by this equation over the entire concn. range.
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    Russina, O.; Sferrazza, A.; Caminiti, R.; Triolo, A. Amphiphile Meets Amphiphile: Beyond the Polar–Apolar Dualism in Ionic Liquid/Alcohol Mixtures J. Phys. Chem. Lett. 2014, 5 (10) 1738– 1742
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    Amphiphile Meets Amphiphile: Beyond the Polar-Apolar Dualism in Ionic Liquid/Alcohol Mixtures
    Russina, Olga; Sferrazza, Alessio; Caminiti, Ruggero; Triolo, Alessandro
    Journal of Physical Chemistry Letters (2014), 5 (10), 1738-1742CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    The mesoscopic morphol. of binary mixts. of ethylammonium nitrate (EAN), the protic ionic liq. par excellence, and methanol is explored using neutron/X-ray diffraction and computational techniques. Both compds. are amphiphilic and characterized by an extended hydrogen bonding network: surprisingly, though macroscopically homogeneous, these mixts. turn out to be mesoscopically highly heterogeneous. Even in methanol-rich mixts., a wide distribution of clusters exists where EAN preserves its bulk, sponge-like morphol. Accordingly, methanol does not succeed in fully dissocg. the ionic liq. that keeps on organizing in a bulk-like fashion. This behavior represents the premise to the more dramatic phenomenol. obsd. with longer alcs. that eventually phase sep. from EAN. These results challenge the commonly accepted polar and apolar moieties segregation in ionic liqs./mol. liqs. mixts. and the current understanding of technol. relevant solvation processes.
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    Weingärtner, H. S.; Merkel, T.; Kashammer, S.; Schröer, W.; Wiegand, S. The Effect of Short-Range Hydrogen-Bonded Interactions on the Nature of the Critical-Point of Ionic Fluids. 1. General-Properties of the New System Ethylammonium Nitrate + n-Octanol with an Upper Consolute Point Near Room-Temperature Ber. Bunsen-Ges. Phys. Chem. 1993, 97, 970– 975
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    Weingärtner, H. S.; Schröer, W. Liquid-Liquid Phase Separations and Critical-Behavior of Electrolyte-Solutions Driven by Long-Range and Short-Range Interactions J. Mol. Liq. 1995, 65–66, 107– 114
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    Sahandzhieva, K.; Tuma, D.; Breyer, S.; Kamps, A. P. S.; Maurer, G. Liquid-Liquid Equilibrium in Mixtures of the Ionic Liquid 1-n-Butyl-3-methylimidazolium Hexafluorophosphate and an Alkanol J. Chem. Eng. Data 2006, 51, 1516– 1525
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    Vale, V. R.; Will, S.; Schroer, W.; Rathke, B. The General Phase Behavior of Mixtures of 1-Alkyl-3-Methylimidazolium Bis[(trifluoromethyl)sulfonyl]amide Ionic Liquids with n-Alkyl Alcohols ChemPhysChem 2012, 13, 1860– 1867
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    Greaves, T. L.; Kennedy, D. F.; Kirby, N.; Drummond, C. J. Nanostructure Changes in Protic Ionic Liquids (PILs) Through Adding Solutes and Mixing PILs Phys. Chem. Chem. Phys. 2011, 13, 13501– 13509
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    Greaves, T. L.; Weerawardena, A.; Fong, C.; Krodkiewska, I.; Drummond, C. J. Protic Ionic Liquids: Solvents with Tunable Phase Behavior and Physicochemical Properties J. Phys. Chem. B 2006, 110, 22479– 22487
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    Protic Ionic Liquids: Solvents with Tunable Phase Behavior and Physicochemical Properties
    Greaves, Tamar L.; Weerawardena, Asoka; Fong, Celesta; Krodkiewska, Irena; Drummond, Calum J.
    Journal of Physical Chemistry B (2006), 110 (45), 22479-22487CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
    The phase behavior, including glass, devitrification, solid crystal melting, and liq. boiling transitions, and physicochem. properties, including d., refractive index, viscosity, cond., and air-liq. surface tension, of a series of 25 protic ionic liqs. and protic fused salts are presented along with structure-property comparisons. The protic fused salts were mostly liq. at room temp., and many exhibited a glass transition occurring at low temps. between -114 and -44 °C, and high fragility, with many having low viscosities, down to as low as 17 mPa·s at 25 °C, and ionic conductivities up to 43.8 S/cm at 25 °C. These protic solvents are easily prepd. through the stoichiometric combination of a primary amine and Bronsted acid. They have poor ionic behavior when compared to the far more studied aprotic ionic liqs. However, some of the other physicochem. properties possessed by these solvents are highly promising and it is anticipated that these, or analogous protic solvents, will find applications beyond those already identified for aprotic ionic liqs. This series of protic fused salts was employed to det. the effect of structural changes on the physicochem. properties, including the effect of hydroxyl groups, increasing alkyl chain lengths, branching, and the differences between inorg. and org. anions. It was found that simple structural modifications provide a mechanism to manipulate, over a wide range, the temp. at which phase transitions occur and to specifically tailor physicochem. properties for potential end-use applications.
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    Bicak, N. A New Ionic Liquid: 2-Hydroxy Ethylammonium Formate J. Mol. Liq. 2005, 116, 15– 18
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    A new ionic liquid: 2-hydroxyethylammonium formate
    Bicak, Niyazi
    Journal of Molecular Liquids (2004), 116 (1), 15-18CODEN: JMLIDT; ISSN:0167-7322. (Elsevier B.V)
    A new ionic liq. (2-hydroxyethylammonium formate), with extremely low melting temp. (-82°), is presented. This ionic liq. of equimolar mixt. of formic acid and 2-hydroxyethylamine shows reasonably high at ionic cond. (3.3 mS cm-1) room temp. and heat stability up to 150°. Both 1H-NMR and FT-IR spectra establish its simple salt structure. Due to its high polarity, the ionic liq. is able to dissolve many inorg. salts. Also some insol. polymers such as polyaniline and polypyrrole are highly sol. in the ionic liq. In the study, the phys. characteristics of the ionic liq., such as cond., viscosity and solvation abilities were investigated.
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    Wakeham, D.; Niga, P.; Ridings, C.; Andersson, G.; Nelson, A.; Warr, G. G.; Baldelli, S.; Rutland, M. W.; Atkin, R. Surface Structure of a “Non-Amphiphilic” Protic Ionic Liquid Phys. Chem. Chem. Phys. 2012, 14, 5106– 5114
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    Wakeham, D.; Warr, G. G.; Atkin, R. Surfactant Adsorption at the Surface of Mixed Ionic Liquids and Ionic Liquid Water Mixtures Langmuir 2012, 28, 13224– 13231
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    Surfactant Adsorption at the Surface of Mixed Ionic Liquids and Ionic Liquid Water Mixtures
    Wakeham, Deborah; Warr, Gregory G.; Atkin, Rob
    Langmuir (2012), 28 (37), 13224-13231CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    Surface tensiometry and neutron reflectivity were used to elucidate the structure of the adsorbed layer of nonionic surfactant tetraethylene glycol tetradecyl ether (C14E4) at the free surface of the ionic liqs. ethylammonium nitrate (EAN) and ethanolammonium nitrate (EtAN) and their binary mixts. with each other and with H2O. Surface tensions reveal that the crit. micelle concn. (cmc) depends strongly on solvent compn. The adsorbed surfactant structure elucidated by neutron reflectivity shows that the level of solvation of the ethylene oxide groups varies for both the pure and mixed solvents. This is attributed to solvent-solvent interactions dominating solvent-surfactant interactions.
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    Greaves, T. L.; Mudie, S. T.; Drummond, C. J. Effect of Protic Ionic Liquids (PILs) on the Formation of Non-Ionic Dodecyl Poly(ethylene oxide) Surfactant Self-Assembly Structures and the Effect of these Surfactants on the Nanostructure of PILs Phys. Chem. Chem. Phys. 2011, 13, 20441– 20452
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    Wakeham, D.; Eschebach, D.; Webber, G. B.; Atkin, R.; Warr, G. G. Surface Composition of Mixtures of Ethylammonium Nitrate, Ethanolammonium Nitrate and Water Aust. J. Chem. 2012, 65, 1554– 1556
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    Kashyap, H. K.; Hettige, J. J.; Annapureddy, H. V. R.; Margulis, C. J. SAXS Anti-peaks Reveal the Length-Scales of Dual Positive–Negative and Polar–Apolar Ordering in Room-Temperature Ionic Liquids Chem. Commun. 2012, 48, 5103– 5105
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    Greaves, T. L.; Drummond, C. J. Solvent Nanostructure, the Solvophobic Effect and Amphiphile Self-Assembly in Ionic Liquids Chem. Soc. Rev. 2013, 42, 1096– 1120
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    Solvent nanostructure, the solvophobic effect and amphiphile self-assembly in ionic liquids
    Greaves, Tamar L.; Drummond, Calum J.
    Chemical Society Reviews (2013), 42 (3), 1096-1120CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. The ability of ionic liqs. (ILs) to support amphiphile self-assembly into a range of mesophase structures was established as a widespread phenomenon. From the ILs evaluated as self-assembly media, the vast majority have supported some lyotropic liq. crystal phase formation. Many neat ionic liqs. segregate into polar and nonpolar domains to form a nanostructured liq. A very strong correlation between the nanostructure of the ionic liq. and its characteristics as an amphiphile self-assembly solvent was found. In this review ionic liqs. as amphiphile self-assembly media, and identify trends that can be used to distinguish which ionic liqs. probably have good promotion properties as self-assembly media are discussed. In particular these trends focus on the nanostructure of neat ionic liqs., their solvent cohesive energy d., and the related solvophobic effect. The authors forecast that many more ILs will be identified as amphiphile self-assembly solvents in the future.
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    Vahvaselka, K. S.; Serimaa, R.; Torkkeli, M. Determination of Liquid Structures of the Primary Alcohols Methanol, Ethanol, 1-Propanol, 1-Butanol and 1-Octanol By X-Ray-Scattering J. Appl. Crystallogr. 1995, 28, 189– 195
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    Determination of liquid structures of the primary alcohols methanol, ethanol, 1-propanol, 1-butanol and 1-octanol by x-ray scattering
    Vahvaselka, Kaarlo Sakari; Serimaa, Ritva; Torkkeli, Mika
    Journal of Applied Crystallography (1995), 28 (2), 189-95CODEN: JACGAR; ISSN:0021-8898. (Munksgaard)
    The four first primary alcs. and 1-octanol were studied with the wide-angle X-ray scattering method using both transmission and reflection techniques at room temp. (293 K). The subsequent radial distribution anal. gives C-O and C-C distances that are in good agreement with the known bond lengths of single alc. mols. The shortest averaged C-H and O-H distances are much smaller than those from the gas-phase data. The shortened distance is caused by the deformed electron distribution between H and C atoms. The intermol. hydrogen bonding between hydroxyl groups occurs at a distance of 2.8 Å, and is a common feature for all the samples. The corresponding coordination no. of 1.7 indicates linear chains of about ten mols. The absence of sharp features in the intensity curves suggests that the arrangement of chains is irregular and that the length of the chains varies.
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    Tomsic, M.; Jamnik, A.; Fritz-Popovski, G.; Glatter, O.; Vlcek, L. Structural Properties of Pure Simple Alcohols from Ethanol, Propanol, Butanol, Pentanol, to Hexanol: Comparing Monte Carlo Simulations with Experimental SAXS Data J. Phys. Chem. B 2007, 111, 1738– 1751
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    Vrhovsek, A.; Gereben, O.; Jamnik, A.; Pusztai, L. Hydrogen Bonding and Molecular Aggregates in Liquid Methanol, Ethanol, and 1-Propanol J. Phys. Chem. B 2011, 115, 13473– 13488
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    Hydrogen Bonding and Molecular Aggregates in Liquid Methanol, Ethanol, and 1-Propanol
    Vrhovsek, Aleksander; Gereben, Orsolya; Jamnik, Andrej; Pusztai, Laszlo
    Journal of Physical Chemistry B (2011), 115 (46), 13473-13488CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
    The authors present a detailed and comprehensive structural study of mol. models of liq. methanol, ethanol, and 1-propanol that originate from reverse Monte Carlo (RMC), mol. dynamics (MD), and united-atom Monte Carlo (UA:MC) simulations. The authors compare several modeling approaches: RMC simulations that employ exptl. neutron and x-ray diffraction data as sole constraints, RMC with diffraction data complemented with partial radial distribution functions (PRDFs) from MD or UA:MC, and conventional MD and UA:MC simulations. The assessment is done in view of the structural parameters of the hydrogen bond and resulting morphol. characteristics of mol. aggregates. To achieve these tasks, a computer program for structural anal. of mol. configurations together with the appropriate aggregate classification scheme was developed. The authors analyzed the morphol. of clusters, their probability, and size distributions. Any cyclic structures that appeared in the configurations were extd. and characterized in the same manner. MD and UA:MC simulations resulted in configurations with bulkier, more threadlike aggregates that were not entirely consistent with the exptl. evidence from diffraction expts. A combination of neutron and x-ray diffraction data with PRDFs from MD simulations, simultaneously applied as constraints in the RMC procedure, proved to be a modeling approach with the most conclusive results.
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    Schröer, W.; Wiegand, S.; Weingärtner, H. The Effect of Short-Range Hydrogen-Bonded Interactions on the Nature of the Critical-Point of Ionic Fluids. 2. Static and Dynamic Light-Scattering on Solutions of Ethylammonium Nitrate in N-Octanol Ber. Bunsen-Ges. Phys. Chem. Chem. Phys. 1993, 97, 975– 982
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    The effect of short-range hydrogen-bonded interactions on the nature of the critical point of ionic fluids. Part II. Static and dynamic light scattering on solutions of ethylammonium nitrate in n-octanol
    Schroer, W.; Wiegand, S.; Weingaertner, H.
    Berichte der Bunsen-Gesellschaft (1993), 97 (8), 975-82CODEN: BBPCAX; ISSN:0005-9021.
    The authors report on static and dynamic light scattering measurements of near-crit. fluctuations of an ionic liq. The system is ethylammonium nitrate (EAN) dissolved in n-octanol which exhibits a liq.-liq. phase transition in the salt-rich regime with an upper crit. point at ∼315 K at a mole fraction of the salt x1 = 0.773. The correlation lengths and scattering intensities scale with temp. corresponding to an Ising-like crit. point. This contrasts with previous observations of mean-field behavior in electrolyte systems with liq.-liq. phase transitions driven by long-range Coulombic interactions. Rationalizations of this discrepancy are offered taking into account a) the competition of intermol. interactions with long-range and short-range character and b) the possibility of crossover from mean-field to Ising behavior as predicted by the Landau-Ginzburg theory.
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  44. Haihui Joy Jiang, Silvia Imberti, Blake A. Simmons, Rob Atkin, Gregory G. Warr. Structural Design of Ionic Liquids for Optimizing Aromatic Dissolution. ChemSusChem 2019, 12 (1) , 270-274. https://doi.org/10.1002/cssc.201802016
  45. Manuel Brunner, Hua Li, Zhezi Zhang, Dongke Zhang, Rob Atkin. Pinewood pyrolysis occurs at lower temperatures following treatment with choline-amino acid ionic liquids. Fuel 2019, 236 , 306-312. https://doi.org/10.1016/j.fuel.2018.09.004
  46. Andrei Filippov, Oleg I. Gnezdilov, Oleg N. Antzutkin. Static magnetic field alters properties of confined alkylammonium nitrate ionic liquids. Journal of Molecular Liquids 2018, 268 , 49-54. https://doi.org/10.1016/j.molliq.2018.07.027
  47. Haihui Joy Jiang, Rob Atkin, Gregory G. Warr. Nanostructured ionic liquids and their solutions: Recent advances and emerging challenges. Current Opinion in Green and Sustainable Chemistry 2018, 12 , 27-32. https://doi.org/10.1016/j.cogsc.2018.05.003
  48. Sraddha Agrawal, Hemant K. Kashyap. Structures of binary mixtures of ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with primary alcohols: The role of hydrogen-bonding. Journal of Molecular Liquids 2018, 261 , 337-349. https://doi.org/10.1016/j.molliq.2018.03.124
  49. Fabrizio Lo Celso, Alessandro Triolo, Lorenzo Gontrani, Olga Russina. Communication: Anion-specific response of mesoscopic organization in ionic liquids upon pressurization. The Journal of Chemical Physics 2018, 148 (21) https://doi.org/10.1063/1.5036588
  50. Marco Campetella, Alessandro Mariani, Claudia Sadun, Boning Wu, Edward W. Castner, Lorenzo Gontrani. Structure and dynamics of propylammonium nitrate-acetonitrile mixtures: An intricate multi-scale system probed with experimental and theoretical techniques. The Journal of Chemical Physics 2018, 148 (13) https://doi.org/10.1063/1.5021868
  51. Andrei Filippov, Oleg N. Antzutkin. Magnetic field effects dynamics of ethylammonium nitrate ionic liquid confined between glass plates. Physical Chemistry Chemical Physics 2018, 20 (9) , 6316-6320. https://doi.org/10.1039/C7CP06554J
  52. Vladimir A. Azov, Ksenia S. Egorova, Marina M. Seitkalieva, Alexey S. Kashin, Valentine P. Ananikov. “Solvent-in-salt” systems for design of new materials in chemistry, biology and energy research. Chemical Society Reviews 2018, 47 (4) , 1250-1284. https://doi.org/10.1039/C7CS00547D
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  55. Hadrián Montes-Campos, José M. Otero-Mato, Trinidad Méndez-Morales, Elena López-Lago, Olga Russina, Oscar Cabeza, Luis J. Gallego, Luis M. Varela. Nanostructured solvation in mixtures of protic ionic liquids and long-chained alcohols. The Journal of Chemical Physics 2017, 146 (12) https://doi.org/10.1063/1.4978943
  56. Gourav Shrivastav, Aditya Gupta, Aman Rastogi, Debdas Dhabal, Hemant K. Kashyap. Molecular dynamics study of nanoscale organization and hydrogen bonding in binary mixtures of butylammonium nitrate ionic liquid and primary alcohols. The Journal of Chemical Physics 2017, 146 (6) https://doi.org/10.1063/1.4975172
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  59. Andrei Filippov, Oleg I. Gnezdilov, Nicklas Hjalmarsson, Oleg N. Antzutkin, Sergei Glavatskih, István Furó, Mark W. Rutland. Acceleration of diffusion in ethylammonium nitrate ionic liquid confined between parallel glass plates. Physical Chemistry Chemical Physics 2017, 19 (38) , 25853-25858. https://doi.org/10.1039/C7CP01772C
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  62. Thomas Murphy, Samantha K. Callear, Gregory G. Warr, Rob Atkin. Dissolved chloride markedly changes the nanostructure of the protic ionic liquids propylammonium and ethanolammonium nitrate. Physical Chemistry Chemical Physics 2016, 18 (26) , 17169-17182. https://doi.org/10.1039/C5CP06947E
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  69. Adam H. Turner, John D. Holbrey. The Solution Structure of 1:2 Phenol/N-Methylpyridinium bis{(trifluoromethyl)sulfonyl}imide Liquid Mixtures. Journal of Solution Chemistry 2015, 44 (3-4) , 621-633. https://doi.org/10.1007/s10953-015-0296-2
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Cite this: J. Phys. Chem. B 2014, 118, 33, 9983–9990
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  • Abstract

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    Figure 1

    Figure 1. Structures of the ILs used in this work.

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    Figure 2

    Figure 2. SAXS/WAXS patterns of pure ionic liquids and aliphatic alcohols at 25 °C.

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    Figure 3

    Figure 3. SAXS/WAXS of amphiphilic ionic liquid + aliphatic n-alcohol mixtures of various compositions at 25 °C: yellow, IL; brown, 10 wt % alkanol; green, 20 wt %; light blue, 40 wt %; blue, 60 wt %; purple, 80 wt %; red, 90 wt %; black, alkanol.

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  • References

    This article references 76 other publications.

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      Huddleston, J. G.; Visser, A. E.; Reichert, W. M.; Willauer, H. D.; Broker, G. A.; Rogers, R. D. Characterization and Comparison of Hydrophilic and Hydrophobic Room Temperature Ionic Liquids Incorporating the Imidazolium Cation Green Chem. 2001, 3, 156– 164
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      Characterization and comparison of hydrophilic and hydrophobic room temperature ionic liquids incorporating the imidazolium cation
      Huddleston, Jonathan G.; Visser, Ann E.; Reichert, W. Matthew; Willauer, Heather D.; Broker, Grant A.; Rogers, Robin D.
      Green Chemistry (2001), 3 (4), 156-164CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
      A series of hydrophilic and hydrophobic 1-alkyl-3-methylimidazolium room temp. ionic liqs. (RTILs) have been prepd. and characterized to det. how water content, d., viscosity, surface tension, m.p., and thermal stability are affected by changes in alkyl chain length and anion. In the series of RTILs studied here, the choice of anion dets. water miscibility and has the most dramatic effect on the properties. Hydrophilic anions (e.g., chloride and iodide) produce ionic liqs. that are miscible in any proportion with water but, upon the removal of some water from the soln., illustrate how sensitive the phys. properties are to a change in water content. In comparison, for ionic liqs. contg. more hydrophobic anions (e.g., PF6- and N(SO2CF3)2-), the removal of water has a smaller affect on the resulting properties. For a series of 1-alkyl-3-methylimidazolium cations, increasing the alkyl chain length from Bu to hexyl to octyl increases the hydrophobicity and the viscosities of the ionic liqs. increase, whereas densities and surface tension values decrease. Thermal analyses indicate high temps. are attainable prior to decompn. and DSC studies reveal a glass transition for several samples. ILs incorporating PF6- have been used in liq./liq. partitioning of org. mols. from water and the results for two of these are also discussed here. On a cautionary note, the chem. of the individual cations and anions of the ILs should not be overlooked as, in the case of certain conditions for PF6- ILs, contact with an aq. phase may result in slow hydrolysis of the PF6- with the concomitant release of HF and other species.
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      Anderson, J. L.; Pino, V.; Hagberg, E. C.; Sheares, V. V.; Armstrong, D. W. Surfactant Solvation Effects and Micelle Formation in Ionic Liquids Chem. Commun. (Cambridge, U. K.) 2003, 2444– 2445
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      Anderson, Jared L.; Pino, Veronica; Hagberg, Erik C.; Sheares, Valerie V.; Armstrong, Daniel W.
      Chemical Communications (Cambridge, United Kingdom) (2003), (19), 2444-2445CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      The formation of micelles in 1-butyl-3-Me imidazolium chloride (BMIM-Cl) and hexafluorophosphate (BMIM-PF6) were explored using different surfactants and the solvation behavior of the new micellar-ionic liq. solns. examd. using inverse gas chromatog.
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      Li, N.; Zhang, S.; Ma, H.; Zheng, L. Role of Solubilized Water in Micelles Formed by Triton X-100 in 1-Butyl-3-methylimidazolium Ionic Liquids Langmuir 2010, 26, 9315– 9320
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      He, Y.; Li, Z.; Simone, P.; Lodge, T. P. Self-Assembly of Block Copolymer Micelles in an Ionic Liquid J. Am. Chem. Soc. 2006, 128, 2745– 2750
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      Self-Assembly of Block Copolymer Micelles in an Ionic Liquid
      He, Yiyong; Li, Zhibo; Simone, Peter; Lodge, Timothy P.
      Journal of the American Chemical Society (2006), 128 (8), 2745-2750CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Four amphiphilic poly((1,2-butadiene)-block-ethylene oxide) (PB-PEO) diblock copolymers were shown to aggregate strongly and form micelles in an ionic liq., 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). The universal micellar structures (spherical micelle, wormlike micelle, and bilayered vesicle) were all accessed by varying the length of the corona block while holding the core block const. The nanostructures of the PB-PEO micelles formed in an ionic liq. were directly visualized by cryogenic transmission electron microscopy (cryo-TEM). Detailed micelle structural information was extd. from both cryo-TEM and dynamic light scattering measurements, with excellent agreement between the two techniques. Compared to aq. solns. of the same copolymers, [BMIM][PF6] solns. exhibit some distinct features, such as temp.-independent micellar morphologies between 25° and 100°. As in aq. solns., significant nonergodicity effects were also obsd. This work demonstrates the flexibility of amphiphilic block copolymers for controlling nanostructure in an ionic liq., with potential applications in many arenas.
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      The phase behaviors of four phytosterol ethoxylates surfactants (BPS-n, n = 5, 10, 20, and 30) with different oxyethylene units in room temp. ionic liq., 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), have been studied. The polarized optical microscopy and small-angle X-ray scattering techniques are used to characterize the phase structures of these binary systems at 25 °C. The structure and ordering of the liq. cryst. (LC) phases in such BPS-n/[Bmim]BF4 systems are found to be influenced by BPS-n concn. and the temp. Due to the bulky and rigid cholesterol group, the phytosterol ethoxylates surfactants exhibit different properties and interaction mechanism from the conventional CnEOm type nonionic surfactant systems. The rheol. measurements indicate a highly viscoelastic nature of these lyotropic LC phases and disclose a lamellar phase characteristic with a rather strong rigidity at high surfactant concns. The control expt. with Brij 97(polyoxyethylene (10) oleyl ether)/[Bmim]BF4 system and the FTIR measurements help to recognize that the solvophobic interaction combining with the hydrogen bonding are the main driving forces for the LC phases formation.
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      Sakai, H.; Saitoh, T.; Misono, T.; Tsuchiya, K.; Sakai, K.; Abe, M. Phase Behavior of Phytosterol Ethoxylates in an Imidazolium-Type Room-Temperature Ionic Liquid J. Oleo Sci. 2012, 61, 135– 141
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      Phase behavior of phytosterol ethoxylates in an imidazolium-type room-temperature ionic liquid
      Sakai, Hideki; Saitoh, Takanori; Misono, Takeshi; Tsuchiya, Koji; Sakai, Kenichi; Abe, Masahiko
      Journal of Oleo Science (2012), 61 (3), 135-141CODEN: JOSOAP; ISSN:1345-8957. (Japan Oil ChemistsÏ Society)
      The temp.-concn. phase behavior of nonionic surfactants in an aprotic imidazolium-type room-temp. ionic liq. (RT-IL) was evaluated on the basis of a combination of visual appearance, polarized optical microscopy, and small angle X-ray scattering data. Phytosterol ethoxylates (BPS-n, where n denotes oxyethylene chain lengths of 5, 10, 20, and 30) were used as surfactants in the RT-IL, 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6). The two component mixts. yielded various phases such as discontinuous cubic, hexagonal, and lamellar phases. An increased tendency toward formation of lesser-curved mol. assemblies was obsd. at higher BPS-n concns., at lower temps., and for shorter oxyethylene chain surfactants. These trends are similar to those obsd. in aq. BPS-n systems; however, notable differences in the phase states of the aq. system vs. the BmimPF6 system were evident. Comparison with the water system showed that the BmimPF6 system yielded fewer phases and generally required higher BPS-n concns. to induce phase transitions. Evaluation of the effects of addn. of a third component (e.g., 1-dodecanol and dodecane) to the binary system on the phase behavior showed that at a given compn. ratio of BPS-20 to BmimPF6, the addn. of 1-dodecanol generally results in the phase transition to lesser-curved assemblies whereas dodecane generated no significant effects. The obsd. phase change is satisfactorily rationalized by localized solubilization of the third component into the binary surfactant assemblies.
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      Anjum, N.; Guedeau-Boudeville, M.-A.; Stubenrauch, C.; Mourchid, A. Phase Behavior and Microstructure of Microemulsions Containing the Hydrophobic Ionic Liquid 1-Butyl-3-methylimidazolium Hexafluorophosphate J. Phys. Chem. B 2009, 113, 239– 244
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      Gao, H. X.; Li, J. C.; Han, B. X.; Chen, W. N.; Zhang, J. L.; Zhang, R.; Yan, D. D. Microemulsions with Ionic Liquid Polar Domains Phys. Chem. Chem. Phys. 2004, 6, 2914– 2916
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      In this work 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4], an ionic liq.)/Triton X-100 (TX-100)/cyclohexane microemulsions have been prepd. and characterized by phase behavior, cond. measurement, dynamic light scattering, freeze-fracturing electron microscopy, and UV-vis techniques, and our attention is concd. on the microemulsions with the ionic liq. as the nano-sized polar domains.
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      Gao, Y. N.; Han, S. B.; Han, B. X.; Li, G. Z.; Shen, D.; Li, Z. H.; Du, J. M.; Hou, W. G.; Zhang, G. Y. TX-100/water/1-butyl-3-methylimidazolium Hexafluorophosphate Microemulsions Langmuir 2005, 21, 5681– 5684
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      Belieres, Jean-Philippe; Angell, C. Austen
      Journal of Physical Chemistry B (2007), 111 (18), 4926-4937CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      The authors give a perspective on the relations between inorg. and org. cation ionic liqs. (ILs), including members with m.ps. that overlap around the borderline 100 °C. The paper presents the synthesis and properties (melting, boiling, glass temps., etc.) of a large no. of an intermediate group of liqs. that cover the ground between equimolar mol. mixts. and ILs, depending on the energetics of transfer of a proton from one member of the pair to the other. These proton-transfer ILs have interesting properties, including the ability to serve as electrolytes in solvent-free fuel cell systems. This work provides a basis for assessing their relation to aprotic ILs by means of a Gurney-type proton-transfer free energy level diagram, with approx. values of the energy levels based on free energy of formation and pKa data. The energy level scheme allows verifying the relation between solvent-free acidic and basic electrolytes, and the familiar aq. variety, and to identify neutral protic electrolytes that are unavailable in the case of aq. systems.
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      Yoshizawa, M.; Xu, W.; Angell, C. A. Ionic Liquids by Proton Transfer: Vapor Pressure, Conductivity, and the Relevance of Delta pKa from Aqueous Solutions J. Am. Chem. Soc. 2003, 125, 15411– 15419
      There is no corresponding record for this reference.
    20. 20
      Greaves, T. L.; Drummond, C. J. Protic Ionic Liquids: Properties and Applications Chem. Rev. 2008, 108, 206– 237
      20
      Protic Ionic Liquids: Properties and Applications
      Greaves, Tamar L.; Drummond, Calum J.
      Chemical Reviews (Washington, DC, United States) (2008), 108 (1), 206-237CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      This review covers the ionicity, physicochem. and thermal properties of protic ionic liqs., along with a description of their applications, and where they have been used, including org. synthesis, chromatog., biol. applications, fuel cells, explosives, and, very recently, industrial lubricants.
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    21. 21
      Angell, C. A.; Byrne, N.; Belieres, J.-P. Parallel Developments in Aprotic and Protic Ionic Liquids: Physical Chemistry and Applications Acc. Chem. Res. 2007, 40, 1228– 1236
      21
      Parallel Developments in Aprotic and Protic Ionic Liquids: Physical Chemistry and Applications
      Angell, C. Austen; Byrne, Nolene; Belieres, Jean-Philippe
      Accounts of Chemical Research (2007), 40 (11), 1228-1236CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review. This account covers research dating from the early 1960s in the field of low-melting molten salts and hydrates, which has recently become popular under the rubric of "ionic liqs.". It covers understanding gained in the principal author's labs. (initially in Australia, but mostly in the U.S.A.) from spectroscopic, dynamic, and thermodn. studies and includes recent applications of this understanding in the fields of energy conversion and biopreservation. Both protic and aprotic varieties of ionic liqs. are included, but recent studies have focused on the protic class because of the special applications made possible by the highly variable proton activities available in these liqs.
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    22. 22
      Evans, D. F.; Yamauchi, A.; Roman, R.; Casassa, E. Z. Micelle Formation in Ethylammonium Nitrate, a Low-Melting Fused Salt J. Colloid Interface Sci. 1982, 88, 89– 96
      22
      Micelle formation in ethylammonium nitrate, a low-melting fused salt
      Evans, D. Fennell; Yamauchi, Akira; Roman, Ronald; Casassa, Ethel Z.
      Journal of Colloid and Interface Science (1982), 88 (1), 89-96CODEN: JCISA5; ISSN:0021-9797.
      Crit. micelle concns. (CMC) were detd. from surface tension measurements for alkyltrimethylammonium bromides and alkylpyridinium bromides at 50° and for Triton X-100 at 20 and 50° in ethylammonium nitrate, a low-melting anhyd. fused salt. The CMC's are ∼5 to 10 times larger than those obsd. in water. From the change of CMC with surfactant chain length, the free energy of transfer of a methylene group from the fused salt to the micelle interior is calcd. to be -370 cal/mol compared to -680 cal/mol for a similar transfer from water to the micelle. With respect to solvophobic behavior, ethylammonium nitrate and water show a no. of similarities.
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    23. 23
      Evans, D. F.; Yamauchi, A.; Wei, G. J.; Bloomfield, V. A. Micelle Size in Ethylammonium Nitrate as Determined by Classical and Quasi-Elastic Light Scattering J. Phys. Chem. 1983, 87, 3537– 3541
      23
      Micelle size in ethylammonium nitrate as determined by classical and quasi-elastic light scattering
      Evans, D. Fennell; Yamauchi, A.; Wei, G. Jason; Bloomfield, Victor A.
      Journal of Physical Chemistry (1983), 87 (18), 3537-41CODEN: JPCHAX; ISSN:0022-3654.
      The aggregation of surfactants to form micelles in ethylammonium nitrate, a low melting fused salt, was investigated by classical and quasi-elastic light scattering. For tetradecylpyridinium bromide and hexadecylpyridinium bromide, the following data are obtained: crit. micelle concns., 8.0 × 10-2 and 2.0 × 10-2 mol kg-1; micellar aggregation nos., 17 and 26; 2nd virial coeffs., 1.64 × 10-3 and 1.30 × 10-3 mol3 g-2; and hydrodynamic radii, 14 and 22 Å, resp. The results are consistent with either a small classical spherical micelle contg. only surfactant or a spherical mixed micelle contg. surfactant and ethylammonium ions as a cosurfactant. The 2nd virial coeffs. are almost equal to those calcd. for hard spheres and reflect highly screened electrostatic interactions in the totally ionized solvent.
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    24. 24
      Araos, M. U.; Warr, G. G. Self-Assembly of Nonionic Surfactants into Lyotropic Liquid Crystals in Ethylammonium Nitrate, a Room-Temperature Ionic Liquid J. Phys. Chem. B 2005, 109, 14275– 14277
      24
      Self-Assembly of Nonionic Surfactants into Lyotropic Liquid Crystals in Ethylammonium Nitrate, a Room-Temperature Ionic Liquid
      Araos, Miguel U.; Warr, Gregory G.
      Journal of Physical Chemistry B (2005), 109 (30), 14275-14277CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      The stability of a variety of lyotropic liq. crystals formed by a no. of polyoxyethylene nonionic surfactants in the room-temp. ionic liq. ethylammonium nitrate (EAN) is surveyed and reported. The pattern of self-assembly behavior and mesophase formation is strikingly similar to that obsd. in water, even including the existence of a lower consolute boundary or cloud point. The only quant. difference from water is that longer alkyl chains are necessary to drive the formation of liq. cryst. mesophases in EAN, suggesting that a rich pattern of "solvophobic" self-assembly should exist in this solvent.
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    25. 25
      Araos, M. U.; Warr, G. G. Structure of Nonionic Surfactant Micelles in the Ionic Liquid Ethylammonium Nitrate Langmuir 2008, 24, 9354– 9360
      25
      Structure of Nonionic Surfactant Micelles in the Ionic Liquid Ethylammonium Nitrate
      Araos, Miguel U.; Warr, Gregory G.
      Langmuir (2008), 24 (17), 9354-9360CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      The structure of micelles formed by nonionic polyoxyethylene alkyl ether nonionic surfactants, CnEm, in room-temp. ionic liq., ethylammonium nitrate (EAN), was detd. by small-angle neutron scattering (SANS) as a function of alkyl and ethoxy chain length, concn., and temp. Micelles form for all surfactant alkyl chain lengths from dodecyl through to octadecyl. The dodecyl-chain surfactants have high crit. micelle concn., around 1%, and form weakly structured micelles. Surfactants with longer alkyl chains readily form micelles in EAN. The obsd. micelle structure changes systematically with alkyl and ethoxy chain length, in parallel with observations in aq. solns. Decreasing ethoxy chain length at const. alkyl chain length leads to a sphere to rod transition. These micelles also grow into rods with increasing temp. as their cloud point is approached in EAN.
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    26. 26
      Atkin, R.; Warr, G. G. Phase Behavior and Microstructure of Microemulsions with a Room-Temperature Ionic Liquid as the Polar Phase J. Phys. Chem. B 2007, 111, 9309– 9316
      26
      Phase Behavior and Microstructure of Microemulsions with a Room-Temperature Ionic Liquid as the Polar Phase
      Atkin, Rob; Warr, Gregory G.
      Journal of Physical Chemistry B (2007), 111 (31), 9309-9316CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      Microemulsions of nonionic alkyl oligoethyleneoxide (CiEj) surfactants, alkanes, and ethylammonium nitrate (EAN), a room-temp. ionic liq., have been prepd. and characterized. Studies of phase behavior reveal that EAN microemulsions have many features in common with corresponding aq. systems, the primary difference being that higher surfactant concns. and longer surfactant tailgroups are required to offset the decreased solvophobicity the surfactant mols. in EAN compared with water. The response of the EAN microemulsions to variation in the length of the alkane, surfactant headgroup, and surfactant tailgroup has been found to parallel that obsd. in aq. systems in most instances. EAN microemulsions exhibit a single broad small-angle X-ray scattering peak, like aq. systems. These are well described by the Teubner-Strey model. A lamellar phase was also obsd. for surfactants with longer tails at lower temps. The scattering peaks of both microemulsion and lamellar phases move to lower wave vector on increasing temp. This is ascribed to a decrease in the interfacial area of the surfactant layer. Phase behavior, small-angle X-ray scattering, and cond. expts. have allowed the weakly to strongly structured transition to be identified for EAN systems.
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    27. 27
      Atkin, R.; De Fina, L.-M.; Kiederling, U.; Warr, G. G. Structure and Self Assembly of Pluronic Amphiphiles in Ethylammonium Nitrate and at the Silica Surface J. Phys. Chem. B 2009, 113, 12201– 12213
      There is no corresponding record for this reference.
    28. 28
      Velasco, S. B.; Turmine, M.; Di Caprio, D.; Letellier, P. Micelle Formation in Ethyl-ammonium Nitrate (an Ionic Liquid) Colloids Surf., A 2006, 275, 50– 54
      There is no corresponding record for this reference.
    29. 29
      Evans, D. F.; Kaler, E. W.; Benton, W. J. Liquid Crystals in a Fused Salt: β,γ-Distearoylphosphatidylcholine in N-Ethylammonium Nitrate J. Phys. Chem. 1983, 87, 533– 535
      There is no corresponding record for this reference.
    30. 30
      Greaves, T. L.; Weerawardena, A.; Fong, C.; Drummond, C. J. Many Protic Ionic Liquids Mediate Hydrocarbon-Solvent Interactions and Promote Amphiphile Self-Assembly Langmuir 2007, 23, 402– 404
      30
      Many Protic Ionic Liquids Mediate Hydrocarbon-Solvent Interactions and Promote Amphiphile Self-Assembly
      Greaves, Tamar L.; Weerawardena, Asoka; Fong, Celesta; Drummond, Calum J.
      Langmuir (2007), 23 (2), 402-404CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      A large no. of protic ionic liqs. (PILs) have been found to mediate solvent-hydrocarbon interactions and promote amphiphile self-assembly. Hexagonal, cubic, and lamellar lyotropic liq. cryst. phases were obsd. in PIL-hexadecyltrimethylammonium bromide systems. The driving force for the formation of the self-assembled aggregate structures has been attributed to an entropic contribution to the free energy of assocn., analogous to the hydrophobic effect in water. The specific aggregate structures formed depend upon the cationic and anionic components of the PIL and their interactions with the amphiphiles.
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    31. 31
      Evans, D. F.; Chen, S.-H.; Schriver, G. W.; Arnett, E. M. Thermodynamics of Solution of Nonpolar Gases in a Fused Salt. Hydrophobic Bonding Behavior in a Nonaqueous System J. Am. Chem. Soc. 1981, 103, 481– 482
      There is no corresponding record for this reference.
    32. 32
      Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. The Nature of Hydrogen Bonding in Protic Ionic Liquids Angew. Chem., Int. Ed. 2013, 52, 4623– 4627
      32
      The Nature of Hydrogen Bonding in Protic Ionic Liquids
      Hayes, Robert; Imberti, Silvia; Warr, Gregory G.; Atkin, Rob
      Angewandte Chemie, International Edition (2013), 52 (17), 4623-4627CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The ion arrangements in protic ionic liqs. (PILs) are a consequence of the balance between intermol. forces and the phys. dimensions of the ions. While similar bicontinuous sponge-like nanostructures form in all systems, there is significant variation in the H-bonding. The PIL nanostructure controls the H-bond strength and structure by dictating the relative orientations of the cations and anions to each other. The distribution of H-bond geometries is related to the ability of each PIL to accommodate H-bonds in the bicontinuous arrangement rather than inducing a different bulk structure. When the nanostructures have a relatively high proportion of H-bonds are linear (RX:HN ≈ 1), attractions between ions increase and phys. properties become more solid-like. At higher RX:HN ratios, bi-or trifurcated H-bonding results, leading to weaker, bent- H-bonds, decreasing cation-anion attractions and leading to a more fluid-like material.
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    33. 33
      Atkin, R.; Warr, G. G. The Smallest Amphiphiles: Nanostructure in Protic Room-Temperature Ionic Liquids with Short Alkyl Groups J. Phys. Chem. B 2008, 112, 4164– 4166
      33
      The Smallest Amphiphiles: Nanostructure in Protic Room-Temperature Ionic Liquids with Short Alkyl Groups
      Atkin, Rob; Warr, Gregory G.
      Journal of Physical Chemistry B (2008), 112 (14), 4164-4166CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      Room-temp. ionic liqs. (ILs) are low-melting-point org. salts that, until recently, were thought to have homogeneous microstructure. In this work, we investigate nanoscale segregation of short (<C4) alkyl chain ILs using propylammonium nitrate (PAN) and ethylammonium nitrate (EAN). Structure peaks at q = 0.54 Å-1 for PAN and at q = 0.66 Å-1 for EAN, corresponding to Bragg spacings (D* = 2π/qmax) of 11.6 and 9.7 Å resp., provide the first exptl. evidence of nanoscale heterogeneity for ILs with alkyl chains less than C4. The observation that these ILs are not optically birefringent and the fits obtained suggest a disordered, locally smectic or sponge-like structure. Solvophobic interaction between alkyl groups is the most important factor for the prodn. of nanoscale heterogeneities, but electrostatic and hydrogen bonding attractions between the amine nitrogen and the nitrate anion will also play a role.
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    34. 34
      Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Amphiphilicity Determines Nanostructure in Protic Ionic Liquids Phys. Chem. Chem. Phys. 2011, 13, 3237– 3247
      34
      Amphiphilicity determines nanostructure in protic ionic liquids
      Hayes, Robert; Imberti, Silvia; Warr, Gregory G.; Atkin, Rob
      Physical Chemistry Chemical Physics (2011), 13 (8), 3237-3247CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      The bulk structure of the two oldest ionic liqs. (ILs), ethylammonium nitrate (EAN) and ethanolammonium nitrate (EtAN), is elucidated using neutron diffraction. The spectra were modelled using empirical potential structure refinement (EPSR). EAN exhibits a long-range structure of solvophobic origin, similar to a bicontinuous microemulsion or disordered L3-sponge phase, but with a domain size of only 1 nm. The alc. (-OH) moiety in EtAN interferes with solvophobic assocn. between cation alkyl chains resulting in small clusters of ions, rather than an extended network.
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    35. 35
      Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Pronounced Sponge-like Nanostructure in Propylammonium Nitrate Phys. Chem. Chem. Phys. 2011, 13, 13544– 13551
      35
      Pronounced sponge-like nanostructure in propylammonium nitrate
      Hayes, Robert; Imberti, Silvia; Warr, Gregory G.; Atkin, Rob
      Physical Chemistry Chemical Physics (2011), 13 (30), 13544-13551CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      The bulk structure of the ionic liq. propylammonium nitrate (PAN) was detd. using neutron diffraction. Empirical potential structure refinement (EPSR) fits to the data show that PAN self-assembles into a quasi-periodic bicontinuous nanostructure reminiscent of an amphiphile L3-sponge phase. Atomic detail on the ion arrangements around the propylammonium cation and nitrate anion yields evidence of hydrogen bonding between ammonium and nitrate groups and of strong alkyl chain aggregation and interdigitation. The resultant amphiphilic PAN nanostructure is more pronounced than that previously detd. for ethylammonium nitrate (EAN) or ethanolammonium nitrate (EtAN).
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    36. 36
      Greaves, T. L.; Kennedy, D. F.; Mudie, S. T.; Drummond, C. J. Diversity Observed in the Nanostructure of Protic Ionic Liquids J. Phys. Chem. B 2010, 114, 10022– 10031
      36
      Diversity Observed in the Nanostructure of Protic Ionic Liquids
      Greaves, Tamar L.; Kennedy, Danielle F.; Mudie, Stephen T.; Drummond, Calum J.
      Journal of Physical Chemistry B (2010), 114 (31), 10022-10031CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      The nanostructure of a series of 20 protic ionic liqs. (PILs) has been investigated using small- and wide-angle X-ray scattering (SAXS and WAXS). The PILs contained alkylammonium, dialkylammonium, trialkylammonium, and cyclic ammonium cations combined with org. or inorg. anions. The presence of hydroxyl and methoxy substituents on the alkyl chains of the cations was also explored. Many of the PILs showed a nanostructure resulting from segregation of the polar and nonpolar components of the ionic liq. It was found that this segregation was enhanced for longer alkyl chains, with a corresponding increase in the length scale, whereas the presence of hydroxyl groups on the alkyl chains led to much less ordered liqs. The broad range of protic ionic liqs. studied allowed several structure-property relationships to be established. The solvophobic effect was shown to be dependent on the nanostructure of the PILs. These PILs support amphiphile self-assembly, and it was shown that the less structured PILs had more "water-like" behavior in the diversity of lyotropic liq.-crystal phases supported, and the thermal stability ranges for these phases.
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    37. 37
      Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. How Water Dissolves in Protic Ionic Liquids Angew. Chem., Int. Ed. 2012, 51, 7468– 7471
      37
      How Water Dissolves in Protic Ionic Liquids
      Hayes, Robert; Imberti, Silvia; Warr, Gregory G.; Atkin, Rob
      Angewandte Chemie, International Edition (2012), 51 (30), 7468-7471, S7468/1-S7468/13CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      When equal masses of water and the protic ionic liq. ethylammonium nitrate are mixed a bicontinuous nanostructure results. This nanostructure resembles aq. surfactant mesophases but has length scales at least an order of magnitude smaller. The local structure of both the water and the ionic liq. are strikingly similar to that found in the pure liqs.
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    38. 38
      Greaves, T. L.; Kennedy, D. F.; Weerawardena, A.; Tse, N. M. K.; Kirby, N.; Drummond, C. J. Nanostructured Protic Ionic Liquids Retain Nanoscale Features in Aqueous Solution While Precursor Bronsted Acids and Bases Exhibit Different Behavior J. Phys. Chem. B 2011, 115, 2055– 2066
      There is no corresponding record for this reference.
    39. 39
      Hadded, M.; Mayaffre, A.; Letellier, P. Surface-Tension Of Ideal Solutions - Application To Binary-Mixtures Of Methanol And Molten Ethylammonium Nitrate At 298-K J. Chim. Phys. Phys.-Chim. Biol. 1989, 86, 525– 537
      39
      Surface tension of ideal solutions: application to binary mixtures of methanol and molten ethylammonium nitrate at 298 K
      Hadded, M.; Mayaffre, A.; Letellier, P.
      Journal de Chimie Physique et de Physico-Chimie Biologique (1989), 86 (3), 525-37CODEN: JCPBAN; ISSN:0021-7689.
      Surface tension and excess vols. measurements of MeOH-molten EtNH2.HNO3 mixts. were detd. at 298 K. In terms of excess vols., the behavior of these solns. can be described approx. by the laws of ideal solns. For the surface tensions, an unusual formalism of the Gibbs equation, which involves concns. of the soln. components and a distance parameter, Δh, is proposed. The parameter Δh does not depend on the choice of surface location. This formalism is able to define the behavior of the surface for an ideal mixt. Surface tensions of MeOH-EtNH2.HNO3 mixts. are described accurately by this equation over the entire concn. range.
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    40. 40
      Russina, O.; Sferrazza, A.; Caminiti, R.; Triolo, A. Amphiphile Meets Amphiphile: Beyond the Polar–Apolar Dualism in Ionic Liquid/Alcohol Mixtures J. Phys. Chem. Lett. 2014, 5 (10) 1738– 1742
      40
      Amphiphile Meets Amphiphile: Beyond the Polar-Apolar Dualism in Ionic Liquid/Alcohol Mixtures
      Russina, Olga; Sferrazza, Alessio; Caminiti, Ruggero; Triolo, Alessandro
      Journal of Physical Chemistry Letters (2014), 5 (10), 1738-1742CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      The mesoscopic morphol. of binary mixts. of ethylammonium nitrate (EAN), the protic ionic liq. par excellence, and methanol is explored using neutron/X-ray diffraction and computational techniques. Both compds. are amphiphilic and characterized by an extended hydrogen bonding network: surprisingly, though macroscopically homogeneous, these mixts. turn out to be mesoscopically highly heterogeneous. Even in methanol-rich mixts., a wide distribution of clusters exists where EAN preserves its bulk, sponge-like morphol. Accordingly, methanol does not succeed in fully dissocg. the ionic liq. that keeps on organizing in a bulk-like fashion. This behavior represents the premise to the more dramatic phenomenol. obsd. with longer alcs. that eventually phase sep. from EAN. These results challenge the commonly accepted polar and apolar moieties segregation in ionic liqs./mol. liqs. mixts. and the current understanding of technol. relevant solvation processes.
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    41. 41
      Weingärtner, H. S.; Merkel, T.; Kashammer, S.; Schröer, W.; Wiegand, S. The Effect of Short-Range Hydrogen-Bonded Interactions on the Nature of the Critical-Point of Ionic Fluids. 1. General-Properties of the New System Ethylammonium Nitrate + n-Octanol with an Upper Consolute Point Near Room-Temperature Ber. Bunsen-Ges. Phys. Chem. 1993, 97, 970– 975
      There is no corresponding record for this reference.
    42. 42
      Weingärtner, H. S.; Schröer, W. Liquid-Liquid Phase Separations and Critical-Behavior of Electrolyte-Solutions Driven by Long-Range and Short-Range Interactions J. Mol. Liq. 1995, 65–66, 107– 114
      There is no corresponding record for this reference.
    43. 43
      Sahandzhieva, K.; Tuma, D.; Breyer, S.; Kamps, A. P. S.; Maurer, G. Liquid-Liquid Equilibrium in Mixtures of the Ionic Liquid 1-n-Butyl-3-methylimidazolium Hexafluorophosphate and an Alkanol J. Chem. Eng. Data 2006, 51, 1516– 1525
      There is no corresponding record for this reference.
    44. 44
      Vale, V. R.; Will, S.; Schroer, W.; Rathke, B. The General Phase Behavior of Mixtures of 1-Alkyl-3-Methylimidazolium Bis[(trifluoromethyl)sulfonyl]amide Ionic Liquids with n-Alkyl Alcohols ChemPhysChem 2012, 13, 1860– 1867
      There is no corresponding record for this reference.
    45. 45
      Greaves, T. L.; Kennedy, D. F.; Kirby, N.; Drummond, C. J. Nanostructure Changes in Protic Ionic Liquids (PILs) Through Adding Solutes and Mixing PILs Phys. Chem. Chem. Phys. 2011, 13, 13501– 13509
      There is no corresponding record for this reference.
    46. 46
      Greaves, T. L.; Weerawardena, A.; Fong, C.; Krodkiewska, I.; Drummond, C. J. Protic Ionic Liquids: Solvents with Tunable Phase Behavior and Physicochemical Properties J. Phys. Chem. B 2006, 110, 22479– 22487
      46
      Protic Ionic Liquids: Solvents with Tunable Phase Behavior and Physicochemical Properties
      Greaves, Tamar L.; Weerawardena, Asoka; Fong, Celesta; Krodkiewska, Irena; Drummond, Calum J.
      Journal of Physical Chemistry B (2006), 110 (45), 22479-22487CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      The phase behavior, including glass, devitrification, solid crystal melting, and liq. boiling transitions, and physicochem. properties, including d., refractive index, viscosity, cond., and air-liq. surface tension, of a series of 25 protic ionic liqs. and protic fused salts are presented along with structure-property comparisons. The protic fused salts were mostly liq. at room temp., and many exhibited a glass transition occurring at low temps. between -114 and -44 °C, and high fragility, with many having low viscosities, down to as low as 17 mPa·s at 25 °C, and ionic conductivities up to 43.8 S/cm at 25 °C. These protic solvents are easily prepd. through the stoichiometric combination of a primary amine and Bronsted acid. They have poor ionic behavior when compared to the far more studied aprotic ionic liqs. However, some of the other physicochem. properties possessed by these solvents are highly promising and it is anticipated that these, or analogous protic solvents, will find applications beyond those already identified for aprotic ionic liqs. This series of protic fused salts was employed to det. the effect of structural changes on the physicochem. properties, including the effect of hydroxyl groups, increasing alkyl chain lengths, branching, and the differences between inorg. and org. anions. It was found that simple structural modifications provide a mechanism to manipulate, over a wide range, the temp. at which phase transitions occur and to specifically tailor physicochem. properties for potential end-use applications.
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    47. 47
      Bicak, N. A New Ionic Liquid: 2-Hydroxy Ethylammonium Formate J. Mol. Liq. 2005, 116, 15– 18
      47
      A new ionic liquid: 2-hydroxyethylammonium formate
      Bicak, Niyazi
      Journal of Molecular Liquids (2004), 116 (1), 15-18CODEN: JMLIDT; ISSN:0167-7322. (Elsevier B.V)
      A new ionic liq. (2-hydroxyethylammonium formate), with extremely low melting temp. (-82°), is presented. This ionic liq. of equimolar mixt. of formic acid and 2-hydroxyethylamine shows reasonably high at ionic cond. (3.3 mS cm-1) room temp. and heat stability up to 150°. Both 1H-NMR and FT-IR spectra establish its simple salt structure. Due to its high polarity, the ionic liq. is able to dissolve many inorg. salts. Also some insol. polymers such as polyaniline and polypyrrole are highly sol. in the ionic liq. In the study, the phys. characteristics of the ionic liq., such as cond., viscosity and solvation abilities were investigated.
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    48. 48
      Wakeham, D.; Niga, P.; Ridings, C.; Andersson, G.; Nelson, A.; Warr, G. G.; Baldelli, S.; Rutland, M. W.; Atkin, R. Surface Structure of a “Non-Amphiphilic” Protic Ionic Liquid Phys. Chem. Chem. Phys. 2012, 14, 5106– 5114
      There is no corresponding record for this reference.
    49. 49
      Wakeham, D.; Warr, G. G.; Atkin, R. Surfactant Adsorption at the Surface of Mixed Ionic Liquids and Ionic Liquid Water Mixtures Langmuir 2012, 28, 13224– 13231
      49
      Surfactant Adsorption at the Surface of Mixed Ionic Liquids and Ionic Liquid Water Mixtures
      Wakeham, Deborah; Warr, Gregory G.; Atkin, Rob
      Langmuir (2012), 28 (37), 13224-13231CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      Surface tensiometry and neutron reflectivity were used to elucidate the structure of the adsorbed layer of nonionic surfactant tetraethylene glycol tetradecyl ether (C14E4) at the free surface of the ionic liqs. ethylammonium nitrate (EAN) and ethanolammonium nitrate (EtAN) and their binary mixts. with each other and with H2O. Surface tensions reveal that the crit. micelle concn. (cmc) depends strongly on solvent compn. The adsorbed surfactant structure elucidated by neutron reflectivity shows that the level of solvation of the ethylene oxide groups varies for both the pure and mixed solvents. This is attributed to solvent-solvent interactions dominating solvent-surfactant interactions.
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    50. 50
      Greaves, T. L.; Mudie, S. T.; Drummond, C. J. Effect of Protic Ionic Liquids (PILs) on the Formation of Non-Ionic Dodecyl Poly(ethylene oxide) Surfactant Self-Assembly Structures and the Effect of these Surfactants on the Nanostructure of PILs Phys. Chem. Chem. Phys. 2011, 13, 20441– 20452
      There is no corresponding record for this reference.
    51. 51
      Wakeham, D.; Eschebach, D.; Webber, G. B.; Atkin, R.; Warr, G. G. Surface Composition of Mixtures of Ethylammonium Nitrate, Ethanolammonium Nitrate and Water Aust. J. Chem. 2012, 65, 1554– 1556
      There is no corresponding record for this reference.
    52. 52
      Kashyap, H. K.; Hettige, J. J.; Annapureddy, H. V. R.; Margulis, C. J. SAXS Anti-peaks Reveal the Length-Scales of Dual Positive–Negative and Polar–Apolar Ordering in Room-Temperature Ionic Liquids Chem. Commun. 2012, 48, 5103– 5105
      There is no corresponding record for this reference.
    53. 53
      Greaves, T. L.; Drummond, C. J. Solvent Nanostructure, the Solvophobic Effect and Amphiphile Self-Assembly in Ionic Liquids Chem. Soc. Rev. 2013, 42, 1096– 1120
      53
      Solvent nanostructure, the solvophobic effect and amphiphile self-assembly in ionic liquids
      Greaves, Tamar L.; Drummond, Calum J.
      Chemical Society Reviews (2013), 42 (3), 1096-1120CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. The ability of ionic liqs. (ILs) to support amphiphile self-assembly into a range of mesophase structures was established as a widespread phenomenon. From the ILs evaluated as self-assembly media, the vast majority have supported some lyotropic liq. crystal phase formation. Many neat ionic liqs. segregate into polar and nonpolar domains to form a nanostructured liq. A very strong correlation between the nanostructure of the ionic liq. and its characteristics as an amphiphile self-assembly solvent was found. In this review ionic liqs. as amphiphile self-assembly media, and identify trends that can be used to distinguish which ionic liqs. probably have good promotion properties as self-assembly media are discussed. In particular these trends focus on the nanostructure of neat ionic liqs., their solvent cohesive energy d., and the related solvophobic effect. The authors forecast that many more ILs will be identified as amphiphile self-assembly solvents in the future.
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    54. 54
      Stewart, G. W.; Morrow, R. M. X-ray Diffraction in Liquids Primary Normal Alcohols Phys. Rev. 1927, 30, 232– 244
      There is no corresponding record for this reference.
    55. 55
      Vahvaselka, K. S.; Serimaa, R.; Torkkeli, M. Determination of Liquid Structures of the Primary Alcohols Methanol, Ethanol, 1-Propanol, 1-Butanol and 1-Octanol By X-Ray-Scattering J. Appl. Crystallogr. 1995, 28, 189– 195
      55
      Determination of liquid structures of the primary alcohols methanol, ethanol, 1-propanol, 1-butanol and 1-octanol by x-ray scattering
      Vahvaselka, Kaarlo Sakari; Serimaa, Ritva; Torkkeli, Mika
      Journal of Applied Crystallography (1995), 28 (2), 189-95CODEN: JACGAR; ISSN:0021-8898. (Munksgaard)
      The four first primary alcs. and 1-octanol were studied with the wide-angle X-ray scattering method using both transmission and reflection techniques at room temp. (293 K). The subsequent radial distribution anal. gives C-O and C-C distances that are in good agreement with the known bond lengths of single alc. mols. The shortest averaged C-H and O-H distances are much smaller than those from the gas-phase data. The shortened distance is caused by the deformed electron distribution between H and C atoms. The intermol. hydrogen bonding between hydroxyl groups occurs at a distance of 2.8 Å, and is a common feature for all the samples. The corresponding coordination no. of 1.7 indicates linear chains of about ten mols. The absence of sharp features in the intensity curves suggests that the arrangement of chains is irregular and that the length of the chains varies.
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    56. 56
      Tomsic, M.; Jamnik, A.; Fritz-Popovski, G.; Glatter, O.; Vlcek, L. Structural Properties of Pure Simple Alcohols from Ethanol, Propanol, Butanol, Pentanol, to Hexanol: Comparing Monte Carlo Simulations with Experimental SAXS Data J. Phys. Chem. B 2007, 111, 1738– 1751
      There is no corresponding record for this reference.
    57. 57
      Vrhovsek, A.; Gereben, O.; Jamnik, A.; Pusztai, L. Hydrogen Bonding and Molecular Aggregates in Liquid Methanol, Ethanol, and 1-Propanol J. Phys. Chem. B 2011, 115, 13473– 13488
      57
      Hydrogen Bonding and Molecular Aggregates in Liquid Methanol, Ethanol, and 1-Propanol
      Vrhovsek, Aleksander; Gereben, Orsolya; Jamnik, Andrej; Pusztai, Laszlo
      Journal of Physical Chemistry B (2011), 115 (46), 13473-13488CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
      The authors present a detailed and comprehensive structural study of mol. models of liq. methanol, ethanol, and 1-propanol that originate from reverse Monte Carlo (RMC), mol. dynamics (MD), and united-atom Monte Carlo (UA:MC) simulations. The authors compare several modeling approaches: RMC simulations that employ exptl. neutron and x-ray diffraction data as sole constraints, RMC with diffraction data complemented with partial radial distribution functions (PRDFs) from MD or UA:MC, and conventional MD and UA:MC simulations. The assessment is done in view of the structural parameters of the hydrogen bond and resulting morphol. characteristics of mol. aggregates. To achieve these tasks, a computer program for structural anal. of mol. configurations together with the appropriate aggregate classification scheme was developed. The authors analyzed the morphol. of clusters, their probability, and size distributions. Any cyclic structures that appeared in the configurations were extd. and characterized in the same manner. MD and UA:MC simulations resulted in configurations with bulkier, more threadlike aggregates that were not entirely consistent with the exptl. evidence from diffraction expts. A combination of neutron and x-ray diffraction data with PRDFs from MD simulations, simultaneously applied as constraints in the RMC procedure, proved to be a modeling approach with the most conclusive results.
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    58. 58
      Dixit, S.; Crain, J.; Poon, W. C. K.; Finney, J. L.; Soper, A. K. Molecular Segregation Observed in a Concentrated Alcohol–Water Solution Nature 2002, 416, 829– 832
      There is no corresponding record for this reference.
    59. 59
      Schröer, W.; Wiegand, S.; Weingärtner, H. The Effect of Short-Range Hydrogen-Bonded Interactions on the Nature of the Critical-Point of Ionic Fluids. 2. Static and Dynamic Light-Scattering on Solutions of Ethylammonium Nitrate in N-Octanol Ber. Bunsen-Ges. Phys. Chem. Chem. Phys. 1993, 97, 975– 982
      59
      The effect of short-range hydrogen-bonded interactions on the nature of the critical point of ionic fluids. Part II. Static and dynamic light scattering on solutions of ethylammonium nitrate in n-octanol
      Schroer, W.; Wiegand, S.; Weingaertner, H.
      Berichte der Bunsen-Gesellschaft (1993), 97 (8), 975-82CODEN: BBPCAX; ISSN:0005-9021.
      The authors report on static and dynamic light scattering measurements of near-crit. fluctuations of an ionic liq. The system is ethylammonium nitrate (EAN) dissolved in n-octanol which exhibits a liq.-liq. phase transition in the salt-rich regime with an upper crit. point at ∼315 K at a mole fraction of the salt x1 = 0.773. The correlation lengths and scattering intensities scale with temp. corresponding to an Ising-like crit. point. This contrasts with previous observations of mean-field behavior in electrolyte systems with liq.-liq. phase transitions driven by long-range Coulombic interactions. Rationalizations of this discrepancy are offered taking into account a) the competition of intermol. interactions with long-range and short-range character and b) the possibility of crossover from mean-field to Ising behavior as predicted by the Landau-Ginzburg theory.
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    60. 60
      Atkin, R.; Bobillier, S. M. C.; Warr, G. G. Propylammonium Nitrate as a Solvent for Amphiphile Self-Assembly into Micelles, Lyotropic Liquid Crystals, and Microemulsions J. Phys. Chem. B 2010, 114, 1350– 1360
      60
      Propylammonium Nitrate as a Solvent for Amphiphile Self-Assembly into Micelles, Lyotropic Liquid Crystals, and Microemulsions
      Atkin, Rob; Bobillier, Sophie M. C.; Warr, Gregory G.
      Journal of Physical Chemistry B (2010), 114 (3), 1350-1360CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      The phase behavior and self-assembled microstructures of a range of oligo(oxyethylene)-n-alkyl ether (CiEj) surfactants was studied in propylammonium nitrate (PAN), a room temp. ionic liq. Micelles and single-phase microemulsions were all found to form at alkyl chain lengths from dodecyl to octadecyl, and lyotropic liq. crystals formed with hexadecyl chains or longer. Small-angle neutron scattering (SANS) shows that self-assembly occurs by solvophobic interactions driving the aggregation of the alkyl chains, but several results indicate that these are weaker in PAN than in water or ethylammonium nitrate, due chiefly to the hydrophobicity of PAN. Longer alkyl chains are needed for lyotropic liq. crystals to form, and higher surfactant concns. are needed to form a single phase microemulsion. Cond. shows these microemulsions to be weakly structured, and relatively insensitive to oil or surfactant mol. structure, unlike water-based systems. However, SANS contrast variation reveals a nanosegregation of oil from the alkyl tails of surfactants within the microemulsion, and may suggest a cosurfactant-like role for the propylammonium cation. Mol. areas within microemulsions and lamellar phases are larger than corresponding water- or ethylammonium nitrate-based systems due to the large mol. vol. of the solvating PANs.
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    61. 61
      Topolnicki, I. L.; Atkin, R.; FitzGerald, P. A.; Warr, G. G. The Effect of Protic Ionic Liquid and Surfactant Structure on Partitioning of Polyoxyethylene Nonionic Surfactants. ChemPhysChem 2014, 15.
      There is no corresponding record for this reference.
    62. 62
      Kline, S. R. Reduction and Analysis of SANS and USANS Data using Igor Pro J. Appl. Crystallogr. 2006, 39 (6) 895– 900
      62
      Reduction and analysis of SANS and USANS data using IGOR Pro
      Kline, Steven R.
      Journal of Applied Crystallography (2006), 39 (6), 895-900CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)
      A software package is presented for performing redn. and anal. of small-angle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS) data. A graphical interface was developed to visualize and quickly reduce raw SANS and USANS data into 1D or 2D formats for interpretation. The resulting reduced data can then be analyzed using model-independent methods or nonlinear fitting to one of a large and growing catalog of included structural models. The different instrumental smearing effects for slit-smeared USANS and pinhole-smeared SANS data are handled automatically during anal. In addn., any no. of SANS and USANS data sets can be analyzed simultaneously. The redn. operations and anal. models are written in a modular format for extensibility, allowing users to contribute code and models for distribution to all users. The software package is based on Igor Pro, providing freely distributable and modifiable code that runs on Macintosh and Windows operating systems.
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    63. 63
      Teubner, M.; Strey, R. Origin of the Scattering Peak in Microemulsions J. Chem. Phys. 1987, 87, 3195– 3200
      63
      Origin of the scattering peak in microemulsions
      Teubner, M.; Strey, R.
      Journal of Chemical Physics (1987), 87 (5), 3195-200CODEN: JCPSA6; ISSN:0021-9606.
      From a Landau theory the static scattering intensity distribution I(q) of microemulsions is obtained. It is shown that the scattering intensity relation describes exptl. literature data remarkably well, using only three fit parameters.
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    64. 64
      Schubert, K. V.; Strey, R. Small-Angle Neutron Scattering from Microemulsions Near the Disorder Line in Water/Formamide--Octane-CiEj Systems J. Chem. Phys. 1991, 95, 8532– 8545
      There is no corresponding record for this reference.
    65. 65
      Vonk, C. G.; Billman, J. F.; Kaler, E. W. Small Angle Scattering of Bicontinuous Structures in Microemulsions J. Chem. Phys. 1988, 88, 3970– 3975
      There is no corresponding record for this reference.
    66. 66
      Schubert, K.-V.; Strey, R.; Kline, S. R.; Kaler, E. W. Small Angle Neutron Scattering Near Lifshitz Lines: Transition from Weakly Structured Mixtures to Microemulsions J. Chem. Phys. 1994, 101, 5343– 5355
      66
      Small angle neutron scattering near Lifshitz lines: transition from weakly structured mixtures to microemulsions
      Schubert, K.-V.; Strey, R.; Kline, S. R.; Kaler, E. W.
      Journal of Chemical Physics (1994), 101 (6), 5343-55CODEN: JCPSA6; ISSN:0021-9606.
      We have studied the phase behavior, wetting transitions, and small angle neutron scattering (SANS) of water, n-alkane, and n-alkyl polyglycol ether (CiEj) systems in order to locate the transition between weakly structured mixts. and microemulsions, and to provide a measure for the transition. We first detd. the wetting transition by macroscopic measurements and then measured the location of the Lifshitz lines by SANS. Starting with well-structured mixts. (exhibiting nonwetting middle phases and well-expressed scattering peaks, features that qualify them as microemulsions) the wetting transition was induced by increasing the chain length of the alkane or by changing the oil/water vol. ratio, and then the Lifshitz line was crossed. Further, starting with systems past the disorder line (weakly structured mixts. that display wetting middle phases and no scattering peaks), local structure was induced by either increasing the surfactant concn. or decreasing the oil/water vol. ratio or the temp. In each case a Lifshitz line was crossed. Analyzing the scattering expts. quant., allows detn. of the amphiphilicity factor, which is a measure of the strength of the surfactant. The results suggest there is a sequence of roughly parallel surfaces within the three-dimensional compn.-temp. space. As the amphiphilicity factor increases, first a disorder surface is encountered, then a Lifshitz surface, and finally a wetting transition surface. How and to what extent these surfaces move in the one-phase region toward smaller surfactant concns., and intersect there with the body of heterogeneous phases, depends on a no. of factors that are discussed in some detail.
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    67. 67
      Barnes, I. S.; Corti, M.; Degiorgio, V.; Zemb, T. X-ray and Neutron-Scattering Measurements on Concentrated Non-Ionic Amphiphile Solutions Prog. Colloid Polym. Sci. 1993, 93, 205– 206
      67
      X-ray and neutron-scattering measurements on concentrated non-ionic amphiphile solutions
      Barnes, I. S.; Corti, M.; Degiorgio, V.; Zemb, T.
      Progress in Colloid & Polymer Science (1993), 93 (TRENDS IN COLLOID AN), 205-6CODEN: PCPSD7; ISSN:0340-255X.
      The structure of aq. solns. of the nonionic amphiphile C12E8 is studied by small-angle x-ray and neutron scattering along the isothermal path across the single-phase region from 0% to 100% amphiphile vol. fraction. Soln. structuring is present even in the pure amphiphile, as shown by x-ray data.
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    68. 68
      Laughlin, R. The Aqueous Phase Behavior of Surfactants; Academic Press: San Diego, 1994.
      There is no corresponding record for this reference.
    69. 69
      Diat, O.; K, M. L.; Touraud, D.; Deme, B.; Grillo, I.; Kunz, W.; Zemb, T. Octanol-Rich and Water-Rich Domains in Dynamic Equilibrium in the Pre-Ouzo Region of Ternary Systems Containing a Hydrotrope J. Appl. Crystallogr. 2013, 46, 1665– 1669
      69
      Octanol-rich and water-rich domains in dynamic equilibrium in the pre-ouzo region of ternary systems containing a hydrotrope
      Diat, Olivier; Klossek, Michael L.; Touraud, Didier; Deme, Bruno; Grillo, Isabelle; Kunz, Werner; Zemb, Thomas
      Journal of Applied Crystallography (2013), 46 (6), 1665-1669CODEN: JACGAR; ISSN:0021-8898. (International Union of Crystallography)
      Ternary mixts. of medium-chain fatty alcs., water and a hydrotrope (such as ethanol), near the immiscibility gap, make stable single phases at const. temp. Interestingly, in this 'pre-ouzo region' these single phases consist of two distinct nanoscopic pseudo-phases, one octanol-rich and one water-rich. This domain of compn., which is known to produce strong light scattering and to sep. under ultracentrifugation into two phases, has been studied using contrast variation in small-angle neutron scattering (SANS) combined with small- and wide-angle X-ray scattering (SWAXS). The existence of fatty alc.-rich domains of well defined size of the order of 2 nm radius is proven. The scattering can be approximated by an Ornstein-Zernike function, which is close to the general expression of Choi, Chen, Sottmann & Strey [Physica B, (1998), 241-243, 976-978] with vanishing quadratic Porod term. Exploitation of the relative intensities at the vanishing scattering angle in SANS demonstrates that the distribution coeff. of ethanol between the octanol-rich and the water-rich domains is close to one. WAXS of the two coexisting pseudo-phases is compared with the corresponding binary water-ethanol and octanol-ethanol samples.
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    70. 70
      Tchakalova, V.; Zemb, T.; Benczédi, D. Evaporation Triggered Self-Assembly in Aqueous Fragrance–Ethanol Mixtures and Its Impact on Fragrance Performance. Colloids Surf., A 2014, in press
      There is no corresponding record for this reference.
    71. 71
      Clint, J. H. Micellization of Mixed Nonionic Surface Active Agents J. Chem. Soc., Faraday Trans. 1 1975, 71 (0) 1327– 1334
      There is no corresponding record for this reference.
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      Kahlweit, M.; Strey, R.; Busse, G. Weakly to Strongly Structured Mixtures Phys. Rev. E 1993, 47, 4197– 4209
      There is no corresponding record for this reference.
    73. 73
      Greaves, T. L.; Drummond, C. J. Ionic Liquids as Amphiphile Self-Assembly Media Chem. Soc. Rev. 2008, 37, 1709– 1726
      73
      Ionic liquids as amphiphile self-assembly media
      Greaves, Tamar L.; Drummond, Calum J.
      Chemical Society Reviews (2008), 37 (8), 1709-1726CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. In recent years, the no. of nonaq. solvents which mediate hydrocarbon-solvent interactions and promote the self-assembly of amphiphiles was markedly increased by the reporting of over 30 ionic liqs. which possess this previously unusual solvent characteristic. This new situation allows a different exploration of the mol. solvophobic effect and tests the current understanding of amphiphile self-assembly. Both protic and aprotic ionic liqs. support amphiphile self-assembly, indicating that it is not required for the solvents to be able to form a hydrogen bonded network. Here, the use of ionic liqs. as amphiphile self-assembly media is reviewed, including micelle and liq. cryst. mesophase formation, their use as a solvent phase in microemulsions and emulsions, and the emerging field of nanostructured inorg. materials synthesis. Surfactants, lipids and block co-polymers are the focus amphiphile classes in this crit. review (174 refs.).
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    74. 74
      Beesley, A. H.; Evans, D. F.; Laughlin, R. G. Evidence For The Essential Role Of Hydrogen-Bonding In Promoting Amphiphilic Self-Assembly - Measurements in 3-Methylsydnone J. Phys. Chem. 1988, 92, 791– 793
      There is no corresponding record for this reference.
    75. 75
      Ray, A. Micelle Formation in Pure Ethylene Glycol J. Am. Chem. Soc. 1969, 91 (23) 6511– 6512
      There is no corresponding record for this reference.
    76. 76
      Ray, A. Solvophobic Interactions and Micelle Formation in Structure Forming Nonaqueous Solvents Nature 1971, 231, 313– 315
      76
      Solvophobic interactions and micelle formation in structure forming nonaqueous solvents
      Ray, Ashoka
      Nature (London, United Kingdom) (1971), 231 (5301), 313-15CODEN: NATUAS; ISSN:0028-0836.
      Solvophobic interactions occur in glycerol, HCONH2, H2N(CH2)2OH, HO(CH2)3OH, HO(CH2)4OH, HCO2H, H2N(CH2)2NH2, HS(CH2)2OH, HOCH2CH2CH(OH)Me, HOCH2CH(OH)Me, and H2NCH2CH(OH)Me (class I). Such interactions do not exist in HCONHMe, HCONMe2, and CH2I2 (class II), or in MeOH, EtOH, and PhMe (class III). A nonionic detergent [e.g., (p-tert-nonylphenoxy)polyethylene glycol] would aggregate into micelles only in class I solvents. The crit. micelle concns. of the detergent, and the free energies of micelle formation were calcd.
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