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ArticleNovember 14, 2020

Crystal-to-Crystal Transitions in Binary Mixtures of Soft Colloids
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Jasper N. Immink*
Jasper N. Immink
Division of Physical Chemistry, Lund University, 221 00 Lund, Sweden
*Tel: +46-46-2223677. E-mail: [email protected]
More by Jasper N. Immink
http://orcid.org/0000-0003-1251-5442
Maxime J. Bergman
Maxime J. Bergman
Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland
More by Maxime J. Bergman
J. J. Erik Maris
J. J. Erik Maris
Inorganic Chemistry and Catalysis Group, Utrecht University, 3584 CS Utrecht, The Netherlands
More by J. J. Erik Maris
http://orcid.org/0000-0003-2591-4864
Joakim Stenhammar
Joakim Stenhammar
Division of Physical Chemistry, Lund University, 221 00 Lund, Sweden
More by Joakim Stenhammar
http://orcid.org/0000-0002-7543-5549
Peter Schurtenberger
Peter Schurtenberger
Division of Physical Chemistry, Lund University, 221 00 Lund, Sweden
Lund Institute of advanced Neutron and X-ray Science (LINXS), Lund University, 221 00 Lund, Sweden
More by Peter Schurtenberger
http://orcid.org/0000-0002-2790-8831

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ACS Nano

Cite this: ACS Nano 2020, 14, 11, 14861–14868

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https://doi.org/10.1021/acsnano.0c03966

Published November 14, 2020

Abstract

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In this article, we demonstrate a method for inducing reversible crystal-to-crystal transitions in binary mixtures of soft colloidal particles. Through a controlled decrease of salinity and increasingly dominating electrostatic interactions, a single sample is shown to reversibly organize into entropic crystals, electrostatic attraction-dominated crystals, or aggregated gels, which we quantify using microscopy and image analysis. We furthermore analyze crystalline structures with bond order analysis to discern between two crystal phases. We observe the different phases using a sample holder geometry that allows both in situ salinity control and imaging through confocal laser scanning microscopy and apply a synthesis method producing particles with high resolvability in microscopy with control over particle size. The particle softness provides for an enhanced crystallization speed, while altering the re-entrant melting behavior as compared to hard sphere systems. This work thus provides several tools for use in the reproducible manufacture and analysis of binary colloidal crystals.

Subjects

Keywords

Colloids are often used as model systems in order to study various phenomena in condensed matter physics. (1) Particular attention has been devoted to the effects that interaction potentials have on the phase behavior of colloids (2,3) and to processes such as crystallization (4−8) or the mechanisms and kinetic pathways of fluid–crystal and crystal–crystal transitions. (9−11) In these contexts, colloids have been employed as an analogue of atomic systems, so that the relevant length and time scales are in a range that makes experimental investigation much simpler. The earliest investigations primarily used standard “hard” colloids such as sterically stabilized PMMA spheres. (12,13) Later, more complex particles have been studied, to explore for instance the influence of long-range electrostatic repulsions (14,15) or the effect of a short-range attraction resulting, for example, from depletion interactions in colloid–polymer mixtures. (2,16,17)

The majority of these investigations were performed with approximately monodisperse particles. Inspired by analogies with “real” atomic materials such as alloys and salts, numerous attempts have also been made to investigate binary mixtures. (18−27) However, investigating equilibrium structures in dense binary mixtures of hard spheres remains difficult, as nucleation and crystal growth may be very slow or hindered due to vitrification of the sample. (28,29) Moreover, the lack of simple annealing mechanisms and the resulting formation of crystals with many small domains make a determination of the 3D crystal structure more difficult with diffraction experiments. (30,31)

Here, the recent development of using soft particles as model systems (32−34) provides us with tools that can overcome several of these hurdles. Their weak repulsions temporarily allow particle overlap, allowing particles to overcome local energy minima and promoting crystal growth speed compared to hard spheres. (28,35) Crystallization involving soft particles has been shown to possess a larger tolerance for polydispersity, (36) and many soft particle types have inherently tunable interaction potentials, (37,38) some as a function of externally controllable parameters such as temperature. (39) Furthermore, many soft systems can be extensively modified to tailor particle behavior or simplify analysis. (40−43) For example, modifying particles with fluorescent labels allows for direct imaging using confocal scanning laser microscopy, which provides sufficient information to determine phase behavior and specific organizations and to quantify kinetics. (44,45)

In this article, we describe several crystalline phases and a crystal-to-crystal transition. We employ oppositely charged microgel particles synthesized via a synthesis method that emphasizes discernibility between particles in confocal scanning laser microscopy (CLSM). The softness of the particles allows for crystallization at very high concentrations, (3) and the thermoresponsiveness of the particles allows for additional annealing mechanisms. (46) Furthermore, these systems allow for precise fine-tuning of volume fraction and size ratio. In the absence of electrostatic interactions, i.e., at sufficiently high salt concentrations, the particles interact via soft repulsive forces. (47,48) We employ a sample geometry that allows in situ salinity control during CLSM imaging, and thus a tuning of the electrostatic contributions to the interaction potential. By applying this geometry we can easily control and analyze the phase behavior of these systems as a function of electrostatic attraction strength. Our work experimentally demonstrates the existence of multiple binary soft crystal phases and how the transition between them can be controlled using in situ control over the electrostatic interactions.

Results and Discussion

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We synthesized core–shell particles with a small fluorescent core and several undyed cross-linked shells. By growing multiple shells, we achieve a thick shell with controllable size that allows good discernibility between individual particles in CLSM, while retaining the corona density distribution similar to a traditional microgel. (48) Particle characteristics can be found in Table 1, with negatively charged pNIPAm particles abbreviated by pN and positively charged pNIPMAm particles by pM.

Table 1. Particles Used in Experiments, with Their Polymer, Dye Type, Colors, Charge Signs, and Hydrodynamic Diameters σ_H at 20 °C for Final Core–Shell Particles and for Cores Only

polymer	abbreviation	dye	color	charge	σ_H(particle) [nm]	σ_H(core) [nm]
pNIPAm	pN	PM546	green	negative	280	73
pNIPMAm	pM	PM605	red	positive	336	103

Samples were prepared with partial number densities of ρ_pN = ρ_pM = 4 × 10¹⁸m^–3 and were inserted in a sample cell as in Figure 1, designed to allow controlled in situ variation of the ionic strength during microscopical imaging. Details on design and manufacture can be found in the Materials and Methods section. The reservoir was filled with a KCl solution and left to equilibrate for at least 24 h, kept at a constant temperature of 20 °C.

Figure 1. Cross-section of the sample holder design, not to scale.

In Figure 2A–D, we show CLSM images and their 3D radial distribution functions (RDFs) for four different salinities. The calculated RDFs are split into three components, pN-to-pN, pM-to-pM, and pN-to-pM (equal to pM-to-pN). At relatively high salt concentrations (2.0 × 10^–3 M and up, Figure 2A), charges on the particles are sufficiently screened and the system crystallizes into a hexagonal lattice due to entropic forces. The three corresponding RDFs overlap, confirming a random distribution of pN and pM particles in the lattice. It is important to note that this crystal forms despite the size ratio of 0.83 between pN and pM, highlighting the permissiveness of crystallization in soft colloids when it comes to polydispersity (36) as compared to that in hard spheres. (49) Interestingly, the first peak of all RDFs of the high-salt crystal, and thus its lattice spacing, appears at approximately σ_H(pN), the hydrodynamic diameter of the smaller particle. This implies that for soft binary crystals the smaller particles govern the lattice spacing, especially when considering that the total volume fraction is significantly above the volume fraction of a hexagonal packing of spheres: based on hydrodynamic radii and number densities, the total volume fraction is ∼1.0. This confirms earlier findings, where it has been shown that dopant-quantity microgels with large radii can adopt highly compressed conformations to fit into a crystal with a much smaller lattice spacing. (36)

Figure 2. Analysis of one sample at different salinities. (A–D) CLSM images with their corresponding radial distribution functions (RDFs) of pN-to-pN, pM-to-pM, and pN-to-pM. (A) 2 × 10^–3 M KCl, showing entropy-driven crystallinity. (B) 1.5 × 10^–3 M KCl, in a fluid phase. (C) 1.25 × 10^–3 M KCl, showing electrostatic forces-driven crystallinity. (D) Sample at 1 × 10^–3 M KCl, in an electrostatically aggregated gel. (E) Mean-square displacements (MSDs) of pN particles for all salinities, together with a line with a slope proportional to t¹ to guide the eye. The MSDs for pM are highly similar to the MSDs of pN. (F) Corresponding P(Z_eq) for all salinities. Dashed lines indicate the theoretical values corresponding to AuCu (0.33) and FCC (0.5) crystal values. Each scale bar length is 10 μm.

A decrease in salinity leads to behavior increasingly dominated by electrostatic interactions, ultimately yielding aggregation and phase separation. Reducing salinity to 1.5 × 10^–3 M KCl leads to melting of the entropic crystal (Figure 2B), caused by weak electrostatic forces driving oppositely charged particles to interpenetrate, opening free space resulting in fluid behavior. It is interesting to note here that, while colloidal attractions have been shown to lead to re-entrant melting behavior, (50) the particles’ soft repulsive potential and resulting interpenetration will cause such behavior to be enhanced, as compared to incompressible hard sphere systems. Further removal of salt to 1.25 × 10^–3 M KCl allows electrostatic forces to overtake entropic contributions and causes the system to recrystallize with a specific pN–pM ordering (Figure 2C). An even further removal of salt induces an additional increase of electrostatic attraction and yields aggregated systems (1.0 × 10^–3 M KCl, Figure 2D). The pN-to-pM RDF reflects the increasing electrostatic attractions, with its initial peak appearing at decreasing separations r, reflecting the larger particle interpenetration that occurs upon increasing the electrostatic attraction strength.

Mean square displacements (MSDs) for pN particles at different salinities are shown in Figure 2E and follow the trends as described above. MSDs for pM are highly similar to those of pN and are therefore left out for clarity. At high salinities, particles are strongly caged, with apparent particle motion below the noise threshold for this analysis method; removal of salt to 1.5 × 10^–3 M KCl causes cage breaking and fluid-like behavior. The slightly subdiffusive behavior is due to the high density and electrostatic attractions. At 1.25 × 10^–3 M KCl, particles are once again caged, but in larger cages than at high salinities due to pN–pM interpenetration. Further removal of salt to 1.0 × 10^–3 M KCl causes irreversible aggregation, where displacement is caused by cluster diffusion.

We define Z_eq as the total number of nearest neighbors of equal type divided by the total number of nearest neighbors, with P(Z_eq) its probability distribution, plotted in Figure 2F. At high salinity, P(Z_eq) is symmetric around 0.5, once again reflecting the random distribution of pN and pM particles. The weak attractions at 1.5 × 10^–3 M KCl cause a preference for Z_eq < 0.5. The electrostatic crystal structure at 1.25 × 10^–3 M KCl, as will be discussed later, has four neighbors of equal type and eight neighbors of unequal type, reflected in the P(Z_eq) peak at Z_eq = 0.33. A further removal of salt and subsequent aggregation leads to a partial loss of preference for unequal particle types, caused by the amorphous nature of the aggregates.

Finally, we note that this behavior is fully reversible: bringing a sample from 2.0 × 10^–3 M KCl to 1.0 × 10^–3 M KCl and back to 2.0 × 10^–3 M KCl causes an entropic crystal to melt, electrostatically aggregate, and re-form into entropic crystals via all described phases at intermediate salinities. Since the return to entropic crystals involves a transition via a fluid phase, remixing occurs while raising salinity, and a random distribution is obtained upon reaching 2.0 × 10^–3 M KCl.

The system is thus capable of forming two different crystal structures (Figure 2A and C), and a change of salinity can reversibly induce a switch between these crystal phases. For the high-salt crystal at 2 × 10^–3 M (shown in Figures 2A and 3A), a comparison with a theoretical FCC RDF confirms the FCC structure of the crystal, as seen in Figure 3B. In contrast to the high-salt crystal, the particles in the low-salt crystal (shown in Figures 2C and 3C) are no longer randomly distributed throughout the lattice, but preferentially interact with the oppositely charged particles. Accordingly, the different RDFs seen in Figures 3D–F, no longer overlap. These RDFs correspond well with the theoretically predicted AuCu crystal structure, with poor agreement with other AB-type binary crystal structures. A comparison between theoretical RDFs of several AB-type crystals and the experimental RDFs can be found in the Supporting Information. Note that the first peak height for the pN-to-pM RDF is significantly higher than its two equal counterparts, reflecting the strength of the electrostatic interactions that drive AuCu crystallization, overtaking entropic forces that drive FCC crystallization. In Figure 4, unit cells of FCC-type and AuCu-type crystal structures are depicted, made using the visualization software OVITO. (51) The AuCu lattice parameters are identical to FCC lattices (given identical particle sizes), but particle type distributions differ. Our observation of AuCu crystallinity corresponds with theoretical predictions for binary systems of weakly attracting, soft particles with size ratios between approximately 0.75 and 0.85. (52)

Figure 3. CLSM images of the same sample at different salinities, with their corresponding radial distribution functions (RDFs). (A) CLSM image at 2 × 10^–3 M KCl. (B) Corresponding RDFs of pN-to-pN, pM-to-pM, and pN-to-pM. The overlapping RDFs illustrate the random distribution of particles throughout the lattice. The RDF peaks are in accordance with the positions and relative magnitudes of those in an FCC lattice (blue, rescaled magnitudes by arbitrary factor for visibility). (C) CLSM image at 1.25 × 10^–3 M KCl. (D–F) Corresponding RDF at 1.25 × 10^–3 M KCl of (D) pN-to-pN, (E) pM-to-pM, and (F) pN-to-pM. Each RDF is shown with the corresponding peaks for AuCu-type crystals. The scale bar length is 10 μm.

Figure 4. Unit cells of (A) a single particle type FCC and (B) a AuCu crystal. The red particles represent the larger Au atoms.

A common method of determining the crystal phase that a particle belongs to is by calculating local bond order parameters q_l. (44,53) This method analyzes the local surrounding of a particle and quantifies its symmetry, with q_l being a measure of the local l-fold symmetrical order around a given particle. It is obtained by (54,55)

(1)

where Z(i) is the number of nearest neighbors of particle i, l and m are integer indices, with l ≥ 0 and m = −l, −l + 1, ..., l – 1, l, Y_lm(r_ij) are the spherical harmonics, and r_ij is a vector pointing from particle i to particle j. q_lm(i) is transformed into q_l through

(2)

The FCC and AuCu lattice parameters are nearly identical, and the unit cells differ mostly by distribution of particle type; we therefore extend the analysis method by discerning three bond order parameters per particle: q_l(all), q_l(equal), and q_l(unequal), which are the q_l calculated considering respectively all particles, only equal-type particles, and only unequal-type particles in the local surrounding. The obtained experimental values were further refined by calculating the average bond order parameter q̅_l, (55) given by

(3)

followed by the transformation in eq 2. This step suppresses individual FCC particles that randomly have surroundings similar to AuCu-type crystallinity to be designated as a particle in an AuCu phase. Order parameters for perfect FCC and AuCu crystals with identical lattice parameters are given in Table 2.

Table 2. Theoretical 3D Local Bond Order Parameters for FCC and AuCu Crystals^a

crystal	q₄	q₆	q₈
FCC	0.19	0.57	0.40
AuCu (all)	0.19	0.57	0.40
AuCu (equal)	0.82	0.59	0.79
AuCu (unequal)	0.44	0.57	0.53

^{^a}

q_l for AuCu is split into q_l(all), q_l(equal), and q_l(unequal).

We calculate q̅_l for particles in 3D CLSM volumes and visualize this by coloring the corresponding Voronoi cells. Average q̅_l and standard deviations of FCC and AuCu crystals can be found in the Supporting Information. Slices from this 3D volume are shown in Figure 5, with Figure 5A,B corresponding to 2.0 × 10^–3 M KCl and Figure 5C,D corresponding to 1.25 × 10^–3 M KCl. While it is clear that this method works well for discerning between crystal phases, it is still sensitive to local ordering and defects. The quality of the bond order analysis benefits from the statistics provided by 3D CLSM data, and 2D microscopy imaging is not sensitive enough to discern between these two crystal structures. One point of interest is the fact that AuCu cells in the FCC lattice (Figure 5B) are generally isolated or only a few cells, while FCC cells in the AuCu lattice (Figure 5D) tend to be connected to other FCC cells. We attribute this to the fact that a single-particle defect in a AuCu lattice affects the local ordering for all surrounding particles, whereas several particles need to cooperate to provide the local organized surrounding of one particle in our FCC lattice. Here, one should consider that varying the ionic strength also changes the free energy landscape, as the interaction potentials change from soft repulsive to attractive, which should also influence the distribution and lifetime of defects.

Figure 5. CLSM image slices from a 3D stack, compared with Voronoi cells colored according to their q̅_l. (A, B) FCC crystal at 2.0 × 10^–3 M KCl. (C, D) AuCu crystal at 1.25 × 10^–3 M KCl. If q̅₄(equal) > 0.45 or q̅₈(equal) > 0.45, AuCu crystallinity is denoted by a blue cell; if q̅₆(all) > 0.35, but q̅₄(equal) < 0.45 and q̅₈(equal) < 0.45, FCC crystallinity is denoted by a red cell; and if q̅₆(all) < 0.35 and q̅₄(equal) < 0.45 or q̅₈(equal) < 0.45, the cell was left white, denoting an amorphous local surrounding.

Conclusions

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In this work, we have demonstrated the feasibility of binary mixtures of soft colloids for forming multiple crystal phases, including a crystal-to-crystal transition. Combining soft particles with opposite charges yields a pathway to a sequence of structural transitions that can be controlled externally via the ionic strength of the system through a re-entrant crystal transition, i.e., from an entropic crystal, via an intermediate fluid regime, to an electrostatic attraction-driven crystal, and into an amorphous aggregated gel state at even stronger mutual attraction. Control over ionic strength is facilitated by the sample cell design, allowing for in situ access to the effective interaction potential. Particles used in this study were synthesized according to a method that enhances discernibility in CLSM compared to other synthesis procedures, while allowing control over particle size during synthesis. We benefit from the softness of these particles, as they are less prone to becoming trapped in nonequilibrium arrested states at high densities and because of their enhanced nucleation and crystal growth that facilitate in situ studies of liquid–solid and solid–solid transitions. In addition to that, the softness and interpenetrability of the particles alter the re-entrant melting behavior as compared to hard sphere systems. Finally, we have analyzed our results using local bond order parameters adapted for discerning between systems with strong crystal similarity.

It is important to note that the use of these types of binary mixtures allows for an extra dimension of tunability: heating these mixtures has the effect that pN particles decrease in size, whereas pM particles are only slightly affected. (56) By thus manipulating the size ratio, even more crystal phases are expected, and our system provides exceptional control over both temperature and salinity. Thus, the systems introduced here are a good candidate for observing multiple in situ crystal-to-crystal transitions and, therefore, help to bring about a deeper understanding of the kinetics and mechanisms of such transitions.

Materials and Methods

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Chemicals

The monomers used were styrene (99%, contains 4-tert-butylcatechol as polymerization inhibitor, Sigma-Aldrich), N-isopropylacrylamide (97%, NIPAm, Sigma-Aldrich), and N-isopropylmethacrylamide (97%, NIPMAm, Sigma-Aldrich). The inhibitor was removed with active basic Al₂O₃ (for chromatography, VWR Chemicals). Surfactants used were sodium dodecyl sulfate (99%, SDS, Duchefa) and cetyltrimethylammonium bromide (99%, CTAB, Sigma-Aldrich). Dyes used were pyrromethene 546 (PM546, Exciton) and pyrromethene 605 (PM605, Exciton). Initiators used were potassium persulfate (99%, KPS, Sigma-Aldrich) and 2,2-azobis(2-methylpropionamidine) dihydrochloride (97%, V50, Sigma-Aldrich). Cross-linker was N,N′-methylene-bis-acrylamide (99%, BIS, Sigma-Aldrich).

Synthesis

A core–multishell particle synthesis method was developed combining elements from previous work, (48,57,58) yielding a small fluorescent core and an undyed soft shell, with a corona similar to traditional microgels. (48)

pNIPAm-interlaced polystyrene cores (PS-pN) were synthesized by purging 100 mL of Millipore-quality water (MQ-H₂O) with N₂ gas for 30 min at room temperature in a round-bottom flask. 27 mL of styrene was run over an Al₂O₃ column to remove polymerization inhibitor and was added to the round-bottom flask together with 3 g of NIPAm, 200 mg of SDS, and 22 mg of pyrromethene 546. The mixture was stirred and purged for 45 min with N₂ at 75 °C, while the mixture was shielded from ambient light. 50 mg of KPS was dissolved in 2 mL of MQ-H₂O, degassed, and added instantaneously to the reaction mixture. The mixture was left stirring for 24 h, filtered through glass wool, and purified through dialysis against MQ-H₂O over the course of 2 weeks. Concentration was performed by centrifugation at 10⁴g and removal of supernatant. pNIPMAm-interlaced polystyrene (PS-pM) cores were synthesized identically but replacing NIPAm with 3 g of NIPMAm, SDS with 100 mg of CTAB, pyrrhomethene 546 with 22 mg of pyrrhomethene 605, and KPS with 50 mg of V50. Dialysis of PS-pM particles was performed against 0.01 M CTAB.

The pNIPAm shells were formed by purging 360 mL of MQ-H₂O with N₂ gas while stirring for 30 min at room temperature in a round-bottom flask. 2.0 g of NIPAm and 138.8 mg of BIS (5 mol %) were added to the flask, and 3.56 g of 15.9 wt % suspended PS-pN was added to the mixture. The mixture was stirred and purged for 45 min with N₂ while stirring at 75 °C, while the mixture was shielded from ambient light. 74.0 mg of KPS was dissolved in 4 mL of MQ-H₂O and added dropwise to the solution over the course of 5 min. After an additional 5 min, a solution of 69.4 mg of BIS (2.5 mol %) in 20 mL of MQ-H₂O was added dropwise to the mixture over the course of 30 min. After 4 h, the sample was filtered through glass wool and purified. Consecutive shell growths were performed by preparing a degassed reaction mixture with all previously grown core–shell particles suspended in a volume of 80% of the previous reaction volume and addition of 80% of the previously added NIPAm, primary BIS addition (5 mol %), secondary BIS addition (2.5 mol %), and KPS, following identical steps. This is required to compensate for reaction yield and to prevent secondary nucleation. The final shell required no secondary BIS addition, only the addition of 5 mol % BIS. pNIPMAm shells were grown following an identical procedure, but on pS-pM particles with 3.0 g of NIPMAm instead of NIPAm, 123.3 mg of BIS (5 mol %), and 61.7 mg (5 mol %) and 74.0 mg of V50 instead of KPS. Hydrodynamic diameters were determined from dynamic light scattering using a modulated 3D cross-correlation instrument (LS Instruments) with a 660 nm diode-pumped laser.

Sample Preparation

Number densities of stock solutions were obtained through preparing single crystals at appropriate volume fractions, imaging a volume in CLSM, followed by particle counting. Binary microgel dispersions were prepared and mixed at 20 °C and 10^–3 M KCl.

Sample holders were prepared as in Figure 1, similar to the ones described by Sato etal. (59) A rigid, composite material (FR-4, glass-reinforced epoxy laminate) slide of dimensions 25 × 75 × 1 mm was centrally perforated with a long, thin hole of 25 × 1 mm. The hole was covered with a dialysis membrane on one side. A capillary was created covering the dialysis membrane by placing two coverslips (5 × 50 × 0.1 mm) parallel on either side of the hole and topped with a third coverslip (25 × 50 × 0.1 mm). The coverslips were glued in place with an air- and water-resistant UV glue (Thorlabs UV glue 83). The opposite side of the composite slide was fitted with a solution reservoir of a volume at least 100 times the capillary volume, with inlet and outlet tubes, and was made air and water tight using hydrophobic, malleable wax. The capillary was rinsed with MQ-H₂O and excess water removed before the sample was inserted. It was then sealed with UV glue, and the reservoir was filled. Measurements can be performed with a constant flow continuously refreshing the solution in the reservoir or equilibrated at a given salinity: in this work, the latter method is used, with a minimum equilibration time of 12 h. Reversibility was tested by slowly cycling samples between low and high salinities at least three times, while checking the appearance of all states shown in Figure 2; this was successful for at least three cycles in three separately prepared samples. All samples were placed in a 0.02% (w/v) NaN₃ solution for 24 h per week to prevent bacterial growth.

Imaging

Samples were mounted on an inverted CLSM (Leica TCS SP5 tandem scanner) and imaged using a 100×/1.4 NA oil immersion objective. The microscope was mounted in an enclosure that allows for temperature control with a 0.2 °C maximum variance using thermostated air circulation. Using standardized image analysis and particle tracking routines, (60) particle center coordinates were obtained for mean square displacements, radial distribution functions, and nearest-neighbor analyses. The uncertainty in these coordinates is approximately 14 nm, obtained by determining particle centers of immobilized polystyrene particles over time. (61) The particle geometry, with its small fluorescent core and large undyed shell, facilitates the enhanced particle center determination. Particle coordinates were determined using methods described in earlier work (62) for at least 10 z-stacks per different salinity.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsnano.0c03966.

Experimental RDFs compared to theoretical AuCu RDF; experimental RDFs compared to theoretical CsCl RDF; experimental RDFs compared to theoretical NaCl RDF; obtained bond order parameters for all particles at 2.0 × 10^–3 M KCl; obtained bond order parameters for all particles at 1.25 × 10^–3 M KCl (PDF)

nn0c03966_si_001.pdf (1.54 MB)

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Author Information

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Corresponding Author
- Jasper N. Immink - Division of Physical Chemistry, Lund University, 221 00 Lund, Sweden; http://orcid.org/0000-0003-1251-5442; Email: [email protected]
Authors
- Maxime J. Bergman - Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland
- J. J. Erik Maris - Inorganic Chemistry and Catalysis Group, Utrecht University, 3584 CS Utrecht, The Netherlands; http://orcid.org/0000-0003-2591-4864
- Joakim Stenhammar - Division of Physical Chemistry, Lund University, 221 00 Lund, Sweden; http://orcid.org/0000-0002-7543-5549
- Peter Schurtenberger - Division of Physical Chemistry, Lund University, 221 00 Lund, Sweden; Lund Institute of advanced Neutron and X-ray Science (LINXS), Lund University, 221 00 Lund, Sweden; http://orcid.org/0000-0002-2790-8831
Notes
The authors declare no competing financial interest.

Acknowledgments

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We gratefully acknowledge financial support from the European Research Council (ERC-339678-COMPASS) and the Swedish Research Council (2015-05449 and 2018-04627).

References

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Rheol. properties and the equil. colloidal phase behavior of concd. dispersions of a temp. sensitive microgel were investigated. The temp. sensitive hydrogel particles consist of poly (N-isopropylacrylamide) (PNiPAM) chem. crosslinked with N,N' methylenebisacrylamide (BIS). With increasing temp. the microgel particles decrease in size (hydrodynamic radius 142 nm at 10 °C and 58 nm at 35 °C) and with it the effective vol. fraction, which leads to dramatic changes in rheol.-vanishing yield stress and decreasing viscosity and elastic properties. The relative zero-shear viscosity and the plateau modulus at different temps. superpose to mastercurves when plotted vs. the effective vol. fraction. The monodisperse hydrogel particles form colloidal crystals and glasses in concd. soln. but at higher effective vol. fractions as compared to model hard sphere suspensions. Comparison of the exptl. f.p. with soft sphere computer simulations indicate a repulsive interaction potential of the order 1/r12. The frequency independent shear modulus exhibited a power law concn. dependence which also agrees with the soft sphere behavior.
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Aastuen, D. J. W.; Clark, N. A.; Cotter, L. K.; Ackerson, B. J. Nucleation and Growth of Colloidal Crystals. Phys. Rev. Lett. 1986, 57, 1733, DOI: 10.1103/PhysRevLett.57.1733
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Nucleation and growth of colloidal crystals
Aastuen, D. J. W.; Clark, N. A.; Cotter, L. K.; Ackerson, Bruce J.
Physical Review Letters (1986), 57 (14), 1733-6CODEN: PRLTAO; ISSN:0031-9007.
Some bcc. cryst. colloidal microsphere suspensions were shear-melted into the metastable liq. phase. Recrystn. occurs via nucleation and growth of single crystallites at dil. sites. The nearly spherical growing crystals have rough interfaces with a time-independent interface velocity, v. The velocity is consistent with an equation for normal growth with a limiting velocity det. by free-particle diffusion, n0 ∼ D0/ξ, where D0 is the Stokes diffusion const. of independent noninteracting spheres, and ξ is a length comparable to the particle spacing.
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Gasser, U.; Weeks, E. R.; Schofield, A.; Pusey, P. N.; Weitz, D. A. Real-Space Imaging of Nucleation and Growth in Colloidal Crystallization. Science 2001, 292, 258– 262, DOI: 10.1126/science.1058457
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Real-space imaging of nucleation and growth in colloidal crystallization
Gasser, U.; Weeks, Eric R.; Schofield, Andrew; Pusey, P. N.; Weitz, D. A.
Science (Washington, DC, United States) (2001), 292 (5515), 258-262CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
Crystn. of concd. colloidal suspensions was studied in real space with laser scanning confocal microscopy. Direct imaging in three dimensions allowed identification and observation of both nucleation and growth of cryst. regions, providing an exptl. measure of properties of the nucleating crystallites. By following their evolution, the authors identified crit. nuclei, detd. nucleation rates, and measured the av. surface tension of the crystal-liq. interface. The structure of the nuclei was the same as the bulk solid phase, random hcp., and their av. shape was rather nonspherical, with rough rather than faceted surfaces.
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Auer, S.; Frenkel, D. Numerical Prediction of Absolute Crystallization Rates in Hard-Sphere Colloids. J. Chem. Phys. 2004, 120, 3015, DOI: 10.1063/1.1638740
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Numerical prediction of absolute crystallization rates in hard-sphere colloids
Auer, S.; Frenkel, D.
Journal of Chemical Physics (2004), 120 (6), 3015-3029CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
Special computational techniques are required to compute abs. crystal nucleation rates of colloidal suspensions. Using crystal nucleation of hard-sphere colloids as an example, we describe in some detail the novel computational tools that are needed to perform such calcns. In particular, we focus on the definition of appropriate order parameters that distinguish liq. from crystal, and on techniques to compute the kinetic prefactor that enters in the expression for the nucleation rate. In addn., we discuss the relation between simulation results and theor. predictions based on classical nucleation theory.
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Sandomirski, K.; Allahyarov, E.; Lowen, H.; Egelhaaf, S. U. Heterogeneous Crystallization of Hard-Sphere Colloids near a Wall. Soft Matter 2011, 7, 8050– 8055, DOI: 10.1039/c1sm05346a
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Heterogeneous crystallization of hard-sphere colloids near a wall
Sandomirski, Kirill; Allahyarov, Elshad; Loewen, Hartmut; Egelhaaf, Stefan U.
Soft Matter (2011), 7 (18), 8050-8055CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
We investigate the most basic situation of heterogeneous crystn.: crystn. of hard-sphere colloids in the presence of a flat hard wall. Using a combination of confocal microscopy and nonequil. Brownian dynamics simulations, microscopic time-resolved information is obtained on an individual-particle level. Initially, particles near the wall rearrange before an extended regime of crystal growth is found. During growth, we can directly observe a depletion zone in the fluid next to the progressing crystal-fluid interface due to the single-particle information provided by microscopy and simulations. This also allows us to follow the relaxation of the crystal layers and the progression of the crystal-fluid interface. In good agreement between our expts. and simulations, as well as previous studies, the growth rate shows a max. in its dependence on the bulk vol. fraction.
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Montanarella, F.; Geuchies, J. J.; Dasgupta, T.; Prins, P. T.; van Overbeek, C.; Dattani, R.; Baesjou, P.; Dijkstra, M.; Petukhov, A. V.; van Blaaderen, A.; Vanmaekelbergh, D. Crystallization of Nanocrystals in Spherical Confinement Probed by in Situ X-ray Scattering. Nano Lett. 2018, 18, 3675– 3681, DOI: 10.1021/acs.nanolett.8b00809
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Crystallization of Nanocrystals in Spherical Confinement Probed by in Situ X-ray Scattering
Montanarella, Federico; Geuchies, Jaco J.; Dasgupta, Tonnishtha; Prins, P. Tim; van Overbeek, Carlo; Dattani, Rajeev; Baesjou, Patrick; Dijkstra, Marjolein; Petukhov, Andrei V.; van Blaaderen, Alfons; Vanmaekelbergh, Daniel
Nano Letters (2018), 18 (6), 3675-3681CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
The formation of supraparticles from nanocrystals confined in slowly evapg. oil droplets in an oil-in-H2O emulsion was studied. The nanocrystals consist of an FeO core, a CoFe2O4 shell, and oleate capping ligands, with an overall diam. of 12.5 nm. In situ small- and wide-angle x-ray scattering expts. were performed during the entire period of solvent evapn. and colloidal crystn. A slow increase in the vol. fraction of nanocrystals inside the oil droplets up to 20%, at which a sudden crystn. occurs was obsd. The computer simulations show that crystn. at such a low vol. fraction is only possible if attractive interactions between colloidal nanocrystals are taken into account in the model as well. The spherical supraparticles have a diam. of ∼700 nm and consist of a few cryst. fcc. domains. Nanocrystal supraparticles bear importance for magnetic and optoelectronic applications, such as color tunable biolabels, color tunable phosphors in LEDs, and miniaturized lasers.
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Anderson, V. J.; Lekkerkerker, H. N. W. Insights into Phase Transition Kinetics from Colloid Science. Nature 2002, 416, 811– 815, DOI: 10.1038/416811a
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Insights into phase transition kinetics from colloid science
Anderson, V. J.; Lekkerkerker, H. N. W.
Nature (London, United Kingdom) (2002), 416 (6883), 811-815CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
A review. Colloids display intriguing transitions between gas, liq., solid, and liq. cryst. phases. Such phase transitions are ubiquitous in nature and were studied for decades. However, the predictions of phase diagrams are not always realized; systems often become undercooled, supersatd., or trapped in gel-like states. In many cases the end products strongly depend on the starting position in the phase diagram and discrepancies between predictions and actual observations are due to the intricacies of the dynamics of phase transitions. Colloid science aims to understand the underlying mechanisms of these transitions. Important advances were made, for example, with new imaging techniques that allow direct observation of individual colloidal particles undergoing phase transitions, revealing some of the secrets of the complex pathways involved.
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Yethiraj, A.; van Blaaderen, A. A Colloidal Model System with an Interaction Tunable from Hard Sphere to Soft and Dipolar. Nature 2003, 421, 513– 517, DOI: 10.1038/nature01328
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A colloidal model system with an interaction tunable from hard sphere to soft and dipolar
Yethiraj, Anand; van Blaaderen, Alfons
Nature (London, United Kingdom) (2003), 421 (6922), 513-517CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
Monodisperse colloidal suspensions of micrometre-sized spheres are playing an increasingly important role as model systems to study, in real space, a variety of phenomena in condensed matter physics-such as glass transitions and crystal nucleation. But to date, no quant. real-space studies have been performed on crystal melting, or have investigated systems with long-range repulsive potentials. Here we demonstrate a charge- and sterically stabilized colloidal suspension-poly(Me methacrylate) spheres in a mixt. of cycloheptyl (or cyclohexyl) bromide and decalin-where both the repulsive range and the anisotropy of the interparticle interaction potential can be controlled. This combination of two independent tuning parameters gives rise to a rich phase behavior, with several unusual colloidal (liq.) cryst. phases, which we explore in real space by confocal microscopy. The softness of the interaction is tuned in this colloidal suspension by varying the solvent salt concn.; the anisotropic (dipolar) contribution to the interaction potential can be independently controlled with an external elec. field ranging from a small perturbation to the point where it completely dets. the phase behavior. We also demonstrate that the elec. field can be used as a pseudo-thermodn. temp. switch to enable real-space studies of melting transitions. We expect studies of this colloidal model system to contribute to our understanding of, for example, electro- and magneto-rheol. fluids.
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Bartlett, P.; Campbell, A. I. Three-Dimensional Binary Superlattices of Oppositely Charged Colloids. Phys. Rev. Lett. 2005, 95, 128302, DOI: 10.1103/PhysRevLett.95.128302
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Three-Dimensional Binary Superlattices of Oppositely Charged Colloids
Bartlett, Paul; Campbell, Andrew I.
Physical Review Letters (2005), 95 (12), 128302/1-128302/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
The authors report the equil. self-assembly of binary crystals of oppositely charged colloidal microspheres at high d. By varying the magnitude of the charge on near equal-sized spheres the structure of the binary crystal may be switched between fcc., CsCl, and NaCl. The authors interpret these transformations in terms of a competition between entropic and Coulombic forces.
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Pusey, P. N.; van Megen, W. Phase Behaviour of Concentrated Suspensions of Nearly Hard Colloidal Spheres. Nature 1986, 320, 340– 342, DOI: 10.1038/320340a0
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Phase behavior of concentrated suspensions of nearly hard colloidal spheres
Pusey, P. N.; Van Megen, W.
Nature (London, United Kingdom) (1986), 320 (6060), 340-2CODEN: NATUAS; ISSN:0028-0836.
The phase diagram of suspensions of colloidal spheres which interact through a steep repulsive potential is studied for colloidal PMMA [9011-14-7] particles, stabilized by poly(12-hydroxystearic acid), in decalin-CS2. With increasing particle concn., the colloidal fluid is transformed to fluid and crystal phases in coexistence, to fully crystd. samples. At the highest concns., very viscous samples are obtained in which full crystn. had not occurred after several months and in which the particles are arranged as an amorphous colloidal glass. The empirical phase diagram can be reproduced reasonably well by an effective hard-sphere model.
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Mewis, J.; Frith, W. J.; Strivens, T. A.; Russel, W. B. The Rheology of Suspensions Containing Polymerically Stabilized Particles. AIChE J. 1989, 35, 415– 422, DOI: 10.1002/aic.690350309
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The rheology of suspensions containing polymerically stabilized particles
Mewis, Jan; Frith, William J.; Strivens, Trevor A.; Russel, William B.
AIChE Journal (1989), 35 (3), 415-22CODEN: AICEAC; ISSN:0001-1541.
The non-Newtonian viscosities of grafted poly(12-hydroxystearic acid)-stabilized PMMA colloidal suspensions are usually predicted and correlated on the basis of data and scaling principles for Brownian hard spheres. Here, the specific effect of the stabilizer layer is investigated using suspensions of monodisperse PMMA particles with a chem. attached stabilizer layer. The ratio between particle radius and stabilizer layer thickness is 5-61. At high values of this ratio the data show Brownian hard sphere behavior. At lower values deviations appear. As a first approxn., the softness of the particles can be characterized through the concn. at max. packing. A more detailed comparison with hard sphere data provides a measure for softness that changes with concn. and shear rate. A theor. est. of the concn. effect is in line with the expts. The crit. shear stress (or Peclet no.) is not a const. but goes through a max. when the concn. is increased.
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Chu, J. H.; I, L. Direct Observation of Coulomb Crystals and Liquids in Strongly Coupled rf Dusty Plasmas. Phys. Rev. Lett. 1994, 72, 4009– 4012, DOI: 10.1103/PhysRevLett.72.4009
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Direct observation of Coulomb crystals and liquids in strongly coupled rf dusty plasmas
Chu, J. H.; I, Lin
Physical Review Letters (1994), 72 (25), 4009-12CODEN: PRLTAO; ISSN:0031-9007.
The strongly coupled dusty plasmas are formed by suspending neg. charged SiO2 fine particles with 10 μm diam. in weakly ionized rf Ar discharges. The Coulomb crystals and liqs. are directly obsd. for the first time using an optical microscope. By properly controlling the system parameters, hexagonal, fcc., and bcc. crystal structures and solids with coexisting different structures can be formed. Increasing the rf power causes the transition to the more disordered liq. state.
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Levitz, P.; Lecolier, E.; Mourchid, A.; Delville, A.; Lyonnard, S. Liquid-Solid Transition of Laponite Suspensions at Very Low Ionic Strength: Long-Range Electrostatic Stabilisation of Anisotropic Colloids. Europhys. Lett. 2000, 49, 672– 677, DOI: 10.1209/epl/i2000-00203-9
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Liquid-solid transition of laponite suspensions at very low ionic strength: long-range electrostatic stabilization of anisotropic colloids
Levitz, P.; Lecolier, E.; Mourchid, A.; Delville, A.; Lyonnard, S.
Europhysics Letters (2000), 49 (5), 672-677CODEN: EULEEJ; ISSN:0295-5075. (EDP Sciences)
The authors study suspensions of synthetic clay laponite at very low ionic strength. The authors show the existence, for these charged disk-like particles, of a liq.-soft solid transition mainly driven by electrostatic repulsive interactions. Such a process defines a reentrant transition line in the phase diagram. Location of this line is predicted using basic arguments. The structure is characterized by ultra-small-angle x-ray scattering (USAXS). Soft-solid suspensions show a correlation peak compatible with long-range electrostatic stabilization. Such a result strongly contrasts with the evolution of the scattering spectra for solid-like suspensions of laponite at high ionic strength (above 10-4 M). Close inspection of this correlation peak reveals that individual particle distribution is not homogeneous in space.
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Shah, S. A.; Chen, Y.-L.; Schweizer, K. S.; Zukoski, C. F. Viscoelasticity and Rheology of Depletion Flocculated Gels and Fluids. J. Chem. Phys. 2003, 119, 8747– 8760, DOI: 10.1063/1.1598192
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Viscoelasticity and rheology of depletion flocculated gels and fluids
Shah, S. A.; Chen, Y.-L.; Schweizer, K. S.; Zukoski, C. F.
Journal of Chemical Physics (2003), 119 (16), 8747-8760CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
The flow properties of high vol. fraction hard sphere colloid-polymer suspensions are studied as a function of polymer concn., depletion attraction range, and solvent quality up to, and well beyond, the gelation boundary. As the gel boundary is approached, the shear viscosity tends to diverge in a crit. power law manner at a polymer concn. that is a function of the polymer radius of gyration and solvency condition. The shear viscosity for different polymer size suspensions can be collapsed onto a master curve motivated by mode coupling theory (MCT). The low frequency elastic modulus grows rapidly with increasing depletion attraction near the gel boundary, but becomes a dramatically weaker function of polymer concn. as the gel state is more deeply entered. A simplified version of MCT with accurate, no adjustable parameter polymer ref. interaction site model (PRISM) theory structural input has been applied to predict the gelation boundaries and elastic shear moduli. The calcd. gel lines are in semiquant. agreement with expt. at high vol. fractions, but increasingly deviate upon particle diln. Calcns. of the dependence of the gel elastic shear moduli on particle-polymer size asymmetry and scaled polymer concn. are in excellent agreement with expt., and deep in the gel follow a power law dependence on polymer concn. Quant., MCT-PRISM elastic moduli are higher than expt. by a nearly const. large factor. This discrepancy is suggested to be due to the heterogeneous nature of the gel structure which small angle scattering expts. show consists of dense clusters and voids of characteristic length scales ∼4-7 particle diams. A simple idea for correcting the particle level MCT modulus by employing cluster network concepts is proposed.
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Tuinier, R.; Rieger, J.; de Kruif, C. G. Depletion-Induced Phase Separation in Colloid–Polymer Mixtures. Adv. Colloid Interface Sci. 2003, 103, 1– 31, DOI: 10.1016/S0001-8686(02)00081-7
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Depletion-induced phase separation in colloid-polymer mixtures
Tuinier, R.; Rieger, J.; de Kruif, C. G.
Advances in Colloid and Interface Science (2003), 103 (1), 1-31CODEN: ACISB9; ISSN:0001-8686. (Elsevier Science B.V.)
A review. Phase sepn. can be induced in a colloidal dispersion by adding non-adsorbing polymers. Depletion of polymer around the colloidal particles induces an effective attraction, leading to demixing at sufficient polymer concn. This communication reviews theor. and exptl. work carried out on the polymer-mediated attraction between spherical colloids and the resulting phase sepn. of the polymer-colloid mixt. Theor. studies have mainly focused on the limits where polymers are small or large as compared to the colloidal size. Recently, however, theories are being developed that cover a wider colloid-polymer size ratio range. In practical systems, size polydispersity and polyelectrolytes (instead of neutral polymers) and/or charges on the colloidal surfaces play a role in polymer-colloid mixts. The limited amt. of theor. work performed on this is also discussed. Finally, an overview is given on exptl. investigations with respect to phase behavior and results obtained with techniques enabling measurement of the depletion-induced interaction potential, the structure factor, the depletion layer thickness and the interfacial tension between the demixed phases of a colloid-polymer mixt.
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Bartlett, P.; Ottewill, R. H.; Pusey, P. N. Superlattice Formation in Binary Mixtures of Hard Sphere Colloids. Phys. Rev. Lett. 1992, 68, 3801– 3805, DOI: 10.1103/PhysRevLett.68.3801
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Superlattice formation in binary mixtures of hard-sphere colloids
Bartlett, P.; Ottewill, R. H.; Pusey, P. N.
Physical Review Letters (1992), 68 (25), 3801-4CODEN: PRLTAO; ISSN:0031-9007.
Binary mixts. of suspended hard-sphere colloidal particles (radius ratio RB/RA = 0.58) were obsd. to undergo entropically driven freezing transitions into both the AB2 and the AB13 superlattice structures at different relative proportions of the 2 species. The structures were identified by powder light crystallog. and by electron microscopy of the dried solid phases. An approx. (const. vol.) phase diagram contg. 3 eutectics was detd. The results are compared with earlier work at size ratio 0.62.
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Eldridge, M. D.; Madden, P. A.; Frenkel, D. Entropy-Driven Formation of a Superlattice in a Hard-Sphere Binary Mixture. Nature 1993, 365, 35– 37, DOI: 10.1038/365035a0
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Entropy-driven formation of a superlattice in a hard-sphere binary mixture
Eldridge, M. D.; Madden, P. A.; Frenkel, D.
Nature (London, United Kingdom) (1993), 365 (6441), 35-7CODEN: NATUAS; ISSN:0028-0836.
The possibility that the formation of an AB13 superlattice might be supported by entropy effects alone was investigated by computer simulations of a binary mixt. of hard spheres. Calcns. show that entropy alone is sufficient to stabilize the AB13 phase. and that the full phase diagram of this system is surprisingly complex. The results also suggest that vitrification or slow crystal nucleation in exptl. studies of colloidal hard spheres can prevent the formation of equil. phases.
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Pusey, P. N.; Poon, W. C. K.; Ilett, S. M.; Bartlett, P. Phase Behaviour and Structure of Colloidal Suspensions. J. Phys.: Condens. Matter 1994, 6, A29, DOI: 10.1088/0953-8984/6/23A/004
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Phase behavior and structure of colloidal suspensions
Pusey, P. N.; Poon, W. C. K.; Ilett, S. M.; Bartlett, P.
Journal of Physics: Condensed Matter (1994), 6 (Suppl. 23A), A29-A36CODEN: JCOMEL; ISSN:0953-8984.
A review of 3 sets of expts. on suspensions of hard-sphere colloids. Suspensions of equal-sized particles exhibit the hard-sphere freezing and glass transitions. Mixts. of spheres of two different sizes can form the ordered binary crystals AB2 and AB13. The addn. of non-adsorbing polymer to a one-component suspension leads, through the depletion mechanism, to a range of phase behavior, which includes colloidal gas, liq. crystal and gel. 28 Refs.
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Imhof, A.; Dhont, J. K. G. Experimental Phase Diagram of a Binary Colloidal Hard-Sphere Mixture with a Large Size Ratio. Phys. Rev. Lett. 1995, 75, 1662– 1665, DOI: 10.1103/PhysRevLett.75.1662
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Experimental phase diagram of a binary colloidal hard-sphere mixture with a large size ratio
Imhof, A.; Dhont, J. K. G.
Physical Review Letters (1995), 75 (8), 1662-5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
We detd. the phase diagram of a binary hard-sphere dispersion with size ratio 9.3. Phase sepn. into a fluid and a crystal of large spheres is obsd. The fluid-solid binodal is detd. by measurements of compns. of coexisting phases. The results agree qual. with recent theories, although the latter strongly overest. the depletion activity of the smaller spheres. By fluorescent labeling we are able to measure the mobility of both particles sep. We found evidence for a new glassy phase in which only the small spheres are mobile.
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Hunt, N.; Jardine, R.; Bartlett, P. Superlattice Formation in Mixtures of Hard-Sphere Colloids. Phys. Rev. E 2000, 62, 900– 913, DOI: 10.1103/PhysRevE.62.900
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Superlattice formation in mixtures of hard-sphere colloids
Hunt, Neil; Jardine, Roger; Bartlett, Paul
Physical Review E: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics (2000), 62 (1-B), 900-913CODEN: PLEEE8; ISSN:1063-651X. (American Physical Society)
A detailed exptl. study of the superlattice structures formed in dense binary mixts. of hard-sphere colloids is reported. The phase diagrams obsd. depend sensitively on the ratio α=RS/RL of the radii of the small (S) and large (L) components. Mixts. of size ratio α=0.72, 0.52, 0.42, and 0.39 are studied. The structures of the colloidal phases formed were identified using a combination of light-scattering techniques and confocal fluorescent microscopy. At α=0.39, ordered binary crystals are formed in suspensions contg. an equal no. of large and small spheres which microscopy shows have a three-dimensional structure similar to either NaCl or NiAs. At the larger size ratio, α=0.52, we observe LS2 and LS13 superlattices, isostructural to the mol. compds. AlB2 and NaZn13, while at α=0.72 the two components are immiscible in the solid state and no superlattice structures are found. These exptl. observations are compared with the predictions of Monte Carlo simulations and cell model theories.
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Schofield, A. B.; Pusey, P. N.; Radcliffe, P. Stability of the Binary Colloidal Crystals AB2 and AB13. Phys. Rev. E 2005, 72, 031407 DOI: 10.1103/PhysRevE.72.031407
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Stability of the binary colloidal crystals AB2 and AB13
Schofield, A. B.; Pusey, P. N.; Radcliffe, P.
Physical Review E: Statistical, Nonlinear, and Soft Matter Physics (2005), 72 (3-1), 031407/1-031407/10CODEN: PRESCM; ISSN:1539-3755. (American Physical Society)
Suspensions of binary mixts. of hard-sphere poly(Me methacrylate) colloidal particles were studied at six different size ratios α. The main aim was to det. the range of size ratios over which the binary colloidal crystals AB2 and AB13 are stable. Combining these results with those of earlier work, we found stability of AB2 for 0.60 ⪆ α ⪆ 0.425, in good agreement with theor. predictions by computer simulation and cell model methods. AB13 was obsd. for 0.62 ⪆ α ⪆ 0.485, the lower limit being significantly smaller than the theor. prediction of about 0.525. Rough measurements of crystn. rates showed that AB2 tended to crystallize fastest at small size ratios, whereas the opposite was true for AB13. These findings should provide a guide to the optimum conditions for materials applications of these binary colloidal crystals.
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Leunissen, M. E.; Christova, C. G.; Hynninen, A.-P.; Royall, C. P.; Campbell, A. I.; Imhof, A.; Dijkstra, M.; van Roij, R.; van Blaaderen, A. Ionic Colloidal Crystals of Oppositely Charged Particles. Nature 2005, 437, 235– 240, DOI: 10.1038/nature03946
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Ionic colloidal crystals of oppositely charged particles
Leunissen, Mirjam E.; Christova, Christina G.; Hynninen, Antti-Pekka; Royall, C. Patrick; Campbell, Andrew I.; Imhof, Arnout; Dijkstra, Marjolein; van Roij, Rene; van Blaaderen, Alfons
Nature (London, United Kingdom) (2005), 437 (7056), 235-240CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
Colloidal suspensions are widely used to study processes such as melting, freezing and glass transitions. This is because they display the same phase behavior as atoms or mols., with the nano- to micrometer size of the colloidal particles making it possible to observe them directly in real space. Another attractive feature is that different types of colloidal interactions, such as long-range repulsive, short-range attractive, hard-sphere-like and dipolar, can be realized and give rise to equil. phases. However, spherically sym., long-range attractions (i.e., ionic interactions) have so far always resulted in irreversible colloidal aggregation. Here we show that the electrostatic interaction between oppositely charged particles can be tuned such that large ionic colloidal crystals form readily, with our theory and simulations confirming the stability of these structures. We find that in contrast to at. systems, the stoichiometry of our colloidal crystals is not dictated by charge neutrality; this allows us to obtain a remarkable diversity of new binary structures. An external elec. field melts the crystals, confirming that the constituent particles are indeed oppositely charged. Colloidal model systems can thus be used to study the phase behavior of ionic species. We also expect that our approach to controlling opposite-charge interactions will facilitate the prodn. of binary crystals of micrometer-sized particles, which could find use as advanced materials for photonic applications.
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Hynninen, A.-P.; Leunissen, M. E.; van Blaaderen, A.; Dijkstra, M. CuAu Structure in the Restricted Primitive Model and Oppositely Charged Colloids. Phys. Rev. Lett. 2006, 96, 018303 DOI: 10.1103/PhysRevLett.96.018303
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CuAu Structure in the Restricted Primitive Model and Oppositely Charged Colloids
Hynninen, A.-P.; Leunissen, M. E.; van Blaaderen, A.; Dijkstra, M.
Physical Review Letters (2006), 96 (1), 018303/1-018303/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
The authors study the phase behavior of oppositely charged equal-size hard spheres both theor. and exptl., using Monte Carlo simulations and confocal microscopy. In the simulations, 2 systems are considered: the restricted primitive model (RPM) and a system of screened Coulomb particles. The authors construct the phase diagrams of both systems by computer simulations and predict a novel solid phase that has the CuAu structure. The CuAu structure is obsd. exptl. in a system of oppositely charged colloids. The qual. agreement between the RPM, the screened Coulomb system, and colloids form a suitable model system to study phase behavior in ionic systems.
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Shevchenko, E. V.; Talapin, D. V.; Kotov, N. A.; O’Brien, S.; Murray, C. B. Structural Diversity in Binary Nanoparticle Superlattices. Nature 2006, 439, 55– 59, DOI: 10.1038/nature04414
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Structural diversity in binary nanoparticle superlattices
Shevchenko, Elena V.; Talapin, Dmitri V.; Kotov, Nicholas A.; O'Brien, Stephen; Murray, Christopher B.
Nature (London, United Kingdom) (2006), 439 (7072), 55-59CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
Assembly of small building blocks such as atoms, mols. and nanoparticles into macroscopic structures-i.e., 'bottom up' assembly-is a theme that runs through chem., biol. and material science. Bacteria, macromols. and nanoparticles can self-assemble, generating ordered structures with a precision that challenges current lithog. techniques. The assembly of nanoparticles of two different materials into a binary nanoparticle superlattice (BNSL) can provide a general and inexpensive path to a large variety of materials (metamaterials) with precisely controlled chem. compn. and tight placement of the components. Maximization of the nanoparticle packing d. is proposed as the driving force for BNSL formation, and only a few BNSL structures were predicted to be thermodynamically stable. Recently, colloidal crystals with micrometre-scale lattice spacings were grown from oppositely charged polymethyl methacrylate spheres. Here the authors demonstrate formation of >15 different BNSL structures, using combinations of semiconducting, metallic and magnetic nanoparticle building blocks. At least ten of these colloidal cryst. structures were not reported previously. Elec. charges on sterically stabilized nanoparticles det. BNSL stoichiometry; addnl. contributions from entropic, van der Waals, steric and dipolar forces stabilize the variety of BNSL structures.
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Diba, F. S.; Boden, A.; Thissen, H.; Bhave, M.; Kingshott, P.; Wang, P.-Y. Binary Colloidal Crystals (BCCs): Interactions, Fabrication, and Applications. Adv. Colloid Interface Sci. 2018, 261, 102– 127, DOI: 10.1016/j.cis.2018.08.005
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Binary colloidal crystals (BCCs): Interactions, fabrication, and applications
Diba, Farhana Sharmin; Boden, Andrew; Thissen, Helmut; Bhave, Mrinal; Kingshott, Peter; Wang, Peng-Yuan
Advances in Colloid and Interface Science (2018), 261 (), 102-127CODEN: ACISB9; ISSN:0001-8686. (Elsevier B.V.)
A review. Therefore, fully understand the mechanism of binary colloidal self-assembly is crucial and new/combinational methods are needed. In this review, we summarize the recent advances in BCC fabrication using particles made of different materials, shapes, and dispersion medium. Depending on the potential application, the degree of order and efficiency of crystal formation has to be detd. in order to induce variability in the intended lattice structures. The mechanisms involved in the formation of highly ordered lattice structures from binary colloidal suspensions and applications are discussed. The generation of BCCs can be controlled by manipulation of their extensive phase behavior, which facilitates a wide range potential applications in the fields of both material and biointerfacial sciences including photonics, biosensors, chromatog., antifouling surfaces, biomedical devices, and cell culture tools.
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Gottwald, D.; Likos, C. N.; Kahl, G.; Löwen, H. Phase Behavior of Ionic Microgels. Phys. Rev. Lett. 2004, 92, 068301 DOI: 10.1103/PhysRevLett.92.068301
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Phase Behavior of Ionic Microgels
Gottwald, D.; Likos, C. N.; Kahl, G.; Loewen, H.
Physical Review Letters (2004), 92 (6), 068301/1-068301/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
The authors employ effective interaction potentials between spherical polyelectrolyte microgels to study theor. the structure, thermodn., and phase behavior of ionic microgel solns. Combining a genetic algorithm with accurate free energy calcns., they are able to perform an unrestricted search of candidate crystal structures. Hexagonal, body-centered orthogonal, and trigonal crystals are stable at high concns. and charges of the microgels, accompanied by reentrant melting behavior and fluid-fcc.-bcc. transitions below the overlap concn.
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Sanz, E.; Valeriani, C.; Zaccarelli, E.; Poon, W. C. K.; Pusey, P. N.; Cates, M. E. Crystallization Mechanism of Hard Sphere Glasses. Phys. Rev. Lett. 2011, 106, 215701, DOI: 10.1103/PhysRevLett.106.215701
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Crystallization Mechanism of Hard Sphere Glasses
Sanz, Eduardo; Valeriani, Chantal; Zaccarelli, Emanuela; Poon, W. C. K.; Pusey, P. N.; Cates, M. E.
Physical Review Letters (2011), 106 (21), 215701/1-215701/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
In supercooled liqs., vitrification generally suppresses crystn. Yet some glasses can still crystallize despite the arrest of diffusive motion. This ill-understood process may limit the stability of glasses, but its microscopic mechanism is not yet known. Here we present extensive computer simulations addressing the crystn. of monodisperse hard-sphere glasses at const. vol. (as in a colloid expt.). Multiple cryst. patches appear without particles having to diffuse more than one diam. As these patches grow, the mobility in neighboring areas is enhanced, creating dynamic heterogeneity with pos. feedback. The future crystn. pattern cannot be predicted from the coordinates alone: Crystn. proceeds by a sequence of stochastic micronucleation events, correlated in space by emergent dynamic heterogeneity.
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Liu, Y.; Guan, Y.; Zhang, Y. Facile Assembly of 3D Binary Colloidal Crystals from Soft Microgel Spheres. Macromol. Rapid Commun. 2014, 35, 630– 634, DOI: 10.1002/marc.201300893
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Facile Assembly of 3D Binary Colloidal Crystals from Soft Microgel Spheres
Liu, Yang; Guan, Ying; Zhang, Yongjun
Macromolecular Rapid Communications (2014), 35 (6), 630-634CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
It still remains a big challenge to fabricate binary colloidal crystals (binary CCs) from hard colloidal spheres, although a lot of efforts have been made. Here, for the first time, binary CCs are assembled from soft hydrogel spheres, PNIPAM microgels, instead of hard spheres. Different from hard spheres, microgel binary CCs can be facilely fabricated by simply heating binary microgel dispersions to 37 °C and then allowing them to cool back to room temp. The formation of highly ordered structure is indicated by the appearance of an iridescent color and a sharp Bragg diffraction peak. Compared with hard sphere binary CCs, the assembly of PNIPAM microgel binary CCs is much simpler, faster and with a higher "atom" economy. The easy formation of PNIPAM microgel binary CC is attributed to the thermosensitivity and soft nature of the PNIPAM microgel spheres. In addn., PNIPAM microgel binary CCs can respond to temp. change, and their stop band can be tuned by changing the concn. of the dispersion.
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Chen, M.; Zhang, Y.; Jia, S.; Zhou, L.; Guan, Y.; Zhang, Y. Photonic Crystals with a Reversibly Inducible and Erasable Defect State Using External Stimuli. Angew. Chem., Int. Ed. 2015, 54, 9257– 9261, DOI: 10.1002/anie.201503004
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Photonic Crystals with a Reversibly Inducible and Erasable Defect State Using External Stimuli
Chen, Mao; Zhang, Yapeng; Jia, Siyu; Zhou, Lin; Guan, Ying; Zhang, Yongjun
Angewandte Chemie, International Edition (2015), 54 (32), 9257-9261CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
The controlled introduction of artificial extrinsic defects is crit. to achieve the functions of photonic crystals. Smart defects capable of responding to external stimuli lead to more advanced applications. A microgel colloidal crystal with a defect state which could be induced and erased reversibly by external stimuli is reported. The crystal was assembled from poly(N-isopropylacrylamide) (PNIPAM) microgel and poly(Nisopropylacrylamide-co-acrylic acid) [P(NIPAM-AAc)] microgel of the same size. The resulting doped crystal does not exhibit a defect state in its stop band because of the similar optical properties of the dopant and the host. By increasing the pH value, the dopant P(NIPAM-AAc) spheres swell to a larger size and turn into real defects in the crystal, resulting in the appearance of defect state. Adjusting the pH value back restores the size of the dopant spheres, and erases the defect state. Temp., a 2nd external stimulus, could be used to induce and erase defect states of the crystal.
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Debord, J. D.; Eustis, S.; Debord, S. B.; Lofye, M. T.; Lyon, L. A. Color-Tunable Colloidal Crystals from Soft Hydrogel Nanoparticles. Adv. Mater. 2002, 14, 658– 662, DOI: 10.1002/1521-4095(20020503)14:9<658::AID-ADMA658>3.0.CO;2-3
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Color-tunable colloidal crystals from soft hydrogel nanoparticles
Debord, Justin D.; Eustis, Susan; Debord, Saet Byul; Lofye, Mark T.; Lyon, L. Andrew
Advanced Materials (Weinheim, Germany) (2002), 14 (9), 658-662CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH)
A method for the formation of color-tunable colloidal crystals from soft thermoresponsive microgel particles, where kinetically trapped colloidal glasses are converted to ordered crystals via a particle-based vol. transition, is described. The annealing step allows the redn. of the polycrystallinity of cryst. assemblies and the prodn. of highly ordered materials. The microgel particles prepd. by free radical pptn. polymn. can be manipulated to form hydrogel colloidal crystals by taking advantage of a large magnitude vol. phase transition, which allows for annealing of the assembly. The lattice const. of the crystals and the wavelength of the resultant Bragg peak can be continuously tuned by varying the water content of the microgel pellet before annealing and crystn. This method is facilitated by the softness of the microgels and by the continuous temp.-induced phase transition showed by these particles. The tunability of the lattice spacing combined with the processability of the crystals may increase the utilization of periodic dielec. assemblies formed from colloidal precursors in a wide array of photonic applications.
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Yunker, P. J.; Chen, K.; Gratale, M. D.; Lohr, M. A.; Still, T.; Yodh, A. G. Physics in Ordered and Disordered Colloidal Matter Composed of Poly(N-isopropylacrylamide) Microgel Particles. Rep. Prog. Phys. 2014, 77, 056601 DOI: 10.1088/0034-4885/77/5/056601
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Physics in ordered and disordered colloidal matter composed of poly(N-isopropyl acrylamide) microgel particles
Yunker, Peter J.; Chen, Ke; Gratale, Matthew D.; Lohr, Matthew A.; Still, Tim; Yodh, A. G.
Reports on Progress in Physics (2014), 77 (5), 056601/1-056601/29CODEN: RPPHAG; ISSN:0034-4885. (IOP Publishing Ltd.)
This review collects and describes expts. that employ colloidal suspensions to probe physics in ordered and disordered solids and related complex fluids. The unifying feature of this body of work is its clever usage of poly(N-isopropylacrylamide) (PNIPAM) microgel particles. These temp.-sensitive colloidal particles provide experimenters with a 'knob' for in situ control of particle size, particle interaction and particle packing fraction that, in turn, influence the structural and dynamical behavior of the complex fluids and solids. A brief summary of PNIPAM particle synthesis and properties is given, followed by a synopsis of current activity in the field. The latter discussion describes a variety of soft matter investigations including those that explore formation and melting of crystals and clusters, and those that probe structure, rearrangement and rheol. of disordered (jammed/glassy) and partially ordered matter. The review, therefore, provides a snapshot of a broad range of physics phenomenol. which benefits from the unique properties of responsive microgel particles.
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Vlassopoulos, D.; Cloitre, M. Tunable Rheology of Dense Soft Deformable Colloids. Curr. Opin. Colloid Interface Sci. 2014, 19, 561– 574, DOI: 10.1016/j.cocis.2014.09.007
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Tunable rheology of dense soft deformable colloids
Vlassopoulos, Dimitris; Cloitre, Michel
Current Opinion in Colloid & Interface Science (2014), 19 (6), 561-574CODEN: COCSFL; ISSN:1359-0294. (Elsevier Ltd.)
In the last two decades, advances in synthetic, exptl. and modeling/simulation methodologies have considerably enhanced our understanding of colloidal suspension rheol. and put the field at the forefront of soft matter research. Recent accomplishments include the ability to tailor the flow of colloidal materials via controlled changes of particle microstructure and interactions. Whereas hard sphere suspensions have been the most widely studied colloidal system, there is no richer type of particles than soft colloids in this respect. Yet, despite the remarkable progress in the field, many outstanding challenges remain in our quest to link particle microstructure to macroscopic properties and eventually design appropriate soft composites. Addressing them will provide the route towards novel responsive systems with hierarchical structures and multiple functionalities. Here we discuss the key structural and rheol. parameters which det. the tunable rheol. of dense soft deformable colloids. We restrict our discussion to non-crystg. suspensions of spherical particles without electrostatic or enthalpic interactions.
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Tang, S.; Hu, Z.; Cheng, Z.; Wu, J. Crystallization Kinetics of Thermosensitive Colloids Probed by Transmission Spectroscopy. Langmuir 2004, 20, 8858– 8864, DOI: 10.1021/la049203h
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Crystallization Kinetics of Thermosensitive Colloids Probed by Transmission Spectroscopy
Tang, Shijun; Hu, Zhibing; Cheng, Zhengdong; Wu, Jianzhong
Langmuir (2004), 20 (20), 8858-8864CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
The kinetics of crystn. of poly-N-isopropylacrylamide (PNIPAM) particles has been investigated using the UV-visible transmission spectroscopy. Since the particle size decreases with the increase in temp., microgel dispersions of different vol. fractions have been obtained by varying the temp. of a single sample. It is found that the rates of the change in crystallinity, the av. crystallite size, and the no. d. of crystallites at the most rapid stage over a certain time interval at various temps. can be described by the power-law relations. At 19 °C, the PNIPAM system behaves as a hard sphere system under microgravity. The hard sphere theory based on Monte Carlo simulation has been used as a ref. point to compare with conventional hard spheres, soft spheres, and PNIPAM spheres.
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St. John Iyer, A.; Lyon, L. A. Self-Healing Colloidal Crystals. Angew. Chem., Int. Ed. 2009, 48, 4562– 4566, DOI: 10.1002/anie.200901670
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There is no corresponding record for this reference.
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Vlassopoulos, D. Colloidal Star Polymers: Models for Studying Dynamically Arrested States in Soft Matter. J. Polym. Sci., Part B: Polym. Phys. 2004, 42, 2931– 2941, DOI: 10.1002/polb.20152
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Colloidal star polymers: Models for studying dynamically arrested states in soft matter
Vlassopoulos, Dimitris
Journal of Polymer Science, Part B: Polymer Physics (2004), 42 (16), 2931-2941CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
A review. The use of well-defined macromol. assemblies with tunable interactions represents the key for exploring the regime of soft-material behavior between hard spheres and polymer coils. Colloidal stars are ideal choices for such a formidable task and esp. for shedding light on the formation and properties of dynamically arrested states. In this brief review, the authors demonstrate the rich variety of kinetic frustration phenomena that can be encountered with such ultrasoft particles. The authors address 2 specific examples in particular: the reversible vitrification upon heating and the melting of star gels upon the addn. of linear polymers.
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Cho, J. K.; Meng, Z.; Lyon, L. A.; Breedveld, V. Tunable Attractive and Repulsive Interactions Between pH-Responsive Microgels. Soft Matter 2009, 5, 3599– 3602, DOI: 10.1039/b912105f
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Tunable attractive and repulsive interactions between pH-responsive microgels
Cho, Jae-Kyu; Meng, Zhiyong; Lyon, L. Andrew; Breedveld, Victor
Soft Matter (2009), 5 (19), 3599-3602CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
We report direct measurements of the pairwise interparticle potential between poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-co-AAc) colloidal microgels as a function of pH, as detd. through Ornstein-Zernike anal. of the pair distribution function of quasi-2D dil. colloidal suspensions. The interaction potential ranges from purely repulsive at high pH due to electrosteric interactions to weakly attractive at low pH due to hydrogen bonding, which explains previous observations on the unique phase behavior of these particles in concd. suspensions.
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Lyon, L. A.; Meng, Z.; Singh, N.; Sorrell, C. D.; John, A. St. Thermoresponsive Microgel-Based Materials. Chem. Soc. Rev. 2009, 38, 865– 874, DOI: 10.1039/b715522k
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Thermoresponsive microgel-based materials
Lyon, L. Andrew; Meng, Zhiyong; Singh, Neetu; Sorrell, Courtney D.; St. John, Ashlee
Chemical Society Reviews (2009), 38 (4), 865-874CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
A review. With the continued development of thermoresponsive colloidal hydrogel particles, a no. of groups have begun to exploit their properties to create dynamic materials self-assembled from those components. The fundamental details of how those building blocks are assembled, the component functionality, and the geometry or length-scales present in the assemblies contribute to the behavior of the resultant material. In this tutorial review, we examine recent progress in the assembly of responsive hydrogel colloids in two and three dimensions, highlighting their potential applications, esp. in the domain of biotechnol.
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Hu, Z.; Huang, G. A New Route to Crystalline Hydrogels, Guided by a Phase Diagram. Angew. Chem., Int. Ed. 2003, 42, 4799– 4802, DOI: 10.1002/anie.200351326
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A new route to crystalline hydrogels, guided by a phase diagram
Hu, Zibing; Huang, Gang
Angewandte Chemie, International Edition (2003), 42 (39), 4799-4802CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Hydrogels are well known for applications that include controlled drug delivery, artificial muscles, devices, and sensors. Thermally sensitive nanoparticles in colloidal glasses can be converted into ordered crystals by particle-based vol. transition and a cryst. hydrogel could be obtained by initiating the crystn. process near the colloidal crystal melting temp. while subsequently bonding the PNIPAM-co-allylamine particles below the glass-transition temp. Monodisperse nanoparticles of PNIPAM-co-allylamine were synthesized using a pptn. polymn. method. The phase diagram of their water dispersion was measured.
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Hoare, T.; Pelton, R. Highly pH and Temperature Responsive Microgels Functionalized with Vinylacetic Acid. Macromolecules 2004, 37, 2544– 2550, DOI: 10.1021/ma035658m
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Highly pH and Temperature Responsive Microgels Functionalized with Vinylacetic Acid
Hoare, Todd; Pelton, Robert
Macromolecules (2004), 37 (7), 2544-2550CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
Temp.-responsive microgels based on poly(N-isopropylacrylamide) (PNIPAM) and functionalized with vinylacetic acid (VAA) are obsd. to exhibit a host of novel swelling responses compared with equally functionalized microgels prepd. using the conventional acrylic acid (AA) and methacrylic acid (MAA) comonomers. VAA-NIPAM microgels are ionized over a narrow pH range and show functional group pKa values which are independent of the degree of ionization. Ionization induces a much larger swelling response in VAA-NIPAM microgels than in the conventional microgels; upon ionization at physiol. temp., VAA-NIPAM swells 3 times more than either AA-NIPAM or MAA-NIPAM. VAA-NIPAM microgels also display sharp, PNIPAM-like thermal deswelling profiles when protonated but, upon ionization, undergo no vol. phase transition up to at least 70 °C. The highly responsive and tunable ionization and swelling profiles obsd. for VAA-NIPAM are consistent with the tendency of VAA to behave as a chain transfer agent, resulting in the incorporation of a large no. of well-sepd. VAA units on highly mobile chain ends at or near the microgel surface. VAA-NIPAM microgels may thus be ideal for use in biomol. sepn., medical diagnostics, and biodelivery applications in which sharp responses to multiple environmental stimuli are required.
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Liu, Y. Y.; Liu, X. Y.; Yang, J. M.; Lin, D. L.; Chen, X.; Zha, L. S. Investigation of Ag Nanoparticles Loading Temperature Responsive Hybrid Microgels and their Temperature Controlled Catalytic Activity. Colloids Surf., A 2012, 393, 105– 110, DOI: 10.1016/j.colsurfa.2011.11.007
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Investigation of Ag nanoparticles loading temperature responsive hybrid microgels and their temperature controlled catalytic activity
Liu, Yun-Yun; Liu, Xiao-Yun; Yang, Jian-Mao; Lin, Dan-Li; Chen, Xiao; Zha, Liu-Sheng
Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2012), 393 (), 105-110CODEN: CPEAEH; ISSN:0927-7757. (Elsevier B.V.)
Silver (Ag) nanoparticles loading temp. responsive hybrid microgels were readily prepd. by in situ redn. of Ag+ ions coordinated into poly(N-isopropylacrylamide) microgels. The wt. percentage content of the entrapped Ag nanoparticles measured by thermogravity anal. tops 25%, and their av. particle sizes detd. by transmission electron microscopy are within the range from 8-11 nm. The results obtained by X-ray diffraction exhibit that the Ag nanoparticles are of face-centered cubic single crystal structure. The particle sizes of the hybrid microgels decrease sharply with environmental temp. increasing from 30-35 °C, and their surface plasmon resonance absorption wavelengths are pronouncedly red-shifted within the same temp. range. The catalytic reactivity of the Ag nanoparticles loading hybrid microgels can be tunable with 4 stages of change vs. temp. from 20 to 45 °C.
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Backes, S.; Witt, M. U.; Roeben, E.; Kuhrts, L.; Aleed, S.; Schmidt, A. M.; von Klitzing, R. Loading of PNIPAM Based Microgels with CoFe2O4 Nanoparticles and Their Magnetic Response in Bulk and at Surfaces. J. Phys. Chem. B 2015, 119, 12129– 12137, DOI: 10.1021/acs.jpcb.5b03778
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Loading of PNIPAM Based Microgels with CoFe2O4 Nanoparticles and Their Magnetic Response in Bulk and at Surfaces
Backes, Sebastian; Witt, Marcus U.; Roeben, Eric; Kuhrts, Lukas; Aleed, Sarah; Schmidt, Annette M.; von Klitzing, Regine
Journal of Physical Chemistry B (2015), 119 (36), 12129-12137CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
The present paper addresses the loading of thermoresponsive poly-N-isopropylacrylamide (PNIPAM) based microgel particles with magnetic nanoparticles (MNP: CoFe2O4@PAA (PAA = poly(acrylic acid))) and their response to an external magnetic field. The MNP uptake is analyzed by TEM. Obviously, the charge combination of MNP and microgels plays an important role for the MNP uptake, but it does not explain the whole uptake process. The MNP uptake results in changes of size and electrophoretic mobility, which was studied by dynamic light scattering (DLS) and a Zetasizer. The microgels loaded with MNP preserve their thermosensitivity, and they show magnetic separability and are considered as magnetic microgels. After adsorption at a surface the magnetic microgels were studied with a scanning force microscope and indentation expts. The magnetic microgels show an elongation along the magnetic field parallel to the surface while the height of the microgels (perpendicular to the surface and to the magnetic field) is compressed. This result is in good agreement with simulations of vol. change of ferrogels in a magnetic field.
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Mohanty, P. S.; Bagheri, P.; Nöjd, S.; Yethiraj, A.; Schurtenberger, P. Multiple Path-Dependent Routes for Phase-Transition Kinetics in Thermoresponsive and Field-Responsive Ultrasoft Colloids. Phys. Rev. X 2015, 5, 011030 DOI: 10.1103/PhysRevX.5.011030
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There is no corresponding record for this reference.
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Meijer, J.-M.; Pal, A.; Ouhajji, S.; Lekkerkerker, H. N. W.; Philipse, A. P.; Petukhov, A. V. Observation of Solid–Solid Transitions in 3D Crystals of Colloidal Superballs. Nat. Commun. 2017, 8, 14352, DOI: 10.1038/ncomms14352
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Observation of solid-solid transitions in 3D crystals of colloidal superballs
Meijer, Janne-Mieke; Pal, Antara; Ouhajji, Samia; Lekkerkerker, Henk N. W.; Philipse, Albert P.; Petukhov, Andrei V.
Nature Communications (2017), 8 (), 14352CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
Self-organization in anisotropic colloidal suspensions leads to a fascinating range of crystal and liq. crystal phases induced by shape alone. Simulations predict the phase behavior of a plethora of shapes while exptl. realization often lags behind. Here, we present the exptl. phase behavior of superball particles with a shape in between that of a sphere and a cube. In particular, we observe the formation of a plastic crystal phase with translational order and orientational disorder, and the subsequent transformation into rhombohedral crystals. Moreover, we uncover that the phase behavior is richer than predicted, as we find two distinct rhombohedral crystals with different stacking variants, namely hollow-site and bridge-site stacking. In addn., for slightly softer interactions we observe a solid-solid transition between the two. Our investigation brings us one step closer to ultimately controlling the exptl. self-assembly of superballs into functional materials, such as photonic crystals.
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Lyon, L. A.; Debord, J. D.; Debord, S. B.; Jones, C. D.; McGrath, J. G.; Serpe, M. J. Microgel Colloidal Crystals. J. Phys. Chem. B 2004, 108, 19099– 19108, DOI: 10.1021/jp048486j
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Microgel Colloidal Crystals
Lyon, L. Andrew; Debord, Justin D.; Debord, Saet Byul; Jones, Clinton D.; McGrath, Jonathan G.; Serpe, Michael J.
Journal of Physical Chemistry B (2004), 108 (50), 19099-19108CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
A review. Colloidal crystals assembled from stimuli-sensitive hydrogel particles composed largely of the thermoresponsive polymer poly(N-isopropylacrylamide) display unusual phase behavior because of the inherent "softness" of their interaction potentials as well as the particle thermoresponsivity. A review on use of such oft-sphere building blocks in the construction of colloidal crystals. We describe the utility of temp.-induced vol. phase transitions in controlling the crystn. and melting of the colloidal crystals. For example, it is proposed that multiple weak attractive interactions between particles can drive crystn. at particle concns. well below the hard-sphere f.p. The utility of soft-sphere crystals in the development of new photonic materials is presented in examples of laser direct writing and photopatterning of colloidal crystals based on a photothermally directed crystn. method.
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Paloli, D.; Mohanty, P. S.; Crassous, J. J.; Zaccarelli, E.; Schurtenberger, P. Fluid–Solid Transitions in Soft-Repulsive Colloids. Soft Matter 2013, 9, 3000– 3004, DOI: 10.1039/c2sm27654b
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Fluid-solid transitions in soft-repulsive colloids
Paloli, Divya; Mohanty, Priti S.; Crassous, Jerome J.; Zaccarelli, Emanuela; Schurtenberger, Peter
Soft Matter (2013), 9 (11), 3000-3004CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
We use monodisperse poly(N-isopropylacrylamide) (PNIPAM) microgels as a model system for soft repulsive colloids and study their d. dependent structural ordering and phase behavior using confocal laser scanning microscopy (CLSM). The expts. are carried out at low temps., where the particles are in the swollen state and interact via a Hertzian potential, evidenced through a quant. comparison of the pair correlation functions g(r) obtained with CLSM and computer simulations. We worked over a broad range of effective vol. fractions [phis]eff below and above close packing ([phis]cp). CLSM allows us to identify a fluid-glass and a fluid-crystal transition by looking at the structure and dynamics of the suspensions. The d. dependent g(r) values exhibit clearly visible anomalies at high [phis]eff > [phis]cp which we interpret as a structural signature of the glass transition related to the particle softness. These results are discussed in light of the previously studied phase behavior of colloidal systems interacting with hard and soft repulsive interaction potentials.
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Dulle, M.; Jaber, S.; Rosenfeldt, S.; Radulescu, A.; Förster, S.; Mulvaney, P.; Karg, M. Plasmonic Gold–poly(N-isopropylacrylamide) Core–Shell Colloids with Homogeneous Density Profiles: a Small Angle Scattering Study. Phys. Chem. Chem. Phys. 2015, 17, 1354– 1367, DOI: 10.1039/C4CP04816D
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Plasmonic gold-poly(N-isopropylacrylamide) core-shell colloids with homogeneous density profiles: a small angle scattering study
Dulle, Martin; Jaber, Sarah; Rosenfeldt, Sabine; Radulescu, Aurel; Foerster, Stephan; Mulvaney, Paul; Karg, Matthias
Physical Chemistry Chemical Physics (2015), 17 (2), 1354-1367CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
Coating metal nanocrystals with responsive polymers provides a model case of smart, functional materials, where the optical properties can be modulated by external stimuli. However the optical response is highly sensitive to the polymer shell morphol., thickness and dielec. contrast. In this paper we study the nature of crosslinked, thermoresponsive polymer shells for the first time using four different scattering approaches to elucidate the d. profile of the shells. Each scattering method provides unique information about the temp.-induced changes of shell thickness in terms of hydrodynamic radius and radius of gyration, the pair-distance distribution functions of the shells as well as the dynamic network fluctuations. Only a combination of these different scattering techniques allows to develop a morphol. model of the core-shell particles. We further demonstrate control of the crosslinker distribution in core-shell synthesis by semi-batch pptn. copolymn. Conducting the polymn. in three steps, we show for the first time that the polymer shell thickness can be successively increased without affecting the shell morphol. and response behavior.
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Fasolo, M.; Sollich, P. Equilibrium Phase Behavior of Polydisperse Hard Spheres. Phys. Rev. Lett. 2003, 91, 068301 DOI: 10.1103/PhysRevLett.91.068301
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Equilibrium Phase Behavior of Polydisperse Hard Spheres
Fasolo, Moreno; Sollich, Peter
Physical Review Letters (2003), 91 (6), 068301/1-068301/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
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Abstract
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Figure 1
Figure 1. Cross-section of the sample holder design, not to scale.
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Figure 2
Figure 2. Analysis of one sample at different salinities. (A–D) CLSM images with their corresponding radial distribution functions (RDFs) of pN-to-pN, pM-to-pM, and pN-to-pM. (A) 2 × 10^–3 M KCl, showing entropy-driven crystallinity. (B) 1.5 × 10^–3 M KCl, in a fluid phase. (C) 1.25 × 10^–3 M KCl, showing electrostatic forces-driven crystallinity. (D) Sample at 1 × 10^–3 M KCl, in an electrostatically aggregated gel. (E) Mean-square displacements (MSDs) of pN particles for all salinities, together with a line with a slope proportional to t¹ to guide the eye. The MSDs for pM are highly similar to the MSDs of pN. (F) Corresponding P(Z_eq) for all salinities. Dashed lines indicate the theoretical values corresponding to AuCu (0.33) and FCC (0.5) crystal values. Each scale bar length is 10 μm.
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Figure 3
Figure 3. CLSM images of the same sample at different salinities, with their corresponding radial distribution functions (RDFs). (A) CLSM image at 2 × 10^–3 M KCl. (B) Corresponding RDFs of pN-to-pN, pM-to-pM, and pN-to-pM. The overlapping RDFs illustrate the random distribution of particles throughout the lattice. The RDF peaks are in accordance with the positions and relative magnitudes of those in an FCC lattice (blue, rescaled magnitudes by arbitrary factor for visibility). (C) CLSM image at 1.25 × 10^–3 M KCl. (D–F) Corresponding RDF at 1.25 × 10^–3 M KCl of (D) pN-to-pN, (E) pM-to-pM, and (F) pN-to-pM. Each RDF is shown with the corresponding peaks for AuCu-type crystals. The scale bar length is 10 μm.
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Figure 4
Figure 4. Unit cells of (A) a single particle type FCC and (B) a AuCu crystal. The red particles represent the larger Au atoms.
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Figure 5
Figure 5. CLSM image slices from a 3D stack, compared with Voronoi cells colored according to their q̅_l. (A, B) FCC crystal at 2.0 × 10^–3 M KCl. (C, D) AuCu crystal at 1.25 × 10^–3 M KCl. If q̅₄(equal) > 0.45 or q̅₈(equal) > 0.45, AuCu crystallinity is denoted by a blue cell; if q̅₆(all) > 0.35, but q̅₄(equal) < 0.45 and q̅₈(equal) < 0.45, FCC crystallinity is denoted by a red cell; and if q̅₆(all) < 0.35 and q̅₄(equal) < 0.45 or q̅₈(equal) < 0.45, the cell was left white, denoting an amorphous local surrounding.
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  Gasser, U.; Weeks, Eric R.; Schofield, Andrew; Pusey, P. N.; Weitz, D. A.
  Science (Washington, DC, United States) (2001), 292 (5515), 258-262CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
  Crystn. of concd. colloidal suspensions was studied in real space with laser scanning confocal microscopy. Direct imaging in three dimensions allowed identification and observation of both nucleation and growth of cryst. regions, providing an exptl. measure of properties of the nucleating crystallites. By following their evolution, the authors identified crit. nuclei, detd. nucleation rates, and measured the av. surface tension of the crystal-liq. interface. The structure of the nuclei was the same as the bulk solid phase, random hcp., and their av. shape was rather nonspherical, with rough rather than faceted surfaces.
6. 6
  Auer, S.; Frenkel, D. Numerical Prediction of Absolute Crystallization Rates in Hard-Sphere Colloids. J. Chem. Phys. 2004, 120, 3015, DOI: 10.1063/1.1638740
  6
  Numerical prediction of absolute crystallization rates in hard-sphere colloids
  Auer, S.; Frenkel, D.
  Journal of Chemical Physics (2004), 120 (6), 3015-3029CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  Special computational techniques are required to compute abs. crystal nucleation rates of colloidal suspensions. Using crystal nucleation of hard-sphere colloids as an example, we describe in some detail the novel computational tools that are needed to perform such calcns. In particular, we focus on the definition of appropriate order parameters that distinguish liq. from crystal, and on techniques to compute the kinetic prefactor that enters in the expression for the nucleation rate. In addn., we discuss the relation between simulation results and theor. predictions based on classical nucleation theory.
7. 7
  Sandomirski, K.; Allahyarov, E.; Lowen, H.; Egelhaaf, S. U. Heterogeneous Crystallization of Hard-Sphere Colloids near a Wall. Soft Matter 2011, 7, 8050– 8055, DOI: 10.1039/c1sm05346a
  7
  Heterogeneous crystallization of hard-sphere colloids near a wall
  Sandomirski, Kirill; Allahyarov, Elshad; Loewen, Hartmut; Egelhaaf, Stefan U.
  Soft Matter (2011), 7 (18), 8050-8055CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
  We investigate the most basic situation of heterogeneous crystn.: crystn. of hard-sphere colloids in the presence of a flat hard wall. Using a combination of confocal microscopy and nonequil. Brownian dynamics simulations, microscopic time-resolved information is obtained on an individual-particle level. Initially, particles near the wall rearrange before an extended regime of crystal growth is found. During growth, we can directly observe a depletion zone in the fluid next to the progressing crystal-fluid interface due to the single-particle information provided by microscopy and simulations. This also allows us to follow the relaxation of the crystal layers and the progression of the crystal-fluid interface. In good agreement between our expts. and simulations, as well as previous studies, the growth rate shows a max. in its dependence on the bulk vol. fraction.
8. 8
  Montanarella, F.; Geuchies, J. J.; Dasgupta, T.; Prins, P. T.; van Overbeek, C.; Dattani, R.; Baesjou, P.; Dijkstra, M.; Petukhov, A. V.; van Blaaderen, A.; Vanmaekelbergh, D. Crystallization of Nanocrystals in Spherical Confinement Probed by in Situ X-ray Scattering. Nano Lett. 2018, 18, 3675– 3681, DOI: 10.1021/acs.nanolett.8b00809
  8
  Crystallization of Nanocrystals in Spherical Confinement Probed by in Situ X-ray Scattering
  Montanarella, Federico; Geuchies, Jaco J.; Dasgupta, Tonnishtha; Prins, P. Tim; van Overbeek, Carlo; Dattani, Rajeev; Baesjou, Patrick; Dijkstra, Marjolein; Petukhov, Andrei V.; van Blaaderen, Alfons; Vanmaekelbergh, Daniel
  Nano Letters (2018), 18 (6), 3675-3681CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
  The formation of supraparticles from nanocrystals confined in slowly evapg. oil droplets in an oil-in-H2O emulsion was studied. The nanocrystals consist of an FeO core, a CoFe2O4 shell, and oleate capping ligands, with an overall diam. of 12.5 nm. In situ small- and wide-angle x-ray scattering expts. were performed during the entire period of solvent evapn. and colloidal crystn. A slow increase in the vol. fraction of nanocrystals inside the oil droplets up to 20%, at which a sudden crystn. occurs was obsd. The computer simulations show that crystn. at such a low vol. fraction is only possible if attractive interactions between colloidal nanocrystals are taken into account in the model as well. The spherical supraparticles have a diam. of ∼700 nm and consist of a few cryst. fcc. domains. Nanocrystal supraparticles bear importance for magnetic and optoelectronic applications, such as color tunable biolabels, color tunable phosphors in LEDs, and miniaturized lasers.
9. 9
  Anderson, V. J.; Lekkerkerker, H. N. W. Insights into Phase Transition Kinetics from Colloid Science. Nature 2002, 416, 811– 815, DOI: 10.1038/416811a
  9
  Insights into phase transition kinetics from colloid science
  Anderson, V. J.; Lekkerkerker, H. N. W.
  Nature (London, United Kingdom) (2002), 416 (6883), 811-815CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  A review. Colloids display intriguing transitions between gas, liq., solid, and liq. cryst. phases. Such phase transitions are ubiquitous in nature and were studied for decades. However, the predictions of phase diagrams are not always realized; systems often become undercooled, supersatd., or trapped in gel-like states. In many cases the end products strongly depend on the starting position in the phase diagram and discrepancies between predictions and actual observations are due to the intricacies of the dynamics of phase transitions. Colloid science aims to understand the underlying mechanisms of these transitions. Important advances were made, for example, with new imaging techniques that allow direct observation of individual colloidal particles undergoing phase transitions, revealing some of the secrets of the complex pathways involved.
10. 10
  Yethiraj, A.; van Blaaderen, A. A Colloidal Model System with an Interaction Tunable from Hard Sphere to Soft and Dipolar. Nature 2003, 421, 513– 517, DOI: 10.1038/nature01328
  10
  A colloidal model system with an interaction tunable from hard sphere to soft and dipolar
  Yethiraj, Anand; van Blaaderen, Alfons
  Nature (London, United Kingdom) (2003), 421 (6922), 513-517CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  Monodisperse colloidal suspensions of micrometre-sized spheres are playing an increasingly important role as model systems to study, in real space, a variety of phenomena in condensed matter physics-such as glass transitions and crystal nucleation. But to date, no quant. real-space studies have been performed on crystal melting, or have investigated systems with long-range repulsive potentials. Here we demonstrate a charge- and sterically stabilized colloidal suspension-poly(Me methacrylate) spheres in a mixt. of cycloheptyl (or cyclohexyl) bromide and decalin-where both the repulsive range and the anisotropy of the interparticle interaction potential can be controlled. This combination of two independent tuning parameters gives rise to a rich phase behavior, with several unusual colloidal (liq.) cryst. phases, which we explore in real space by confocal microscopy. The softness of the interaction is tuned in this colloidal suspension by varying the solvent salt concn.; the anisotropic (dipolar) contribution to the interaction potential can be independently controlled with an external elec. field ranging from a small perturbation to the point where it completely dets. the phase behavior. We also demonstrate that the elec. field can be used as a pseudo-thermodn. temp. switch to enable real-space studies of melting transitions. We expect studies of this colloidal model system to contribute to our understanding of, for example, electro- and magneto-rheol. fluids.
11. 11
  Bartlett, P.; Campbell, A. I. Three-Dimensional Binary Superlattices of Oppositely Charged Colloids. Phys. Rev. Lett. 2005, 95, 128302, DOI: 10.1103/PhysRevLett.95.128302
  11
  Three-Dimensional Binary Superlattices of Oppositely Charged Colloids
  Bartlett, Paul; Campbell, Andrew I.
  Physical Review Letters (2005), 95 (12), 128302/1-128302/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  The authors report the equil. self-assembly of binary crystals of oppositely charged colloidal microspheres at high d. By varying the magnitude of the charge on near equal-sized spheres the structure of the binary crystal may be switched between fcc., CsCl, and NaCl. The authors interpret these transformations in terms of a competition between entropic and Coulombic forces.
12. 12
  Pusey, P. N.; van Megen, W. Phase Behaviour of Concentrated Suspensions of Nearly Hard Colloidal Spheres. Nature 1986, 320, 340– 342, DOI: 10.1038/320340a0
  12
  Phase behavior of concentrated suspensions of nearly hard colloidal spheres
  Pusey, P. N.; Van Megen, W.
  Nature (London, United Kingdom) (1986), 320 (6060), 340-2CODEN: NATUAS; ISSN:0028-0836.
  The phase diagram of suspensions of colloidal spheres which interact through a steep repulsive potential is studied for colloidal PMMA [9011-14-7] particles, stabilized by poly(12-hydroxystearic acid), in decalin-CS2. With increasing particle concn., the colloidal fluid is transformed to fluid and crystal phases in coexistence, to fully crystd. samples. At the highest concns., very viscous samples are obtained in which full crystn. had not occurred after several months and in which the particles are arranged as an amorphous colloidal glass. The empirical phase diagram can be reproduced reasonably well by an effective hard-sphere model.
13. 13
  Mewis, J.; Frith, W. J.; Strivens, T. A.; Russel, W. B. The Rheology of Suspensions Containing Polymerically Stabilized Particles. AIChE J. 1989, 35, 415– 422, DOI: 10.1002/aic.690350309
  13
  The rheology of suspensions containing polymerically stabilized particles
  Mewis, Jan; Frith, William J.; Strivens, Trevor A.; Russel, William B.
  AIChE Journal (1989), 35 (3), 415-22CODEN: AICEAC; ISSN:0001-1541.
  The non-Newtonian viscosities of grafted poly(12-hydroxystearic acid)-stabilized PMMA colloidal suspensions are usually predicted and correlated on the basis of data and scaling principles for Brownian hard spheres. Here, the specific effect of the stabilizer layer is investigated using suspensions of monodisperse PMMA particles with a chem. attached stabilizer layer. The ratio between particle radius and stabilizer layer thickness is 5-61. At high values of this ratio the data show Brownian hard sphere behavior. At lower values deviations appear. As a first approxn., the softness of the particles can be characterized through the concn. at max. packing. A more detailed comparison with hard sphere data provides a measure for softness that changes with concn. and shear rate. A theor. est. of the concn. effect is in line with the expts. The crit. shear stress (or Peclet no.) is not a const. but goes through a max. when the concn. is increased.
14. 14
  Chu, J. H.; I, L. Direct Observation of Coulomb Crystals and Liquids in Strongly Coupled rf Dusty Plasmas. Phys. Rev. Lett. 1994, 72, 4009– 4012, DOI: 10.1103/PhysRevLett.72.4009
  14
  Direct observation of Coulomb crystals and liquids in strongly coupled rf dusty plasmas
  Chu, J. H.; I, Lin
  Physical Review Letters (1994), 72 (25), 4009-12CODEN: PRLTAO; ISSN:0031-9007.
  The strongly coupled dusty plasmas are formed by suspending neg. charged SiO2 fine particles with 10 μm diam. in weakly ionized rf Ar discharges. The Coulomb crystals and liqs. are directly obsd. for the first time using an optical microscope. By properly controlling the system parameters, hexagonal, fcc., and bcc. crystal structures and solids with coexisting different structures can be formed. Increasing the rf power causes the transition to the more disordered liq. state.
15. 15
  Levitz, P.; Lecolier, E.; Mourchid, A.; Delville, A.; Lyonnard, S. Liquid-Solid Transition of Laponite Suspensions at Very Low Ionic Strength: Long-Range Electrostatic Stabilisation of Anisotropic Colloids. Europhys. Lett. 2000, 49, 672– 677, DOI: 10.1209/epl/i2000-00203-9
  15
  Liquid-solid transition of laponite suspensions at very low ionic strength: long-range electrostatic stabilization of anisotropic colloids
  Levitz, P.; Lecolier, E.; Mourchid, A.; Delville, A.; Lyonnard, S.
  Europhysics Letters (2000), 49 (5), 672-677CODEN: EULEEJ; ISSN:0295-5075. (EDP Sciences)
  The authors study suspensions of synthetic clay laponite at very low ionic strength. The authors show the existence, for these charged disk-like particles, of a liq.-soft solid transition mainly driven by electrostatic repulsive interactions. Such a process defines a reentrant transition line in the phase diagram. Location of this line is predicted using basic arguments. The structure is characterized by ultra-small-angle x-ray scattering (USAXS). Soft-solid suspensions show a correlation peak compatible with long-range electrostatic stabilization. Such a result strongly contrasts with the evolution of the scattering spectra for solid-like suspensions of laponite at high ionic strength (above 10-4 M). Close inspection of this correlation peak reveals that individual particle distribution is not homogeneous in space.
16. 16
  Shah, S. A.; Chen, Y.-L.; Schweizer, K. S.; Zukoski, C. F. Viscoelasticity and Rheology of Depletion Flocculated Gels and Fluids. J. Chem. Phys. 2003, 119, 8747– 8760, DOI: 10.1063/1.1598192
  16
  Viscoelasticity and rheology of depletion flocculated gels and fluids
  Shah, S. A.; Chen, Y.-L.; Schweizer, K. S.; Zukoski, C. F.
  Journal of Chemical Physics (2003), 119 (16), 8747-8760CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  The flow properties of high vol. fraction hard sphere colloid-polymer suspensions are studied as a function of polymer concn., depletion attraction range, and solvent quality up to, and well beyond, the gelation boundary. As the gel boundary is approached, the shear viscosity tends to diverge in a crit. power law manner at a polymer concn. that is a function of the polymer radius of gyration and solvency condition. The shear viscosity for different polymer size suspensions can be collapsed onto a master curve motivated by mode coupling theory (MCT). The low frequency elastic modulus grows rapidly with increasing depletion attraction near the gel boundary, but becomes a dramatically weaker function of polymer concn. as the gel state is more deeply entered. A simplified version of MCT with accurate, no adjustable parameter polymer ref. interaction site model (PRISM) theory structural input has been applied to predict the gelation boundaries and elastic shear moduli. The calcd. gel lines are in semiquant. agreement with expt. at high vol. fractions, but increasingly deviate upon particle diln. Calcns. of the dependence of the gel elastic shear moduli on particle-polymer size asymmetry and scaled polymer concn. are in excellent agreement with expt., and deep in the gel follow a power law dependence on polymer concn. Quant., MCT-PRISM elastic moduli are higher than expt. by a nearly const. large factor. This discrepancy is suggested to be due to the heterogeneous nature of the gel structure which small angle scattering expts. show consists of dense clusters and voids of characteristic length scales ∼4-7 particle diams. A simple idea for correcting the particle level MCT modulus by employing cluster network concepts is proposed.
17. 17
  Tuinier, R.; Rieger, J.; de Kruif, C. G. Depletion-Induced Phase Separation in Colloid–Polymer Mixtures. Adv. Colloid Interface Sci. 2003, 103, 1– 31, DOI: 10.1016/S0001-8686(02)00081-7
  17
  Depletion-induced phase separation in colloid-polymer mixtures
  Tuinier, R.; Rieger, J.; de Kruif, C. G.
  Advances in Colloid and Interface Science (2003), 103 (1), 1-31CODEN: ACISB9; ISSN:0001-8686. (Elsevier Science B.V.)
  A review. Phase sepn. can be induced in a colloidal dispersion by adding non-adsorbing polymers. Depletion of polymer around the colloidal particles induces an effective attraction, leading to demixing at sufficient polymer concn. This communication reviews theor. and exptl. work carried out on the polymer-mediated attraction between spherical colloids and the resulting phase sepn. of the polymer-colloid mixt. Theor. studies have mainly focused on the limits where polymers are small or large as compared to the colloidal size. Recently, however, theories are being developed that cover a wider colloid-polymer size ratio range. In practical systems, size polydispersity and polyelectrolytes (instead of neutral polymers) and/or charges on the colloidal surfaces play a role in polymer-colloid mixts. The limited amt. of theor. work performed on this is also discussed. Finally, an overview is given on exptl. investigations with respect to phase behavior and results obtained with techniques enabling measurement of the depletion-induced interaction potential, the structure factor, the depletion layer thickness and the interfacial tension between the demixed phases of a colloid-polymer mixt.
18. 18
  Bartlett, P.; Ottewill, R. H.; Pusey, P. N. Superlattice Formation in Binary Mixtures of Hard Sphere Colloids. Phys. Rev. Lett. 1992, 68, 3801– 3805, DOI: 10.1103/PhysRevLett.68.3801
  18
  Superlattice formation in binary mixtures of hard-sphere colloids
  Bartlett, P.; Ottewill, R. H.; Pusey, P. N.
  Physical Review Letters (1992), 68 (25), 3801-4CODEN: PRLTAO; ISSN:0031-9007.
  Binary mixts. of suspended hard-sphere colloidal particles (radius ratio RB/RA = 0.58) were obsd. to undergo entropically driven freezing transitions into both the AB2 and the AB13 superlattice structures at different relative proportions of the 2 species. The structures were identified by powder light crystallog. and by electron microscopy of the dried solid phases. An approx. (const. vol.) phase diagram contg. 3 eutectics was detd. The results are compared with earlier work at size ratio 0.62.
19. 19
  Eldridge, M. D.; Madden, P. A.; Frenkel, D. Entropy-Driven Formation of a Superlattice in a Hard-Sphere Binary Mixture. Nature 1993, 365, 35– 37, DOI: 10.1038/365035a0
  19
  Entropy-driven formation of a superlattice in a hard-sphere binary mixture
  Eldridge, M. D.; Madden, P. A.; Frenkel, D.
  Nature (London, United Kingdom) (1993), 365 (6441), 35-7CODEN: NATUAS; ISSN:0028-0836.
  The possibility that the formation of an AB13 superlattice might be supported by entropy effects alone was investigated by computer simulations of a binary mixt. of hard spheres. Calcns. show that entropy alone is sufficient to stabilize the AB13 phase. and that the full phase diagram of this system is surprisingly complex. The results also suggest that vitrification or slow crystal nucleation in exptl. studies of colloidal hard spheres can prevent the formation of equil. phases.
20. 20
  Pusey, P. N.; Poon, W. C. K.; Ilett, S. M.; Bartlett, P. Phase Behaviour and Structure of Colloidal Suspensions. J. Phys.: Condens. Matter 1994, 6, A29, DOI: 10.1088/0953-8984/6/23A/004
  20
  Phase behavior and structure of colloidal suspensions
  Pusey, P. N.; Poon, W. C. K.; Ilett, S. M.; Bartlett, P.
  Journal of Physics: Condensed Matter (1994), 6 (Suppl. 23A), A29-A36CODEN: JCOMEL; ISSN:0953-8984.
  A review of 3 sets of expts. on suspensions of hard-sphere colloids. Suspensions of equal-sized particles exhibit the hard-sphere freezing and glass transitions. Mixts. of spheres of two different sizes can form the ordered binary crystals AB2 and AB13. The addn. of non-adsorbing polymer to a one-component suspension leads, through the depletion mechanism, to a range of phase behavior, which includes colloidal gas, liq. crystal and gel. 28 Refs.
21. 21
  Imhof, A.; Dhont, J. K. G. Experimental Phase Diagram of a Binary Colloidal Hard-Sphere Mixture with a Large Size Ratio. Phys. Rev. Lett. 1995, 75, 1662– 1665, DOI: 10.1103/PhysRevLett.75.1662
  21
  Experimental phase diagram of a binary colloidal hard-sphere mixture with a large size ratio
  Imhof, A.; Dhont, J. K. G.
  Physical Review Letters (1995), 75 (8), 1662-5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  We detd. the phase diagram of a binary hard-sphere dispersion with size ratio 9.3. Phase sepn. into a fluid and a crystal of large spheres is obsd. The fluid-solid binodal is detd. by measurements of compns. of coexisting phases. The results agree qual. with recent theories, although the latter strongly overest. the depletion activity of the smaller spheres. By fluorescent labeling we are able to measure the mobility of both particles sep. We found evidence for a new glassy phase in which only the small spheres are mobile.
22. 22
  Hunt, N.; Jardine, R.; Bartlett, P. Superlattice Formation in Mixtures of Hard-Sphere Colloids. Phys. Rev. E 2000, 62, 900– 913, DOI: 10.1103/PhysRevE.62.900
  22
  Superlattice formation in mixtures of hard-sphere colloids
  Hunt, Neil; Jardine, Roger; Bartlett, Paul
  Physical Review E: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics (2000), 62 (1-B), 900-913CODEN: PLEEE8; ISSN:1063-651X. (American Physical Society)
  A detailed exptl. study of the superlattice structures formed in dense binary mixts. of hard-sphere colloids is reported. The phase diagrams obsd. depend sensitively on the ratio α=RS/RL of the radii of the small (S) and large (L) components. Mixts. of size ratio α=0.72, 0.52, 0.42, and 0.39 are studied. The structures of the colloidal phases formed were identified using a combination of light-scattering techniques and confocal fluorescent microscopy. At α=0.39, ordered binary crystals are formed in suspensions contg. an equal no. of large and small spheres which microscopy shows have a three-dimensional structure similar to either NaCl or NiAs. At the larger size ratio, α=0.52, we observe LS2 and LS13 superlattices, isostructural to the mol. compds. AlB2 and NaZn13, while at α=0.72 the two components are immiscible in the solid state and no superlattice structures are found. These exptl. observations are compared with the predictions of Monte Carlo simulations and cell model theories.
23. 23
  Schofield, A. B.; Pusey, P. N.; Radcliffe, P. Stability of the Binary Colloidal Crystals AB2 and AB13. Phys. Rev. E 2005, 72, 031407 DOI: 10.1103/PhysRevE.72.031407
  23
  Stability of the binary colloidal crystals AB2 and AB13
  Schofield, A. B.; Pusey, P. N.; Radcliffe, P.
  Physical Review E: Statistical, Nonlinear, and Soft Matter Physics (2005), 72 (3-1), 031407/1-031407/10CODEN: PRESCM; ISSN:1539-3755. (American Physical Society)
  Suspensions of binary mixts. of hard-sphere poly(Me methacrylate) colloidal particles were studied at six different size ratios α. The main aim was to det. the range of size ratios over which the binary colloidal crystals AB2 and AB13 are stable. Combining these results with those of earlier work, we found stability of AB2 for 0.60 ⪆ α ⪆ 0.425, in good agreement with theor. predictions by computer simulation and cell model methods. AB13 was obsd. for 0.62 ⪆ α ⪆ 0.485, the lower limit being significantly smaller than the theor. prediction of about 0.525. Rough measurements of crystn. rates showed that AB2 tended to crystallize fastest at small size ratios, whereas the opposite was true for AB13. These findings should provide a guide to the optimum conditions for materials applications of these binary colloidal crystals.
24. 24
  Leunissen, M. E.; Christova, C. G.; Hynninen, A.-P.; Royall, C. P.; Campbell, A. I.; Imhof, A.; Dijkstra, M.; van Roij, R.; van Blaaderen, A. Ionic Colloidal Crystals of Oppositely Charged Particles. Nature 2005, 437, 235– 240, DOI: 10.1038/nature03946
  24
  Ionic colloidal crystals of oppositely charged particles
  Leunissen, Mirjam E.; Christova, Christina G.; Hynninen, Antti-Pekka; Royall, C. Patrick; Campbell, Andrew I.; Imhof, Arnout; Dijkstra, Marjolein; van Roij, Rene; van Blaaderen, Alfons
  Nature (London, United Kingdom) (2005), 437 (7056), 235-240CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  Colloidal suspensions are widely used to study processes such as melting, freezing and glass transitions. This is because they display the same phase behavior as atoms or mols., with the nano- to micrometer size of the colloidal particles making it possible to observe them directly in real space. Another attractive feature is that different types of colloidal interactions, such as long-range repulsive, short-range attractive, hard-sphere-like and dipolar, can be realized and give rise to equil. phases. However, spherically sym., long-range attractions (i.e., ionic interactions) have so far always resulted in irreversible colloidal aggregation. Here we show that the electrostatic interaction between oppositely charged particles can be tuned such that large ionic colloidal crystals form readily, with our theory and simulations confirming the stability of these structures. We find that in contrast to at. systems, the stoichiometry of our colloidal crystals is not dictated by charge neutrality; this allows us to obtain a remarkable diversity of new binary structures. An external elec. field melts the crystals, confirming that the constituent particles are indeed oppositely charged. Colloidal model systems can thus be used to study the phase behavior of ionic species. We also expect that our approach to controlling opposite-charge interactions will facilitate the prodn. of binary crystals of micrometer-sized particles, which could find use as advanced materials for photonic applications.
25. 25
  Hynninen, A.-P.; Leunissen, M. E.; van Blaaderen, A.; Dijkstra, M. CuAu Structure in the Restricted Primitive Model and Oppositely Charged Colloids. Phys. Rev. Lett. 2006, 96, 018303 DOI: 10.1103/PhysRevLett.96.018303
  25
  CuAu Structure in the Restricted Primitive Model and Oppositely Charged Colloids
  Hynninen, A.-P.; Leunissen, M. E.; van Blaaderen, A.; Dijkstra, M.
  Physical Review Letters (2006), 96 (1), 018303/1-018303/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  The authors study the phase behavior of oppositely charged equal-size hard spheres both theor. and exptl., using Monte Carlo simulations and confocal microscopy. In the simulations, 2 systems are considered: the restricted primitive model (RPM) and a system of screened Coulomb particles. The authors construct the phase diagrams of both systems by computer simulations and predict a novel solid phase that has the CuAu structure. The CuAu structure is obsd. exptl. in a system of oppositely charged colloids. The qual. agreement between the RPM, the screened Coulomb system, and colloids form a suitable model system to study phase behavior in ionic systems.
26. 26
  Shevchenko, E. V.; Talapin, D. V.; Kotov, N. A.; O’Brien, S.; Murray, C. B. Structural Diversity in Binary Nanoparticle Superlattices. Nature 2006, 439, 55– 59, DOI: 10.1038/nature04414
  26
  Structural diversity in binary nanoparticle superlattices
  Shevchenko, Elena V.; Talapin, Dmitri V.; Kotov, Nicholas A.; O'Brien, Stephen; Murray, Christopher B.
  Nature (London, United Kingdom) (2006), 439 (7072), 55-59CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  Assembly of small building blocks such as atoms, mols. and nanoparticles into macroscopic structures-i.e., 'bottom up' assembly-is a theme that runs through chem., biol. and material science. Bacteria, macromols. and nanoparticles can self-assemble, generating ordered structures with a precision that challenges current lithog. techniques. The assembly of nanoparticles of two different materials into a binary nanoparticle superlattice (BNSL) can provide a general and inexpensive path to a large variety of materials (metamaterials) with precisely controlled chem. compn. and tight placement of the components. Maximization of the nanoparticle packing d. is proposed as the driving force for BNSL formation, and only a few BNSL structures were predicted to be thermodynamically stable. Recently, colloidal crystals with micrometre-scale lattice spacings were grown from oppositely charged polymethyl methacrylate spheres. Here the authors demonstrate formation of >15 different BNSL structures, using combinations of semiconducting, metallic and magnetic nanoparticle building blocks. At least ten of these colloidal cryst. structures were not reported previously. Elec. charges on sterically stabilized nanoparticles det. BNSL stoichiometry; addnl. contributions from entropic, van der Waals, steric and dipolar forces stabilize the variety of BNSL structures.
27. 27
  Diba, F. S.; Boden, A.; Thissen, H.; Bhave, M.; Kingshott, P.; Wang, P.-Y. Binary Colloidal Crystals (BCCs): Interactions, Fabrication, and Applications. Adv. Colloid Interface Sci. 2018, 261, 102– 127, DOI: 10.1016/j.cis.2018.08.005
  27
  Binary colloidal crystals (BCCs): Interactions, fabrication, and applications
  Diba, Farhana Sharmin; Boden, Andrew; Thissen, Helmut; Bhave, Mrinal; Kingshott, Peter; Wang, Peng-Yuan
  Advances in Colloid and Interface Science (2018), 261 (), 102-127CODEN: ACISB9; ISSN:0001-8686. (Elsevier B.V.)
  A review. Therefore, fully understand the mechanism of binary colloidal self-assembly is crucial and new/combinational methods are needed. In this review, we summarize the recent advances in BCC fabrication using particles made of different materials, shapes, and dispersion medium. Depending on the potential application, the degree of order and efficiency of crystal formation has to be detd. in order to induce variability in the intended lattice structures. The mechanisms involved in the formation of highly ordered lattice structures from binary colloidal suspensions and applications are discussed. The generation of BCCs can be controlled by manipulation of their extensive phase behavior, which facilitates a wide range potential applications in the fields of both material and biointerfacial sciences including photonics, biosensors, chromatog., antifouling surfaces, biomedical devices, and cell culture tools.
28. 28
  Gottwald, D.; Likos, C. N.; Kahl, G.; Löwen, H. Phase Behavior of Ionic Microgels. Phys. Rev. Lett. 2004, 92, 068301 DOI: 10.1103/PhysRevLett.92.068301
  28
  Phase Behavior of Ionic Microgels
  Gottwald, D.; Likos, C. N.; Kahl, G.; Loewen, H.
  Physical Review Letters (2004), 92 (6), 068301/1-068301/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  The authors employ effective interaction potentials between spherical polyelectrolyte microgels to study theor. the structure, thermodn., and phase behavior of ionic microgel solns. Combining a genetic algorithm with accurate free energy calcns., they are able to perform an unrestricted search of candidate crystal structures. Hexagonal, body-centered orthogonal, and trigonal crystals are stable at high concns. and charges of the microgels, accompanied by reentrant melting behavior and fluid-fcc.-bcc. transitions below the overlap concn.
29. 29
  Sanz, E.; Valeriani, C.; Zaccarelli, E.; Poon, W. C. K.; Pusey, P. N.; Cates, M. E. Crystallization Mechanism of Hard Sphere Glasses. Phys. Rev. Lett. 2011, 106, 215701, DOI: 10.1103/PhysRevLett.106.215701
  29
  Crystallization Mechanism of Hard Sphere Glasses
  Sanz, Eduardo; Valeriani, Chantal; Zaccarelli, Emanuela; Poon, W. C. K.; Pusey, P. N.; Cates, M. E.
  Physical Review Letters (2011), 106 (21), 215701/1-215701/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  In supercooled liqs., vitrification generally suppresses crystn. Yet some glasses can still crystallize despite the arrest of diffusive motion. This ill-understood process may limit the stability of glasses, but its microscopic mechanism is not yet known. Here we present extensive computer simulations addressing the crystn. of monodisperse hard-sphere glasses at const. vol. (as in a colloid expt.). Multiple cryst. patches appear without particles having to diffuse more than one diam. As these patches grow, the mobility in neighboring areas is enhanced, creating dynamic heterogeneity with pos. feedback. The future crystn. pattern cannot be predicted from the coordinates alone: Crystn. proceeds by a sequence of stochastic micronucleation events, correlated in space by emergent dynamic heterogeneity.
30. 30
  Liu, Y.; Guan, Y.; Zhang, Y. Facile Assembly of 3D Binary Colloidal Crystals from Soft Microgel Spheres. Macromol. Rapid Commun. 2014, 35, 630– 634, DOI: 10.1002/marc.201300893
  30
  Facile Assembly of 3D Binary Colloidal Crystals from Soft Microgel Spheres
  Liu, Yang; Guan, Ying; Zhang, Yongjun
  Macromolecular Rapid Communications (2014), 35 (6), 630-634CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
  It still remains a big challenge to fabricate binary colloidal crystals (binary CCs) from hard colloidal spheres, although a lot of efforts have been made. Here, for the first time, binary CCs are assembled from soft hydrogel spheres, PNIPAM microgels, instead of hard spheres. Different from hard spheres, microgel binary CCs can be facilely fabricated by simply heating binary microgel dispersions to 37 °C and then allowing them to cool back to room temp. The formation of highly ordered structure is indicated by the appearance of an iridescent color and a sharp Bragg diffraction peak. Compared with hard sphere binary CCs, the assembly of PNIPAM microgel binary CCs is much simpler, faster and with a higher "atom" economy. The easy formation of PNIPAM microgel binary CC is attributed to the thermosensitivity and soft nature of the PNIPAM microgel spheres. In addn., PNIPAM microgel binary CCs can respond to temp. change, and their stop band can be tuned by changing the concn. of the dispersion.
31. 31
  Chen, M.; Zhang, Y.; Jia, S.; Zhou, L.; Guan, Y.; Zhang, Y. Photonic Crystals with a Reversibly Inducible and Erasable Defect State Using External Stimuli. Angew. Chem., Int. Ed. 2015, 54, 9257– 9261, DOI: 10.1002/anie.201503004
  31
  Photonic Crystals with a Reversibly Inducible and Erasable Defect State Using External Stimuli
  Chen, Mao; Zhang, Yapeng; Jia, Siyu; Zhou, Lin; Guan, Ying; Zhang, Yongjun
  Angewandte Chemie, International Edition (2015), 54 (32), 9257-9261CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The controlled introduction of artificial extrinsic defects is crit. to achieve the functions of photonic crystals. Smart defects capable of responding to external stimuli lead to more advanced applications. A microgel colloidal crystal with a defect state which could be induced and erased reversibly by external stimuli is reported. The crystal was assembled from poly(N-isopropylacrylamide) (PNIPAM) microgel and poly(Nisopropylacrylamide-co-acrylic acid) [P(NIPAM-AAc)] microgel of the same size. The resulting doped crystal does not exhibit a defect state in its stop band because of the similar optical properties of the dopant and the host. By increasing the pH value, the dopant P(NIPAM-AAc) spheres swell to a larger size and turn into real defects in the crystal, resulting in the appearance of defect state. Adjusting the pH value back restores the size of the dopant spheres, and erases the defect state. Temp., a 2nd external stimulus, could be used to induce and erase defect states of the crystal.
32. 32
  Debord, J. D.; Eustis, S.; Debord, S. B.; Lofye, M. T.; Lyon, L. A. Color-Tunable Colloidal Crystals from Soft Hydrogel Nanoparticles. Adv. Mater. 2002, 14, 658– 662, DOI: 10.1002/1521-4095(20020503)14:9<658::AID-ADMA658>3.0.CO;2-3
  32
  Color-tunable colloidal crystals from soft hydrogel nanoparticles
  Debord, Justin D.; Eustis, Susan; Debord, Saet Byul; Lofye, Mark T.; Lyon, L. Andrew
  Advanced Materials (Weinheim, Germany) (2002), 14 (9), 658-662CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH)
  A method for the formation of color-tunable colloidal crystals from soft thermoresponsive microgel particles, where kinetically trapped colloidal glasses are converted to ordered crystals via a particle-based vol. transition, is described. The annealing step allows the redn. of the polycrystallinity of cryst. assemblies and the prodn. of highly ordered materials. The microgel particles prepd. by free radical pptn. polymn. can be manipulated to form hydrogel colloidal crystals by taking advantage of a large magnitude vol. phase transition, which allows for annealing of the assembly. The lattice const. of the crystals and the wavelength of the resultant Bragg peak can be continuously tuned by varying the water content of the microgel pellet before annealing and crystn. This method is facilitated by the softness of the microgels and by the continuous temp.-induced phase transition showed by these particles. The tunability of the lattice spacing combined with the processability of the crystals may increase the utilization of periodic dielec. assemblies formed from colloidal precursors in a wide array of photonic applications.
33. 33
  Yunker, P. J.; Chen, K.; Gratale, M. D.; Lohr, M. A.; Still, T.; Yodh, A. G. Physics in Ordered and Disordered Colloidal Matter Composed of Poly(N-isopropylacrylamide) Microgel Particles. Rep. Prog. Phys. 2014, 77, 056601 DOI: 10.1088/0034-4885/77/5/056601
  33
  Physics in ordered and disordered colloidal matter composed of poly(N-isopropyl acrylamide) microgel particles
  Yunker, Peter J.; Chen, Ke; Gratale, Matthew D.; Lohr, Matthew A.; Still, Tim; Yodh, A. G.
  Reports on Progress in Physics (2014), 77 (5), 056601/1-056601/29CODEN: RPPHAG; ISSN:0034-4885. (IOP Publishing Ltd.)
  This review collects and describes expts. that employ colloidal suspensions to probe physics in ordered and disordered solids and related complex fluids. The unifying feature of this body of work is its clever usage of poly(N-isopropylacrylamide) (PNIPAM) microgel particles. These temp.-sensitive colloidal particles provide experimenters with a 'knob' for in situ control of particle size, particle interaction and particle packing fraction that, in turn, influence the structural and dynamical behavior of the complex fluids and solids. A brief summary of PNIPAM particle synthesis and properties is given, followed by a synopsis of current activity in the field. The latter discussion describes a variety of soft matter investigations including those that explore formation and melting of crystals and clusters, and those that probe structure, rearrangement and rheol. of disordered (jammed/glassy) and partially ordered matter. The review, therefore, provides a snapshot of a broad range of physics phenomenol. which benefits from the unique properties of responsive microgel particles.
34. 34
  Vlassopoulos, D.; Cloitre, M. Tunable Rheology of Dense Soft Deformable Colloids. Curr. Opin. Colloid Interface Sci. 2014, 19, 561– 574, DOI: 10.1016/j.cocis.2014.09.007
  34
  Tunable rheology of dense soft deformable colloids
  Vlassopoulos, Dimitris; Cloitre, Michel
  Current Opinion in Colloid & Interface Science (2014), 19 (6), 561-574CODEN: COCSFL; ISSN:1359-0294. (Elsevier Ltd.)
  In the last two decades, advances in synthetic, exptl. and modeling/simulation methodologies have considerably enhanced our understanding of colloidal suspension rheol. and put the field at the forefront of soft matter research. Recent accomplishments include the ability to tailor the flow of colloidal materials via controlled changes of particle microstructure and interactions. Whereas hard sphere suspensions have been the most widely studied colloidal system, there is no richer type of particles than soft colloids in this respect. Yet, despite the remarkable progress in the field, many outstanding challenges remain in our quest to link particle microstructure to macroscopic properties and eventually design appropriate soft composites. Addressing them will provide the route towards novel responsive systems with hierarchical structures and multiple functionalities. Here we discuss the key structural and rheol. parameters which det. the tunable rheol. of dense soft deformable colloids. We restrict our discussion to non-crystg. suspensions of spherical particles without electrostatic or enthalpic interactions.
35. 35
  Tang, S.; Hu, Z.; Cheng, Z.; Wu, J. Crystallization Kinetics of Thermosensitive Colloids Probed by Transmission Spectroscopy. Langmuir 2004, 20, 8858– 8864, DOI: 10.1021/la049203h
  35
  Crystallization Kinetics of Thermosensitive Colloids Probed by Transmission Spectroscopy
  Tang, Shijun; Hu, Zhibing; Cheng, Zhengdong; Wu, Jianzhong
  Langmuir (2004), 20 (20), 8858-8864CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
  The kinetics of crystn. of poly-N-isopropylacrylamide (PNIPAM) particles has been investigated using the UV-visible transmission spectroscopy. Since the particle size decreases with the increase in temp., microgel dispersions of different vol. fractions have been obtained by varying the temp. of a single sample. It is found that the rates of the change in crystallinity, the av. crystallite size, and the no. d. of crystallites at the most rapid stage over a certain time interval at various temps. can be described by the power-law relations. At 19 °C, the PNIPAM system behaves as a hard sphere system under microgravity. The hard sphere theory based on Monte Carlo simulation has been used as a ref. point to compare with conventional hard spheres, soft spheres, and PNIPAM spheres.
36. 36
  St. John Iyer, A.; Lyon, L. A. Self-Healing Colloidal Crystals. Angew. Chem., Int. Ed. 2009, 48, 4562– 4566, DOI: 10.1002/anie.200901670
  There is no corresponding record for this reference.
37. 37
  Vlassopoulos, D. Colloidal Star Polymers: Models for Studying Dynamically Arrested States in Soft Matter. J. Polym. Sci., Part B: Polym. Phys. 2004, 42, 2931– 2941, DOI: 10.1002/polb.20152
  37
  Colloidal star polymers: Models for studying dynamically arrested states in soft matter
  Vlassopoulos, Dimitris
  Journal of Polymer Science, Part B: Polymer Physics (2004), 42 (16), 2931-2941CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
  A review. The use of well-defined macromol. assemblies with tunable interactions represents the key for exploring the regime of soft-material behavior between hard spheres and polymer coils. Colloidal stars are ideal choices for such a formidable task and esp. for shedding light on the formation and properties of dynamically arrested states. In this brief review, the authors demonstrate the rich variety of kinetic frustration phenomena that can be encountered with such ultrasoft particles. The authors address 2 specific examples in particular: the reversible vitrification upon heating and the melting of star gels upon the addn. of linear polymers.
38. 38
  Cho, J. K.; Meng, Z.; Lyon, L. A.; Breedveld, V. Tunable Attractive and Repulsive Interactions Between pH-Responsive Microgels. Soft Matter 2009, 5, 3599– 3602, DOI: 10.1039/b912105f
  38
  Tunable attractive and repulsive interactions between pH-responsive microgels
  Cho, Jae-Kyu; Meng, Zhiyong; Lyon, L. Andrew; Breedveld, Victor
  Soft Matter (2009), 5 (19), 3599-3602CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
  We report direct measurements of the pairwise interparticle potential between poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-co-AAc) colloidal microgels as a function of pH, as detd. through Ornstein-Zernike anal. of the pair distribution function of quasi-2D dil. colloidal suspensions. The interaction potential ranges from purely repulsive at high pH due to electrosteric interactions to weakly attractive at low pH due to hydrogen bonding, which explains previous observations on the unique phase behavior of these particles in concd. suspensions.
39. 39
  Lyon, L. A.; Meng, Z.; Singh, N.; Sorrell, C. D.; John, A. St. Thermoresponsive Microgel-Based Materials. Chem. Soc. Rev. 2009, 38, 865– 874, DOI: 10.1039/b715522k
  39
  Thermoresponsive microgel-based materials
  Lyon, L. Andrew; Meng, Zhiyong; Singh, Neetu; Sorrell, Courtney D.; St. John, Ashlee
  Chemical Society Reviews (2009), 38 (4), 865-874CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
  A review. With the continued development of thermoresponsive colloidal hydrogel particles, a no. of groups have begun to exploit their properties to create dynamic materials self-assembled from those components. The fundamental details of how those building blocks are assembled, the component functionality, and the geometry or length-scales present in the assemblies contribute to the behavior of the resultant material. In this tutorial review, we examine recent progress in the assembly of responsive hydrogel colloids in two and three dimensions, highlighting their potential applications, esp. in the domain of biotechnol.
40. 40
  Hu, Z.; Huang, G. A New Route to Crystalline Hydrogels, Guided by a Phase Diagram. Angew. Chem., Int. Ed. 2003, 42, 4799– 4802, DOI: 10.1002/anie.200351326
  40
  A new route to crystalline hydrogels, guided by a phase diagram
  Hu, Zibing; Huang, Gang
  Angewandte Chemie, International Edition (2003), 42 (39), 4799-4802CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Hydrogels are well known for applications that include controlled drug delivery, artificial muscles, devices, and sensors. Thermally sensitive nanoparticles in colloidal glasses can be converted into ordered crystals by particle-based vol. transition and a cryst. hydrogel could be obtained by initiating the crystn. process near the colloidal crystal melting temp. while subsequently bonding the PNIPAM-co-allylamine particles below the glass-transition temp. Monodisperse nanoparticles of PNIPAM-co-allylamine were synthesized using a pptn. polymn. method. The phase diagram of their water dispersion was measured.
41. 41
  Hoare, T.; Pelton, R. Highly pH and Temperature Responsive Microgels Functionalized with Vinylacetic Acid. Macromolecules 2004, 37, 2544– 2550, DOI: 10.1021/ma035658m
  41
  Highly pH and Temperature Responsive Microgels Functionalized with Vinylacetic Acid
  Hoare, Todd; Pelton, Robert
  Macromolecules (2004), 37 (7), 2544-2550CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  Temp.-responsive microgels based on poly(N-isopropylacrylamide) (PNIPAM) and functionalized with vinylacetic acid (VAA) are obsd. to exhibit a host of novel swelling responses compared with equally functionalized microgels prepd. using the conventional acrylic acid (AA) and methacrylic acid (MAA) comonomers. VAA-NIPAM microgels are ionized over a narrow pH range and show functional group pKa values which are independent of the degree of ionization. Ionization induces a much larger swelling response in VAA-NIPAM microgels than in the conventional microgels; upon ionization at physiol. temp., VAA-NIPAM swells 3 times more than either AA-NIPAM or MAA-NIPAM. VAA-NIPAM microgels also display sharp, PNIPAM-like thermal deswelling profiles when protonated but, upon ionization, undergo no vol. phase transition up to at least 70 °C. The highly responsive and tunable ionization and swelling profiles obsd. for VAA-NIPAM are consistent with the tendency of VAA to behave as a chain transfer agent, resulting in the incorporation of a large no. of well-sepd. VAA units on highly mobile chain ends at or near the microgel surface. VAA-NIPAM microgels may thus be ideal for use in biomol. sepn., medical diagnostics, and biodelivery applications in which sharp responses to multiple environmental stimuli are required.
42. 42
  Liu, Y. Y.; Liu, X. Y.; Yang, J. M.; Lin, D. L.; Chen, X.; Zha, L. S. Investigation of Ag Nanoparticles Loading Temperature Responsive Hybrid Microgels and their Temperature Controlled Catalytic Activity. Colloids Surf., A 2012, 393, 105– 110, DOI: 10.1016/j.colsurfa.2011.11.007
  42
  Investigation of Ag nanoparticles loading temperature responsive hybrid microgels and their temperature controlled catalytic activity
  Liu, Yun-Yun; Liu, Xiao-Yun; Yang, Jian-Mao; Lin, Dan-Li; Chen, Xiao; Zha, Liu-Sheng
  Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2012), 393 (), 105-110CODEN: CPEAEH; ISSN:0927-7757. (Elsevier B.V.)
  Silver (Ag) nanoparticles loading temp. responsive hybrid microgels were readily prepd. by in situ redn. of Ag+ ions coordinated into poly(N-isopropylacrylamide) microgels. The wt. percentage content of the entrapped Ag nanoparticles measured by thermogravity anal. tops 25%, and their av. particle sizes detd. by transmission electron microscopy are within the range from 8-11 nm. The results obtained by X-ray diffraction exhibit that the Ag nanoparticles are of face-centered cubic single crystal structure. The particle sizes of the hybrid microgels decrease sharply with environmental temp. increasing from 30-35 °C, and their surface plasmon resonance absorption wavelengths are pronouncedly red-shifted within the same temp. range. The catalytic reactivity of the Ag nanoparticles loading hybrid microgels can be tunable with 4 stages of change vs. temp. from 20 to 45 °C.
43. 43
  Backes, S.; Witt, M. U.; Roeben, E.; Kuhrts, L.; Aleed, S.; Schmidt, A. M.; von Klitzing, R. Loading of PNIPAM Based Microgels with CoFe2O4 Nanoparticles and Their Magnetic Response in Bulk and at Surfaces. J. Phys. Chem. B 2015, 119, 12129– 12137, DOI: 10.1021/acs.jpcb.5b03778
  43
  Loading of PNIPAM Based Microgels with CoFe2O4 Nanoparticles and Their Magnetic Response in Bulk and at Surfaces
  Backes, Sebastian; Witt, Marcus U.; Roeben, Eric; Kuhrts, Lukas; Aleed, Sarah; Schmidt, Annette M.; von Klitzing, Regine
  Journal of Physical Chemistry B (2015), 119 (36), 12129-12137CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
  The present paper addresses the loading of thermoresponsive poly-N-isopropylacrylamide (PNIPAM) based microgel particles with magnetic nanoparticles (MNP: CoFe2O4@PAA (PAA = poly(acrylic acid))) and their response to an external magnetic field. The MNP uptake is analyzed by TEM. Obviously, the charge combination of MNP and microgels plays an important role for the MNP uptake, but it does not explain the whole uptake process. The MNP uptake results in changes of size and electrophoretic mobility, which was studied by dynamic light scattering (DLS) and a Zetasizer. The microgels loaded with MNP preserve their thermosensitivity, and they show magnetic separability and are considered as magnetic microgels. After adsorption at a surface the magnetic microgels were studied with a scanning force microscope and indentation expts. The magnetic microgels show an elongation along the magnetic field parallel to the surface while the height of the microgels (perpendicular to the surface and to the magnetic field) is compressed. This result is in good agreement with simulations of vol. change of ferrogels in a magnetic field.
44. 44
  Mohanty, P. S.; Bagheri, P.; Nöjd, S.; Yethiraj, A.; Schurtenberger, P. Multiple Path-Dependent Routes for Phase-Transition Kinetics in Thermoresponsive and Field-Responsive Ultrasoft Colloids. Phys. Rev. X 2015, 5, 011030 DOI: 10.1103/PhysRevX.5.011030
  There is no corresponding record for this reference.
45. 45
  Meijer, J.-M.; Pal, A.; Ouhajji, S.; Lekkerkerker, H. N. W.; Philipse, A. P.; Petukhov, A. V. Observation of Solid–Solid Transitions in 3D Crystals of Colloidal Superballs. Nat. Commun. 2017, 8, 14352, DOI: 10.1038/ncomms14352
  45
  Observation of solid-solid transitions in 3D crystals of colloidal superballs
  Meijer, Janne-Mieke; Pal, Antara; Ouhajji, Samia; Lekkerkerker, Henk N. W.; Philipse, Albert P.; Petukhov, Andrei V.
  Nature Communications (2017), 8 (), 14352CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
  Self-organization in anisotropic colloidal suspensions leads to a fascinating range of crystal and liq. crystal phases induced by shape alone. Simulations predict the phase behavior of a plethora of shapes while exptl. realization often lags behind. Here, we present the exptl. phase behavior of superball particles with a shape in between that of a sphere and a cube. In particular, we observe the formation of a plastic crystal phase with translational order and orientational disorder, and the subsequent transformation into rhombohedral crystals. Moreover, we uncover that the phase behavior is richer than predicted, as we find two distinct rhombohedral crystals with different stacking variants, namely hollow-site and bridge-site stacking. In addn., for slightly softer interactions we observe a solid-solid transition between the two. Our investigation brings us one step closer to ultimately controlling the exptl. self-assembly of superballs into functional materials, such as photonic crystals.
46. 46
  Lyon, L. A.; Debord, J. D.; Debord, S. B.; Jones, C. D.; McGrath, J. G.; Serpe, M. J. Microgel Colloidal Crystals. J. Phys. Chem. B 2004, 108, 19099– 19108, DOI: 10.1021/jp048486j
  46
  Microgel Colloidal Crystals
  Lyon, L. Andrew; Debord, Justin D.; Debord, Saet Byul; Jones, Clinton D.; McGrath, Jonathan G.; Serpe, Michael J.
  Journal of Physical Chemistry B (2004), 108 (50), 19099-19108CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
  A review. Colloidal crystals assembled from stimuli-sensitive hydrogel particles composed largely of the thermoresponsive polymer poly(N-isopropylacrylamide) display unusual phase behavior because of the inherent "softness" of their interaction potentials as well as the particle thermoresponsivity. A review on use of such oft-sphere building blocks in the construction of colloidal crystals. We describe the utility of temp.-induced vol. phase transitions in controlling the crystn. and melting of the colloidal crystals. For example, it is proposed that multiple weak attractive interactions between particles can drive crystn. at particle concns. well below the hard-sphere f.p. The utility of soft-sphere crystals in the development of new photonic materials is presented in examples of laser direct writing and photopatterning of colloidal crystals based on a photothermally directed crystn. method.
47. 47
  Paloli, D.; Mohanty, P. S.; Crassous, J. J.; Zaccarelli, E.; Schurtenberger, P. Fluid–Solid Transitions in Soft-Repulsive Colloids. Soft Matter 2013, 9, 3000– 3004, DOI: 10.1039/c2sm27654b
  47
  Fluid-solid transitions in soft-repulsive colloids
  Paloli, Divya; Mohanty, Priti S.; Crassous, Jerome J.; Zaccarelli, Emanuela; Schurtenberger, Peter
  Soft Matter (2013), 9 (11), 3000-3004CODEN: SMOABF; ISSN:1744-683X. (Royal Society of Chemistry)
  We use monodisperse poly(N-isopropylacrylamide) (PNIPAM) microgels as a model system for soft repulsive colloids and study their d. dependent structural ordering and phase behavior using confocal laser scanning microscopy (CLSM). The expts. are carried out at low temps., where the particles are in the swollen state and interact via a Hertzian potential, evidenced through a quant. comparison of the pair correlation functions g(r) obtained with CLSM and computer simulations. We worked over a broad range of effective vol. fractions [phis]eff below and above close packing ([phis]cp). CLSM allows us to identify a fluid-glass and a fluid-crystal transition by looking at the structure and dynamics of the suspensions. The d. dependent g(r) values exhibit clearly visible anomalies at high [phis]eff > [phis]cp which we interpret as a structural signature of the glass transition related to the particle softness. These results are discussed in light of the previously studied phase behavior of colloidal systems interacting with hard and soft repulsive interaction potentials.
48. 48
  Dulle, M.; Jaber, S.; Rosenfeldt, S.; Radulescu, A.; Förster, S.; Mulvaney, P.; Karg, M. Plasmonic Gold–poly(N-isopropylacrylamide) Core–Shell Colloids with Homogeneous Density Profiles: a Small Angle Scattering Study. Phys. Chem. Chem. Phys. 2015, 17, 1354– 1367, DOI: 10.1039/C4CP04816D
  48
  Plasmonic gold-poly(N-isopropylacrylamide) core-shell colloids with homogeneous density profiles: a small angle scattering study
  Dulle, Martin; Jaber, Sarah; Rosenfeldt, Sabine; Radulescu, Aurel; Foerster, Stephan; Mulvaney, Paul; Karg, Matthias
  Physical Chemistry Chemical Physics (2015), 17 (2), 1354-1367CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  Coating metal nanocrystals with responsive polymers provides a model case of smart, functional materials, where the optical properties can be modulated by external stimuli. However the optical response is highly sensitive to the polymer shell morphol., thickness and dielec. contrast. In this paper we study the nature of crosslinked, thermoresponsive polymer shells for the first time using four different scattering approaches to elucidate the d. profile of the shells. Each scattering method provides unique information about the temp.-induced changes of shell thickness in terms of hydrodynamic radius and radius of gyration, the pair-distance distribution functions of the shells as well as the dynamic network fluctuations. Only a combination of these different scattering techniques allows to develop a morphol. model of the core-shell particles. We further demonstrate control of the crosslinker distribution in core-shell synthesis by semi-batch pptn. copolymn. Conducting the polymn. in three steps, we show for the first time that the polymer shell thickness can be successively increased without affecting the shell morphol. and response behavior.
49. 49
  Fasolo, M.; Sollich, P. Equilibrium Phase Behavior of Polydisperse Hard Spheres. Phys. Rev. Lett. 2003, 91, 068301 DOI: 10.1103/PhysRevLett.91.068301
  49
  Equilibrium Phase Behavior of Polydisperse Hard Spheres
  Fasolo, Moreno; Sollich, Peter
  Physical Review Letters (2003), 91 (6), 068301/1-068301/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  We calc. the phase behavior of hard spheres with size polydispersity, using accurate free energies for the fluid and solid phases. Cloud and shadow curves are found exactly by the moment free energy method, but we also compute the complete phase diagram, taking full account of fractionation. In contrast to earlier, simplified treatments we find no point of equal concn. between fluid and solid or reentrant melting at higher densities. Rather, the fluid cloud curve continues to the largest polydispersity that we study (14%); from the equil. phase behavior a terminal polydispersity can thus be defined only for the solid, where we find it to be around 7%. At sufficiently large polydispersity, fractionation into several solid phases can occur, consistent with previous approx. calcns.; we find, in addn., that coexistence of several solids with a fluid phase is also possible.
50. 50
  Eckert, T.; Bartsch, E. Re-entrant Glass Transition in a Colloid-Polymer Mixture with Depletion Attractions. Phys. Rev. Lett. 2002, 89, 125701, DOI: 10.1103/PhysRevLett.89.125701
  50
  Re-entrant glass transition in a colloid-polymer mixture with depletion attractions
  Eckert, T.; Bartsch, E.
  Physical Review Letters (2002), 89 (12), 125701/1-125701/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  Modeling and light scattering expts. indicate that introducing short-ranged attractions to a colloid suspension of nearly hard spheres by addn. of a free polymer produces new glass-transition phenomena. The system is a binary mixt. of polystyrene micro-network spheres with highly crosslinked chains swollen in th good, isorefractive solvent 2-ethyl-naphthalene. A dramatic acceleration was obsd., of the d. fluctuations amounting to the melting of a colloidal glass. Upon increasing the strength of the attractions the system freezes into another nonergodic state sharing some qual. features with gel states occurring at lower colloid packing fractions. This re-entrant glass transition is in qual. agreement with recent theor. predictions.
51. 51
  Stukowski, A. Visualization and Analysis of Atomistic Simulation Data with OVITO - the Open Visualization Tool. Modell. Simul. Mater. Sci. Eng. , 2010, 18, 015012 DOI: 10.1088/0965-0393/18/1/015012 .
  There is no corresponding record for this reference.
52. 52
  Horst, N.; Travesset, A. Prediction of Binary Nanoparticle Superlattices from Soft Potentials. J. Chem. Phys. 2016, 144, 014502 DOI: 10.1063/1.4939238
  52
  Prediction of binary nanoparticle superlattices from soft potentials
  Horst, Nathan; Travesset, Alex
  Journal of Chemical Physics (2016), 144 (1), 014502/1-014502/12CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  Driven by the hypothesis that a sufficiently continuous short-ranged potential is able to account for shell flexibility and phonon modes and therefore provides a more realistic description of nanoparticle interactions than a hard sphere model, the authors compute the solid phase diagram of particles of different radii interacting with an inverse power law potential. From a pool of 24 candidate lattices, the free energy is optimized with respect to addnl. internal parameters and the p-exponent, detg. the short-range properties of the potential, is varied between p = 12 and p = 6. The phase diagrams contain the phases found in ongoing self-assembly expts., including DNA programmable self-assembly and nanoparticles with capping ligands assembled by evapn. from an org. solvent. The resulting phase diagrams can be mapped quant. to existing expts. as a function of only two parameters: Nanoparticle radius ratio (γ) and softness asymmetry. (c) 2016 American Institute of Physics.
53. 53
  Yethiraj, A.; Wouterse, A.; Groh, B.; van Blaaderen, A. Nature of an Electric-Field-Induced Colloidal Martensitic Transition. Phys. Rev. Lett. 2004, 92, 058301 DOI: 10.1103/PhysRevLett.92.058301
  53
  Nature of an Electric-Field-Induced Colloidal Martensitic Transition
  Yethiraj, Anand; Wouterse, Alan; Groh, Benito; van Blaaderen, Alfons
  Physical Review Letters (2004), 92 (5), 058301/1-058301/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  We study the properties of a solid-solid close-packed to body-centered tetragonal transition in a colloidal suspension via fluorescence confocal laser scanning microscopy, in three dimensions and in real space. This structural transformation is driven by a subtle competition between gravitational and elec. dipolar field energy, the latter being systematically varied via an external elec. field. The transition threshold depends on the local depth in the colloidal sediment. Structures with order intermediate between close-packed and body-centered tetragonal were obsd., with these intermediate structures also being stable and long lived. This is essentially a colloidal analog of an "at.-level" interfacial structure. We find qual. agreement with theory (based purely on energetics). Quant. differences can be attributed to the importance of entropic effects.
54. 54
  Steinhardt, P. J.; Nelson, D. R.; Ronchetti, M. Bond-Orientational Order in Liquids and Glasses. Phys. Rev. B: Condens. Matter Mater. Phys. 1983, 28, 784, DOI: 10.1103/PhysRevB.28.784
  54
  Bond-orientational order in liquids and glasses
  Steinhardt, Paul J.; Nelson, David R.; Ronchetti, Marco
  Physical Review B: Condensed Matter and Materials Physics (1983), 28 (2), 784-805CODEN: PRBMDO; ISSN:0163-1829.
  Bond orientational order in mol. dynamics simulations of supercooled liqs. and in models of metallic glasses is studied. Quadratic and 3rd-order invariants formed from bond spherical harmonics allow quant. measures of cluster symmetries in these systems. A state with short-range translational order, but extended correlations in the orientations of particle clusters, starts to develop about 10% below the equil. melting temp. in a supercooled Lennard-Jones liq. The order is predominantly icosahedral, although there is also a cubic component which we attribute to the periodic boundary conditions. Results are obtained for liqs. cooled in an icosahedral pair potential as well. Only a modest amt. of orientational order appears in a relaxed Finney dense-random-packing model. In contrast, essentially perfect icosahedral bond correlations are found in alternative "amorphon" cluster models of glass structure.
55. 55
  Lechner, W.; Dellago, C. Accurate Determination of Crystal Structures Based on Averaged Local Bond Order Parameters. J. Chem. Phys. 2008, 129, 114707, DOI: 10.1063/1.2977970
  55
  Accurate determination of crystal structures based on averaged local bond order parameters
  Lechner, Wolfgang; Dellago, Christoph
  Journal of Chemical Physics (2008), 129 (11), 114707/1-114707/5CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  Local bond order parameters based on spherical harmonics, also known as Steinhardt order parameters, are often used to det. crystal structures in mol. simulations. Here we propose a modification of this method in which the complex bond order vectors are averaged over the first neighbor shell of a given particle and the particle itself. As demonstrated using soft particle systems, this averaging procedure considerably improves the accuracy with which different crystal structures can be distinguished. (c) 2008 American Institute of Physics.
56. 56
  Immink, J. N.; Maris, J. J. E.; Crassous, J. J.; Stenhammar, J.; Schurtenberger, P. Reversible Formation of Thermoresponsive Binary Particle Gels with Tunable Structural and Mechanical Properties. ACS Nano 2019, 13, 3292– 3300, DOI: 10.1021/acsnano.8b09139
  56
  Reversible Formation of Thermoresponsive Binary Particle Gels with Tunable Structural and Mechanical Properties
  Immink, Jasper N.; Maris, J. J. Erik; Crassous, Jerome J.; Stenhammar, Joakim; Schurtenberger, Peter
  ACS Nano (2019), 13 (3), 3292-3300CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
  We investigate the collective behavior of suspended thermoresponsive microgels that expel solvent and subsequently decrease in size upon heating. Using a binary mixt. of differently thermoresponsive microgels, we demonstrate how distinctly different gel structures form, depending on the heating profile used. Confocal laser scanning microscopy (CLSM) imaging shows that slow heating ramps yield a core-shell network through sequential gelation, while fast heating ramps yield a random binary network through homogelation. Here, secondary particles are shown to aggregate in a monolayer fashion upon the first gel, which can be qual. reproduced through Brownian dynamics simulations using a model based on a temp.-dependent interaction potential incorporating steric repulsion and van der Waals attraction. Through oscillatory rheol. it is shown that secondary microgel deposition enhances the structural integrity of the previously formed single species gel, and the final structure exhibits higher elastic and loss moduli than its compositionally identical homogelled counterpart. Furthermore, we demonstrate that aging processes in the scaffold before secondary microgel deposition govern the final structural properties of the bigel, which allows a detailed control over these properties. Our results thus demonstrate how the temp. profile can be used to finely control the structural and mech. properties of these highly tunable materials.
57. 57
  Appel, J.; de Lange, N.; van der Kooij, H. M.; van de Laar, T.; ten Hove, J. B.; Kodger, T. E.; Sprakel, J. Temperature Controlled Sequential Gelation in Composite Microgel Suspensions. Part. Part. Syst. Char. 2015, 32, 764– 770, DOI: 10.1002/ppsc.201500007
  57
  Temperature Controlled Sequential Gelation in Composite Microgel Suspensions
  Appel, Jeroen; de Lange, Niek; van der Kooij, Hanne M.; van de Laar, Ties; ten Hove, Jan Bart; Kodger, Thomas E.; Sprakel, Joris
  Particle & Particle Systems Characterization (2015), 32 (7), 764-770CODEN: PPCHEZ; ISSN:1521-4117. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Depending on the vol. fraction and interparticle interactions, colloidal suspensions can exhibit a variety of phys. states, ranging from fluids, crystals, and glasses to gels. For microgel particles made of thermoresponsive polymers, both parameters can be tuned using environmental parameters such as temp. and ionic strength, making them excellent systems to exptl. study state transitions in colloidal suspensions. Using a simple two-step synthesis it is shown that the properties of composite microgels, with a fluorescent latex core and a responsive microgel shell, can be finely tuned. With this system the transitions between glass, liq., and gel states for suspensions composed of a single species are explored. Finally, a suspension of two species of microgels is demonstrated, with different transition temps., gels in a sequential manner. Upon increasing temp. a distinct core-sheath structure is formed with a primary gel composed of the species with lowest transition temp., which acts as a scaffold for the aggregation of the second species.
58. 58
  Rauh, A.; Honold, T.; Karg, M. Seeded Precipitation Polymerization for the Synthesis of Gold-Hydrogel Core-Shell Particles: the Role of Surface Functionalization and Seed Concentration. Colloid Polym. Sci. 2016, 294, 37– 47, DOI: 10.1007/s00396-015-3782-6
  58
  Seeded precipitation polymerization for the synthesis of gold-hydrogel core-shell particles: the role of surface functionalization and seed concentration
  Rauh, Astrid; Honold, Tobias; Karg, Matthias
  Colloid and Polymer Science (2016), 294 (1), 37-47CODEN: CPMSB6; ISSN:0303-402X. (Springer)
  Polymer encapsulation is an important pathway to stabilize inorg. nanoparticles, allow their phase transfer to different media, and access inter-particle distance control in particle assembly. In the past, hydrogels were shown to be a versatile encapsulation material offering rather thick polymeric shells through free radical pptn. polymn. In this work, we systematically investigate the influence of nanoparticle surface functionalization and concn. on the formation of core-shell microgels. Spherical gold nanoparticles are used as seeds in the radical polymn. of N-isopropylacrylamide and N,N'-methylenebisacrylamide. We find that the encapsulation occurs via pptn. of oligomers/polymers onto the seed particle surface, independent of the presence of polymerizable groups. Furthermore, we identify the seed concn. regime where almost exclusively core-shell particles are formed. In this concn. range, the hydrogel thickness is precisely controllable by the amt. of seeds. Monitoring the polymns. in situ by dynamic light scattering and absorbance spectroscopy provides first insights into the encapsulation mechanism and its time dependence.
59. 59
  Sato, J.; Breedveld, V. Transient Rheology of Solvent-Responsive Complex Fluids by Integrating Microrheology and Microfluidics. J. Rheol. 2006, 50, 1– 19, DOI: 10.1122/1.2135329
  59
  Transient rheology of solvent-responsive complex fluids by integrating microrheology and microfluidics
  Sato, Jun; Breedveld, Victor
  Journal of Rheology (New York, NY, United States) (2006), 50 (1), 1-19CODEN: JORHD2; ISSN:0148-6055. (American Institute of Physics)
  A new microrheol. set-up which allows to quant. measure the transient rheol. properties of solvent-responsive complex fluids was constructed by integrating particle tracking microrheol. and microfluidics. The dialysis cell consists of a reservoir, porous dialysis membrane, and sample chamber. Solvent mols. can freely diffuse between the reservoir and the sample chamber while macromol. sample components are trapped in the sample chamber with a rigid semipermeable dialysis membrane. The design enables manipulation of the solvent compn. in the sample chamber by simply switching the fluid compn. in the reservoir. Validation expts. for solvent diffusion in the dialysis cell showed good agreement with numerical solns. of the transport equations and confirmed that the solvent compn. in a sample can be changed in a controlled and predictable fashion within a few minutes due to the small device dimensions. For aq. solns. of sodium alginate and sodium polystyrene sulfonate, transient rheol. properties were measured in response to changes in salt concn. The results showed that the dialysis cell is a useful and versatile tool to study the response of complex fluids to reversible changes in solvent compn.
60. 60
  Crocker, J. C.; Grier, D. G. Methods of Digital Video Microscopy for Colloidal Studies. J. Colloid Interface Sci. 1996, 179, 298– 310, DOI: 10.1006/jcis.1996.0217
  60
  Methods of digital video microscopy for colloidal studies
  Crocker, John C.; Grier, David G.
  Journal of Colloid and Interface Science (1996), 179 (1), 298-310CODEN: JCISA5; ISSN:0021-9797. (Academic)
  A set is described of image processing algorithms for extg. quant. data from digitized video microscope images of colloidal suspensions. In a typical application, these direct imaging techniques can locate submicrometer spheres to within 10 nm in the focal plane and 150 nm in depth. By combining information from a sequence of video images into single-particle trajectories makes possible measurements of quantities of fundamental and practical interest such as diffusion coeffs. and pair-wise interaction potentials. The measurements were describe in detail combine the outstanding resoln. of digital imaging with to obtain highly accurate and reproducible results very rapidly.
61. 61
  Bergman, M. J.; Garting, T.; Schurtenberger, P.; Stradner, A. Experimental Evidence for a Cluster Glass Transition in Concentrated Lysozyme Solutions. J. Phys. Chem. B 2019, 123, 2432– 2438, DOI: 10.1021/acs.jpcb.8b11781
  61
  Experimental Evidence for a Cluster Glass Transition in Concentrated Lysozyme Solutions
  Bergman, Maxime J.; Garting, Tommy; Schurtenberger, Peter; Stradner, Anna
  Journal of Physical Chemistry B (2019), 123 (10), 2432-2438CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)
  Lysozyme is known to form equil. clusters at pH ≈ 7.8 and at low ionic strength as a result of a mixed potential. While this cluster formation and the related dynamic and static structure factors have been extensively investigated, its consequences on the macroscopic dynamic behavior expressed by the zero shear viscosity η0 remain controversial. Here we present results from a systematic investigation of η0 using two complementary passive microrheol. techniques, dynamic light scattering based tracer microrheol., and multiple particle tracking using confocal microscopy. The combination of these techniques with a simple but effective evapn. approach allows for reaching concns. close to and above the arrest transition in a controlled and gentle way. We find a strong increase of η0 with increasing vol. fraction .vphi. with an apparent divergence at .vphi. ≈ 0.35, and unambiguously demonstrate that this is due to the existence of an arrest transition where a cluster glass forms. These findings demonstrate the power of tracer microrheol. to investigate complex fluids, where weak temporary bonds and limited sample vols. make measurements with classical rheol. challenging.
62. 62
  Mohanty, P. S.; Paloli, D.; Crassous, J. J.; Zaccarelli, E.; Schurtenberger, P. Effective Interactions between Soft-Repulsive Colloids: Experiments, Theory, and Simulations. J. Chem. Phys. 2014, 140, 094901 DOI: 10.1063/1.4866644
  62
  Effective interactions between soft-repulsive colloids: Experiments, theory, and simulations
  Mohanty, Priti S.; Paloli, Divya; Crassous, Jerome J.; Zaccarelli, Emanuela; Schurtenberger, Peter
  Journal of Chemical Physics (2014), 140 (9), 094901/1-094901/9CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  We describe a combined exptl., theor., and simulation study of the structural correlations between crosslinked highly monodisperse and swollen Poly(N-isopropylacrylamide) microgel dispersions in the fluid phase in order to obtain the effective pair-interaction potential between the microgels. The d.-dependent exptl. pair distribution functions g(r)'s are deduced from real space studies using fluorescent confocal microscopy and compared with integral equation theory and mol. dynamics computer simulations. We use a model of Hertzian spheres that is capable to well reproduce the exptl. pair distribution functions throughout the fluid phase, having fixed the particle size and the repulsive strength. Theor., a monodisperse system is considered whose properties are calcd. within the Rogers-Young closure relation, while in the simulations the role of polydispersity is taken into account. We also discuss the various effects arising from the finite resoln. of the microscope and from the noise coming from the fast Brownian motion of the particles at low densities, and compare the information content from data taken in 2D and 3D through a comparison with the corresponding simulations. Finally different potential shapes, recently adopted in studies of microgels, are also taken into account to assess which ones could also be used to describe the structure of the microgel fluid. (c) 2014 American Institute of Physics.
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- Experimental RDFs compared to theoretical AuCu RDF; experimental RDFs compared to theoretical CsCl RDF; experimental RDFs compared to theoretical NaCl RDF; obtained bond order parameters for all particles at 2.0 × 10^–3 M KCl; obtained bond order parameters for all particles at 1.25 × 10^–3 M KCl (PDF)
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Crystal-to-Crystal Transitions in Binary Mixtures of Soft Colloids
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Crystal-to-Crystal Transitions in Binary Mixtures of Soft Colloids
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