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Alloy structures for binary mixtures of different sizes of monodisperse polystyrene spheres at sedimentation equilibrium and in deionized suspensions are studied by the reflection spectrum method and ultramicroscopic observation. Substitutional solid solution (sss)-like alloy structures form in mixtures of D1C25(85 nm in diameter) and D1C27 (91 nm). When D1C25 and D1B76 (109 nm) are mixed, the structures are eutectic mixtures of sss-type lattices and the MgCu2-type super lattices. The alloy structures of D1C25 and D1B72 (137 nm) spheres are the eutectic mixtures of (1) sss-like lattices, (2) MgCu2-type super lattices, (3) fcc crystals of D1B72 spheres, and (4) crystals of D1C25 spheres. D1C25 and D1B41 (173 nm) suspensions are also eutectic mixtures of (1) NaZn13-type super lattices, (2) D1C25 lattices, and (3) lattices of D1B41 spheres. These dramatic changes in the alloy structures depending on the combination of the spheres are explained reasonably by the changes in the effective size ratio (effective size of small spheres containing the electrical double layer thickness against that of large spheres) and the segregation effect. The intersphere distances in the alloy structures agree with the effective sizes of spheres including the Debye-screening length. The elastic moduli of the alloy structures are between 18 and 108 Pa. These results are consistent with the significant role played by the electrical double layers under the influence of purely electrostatic repulsion in the effective hard-sphere model. [ABSTRACT FROM AUTHOR]

Studies the ordering of deionized polystyrene colloids in a sedimentation equilibrium. Distance distribution function; Intersphere distances in the liquid-like and crystal-like structures; Electrostatic interparticle repulsion and elongated Debye-screening length around the spheres.

A metallurgical microscope is used to directly observe the ordered structures of colloidal silica spheres (340 nm in diameter, specific gravity=1.58) in sedimentation equilibrium and in aqueous suspensions. The two-dimensional distance distribution function is obtained for the crystal-like structures. The center-to-center interparticle distances (2Dexp) in the hexagonal ordering increase with time after the sample is set into the cell, and reach equilibrium values after ∼10 days, which shows that complete deionization is essential to get reliable data for 2Dexp. 2Dexp continues to decrease as the initial concentration of the spheres increases and from these data Young’s modulus for the ordered lattices is estimated to be 0.30 Pa. The way 2Dexp is influenced by the concentration and ionic strength shows that electrostatic interparticle repulsion and the elongated Debye-screening length around the spheres are both essential for the ordering. [ABSTRACT FROM AUTHOR]

A metallurgical microscope is used to directly observe the ordered structures of heavy and monodisperse polystyrene-type spheres (specific gravity=1.50) in sedimentation equilibrium and in organic solvent aqueous mixtures. Eight kinds of water miscible organic solvents, i.e., methanol, ethanol, propanol, 1,4-dioxane, ethylene glycol, propylene glycol, N-methylformamide (NMF), and N-methylacetamide (NMA) are used. The center-to-center interparticle distances (D) in the hexagonal ordering increase by the addition of organic solvents of dielectric constants lower than that of water, whereas D decreases in the presence of NMF or NMA, which has a dielectric constant higher than that of water. Young’s modulus for the ordered lattices is estimated to be from 0.44 to 1.5 Pa in methanol (0 to 30 vol %) aqueous mixtures. These results show that electrostatic interparticle repulsion and the elongated Debye-screening length around the spheres are essential for the ordering. [ABSTRACT FROM AUTHOR]

Viscosities of colloidal spheres, i.e., colloidal silica (diameter 8 and 45 nm) and monodisperse polystyrene latices (diameter 85 to 780 nm), are measured in deionized (‘‘salt-free’’) suspensions and in the presence of a small amount of NaCl. The reduced viscosities (specific viscosity divided by concentration) of deionized silica (diameter 8 nm) are much higher than would be expected by Einstein’s prediction and decrease sharply with increasing concentration. A sharp peak is observed in the reduced viscosity vs concentration curves of deionized colloidal silica of 45 nm diameter and the deionized latex spheres. The peak corresponds to the transition between ‘‘liquid-like’’ and ‘‘crystal-like’’ structures. These results show that electrostatic intersphere repulsion and the elongated Debye-screening length around the colloidal spheres are essential to explain the extraordinary properties. [ABSTRACT FROM AUTHOR]

A metallurgical microscope is used to directly observe the two-dimensional structures of the binary mixtures of different sizes and specific gravities of monodisperse polystyrene spheres in sedimentation equilibrium and in deionized suspensions. When the sizes of small particles are smaller than 300 nm, large (diam 1.0 μm) and dense (specific gravity=1.5) spheres are often segregated upward by the ordered structures formed by the small less dense (specific gravity=1.05) spheres and Brownian movement of the larger spheres are restricted significantly. When the sizes of the small particles in the mixtures of large dense and small less dense particles are between 300 and 500 nm, the segregation effect is prevented and various kinds of ‘‘alloy’’ structures of triangular, square, pentagonal, hexagonal, heptagonal, and octagonal patterns are observed. The interparticle distances between large–large, large–small, and small–small particles agree well with the effective sizes of spheres including the Debye-screening length. These results are consistent with the significant role of the electrical double layers under the influence of purely electrostatic repulsive forces in the effective hard-sphere model. [ABSTRACT FROM AUTHOR]

Structural relaxation time (τ) of ordered structures is observed for the first time by the spectrophotometric and conductance stopped-flow techniques for deionized polystyrene latex spheres (35–500 nm in diameter), for which the distributions are both ‘‘crystal-like’’ and ‘‘liquid-like.’’ Two kinds of τ values, fast (τf) and slow steps, are observed. The τf values decrease with latex concentration. Theoretical values for τf, calculated using the translational diffusion constants of the latex spheres evaluated by the Einstein–Stokes equation, agree very well with the observed τf values for the strongly interacting colloids. The results support the hypothesis that electrostatic intersphere repulsion is essential to explain the dynamic properties of the spheres. The effective diameter of the spheres must include the Debye-screening length. The rigidity of the deionized and crystal-like latex suspension, which is estimated from the τf values, ranges from 0.005 to 10 dyn cm-2, and increases as the concentration and the charge density of the spheres increase and/or the size decreases. [ABSTRACT FROM AUTHOR]

A metallurgical microscope is used to observe directly the ordered structures of monodispersed polystyrene spheres (specific gravity=1.05) in water and methanol–water mixtures. Sedimentation occurs for all the spheres examined for which the diameters are between 369 and 1020 nm. The interparticle distances (2Dexp) increase with time after the latex sample is set into the cell, and reach equilibrium values after seven to ten days, which shows that complete deionization is essential to get reliable data for 2Dexp. 2Dexp continues to decrease as the initial concentration of the spheres increases and from these data Young’s modulus for the ordered lattices is estimated to be 1 dyn cm-2 for spheres of 0.5 μm. The influences on 2Dexp by the concentration and charge density of the spheres, and ionic strength show that the electrostatic interparticle repulsion and the elongated Debye-screening length around the spheres are essential for the ordering phenomenon. [ABSTRACT FROM AUTHOR]

The number of effective charges of colloidal particles was determined for polystyrene-based polymer latices by transference measurement. The fraction of free counterions (f) was surprisingly low and appeared to decrease with the analytical valency; the f values were about 0.1 for a latex having 1.7×104 SO3H groups per particle. A more highly charged latex (with 7.2×105 sulfonate groups) had f values of about 0.04. These values are definitely smaller than those reported for soluble polyelectrolytes (about 0.4). [ABSTRACT FROM AUTHOR]

Drying dissipative patterns during drying of marine colloidal (MC) clays were observed in the deionized aqueous suspension on a cover glass, a watch glass, and a Petri glass dish. Two kinds of broad rings (BR), i.e., BR of small particles at the outside edge and BR of large particles at the inner area from the edge, were observed. The size of the outside BR was the same as that of the initial suspension irrespective of colloidal concentration, whereas the size of the inner BR increased as colloidal concentration increased. Highly distorted multi-rings, i.e., branch-like or net-like patterns, appeared. Furthermore, no spoke lines formed except the areas at the outside edge of the dried film. These observations support the circular stacking of the anisotropic-shaped MC particles during the convectional flow process. The B type of solutes was deduced for MC from the drying patterns, where strong solute-substrate affinity especially for the small particles and weak inter-solute affinity coexist. [ABSTRACT FROM AUTHOR]

Colloidal crystallization of poly( n-butyl acrylate) spheres (ammonium persulfate-poly( n-butyl acrylate) (APS-PBA), 320 ± 50 nm in diameter) was studied in deionized aqueous suspension. Coexistence of the crystal and distorted crystal structures was observed by the reflection spectroscopy. The critical concentrations of melting were ca. 0.01 and 0.03 in volume fraction in the presence of ion-exchange resins and in their absence, respectively. Crystal structures melted away during dryness by fusion of each spheres on the substrates, i.e., cover glass, watch glass, and Petri glass dish. Thickness profiles of the dried film changed sharply from the broad ring to the round hill as sphere concentration increased. The sharpness parameter S was evaluated from the ratio of the film size (diameter) against the full width at half maximum in the thickness profiles of the ring and/or the round hill. The S values decreased sharply from 30 to 1.2 as initial volume fraction of the spheres increased from 0.0005 to 0.1. The S values were significantly low compared with those of typical colloidal spheres, which supports the aggregate and/or fusion of the spheres resulting in their low convectional flow during dryness. The round hill profile at the high sphere concentration also supports that the fusion takes place easier during dryness. Microscopic observation of the dried film supports the formation of the homogeneous fused structures. It was clarified that colloidal crystallization of APS-PBA spheres takes place by the extended electrical double layers around the spheres like typical colloidal crystals of hard spheres. However, APS-PBA spheres are not so stable by the fusion especially at the high sphere concentrations and on the substrates. [ABSTRACT FROM AUTHOR]

Colloidal crystallization of deionized suspensions of the cationic gel spheres of lightly cross-linked poly(2-vinylpyridine) (PEGMA-P2VP) has been studied from the microscopic observation, morphology, phase diagram, and elastic property. Critical concentrations of melting coexisted with ion-exchange resins were low compared with those without resins and increased but slightly as the degree of cross-linking decreased. The densities of the gel spheres, i.e., weight percent of the gel spheres divided by the corresponding volume percent, were between 0.7 and 0.9 and rather insensitive to the degree of cross-linking of the spheres examined from 0.1 to 1 mol%. This means that the gel spheres are rather dense. The closest inter-sphere distances of the crystals were much longer than the hydrodynamic diameters of the gel spheres especially at low sphere concentrations. Fluctuation parameters evaluated from the rigidities of the crystals of PEGMA-P2VP were similar to those of colloidal crystals of typical hard spheres. Mono-layered adsorption of cationic gel spheres at the nearest-neighbored layer from a cover glass of the cell was observed microscopically. The stable ordered layers, however, formed beyond the monolayer in the suspension phase. These experimental findings support the important role of the extended electrical double layers around the cationic gel spheres in addition to the excluded volume effect of the sphere themselves on the crystallization. [ABSTRACT FROM AUTHOR]

Drying dissipative patterns of deionized and colloidal crystal-state suspensions of the cationic gel spheres of lightly cross-linked poly(2-vinyl pyridine) stabilized with poly(ethylene glycol) were observed on a cover glass, a watch glass, and a Petri glass dish. Convectional patterns were recognized with the naked eyes. The broad rings were observed in the drying pattern and their size and width decreased as gel concentration decreased. Formation of the monodispersed agglomerated particles and their ordered arrays were observed. This work clarified the formation of the drying microscopic structures of (a) ordered rings, (b) flickering ordered spoke-lines, (c) net structure, and (d) lattice-like ordered structures of the agglomerated particles. The ordering of the agglomerated particles of the cationic gel spheres is similar to that of the anionic thermo-sensitive gel spheres of poly( N-isopropyl acrylamide). The role of the electrical double layers around the agglomerated particles and the interaction of the particles with the substrates during dryness are important for the ordering. The microscopic drying patterns of gel spheres were different from those of linear-type polymers and also from typical colloidal hard spheres, though the macroscopic patterns such as broad ring formation at the edges were similar to each other. The addition of sodium chloride shifted the microscopic patterns from lattice to net structures. [ABSTRACT FROM AUTHOR]

Static light-scattering measurements of deionized suspensions of the thermosensitive gels of poly( N-isopropylacrylamide) with various degrees of cross-linking and sizes were made at 20 and 40 °C. Sharp scattering peaks are observed in the scattering curve, and they were attributed to the face-centered cubic ( fcc) and/or body-centered cubic lattices ( bcc) in the distribution of gel spheres. The fcc and bcc crystal structures formed in the stable and unstable conditions, respectively, i.e., the former formed more favorably at high sphere concentrations and/or low temperatures. The closest intersphere distances were much longer than the hydrodynamic diameters of the gel spheres especially at low sphere concentrations. These experimental results emphasize the important role of the extended electrical double layers in the crystallization of gel spheres, though the contribution of the double layers in gel systems is weak compared with that in the typical colloidal spheres. [ABSTRACT FROM AUTHOR]

Drying dissipative patterns of de-ionized suspensions (colloidal crystal-state at high concentrations) of the thermosensitive gels of poly ( N-isopropylacrylamide) with various sizes (ca. 400-1,500 nm in diameter at 20 °C) were observed at 20 and 45 °C on a cover glass, a watch glass, and a Petri glass dish. The broad rings were observed and their size decreased as gel concentration decreased. Formation of the monodispersed agglomerated particles and their ordered arrays were observed irrespective of gel size. The macroscopic flickering spoke-like patterns were observed for the gel spheres from 70 to 600 nm in diameter at 20 °C, but almost disappeared for extremely large spheres, poly( N-isopropylacrylamide)(1500-5). This work clarified the formation of the drying microscopic structures of (a) ordered rings, (b) flickering ordered spoke lines, (c) net structure, and (d) lattice-like ordered structures of the agglomerated particles. The ordered rings became rather vague as gel size increased. The large net structures formed so often for large gels. Size effect on the lattice patterns was not recognized so clearly. The role of the electrical double layers around the agglomerated particles and the interaction of the particles with the substrate surfaces during dryness are important for the ordering. The microscopic drying patterns of gel spheres were quite different from those of linear type polymers and also from typical colloidal hard spheres, though the macroscopic patterns such as broad ring formation at the edges of the dried film were similar to each other. [ABSTRACT FROM AUTHOR]

Drying dissipative patterns of deionized suspensions (colloidal crystal state at high concentrations) of the thermo-sensitive gels of poly( N-isopropylacrylamide) with low degree of cross-linking of 0.5% (318 nm and 116 nm in the hydrodynamic diameter at 25 °C and 45 °C) were observed at 20 °C and 45 °C on a cover glass, a watch glass and a Petri glass dish. The broad rings were observed and their size decreased as micro-gel concentration decreased. Formation of the monodispersed agglomerated particles and their ordered arrays were observed. This work clarified the formation of the drying microscopic structures of (a) flickering ordered spoke-lines, (b) ordered rings, (c) net structure, and finally (d) lattice-like ordered structures of the agglomerated particles. The net and lattice structures formed more favorably at higher temperatures and/or higher degree of cross-linking of the gels. Importance of the convectional flow of the agglomerated particles during the drying processes is supported for the ordered array formation. The role of the electrical double layers around the agglomerated particles and the interaction of the particles with the substrate surfaces during dryness are also important for the ordering. The microscopic drying patterns of gel spheres were quite different from those of linear-type polymers and also from typical colloidal spheres, though the macroscopic patterns such as broad ring formation at the edges of the dried film were similar to each other. [ABSTRACT FROM AUTHOR]

Drying dissipative patterns were observed at 25 °C, 33 °C, and 45 °C on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of colloidal crystals of the thermo-sensitive gels of poly( N-isopropylacrylamide) (PNIPA). Two kinds of broad rings, i.e., transparent ring at the outside edge and the ring in the inner area from the edge, were observed. Sizes of the former were the same as those of the initial liquids irrespective of gel concentration, whereas sizes of the latter decreased as gel concentration decreased. These broad rings were composed mainly of the monomeric and the agglomerated gel particles, respectively. Formation of the monodispersed agglomerated particles and their ordered arrays in the inner area of the dried film were observed especially on a Petri glass dish and a watch glass. The important role of the electrical double layers formed around the agglomerated particles is supported for the ordering of the agglomerated particles. The essential differences in the drying patterns between PNIPA gel spheres and the typical colloidal particles did not appear. [ABSTRACT FROM AUTHOR]

Morphology, phase diagram, and reflection spectroscopy of the colloidal crystals of thermo-sensitive gel spheres, poly ( N-isopropylacrylamide) (224 nm in the hydrodynamic diameter at 25 °C) were studied. Giant colloidal single crystals formed at very low gel concentrations. Critical concentration of melting of gel spheres (0.8 wt.% without ion-exchange resins) decreased sharply to 0.01 wt.% as the gel suspension was deionized exhaustively with coexistence of the mixtures of cation- and anion-exchange resins and increased substantially as concentration of sodium chloride increased. These studies demonstrated that the colloidal crystallization takes place by the extended electrical double layers formed around the gel spheres in addition of the excluded-volume effect of the gels. Most of the researchers including the authors have believed that the crystallization of the gel spheres takes place by the excluded-volume effect, in other words, by the hard-sphere model, exclusively. However, the present work clarified that the colloidal interfaces, which are inevitable for the formation of the electrical double layers, are formed firmly between the water phase and gel spheres, though the gel spheres contain a lot of water molecules in the inner the sphere region. [ABSTRACT FROM AUTHOR]

Abstract: Drying dissipative structures of aqueous dispersions of lycopodium particles (31μm in average diameter) from the spores of Lycopodium clavatum were studied as a function of the particle concentrations in the presence and the absence of sodium chloride. The drying patterns formed on a cover glass, a watch glass and a Petri glass dish were observed macroscopically and microscopically. Lycopodium particles were the combination of hemisphere and tetrahedron in their shape and possessed the weakly acidic groups on their surfaces. The vague broad ring structure was observed even for the very large colloidal particles, and their size on a cover glass decreased as particle concentration decreased. Microscopic drying patterns almost disappeared except the short chain-like patterns. These observations support that the convectional contribution on the dissipative drying pattern formation is still effective in the lycopodium suspensions, though the convectional forces in the suspension are very weak compared with the sedimentation forces. [Copyright &y& Elsevier]

Drying patterns of colloidal crystals of colloidal silica spheres coated with the brushes of zwitterionic poly(carboxymethyl betaine) (SiP-PCMB) and their parent silica spheres (SiP) were studied on a cover glass, a watch glass, and a Petri glass dish. Crystal structures kept the whole process of dryness of the suspensions of SiP-PCMB and SiP. Crystal structures of the dried films of SiP-PCMB were kept stable even when the initial suspensions contained 5 mM of sodium chloride, which is the important role of the excluded volume effects of the shells of the polymer brushes. On the other hand, crystal structures of SiP spheres in the dried films were much unstable and melted in the presence of 5 mM sodium chloride. In the suspension state, colloidal crystallization of SiP-PCMB took place stably by the contribution of the excluded volume effects besides the extended electrical double layers compared with that of SiP spheres, where only the double layer effect contributes to the crystallization. The fractal patterns of the complexation of SiP-PCMB or SiP spheres with sodium chloride were observed microscopically in the dried films. Several kinds of dissipative crystallization such as array and/or accumulation of the crystallites were observed, and the importance of the convectional and sedimentation processes during the course of dryness was demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: Drying dissipative structural patterns of the colloidal crystals of silica spheres were studied under an dc-electric field. Platinum plate electrodes of anode and cathode were set on a cover glass. The broad hills accumulated with the spheres were observed at the outer edges of the dried film without and also with the electric fields. The column-like structures were formed by the electric flux, and movement of the spheres took place toward anode. The dried film kept colloidal crystal structure, where the nearest-neighbored spheres contact each other more compactly in the areas closer to the anode. Drying times needed for the complete dryness of the suspensions decreased as the strength of the electric field increased. Addition of sodium chloride to the suspensions retarded the movement of spheres toward the anode substantially. [Copyright &y& Elsevier]

Electric and photometric properties of colloidal crystals deformed in an external electric field have been studied. The colloidal crystals show the electric potential storage ability as an electric energy capacitor. Two components of decay times—slow and fast—are obtained from the decay curves of the internal electric potential voltage and the reflection intensity. The decay times range from 4 to 60 s and from 0.05 to 0.6 s for the slow and fast decays, respectively. The former is attributed to the visco-elastic fluctuation of the constituent particles in the colloidal lattices and the latter to their synchronous elastic fluctuation. The slow decay times obtained from the electric potential measurements are larger than those obtained from the reflection measurements, whereas the fast decay times obtained by the former are smaller than those obtained by the latter. The electric measurements observe the change in the crystal lattices in the total area between electrodes, whereas the reflection method observes mainly those in the surface area of the cell. [Copyright &y& Elsevier]

Abstract: Rheological properties for Chinese ink in exhaustively deionized aqueous media were carefully examined. In the steady shear measurement, the shear viscosities of the ink could be well explained by considering the “effective” volume fraction of the particles in the ink including the electrical double layers and by using Einstein''s equation for dilute suspension viscosity, when the particle volume fraction was substantially low. In the case that the volume fraction was higher, the shear viscosities showed extremely higher than those from Einstein''s prediction, though the ink remained a Newtonian liquid. In the stress-strain measurement, the shear moduli were observed at strain smaller than 0.2. The “weak” aggregation among the particles in the ink under no shear or low shear rates was supported. It should be noted that the glue in the suspension plays an important role for the good liquidity of the ink and for the “weak” bridges among the particles resulting its good dispersion stability. [Copyright &y& Elsevier]