Colloidal crystallization of cationic gel spheres of lightly cross-linked poly(2-vinylpyridine) in the deionized aqueous suspension

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.     

Drying dissipative structures of lightly cross-linked poly(2-vinyl pyridine) cationic gel spheres stabilized with poly(ethylene glycol) in the deionized aqueous suspension

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.     

Cationic gel crystals and amorphous solids of lightly cross-linked poly(2-vinylpyridine) spheres in the deionized aqueous suspension

Colloidal crystallization and amorphous solidification of deionized suspensions of the polydispersed cationic gel spheres of lightly cross-linked poly(2-vinylpyridine), CAIBA-P2VP (107～113 nm in diameter, ±19～22 nm in dispersity), have been studied from the reflection spectroscopy, morphology, phase diagram, and elastic property. Crystallization takes place even for the polydispersed cationic gel spheres by the significant contribution of the extended electrical double layers formed around the spheres. Critical concentrations of melting coexisted with ion exchange resins were around 0.02 in volume fraction and high compared with those of other cationic and anionic gel crystals examined hitherto. The densities (ρ) of CAIBA-P2VP in suspension state, i.e., weight percent of the gel spheres divided by the corresponding volume percent, was around 0.3. The ρ values decreased sharply with decreasing size of P2VP gel spheres, which supports the small gel spheres containing much water inside and being softer than the large ones. The closest intersphere distances of the crystals and/or amorphous solids were much longer than the hydrodynamic diameters of the gel spheres especially at low sphere concentrations. Fluctuation parameters (b) evaluated from the rigidities of CAIBA-P2VP (0.15～0.28) were large compared with those of gel crystals of large-sized P2VP-based cationic gel spheres, anionic thermosensitive gel spheres of poly(N-isopropylacrylamide) (0.05～0.09) and further much larger than those of typical colloidal hard spheres (around 0.03). The dispersity in sphere size played an important role for distinguishing crystal and amorphous solid. Importance of the extended electrical double layers around the cationic gel spheres is supported in addition to the excluded volume effect of the sphere themselves on the crystallization and/or solidification.     

Drying dissipative structures of thermosensitive gel spheres of poly (N-isopropylacrylamide). Influence of gel size

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.     

Crystal structure of thermosensitive gel spheres of poly(N-isopropylacrylamide) in the deionized aqueous suspension as studied by the static light-scattering measurements

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.     

Colloidal crystallization of poly(n-butyl acrylate) spheres in deionized aqueous suspension and the melting during dryness

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.     

Drying dissipative structures of poly(N-isopropylacrylamide) homopolymer

Drying dissipative patterns of the linear-type thermosensitive homopolymer poly(N-isopropylacrylamide) lpNIPAm in deionized aqueous solution and suspension were observed on a cover glass, a watch glass, and a Petri glass dish at 22 and 50 °C, respectively. The size and ζ potential of the globule aggregates of lpNIPAm at 47.5 °C were 140 nm in diameter and ?22 mV from the electrophoretic light-scattering measurements. A single broad ring formed in the inner region (on a cover glass and a watch glass) and near the outside edge (in a glass dish) in the macroscopic drying pattern at 22 °C. On the other hand, two to three kinds of broad rings were observed at the outside edge and inner region at 50 °C. Microscopic drying structures of ordered rings, flickering ordered spoke-lines, and net structures of the agglomerated particles were observed. Formation of the similar-sized agglomerates and their ordered arrays were observed during the course of dryness. These results of lpNIPAm at 50 °C are quite similar to the agglomeration and the ordering of the thermosensitive gel spheres of poly(N-isopropylacrylamide), pNIPAm. The surface structures of the similar-sized agglomerates of lpNIPAm will be similar to those of pNIPAm gel spheres, since the chemical components of the homopolymers and the gels are almost the same. The role of the electrical double layers around the agglomerates and their interaction with the substrates are important for the ordering. Dendritic large aggregates (from 50 to 600 μm in size) formed in the presence of sodium chloride.     

Stimulus-responsive particulate emulsifiers based on lightly cross-linked poly(4-vinylpyridine)-silica nanocomposite microgels

Lightly cross-linked poly(4-vinylpyridine)-silica nanocomposite microgel particles have been recently reported to act as pH-responsive particulate emulsifiers [Fujii, S.; Read, E. S.; Armes, S. P.; Binks, B. P. Adv. Mater. 2005, 17, 1014]. In this work, the synthesis and performance of such nanocomposite microgel particles are studied in more detail. Scanning electron microscopy, dynamic light scattering, nitrogen microanalyses, thermogravimetric analysis, aqueous electrophoresis, and acid-base titration were used to characterize the nanocomposites in terms of their particle size and morphology, polymer and silica contents, surface compositions, and critical swelling pH, respectively. Depending on the polarity of the oil phase and the purity of the nanocomposite particles, either oil-in-water or water-in-oil emulsions could be prepared at pH 8-9, but not at pH 2-3. These emulsions were characterized in terms of their emulsion type, mean droplet diameter, and morphology using electrical conductivity, light diffraction, and both electron and optical microscopy. In some cases, rapid demulsification could be induced by lowering the solution pH: addition of acid led to protonation of the 4-vinylpyridine residues, which imparted cationic microgel character to the nanocomposite particles. Cross-linking of the nanocomposite microgel particles is essential for their optimum performance as a pH-responsive emulsifier, but unfortunately it is not sufficient to allow recycling.     

Drying dissipative structures of thermo-sensitive gel spheres of poly(N-isopropylacrylamide). Influence of degree of cross-linking of the gels

Drying dissipative patterns of de-ionized suspensions (colloidal crystal state above the critical concentrations of crystallization) of the thermo-sensitive gels of poly(N-isopropylacrylamide) with degrees of cross-linking of 10% and 2% (pNIPAm(200–10) and pNIPAm(200–2)) 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. Microscopic drying structures of (a) flickering ordered spoke-lines, (b) ordered rings, (c) net structure, and (d) lattice-like ordered structures of the agglomerated particles are observed. The net and lattice structures formed more favorably at high degrees of cross-linking, at high concentrations of the gels, and/or high temperatures. By the addition of sodium chloride, very large dendrite-like and net structures of the large agglomerated particles formed at 20?°C and 45?°C, respectively. Importance of the cooperated 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 different from those of linear type polymers and also from typical colloidal spheres, though the macroscopic patterns of gel system such as broad ring formation at the edges of the dried film were similar to other two systems.     

Drying dissipative structures of thermo-sensitive gel spheres of poly(<Emphasis Type=Italic>N</Emphasis>-isopropylacrylamide)

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.     

Drying dissipative structures of aqueous solution of poly (ethylene glycol) on a cover glass

Macroscopic and microscopic dissipative structural patterns formed in the course of drying a series of poly (ethylene glycol) (PEG) having molecular weights ranging from 1,000 to 2×10⁶ in aqueous solution have been studied on a cover glass. The broad ring patterns of the hill accumulated with the polymers are formed irrespective of the molecular weights of PEG molecules. The single round hills are formed also in the center in the macroscopic scale, when the molecular weight is large. The characteristic convection flow of the polymers and the interactions among the polymers and substrate are important for the macroscopic pattern formation. Cross-like fractal patterns are observed, especially for the diluted solutions in the microscopic scale. These patterns are determined mainly by the electrostatic and polar interactions between the polymers and/or between the polymer and the substrate in the course of solidification. Interestingly, these microscopic patterns are reflected based on the shape and size of the PEG polymers.     

Drying dissipative structures of colloidal crystals of silica spheres coated with polymer brushes of poly(carboxymethyl betaine)

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.     

Drying dissipative patterns of aqueous solutions of poly (4-vinyl-N-alkyl-pyridinium halide)

Drying dissipative structural patterns of aqueous solutions of poly (4-vinyl-N-alkyl-pyridinium halide) were studied on a cover glass. The broad rings were observed at the outside edge of the dried film. The broad ring size (or the area of the dried film, S) increased as polymer concentration increased. The broad ring size decreased and then turned to increase when the hydrophobicity of the polymers increased. The drying time from the initial liquid (T) was insensitive to the polymer concentration. But, T was sensitive to the kind of polymers, i.e., hydrophobicity of polycations, and roughly in the opposite order to that of S. Spoke-like macroscopic patterns appeared clearly for poly (4-vinyl-N-n-butylpyridinium bromide) (C4PVP), but were not observed clearly for the other polymers. Cross-like microscopic patterns appeared from which the polymers with the extended conformation are deduced to be crystallized during the course of dryness. The cooperative crystallization took place between the polymer and the salt in the C4PVP + KCl mixtures. When two different polymers were mixed, segregation and then independent crystallization of each single component polymers were observed. The dissipative effect is important for determining of the polymer crystal structure during the course of crystallization.     

Drying dissipative structures of nonionic surfactants in aqueous solution

Macroscopic and microscopic dissipative structural patterns form in the course of drying a series of aqueous solutions of polyoxyethylenealkyl ethers. The shift from the single round hill with accumulated surfactant molecules to the broad ring patterns of the hill in a macroscopic scale occurs as the HLB (hydrophile-liophile balance) of the surfactant molecules increases. The patterns correlate intimately with the HLB values of the surfactants. Microscopic patterns of small blocks, starlike patterns, and branched strings are formed. The size and shape of the surfactant molecules themselves influence the drying patterns in part. The pattern area and the time to dryness have been discussed as a function of surfactant concentration and HLB of the surfactants. The convection flow of water accompanying the surfactant molecules, the change in the contact angles at the drying frontier between solution and substrate in the course of dryness, and interactions among the surfactants and substrate are important for the macroscopic pattern formation. Microscopic patterns are determined in part by the shape and size of the molecules, translational Brownian movement of the surfactant molecules, and the electrostatic and hydrophobic interactions between surfactants and/or between the surfactant and substrate in the course of solidification.     

Novel use of cross-linked poly(N-isopropylacrylamide) gel for organic reactions in aqueous media

A poly(N-isopropylacrylamide) (PNIPAAm) gel cross-linked with quaternized aminoalkyls was designed. A novel recyclable system based on the external solvent-responsive oil-absorption/elution transition ability of the PNIPAAm gel matrix was then developed.     

Characterisation of cross-linked poly(acryloylmorpholines) as matrices for aqueous gel permeation chromatography

The characterisation of two cross-linked poly(acryloylmorpholines), Enzacry Gel K1 and Enzacryl Gel K2, as matrices for aqueous gel permeation chromatography is described. Near ideal plots of logarithm molecular weight versus distribution coefficient, K_d, are obtained for polyethylene glycols and linear, oligomeric α,ω-diols approximate molecular weight ( _n) fractionation ranges being 0–4000 and 0–20,000 for Enzacryl Gel K1 and Enzacryl Gel K2, respectively. Anomalous retardation of the Schardinger dextrins, cyclomaltohexose and cyclomaltoheptose, is observed although linear maltosaccharides behave normally. The internal gel volumes, calculated from column elution data in water, are significantly larger than the volumes of solvent imbibed by the dry column packings on constituting the gel. Internal gel volumes and solvent imbibition volumes in water are compared with the corresponding values obtained in chloroform and tetrahydrofuran. The two parameters are discussed, in the case of Enzacryl Gel K2 in water and chloroform, in the light of plots of logarithm viscometric hydrodynamic volume versus K_d for polyethylene glycols.     

Drying dissipative structures of thermo-sensitive gel spheres of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) with low degree of cross-linking

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.     

Stereoregularity of poly(2-vinylpyridine) and poly-(4-vinylpyridine)

In order to determine the stereoregularity of poly(4-vinylpyridine), 4-vinylpyridine-β,β-d₂ was synthesized from 4-acetylpyridine. The ¹H-NMR spectra of the deuterated and nondeuterated polymers were measured and analyzed. From the ¹H-NMR spectra of poly(4-vinylpyridine-β,β-d₂), triad tacticity can be obtained, while the ¹H-NMR spectra of nondeuterated poly(4-vinylpyridine) give the fraction of isotactic triad. The ¹³C-NMR spectra of poly(4-vinylpyridine) were also observed, and the spectra of C₄ carbon of polymers were assigned by the pentad tacticities. The fraction of isotactic triad of poly(2-vinylpyridine) and poly(4-vinylpyridine) obtained under various polymerization conditions were determined. The radical polymerization and anionic polymerizations with phenylmagnesium bromide and n-butyllithium as catalysts of 4-vinylpyridine gave atactic polymers.