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

Drying dissipative patterns of cationic gel crystals of lightly cross-linked poly(2-vinylpyridine) spheres (CAIBA-P2VP(0.1), CAIBA-P2VP(0.5), and CAIBA-P2VP(1), 107?~?113 nm in diameter and 0.1, 0.5, and 1 in degrees of cross-linking) were observed on a cover glass, a watch glass, and a Petri glass dish. Convectional spoke line and cluster patterns were recognized with the naked eyes, which supports that these poly(2-vinylpyridine) gel spheres aggregate temporarily and reversibly during the course of drying. Two kinds of broad rings were observed at the outside edge and inner region in the macroscopic drying pattern. The size of the inner rings decreased with gel concentration. Formation of similar-sized aggregates (or agglomerates) and their ordered arrays ((a) ordered ring, (b) spoke lines, (c) net structures, and (d) lattice structures) were observed, though the arrays were not so complete compared with those of large-sized analogous gel spheres. One of the main causes of the incomplete ordering of the aggregates is the rather high polydispersities in the sphere size. The ordering of similar-sized aggregates is common among the gel spheres including anionic poly(N-isopropylacrylamide) and cationic poly(2-vinylpyridine). Size effect of cationic gel spheres on the ordering of the agglomerates was clarified definitely in this work. The role of the convectional flow and the electrical double layers around the agglomerates and their interaction with the substrates during drying was also clarified to be very important for the drying pattern formation.     

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.     

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.     

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.     

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.     

Rigidity of the crystals of thermo-sensitive gel spheres of poly (N-isopropyl acrylamide) in the deionized aqueous media as studied by the reflection spectroscopy in the sedimentation equilibrium

Reflection spectroscopy of deionized suspensions of the thermo-sensitive gels of poly (N-isopropylacrylamide) with various degrees of cross-linking were made in the sedimentation equilibrium at 20 °C. Rigidity of the crystals increased as sphere concentration increased and increased slightly as the degree of the cross-linking of the gel spheres increased. The fluctuation parameters of the gel crystals were between 0.05 and 0.07 and slightly larger than those of typical hard-sphere systems. These experimental results emphasize that the gel crystals are soft compared with those of typical hard-sphere systems and role of the extended electrical double layers for the crystallization of gel spheres is important but weak compared with that of hard colloidal spheres.     

Large single crystals of colloidal silica spheres appearing in deionized and diluted suspension

Close-up color photographs are taken for crystallites (single crystals surrounded by the grain boundaries) in the colloidal crystals of monodisperse silica spheres (diameter: 110 nm±4.5 nm (standard deviation)). Very large crystallites (34 mm) are observed with the naked eye (for the first time) for the completely deionized and diluted suspensions. Deionization is carefully made with the mixed beds of ion-exchange resins more than 2 weeks old. Size of the crystallites increases sharply as the concentration of spheres decreases, and becomes small at the concentrations slightly higher than the critical concentration of melting toward liquid-like structure. Shape of the crystallites, i.e., mixture of triangle, cubic, pentagonal, hexagonal, cone-like, etc., is recognized in the photographs.     

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.     

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.     

First-order conformation transition of single poly(2-vinylpyridine) molecules in aqueous solutions

By measuring diffusion rate, the conformation change of single poly(2-vinylpyridine) chain in aqueous solution was studied by fluorescence correlation spectroscopy. The data showed a stepwise change of hydrodynamic radius when pH value was tuned, reflecting a sign of first-order conformation transition, and a continuous change was found at varying salt concentration.     

Giant colloidal crystals of fluorine-containing polymer spheres in exhaustively deionized aqueous suspensions and in the presence of sodium chloride

 Gigantic colloidal single crystals (2–6 mm) are formed for fluorine-containing polymer spheres (120–210 nm in diameter) in exhaustively deionized aqueous suspensions. The spheres used are poly(tetrafluoroethylene) (PTFEA and PTFEB), copolymer of tetrafluoroethylene and perfluorovinylether (PFA) and copolymer of tetrafluoroethylene and perfluoropropylene (PTP). The phase diagrams of these spheres are obtained in the deionized suspensions and also in the presence of sodium chloride for PFA. The critical sphere concentrations of crystal melting (φ _c) for these spheres are around 0.0006 in volume fraction, which are close to, but slightly larger than, those of monodispersed polystyrene spheres (φ _c ≈ 0.00015) and colloidal silica spheres(φ _c = 0.0002–0.0004) reported previously. The crystals are largest when the sphere concentrations are a bit higher than the φ _c value and their size decreases as the sphere concentration increases. Reflection spectra are taken in sedimentation equilibrium as a function of the height from the bottom of the suspension. The static elastic modulus is estimated to be 10.8 and 28.7 Pa for PTFEA and PTP spheres at the sphere concentrations 0.00325 and 0.00322 in volume fraction, respectively. Received: 27 October 1999 Accepted in revised form: 16 November 1999     

Effect of syndiotacticity on the aqueous poly(vinyl alcohol) gel 2. Syneresis of gel

Summary The mechanism of syneresis of an aqueous gel of syndiotacticity-rich poly(vinyl alcohol) (PVA) with the rise of temperature was studied using the PVA having the content of syndiotacticity in diad from 58.4 to 66.2%. The extent of syneresis was estimated by gravimetry. Syneresis of gel with the rise of temperature depends upon the syndiotacticity and gelling temperature. The gel chilled at lower temperature of PVA having the content of syndiotacticity in diad above 60.9% showed remarkable syneresis with the rise of temperature. The maximum of the extent of syneresis appeared between the content of syndiotacticity in diad of 60.9% and that of 64.2%. The phenomena of syneresis was not thermally reversible. Syneresis occurs accompanying the breakdown of the unstable junction and further growth of the crystallite.

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Zusammenfassung Der Mechanismus der Synärese an wäßrigen Gelen von Polyvinylalkohol, reich an syndiotaktischem Anteil, wurde mit steigender Temperatur untersucht, wobei der Polyvinylalkohol in Bezug auf seinen Gehalt an syndiotaktischen Diaden zwischen 58,4 und 66,2% variiert. Die Synärese wurde gewichtsmäßig verfolgt. Die Synärese hängt von der Syndiotaktizität und der Gelierungstemperatur ab. Gele, erstarrt bei tieferen Temperaturen mit einer Syndiotaktizität von 60,9%, zeigten beträchtliche Synärese mit steigender Temperatur. Das Maximum an Synärese wurde zwischen 60,9 und 64,2% Syndiotaktizität beobachtet. Das Phänomen der Synärese ist nicht thermisch reversibel. Die Synärese läuft ab unter Zusammenbruch von unstabilen Bindungen und weiterem Wachstum der Kristallite.

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Part 1. cf. reference 4.     

Interactions between silica particles and poly(2-vinylpyridine) brushes in aqueous solutions of monovalent and multivalent salts

AFM colloidal probe technique, scratch tests, and spectroscopic ellipsometry are employed to study the conformation of a poly(2-vinyl pyridine) brush grafted to a planar surface and its interaction with microsized silica spheres in solutions containing monovalent (Cl^?) and multivalent counterions (SO₄ ^2? and PO₄ ^3?) at pH 2.5. During approach of the sphere, steric repulsion is observed with all salts at any concentration. The approach force-distance curves are fitted according to the Alexander-de Gennes model in order to calculate the equilibrium brush thickness L. These data are compared to the brush thickness determined by ellipsometry and AFM scratch tests. Different values are obtained but all of them decrease with increasing salt concentration. This effect is enhanced by counterions of higher valence because they have a stronger screening effect and ion correlation due to their greater charge per unit volume. With NaCl solutions, a reswelling of diluted P2VP coils is observed at Cl^? concentrations >1 M. When the sphere is retracted, weak adhesion forces occur at Cl^? concentrations >1.3?×?10^?2 M and at all concentrations of SO₄ ^2? and PO₄ ^3?.     

Colloidal crystals formed by aqueous suspensions of monodispersed silica, polystyrene, and poly(methyl methacrylate) colloidal spheres

Colloidal crystals consisted of silica, polystyrene, and poly(methyl methacrylate) monodispersed suspensions; deionized sufficiently in water at the same condition; were formed; and their properties were compared changing sphere diameter and volume fraction systematically. The size of these colloidal crystals was maximized at their critical sphere concentration irrespective of their sphere size. The Bragg peak wavelengths of these colloidal crystals were uniquely determined only by the sphere diameter and volume fraction for all kinds of colloidal spheres used in this work. The larger the sphere volume fraction, the larger the crystal growth rates, and there were no significant differences among the colloidal spheres. The rigidity of colloidal crystals increased in proportion to the number density of spheres. Consequently, the crystallization mechanism and properties of colloidal crystals formed by these spheres are not dependent on the kind of spheres, but they are dependent only on the sphere diameter and number density.     

Synthesis of poly(N-isopropylacrylamide)-b-poly(2-vinylpyridine) block copolymers via RAFT polymerization and micellization behavior in aqueous solution

Poly(N-isopropylacrylamide)-b-poly(2-vinylpyridine) (PNIPAM-b-P2VP) block copolymers were synthesized for the first time via reversible addition-fragmentation chain transfer (RAFT) polymerization in the presence of S-1-dodecyl-S(')-(a,a(')-dimethyl-a(')-acetic acid)trithiocarbonate as chain transfer agent (CTA) and 2,2(')-azobis(isobutyronitrile) as initiator. Both pH- and thermo-induced micellization behavior of the PNIPAM(59)-b-P2VP(102) block copolymer in dilute aqueous solution was investigated by pyrene fluorescence, dynamic and static light scattering, transmission electron microscopy and (1)H NMR. The results show that the critical aggregation pH value of the block copolymer is around 5 and the critical aggregation temperature of the block copolymer is around 42 degrees C. A reversible transition between P2VP-core and PNIPAM-core micelles can be observed through an intermediate unimer state in aqueous solution.