Evgeny A. Karpushkin

Rheological properties of polyacrylonitrile solutions containing highly dispersed carbon nanotubes

Rheological properties of dispersions of carbon nanotubes in dimethylsulfoxide solutions of polyacrylonitrile are studied at different concentrations of the components. The viscosity values of all the studied dispersions are substantially dependent on shear rate. For a number of systems, the energies of activation of viscous flow are determined. The relationship of viscosity and the energy of activation of flow to the compositions and possible structural features of dispersions is discussed. The concentration regime where a thermally reversible mixed network exists with crosslinks formed by physical contacts of the polymer with nano-tubes is characterized.

Interpolyelectrolyte reaction between the particles of oppositely charged microgels

Processes that take place in oppositely charged microgel particles were studied. It was shown that water-swollen microgel particles about 100 μm in size were capable of interacting in dilute and concentrated dispersions to produce continuous dispersed systems. This interaction is accompanied by the release of water and low-molecular-mass counterions of network polyelectrolytes. Their liberation is due to the interpolyelectrolyte reaction between peripheral regions of unlike charged microgel particles in the particle contact zone.

Electrically conducting polymeric microspheres comprised of sulfonated polystyrene cores coated with poly(3,4-ethylenedioxythiophene)

Oxidative chemical polymerization of 3,4-ethylenedioxythiophene was carried with 5.8-μm sulfonated polystyrene latex particles as template. Polymerization led to formation of poly(3,4-ethylenedioxythiophene) distributed over the surface of template particles. Increase in initial monomer concentration resulted in the change of poly(3,4-ethylenedioxythiophene) morphology from isolated clusters to continuous 0.2–0.5-μm-thick surface shells. Structure of poly(3,4-ethylenedioxythiophene) coatings had crucial influence on the surface charge and macroscopic electrical conductivity of composite latex particles.

Shear-induced structure evolution of carbon nanotubes dispersions in polyacrylonitrile–dimethylsulfoxide solution

Rheological behavior of carbon nanotubes finely dispersed in polyacrylonitrile–dimethylsulfoxide solution has been studied as function of the applied pre-shear stress and discussed in view of possible structural changes induced by the pre-shearing of the samples. The observed effects can be ascribed to a combination of internal processes involving alignment and association of the macromolecules as well as orientation and association of carbon nanotubes. The effects caused by the macromolecules alignment and association are mainly observed at low concentration of the filler and at higher shear stress, whereas the processes involving carbon nanotubes reorganization are mainly observed at the higher filler content and at low pre-shear stress.

Anionic Polymer Hydrogel Degradation by Ascorbic Acid

Polymer hydrogel based on sodium 2-acrylamido-2-methylpropansulfonate, covalently crosslinked with N,N′-methylenebisacrylamide has been shown to degrade in aqueous ascorbic acid. The hydrogel degradation is induced by chemical interaction of the polymer crosslink and an ascorbic acid oxidation intermediate.

Hydrogels for Treatment of Water Polluted with Macromolecules: Effect of Network Polyelectrolyte Composition on the Sorption Rate

Globular proteins uptake kinetics by hydrogels of oppositely charged network polyelectrolytes was studied with relation to the polyelectrolyte composition. It was shown that introduction of hydrophilic neutral units of acrylamide, inert towards proteins studied, significantly accelerated the uptake process, with no effect on the polyelectrolyte capacity towards proteins (with respect to ionic groups). The results obtained allow for optimization of the sorbent composition in order to enhance the polymeric pollutants uptake and/or tune their release rate.

Intergel Interpolyelectrolyte Reaction and Synthesis of Hybdrid Composites Based on Charged Microgels and Inorganic Nanocrystals

We have studied the interaction between oppositely charged microparticles of polyelectrolyte hydrogels whose low-molecular-mass counterions form insoluble compounds. The intergel polyelectrolyte reaction of such polymers leads to formation of a crystalline compound in the microgel mixture phase. The asprepared samples are composites containing, along with unreacted microgel regions, the interpolyelectrolyte complex comprising the intercrystalline low-molecular-mass compound. It has been shown that both unreacted microgel regions and insoluble compound incorporated into the intergel complex can be involved in chemical modification.

Embedding of Bacterial Cellulose Nanofibers within PHEMA Hydrogel Matrices: Tunable Stiffness Composites with Potential for Biomedical Applications

Bacterial cellulose (BC) and poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels are both considered as biocompatible materials with potential use in various biomedical applications including cartilage, cardiovascular stent, and soft tissue engineering. In this work, the “ever-wet” process based on in situ UV radical polymerization of HEMA monomer in BC nanofibrous structure impregnated with HEMA was used, and a series of BC-PHEMA composites was prepared. The composite structures were characterized by ATR FT-IR spectroscopy, WAXD, SEM, and TEM techniques. The strategy of using densified BC material of various cellulose fiber contents was applied to improve mechanical properties. The mechanical properties were tested under tensile, dynamic shear, and relaxation modes. The final composites contained 1 to 20 wt% of BC; the effect of the reinforcement degree on morphology, swelling capacity, and mechanical properties was investigated. The biocompatibility test of BC-PHEMA composites was performed using mouse mesenchymal stem cells.

Preparation and morphology characterization of core-shell water-dispersible polystyrene/poly(3,4-ethylenedioxythiophene) microparticles

Ultrafine electrically conductive microparticles have been prepared by in situ oxidative polymerization of 3,4-ethylenedioxythiophene in the presence of sulfonated polystyrene latex beads either in water or in an aqueous solution of poly(4-styrenesulfonic) or 4-toluenesulfonic acid. The particles consist of polystyrene core and continuous poly(3,4-ethylenedioxythiophene) shell which incorporate different counter-ions derived from the oxidant or the sulfonic acid. The presence of poly(4-styrenesulfonic acid) in the polymerization medium enhances the electrical conductivity of the resulting particles by up to two orders of magnitude. The particles prepared in the presence of poly(4-styrenesulfonic acid) exhibit smooth surface morphology and high colloidal stability, while these prepared in the presence of 4-toluenesulfonic acid or in the absence of sulfonic acid show rough sponge-like morphology and do not form stable dispersions.

Correction to: Sol-gel-modified membranes for all-organic battery based on bis-(tert-butylphenyl)nitroxide

The author would like to add photos and biographies as the paper is a Special Issue dedicated to Prof. Vladimir Sergeyev. The original article has been corrected.