N. A. Churochkina

Swelling and collapse of the gel composites based on neutral and slightly charged poly(acrylamide) gels containing Na-montmorillonite

Abstract Clay-polymer hydrogel composites were prepared on the basis of neutral and slightly charged cationic and anionic poly(acrylamide) gels containing different amounts of the clay mineral Na-montmorillonite. The swelling and collapse in water–acetone media and the mechanical behavior of such gels were studied. It is shown that the clay incorporated into neutral poly(acrylamide) gel hardly influences its degree of swelling in water. On the other hand, for the anionic and especially for the cationic gels, the swelling in the presence of clay decreases. The elastic modulus of gels with incorporated clay is higher, while the amplitude of the acetone-induced collapse is lower than for the corresponding pure gel systems.

Liquid crystals stabilized by polymer networks

This review is devoted to the characteristics of a new class of polymer composites, dispersions of chemical polymer networks in LCs. Photopolymerization of various bifunctional monomers in the medium of LCs leads to the formation of a polymer network that stabilizes the structure of crystals. Methods for the preparation of the above composites, their structure, morphology, and optical characteristic are reviewed, and areas of practical application of such materials are described.

Novel condensation functional polymers having highly basic groups

Abstract The cardo polyimides and polyamides having highly nucleophilic quinuclidine groups have been synthesized with the usage of 3,3-bis(4-aminophenyl)quinuclidine as amine monomer. The latter has been obtained by the condensation of quinuclidone-3 with aniline. The characterization of such amine, including quaternization reaction, is performed. Polyimides have been derived from this monomer and various tetracarboxylic dianhydrides by one- and two-step polycyclization. Quinuclidine moieties enhance the one-step polyimide formulation leading to high molecular polymers including corresponding poly- 1,4,5,8-naphthoyleneimides even without any added catalyst. It is stated that polyamic acid formation is hindered by the side tertiary-amine-COOH salt formation. The latter reaction is eliminated by the preliminary quaternization of amine monomer. The high molecular polyamides have been prepared by low-temperature solution polycondensation of cited monomer and diacid chlorides. The obtained polymers are characterized by high thermal properties, solubility in organic solvents and represent the quite efficient catalysts for polyamic acid imidation in homo- and heterogeneous systems.

Liquid crystals stabilized by physical networks

This review concerns the behavior of a new class of LC composites with physical networks. These composites are prepared through the addition of some low-molecular-mass compounds (gelators) containing various functional groups to liquid crystals. In the medium of liquid crystals, gelators can form gels via non-covalent interactions, thereby stabilizing their structures. The structures of LC composites, their morphologies, and their optical and electro-optical properties are examined, and some application areas of these materials are illustrated.

Rheological properties of solutions and gels of combined systems hydrophobically modified polyacrylamides-new viscoelastic cationic surfactants

The rheological properties (viscosity and dynamic elasticity modulus) of solutions and gels of combined systems composed of hydrophobically modified polymers containing main-chain charged groups or lacking these groups and of newly synthesized viscoelastic cationic surfactants with different amounts of OH groups and long nonpolar saturated and trans monounsaturated radicals have been studied. It has been shown that the maximum viscosity of solutions of polymer-surfactant complexes corresponds to the very low concentration of the surfactant. Regions where homogeneous and heterogeneous combined solutions and gels exist are considered. An increase in the viscosity of the combined solutions with temperature is discovered and discussed. The synergistic effect of polymers and surfactants is demonstrated, and a more efficient role of surfactants in the case of uncharged polymers is revealed. The roles of the number of OH groups and the length of the nonpolar radical in a surfactant molecule and a difference in the properties of systems containing surfactants with saturated and unsaturated radicals are considered.

Local mobility of micelles of new cationic surfactants and their interactions with hydrophobically modified polyacrylamides

The local dynamics and organization of micelles of new long-chain cationic surfactants with saturated hydrocarbon fragments (from C16 to C22) are investigated via the EPR spin-probe technique. The local mobility of spin probes in the hydrocarbon core of a micelle changes insignificantly, while the order parameter noticeably increases with lengthening of the hydrocarbon fragment of the surfactant molecule. The specific features of the interaction of the surfactants with network junctions of the gels formed by two types of hydrophobically modified polyacrylamides—either containing charged groups (sodium acrylate) in the backbone or lacking these groups—are studied. In both cases, the local mobility of network junctions of the gel increases after the introduction of the surfactant (C18). Moreover, for surfactant with a long alkyl group (C2), the microscopic viscosity of the gel based on the uncharged polymer decreases, although the local mobility of the network junctions increases. Possible causes of the observed specific features are discussed.

Rheology of Hydrophobically Modified Polymers

A study has been made of the rheological characteristics of the aqueous and water‐salt solutions and gels of one class of hydrophobically modified polymers: acrylamide copolymers with a hydrophobic monomer which can be either acrylamide with a hydrophobic “tail” consisting of 9 or 12 carbon atoms or methacrylate with the same “tail.” It has been shown that a sharp growth in the viscosity of the solutions and in the limiting stress, the highest Newtonian viscosity, and the elastic modulus of the gels is the greater, the larger the length and the number of hydrophobic groups in the copolymer and the smaller the amount of a surfactant in the process of its synthesis, which leads to a hydrophobicity growth of the copolymer. Consideration has been given to the role of the number of charges introduced into the copolymer apart from the hydrophobic groups and to other factors determining the rheological properties of the gels and their resistance to temperature.

The electro-optics of nematic liquid crystals stabilized by a polymer network

Samples of nematics stabilized by a polymer network, which are new composite materials, were prepared. A ZhK-1277 nematic composite and a bisphenyl-A-dimethacrylate monomer were used. Polymerization was conducted via UV radiation. The electro-optic properties, i.e., the dependence of transmittance and the turn-on and turn-off times on the electric voltage and layer thickness, of the resulting material and a pure nematic were studied. The experimental results are explained by the domain structure of the nematic in a polymer network, according to which the liquid crystal in an electro-optic cell is composed of oriented domains separated by thin partitions of the polymer. The size of the domain regions of the liquid crystal is 2 μm.

Mineral liquid crystals

The contemporary state of studying mineral liquid crystals has been analyzed. Such crystals are lyotropic aqueous or water–organic colloidal solutions, the dispersed phases of which are represented by nano- and microsized crystalline particles. The methods of production, structure, and physicochemical properties of these systems, as well as the influence of electric and magnetic fields on them, have been discussed in detail.

The electro-optics of nematic liquid crystals stabilized by physical networks

A new composite material based on the 5CB nematic stabilized by a physical network formed by 12-hydroxyoctadecane acid has been prepared. The electro-optical properties of the material—the dependence of the transmittance and the turn-on and turn-off times on the voltage—have been studied. Two turn-on and turn-off times have been found. It has been found that the gelling agent (acid) strongly violates the orientation of the liquid crystal to form two systems of its regions. One has a planar orientation; the other, an inclined orientation. The effective sizes of these regions are different and significantly smaller than the thickness of the cell.