E. I. Rjumtsev

Flow birefringence of xanthan and other polysaccharide solutions

A xanthan sample with molecular weight M = 2.2 x 10(6) was investigated in three solvents: bidistilled water, 0.2 M aqueous NaCl and cadoxen by flow birefringence and viscometry methods in dilute solutions. It was shown that the optical shear rate coefficients of xanthan in aqueous and cadoxen media differ by two orders of magnitude. An estimation of xanthan optical anisotropy in different conformational states has been made and compared with values for other polysaccharides: dextran, pullulan, cellulose and chitosan. The process of denaturation and the flow birefringence of renaturated xanthan in aqueous solutions (after heat treatment at 121 degrees C) have also been studied.

Star‐like Fullerene Containing Poly(Vinylpyrrolydone) Derivatives: Chloroform Solution Properties

Abstract Star‐like fullerene C60 derivatives with different branch number, synthesized by the reaction of fullerene with poly(vinylpyrrolydone) (PVP) macromolecules bearing the terminal amino‐groups, were investigated in solution by the viscometry, dielectric, and electrooptical Kerr‐effect methods in comparison with the ordinary linear PVPs of the same molecular mass. It was shown that covalent linkage of branches to fullerene through amino‐groups leads to appearance of a polar and optically anisotropic nanoparticle (amine‐substituted C60) in the center of the coil of star‐like polymers that radically changes dielectric and electrooptical properties of the initial polymer. Effect of fullerene on the dimension of polymer coil had been detected also.

Local Dynamics of Director Reorientation under Electric Field in Helical LC Structure

The influence of an electric field on the trajectory of an extraordinary light ray in a layer of a chiral liquid crystal (LC) with a 180° turn of the director is studied. In the absence of the electric field and at a large angle of incidence the ray reflects inside the layer and return back through the surface which it entered. The applied electric field distorts the initial configuration of the director. It results in a change of the ray trajectory so that the light is propagated through the LC cell. The study of the temporal characteristics of the effect at various angles of incidence of light on the layer makes it possible to examine the local reorientation of the director inside the cell.

Effect of Aliphatic Spacers on Electro-Optical and Dielectric Properties of Strongly Polar Liquid Crystals

Abstract The molecular mechanism of dipolar polarisation in liquid crystals containing a nitrile group “not rigidly” bonded to the mesogenic fragment of molecules with different chemical structures was considered.

Effect of Field Strength on Electrooptical Properties of Low-Molecular Weight and Polymer Liquid Crystals

The influence of a strong electric field on isotropic melts of 6-cyanobiphenyl and comb-shaped polyacrylate with side mesogenic groups was investigated. It was established that the electric field induces the isotropic—nematic phase transition in melts of these compounds. A relaxation process was discovered that destroys the nematic ordering induced in substances by electric fields. It was found that the relaxation time τ of the orientational order parameter is proportional to the square of electric field strength. For comb-shaped polymer liquid crystals, the time of transition from the nematic to the isotropic phase is several orders longer then that for low-molecular liquid crystal.

ELECTRO-OPTICAL PROPERTIES AND POLAR STRUCTURE OF LIQUID CRYSTALLINE PHENACYL ESTERS

Abstract Kerr-constants and dipole moments in solutions of liquid crystalline phenacyl esters of different carboxylic acids were measured. On the base of experimental data the influence of the changes in esters chemical structure to ones properties are discussed.

Molecular Properties of Mesomorphic Poly (decamethyl-cyclohexasiloxane) in Solution

Abstract The molecular properties of a non-classical mesogenic polymer - poly (decamethyl-cyclohexasiloxane), and low molecular analogs of its monomer unit have been studied by electrooptical Kerr effect in solution. It was shown that every polar hexasiloxane cycle in the polymer chain acts independently under influence of external electric field. Based on the results of the study of dipole moments and electrooptical properties of low- molecular-mass cyclohexasiloxanes with different polar side-groups (CH3, -C6H5, -OH, -OC2H5) it was established that hexasiloxane cycle is able to preserve its conformation (i.e. its form and size) because of its polar properties depend weakly on the type of side-substituents. An observed stability of polar hexasiloxane cycle under the external action may be considered as responsible for the ability of poly(cyclohexasiloxanes) to form highly organized mesomorphic phases.

Dielectric relaxation in mixtures of liquid crystals of different molecular length

It is experimentally investigated the dispersion of the dielectric permittivities in the frequency range of 1 kHz divided by 100 MHz in both nematic and isotropic phases of binary mixtures of liquid crystals with different molecular lengths. Two low-frequency relaxation processes related to the dielectric relaxation of the mixture components are separated. The relaxation times and the nematic potentials of each components are determined and compared with molecular sizes.

Kerr-effect in solutions and molecular polarity of liquid crystalline fluorenes

Abstract As part of a broader study of liquid crystal polymers with side groups containing fluorene moieties, more information was required about the properties of fluorene derivatives. With this aim in mind, the solution Kerr-effects for five fluorene-based mesogens have been measured and used in conjunction with other results to determine the polarizability anisotropies and dipole moments.

The Influence of Aliphatic Spacers Posititon on the Polarity and Dielectric Properties of Liquid Crystalline Molecules

Abstract For liquid crystals with the polar CN-end-group and variation of aliphatic spacer position, the dipole moments and Kerr effect in solutions as well as the dielectric permitivity in melts had been studied. It was shown that a strong change of their physical properties took place when the spacer separated CN-group from the main molecular chain.