A. N. Chuvyrov

The Structure and Properties of Quartz Crystals Grown from Fluoride Solutions: Part II. The Burgers Vector of the Growth Screw Superdislocations

The birefringence method is used to investigate the distribution of microstresses around screw superdislocations with a hollow core in quartz crystals and to determine the Burgers vector and core size. The core size was found to be 5 × 10−7 m; this value was confirmed independently by studying the light diffraction on hollow cores in different quartz cuts.

Structure and dynamics of the Frenkel-Kontorova dislocations in electroconvection in liquid crystals

The Frenkel-Kontorova instability is studied in a 1D lattice of domains formed during electroconvection in nematic liquid crystals twisted by π/2. It is found that generation of defects by such instability can be observed in this model medium. Among other things, it is shown that several types of defects with singular and nonsingular cores, as well as with a extended core, are formed in the 1D domain structure above the electroconvective instability threshold. The extended cores of dislocations are dissociated into a line, and the entire structure is isomorphic to two partial dislocations spaced by a certain distance, which are not observed in free form. Defects with a nonsingular core (zero topological index) exist owing to spiral hydrodynamic flows in convective rolls and are not observed in layers with a homogeneous orientation of molecules. It is shown that the formation of both types of defects follows the scenario of decay of dislocations with extended cores via detachment of nonsingular defects (i.e., discretely); as a result, a dislocation with a singular core is left. “Breather” defects, which are the result of periodic creation and annihilation of dislocations with a topological index of ±1, are also observed. The effect of defects on the transition from the 1D to 2D structures is considered.

EPR spectra and relaxation times of natural π-conjugated polymers doped with iodine

The magnetic properties of natural π-conjugated polymers doped with iodine have been studied by EPR spectroscopy. It is established that an increase in the spin susceptibility upon doping is caused by the formation of π-electron radicals localized at the aromatic fragments of the polymer. Dependences of the spin-spin and spin-lattice relaxation times of these radicals on the doping level have been experimentally determined.

Graphitization of Polyacetylenes Prepared by Phase-Transfer Dehydrochlorination of Polyvinyl Chloride

To develop procedures for producing graphite from polyacetylene, the effect of crystalline regions in the structure of homo- and copolymers of acetylene with vinyl chloride on the structure and properties of the products of their profound carbonization was studied.

Soliton-like defects in nematic liquid crystal thin layers

The nonsingular soliton-like defects in plane nematic liquid crystal (NLC) layers and spherical NLC drops are experimentally detected and studied when the interaction of NLC molecules with a bounding surface is varied. The dynamics and the annihilation of nonsingular defects of opposite signs on a plane surface are investigated. Periodic transformations of the soliton-like defects in NLC drops in an electric field are detected. The theory of elasticity is used to show that the surface energy taken into account in the total free energy of NLC in the case of weak anchoring leads to the possibility of nonsingular solutions of a director equilibrium equation. The calculated pictures of director distribution in a plane NLC layer and in a spherical NLC drop characterized by weak surface anchoring agree well with the results of polarized light optical observations.

Change in the Molecular Structure of Components of Isotropic Fractions of Petroleum Pitches in the Thermopolycondensation Process

The effect of heat-treatment temperature and time on the mesophase formation process in the thermopolycondensation of isotropic petroleum pitch is studied by fluorescence and UV spectroscopy. The molecular structure of the basic components of isotropic petroleum pitch fractions is established. It is shown that UV spectroscopy is ineffective for analysis of multicomponent oil systems, whereas fluorescence spectroscopy allows study of the mechanism of molecular transformations in the mesophase petroleum pitch conversion process.

On the synthesis of polyacetylene by the interphase dehydrochlorination of polyvinyl chloride

Abstract The dehydrochlorination of PVC has been studied under interphase catalysis conditions, using various solvents and dehydrochlorinating agents. The predominating effect of the interface on the parameters of the process and on the properties of the polyacetylene prepared by the dehydrochlorination of PVC was observed. It is shown that a clearcut liquid-liquid interface (PVC solution-solution of the dehydrochlorinating agent) promotes the formation of crystalline polyacetylene structures. The formation of mainly amorphous polymer is promoted when the interface is a rather diffuse region as when dehydrochlorination takes place at interfaces such as:PVC film or PVC powder-solution of the dehydrochlorinating agent, or PVC solution-powder of the dehydrochlorinating agent, i.e. where a solid body-liquid type of interface is involved.