V. N. Tsvetkov

Diffusion and flow birefringence of alkylene-aromatic thermotropic polyesters

Abstract Hydrodynamic and optical properties of dilute solutions of polydecamethylene-terephthaloyl-di- p -oxybenzoate (P-10-TOB), polypentamethylene-terephthaloyl-di- p -oxybenzoate (P-5-TOB) and polytetramethylene-terephthaloyl-di- p -oxybenzoate (P-4-TOB) in dichloroacetic and trifluoroacetic acids were investigated by translational diffusion, velocity sedimentation, viscometry and flow birefringence. The results of hydrodynamic investigations are interpreted from the standpoint of theories taking account of the draining effect in macromolecules. It is shown, on the basis of hydrodynamic and optical data, that the equilibrium rigidity of molecules (the Kuhn statistical segment) is several times higher for P-10-TOB, P-5-TOB and P-4-TOB than for polyethyleneterephthalate.

Orientational Order and Elastic Deformations in Nematic Texturfs of bis-4-Cyanobiphenyloxyalkanes in an Electric Field

Abstract Using the method of orientational elastic deformations in an electric field we investigated the electrooptical properties of nematics of the bis-4-cyanobiphenyloxyalkanes series differing in the number n of CH2 groups in the oxymethylene chain of the molecule. The value of optical anisotropy of nematics (Δ n=ne - no) and threshold electric potentials Vo of deformations of their monodomain planar texture were determined at different temperatures. In both dependences of Δ n and I/Vo on n strong odd-even effect is manifested. However, the characters of alternations observed in them differ greatly. These differences are due to the fact that the value and sign of I/Vo depend not only on the intermolecular (nematic) orientational order but is determind to a much greater extent by intramolecular order which depends on the polar and polarizing architecture of the molecule.

Kerr effect in solutions of a thermotropically mesogenic alkylene-aromatic polyester

Abstract Electric birefringence (EB, Kerr effect) has been investigated for solutions of fractions of thermotropically liquid-crystalline alkylene-aromatic polyester (PE-10) and of its monomer. A very specific dependence of EB on the molecular weight (M) of the polymer was found: for low molecular weight substances the Kerr constant is negative, changes its sign with increasing M and, in the range of positive values, increases with M. These data are in quantitative agreement with the dependence of K on M predicted by the EB theory for kinetically rigid worm-like chains in which the longitudinal components of dipole moments of monomer units are “accumulated” with increasing chain length. The detected relationships show that in PE-10 solutions the Kerr effect is due to the large-scale chain motion in which the behaviour of a dipole molecule is similar to the motion of a kinetically rigid particle rotating as a whole by the action of the field.

Hydrodynamic and dynamo-optical properties of molecules of an aromatic polyester with para- and meta-phenyl rings in the main chain

Abstract The hydrodynamic and optical properties of molecules of an aromatic polyester (PE) dissolved in dichloroacetic acid have been investigated by the methods of translational diffusion, viscometry and flow birefringence. The chain of the PE investigated contains one phenyl ring in the meta-position alternating with three phenyl rings in the para-position. The Mark-Kuhn equations relating intrinsic viscosity and the translational diffusion coefficient to molecular weight have been obtained: [η] = 2.6 × 10−3 M1.1 cm3 g−1 and D = 5.6 × 10−5 M−0.70 cm2 sec−1. The results are interpreted in terms of theories of hydrodynamic and dynamo-optical properties of wormlike chains. It is shown that the PE macromolecules in solution exhibit equilibrium rigidity determined by the length of the Kuhn statistical segment A = 120 ± 20 A and the anisotropy of unit chain length β = 5 × 10−17 cm2.

Electric birefringence in solutions of rigid-chain aromatic polyamides

Abstract Electric birefringence (EB) in solutions of a number of fractions and samples of polyamide benzimidazole (PABI) in dimethylacetamide (DMAA) and polyamide hydrazide (PAH) in dimethylsulphoxide (DMSO) has been investigated by using rectangular pulsed and sinusoidal pulsed fields. Study of EB dispersion in sinusoidal fields and the kinetics of rise and decay of EB in rectangular pulse fields indicates that the main mechanism responsible for the measured EB for both polymers is the large-scale motion of their polar molecules caused by the orienting effect of the field on rigid permanent dipoles of their chains. Relaxation times τ are determined from the dispersion of EB. The Kuhn segment lengths are estimated from the dependence of τ on molecular weight. The values of these length for PABI and PAH chains virtually coincide at (25 ± 10) nm. Study of the value of the Kerr constant and its dependence on molecular weight shows that strongly polar and electroconducting solvents, DMAA and DMSO, used in this work play an important part in the formation of macromolecular dipoles.

Electric Birefringence in Solutions of Bis-4-Cyano-Biphenyloxyalkanes

Abstract The electrooptical properties of 4,4′-bis- cyanobiphenyloxyalkanes in dioxane and benzene were investigated by the method of equilibrium electric birefringence. A non-monotonic dependence of the Kerr molar constant of these compounds on the length of the oxyalkane spacer was found. This dependence is due to the influence of the odd-even effect on the intramolecular orientational polar and anisotropic order. The problems are discussed of the effect of equilibrium and kinetic spacer flexibility on the value and sign of the observed birefringence and on the degree of correlation in orientations of mesogenic chain fragments in an electric field.

Kerr effect in solutions of cellulose carbanilate in polar solvents

Abstract Electric birefringence has been investigated by using rectangular-pulse and sinusoidal-pulse fields in four low molecular weight liquids with different molecular polarities and also in solutions of cellulose carbanilate (CC) in these liquids. The parameters of equilibrium and kinetic flexibility of molecules of this polymer in various solvents were determined from the data on the dispersion of the Kerr effect in sinusoidal-pulse fields in solutions of CC. The data on equilibrium electro-optical and dynamo-optical properties of solutions of CC led to the conclusion that orientational correlation exists between the dipolar molecules of the solvent and the polar units of the polymer chain.

Electric birefringence in polybutylisocyanate solutions

Abstract Electric birefringence (EB) in solutions of a series of fractions of polybutylisocyanate (PBIC) in tetrachloromethane in the range of molecular weights ( M ) from 5 × 10 3 to 8 × 10 5 was investigated by using sinusoidal and rectangular pulse fields. Dispersion relaxation times (τ) were determined from dispersion of EB in a sinusoidal field. The times of free relaxation (〈 τ 0 〉) and the times ( Q R ) of the rise in EB were determined from the rise and decay of EB. It is shown that, for M ⩽ 10 5 , EB in PBIC solutions is entirely determined by the large-scale orientation of kinetically rigid polar molecules whereas, for M ⩾ 2 × 10 5 , the EB phenomenon reveals the kinetic flexibility of polymer chains. By using the theory of rotational friction and the dependence of τ on M , the persistence length of PBIC molecules was found as (40 ± 5) nm. The number of monomer units in the Kuhn segment, S = 360, was determined from the dependence of the Kerr constant K on M . The longitudinal component of the dipole moment of the monomer unit, μ 011 = 1.9 D , was determined from the comparison of data on EB with those on flow birefringence. This value agrees with the dipolar structure of PBIC chain. Apart from the conjugation effect, an important role in the hindrance to rotation in the PBIC chain is also played by the interaction between side groups.

Conformational characteristics of para-aromatic polyester molecules as shown by diffUSAion, viscometry and flow birefringence of their solutions☆

Translational diffUSAion, viscometry and f.b.r. have been USAed to study the hydrodynamic and optical properties of a p-aromatic polyester of different MW in dichloroacetic acid. It is shown that the polyester macromolecules display in the f.b.r. phenomenon properties of kinetically rigid worm-like chains and are characterized by the parameter of equilibrium rigidity-length of the Kuhn segment A = (380 ±50) A, the factor of braking of internal rotation σ=1·1 and the anisotropy of the chain unit length β=8·6×10−17 cm2.

Orientational Elasticity of Nenatic Dimers

Abstract Using the method of threshold Fredericks transitions in magnetic field were determined the values of splay orientational elastic constants K11 of the nematic dimers 4,4′-bis-cyanobiphe-nyloxyalkanes with the number n of CH2 groups in their spacers from 2 to 12. The dramatic odd-even effect in the dependence of K11 versus n was evaluated. This effect is mainly due to the oscillations of the degree of intermolecular orientational order in the series of the compounds under investigation. The increase of the values of the splay elastic constant K11 of both odd and even homologous series of nematic dimers with increase of the spacer length was determined.