Solutions of Rigid Chain Polymers

Papkov, S. P. Liquid Crystalline Order in Solutions of Rigid-Chain Polymers. Vol. 59, pp. 75— 102. 

Two approaches to the attainment of the oriented states of polymer solutions and melts can be distinguished. The first one consists in the orientational crystallization of flexible-chain polymers based on the fixation by subsequent crystallization of the chains obtained as a result of melt extension. This procedure ensures the formation of a highly oriented supramolecular structure in the crystallized material. The second approach is based on the use of solutions of rigid-chain polymers in which the transition to the liquid crystalline state occurs, due to a high anisometry of the macromolecules. This state is characterized by high one-dimensional chain orientation and, as a result, by the anisotropy of the main physical properties of the material. Only slight extensions are required to obtain highly oriented films and fibers from such solutions. 

Liquid Crystalline Order in Solutions of Rigid-Chain Polymers... 

Orientational order appears in the solutions of rigid-chain polymers because a random mutual arrangement of their macromolecules is possible only up to a certain concentration of the solution. To retain a minimal volume (minimal free energy) above a certain critical concentration, asymmetric macromolecules must acquire an ordered mutual arrangement, which corresponds to a transition to the state typical for liquid crystals. In this case the solution becomes anisotropic. The degree of this anisotropy is still less than strict three-dimensional ordering typical of crystalline systems, but at the same time it differs from that of the isotropic state typical of amorphous systems. 

Aikawa et al. considered the effect of electric field on the phase transition in solutions of rigid-chain polymers for a PBLG solution in dioxane. Theoretical calculations have shown that the application of an electric field must shift the values of v towards lower concentrations. This conclusion was confirmed in experiments. According to the results obtained by Patel et al the application of electric fields also causes a shift in the temperature of the liquid crystalline transitions. 

It has been shown that the main medianism responsible for EB in solutions of rigid-chain polymers is the rotation of their polar molecules as a whole whereas the anisotropy of the dielectric polarizability of the macromolecules only provides a small contribution to the Kerr effect. Hence, the general theory of the Kerr effect for rigid dipole particles with axial symmetry of the optical polarizability can be... 

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