Nematic Ordering and Anisotropic Viscoelastic Properties in a Main-Chain Polymer System.
The fundamental features of macroscopic phenomena in polymer nematics formed from solutions of long rigid or semirigid macromolecules are studied from theoretical and experimental points of view. Firstly, the theoretical study of nematic ordering, curvature elasticity, and nematodynamic behavior in main -chain polymer systems is completely carried out. Analytical formulations as well as numerical analyses are performed for basic understanding of the phenomena in terms of the intrinsic material parameters such as the great length of the polymers and the degree of their flexibility. The Onsager-type free energy are formulated for studying the effect of charge, chain flexibility, and an external flow field on the stability of the nematic phase. A self-consistent functional scaling is also proposed to analyze the phase behavior and elastic properties of liquid-density nematics in which the low density approximation is obviously not appropriate. The generalized molecular kinetic theory is described, and molecular expressions for the Leslie coefficients are obtained. Secondly, quasi-elastic Rayleigh scattering on well oriented nematic liquid crystals of Poly- gamma-Benzyl-Glutamate (PBG), which belongs to a class of synthetic polypeptides, is performed to determine their elastic and nematodynamic viscosity coefficients as a function of molecular chain length. The first observation of the crossover from rigid to semiflexible behavior of the viscoelastic coefficients for a PBG nematic system is reported. The experimental results are compared with existing theoretical predictions in detail. The speculative and qualitative ideas are also presented.
- Pub Date:
- Physics: Molecular