Elastic deformations of liquid-crystalline polymers and their monomers in magnetic and electric fields

Abstract

A thermotropically mesogenic aromatic polyester and its low molecular weight analogue (“monomer”) in the nematic phase in thin layers form homeotropic textures which can be deformed under the influence of magnetic or electric fields. The elastic orientational deformations generated are of the threshold character (Freederiksz's transition) and are used for the determination of bend elastic constants, K 3, of the polymer and low molecular weight nematics. The optical anisotropies ( n e − n o ), of the samples investigated were determined from the polarized-microscopic patterns of the deformed layers. The values of ( n e − n o ) for the polymeric and the low molecular weight nematics virtually coincide and over the investigated temperature range vary from 0.08 to 0.17. The bend constants, K 3, are close in order of magnitude for the polymer and the monomer and vary with temperature in the ranges (5–20) · 10 −7 and (3–10) · 10 −7 dyn respectively. The orientation of molecules of the polymer nematic in magnetic and electric fields follows the mechanism of local small-scale chain motion.