The Formation Process of the Cholesteric Structure in Poly (γ-benzyl L-Glutamate) Liquid Crystalt

Abstract

The kinetic mechanism of the cholesteric-phase formation from the nematic state was investigated by polarizing microscopy and polarized light scattering. The concentrated solution of Poly(γ-benzyl L-glutamate) (Mv=1.5 x 10⁵) in N, N-dimethylformamide at a volume fraction of 0.191 (v/v) was prepared in a glass tube (thickness=2, 0 mm) sealed to prevent solvent evaporation. This sample was held at nematic temperature of 90°C for 5 days andsuddenly cooled to 20°C. Microscopic pictures and light scattering patterns were taken at successive time intervals. The qualitative interpretation of the light scattering patterns was performed by reference to the results on the study of the distortion of an ordered structure in the suspension of ionic polymer latex particles by Ise et al..
It was found from the results of these experiments that the formation of the cholesteric structure from nematic state occurred in three steps as follows: ( 1 ) At first the uniform nematic domain was divided into some polydomains (Fig.1), in which the cholesteric pitch was not observed; ( 2 ) Irregular cholesteric pitch appeared in each domain under a polarizing microscope and the pitch became more regular at successive times (Fig.2). The average value of the pitch did not change with time (Fig.5) but only its standard deviation gradually diminished and reached at a constant value (Figs.3 and 4). The direction of the cholesteric axis normal to the retardation line does not, on the whole, oriented at this step; ( 3 ) During successive long time further change occurred in the cholesteric structure. Some cholesteric domains assembled together and became progressively greater in size. On the other hand, cholesteric axis was oriented along equatorial direction as depicted by arrow in Fig.6-1. Thus macroscopically homogeneous structure of the cholesteric phase was formed in equillibrium state. Liquid Crystalline Structures of Poly-a-amino Acids. VI.