SIGN INVERSION OF LIQUID-CRYSTAL-INDUCED CIRCULAR-DICHROISM OBSERVED IN THE SMECTIC-A AND CHIRAL SMECTIC-C-ALPHA PHASES OF BINARY MIXTURE SYSTEMS

Liquid-crystal-induced circular dichroism (LCICD) measurements have be en made to investigate the structure of smectic-C-alpha using liquid- crystal-mixture systems, in which zero spontaneous polarization P-s=0 or infinite pitch is realized. Two main observations are as follows: ( 1) LCICD shows a cusp bur not a discontinuous change at the Sm-A-Sm-C- alpha phase transition; and (2) the sign of the LCICD in Sm-A and Sm- C-alpha is correlated with the sign of P-s, and LCICD is hardly obser ved near a mixing ratio of zero P-s. Based on these observations. we h ave concluded a dynamic helical structure with very a long average pit ch in Sm-C-alpha and an important role played by the flexoelectric ef fect.