SMECTIC-A - CHOLESTERIC LIQUID-CRYSTAL PHASE-TRANSITION - A DENSITY STUDY

The present work is focused on density measurements near the smectic A -cholesteric liquid crystal phase transition for cholesteryl myristate (C-14), cholesteryl nonanoate (C-9) and binary mixtures of C-14 and C -9 and cholesteryl caproate (C-9) and C-9. The results have evidenced that the transition crosses over from first to second order when both the mean molecular length and the reduced temperature, r (ratio betwee n the smectic A-cholesteric and cholesteric-isotropic phase transition temperatures); decrease in the system. The occurrence of a second ord er phase transition is observed for a concentration very near 63.1 mol ar percent of C-9 in the C-6-C-9 mixture at r congruent to 0.92.