THE EFFECT OF CHIRALITY ON THE PHASE-TRANSITIONS OF CHIRAL 8CB MIXTURES/

We report on a study of mixtures of octylcyanobiphenyl (8CB) and equal amounts of two chiral agents (CE2 and CB15) as a function of chiral p itch (concentration). Bulk studies reveal a widening cholesteric tempe rature range with increasing chirality. The first order cholesteric-is otropic (Ch-I) transition shifts marginally to lower temperature with increasing chirality while exhibiting a pretransition feature near its C-p maximum. The smectic-A-cholesteric (SmA-Ch) C-p anomaly becomes s maller and continuously shifts to lower temperatures with increasing c hirality while exhibiting the unique feature of a discontinuous jump o n the low temperature side of the C-p peak. The increased chirality su ppresses the smectic formation through twist elastic distortion. Upon Anopore confinement, the C-p maximum of the Ch-I transition increases as compared to bulk with the disappearance of the pre-transition featu re; the SmA-Ch transition becomes extremely rounded and suppressed. Th e transitions shift to lower temperatures while retaining the bulk cho lesteric temperature range.