Elasticity and orientational order in some 4'-n-alkyl-4-cyanobiphenyls: Part II

Abstract

The splay and twist elastic constants (k11 and k22) of pentyl, hexyl, heptyl and octyl cyanobiphenyls (5CB, 6CB, 7CB and 8CB respectively) have been determined by the Freedericksz transition method. The results are compared with the bend elastic constants (k33) and order parameters (S) of these compounds reported by us in an ealier paper, as also with the heats of transition (b.deltaH) determined using a differential scanning calorimeter and the temperatures of transitions (TNI). TNI, and k33 near TNI, exhibit alternation for all the four compounds. On the other hand, S, b.deltaH, and k11 and k22, near TNI exhibit alternation only for the first three compounds and increase between 7CB and 8CB. It is concluded that (b.zetabottom/b.zetapar), the ratio of the transverse to the longitudinal correlation lengths of the smectic A type cybotactic order increases between 7CB and 8CB.