Elasticity and Orientational Order in Some 4′-n-Alkyl-4-Cyanobiphenyls: Part II

Abstract

The splay and twist elastic constants (k ₁₁ and k ₂₂) 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 (k ₃₃) and order parameters (S) of these compounds reported by us in an ealier paper, as also with the heats of transition (δH) determined using a differential scanning calorimeter and the temperatures of transitions (T _NI). T _NI, and k ₃₃ near T _NI, exhibit alternation for all the four compounds. On the other hand, S, δH, and k ₁₁ and k ₂₂, near T _NI exhibit alternation only for the first three compounds and increase between 7CB and 8CB. It is concluded that (ζ_⊥/ζ_∥), the ratio of the transverse to the longitudinal correlation lengths of the smectic A type cybotactic order increases between 7CB and 8CB.