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 (δH) determined using a differential scanning calorimeter and the temperatures of transitions (T_NI). T_NI, and k₃₃ near T_NI, exhibit alternation for all the four compounds. On the other hand, S, dH, and k₁₁ and k₂₂, 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.