Optical Properties and Phenomenological Theory of Ferri-Ferri Phase Transitions in Antiferroelectric Liquid Crystals

(Received 20 January 1997, revised 16 July 1997, accepted 2 September 1997)

Abstract
Optical rotatory power and Raman scattering experiments on chiral liquid crystals belonging to a series which exhibits one or two ferrielectric phases have been performed. The results of these non-perturbative techniques show that, depending upon the aliphatic chain length, a first order transition with a jump in sign and value of the helical pitch, or a divergence and sign reversal of the pitch with no transition can occur in these systems. These observations are in agreement with a generalized Landau-de Gennes phenomenological model predicting that the ferrielectric phases, when both exist, should be isostructural.