Evidence of tilted monolayer cybotactic groups in a partially bilayer SA phase

Abstract

A study using X-ray diffraction for 4 nonanoate 4' cyanobiphenyl (8 COO CB) shows that the SA phase has a partially bilayer structure with layer thickness d = 1.4 L (L : molecular length). It also shows monolayer fluctuations inside this phase. Moreover, it points out that there exist skewed cybotactic groups of single molecules in the partially bilayer S A phase in the supercooled range of the SA phase. The size of these groups is about 500 molecules, the tilt angle is about 35°. A study using dielectric relaxation for this compound has also been performed. It shows that the activation energy for reorientational movement of the molecule has unusual behaviour. With decreasing temperature, this energy decreases to the N-SA transition but it increases in smectic supercooled range. Variations obtained are in agreement with information obtained from X-ray experiments.