Temperature variation of the layer spacing in the smectic A, reentrant nematic and reentrant smectic A phases of 9 OBCAB

Abstract

Precise X-ray determinations have been made of the temperature variation of the layer spacing in the smectic A, reentrant nematic and reentrant smectic A phases of a pure reentrant mesogen, viz., 4-nonyloxy-benzoyloxy-4'-cyanoazobenzene (9 OBCAB). The higher temperature smectic phase is (partially) bilayer in nature, the extent of the overlap increasing with decrease of temperature. The reentrant smectic A has a monolayer structure whose spacing is temperature independent. The change from the bilayer to monolayer arrangement is a continuous process which commences in the reentrant nematic phase and continues right through it.