An experimental study of the smectic A-smectic C transitions in monolayer, partially bilayer and bilayer systems

Abstract

The smectic A-smectic C (A-C) transition in several compounds has been shown to be mean-field-like (MF) with a substantial tricritical crossover effect. However, a simple MF behaviour, i.e., with negligible tricritical influence, had not been reported till recently. The heat capacity measurements of the MIT group in two compounds exhibiting the bilayer A₂-C₂ transition revealed such a behaviour. It is of interest to investigate whether a simple MF behaviour can be observed for partially bilayer A_dminusC_d and monolayer A¹-C₁ transitions also. We report the first systematic order parameter measurements in the vicinity of the A₂-C₂, A_d-C_d and A₁-C₁ transitions. The data analysed in terms of power law and extended mean field expressions provide clear evidence of a simple MF behaviour in all three cases. The significance of this result is discussed.