Ordering of Chiral Smectics in Freely Suspended Film

Abstract

The method to study phase transitions of thin systems on the basis of a bulk phase diagram is applied to a freely suspended film of ferroelectric smectics showing a first order phase transition in the bulk, where an ordering effect due to surface layers is replaced by an effective field which is conjugate to the order parameter. In the framework of a phenomenological free energy whose coefficients are determined form the experimental evidence about C7, the behaviour of the transition is being clarified, which coincides with experimental findings, and especially the small shift of transition temperature from the bulk one is elucidated. The mechanism of the continuous change occurring in the system of thickness just below a critical thickness is clarified, where an unstable state which is never realised in the bulk appears at the interior layers. The behaviour of this continuous change discloses the difference between the ordering effects due to the boundaries and the external fields.