Smectic-C* to Smectic-A Transition in Variable-Thickness Liquid-Crystal Films: Order-Parameter Measurements and Theory

This paper presents the results of experimental measurements and a mean-field-theory analysis of the behavior of the average tilt angle near the smectic-C^* to smectic-A transition in thin films of two through ten molecular layers. These films provide one of the few physical realizations of systems where the surface layers remain ordered to a higher temperature than the bulk. The mean-field theory provides excellent quantitative fits to the critical-temperature spectrum and good qualitative fits to the order-parameter behavior.