Layer-by-layer ordering of ultrathin liquid crystal films on the three-level Potts model

¹ Department of Physics, State University of New York at Buffalo Buffalo, New York 14260, USA
² Department of Physics, Nankai University - Tianjin 300071, PRC
³ Department of Physics, Zhongshan University - Guangzhou 510275, PRC
⁴ Department of Physics, Hong Kong University of Science and Technology Kowloon, Hong Kong, PRC
⁵ Applied Materials Co. - 3320 Scott Boulevard, M/S 1114 Santa Clara, CA 95054, USA

Received: 5 July 1999
Accepted: 10 April 2000

Abstract

The three-level Potts model with variable coupling strengths is proposed to describe the newly observed smectic- to smectic-A phase transition in free-standing liquid crystal films. In a film of L molecular layers, the transition temperature for individual layers is determined separately by the bifurcation point of the free energy in the variational cumulant expansion (VCE), from which the heat capacity is also calculated analytically. By adjusting the interlayer and intralayer coupling between nearest-neighboring molecules, it is shown that the calculated heat capacity qualitatively reproduces the observed anomaly around transition temperatures in experiments on free-standing 54COOBC films of two and more molecular layers.