STATISTICAL THERMODYNAMICS OF POLYMER LIQUID-CRYSTALS - COMPETITION BETWEEN ENERGETIC AND ENTROPIC EFFECTS

A system of linear polymer liquid crystal (PLC) macromolecules is cons idered in which each macromolecule constitutes an alternating copolyme r of flexible and LC sequences. The distribution function of the syste m is factorized so that the Gibbs distribution is used for anisotropic ally interacting LC sequences while Dirac delta functions represent fl exible polymer sequences modeled by linear chains of freely jointed st atistical segments. A general formula for the Helmholtz function is de rived for arbitrary types of anisotropic interactions between LC seque nces; the formula of Maier and Saupe for monomer LCs is obtainable fro m it as a special case. The phase diagram of the system is obtained in the limit of the mean-field approach. Types and orders of phase trans itions that the system can undergo are defined and discussed in terms of the Landau classification; all transitions are of the first order. Formation of cholesteric phases in addition to isotropic and nematic o r smectic is predicted without involving additional assumptions such a s the biaxiality of the LC interactions. (C) 1996 American Institute o f Physics.