Spinodal decomposition in mixtures containing nematogens

Abstract

A general stability criterion is presented for mixtures containing nematic liquid crystals. Conditions for absolute phase instability are found and represent a generalization of the usual spinodal concept. Physically, these conditions represent instabilities with respect to variations in the systems composition, degree of molecular ordering or some combination thereof. An example calculation corresponding to a liquid-crystalline polymer is presented. This calculation is based upon a well known lattice model which includes energetics that are dependent upon molecular orientation. Spinodal decomposition has profound effects on the morphology of a system which undergoes phase separation. Recent experimental and theoretical studies have attempted to explore these consequences in liquid-crystalline systems. None gives a rigorous definition of what is meant by spinodal in a mixture with orientational degrees of freedom; the material presented here clarifies this issue.