The Region of Coexistence of Isotropic and Anisotropic Solutions in Polymer Liquid Crystals

Abstract

The width of the biphasic gap separating the pure isotropic and anisotropic phases has been investigated for samples of poly(p-benzamide), poly(γ-benzyl-L-glutamate), and poly(n-hexyl isocyanate). The determination was performed by studying the variation of the volume fraction of isotropic phase, φ with polymer volume fraction, v ₂, particular emphasis being placed on the behavior at low values of φ. The dependence of φ upon v ₂ is more complex than previously reported. Still the biphasic gap, defined by the ratio of the limiting compositions of anisotropic (v”₂)φ₌₀ and isotropic (v'₂)φ₌₁ phases, is a rather narrow one. (v”₂)φ=₀/(v ₂)φ₌₁ does not exceed 1.9 for the polymer investigated. By contrast, theoretical predictions which account for the polydispersity of chain length suggest ratios at least one order of magnitude larger. The behavior of polydisperse system is close to the prediction for a monodisperse one. The origin of the discrepancy is not known.