Isotropic−Cholesteric Phase Equilibrium in Solutions of Cellulose Tris(phenyl carbamate)

Abstract

The isotropic−cholesteric phase boundary concentrations and interfacial tension were measured for tetrahydrofuran (THF) solutions of fractionated cellulose tris(phenyl carbamate) (CTC) samples. The phase boundary concentrations are compared with the scaled particle theory for the hard wormlike spherocylinder model as favorably as those for other stiffer polymer systems, though the theory does not consider effects of the intramolecular excluded-volume and intermolecular multiple contacts, both of which are appreciable for high molecular weight CTC samples. This may be due to cancellation of the two effects in the isotropic−cholesteric phase equilibrium. The interfacial tension γ between the coexisting isotropic and cholesteric phases for the CTC−THF system slightly decreases with molecular weight, and the asymptotic value is higher than those of other stiffer polymer systems. The dependence of the asymptotic γ on the persistence length is consistent with Cui et al.'s theory based on the second virial approximation, but its magnitude is much larger than the prediction of the theory, indicating that higher virial terms in thermodynamic quantities play a significant role in γ .