Phase Equilibrium of a Three-Component System Consisting of Polystyrene, N,N-Dimethylformamide, and Cyclohexane

Abstract

Phase equilibrium and light scattering experiments were performed on a three-component system consisting of polystyrene (PS), N,N-dimethylformamide (DMF, good solvent), and cyclohexane (CH, poor solvent). The interaction function χ was expressed in the form proposed by Einaga et al., i.e., χ=ξ12χ11b(φ1)+ξ22χ22b(φ2)+2ξ1ξ2χ12t(φ1,φ2), where χ11b is the interaction function for the binary system of DMF and CH, χ22b, that for the binary system of PS and CH, and χ12t a function describing the interaction of PS and DMF in the presence of CH, with φ1 and φ2 denoting the volume fractions of DMF and PS in the system, respectively, and ξi=φi/(φ1+φ2) (i=1, 2). χ11b was determined by the Renon-Prausnitz theory along with cloud-point data, χ22b was calculated by the empirical equation of Einaga et al., and χ12t was estimated from light scattering data using χiib (i=1, 2). With χ so obtained, binodals of the system at various temperatures on the triangular phase diagram were calculated and compared with those determined from cloud-point data. The agreement was only moderate. Reasons for this are discussed.