DETERMINATION OF CLOUD-POINT, SHADOW AND OTHER COEXISTENCE CURVES IN MULTICOMPONENT SYSTEMS FROM MEASUREMENTS OF PHASE VOLUME RATIOS

Liquid-liquid demixing of polydisperse polymer systems is described by volume balance equations relating the phase volume ratio to the bulk concentration of a polymer and its equilibrium concentrations. It is s hown that in a system of a solvent and a polydisperse polymer, cloud-p oint and shadow curves and the concentrations of coexisting phases may be obtained from the linearized volume or mass conservation equation. Also half meter curves for different phase volume ratios are obtained . The intersection of the half meter curve for equal phase volumina of coexisting phases with the cloud-point or shadow curve leads to a det ermination of the critical point. The findings are illustrated in the system poly(ethylene oxide)/water, where the thresholds of cloud-point and shadow curves do not coincide with the critical demixing point. T his is typical of a multicomponent polymer/solvent system.