ON THE WATER-INDUCED CRITICAL DOUBLE POINT IN A POLYMER-SOLUTION - THE ROLE OF ISOTOPIC-SUBSTITUTION

This paper examines the effect of substitution of water by heavy water in a polymer solution of polystyrene (molecular weight = 13000) and a cetone. A critical double point (CDP), at which the upper and the lowe r partially-miscible regions merge, occurs at nearly the same coordina tes as for the system [polystyrene + acetone + water]. The shape of th e critical line for [polystyrene + acetone + heavy water] is highly as ymmetric. An explanation for the occurrence of the water-induced CDP i n [polystyrene + acetone] is advanced in terms of the interplay betwee n contact energy dissimilarity and free-volume disparity of the polyme r and the solvent. The question of the possible existence of a one-pha se hole in an hourglass phase diagram is addressed in [polystyrene + a cetone + water]. Our data exclude such a possibility.