INTERFACIAL-TENSIONS OF PHASE-SEPARATED POLYMER-SOLUTIONS

Measurements of the capillary length in phase-separated solutions of polymethylmethacrylate in 3-octanone (PMMA/3-OCT) for each of five different molecular weights of PMMA, and in phase-separated solutions of polystyrene in methylcyclohexane (PS/MCH) for a single molecular weight of polymer, are reported. Measurements on PMMA/3-OCT were by the sessile-drop method; those on PS/MCH were by both the sessile-drop and capillary-rise methods. Interfacial tensions are estimated from estimated density differences and the measured capillary lengths. A theoretically predicted scaling law for the dependence of capillary length on polymer molecular weight and temperature is tested and at least semiquantitatively verified. As by-products of the sample preparation, the molecular-weight dependences of the critical composition and critical solution temperature of PMMA/3-OCT were also determined. The volume fraction of polymer at the critical point, phi(c), is found to be proportional to the -0.37+/-0.01 power of the molecular weight, in agreement with values of this exponent found by others for polystyrene solutions.