Thermodynamic characterization of polymer-polymer interfaces

The properties of multiphase polymer blends are determined in part by the nature of the polymer-polymer interface. The interfacial tension, gamma, influences morphology development during melt mixing while interfacial thickness, lambda, is related to the adhesion between the phases in the solid blend. A quantitative relation between the thermodynamic interaction energy and these interfacial properties was first proposed in the theory of Helfand and Tagami and has since been correlated with experimental measurements with varying degrees of success. This paper demonstrates that the theory and experiment can be unified for polymer pairs of some technological importance: copolymers of styrene and acrylonitrile (SAN) with poly (2, 6-dimethyl-1, 4-phenylene oxide) (PPO) and with bisphenol-A polycarbonate (PC). For each pair, the overall interaction energy was calculated using a mean-field binary interaction model expressed in terms of the interactions between repeat unit pairs extracted from blend phase behavior. Predictions of gamma and lambda as a function of copolymer composition made by combining the binary interaction model with the Helfand-Tagami theory compare favorably with experimental measurements.