Thermodynamic characterization of polymer-polymer interfaces

The properties of multiphase polymer blends are determined in part by the n ature of the polymer-polymer interface. The interfacial tension, gamma, inf luences morphology development during melt mixing while interfacial thickne ss, lambda, is related to the adhesion between the phases in the solid blen d. A quantitative relation between the thermodynamic interaction energy and these interfacial properties was first proposed in the theory of Helfand a nd Tagami and has since been correlated with experimental measurements with varying degrees of success. This paper demonstrates that the theory and ex periment 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 bina ry interaction model expressed in terms of the interactions between repeat unit pairs extracted from blend phase behavior. Predictions of gamma and la mbda as a function of copolymer composition made by combining the binary in teraction model with the Helfand-Tagami theory compare favorably with exper imental measurements.