Interfacial tensions between immiscible homopolymers are measured using an automated pendant drop apparatus, which utilizes Video Digital Image Processing techniques. A recently developed robust shape analysis algorithm is used to analyze the experimental drop profiles. The data show the effect of temperature and number average molecular weight (Mn) on the interfacial tension for the immiscible blends polystyrene-poly(methyl methacrylate), polybutadiene-poly(dimethyl siloxane) and polystyrene-hydrogenated 1,2 polybutadiene. Interfacial tension decreases linearly with temperature and increases with molecular weight. The data for all three systems can be approximated by an empirical relationship. The interfacial tension data for the latter blend system are compared with thermodynamic theories of polymeric interfaces. A square gradient theory approach, in conjunction with the Flory-Huggins expressions for the free energy of mixing, predicts a magnitude and temperature dependence of interfacial tension which are in reasonable agreement with experimental data, and does predict a molecular weight dependence which roughly follows the empirical relationship.
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Anastasiadis et al. (1988) studied this question.