THE EFFECT OF MOLECULAR-WEIGHT AND POLYDISPERSITY OF POLYSTYRENE ON THE INTERFACIAL-TENSION BETWEEN POLYSTYRENE AND POLYBUTADIENE

The effect of molecular weight and polydispersity on the interfacial t ensions between polystyrene and polybutadiene homopolymer is examined by using a pendant drop apparatus. The data show that the interfacial tension of the monodisperse homopolymer decreases linearly with temper ature and increases with molecular weight. The interfacial tension bec omes lower as the polydispersity of polystyrenes having the same numbe r-average molecular weight increases. It is also found that the interf acial tensions of unimodal polystyrene mixtures are quite different fr om those of bimodal polystyrene mixtures. In the case of bimodal polym er systems, the lower-molecular-weight species is considered to migrat e preferentially to the interface in order to reduce the free energy o f the interface, which results in lowering the interfacial tension. Fr om the slope of the plot of interfacial tension versus temperature, th e interfacial entropy increases with the polydispersity, indicating th at the higher polydispersity gives rise to more aggregation of the low er-molecular-weight species at the interface.