Coalescence and interfacial tension measurements for polymer melts: experiments on a PS-PE model system

Abstract

A novel technique to measure coalescence phenomena in polymer blends was developed using a spinning drop apparatus. To date, coalescence experiments on polymers were performed by the slow process of gravity driven collisions. In comparison, the spinning drop method is more rapid and more versatile in its control of the contact radius and coalescent force. The governing parameters of the coalescence process, notably interfacial mobility and matrix film rupture thickness, can be assessed by testing a range of droplets of varying size. The relatively high mobility of the interface demonstrated by the experiments explains the dominant role played by coalescence in controlling the dispersion size in polymer melt blending. Estimates of the matrix film rupture thickness are in the order of 20–40 nm for the purified systems. This suggests that in the final stages of film drainage and rupture, entropic effects of the macromolecules play only a minor part. Commercial polymers were shown to coalesce considerably faster than a purified system. Here, impurities may lead to premature coalescence through lubrication of the interface (increasing its mobility) or by third-phase particles destabilising the matrix film.