Glass transition of miscible binary polymer-polymer thin films

The average glass transition temperatures, T-g, of thin homopolymer films exhibit a thickness dependence, T-g(h), associated with a confinement effect and with polymer-segment-interface interactions. The T-g's of completely miscible thin film blends of tetramethyl bisphenol-A polycarbonate (TMPC) and deuterated polystyrene (dPS), supported by SiOx/Si, decrease with decreasing h for PS weight fractions phi > 0.1. This dependence is similar to that of PS and opposite to that of TMPC thin films. Based on an assessment of T-g(h,phi), we suggest that the T-g(h,phi) of miscible blends should be rationalized, additionally, in terms of the notion of a self-concentration and associated heterogeneous component dynamics.