The Glass Transition of Miscible Binary Polymer-Polymer Thin Films

Studies of the glass transition temperatures, T$_{g}$, of completely miscible thin film blends of tetramethyl bisphenol-A polycarbonate (TMPC) and deuterated polystyrene (dPS), supported by SiO$_{x}$/Si, were examined using spectroscopic ellipsometry (SE) and incoherent elastic neutron scattering (INS). While both sets of measurements independently reveal that T$_{g}$ exhibits qualitatively similar trends with film thickness, h, there were important quantitative differences, which depended on composition. The T$_{g}$s measured by INS were consistently larger than those determined by SE for PS weight fractions $\phi$$>$0.1. These observations are rationalized in terms of theory based on the notion of a self- concentration and reveal evidence of heterogeneous component behavior in these miscible polymer-polymer systems.