The Calorimetric Glass Transition of Polystyrene Ultrathin Films

Although the glass transition behavior of polystyrene ultrathin films has been widely studied, calorimetric measurements are limited due to difficulties in sample preparation. Here we report the use of a rapid scanning calorimeter based on a membrane sensor to measure the rate-dependent glass transition temperature (T$_{g})$ for single ultrathin films. Both microtomed and spin-coated films are investigated. Preliminary results suggest that the magnitude of the T$_{g}$ depression is similar to that observed for freely-standing films. The T$_{g}$ depression also depends on the cooling rate such that at the highest rates used (1000 K/s), the depression is only a few degrees. The kinetics of dewetting are followed, with T$_{g}$ values increasing as a function of time and finally reverting to the bulk values after several hours at 160 \r{ }C.