Optical probes of the glass transition in thin polymer films

We have used three optical techniques, ellipsometry, Brillouin light scattering and photon correlation spectroscopy, to study the glass transition in a variety of polymer thin film geometries. Following a description of the essential features of these techniques, we summarize the results of our recent glass transition measurements for thin polystyrene (PS) films. In particular, for very thin freely-standing PS films, we have measured Tg values and corresponding structural relaxations that occur at temperatures that are reduced from the bulk value of Tg by more than 70 K.