Effect of atmosphere on reductions in the glass transition of thin polystyrene films

We have used nulling ellipsometry to measure the glass transition temperature, Tg , of thin films of polystyrene in ambient, dry nitrogen, and vacuum environments. For all environments, the measured Tg values decrease with decreasing film thickness in a way that is quantitatively similar to previously reported studies in ambient conditions. These results provide strong reinforcement of previous conclusions that such reduced Tg values are an intrinsic property of the confined material. Furthermore, the results are in contrast to recent reports which suggest that the Tg reductions measured by many researchers are the results of artifacts (i.e. degradation of the polymer due to annealing in ambient conditions, or moisture content).