What have we learned after 20 years of measuring glass transitions in thin polymer films?

For the past 20 years, there has been significant experimental, computational, and theoretical work on anomalous dynamics in thin films of glass forming polymers. Even considering only the single material, polystyrene(PS), the number of experiments, and the wide range of conclusions that have been reached from these experiments is striking. In this talk, I will discuss dilatometric measurements of the glass transition temperature in thin PS films, measures of enhanced surface mobility in glassy PS, and a simple picture of how we can use surface mobility to develop an understanding of the thin film glass transition. Finally, I will discuss the relation between the length scale of surface mobility to the long discussed length scale for dynamic correlation in general glass forming materials.