Polymer Surface Melting Mediated by Capillary Waves

Nuclear magnetic resonance investigations of atactic polystyrene emulsions yield direct evidence that the polymer surface exhibits a rather well-defined molten layer. Its thickness $d$ grows continuously as the temperature is increased towards the bulk glass transition, according to $d\propto (T_g-T{)}^{-1}$. This is precisely what was recently predicted by a simple continuum model considering viscoelastic surface waves. Furthermore, this model is capable of explaining the frequently reported depression of the glass transition temperature in thin polymer films, and thus suggests a quite simple mechanism to underlie all these effects.