A Simple Approach to Free Volume Transport in Molten/Glassy Material*

A key component of microscopic models for the glass transition, in polymer thin films and more generally, is the local dynamics of free volume, which governs what portions of a near-glassy liquid are mobile at a given instant in time. For example, our recent Delayed Glassification (DG) model implements a proposal of de Gennes that segment-sized kinks of free volume may travel from a free surface into a film along polymeric loops or bridges, helping to plasticize material within some accessible distance from the surface. Recently, we have constructed a simple model for `the mobility of mobility', i.e., how local mobility is itself transported through a dense liquid slightly above Tg. Our simple model results in growing cooperativity lengths and intermittency timescales as Tg is approached from above. If time permits, we shall also describe how the model may be adapted to describe the approach to glassy behavior in supported and freestanding films.