Thermodynamic treatment of polymer thin-film glasses

We propose a new, simple, thermodynamically based model in order to study the effect of film thickness on the glass transition of a polymer. The model equation of state incorporates the effect of a free surface by accounting for missing interactions, and is parametrized using experimental data for bulk samples, leaving no freely adjustable parameters. To this end we focus on connecting model agreement in the bulk limit with two key physical properties: pressure-volume-temperature data and surface tension data. For the case of polystyrene we show that accounting for these effects, alone, yields results in surprisingly good agreement with experiment for the shift in glass transition in going from bulk to freestanding film. Insight from this simple model indicates that only a small increase in the specific volume of a thin film (compared to bulk) may drive the shift in the glass transition temperature. Herein we focus on a molecular weight independent regime. Looking ahead we consider the possible contributions of chain confinement to the thermodynamic properties of the film.