Differential pressure experiment to probe hole growth in freely standing polymer films

We have developed a sensitive experiment which allows the measurement of the growth of holes in thin freely standing polystyrene (PS) films at elevated temperatures. In the experiment, a constant small pressure difference is applied and maintained across the freely standing film, and the formation and growth of holes is detected as a flow of air through the film. From measurements of freely standing PS films for which the glass transition temperature Tg is equal to the bulk value Tgbulk, as well as for films that are sufficiently thin that Tg is 30 °C less than Tgbulk, we find that substantial chain mobility occurs only at temperatures that are comparable to Tgbulk. The results can be interpreted as a shear thinning effect, which is consistent with previous optical microscopy measurements of hole growth in freely standing PS films.