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 T_g is equal to the bulk value T_g^bulk, as well as for films that are sufficiently thin that T_g is 30 °C less than T_g^bulk, we find that substantial chain mobility occurs only at temperatures that are comparable to T_g^bulk. 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. © 2003 American Institute of Physics.