Surface diffusivity of thin polymer films measured by a curvature driven flow and Rouse dynamics

Nanodefects induced by nanoindentation on thin polystyrene (PS) films spin cast on silicon (Si) relax upon annealing at 110 °C. The relaxation process for low molecular weight PS is interpreted in terms of a curvature driven flow which leads to the measurement of a diffusion coefficient. The latter is compared with the expected Rouse predictions using (i) bulk Tgbulk and (ii) surface Tgsurf glass transition temperature data, found in the literature. Deviations from the Rouse predictions are observed when Tgbulk is used for the analysis of the data. On the contrary, excellent agreement with the Rouse model is reported when Tgsurf is used.