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 T g bulk and (ii) surface T g surf glass transition temperature data, found in the literature. Deviations from the Rouse predictions are observed when T g bulk is used for the analysis of the data. On the contrary, excellent agreement with the Rouse model is reported when T g surf is used.