Swelling process of thin polymer film studied via in situ spectroscopic ellipsometry

The swelling process of thin polystyrene films in quantity was studied in this paper using the in situ spectroscopic ellipsometry. We systematically investigated the influence of film thickness on the swelling process of thin polystyrene films. The results show that in the case of high Mw polystyrene(Mw=400000), the curve of the swelling degree as a function of time discloses that the relaxation of the long polymer chains accompanies the diffusion of acetone molecules. The swelling process is via the Fickian relaxation mechanism. Both the values of the equilibrium swelling degree and the diffusion coefficient of acetone molecules in the polystyrene film decrease as the film thickness reduces under confinement. However, in the case of low Mw PS(Mw=4100), the dewetting process is so fast before the equilibrium of swelling that the whole swelling process cannot be observed.