Segmental Relaxations Have Macroscopic Consequences in Glassy Polymer Films

Abstract

We have investigated the consequences of physical aging in thin spin-coated glassy polystyrene films through detailed dewetting studies. A simultaneous and equally fast exponential decay of dewetting velocity, width and height of the rim with aging time was observed, which is related to a reduction of residual stresses within such films. The temperature dependence of these decay times followed an Arrhenius-behavior, yielding an activation energy of 70+/-6 kJ/mol, on the same order of magnitude as values for the beta-relaxation of polystyrene and for relaxations of surface topographical features. Our results suggest that rearrangements at the level of chain segments are sucient to partially relax frozen-in out-of-equilibrium chain conformations, i.e. the cause of residual stresses, and they might also be responsible for macroscopic relaxations at polymer surfaces.