Dewetting Rheology for Determining Viscoelastic Properties of Nonequilibrated Thin Polymer Films

Abstract

We performed systematic dewetting experiments on isotactic poly(para-methylstyrene) (iPpMS) films to explore the temperature dependence of the viscoelastic behavior of these films. We quantified the amount of residual stresses σres induced through film preparation by spin-coating. As anticipated, σres was found to be independent of the temperature Tdew at which dewetting was done. A particular focus was on the temperature dependence of the relaxation time τ of σres, which was measured with the help of three independent dewetting parameters. Within error, all three values of τ were identical and followed an Arrhenius behavior yielding an activation energy of 60 ± 10 kJ/mol. The initial dewetting velocity, being proportional to the ratio of surface tension of iPpMS and the corresponding viscosity, increased significantly with Tdew. Assuming a linear stress–strain response, we deduced that the elastic deformation responsible for the maximum height of the dewetting rim increased with temperature, although σre...