Rheological Properties Of Blends Of Isotactic Polystyrene-Isotactic Poly(Para-Methylstyrene) Films Derived From A Comparative Dewetting Study

We examined changes in rheological properties of nonequilibrated spin-coated thin films of isotactic polystyrene (iPS) and isotactic poly(para-methylstyrene) and blends thereof by dewetting experiments. For 200 nm thick films and a systematic variation of dewetting temperature, we focused on changes in the amount of residual stresses and the corresponding relaxation times as a function of iPS content. We found that both parameters increased in an approximately logarithmic fashion with iPS content, suggesting an increased tendency for the formation of transient clusters in blends with increased iPS content. Assuming linear elasticity, we determined a nonequilibrium shear modulus and a nonequilibrium viscosity, which we compared with published data of the equilibrium properties. Particularly for the viscosity, huge deviations from published values were observed. We provide a tentative explanation.