Tuning the Plasticization to Decouple the Effect of Molecular Recoiling Stress from Modulus and Viscosity in Dewetting Thin Polystyrene Films

During dewetting, thin polymer films show the combined effect of molecular recoiling stress, modulus, and viscosity. Dewetting experiments in thin polystyrene films have demonstrated the possibility of quantifying molecular recoiling stress simultaneously with modulus and viscosity in the same experiment involving controlled plasticization. While plasticization reduces viscosity and modulus in polymer films, it enhances molecular recoiling stress originating from nonequilibrium molecular conformations of the polymer chains. Plasticized polymer films with reduced entanglement density and enhanced free volume lead to largely distorted polymer chains during the spin-coating, resulting in a greater extent of molecular recoiling stress. The results indicate that a plasticized polymer is representative of dilated and softened mechanical properties and it can subsequently lead to the accumulation of molecular recoiling stress, instead of its relaxation. Thus, upon plasticization, a decoupling of molecular recoiling stress is observed compared to viscosity and modulus.