How does solvent annealing influence stress-driven surface undulations in polymer composite films with immobilized film-spanning nanoparticles?

Our study on poly(methyl methacrylate) (PMMA) films with fixed nanoparticles (NPs) on the supporting substrate, where the nanoparticles span the film thickness, reveal a three-stage evolution of wavelike undulations on the film surface: early stage, intermediate stage and late stage. The wavelike height undulations are induced by the compressive stresses, which are enhanced by introducing fix constrians (NPs) that resist the in-plane thermal expansion of the polymer film. We quantified the evolution of surface undulations, in an effort to understand the effect of solvent annealing on the undulations. The polymer chains in PMMA films prepared by spin coating are not fully equilibrated due to the rapid solvent evaporation during drying. Solvent annealing increases the molecular mobility and enables relaxation of the polymer network. This solvent treatment could perhaps give rise to an increase in entanglement density and associated film modulus. The surface undulations increase with the solvent annealing time before they reach the equilibrium values. The wavelike surface undulations might be associated with the entanglement density of polymer chains.

The overall evolutionary process of wavelike surface undulations of nanoparticle-filled polymer thin films annealed in solvent vapor.Figure optionsDownload as PowerPoint slide