"The Good, the Bad, and the Slippery": A Tale of Three Solvents in Polymer Film Dewetting

We investigated the dynamics and morphology of demietting of bilayers of thin polymer films, made of a top poly(4-vinylpyridine) (P4VP) film on a polystyrene film on silicon substrates, upon exposure to vapors of binary and ternary mixtures of ethanol, acetone, and water, respectively a good solvent, a poor solvent, and a nonsolvent for P4VP. The composition of the vapor mixtures affected dramatically dewetting rate, dewetting dynamics and the morphology of the dewetted features, with vapor mixtures leading always to much higher dewetting rates than both pure solvent vapors and thermal annealing. We identified the role that each of the solvent vapors plays in the mixture, and concluded that water and acetone induce a transition of the polymer chains to a globule conformation reducing viscosity and modify the interfacial energies, two effects that strongly drive the dewetting. In an acetone environment, dewetting further speeds up, under the effect of a lubricated flow.