Influence of physical ageing on rim instability during solvent-induced dewetting of a thin polymer film

Abstract

In this work, we use in situ experiments and a molecular dynamics (MD) simulation to study the influence of physical ageing on rim instability during the solvent-induced dewetting. We firstly combine a molecular dynamics (MD) simulation with ellipsometry to study the influence of physical ageing on the change of the initial state of the thin polymer film. Based on the results of the MD simulation, during the ageing process, the film thickness gradually decreases and the interaction between polymer chains and the solid substrate is obviously enhanced as a result of the changing of the chain's conformation. The increase of polymer density mainly focuses on two sharp increasing points at the film/vapor interface and the film/substrate interface. The change of film thickness obtained by the MD simulation is in good agreement with that from ellipsometry. Besides, the increase of the interaction between the polymer chains and solid substrate during the ageing process leads to a decrease of the contact angle of polystyrene (PS) on the solid substrate. From the experimental results, it is found that the maximum characteristic wavelength λ_max, the maximum width of the rim and the critical radius R_C increase with prolonged ageing time, which results from the decrease of the contact angle θ with ageing time prolonged. In a word, physical ageing of thin polymer films can strongly affect the rim instability during the dewetting of thin PS films via changing the initial state of thin PS films.