Morphology response by solvent and vapour annealing using polystyrene/poly(methyl methacrylate) brushes

Abstract

The aim of this work is to evaluate the switching behaviour of polymer brushes. Polystyrene (PS) and poly(methyl methacrylate) (PMMA) were grafted onto a silicon surface by radical polymerization where molecular weight of PMMA to be higher than molecular weight of PS. The morphology of polymer brushes was switched by modifying the surrounding environment using solvent and vapour annealing treatments. As selective solvent for PMMA acetic acid was chosen and cyclohexane at 55°C for PS. Using acetic acid as solvent or its vapours PS/PMMA brushes adopted dimple-like morphology composed mostly by PMMA chains resulting in contact angle values (~74° and 76°, respectively). In the case of cyclohexane, surface topography changed and the outermost layer was occupied by PS and PMMA chains. In this case, the topography adopted a slightly rough surface. In addition, PS/PMMA showed a smoother surface after treated with cyclohexane vapour annealing due to poor solubility of PS in cyclohexane at room temperature. Contact angle values changed from 85° with cyclohexane solvent annealing to 80° with cyclohexane vapour annealing suggesting that switching behaviour did not completed.