Switching of Surface Properties with Polymer Brushes

Abstract

Switchable surfaces were fabricated by grafting of two different polymers: polystyrene (PS) and poly-2-vinylpyridine (PVP) onto the surface of Si-wafers. The binary brushes of various composition, molecular weight and grafting density were synthesized via free radical polymerization initiated by the azo-initiator covalently attached to the surface of Si-wafers. Investigations showed that the binary brushes are very sensitive to the surrounding media. After exposition to a solvent selective for PVP (ethanol, water + HCl) the surface becomes hydrophilic and the top of the layer is covered by PVP. After exposition to a solvent selective for PS (toluene) the surface becomes hydrophobic and the top of the layer is enriched with PS segments. Switching kinetics depends on grafting density and layer composition and varies from several seconds to several minutes at room temperature. Surface morphology of the layers switches as well as the wetting behavior. Results show that the layer reconstruction is reversible and can be repeated many times.