Temperature- and/or pH-Responsive Surfaces with Controllable Wettability: From Parahydrophobicity to Superhydrophilicity

Multifunctional surfaces with reversible wetting characteristics are fabricated utilizing end-anchored polymer chains on hierarchically roughened surfaces. Temperature- and/or pH-responsive surfaces are developed that exhibit reversible and controllable wettability, from the parahydrophobic behavior of natural plant leaves all the way to superhydrophilic properties in response to the external stimuli. For this purpose, dual scale micro/nanoroughened surfaces were prepared by laser irradiation of inorganic surfaces (Si wafers) utilizing ultrafast (femtosecond) laser pulses under a reactive gas atmosphere. End-functionalized polymer chains were anchored onto those surfaces utilizing the grafting to method; poly(N-isopropylacrylamide), PNIPAM, and poly(2-vinylpyridine), P2VP, were used for the formation of monofunctional as well as mixed brushes. The surfaces exhibit parahydrophobic behavior in the hydrophobic state (high temperature and/or high pH), with high static contact angles (similar to 120 degrees) and high water adhesion (similar to 30 degrees contact angle hysteresis), whereas they show superhydrophilic behavior in the hydrophilic state (low temperature and/or low pH). The surfaces were tested for their wettability under repetitive cycles and found to be stable and reproducible.