Precise control of wettability from LCST tunable surface

In this study, we demonstrated precise control of wettability from a thermally-responsive surface and investigated the effects of chemical composition and surface roughness. By altering feeding manners of initiators during surface grafting process of poly(N-isopropylacrylamide-co-N- isopropylmethylacrylamide) [poly(NIPAAm-co-NIPMAM)], two thermally-responsive wettability transitions were achieved and could be precisely controlled. Only using initiators grafted on surface for grafting copolymerization, surface wettability exhibited a gradual even linear transition between hydrophilic and hydrophobic within 25-45 °C, whereas for initiators both grafted on surface and dissolved in solution, surface wettability sharply switched within 2 °C and their lower critical solution temperature (LCST) can be tuned with every step of about 3 °C in the range 32-45 °C by adjusting the ratios of comonomers. The underlying mechanism was proposed to clarify the relations between different thermally-responsive behaviors of surface wettability and surface chemical composition induced by different feeding manners of initiators. Furthermore, the introduction of surface roughness could not only enlarge the changing range of water contact angle (CA) by 60-100°, but also affect the thermally-responsive behaviors of surface wettability from the gradual changing to sharp switching in partial region of temperature.