Super-hydrophobic surface with switchable adhesion responsive to both temperature and pH

In this article, we report a new super-hydrophobic surface with switchable adhesion that is responsive to both temperature and pH. When the water pH is fixed (pH 7), a water droplet (4 mL) can roll on the surface at high temperature (45 degrees C) and be pinned at low temperature (20 degrees C). Simultaneously, the surface shows strong dependence on the pH of the water droplet, an acid droplet (pH 2, 4 mu L) can roll on the surface while a basic droplet (pH 11, 4 mu L) is pinned when the temperature is constant (45 degrees C). Reversible transition between the low adhesive rolling state and the high adhesive pinning state can be achieved by simply changing the temperature and/or the pH alternately. The smart effect of the surface is attributed to the cooperation of chemical variation of the poly(N-isopropylacrylamide-co-acrylic acid) P(NIPAAm-co-AAc) and the hierarchical structures on the surface. Such a novel super-hydrophobic surface with dual-responsive adhesion could potentially be used in a wide range of applications with more complex environments, such as biochemical separation, lab-on-chip devices and in situ detection.