Switching water droplet adhesion using responsive polymer brushes

Two stimuli-responsive polymers, poly(N-isopropylacrylamide) (PNIPAM) and poly(dimethylamino) ethyl methacrylate (PDMAEMA), were grafted from initiator-modified anodized alumina substrates with irregular micro/nanoscale surface topography. The resulting polymer-coated surfaces exhibited highly unusual wettability properties, as spherical water/acid/alkali/salt droplets could be reversibly switched between pinned states and rolling states due to the changes of temperature, pH, and electrolytes. The key to this effect is the combination of a mixed monolayer which provides initiator points for brush growth as well as a permanently hydrophobic substrate and a surface roughness.