Bioinspired programmable wettability arrays for droplets manipulation.

The manipulation of liquid droplets demonstrates great importance in various areas from laboratory research to our daily life. Here, inspired by the unique microstructure of plant stomata, we present a surface with programmable wettability arrays for droplets manipulation. The substrate film of this surface is constructed by using a coaxial capillary microfluidics to emulsify and pack graphene oxide (GO) hybrid N-isopropylacrylamide (NIPAM) hydrogel solution into silica nanoparticles-dispersed ethoxylated trimethylolpropane triacrylate (ETPTA) phase. Because of the distribution of the silica nanoparticles on the ETPTA interface, the outer surface of the film could achieve favorable hydrophobic property under selective fluorosilane decoration. Owing to the outstanding photothermal energy transformation property of the GO, the encapsulated hydrophilic hydrogel arrays could shrink back into the holes to expose their hydrophobic surface with near-infrared (NIR) irradiation; this imparts the composite film with remotely switchable surface droplet adhesion status. Based on this phenomenon, we have demonstrated controllable droplet sliding on programmable wettability pathways, together with effective droplet transfer for printing with mask integration, which remains difficult to realize by existing techniques.