Design of honeycomb structure surfaces with controllable oil adhesion underwaterElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ra10514e

In this paper, we fabricate honeycomb-like poly acrylic acid (PAA) surfaces and achieve oil adhesion transitions underwater. Characterization of the adhesion indicates that the porous honeycomb structure PAA films can serve as high oil adhesive surfaces both in acidic and in basic aqueous phases. Besides, the adhesion can be controlled by changing the size of the pores and the solution pH. The honeycomb structure film prepared using a template with a theoretical diameter of 6 μm has the highest adhesion in basic solution, which can snap some oil droplets from the original oil. In contrast, the smooth films and other honeycomb structure films in acidic and basic solutions cannot snap an oil droplet. The switchable oil adhesion is attributed to the change of the triple-phase liquid/liquid/solid contact line (TCL) continuity and the negative pressure induced by the pores. This highly adhesive porous film was used as a "mechanical hand" to transfer micro-droplets successfully underwater. The unique adhesive phenomenon of the honeycomb structure will be useful for manipulating oil droplet behavior and suitable for the application of controlling liquid collection and transportation underwater. We fabricate honeycomb-like poly acrylic acid (PAA) surfaces and achieve oil adhesion regulation underwater by changing the pore size and the solution pH, which affect triple-phase contact line (TCL) continuity and the negative pressure in the pores.