Conformal and non-conformal surface modification of honeycomb-patterned porous films via tunable Cassie–Wenzel transition

Abstract

We describe here a facile and robust approach to conformal and non-conformal surface modification by tuning the wetting transition between the Wenzel state and the Cassie state. Highly ordered honeycomb-patterned porous films were prepared from a diblock copolymer by the breath figure method, and pincushion-like surfaces were obtained by removing the top surface layer of honeycomb films. It is found that the surface modification is highly dependent on the pre-wetting process. After complete pre-wetting, polydopamine (PDA) and polyetherimide (PEI) deposit both inside and outside of the pores, and thus the whole honeycomb film surface becomes hydrophilic. Water droplets on the surfaces transform from a Cassie state to a Wenzel state after 6–12 h PDA/PEI deposition, during which the apparent water contact angles decrease from above 90° (e.g., 115°) to below 90° (e.g., 55°). If the honeycomb-patterned porous films are not pre-wetted, PDA/PEI deposit only on the external surfaces, forming a top layer covering the pores, and the pore walls are not modified. This approach provides a versatile route for controlling water spreading and impregnation behaviors on patterned porous films, which will be useful in fields such as microreactors, supercapacitors, and wearable electronics.