One-step preparation of regular micropearl arrays for two-direction controllable anisotropic wetting.

In this paper, one simple method to control two-direction anisotropic wetting by regular micropearl arrays was demonstrated. Various micropearl arrays with large area were rapidly fabricated by a kind of improved laser interference lithography. Specially, we found that the parallel contact angle (CA) theta(2) decreased from 93 degrees to 67 degrees as the intensity ratio of four laser beams increased from 2:1 to 30:1, while the perpendicular CA theta(1) determined by the thickness of the resin remained constant. This was interpreted as the decrease of height variations Delta h from 1100 to 200 nm along the parallel direction caused by the increase of the intensity ratio. According to this rule, both theta(1) and theta(2) could be simultaneously controlled by adjusting the height variation Delta h and the resin thickness. Moreover, by combining appropriate design and low surface energy modification, a natural anisotropic rice leaf exhibiting CAs of 146 degrees +/- 2 degrees/153 degrees +/- 3 degrees could be mimicked by our anisotropic biosurface with the CAs 145 degrees +/- 1 degrees/150 degrees +/- 2 degrees. We believe that these controlled anisotropic biosurfaces will be helpful for designing smart, fluid-controllable interfaces that may be applied in novel microfluidic devices, evaporation-driven micro/nanostructures, and liquid microdroplet directional transfer.