A simple strategy to realize biomimetic surfaces with controlled anisotropic wetting

The study of anisotropic wetting has become one of the most important research areas in biomimicry. However, realization of controlled anisotropic surfaces remains challenging. Here we investigated anisotropic wetting on grooves with different linewidth, period, and height fabricated by laser interference lithography and found that the anisotropy strongly depended on the height. The anisotropy significantly increased from 9 degrees to 48 degrees when the height was changed from 100 nm to 1.3 mu m. This was interpreted by a thermodynamic model as a consequence of the increase of free energy barriers versus the height increase. According to the relationship, controlled anisotropic surfaces were rapidly realized by adjusting the grooves' height that was simply accomplished by changing the resin thickness. Finally, the perpendicular contact angle was further enhanced to 131 degrees +/- 2 degrees by surface modification, which was very close to 135 degrees +/- 3 degrees of a common grass leaf.