ABSTRACT
Butterfly is a beautiful insect in nature.1 Interestingly, many smart multifunctions may be found on wings,2 for example, water repellency. These biological functions are result of micro-and nanostructure, which serve well for survival of butterfly in nature.3-6 In recent year, Morpho blue butterfly wing (Fig. 2.1, top) has been revealed into special wettability. For example, butterfly wing has selfcleaning property similar to lotus leaf. In addition, butterfly wing has anisotropic multistructure that leads to anisotropic wetting just as observed on plant leaves,7 flower petals,8,9 and bird feathers.10,11 More interestingly, butterfly wing displays the unidirectionality of droplet shedding-off, which can be defined as anisotropic wettability. For example, butterfly wings of iridescent blue Morpho aega butterflies have a typical character of excellent directional adhesion for fluidic controlling.3,12 This directionality on wettability can be attributed to the multilevel regular micro-/nanostructures of wings. So, such multiple-anisotropic wettability can be herein defined as “effect of butterfly wing,” which guards us to design novel functional surfaces. For extending aspect, some structures similar to wing of butterfly can be extracted; for example, oriented structure, geometry, ratchet, step structure, and so on. It has become an interest area how to design the structured surfaces via some novel methods.
