Biological Surface: Lotus Leaves and Butterfly Wings

In this chapter, we introduce two natural surfaces with a self-cleaning property: lotus leaves and butterfly wings. Their similarity - the micro-/nanostructure covering the surfaces - is the key factor that causes superhydrophobicity and self-cleaning. However, as the multi-scale structure is randomly arranged on the surface of the lotus leaves, water can roll off the leaves in any direction, which means the self-cleaning on the leaves is isotropic. In contrast, due to the directional arrangement of the scales and ridges on the butterfly wings, water droplets can only roll off along the RO direction but will get pinned against the RO direction, which means the self-cleaning property on the butterfly wings is anisotropic.