Lotus Versus Rose: Biomimetic Surface Effects

Abstract

The Lotus and rose petal effects have become a subject of active investigation by scientists, as they involve different modes of the interaction of wetting with roughness. The contact angle (CA) and CA hysteresis are two parameters, which characterize the hydrophobicity/philicity of a solid surface. Lotus-effect surfaces have a high CA and low CA hysteresis. However, it was found recently that a high CA can coexist with strong adhesion between water and a solid surface (and high CA hysteresis) in the case of the so-called "rose petal effect." It is clear now that wetting cannot be characterized by only the CA, since several modes or regimes of wetting of a rough surface can exist, including the Wenzel, Cassie, Lotus, and Petal regimes. This is due to the hierarchical structure of rough surfaces built of micro- and nanoscale roughness, so that a composite interface can exist at the microscale, while a homogeneous interface can exist at the nanoscale or vice versa. The understanding of the wetting of rough surfaces is important in order to design non-adhesive surfaces for various applications, including environmental. © Springer-Verlag Berlin Heidelberg 2012.