The hydrophobicity of surfaces with micro-structures

Micro/nano structures on the surface of the superhydrophobic lotus leaves have been observed with scanning electron microscope (SEM) images, and the hydrophobicity enhanced by rough structures on hydrophobic surface has attracted lots of interests. This paper studied on the effects of micro-structures. From replication of lotus leaves surface by using poly-dimethylsiloxane (PDMS), micro-structures can be obtained on the artificial surface. The contact angle (CA) on this surface is about 140deg, which means the microstructures make important efforts. Considering the characteristics of Cassie´s law and Wenzel´s law, this paper proposes a revised formula to describe the relations between contact angles and geometric sizes of surface micro-structures. An optimum value of b/a (a is the width of the micro-structures, b is the interspace between micro- structures) is given for maximum CA.