Cicada wing with adhesive superhydrophobicity and their biomimetic fabrication

Cicada is hymenoptera insect. It is found that cicada wing exhibit super-hydrophobicity and a high adhesive force with water, which is different from lotus leaf. The water contact angle (WCA) on cicada wing is 145.81±4.83°. The water droplet does not slide on the cicada wing surface when the surface is tilted at 90°. Observed from the SEM data, the cicada wing surface is covered by the columnar structure in regularly rule. To copy the wettability of cicada wing surfaces, we report a new approach for fabricating a super-hydrophobic surface on copper substrate using reciprocating type high speed wire cut electrical discharge machining (HS-WEDM). The resultant samples were characterized by scanning electron microscopy (SEM) and contact angle measuring instrument, It was found that water contact angle of the resulting surface was increased from 82.11° to 152.91±4.02°, realizing the transition from the hydrophilic to super-hydrophobic. When the sample is tilted at 90°, the water droplet does not roll off from the surface or even upside down, indicating the resulting surface has a high adhesive force to water. The resulting surface were covered with composite structures composed of micro-scale diamond cylinder structure and concave and protuberance, and nano-scale granular structure, which was the reason of super-hydrophobicity and high adhesive force of copper surface. Moreover, new copper oxide generated in the process of HS-WEDM is another reason of copper surface.