1, Key Laboratory of Low-Grade Energy Utilization Technologies and Systems, Chongqing University, Chongqing, , China
Advances in microfluidics technologies have stimulated the development of new materials and the design of surfaces which should require hydrophobic surfaces and interfaces with low adhesion. Biological surfaces are good and natural models for the development of functional surfaces, such as wettability,optical characteristics and water directional transmission. Therefore, learning the microstructure of biological prototype is meaningful for the design of surfaces. Here, a novel and fast molding method has been used to replicate the microstructures of different leaves, and their surfaces decorated with Nano particles or wires by hydrothermal method, and eventually obtained the superhydrophobic property by silane treatment. Molding is a fast, simple and low-cost replication technique for biomimetic surfaces compared with other methods such as etching, lithography, electrochemical deposition and micromachining. The surface preparation process is as follows. At first, a negative is generated by molding. Then, we get the positive by filling the negative with liquid epoxy resin. In this way, we easily replicate the microstructure of lotus leaf, rice leaf and Salvinia Natans on the resin substrate. The method of molding easily gets the microstructure of various biologic surfaces, but the replicated surfaces just reach the hydrophobic degree after molding. As we known, there are many superhydrophobic plants with the hierarchical structure which combined with Micro and Nano Structures. Inspired by this, the ZnO hydrothermal method was used to build the nanostructure on the microstructure of molding, which was easy to control the length and diameter of nanohair. Specially, we focused on the most typical superhybrophobic plant —lotus leaf. Changing the concentration of ZnO growth liquid to control the nanostructure, the replica with 0.025M ZnO growth liquid(static contact angle 151°,sliding angle 6.5°) had a very close wettability with the original dry lotus leaf(static contact angle 152°，sliding contact 8.5°). Furthermore, we found the nanostructure is a key factor to achieve superhydrophobicity. The rolling contact angle increases with the increase of the length and diameter of nanostructure, which increases the solid-liquid contact area and reduces the air gap caused by the micro and nanostructure.