Bionic Fabrication Of Superhydrophobic Surfaces

Wettability is an important property governed by both the chemical composition and the geometrical structures of solid surfaces. Recently, inspired by the "lotus effect", superhydrophobic surfaces with water contact angle higher than 150°have attracted much attention. In this dissertation, the recent research on superhydrophobic surfaces was reviewed, and the investigation idea was brought forward on the understanding of the previous literatures. The four kinds of methods were developed to fabricate superhydrophobic surfaces. The main work and innovation of the thesis are listed as following:1. Based on the soft lithography and casting, a superhydrophobic taro-leaf-like polystyrene film has been obtained using the natural taro leaf as templates and replicating it. Using the similar method, a lotus-leaf-like poly(vinyl chloride) film was also fabricated. On the basis of Wenzel and Cassie models, a simplified model was proposed to study the relationship between rough papillae and superhydrophobicity. It has been shown that the rough papillae greatly enhanced the hydrophobicity of polystyrene and poly(vinyl chloride) films. The water contact angles of the as-prepared taro-leaf-like polystyrene and lotus-leaf-like poly(vinyl chloride) surfaces were 158±1.6°and 157±1.8°, respectively. The superhydrophobic polystyrene and poly(vinyl chloride) films showed excellent stability and self-cleaning property. The superhydrophobic polystyrene and poly(vinyl chloride) surfaces could be applied to other liquids. The investigation on water condensation showed that the condensed water increased contact angle hysteresis.2. Based on the phase separation of polymer solution, a novel porous superhydrophobic polystyrene surface with water contact angle of 156±1.9°was obtained by adding ethanol. SEM showed that the as-prepared polystyrene surface was comprised of many uniform microspheres. The wetting investigation showed that the superhydrophobic property could maintain in a wide pH range, but ethanol and acetone could wet the polystyrene surface. Water condensation on the superhydrophobic polystyrene surface was studied. The effect of addition amount of ethanol on the water contact angle of the resulting polystyrene surface was studied, and the possible formation process of uniform polystyrene microspheres was discussed. It has been shown that the addition amount of ethanol is a crucial factor for the formation of polystyrene surface microstructure. Using the same method, porous superhydrophobic poly(vinyl chloride) surface and poly(methyl methacrylate) surface were also obtained.3. A novel porous superhydrophobic high-density polyethylene surface comprised of many micro-petals was obtained by the control of the drying temperature and adding ethanol. The water contact angle and sliding angle of the as-prepared superhydrophobic high-density polyethylene surface were 160±1.9°and 2±1.6°, respectively. Viarous influence factors such as drying temperature, relative humidity, concentration, and ethanol were studied in the preparation of superhydrophobic high-density polyethylene surface. The results showed that the water contact angle increased with the decrease of drying temperature. The proper relative humidity was about 60~75%, and the addition of ethanol could increase the water contact angle. The stability and self-cleaning property of the as-prepared high-density polyethylene surface were investigated. A superhydrophobic linear low-density polyethylene surface was also obtained using the same method.4. A lotus-leaf-like superhydrophobic surface was obtained on a common hydrophilic paper by a simple novel wax immersing method. SEM showed that many separate wax papillae with the average diameter of 5μm were distributed on the surface of paper, and the distance ranges of the papillae were between 1μm and 8μm. The separated papillae made the paper change from superhydrophilic to superhydrophobic. The as-prepared superhydrophobic paper showed excellent waterproof and self-cleaning property. It has been shown that the addition amount of water was an important influence factor for the fabrication of superhydrophobic paper, and the proper addition amount was about 4%～6% of the solvent. The effect of relative humidity and concentration on the fabrication of the superhydrophobic paper were studied also. The mechanical stability was tested. 5. The blood compatibility of the as-prepared superhydrophobic surfaces was investigated. It has been shown that the superhydrophobic surfaces showed higher blood compatibility than common smooth surfaces.Compared with other methods to fabricate superhydrophobic surfaces, the above methods are much simpler to control, without any special equip or expensive low surface energy materials. In addition, the present methods can also be used to create other superhydrophobic surfaces, indicating great potential applications in industry.