Preparation of lotus-like superhydrophobic fluoropolymer films
Introduction
The wetting behavior of solid surface is governed by both surface roughness and chemical composition. Consequently, increasing surface roughness and lowering surface tension can dramatically enhance surface water repellency [1], [2], [3], [4]. Nature provides a unique example in the lotus flower, in which the leaves utilize superhydrophobicity as the basis of a mechanism to control the surface morphology for the protection and self-cleaning of that surface [5], [6], [7], [8]. Inspired by the natural superhydrophobicity, similar mimetic surfaces with water contact angles greater than 150°, have attracted considerable interest over the past few years for both fundamental research and practical applications. Generally, in order to create a superhydrophobic surface, two strategies are adopted. One is fabricating a rough surface by using low surface energy materials; the other is preparing a rough surface first and then modifying the rough surface with low surface energy compounds. More recently, superhydrophobic surfaces with a hierarchical structure in nano-scale and micron scale mimicking that of a lotus leaf have also been reported [9], [10], [11], [12], [13], [14].
Based on previous reports, most methods for obtaining superhydrophobic surfaces typically use either expensive materials or severe conditions, limiting the applications of superhydrophobic surfaces [15], [16]. In this study, a rough surface with low surface tension exhibits superhydrophobicity and stability, which can be facilely fabricated in one step by casting the copolymer solution. Rough surface morphology, prepared by phase separation technique in the work [17], [18], is like that of nature lotus leaf. Meanwhile, the film surface roughness can be controlled by the degree of phase separation.
Section snippets
Synthesis of copolymer
A typical preparation procedure was as follows: a dry round-bottom flask was filled with styrene (St, 5 ml), 2,2,3,4,4,4-hexafluorobutyl methacrylate (HFMA, 5 ml) and benzoyl peroxide (BPO, 0.17 g), [St]:[HFMA]:[BPO] = 62:38:1. After fully mixing, the flask was immersed in an oil bath at 95 °C for 8 h. After synthesis the copolymer was purified by dissolving in THF and precipitating in the mixture of methanol and water, and then the purified copolymer was placed into oven for drying. The procedure
Characterization of the copolymer
According to the results of elemental analysis, we can calculate the composition of the copolymer (see Table 1). The molar ratio of St and HFMA is 1.32 in the copolymer. PS in the copolymer is 35.4 wt%, and PHFMA in the copolymer is 64.6 wt%. According to the results of GPC measurement (See Table 2), we can know Mn, Mw and PDI of the copolymer were 34966.1 g/mol, 55544.1 g/mol and 1.59 respectively.
A typical 1H NMR spectrum, shown in Fig. 1, confirms the formation of the copolymers. The peaks at
Conclusions
The superhydrophobic films of the fluoropolymer with binary hierarchical structure can be obtained by a facile approach. The surface roughness of the films can be controlled by the degree of phase separation. When the content of ethanol was tuned to 50% by volume, the surface resembled the structure of the lotus leaf, was superhydrophobic with water contact angle 154.3° and sliding angle 5.8°. Because of the excellent performance, this fluoropolymer film is expected to be a potential candidate
Acknowledgements
This work is supported by the Youth Scientist Fund of Shandong Province (2007BS04007), the Doctoral Startup Foundation of Shandong Institute of Light Industry, National Natural Science Foundation of China (50772059) and the foundation for the author of National Excellent Doctoral Dissertation (No. 200539) for PR China.
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