Spatial Variations and Temporal Metastability of the Self-Cleaning and Superhydrophobic Properties of Damselfly Wings

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• 作者：Jafar Hasan ; Hayden K. Webb ; Vi Khanh Truong ; Gregory S. Watson ; Jolanta A. Watson ; Mark J. Tobin ; Gediminas Gervinskas ; Saulius Juodkazis ; James Y. Wang ; Russell J. Crawford ; Elena P. Ivanova
• 刊名：Langmuir
• 出版年：2012
• 出版时间：December 18, 2012
• 年：2012
• 卷：28
• 期：50
• 页码：17404-17409
• 全文大小：373K
• 年卷期：v.28,no.50(December 18, 2012)
• ISSN：1520-5827

文摘

Self-cleaning surfaces found in nature show great potential for application in many fields, ranging from industry to medicine. The ability for a surface to self-clean is intimately related to the wetting properties of the surface; for a surface to possess self-cleaning ability it must exhibit extremely high water contact angles and low water adhesion. While investigating the self-cleaning properties of damselfly wings, significant spatial variations in surface wettability were observed. Within an area of 100 渭m 脳 100 渭m of the wing surface the water contact angle was found to vary up to 17.8掳, while remaining consistently superhydrophobic. The contributions of both surface chemistry and topography to the hydrophobicity of the wings were assessed in an effort to explain these variations. Synchrotron-sourced Fourier-transform infrared microspectroscopy revealed that some of the major components of the wing were aliphatic hydrocarbons and esters, which are attributable to epicuticular lipids. The wing topography, as determined by optical profilometry and atomic force microscopy (AFM), also showed only minor levels of heterogeneity arising from irregular ordering of surface nanostructures. The measured contact angle of a single droplet of water was also found to decrease over time as it evaporated, reaching a minimum of 107掳. This is well below the threshold value for superhydrophobicity (i.e., 150掳), demonstrating that when the surface is in contact with water for a prolonged period, the damselfly wings lose their superhydrophobicity and subsequently their ability to self-clean. This decrease in hydrophobicity over time can be attributed to the surface undergoing a transition from the Cassie鈥揃axter wettability state toward the Wenzel wettability state.