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200007Colloids and Surfaces A: Physicochem. Eng. Aspects 384 (2011) 109–114

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Colloids and Surfaces A: Physicochemical and Engineering Aspects
journal homepage: www.elsevier.com/locate/colsurfa

Gecko-inspired synthesis of superhydrophobic ZnO surfaces with high water adhesion
Jian Li a,b,c , Xiaohong Liu a , Yinping Ye a , Huidi Zhou a , JianminChen a,∗
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China Graduate School, Chinese Academy of Sciences, Beijing 100039, People’s Republic of China Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education and Gansu Province, College of Chemistry and ChemicalEngineering, Northwest Normal University, Lanzhou 730070, People’s Republic of China
b c a

a r t i c l e

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a b s t r a c t
This paper reports an easy means to imitate the “gecko’s feet” by constructing ZnO nanorods on Zn foil through a simple and inexpensive solution chemistry approach. The ZnO nanorods with various densities have been fabricated by controlling the synthesis temperatureand time. After being modified with fluoroalkylsilane, the ZnO nanorods surfaces show analogous superhydrophobic property and tunable high water adhesion. The as-prepared superhydrophobic ZnO surface allows water droplets to pin on the surface without any movement, even if it is tilted to a vertical position or turned upside down. Furthermore, the adhesive force of the surface is found to be strongenough to catch a water droplet that rolls down quickly from a tilted low adhesive superhydrophobic surface. © 2011 Elsevier B.V. All rights reserved.

Article history: Received 10 January 2011 Received in revised form 3 March 2011 Accepted 9 March 2011 Available online 16 March 2011 Keywords: Superhydrophobicity Contact angle ZnO Nanorod arrays Gecko-inspired

1. Introduction Geckos areremarkable in their ability to climb rapidly up smooth, vertical surfaces [1,2]. This extraordinary ability is explained by the nearly 500,000 keratinous hairs called setae in a gecko’s feet that provide a sufficiently large surface area in close contact with the substrate for adhesion through van der Waals’ forces [1,3]. Taking from the inspiration of these findings, many surfaces with novel adhesionhave been prepared [4–9]. In addition to the application in dry adhesion, the animals’ remarkable ability can also be applied in other fields, for example, superhydrophobic surfaces. Superhydrophobic surfaces, which are characterized by static water contact angles higher than 150◦ , are divided into two classes. One is the “low adhesive surface”, which has a low sliding angle (i.e., self-cleaningsurface). Such surfaces have recently attracted much attention for their promising applications in various fields from daily life to industry [10–18]. The other superhydrophobic surface is the one with “high adhesion to water”. Highly adhesive surfaces show both high water contact angle and large contact angle hysteresis. Recently, inspired by the high adhesive property of the gecko’s feet,superhydrophobic surfaces with high adhesion have also aroused

∗ Corresponding author. Tel.: +86 931 4968018. E-mail address: chenjm@lzb.ac.cn (J. Chen). 0927-7757/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2011.03.024

much attention [19–28]. The high adhesive superhydrophobic surfaces may be promising in potential application, such as no lossmicrodroplet reversible transportation [19,20]. As representative example, a superhydrophobic polystyrene nanotube layer was aligned via template wetting method [19]. Polymeric nanopillar structures with high aspect ratio were also generated by the combination of colloidal nanolithography, deep-silicon etching, and nanomolding [21]. Hairy hard poly(dimethylsiloxane) (h-PDMS) composed of nanopillars with...