PAPER Cite this: CrystEngComm, 2013, 15, 8475 Received 1st August 2013, Accepted 4th September 2013 DOI: 10.1039/c3ce41534a www.rsc.org/crystengcomm Controllable wettability by tailoring one-dimensional tellurium micro–nanostructures† Qisheng Wang,‡ Muhammad Safdar,‡ Xueying Zhan and Jun He * Controllable wettability is significant for fundamental research and practical applications such as smart and fluid-controllable devices, cell proliferation and inkjet printing. In this work, four one-dimensional Te micro– nanostructures have been fabricated by one-step physical vapor deposition method on the surface of the widely used engineering material FeCoCr alloy. The top morphology and framework of the one-dimensional Te micro–nanostructures can be precisely controlled by the source and deposition temperature, which enables us to design the desired wettability of a solid surface. The wettability of the FeCoCr alloy surface dramatically changes from the near-superhydrophilicity of a Te microscale triangle array to the complete superhydrophobicity of a random-oriented Te nanoscale needle array. Significantly, a complete non-stick superhydrophobic surface with a contact angle of 171° is achieved, for the first time, by adjusting the framework of Te micro–nanostructures from needle microrod arrays to random-oriented needle nanowire networks, which form a special three dimensional (3D) nanoporous network structure. The controllable wettability is suggested to arise from the synergy between the roughness and the framework of Te micro–nanostructures. Our finding not only opens an avenue for the applica- tion of Te micro–nanostructures but also paves a way towards the design for controlling the wettability of one- dimensional micro–nanostructure arrays. Introduction Inspired by natural superhydrophobic phenomena like the “petal effect” 1,2 and the “lotus effect”, 3,4 the wettability of solid surfaces has been widely studied and shows very promising applications in self-cleaning, 5 intelligent microfluidic switches 6 and bionic designs. 7 The static contact angle and dynamic con- tact angle hysteresis, two important standards of wetting prop- erties, are basically determined by surface energy (chemical composition) 8–10 and the roughness of the surfaces. 11–13 By modulating these two factors, the specific wettability of a solid surface can be obtained. 14–16 For example, superhydrophobic surfaces with a contact angle above 150° and contact angle hys- teresis no more than 5° are obtained by decreasing the surface free energy and increasing the surface roughness. 17–20 Recently, special attention has been focused on controllable wettability due to its importance for fundamental research and practical applications in smart and fluid-controllable devices, 21 cell proliferation 7 and the inkjet printing technique. 22 By simultaneously modulating the surface chemistry and rough- ness, reversible switching between superhydrophilicity and superhydrophobicity are realized. 16,23–25 Compared with surface chemical composition, roughness plays a more important role on wettability. Many works have been done to manipulate the wettability of solid sur- faces by choosing suitable materials and designing micro– nanostructures. 26–29 For example, controlled adhesion on a superhydrophobic surface has been obtained by adjusting the pattern and size of solid surface micro–nanostructures of TiO 2 , 30,31 Cu(OH) 2 , 32 PDMS 33 and MnO 2 . 34 In addition, tunable wettability has been achieved by modulating the morphology of a copper nanowire array. 35 The controlled transition between Wenzel and Cassie states is also achieved by changing the surface structure of a nanoporous alumina surface. 36 The mechanisms of the controllable wetting behavior have been proposed based on two distinct well-developed models: 37 Wenzel 38 and Cassie-Baxter. 39,40 However, most of the previous works involve complicated chemical synthesis methods, such as electrochemical method, porous alumina template approach, wet chemical method and hydrothermal method, and even the employ- ment of poisonous and corrosive low surface energy mate- rials such as 1H,1H,2H,2H-perfluorodecyltriethoxysilane. Consequently, in order to achieve controllable wettability of a solid surface, it is very important to develop a facile National Center for Nanoscience and Technology, Beijing, 100190, China. E-mail: hej@nanoctr.cn † Electronic supplementary information (ESI) available: Schematic view of PVD process, magnification SEM images of Te nanostructures, average spacing of Te nanostructures, SEM images of near flat surface, static contact angle photographs of water droplet (6 μL) on flat Te surface, static contact angle photographs of water droplet (10 μL) on triangle microrod array surface and fraction of liquid–solid contact area. See DOI: 10.1039/c3ce41534a ‡ Equal contribution CrystEngComm, 2013, 15, 8475–8482 | 8475 This journal is © The Royal Society of Chemistry 2013 CrystEngComm Published on 04 September 2013. Downloaded by National Center for NanoScience and Technology, China on 08/11/2013 07:02:25. View Article Online View Journal | View Issue