Designing transparent superamphiphobic coatings directed by carbon nanotubes Xiaotao Zhu a , Zhaozhu Zhang a,⇑ , Guina Ren a,b , Xuehu Men a,⇑ , Bo Ge a,b , Xiaoyan Zhou a,b a State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Tianshui Road 18th, Lanzhou 730000, PR China b University of Chinese Academy of Sciences, Beijing 100039, PR China article info Article history: Received 27 November 2013 Accepted 21 January 2014 Available online 27 January 2014 Keywords: Superamphiphobic Transparent coating Controllable surface wettability Thermal durability abstract Creating surfaces with superamphiphobic property and optical transparency simultaneously would have fundamental and practical significance but has been proven extremely challenging. Herein, we develop a transparent superamphiphobic coating using carbon nanotubes (CNTs) as the template by a facile approach. CNTs enwrapped with SiO 2 coating was produced by a sol–gel method and then sprayed onto the glass slides to form coatings. Subsequent thermal treatment and surface fluoration allowed the sprayed coating to exhibit enhanced transparency across a broad spectrum of ultraviolet and visible wavelengths and also display superrepellency toward water and a number of organic liquids, such as dodecane. The obtained transparent coating can sustain its superamphiphobicity even after thermal treatment at 400 °C. Separate experiment demonstrated that the CNTs-directed geometrical structure played a key role in establishing superamphiphobicity. Ó 2014 Published by Elsevier Inc. 1. Introduction There has recently been significant amount of research direc- ted toward achieving superamphiphobic (namely superhydropho- bic and superoleophobic) surfaces [1–8] due to their wide applicability in various fields, including the development of self- cleaning surfaces, liquid–liquid separation membranes, and anti- fouling materials [9–12]. For superamphiphobic surfaces use in applications of self-cleaning windows, optical devices, and solar panels, high optical transparency is additionally needed. How- ever, producing transparent superamphiphobic surfaces has proved extremely challenging. The challenge results from the competitive relation between surface roughness and transparency and also the difficulty in producing superamphiphobic surfaces. Increasing surface roughness, which is an indispensable require- ment for superamphiphobic establishment, often causes light scattering and thus makes the surface become translucent or even opaque [13,14]. Moreover, to design superamphiphobic surfaces, some special structures such as the re-entrant geometries or overhanging architectures have to be introduced into the surfaces [7,15–20], which poses another tough fabrication challenge. Thus, despite various types of transparent superhydrophobic surfaces [21–23], transparent superamphiphobic surfaces are extremely rare. Until recently, Zhang and Seeger developed transparent superoleophobic surfaces by combination of versatile organosi- lanes in a grow-from method [24]. Vollmer et al. reported a trans- parent superamphiphobic coating using candle soot as the template [25]. Nair et al. developed electrospun SiO 2 nanofibers as template to produce a transparent superamphiphobic coating [26]. However, the optical transparency of these obtained coat- ings is relatively limited or the fabrication process is laborious, and thus many aspects of transparent superamphiphobic coating have still to be explored. In this study, we for the first time demonstrated that roughed surface texture directed by pristine CNTs, in conjunction with the low surface energy of fluorinated silane, can be used to produce transparent superamphiphobic coatings, and the designing strat- egy was shown in Fig. 1a. We firstly coated carbon nanotubes (CNTs) with SiO 2 by a sol–gel approach and used it to form coatings by spray coating. The sprayed coating became transparent toward a broad spectrum of ultraviolet and visible wavelengths after ther- mal treatment. Subsequent surface fluoration allowed this trans- parent coating to exhibit superrepellent toward water and numbers of extremely low surface tension liquids, such as dode- cane (c lm = 25.3 mN/m). We also investigated the effect of pure SiO 2 -directed and carbon black-directed geometrical structure on surface wettability, and such information allowed us to engineer coatings with specific liquid-repellency behavior. http://dx.doi.org/10.1016/j.jcis.2014.01.026 0021-9797/Ó 2014 Published by Elsevier Inc. ⇑ Corresponding authors. Fax: +86 931 4968098. E-mail addresses: zzzhang@licp.cas.cn (Z. Zhang), xhmen@licp.cas.cn (X. Men). Journal of Colloid and Interface Science 421 (2014) 141–145 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis