Journal of Colloid and Interface Science 316 (2007) 233–237 www.elsevier.com/locate/jcis Effects of nanorod structure and conformation of fatty acid self-assembled layers on superhydrophobicity of zinc oxide surface Chantal Badre a , P. Dubot c , Daniel Lincot b , Thierry Pauporte b , Mireille Turmine a,∗ a Université Pierre et Marie Curie-Paris 6, LECA, UMR 7575, case 39, 4 place Jussieu, 75252 Paris cedex 05, France b Ecole Nationale Supérieure de Chimie Paris, LECA, UMR 7575, 11 rue Pierre et Marie Curie, 75231 Paris cedex 05, France c Ecole Nationale Supérieure de Chimie Paris, Laboratoire de Physicochimie des Surfaces, UMR 7045, 11 rue Pierre et Marie Curie, 75231 Paris cedex 05, France Received 12 April 2007; accepted 11 July 2007 Available online 27 July 2007 Abstract Superhydrophobic surfaces have been prepared from nanostructured zinc oxide layers by a treatment with fatty acid molecules. The layers are electrochemically deposited from an oxygenated aqueous zinc chloride solution. The effects of the layer’s structure, from a dense film to that of a nanorod array, as well as that of the properties of the fatty acid molecules based on C18 chains are described. A contact angle (CA) as high as 167 ◦ is obtained with the nanorod structure and the linear saturated molecule (stearic acid). Lower values are found with molecules having an unsaturated bond on C9, in particular with a cis conformation (140 ◦ ). These results, supplemented by infrared spectroscopy, indicate an enhancement of the sensitivity to the properties of the fatty acid molecules (conformation, flexibility, saturated or not) when moving from the flat surface to the nanostructured surface. This is attributed to a specific influence of the structure of the tops of the rods and lateral wall properties on the adsorption and organization of the molecules. CA measurements show a very good stability of the surface in time if stored in an environment protected from UV radiations.  2007 Elsevier Inc. All rights reserved. Keywords: Biomimetic; Superhydrophobic zinc oxide; Electrodeposition; Surface derivatization; Fatty acids orientation; Well-packed monolayers 1. Introduction Fascinating superhydrophobic surfaces can be found in na- ture, for example, the well-known lotus leaves or Lepidoptera wings [1,2]. On theses surfaces, the contact angle (CA) of water can be as high as 160 ◦ . It is widely accepted that this property is due to the special micro/nanobinary structure and the epicu- ticular wax [1,2]. Superhydrophobic surfaces have recently at- tracted great interest for their many practical applications [3]. In general, materials combining high surface roughness [4,5] and low surface energy terminal groups, such as –CF 3 [6], are re- quired for superhydrophobicity [7]. A large variety of methods [8–10] have been reported for their fabrication and many mate- rials were used to produce superhydrophobic surfaces [11–13]. Herein, we describe a very simple low-cost method for prepar- * Corresponding author. Fax: + 33 (0)1 44 27 30 35. E-mail address: turmine@ccr.jussieu.fr (M. Turmine). ing artificial superhydrophobic surfaces. ZnO was chosen as host substrate due to its unique optical, electronic, and struc- tural properties [14]. In our case, superhydrophobicity has been reproduced by combining the electrodeposition of nanostruc- tured ZnO [15] and subsequent surface derivatization with low cost fatty acid molecules. Fatty acids are among the essential components of wax fabricated by plants [1,2]. When their chain length increases, they become insoluble in water and can or- ganize as molecular film on the air–water interface, or even form micelles. All these characteristics give them their wetting and lathering properties. Three different C 18 fatty acids (FA), namely stearic, oleic, and elaidic, were chosen. Stearic acid has a saturated flexible hydrocarbon chain that can stretch out into a long zig-zag. Oleic and elaidic acids are two unsaturated forms of the stearic acid. They present a cis and trans double bond, respectively, on carbon 9. We extend this study by investigat- ing the influence of the alkyl conformation chain of these FA on CA values. CA is usually used to follow the assembly of 0021-9797/$ – see front matter  2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2007.07.046