Thermal effect on superhydrophobic performance of stearic acid modified ZnO nanotowers N. Saleema * , M. Farzaneh Canada Research Chair on Atmospheric Icing Engineering of Power Networks (CIGELE) and Industrial Chair on Atmospheric Icing of Power Network Equipment (INGIVRE), Universite ´ du Que ´bec a ` Chicoutimi, G7H 2B1, Canada Received 28 March 2007; received in revised form 5 August 2007; accepted 5 October 2007 Available online 11 October 2007 Abstract The thermal desorption of stearic acid on superhydrophobic zinc oxide nanotowers has been investigated. The stearic acid passivated zinc oxide nanotowers provide a very high contact angle of 173  1.18 with a very low hysteresis of 1.4  0.58 due to the presence of a binary structure composed of several nanosteps on each nanotower of height 700 nm that eventually reduces the area of contact between the drop and the nanotowers and trapping more air as revealed by the field emission scanning electron microscopy images. The superhydrophobic performance of these nanotowers, however, declines following annealing at elevated temperatures. Fourier transform infrared spectra show a reduction in the intensity of stearic acid –CH n peaks at elevated temperatures revealing the cause of the decrease in contact angle and confirming the occurrence of thermal desorption at 184 8C. The corresponding activation energy for desorption determined from our data is 0.34  0.05 eV. It is found that the stearic acid has completely disappeared at 350 8C, making the sample hydrophilic. # 2007 Elsevier B.V. All rights reserved. Keywords: Superhydrophobicity; ZnO nanotowers; Thermal desorption; FTIR; Contact angle; SEM 1. Introduction Nanostructured hybrid organic–inorganic nanocomposites present paramount advantages to facilitate the integration and miniaturization of the devices in nanotechnology [1]. Metals and metal oxide nanoparticles hybridized with organic compounds have potential applications in many technological fields such as microfluidics, tribology, biosensors, optics, catalysis, etc., and have been of considerable interest recently [2,3]. Such organic–inorganic hybrid films possess properties such as superhydrophobicity, facilitating protection from surface contamination by self cleaning, corrosion inhibition, etc. [3–7]. Several attempts have been made to produce such hybrids; however, very little effort has been made to study the chemical and thermal stability of the organic coatings [8–11]. Studies on the thermal decomposition of surfactant coatings, such as oleic acid, stearic acid and polyethylene glycol, have been carried out on nanostructured metal surfaces [12–15] Several methods have been used to study the thermal desorption of organic layers such as thermogravimetry (TGA), differential thermal analysis (DTA), temperature programmed desorption mass spectrometry (TPD-MS), etc [16]. Wang et al. [13], used TPD to study the thermal desorption of stearic acid on Pd x Ni 1x composites. Pimbley and MacQueen [15] used ellipsometry to study desorption of stearic acid on platinum and nickel surfaces and Consalvo et al. [17] used atomic force microscopy (AFM) to investigate the thermal stability of stearic acid on plasma- oxidized silicon substrates. Hybrid structures of oxides and organic coatings have important applications in many fields, for example, electrical insulation, photonics, piezoelectric devices, photovoltaic devices, photocatalysis, microelectronic circuits, etc. [1,3], thus, thermal stability of these organic molecules on metal oxides is an important question. Several superhydro- phobicity studies have been carried out recently on metal oxide surfaces passivated with organic molecules [18–20], however, the superhydrophobicity behavior of these organic–inorganic hybrids has not yet been investigated following exposure to elevated temperatures. In this paper, we present highly superhydrophobic stearic acid passivated zinc oxide nanotowers and we investigate the www.elsevier.com/locate/apsusc Available online at www.sciencedirect.com Applied Surface Science 254 (2008) 2690–2695 * Corresponding author. E-mail address: snoormoh@uqac.ca (N. Saleema). 0169-4332/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2007.10.004