22 nd I nternational Symposium on Plasma Chemistry July 5-10, 2015; Antwerp, Belgium O-21-2 1 Solution precursor plasma sprayed superhydrophobic surface Y. Cai 1 , J. Mostaghimi 1 , T.W. Coyle 1 and G. Azimi 2 1 Centre for Advanced Coating Technologies (CACT), Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, ON, Canada 2 Department of Chemical Engineering, University of Toronto, Toronto, ON, Canada Abstract: This work presents the first transition metal oxide superhydrophobic surfaces fabricated by using the solution precursor plasma spraying technique. The water contact angle measured on the surface is 155°. The dynamic impact of a water droplet is also captured by a high speed camera. The topography and cross-sectional microstructures of the coated surface are examined by scanning electron microscopy. Keywords: solution precursor plasma spray, superhydrophobic surface 1. Introduction Since the development of electron microscopy in the last century, people have been able to study nanotextures of plant surfaces and animal skins. It has been found that a unique surface architecture provides a self-cleaning ability to leaves (e.g., lotus leaves), which is shown in Fig. 1, and allows the wings of insects to remain dirt-free and shed water when they fly in the rain [1]. This type of surface is called a hydrophobic surface. Hydrophobic surfaces are characterized by a high water contact angle (>90°) and a low roll-off angle. When the water contact angle on the surface is higher than 150°, the surface is called superhydrophobic. Due to these properties, hydrophobic surfaces have a wide range of potential applications to benefit the environment in energy conservation, including enhancement of condensation in steam power plants in order to increase the efficiency of electricity generation [2]; and promotion of nucleation for pool boiling at low heat flux to enhance boiling heat transfer [3]. Very recently, transition metal oxides have been proposed as a means of creating hydrophobic surfaces [4]. Due to their unique electron configuration and high melting temperature (over 1500 °C), transition metal oxide surfaces exhibit a high water contact angle even when they are smooth and at elevated temperatures. However, the link between this research and industrial applications has not been firmly established due to the difficulties of large scale fabrication, and complex processing procedures. Plasma spray deposition is a technique which has been widely used in industry to produce coatings due to its high deposition rate, near-net shape finishing, and most importantly, its ability to process almost all materials. Conventional plasma spray uses micro scale powder particles as the feedstock for the material to be deposited. Solution precursor plasma spray (SPPS) is a relatively new technique that, rather than using powder particles, uses a solution which decomposes during deposition to form the coating. The coating formation mechanisms for solution precursor plasma spray are different than for conventional plasma spray, and lead to nano- and Fig. 1. a) Lotus leaves, which exhibit extraordinary water repellency on their upper side. b) Scanning electron microscopy (SEM) image of the upper leaf side prepared by ‘glycerol substitution’ shows the hierarchical surface structure consisting of papillae, wax clusters and wax tubules. c) Wax tubules on the upper leaf side [1]. submicron-structured coatings [5]. This type of hierarchical structured surface is very desirable in fabricating hydrophobic surfaces since it captures the essence of self-cleaning leaves and wings in nature. To our knowledge, there has yet to be a superhydrophobic surface produced by the solution plasma spray method. In this work, superhydrophobic coatings were fabricated using axial-injection SPPS. Transition metal salt dissolved in the water and alcohol mixture was used as the liquid feedstock to the plasma torch. The wetting behavior of the coated surface is characterized by measuring the static water contact angle, roll-off angle and the dynamic impacts of water droplets on the surface. Surface and cross-sectional microstructures were analyzed by scanning electron microscopy (SEM).