Developing hydrophobic and superhydrophobic TiO2 coatings by plasma spraying

In this work, atmospheric plasma spraying (APS) and suspension plasma spraying (SPS) are employed for developing micro/nano morphologies of superhydrophobic coatings with high water repellence and mobility. Accordingly, multiple coatings were developed with different surface morphologies, then by isolating the effect of surface chemistry using a stearic acid treatment, the importance and influence of the achieved morphologies on wetting behavior of the coatings were investigated. Experimental results show that, although coatings developed by the APS process may reach water contact angles as high as 145 degrees, the water mobility of these coatings is low due to relatively large morphological features resulting from the micron-sized feedstock powder. On the other hand, coatings developed by SPS show superior water repellence (manifested through water contact angles as high as 167 degrees) as well as improved mobility (displayed through water sliding angles as small as 1.3 degrees) due to dual-scale submicron/nano (hierarchical) roughness attributed to the submicron size particles in the feedstock. The dynamic behavior of an impinging water droplet is studied and compared to other existing natural and fabricated superhydrophobic surfaces. (C) 2016 Elsevier B.V. All rights reserved.