Enhancement of water-repellent performance on functional coating by using the Taguchi method

The present work investigates the enhancement of water-repellency on rough surfaces using nanoscale roughness inherent in metal-oxide nanoparticles together with a hydrophobic fluoromethylic copolymer coating via the Taguchi and analysis of variance (ANOVA) methodologies. Based on the concepts of nanocoating processing, seven operating factors including type of nanoparticle, solid ratio, dispersion time, F-binder ratio, distance between nozzle and substrate, spray direction and layer number can be considered. Through the Taguchi method, solid ratio plays the most significant role in affecting the ideal function and robust design of a water-repellent coating. Since surface roughness is generally influenced by solid ratio, more nanoparticles can randomly stack to build up a rougher surface, causing more air to be trapped on the nanostructured surface. This argument supported by the Cassie-Baxter equation indicates that the water droplet is partially sitting on an air film, capable of promoting the superhydrophobic behavior. The reconfirmation test using the optimal parameter settings demonstrates that the superhydrophobic surface can be achieved, and its contact angle is as high as 161.4°.