Water-Repellency Enhancement of Nanostructured Plasma-Polymerized HMDSO Coatings Using Grey-Based Taguchi Method

This paper presents results showing the improvement of water repellency on an aluminium substrate after immersion in boiling water followed by plasma polymerization of Hexamethyldisiloxane (HMDSO) via a Grey-based Taguchi method. Immersion in boiling water was used to create a rough nanostructured surface on the aluminium alloy substrate; surface roughness was investigated by SEM and AFM analyses. The water-repellent characteristics on the rough surface were obtained by plasma polymerization of HMDSO. In order to optimize the plasma polymerization, four controlling parameters of the plasma process namely input power, deposition time, monomer flow, and distance from monomer inlet were considered. The Taguchi approach followed by Grey relational analysis was applied to solve this multi-response optimization problem (high contact angle and low contact angle hysteresis). Through the Grey-based Taguchi method, it was found that distance between the monomer inlet and substrate plays the most significant role in affecting the coating wettability. The optimal condition proposed by this method has been verified through additional experiments which showed an increase in static contact angle up to 163 degrees and a decrease in contact angle hysteresis up to 13 degrees.