Understanding Wetting Phenomena and Petal Effect in Plasma Sprayed Rare Earth Oxide Ceramic Coating

A sticky hydrophobic surface has prospective applications in microfluidic chips, no loss microdroplet transportation, biochemical detection and separation, quantitative transportation in biochips, and chemical microreactors, among others. Here we report fabrication and characterization of a novel sticky parahydrophobic cerium oxide (CeO2) coating using a facile and industrially viable plasma spray technique. Our coating displays significantly high water contact angle (WCA=159.02˚) along with a high contact angle hysteresis (CAH≥90˚), very much similar to a 'Rose petal'. This is further strengthened by the fact that the coating displayed remarkable adhesion even with large inverted water droplets of 70 μL, which is significantly higher than the reported values of 18 μL for polymer and 20 μL for drop casted CeO2 nanotubes. We also present systematic characterization results to clarify the ongoing confusion regarding the hydrophobicity of CeO2 coatings often reported in literature. Meanwhile, our parahydrophobic coating also showed remarkable thermal and mechanical stability even at a significantly high temperature of 200˚C for 14 hours and with 50 g abrasive paper. We believe that this study not only clarifies the ongoing debate regarding the wettability of rare earth coatings, but also offers a new paradigm for realizing robust industrial scale coatings for applications such as no loss microdroplets transportation.