Super water- and oil-repellencies from silica-based nanocoatings

This study develops a one-step coating technique to synthesize super water- and oil-repellent silica-based coatings without any additional low-surface energy treatment. Surface topography observation showed that stacking of spherical silica nanoparticles of 20 nm diameter forms primary surface roughness. The atomic ratio of fluorine to silicon in the silica coating plays the crucial role in affecting water- and oil-repellencies, i.e., an optimal ratio of F/Si: 2.13 for the best water-repellency (168.1°) and oil-repellency (165.2°). The Cassie–Baxter model analyzes that the combined effect of silica sphere stacking and surface fluorination contributes a high area fraction of water and ethylene glycol droplet in contact with air, leading to stable water- and oil-repellencies. Such multifunctional nanocoating through the one-step fabrication imparts a variety of promising potentials for the engineering of polymeric or flexible substrates with superhydrophobicity and superoleophobicity.