Counterion-Dictated Self-Cleaning Behavior of Polycation Coating upon Water Action: Macroscopic Dissection of Hydration of Anions

Viscous Oil De-Wetting Surfaces Based on Robust Superhydrophilic Barium Sulfate Nanocoating

Viscous oil adherence onto solid surfaces is ubiquitous and has caused intractable fouling problems, impairing the function of solid surfaces in various areas such as optics and separation membranes. Materials with superhydrophilicity and underwater superoleophobicity are very effective in elimination of oil fouling. However, most of them cannot dewet viscous oils and may malfunction without prehydration treatment. Herein, we report a facile and environmental strategy to prepare barium sulfate (BaSO₄) nanocoating to dewet viscous oils on dry surfaces. Abundant surface polar groups (surface hydroxyl) on BaSO₄ nanocoating enhance both hydrophilicity after oil fouling (underoil water contact angle <10°) and underwater superoleophobicity (underwater-oil contact angle >155°) and then facilitate oil dewetting ability. Different oils with viscosity up to 900 mPa·s can be easily eliminated after immersion into water. The results and force analysis also demonstrate that small surface roughness and ultrahydrophilicity under oil are beneficial to achieve oil dewetting property on dry surfaces. Furthermore, BaSO₄ nanocoating displays excellent mechanical, thermal and chemical stability and can maintain oil repellency through various harsh conditions. Outstanding antioil fouling ability also enables the fabric coated by BaSO₄ nanocoating to separate crude oil/water with flux higher than 28 000 Lm^2-h^-1 and separation efficiency larger than 99.9% and maintain effective separation performance even after 100 times of separation. Thus, the robust superhydrophilic BaSO₄ nanocoating is potential in oil dewetting and waste oil remediation.