Control of Surface Wettability of Aluminum Mesh with Hierarchical Surface Morphology by Monolayer Coating: From Superoleophobic to Superhydrophilic

Abstract

This paper reports the formation of hierarchically structured aluminum mesh by a combination of simple chemical etching and anodizing. The former introduced micrometer-sized etch pits, and the latter produced nanopores of the order of 10 nm on the mesh with 150 μm mesh openings. Coating the mesh with a monolayer of fluoroalkyl phosphate made the surface superoleophobic to practically any liquid, including hexane with a surface tension as low as 18.4 mN m–1. The hierarchical triple ∼100 μm/∼1 μm/∼10 nm pore surface morphology improved the superoleophobicity compared to the dual ∼100 μm/∼10 nm and ∼1 μm/∼10 nm pore structures. When the aluminum mesh was coated with a fluorine-free alkylphosphate monolayer, the surface was superhydrophobic, but superoleophilic. The noncoated aluminum mesh was superhydrophilic and superoleophilic with a liquid contact angle close to 0°. Using the aluminum mesh with an alkylphosphate coating, a water/oil mixture was successfully separated by allowing only the oil to pass throu...