Fabrication Technology of Low Adhesive Superhydrophobic and Superamphiphobic Surfaces Based on Electrochemical Machining Method

Abstract

Lowadhesive superhydrophobic and superamphiphobic (both superhydrophobic and superoleophobic) surfaces with a liquid contact angle larger than 150 deg and rolling angle less than 10 deg have attracted great interest for fundamental research and potential application. However, the existing methods to fabricate the aforementioned surfaces are contaminative, dangerous, expensive, and timeconsuming. Lowadhesive superhydrophobic surfaces on aluminum substrates and steel substrates were fabricated via electrochemical etching method and electrochemical deposition method, respectively. Lowadhesive superamphiphobic surfaces on magnesium alloy substrates were fabricated via onestep electrochemical etching method. The sample surfaces were investigated using electron microscopy, energydispersive Xray spectroscopy (EDS), Fouriertransform infrared spectrophotometry (FTIR), Xray diffraction (XRD), optical contact angle measurements, and digital roughness and microhardness measurements. The SEM results show that the hierarchical rough structures composed of micrometerscale pits, protrusions, rectangularshaped plateaus, and smaller steplike structures and particles are present on the aluminum surfaces after electrochemical etching; meanwhile, the hierarchical micro/nanometerscale rough structures composed of micrometerscale globular structures and nanometerscale SiO2 particles are present on the steel surfaces. After being modified with a low surface energy material, superhydrophobic surfaces on aluminum substrates with 167.0 deg water contact angle and 2 deg rolling angle and superhydrophobic surfaces on steel substrates with 172.9 deg water contact angle and 1 deg rolling angle are obtained. For magnesium alloy, the hierarchical micro/nanometerscale rough structures composed of micrometerscale, grainlike structures, protrusions, pits, globular structures, lumplike structures, and nanometerscale sheets and needles are present on the magnesium alloy surfaces. After obtaining the hierarchical micro/nanometerscale rough structures, the magnesium alloy surfaces directly show a superamphiphobicity without any chemical modification. The hierarchical rough structures are essential to fabricate superhydrophobic surfaces. In addition, the reentrant structures are important to fabricate superamphiphobic surfaces. Furthermore, the proposed electrochemical machining method is simple, economic, and highly effective.