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

Abstract

Low-adhesive 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 time-consuming. Low-adhesive superhydrophobic surfaces on aluminum substrates and steel substrates were fabricated via electrochemical etching method and electrochemical deposition method, respectively. Low-adhesive superamphiphobic surfaces on magnesium alloy substrates were fabricated via one-step electrochemical etching method. The sample surfaces were investigated using electron microscopy, energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectrophotometry (FTIR), X-ray diffraction (XRD), optical contact angle measurements, and digital roughness and microhardness measurements. The SEM results show that the hierarchical rough structures composed of micrometer-scale pits, protrusions, rectangular-shaped plateaus, and smaller step-like structures and particles are present on the aluminum surfaces after electrochemical etching; meanwhile, the hierarchical micro/nanometer-scale rough structures composed of micrometer-scale globular structures and nanometer-scale 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/nanometer-scale rough structures composed of micrometer-scale, grain-like structures, protrusions, pits, globular structures, lump-like structures, and nanometer-scale sheets and needles are present on the magnesium alloy surfaces. After obtaining the hierarchical micro/nanometer-scale 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 re-entrant structures are important to fabricate superamphiphobic surfaces. Furthermore, the proposed electrochemical machining method is simple, economic, and highly effective.