Fabrication Of Superhydrophobic Coating On Copper And Aluminum Substrates And Investigation Of The Tribological Properties

The application and value of materials largely depend on their own surface wettability. In recent years,superhydrophobic materials have shown enormous potential application in production and daily life.Copper and aluminum are the major engineered materials, but wear and corrosion are two serious problemswhich they are still faced with. Based on these questions, we adopted different surface fabricationtechniques to construct three kinds of bionic superhydrophobic surface geometry morphology on copperand aluminum substrates, respectively. Moreover, the tribological properties and anti-corrosion abilityagainst acid and basic as well as superhydrophobic stability were also investigated in this thesis. The maincontents and conclusions are listed as follows:1. A simple two-step solution immersion process was combined with surface-modification by stearicacid to prepare superhydrophobic surfaces on copper substrates so as to reduce friction coefficient andimprove the anticorrosion ability against acid and basic of copper. Briefly, cuprous oxide (Cu2O) crystalcoating with uniform and compact tetrahedron structure was firstly created by immersing copper substratein2mol·L-1NaOH solution. As-obtained Cu2O coating was then immersed in0.33mmol·L-1AgNO3solution to incorporate silver nanoparticles, followed by modification with stearic acid (denoted as STA)coating to achieve superhydrophobicity. The surface morphology and chemical composition ofsilver-cuprous oxide/stearic acid (denoted as Ag-Cu2O/STA) surface were investigated using a scanningelectron microscope and an X-ray photoelectron spectroscope; and its phase structure was examined withan X-ray diffractometer. Moreover, the contact angle of water on as-prepared Ag-Cu2O/STA surface wasmeasured, and its friction-reducing and anticorrosion abilities were also evaluated. It was found thatas-prepared Ag-Cu2O/STA surface has a water contact angle of as high as162.4°and can provide effectivefriction-reducing and anticorrosion ability against acid and basic for copper substrate, showing greatpotential for surface-modification of copper.2. A copper substrate was etched in the mixed solution of (NH4)2S2O8and HCl by oxidation-assistedsurface acid etching process to generate a desired roughened structure (coded as etched Cu). Resultantetched Cu surface was then immersed in silver nitrate solution to allow incorporation of silversubmicro-particles through replacement reaction to afford etched Cu-Ag lotus-leaf-like structure. EtchedCu-Ag surface was finally modified with STA to provide etched Cu-Ag/STA surface withsuperhydrophobicity. The morphology and microstructure of as-prepared etched Cu-Ag surface wereobserved with a scanning electron microscope, and its antiwear and anticorrosion abilities were evaluatedin relation to water contact angle measurements. It was found that as-prepared etched Cu-Ag surface iscomposed of micro-protrusions and submicro-mastoids with dual-scale structure similar to the one of lotusleaf. Besides, etched Cu-Ag/STA superhydrophobic surface has a static water contact angle of160.5°andshows very low adhesion for water droplet, and it possesses good friction-reducing ability as well as goodanticorrosion ability against acid and basic, showing potential application for protection of Cu substrate in engineering.3. A lotus-leaf-like hierarchical structure with superhydrophobicity was created on aluminum foil by afacile three-step solution-immersion method involving etching in hydrochloric acid solution and immersingin hot water as well as surface-modification by STA. As-prepared etched-immersed Al/STA compositesurface was characterized by means of scanning electron microscopy and X-ray photoelectron spectroscopy.Moreover, the water contact angles and water sliding angles of as-prepared Al/STA surface were measured,and its friction-reducing performance and self-cleaning ability were also evaluated. Results indicate thatetched-immersed Al/STA surface consists of interconnected convex-concave micro-structure and uniformlydistributed nano-sheets. Besides, it exhibits stable superhydrophobicity and good friction-reducing ability.Namely, it has a water contact angle of as high as164.2°and a water sliding angle of below5°, while itretains good friction-reducing ability during extended sliding and possesses good self-cleaning ability aswell. This demonstrates that etched-immersed Al/STA superhydrophobic surface may favor the applicationsof Al and its alloys in various industrial fields.