Preparation And Properties Of Superhydrophobic Coating With Micro/Nano Structure On Aluminum Surface

Superhydrophobic surface has attracted extensive attention and in-depth research in the scientific community because of its corrosion resistance and self-cleaning effect.Although the superhydrophobic surface prepared at present has excellent wettability,the mechanical properties of superhydrophobic surface are still the main factor restricting its large-scale application.In this paper,the surface of aluminum matrix was treated by chemical and electrochemical methods to obtain different surface microstructure.The effect of different microstructure on the properties of superhydrophobic surface was studied.In order to improve the mechanical properties and prolong the service life of superhydrophobic surface,a superhydrophobic surface with wear resistance and self-healing was constructed by coating the aluminum substrate with different organic coatings and inorganic particles.The properties of aluminum superhydrophobic surface were studied in order to develop a method with stable micro/nano structure and superhydrophobic surface for industrial preparation.The main research contents of this paper are as follows:（1）The multiple roughened structures were prepared on aluminum alloy surfaces via acid etching method,anodic oxidation method,and phosphoric acid-dichromate method they are respectively tepladder,acicular,ellipsoid,columnar and triangle.These multiple roughened structures were coated with PHPS,the wear resistance and corrosion resistance of different microstructure on superhydrophobic aluminum alloy surfaces were studied,in order to obtain optimum surface roughened structures.（2）A multifunctional composite superhydrophobic coating with anti-corrosion and wear-resistance has been fabricated on the surface of the aluminum.The superhydrophobic coating resembles a sandwich structure that contains a silane coupling agent layer at the bottom,a Si O₂-hybridized silicone resin adhesive layer at the middle,and a sperhydropolysilazane（PHPS）layer on the top.The superhydrophobic multilayer coating not only effectively improved the corrosion resistance of metal surfaces but also had wear resistance.The contact angle of the aluminum coated by PHPS and was 152.7°.The contact angle of aluminum with sandwich coating structure was 161.3°.Compared with the original aluminum,the corrosion current density of aluminum which was coated by PHPS coating and sandwich structure coating were decreased by 2 and 4 orders respectively.What’s more,the contact angle of the aluminum which was moved 1m on 600#Si C sandpaper under 1KPa pressure was decreased by9°.Under the same conditions,the aluminum with a single PHPS coating decreased by 70°.The study provides a valuable way not only to fabricate superhydrophobic surfaces on the aluminum but also modify the surface of commodity and industry supplies to facilitate their maintenance.（3）The micro-nano structures which are necessary factors to generate superhydrophobic performance are easily destroyed,especially by scraping with tough objects.As a result of the damage,superhydrophobicity will be lost.Herein,water-soluble polyvinyl alcohol（PVA）polymer binder is introduced to act as a cushion and sacrifice layer.In this approach,the lower superhydrophobic layer was prepared by spraying polytetrafluoroethylene（PTFE）on the surface of aluminum matrix with stepped rough structure.The PVA binder is in the middle.The topmost layer is the superhydrophobic polydimethylsiloxane（PDMS）and nano-silica（Si O₂ NPs）layer.When the mass fraction of Si O₂ NPs is 15%,The contact angle of PDMS-Si O₂ is 154°.The PDMS-Si O₂ fall off after wearing 40cm on 600#sandpaper at a pressure of 1KPa.The superhydrophobicity of the sample disappear temporarily.After soaking the damaged sample in water for about 3h,the PVA layer is dissolved.The contact angle of the exposed lower superhydrophobic layer is 152°.The corrosion current densities of the double-layer superhydrophobic sample,the PTFE coated sample and the repaired superhydrophobic sample are1.2×10^-6A/cm²,1.1×10^-5A/cm² and 3.3×10^-6A/cm².The method is critical to the applications of superhydrophobic Al materials in engineering.