| Superhydrophobic surfaces have attracted increasing attention in both fundamental research and industrial field due to their special functions and potential application in self-cleaning,anti-icing,corrosion resistance,drag reduction and oil/water separation etc.Great advancement has been achieved to fabricate surfaces with superhydrophobic property,but some obvious limitations hamper their application,including the sophisticated equipments,complicated process and harsh condition for experiment etc.It is an urgent task in the field to turn the research into products and to develop the innovative technology suitable for industrial production of superhydrophobic materials.Meanwhile,the application of superhydrophobic surfaces is relatively limited.In the process of developing new production technology,it is also necessary to solve the problem by giving the products more and better performance.Therefore,it is of great academic and practical value to study the fabrication methods,simplify the preparation process,upgrade production technology and improve the performance of superhydrophobic materials.In this dissertation,three methods,the electroless plating,solution growth and mechanical processing were used to fabricate superhydrophobic surfaces on metallic magnesium,copper and aluminum substrates.The problems such as surface wettability,corrosion resistance and switchable adhesion of the prepared surfaces were studied too.Novel fabrication methods were attempted to prepare the superhydrophobic surfaces by combining mechanical processing with modification of low surface free energy materials.Through theoretical analysis and experimental research,this dissertation explores the preparation and performance of superhydrophobic surfaces,which broadens the scope of this field.The main research results are as follows:(1)The expressions of contact angle hysteresis and surface free energy were established.Based on the proposed expressions,relationship between contact angle hysteresis,surface free energy and micro-nanostructure was investigated.The hydrophobic properties of the superhydrophobic surface with one-scale microstructures and dual-scale micro-nanostructures were discussed too.Under the composite wetting state,the surface has a larger surface free energy and smaller contact angle hysteresis.The droplets are prone to slide.A reasonable selection of the solid fraction can achieve the transition from hydrophilicity to hydrophobicity or even superhydrophobicity.Under the homogeneous wetting state,the surface has a larger contact angle hysteresis.The droplets cannot roll easily.Since the Cassie state and Wenzel state may change,the transformation conditions are solved and demonstrated.For one-scale microstructures,the critical roughness factor(Rf)for the transition is 1.8 and for dual-scale miro-nanostructures,the critical roughness factor(Rf)for the transition is between 1.9-2.(2)A stable and corrosion-resistant superhydrophobic surface was fabricated by a two-step deposition method.Firstly,electroless nickel–phosphorous(Ni–P)plating was carried out on ZK60 magnesium alloy.Subsequently,the silver nanocoatings were deposited on the as-prepared substrate.After the modification with stearic acid,a superhydrophobic surface with a contact angle as high as 158.8° was obtained.The wettability,morphology and corrosion resistance of the samples were tested,which proves the superhydrophobic surface fabricated by electroless Ni-P plating possesses the best corrosion resistance and the contact angle increases first and then decreases with the increasing treatment time.The method can effectively improve the corrosion resistance of magnesium and its alloys and expand their application in engineering.(3)A superhydrophobic surface with switchable adhesion property based on ZnO nanostructure arrays was developed on copper substrate at low temperature by solution growth method.The superhydrophobic surface was prepared through immersing the bare substrate in the growth solution at 35°C.After modification by low surface energy material,the static water contact angle of the surface ranged from 151.2° to 154.9° and rolling angle from 5° to 88.5°.It also showed excellent corrosion resistance.The adhesion of the superhydrophobic surface is mainly affected by its microstructure.On the upside of the substrate in parallel with the solution surface,ZnO nanorods gather as small thorn balls,which has a micro/nanoscale hierarchical structure and a small solid liquid contact area and low adhesion.The other three surfaces have large solid liquid contact areas and high adhesion.The method is not time-consuming and easy to operate.A lower growth temperature will make the operation process energy-saving and very suitable for large-scale industrial production.(4)A novel method was reported to prepare a superhydrophobic surface via turning operation and stearic acid modification.The end faces of copper and aluminum alloy bars were processed by machine cutting on Lathe C6140 using 60° thread cutters,respectively.By adjusting the speed of spindle and feeding,regular microstructures were created.Followed by modification with stearic acid solution,superhydrophobic surface with a static water contact angle as high as 155.3° was obtained.The as-prepared surface had excellent corrosion resistance.Residual area of cutting layers is created on the surface due to the feed movement of cutters.So the microstructure of the superhydrophobic surfaces is determined by the tool shape and feed.With a rational design for the ideal morphology and proper choice for cutting tool angle and cutting parameters,the surface morphology and wettability can be controlled.This solves the problem of random surface roughness,uncontrollable structure size or shape and poor performance of some superhydrophobic surfaces.The equipment used is a common lathe and the surface microstructures can be controlled.This simple,efficient and environment-friendly method can be applied to achieve large area production of superhydrophobic surfaces.(5)A new route was reported to prepare a superhydrophobic surface via milling operation which is applicable to a variety of panel.A self-made milling cutter was made to fabricate controllable microstructures on copper and aluminium alloy.After milling,the surfaces of the materials had groove-like structures of the same height.The spacings of the grooves were uniform.After the modification with stearic acid,the superhydrophobic surfaces with a static water contact angle of 156°on the copper substrate and 157.4° on the aluminium alloy were prepared.Both surfaces had excellent corrosion resistance in a 3.5 wt.% NaCl aqueous solution.The Icorr for superhydrophobic surface is smaller by 2-3 orders of magnitude than that for bare substrate The method is of great value and expand the application of superhydrophobic surfaces.By adjusting the rotational speed,the feed rate and cutting depth of the worktable,the surface microstructure and wettability can be controlled and adjusted.The method is more widely applicable and suitable for industrial application. |
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