Preparation And Characterization Of Biomimetic Multifunctional Surfaces

Corrosion is a spontaneous reaction process.The economic loss caused by material corrosion all over the world is inexhaustible every year.Material corrosion and protection is an important problem to be solved urgently.In recent years,the vigorous development of biomimicking in the field of surface engineering provides a new idea for the design of new anti-corrosion coatings with friendly environment and diverse functions.Based on the surface structure and related interface phenomena with excellent interface functionality in nature,the construction of biomimetic micro/nano superhydrophobic coating on the material surface has broad application prospects in biomedical equipment,architecture and other fields.However,the inherent limitations of biomimetic superhydrophobic anti-corrosive interface in the design and preparation of low surface energy,the complexity of biomimetic structure preparation process,poor chemical stability,and mechanical durability during service severely restrict the wide applications of biomimetic superhydrophobic surface/interface.In this dissertation,three typical hydrophobic structures,micro biomimetic superhydrophobic structure,lubricant infused surface（LIS）and biomimetic composite micro/nano structure,are studied.The preparation techniques of various interface structures are studied based on electrochemical methods.In the meanwhile,the relevant interfacial phenomena are fitted and analyzed with the help of phase field simulation,density functional theory and other numerical means.Combined with the experimental data,the hydrophobicity and corrosion resistance of the above three kinds of biomimetic interfaces in various working conditions are comprehensively evaluated.On the basis of clarifying their preparation technology,advantages and disadvantages,their suitable application environments and prospects are discussed.The main research results of this dissertation are summarized as follows:（1）A low-cost biomimetic superhydrophobic surface was constructed on steel 316L by one-step electrochemical co-deposition in ethanol solution containing cerium nitrate hexahydrate and myristic acid.The results show that the chemical composition and cauliflower-like microstructures have low surface energy.The maximum contact angle of water droplets is 167.7±2.4°and the minimum contact angle hysteresis is less than 1°,It has self-cleaning ability and long-term stability in mild environment.Additionally,the phase field simulation of the transient wetting evolution of water droplets on this surface shows that the increase rate of contact angle first increases and then decreases,and the increase rate of contact angle is smaller when it reaches at equilibrium state.The potentiodynamic polarization and electrochemical impedance spectroscopy（EIS）test in 3.5 wt.%Na Cl solution show the strong corrosion resistance（3 times higher than the bare substrate）,which is as high as 1.98×10⁶Ω.This research provides a new method for SHPB coating through selection and design of coating materials with low surface energy and the regulation of microstructure interface by electrochemical process to obtain surface with low surface energy and hydrophobicity index（β_S=-0.937）with mechanochemical stability,environmental protection and corrosion resistance.（2）A biomimetic lubricant infused surface（LIS）based on Ni-TiO₂ superhydrophobic structure was constructed on copper substrate by electrochemical co-deposition technique and its interface phenomenon and corrosion resistance properties in various application environments were discussed.The biomimetic slippery surface has long-term durability,and its corrosion rate（0.10153 mpy）is lower than that of Ni-TiO₂/MA structure（0.12922 mpy）and Ni-TiO₂ structure（0.226135 mpy）.The theoretical investigations of phase field simulation with a droplet impact on artificially patterned surfaces with rebound dynamics of liquid droplet to its equilibrium state correspond with SHPB and LIS surfaces,having contact angles（161°and 116°）and the hydrophobicity indexα_S（-0.8822 and-0.4329）,respectively.This dissertation not only unveils the close attention for lubricant selection to create durable LIS but also provides new insights into designing and preparation of multifunctional surfaces,which could be developed for various applications.（3）A biomimetic micro/nano superhydrophobic composite coating is proposed for steel304 substrate,which is composed of modified micro/nano-structure crosslinked with organic resin.The perfluoro-octyl-triethoxy silane（POTS）modified ZIF-67 and SiO₂ coating was applied on primary coated polytetrafluoroethylene（PTFE）and epoxy resin（EP）via spray coating method.Biomimetic micro/nano superhydrophobic composite coatings were successfully prepared on metal substrates.Here,we present that the robust superhydrophobicity can be realized by structuring surfaces at two different length scales,with a nanostructure design to provide water repellency and a microstructure design to provide durability.The coating shows excellent hydrophobicity（CA=167.4°）,chemical stability（p H=1-14）and mechanical durability(after 120^th linear abrasion or 35^th rotary abrasion cycles).The coating can still maintain excellent hydrophobicity in acidic and alkaline corrosive media and under various weathering conditions.To get a better insight of interaction between inhibitor molecules and metal surface,density functional theory（DFT）calculations were performed,showing lower energy gap and increased binding energy of ZPS/SiO₂/PTFE/EP（ZPS=ZIF-67+POTS）multilayer coating compared to the ZIF-67/SiO₂/PTFE/EP,thereby supporting the experimental findings and developing the design and preparation of micro/nano composite structure coatings with strong interface bonding properties.Additionally,the composite coating constructed by this method can be applied in many fields such as corrosion resistance,self-cleaning and anti-icing multi-functionalities.