Research On Wetting Mechanism Of Micro-Nano Textured Superamphiphobic Surface Of Copper Metal And Processing By Femtosecond Laser

As the micro-nano textured superamphiphobic surface has special properties such as self-cleaning,anti-icing,slip resistance reduction,biological anti-fouling,and microfluidic control,it has broad application prospects in aerospace,national defense and military,petrochemical,electronic information,biomedical and other fields.Due to its extremely short pulse width and extremely high peak power,femtosecond laser has the characteristics of non-contact,high precision,high flexibility,and material universality in micro-nano processing,and is an important solution to the preparation of multi-scale micro-nano textured superamphiphobic surfaces.In this thesis,the wetting mechanism of the micro-nano textured superamphiphobic surface and processing by femtosecond laser have been studied.The numerical relationship between the microstructure and the macroscopic wettability is established.And based on the optimized design of the superamphiphobic structure,the femtosecond laser is used to prepare a three-stage micro-nano textured superamphiphobic surface,which has important scientific significance and research value.Compared with the traditional wetting theory from the perspective of mechanics,the wetting theory based on Gibbs free energy can establish the relationship between surface structure morphology and wettability,but it cannot simulate special structures with complex shape characteristics.Based on the research of the energy theory,this thesis introduces the overlap ratio parameter to reestablish the relationship between the solid phase and gas phase fractions,modifies the energy wetting theory,and expands the application range of it.The three specific structures were simulated,and the lowest surface tensions when the three structures can realize the Cassie state are 10 m N/m,21.2 m N/m and 27.9 m N/m,respectively.Compared with the experimental results,the contact angle prediction error is less than 3.9°.The wetting simulation model of the two-stage micro-nano structures was constructed using the above theory to optimize the design of the micro-cone structures.After that,the femtosecond laser was used to prepare a secondary micro-nano structure with a micro-cone structure and a nano-particle structure,and the independent control of the micro-and nano-structures was achieved by adjusting the scanning speed and the number of scanning.Through the wettability test of the two-stage micro-nano textured surface,the results indicate that the superhydrophobicity is best when the height of the cone structure is 80 μm and the nanoparticle density is moderate.The advancing angle of the surface to water is 170.1° and the receding angle is 163.0°.The surface still retains superhydrophobicity when the droplet is extruded to the extreme position,and the critical pressure is 354.9 Pa.Compared with the raindrop pressure of about 40 Pa in heavy rain,the two-stage micro-nano textured surface prepared in this thesis can fully meet the requirements of routine environment for the wetting stability of superhydrophobic surfaces.In order to further improve the super-hydrophobic performance of the micro-nano composite structure,the new secondary grid structure is added.And the three-stage structures simulation model is constructed to design and optimize the newly added grid structure.Afterwards,the femtosecond laser was used to prepare the three-stage micro-nano textured surface with the micro-cone structure,the secondary grid structure and the nano-particle structure.The methods of step-by-step processing and combined multi-spot processing were used to control height ratio of grid structure and grid spacing.The results indicate that the three-stage structure with a grid spacing of 130 μm and a height ratio of grid structure of0.40 has the best superamphiphobicity.The advancing angle of the surface for1,2-propanediol with γ = 32.9 m N/m is 163.4°,the receding angle is 144.8°,and the critical pressure is 480.1 Pa.The three-stage micro-nano textured surface prepared in this thesis can achieve superamphiphobicity for the liquids with a surface tension higher than 31.6 m N/m.