Study On The Effect Of Micron-nanoscale Hierarchical Structure On Anti-icing Performance And Its Mechanism

Ice formation or accumulation on the external surfaces of ships,power transmission lines,aircraft wings,communication devices,etc.,may lead to equipment damage or pose certain safety hazards.Existing de-icing or anti-icing methods（such as mechanical de-icing,thermal de-icing,and fluid anti-icing,etc.）can achieve de-icing or reduce icing,but there are problems such as higher costs,low efficiency,and environmental pollution.Icephobic or anti-icing coatings are methods of preventing or reducing ice accretion by inhibiting or retarding ice nucleation and lowering ice adhesion strength,of which superhydrophobic anti-icing coatings have attracted a great deal of attention.The large contact angle of water droplets on superhydrophobic surfaces reduces the actual solid-liquid contact area,which is beneficial for delaying droplet freezing and achieving anti-icing;and the superhydrophobicity allows water droplets to slide off the surface by their own gravity or airflow,reducing ice accretion.Therefore,superhydrophobic surfaces have broad application prospects in the field of anti-icing.However,the microstructure of superhydrophobic surfaces is prone to damage under mechanical load or chemical reagent erosion,resulting in loss of superhydrophobicity;and the research on the characteristics of droplet movement on superhydrophobic surfaces mainly focuses on the microscopic process of droplet wetting behavior.The lack of water molecules separating from the solid surface is conductive to the discussion of the mechanism of reducing icing or frosting.The development of superhydrophobic surfaces with mechanical durability and chemical stability is of great significance in practical applications.This dissertation is inspired by the nature of superhydrophobic surfaces and adopts a combination of surface“pre-roughening”and low-surface energy modification to prepare biomimetic superhydrophobic surfaces with micron-nanoscale hierarchical structures.The focus is on exploring the changes in surface wettability with surface microstructure and chemical composition,and on this basis,analyzing the effects of micron-nanoscale hierarchical structures on reducing frosting,self-cleaning,and delaying droplet freezing.The microscopic mechanisms of spreading process,wettability,and detachment of water droplets on smooth and rough structured solid surfaces with different surface energies are explored by adjusting the solid-liquid interaction strength with a view to supporting the development of efficient anti-icing or icephobic surfaces.The details of the study are as follows:（1）By combining alkali chemical-etching and hydrothermal treatment,a micron-nanoscale hierarchical structure was constructed on the surface of 1060 aluminum alloy and H62 brass metal substrates,followed by low-surface energy modification with stearic acid to obtain biomimetic superhydrophobic surfaces with micron-nanoscale hierarchical structures.Scanning electron microscopy（SEM）,atomic force microscopy（AFM）,and contact angle measurement were used to explore the effects of the alkali chemical-etching process on the surface morphology and to analyze the changes of surface wettability with surface microstructure and chemical composition.It was confirmed that the micron-nanoscale hierarchical structure surfaces prepared by alikali chemical-etching have been hydrophobically modified by stearic acid with the use of fourier transform infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）,transforming the hydrophilic micron-nanoscale hierarchical structure surfaces into biomimetic superhydrophobic surfaces.Comparing the freezing delay time of water droplets on the metal substrates with different surface morphologies after alkali chemical-etching,it was found that the freezing delay time of water droplets on the modified micron-nanoscale hierarchical structure surfaces was prolonged and exhibited certain anti-icing performances.（2）The combination of chemical-etching process and hydrothermal treatment enables the formation of micron-nanoscale hierarchical structure on the metal substrate surfaces.However,due to the influence of the activity of metal elements in the metal substrate,the process of constructing rough structures on some metal substrate surfaces based on alkali solution etching will be limited.Hydrofluoric acid（HF）and hydrochloric acid（HCl）solutions were used as etchants to“pre-rough”the surface of 1060 aluminum alloy and H62 brass metal substrates,which were then hydrophobic modified with low-surface energy to obtain a biomimetic superhydrophobic surface with micron-nanoscale hierarchical structure and possesses self-cleaning performance that imitate the“lotus effect”.Compared to the alkali chemical-etching process,the acid chemical-etching treatment results in a stable micron-scale step structure on the metal substrate surface,which helps increase the surface roughness,while protecting low-surface energy components,leading to improved mechanical durability and chemical stability of the biomimetic superhydrophobic surfaces.（3）Inorganic nanoparticles are easily modified and are ideal raw materials for the fabrication of biomimetic superhydrophobic surfaces.The hydrophobic modification of silica（Si O₂）nanoparticles by trimethylethoxysilane and the grafting foundation of hydrophobic silica（Si O₂）nanoparticles by using the micron-scale ladder structure obtained after acid chemical-etching to prepare a bio-inspired superhydrophobic surface with micron-nanoscale hierarchical structure.The anti-icing and anti-frosting performance of the micron-nanoscale hierarchical structure surface prepared by the dip-coating method was analyzed,and the results showed that the freezing delay time of water droplet on the 1060 aluminum alloy surface with micron-nanoscale hierarchical structure was extended to 4973.87 s from 13.31 s of the pristine 1060 aluminum alloy surface,the frost formation amount was reduced and the frost layer on the 1060 aluminum alloy surface with micron-nanoscale hierarchical structure could be rapidly melted into independently dispersed spherical water droplets in about 20 s,which shows better anti-icing and anti-frosting performance.（4）By applying the synergistic effect between micron-scale stepped structure and hydrophobic silica（Si O₂）nanoparticles,the biomimetic superhydrophobic surface of micron-nanoscale hierarchical structure prepared by dip-coating method has good mechanical stability.However,the dip-coating method is limited by the substrate size and material properties.In order to achieve large-scale preparation of biomimetic superhydrophobic surfaces,hydrophobic fumed nano silica sol（Sol-H-Si O₂）was prepared by using methyltriethoxysilane as silane coupling agent,and the hydrophobic nano silica sol（Sol-H-Si O₂）was sprayed on the micron-scale ladder structure by spray-coating method to obtain the micron-nanoscale hierarchical structure surface and analyze its wetting characteristics,surface morphology,and chemical composition.Due to the superhydrophobicity of the micron-nanoscale hierarchical structure surface prepared by spray-coating method,the actual solid-liquid contact area is reduced,which is conductive to delaying freezing or reducing frosting;and the reduction of water adhesion is conductive to improving the surface self-cleaning and defrosting efficiency.The freezing delay time of water droplet on the H62 brass surface with micron-nanoscale hierarchical structure prepared by spray-coating method was prolonged to 5013.57 s from 21.60 s of the pristine H62 brass surface,and the frost layer on the surface quickly melted into individually scattered spherical water droplets within 7 s.After several frosting-melting cycles,the H62 brass surface with micron-nanoscale hierarchical structure prepared by spray-coating method still exhibited superhydrophobicity.（5）The surface energy of H62 brass substrate surface with micron-nanoscale hierarchical structure prepared by spray-coating method is analyzed by v OCG method,the wetting behavior of water droplets on smooth and rough surfaces with different solid-liquid interaction strength is analyzed by molecular dynamics simulation,and the microscopic process of water molecules detaching from smooth and rough surfaces with different energies is studied to provide theoretical support for the preparation of biomimetic superhydrophobic surfaces and their anti-icing or anti-frosting properties.It’s confired that the synergistic effect of low-surface energy and rough structure enables the surface with superhydrophobicity and facilitates the detachment of water molecules,which in turn reduces icing or frosting and is the key to developing an efficient anti-icing or anti-frosting surface.