Fabrication Method Of Metal-based Superamphiphobic Surfaces And Study Of Drag Reduction Effect

The drag reduction property of superhydrophobic surface has always been a hot research topic.Due to its unique micro/nano interface effect,the superhydrophobic surface can trap a layer of air film underwater,showing the features of multiphase flow and boundary in the flow field near the wall.It is of great sig nificance to apply this technology to the fields of microfluidic chips,marine engineering and pipeline transportation.However,the current research on the drag reduction technology of superhydrophobic surfaces is not perfect,First,the research on the drag reduction mechanism of superhydrophobic surfaces still needs to be further improved;second,the durability of most superhydrophobic surfaces is poor and cannot meet the requirements of long-term application in the field of drag reduction.This paper studies the drag reduction properties of superhydrophobic surfaces from both theoretical and experimental aspects,reveals the law of drag reduction about superhydrophobic surfaces,and develops research on the preparation methods of durable superhydrophobic surfaces.Most of the drag reduction models of superhydrophobic surfaces are based on the stable existence of surface microbubbles,and do not consider the impact of solid surface wettability and the state of microbubbles on the drag reduction.In respon se to these problems,this paper established a dynamic bubble drag reduction model of superhydrophobic surface based on the microstructure,and comprehensively analyzed the effects of surface wettability and surface morphology on bubble stability and drag reduction.Through systematic research on factors such as surface hydrophobicity,microstructure size,solid-liquid interface fraction,water flow velocity,etc.,the simulation results show that the ability of microstructures to trap air bubbles increases with the surface hydrophobicity,and the drag reduction effect is significantly improved;The superhydrophobic surface with micro/nano hierarchical structures has better ability to trap air bubbles than the superhydrophobic surface of single structure,and the drag reduction effect is also greatly improved.According to the theoretical guidance of the drag reduction model,this paper uses the microporous corrosion method under strong electric field and the PEI-assisted zinc oxide growth method to prepare samples of micro-structure,nano-structure and micro/nano hierarchical structure respectively.After modification with low surface energy materials,it is found that the surface of the sample with the micro/nano hierarchical structure has the best superhydrophobicity.Superhydrophobic surfaces with different microstructures are tested using a friction resistance test system.The test results show that the superhydrophobic surface with micro/nano hierarchical structure has the best drag reduction effect under the same water flow velocity.Compared with the superhydrophobic surface with only the microstructure,the drag reduction rate is increased by more than 20%.The experimental results are consistent with the simulation results,verifying the correctness of the dynamic bubble drag reduction model on the superhydrophobic surface.In response to the actual application requirements of drag reducing surfaces,this paper carried out experimental research from two aspects of microstructure and hydrophobic coating,and proposed a method for preparing durable superhydrophobic drag reducing surfaces.By studying the effects of microstructures prepared by different methods on the drag reduction and durability of superhydrophobic surfaces,it was found that in a short time test,the greater the contact angle,the better the drag reduction property;but as the flushing time increases,the contact angle and drag reduction effect of the water droplets on the superhydrophobic surface prepared by the growth method will rapidly decrease;while the superhydrophobic surface prepared by the etching method can maintain a higher contact angle and a good drag reduction effect for a long period of time.Next,the effect of different coatings on the durability of superhydrophobic surfaces was studied,and the results showed that the surface durability of hydrophobic coatings of rosin and Si O₂particles was better than that of hydrophobic coatings of single-molecule fluorinating agents.Therefore,a superhydrophobic drag-reducing surface with good durability can be prepared by a combination of etching and spraying.Aiming at the problem of superhydrophobic surface being easily contaminated by grease and solid-liquid interface drag reduction of other liquid in practical applications,this paper has carried out the research about the fabrication and drag reduction of superamphiphobic surfaces.Superamphiphobic surfaces have repellent characteristics to a variety of liquids.At present,most of the super amphiphobic surfaces preparation processes are relatively complicated,and have strict requirements on substrates.In this paper,a surfactant is introduced to the composite method based on laser etching and spraying to prepare FS-61/PTFE superamphiphobic surface on common metals,which has excellent drag reduction,anti-fouling and anti-corrosion properties.For example,the superamphiphobic surface prepared on aluminum alloy has superamphiphobic effect on liquids with a surface tension greater than 30m N/m.Among them,the contact angle of water is as high as 164°,and the contact angle of rapeseed oil is about 160°.The roll an gles are all less than 5°.The superamphiphobic surface has a drag reduction effect on a variety of flowing liquids and the surface durability is good.