Preparation Of Biomimetic Non-uniform Wettability Surface And Study Of Its Water Collection Performanc

The shortage of fresh water resources has become a major constraint on global social and economic development.In search of new water sources,some plants and animals in the desert have shown effective solutions to collect water from the fog.Desert beetles use the surface energy gradient provided by the non-uniform wettability of the back to accelerate the nucleation efficiency and shedding efficiency of the fog on the surface.Cactus use the Laplacian force provided by the wedge needle structure to realize the directional transport of droplets.Coupling biomimetic water-collecting surfaces inspired by these two organisms have received increasing attention.In this paper,the desert beetles and cactus were used as biomimetic prototype,and the wedge-shaped pattern of superhydrophobic/hydrophilic non-uniform wettability surface was constructed on the copper surface by the method of chemical etching and hydrophobic modification after mask,and its water collecting performance was studied.The main research contents and results are as follows:（1）Explore the influence of alkaline ammoniμm persulfate concentration,etching time and modification time on surface wettability.The effects of different reaction conditions on the surface microstructure,surface roughness,surface composition and surface wettability of copper sheet were analyzed by the surface 3D morphology,3D profile,surface energy spectrμm and contact angle.The results show that three kinds of rough microstructures are produced on the surface of copper sheet after chemical etching,and the surface is superhydrophilic.After hydrophobic modification,the surface of copper sheet is combined with hydrophobic functional groups and becomes superhydrophobic.Among the three kinds of rough microstructures,acupuncture of fibrous Cu（OH）₂ has the largest surface wettability change.With the increase of etching time,acupuncture of fibrous Cu（OH）₂ will transform into Cu O sheets,and the surface hydrophobic property increases continuously.When the etching time is 10min and the modification time is 12h,the surface hydrophobic property is the highest（164.8°）.（2）The dynamic behavior of droplets on different wettability surfaces was analyzed.By setting up a visual condensation experiment platform,the condensation process of droplets on single wettability surface and bionic wedge pattern surface was observed,and the influence on the surface water collection effect was analyzed.The results show that the superhydrophilic and hydrophilic surfaces will restrict the nucleation of new droplets on the surface due to the film condensation,which is not conducive to fog collection.Due to droplet condensation,there are frequent droplet coalescence and bouncing phenomena on the surface of superhydrophobic surface for nucleation and growth of new droplets,which is conducive to fog collection.The bionic wedge pattern surface brings the droplets together in the hydrophilic region under the action of the surface energy gradient provided by the non-uniform wettability and the Laplacian pressure provided by the wedge pattern.（3）Study the water collection performance of bionic non-uniform wettability surface.The effects of different pattern parameters and different working conditions on the water collection efficiency of bionic non-uniform wettability surface were studied by water collection experiments.The experimental results show that the surface water collection efficiency is higher when the number of main wedge angles is 30°,which increases by 22.3%compared with that of ordinary copper surface.The surface water collection efficiency can be effectively improved by adding the branch wedge Angle to the trunk wedge Angle.When the branch series is increased toⅤ,the surface water collection efficiency is increased by 70.6%compared with the ordinary copper surface.When the working conditions change,the bionic wedge pattern non-uniform wettability surface water collection advantage is further expanded.When the fog flow velocity changes from 1m/s to 2m/s,the water collection efficiency is 2.01 times that of ordinary copper surface;when the sample temperature changes from 25℃to 10℃,the water collection efficiency is 1.87 times that of ordinary copper surface.The surface water collection efficiency of bionic wedge pattern is anisotropic,and the surface water collection efficiency is different with different sample placement methods.