Research On Directional Transport Of Droplets On Micro-structure Surface

The directional movement of liquid has a wide range of applications in fields such as mist collection,oil-water analysis,micro-fluidics,condensation heat transfer,protein adsorption,and cell migration.In the thesis,chemical corrosion,laser etching,and electrical discharge machining techniques are used to prepare specimen surfaces with wetting gradients,structural gradients,and composite gradients on the surface of brass,and the directional movement behavior of droplets on the surface of the specimens is studied and analyzed.By using chemical etching to process the brass surface,the wettability of the test piece surface and its change mechanism are observed and analyzed,also the effect of reaction time on surface wettability is studied.By using the contact angle lag theory,the effect of reaction time on surface adhesion is studied.According to the spreading distance of the droplet on the surface of the test piece,the surface of the test piece with different processing lengths is designed.By adjusting the reaction time,the wetted gradient surface is prepared.By Observing and analyzing the process of directional movement of droplets on the wetted gradient surface,the study found that within the range of the droplet contact line,the longer the surface processing length of the test piece,the smaller the droplet moving speed and the greater the moving distance.The nanosecond laser is used to construct the surface of the grooved structure,observe the change of the surface micro-structure geometry and wettability,and optimize the processing parameters.By adjusting the laser power,the study processes the groove-shaped micro-structure surface and observing the surface wettability.It is found that during the transition process of the surface wettability,a relatively obvious wetting gradient is built.The research has shown that the groove spacing changes the range of the wetting gradient.By observing the directional movement process of the droplet on the surface of the test piece,differences are found between the test pieces processed with constant power and gradual power in the phenomena of droplet's directional movement on the pieces' surface.The range of the wetting gradient has a greater impact on the directional movement of the droplets.When the wetting gradient range of the surface is larger,the directional movement performance of the droplets is weaker.The range of the wetting gradient continues to increase,and the directional movement of the droplets on the surface of the specimen gradually weakens until they disappear.The surface contact angle varies from 16° to 91° is the optimal range of the function of the directional movement of the droplet.The gradient surface of the quadrangular pyramid is constructed by wire-cut electric discharge.Comparing the directional movement behavior of droplets on surfaces with different cone angles and surface roughness,it is shown that the moving distance of the droplet decreases when the cone angle ? gradually increases,and increases when the surface roughness decrease.The wetting gradient is prepared on the surface of the quadrangular pyramid structure by chemical etching.the influence of the wetting gradient on the directional movement of droplets on the structure gradient surface is analyzed.The study found that when the effect of the surface structure gradient of the test piece on the droplets is balanced with the adhesion resistance,the wetting gradient can continue to drive the droplets to move.The change in the directional movement distance of the droplet increases with the cone angle.Under the co-reaction of the structural gradient and the wetting gradient,the overall movement distance of the droplet on the composite gradient surface increases,and the difference in the movement distance of the droplet is vague under different cone angles.