Dynamics Of Droplet Impacting And Wetting On The Hydrophilic And Hydrophobic Surfaces With Different Shapes

The process of droplets hitting the wall exists widely in nature,industrial equipment and agricultural production,and is of great significance for many technical applications: such as spray cooling applications in electronic components;Seawater spray application;in addition,it has broad application prospects in the fields of agricultural raw tea,aerospace,and biomedicine.By changing the wetting properties of the surface,droplets can be cut without forming tiny satellite droplets;or they can be moved,deflected,and transported without electrical input;or they can be fabricated in the biomedical field Hydrogel micropads are used to separate cells.In order to deeply analyze the dynamic behavior characteristics of non-uniform wettability walls,by combining the hydrophobic and hydrophilic characteristics on one surface,and using a high-speed imaging method,the impact of droplets on horizontal/oblique lines,diagonal lines,waves The morphological change process of the hydrophilic-hydrophobic spacer surface was experimentally studied,and the dynamic behaviors such as droplet spreading and retraction,centroid offset distance,contact diameter in the horizontal and vertical expansion process on each hydrophilichydrophobic spacer surface under different experimental conditions were compared and analyzed.parameter.The main research contents include:In this paper,the vertical tooth structure aluminum sheet with a special surface shape is first processed by wire cutting,and then embedded into the resin surface,and then the surface of the aluminum sheet is processed by chemical etching and surface material modification methods to obtain hydrophilic properties.And hydrophobic properties of straight lines,diagonal lines,wavy lines hydrophilic and hydrophobic spaced surface.Based on the visualization experiment of droplets hitting various hydrophilic and hydrophobic spaced surfaces horizontally,the effects of droplet diameter,droplet impact velocity,and hydrophilic and hydrophobic spaced surfaces of different surface shapes on the behavior of single droplets hitting solid surfaces were studied,such as:Morphological changes of spreading and retraction during impact,centroid offset distance due to non-uniform wettability of walls,height of central liquid film,etc.The experimental results show that when the droplet hits the wall and spreads to the maximum contact diameter,the moving speed of the three-phase contact line is different due to the different wettability of the wall contacted by the edge liquid film,resulting in the phenomenon of "edge disturbance",which is similar to the wall surface.The shape is related and the perturbation direction is along the hydrophilic and hydrophobic grain direction.At the same time,during the retraction process,due to the dragging effect of the vertical surface tension on the hydrophobic surface under the action of the adhesive force of the hydrophilic surface,the droplet will move obliquely upward and then fold over to the hydrophilic surface,resulting in a certain amount of droplets.The center of mass shift phenomenon,which makes the center position of the droplet shift.The process of the droplet impacting the inclined profiled hydrophilichydrophobic spacer surface was photographed and recorded by a high-speed camera system,and three factors,the hydrophilic-hydrophobic spacer surface,the slope angle of the inclined plane,and the droplet drop height,were emphatically discussed on the surface of different shapes.Dynamic properties of the wall.The results show that during a period of time when the droplet spreads to the maximum contact diameter and slides down the slope,the wettability of the contact points before and after the droplet is different and the contact angle is very different,and "pinning phenomenon" and "transition behavior" appear..The larger the angle of inclination and the larger the impact velocity of the droplet,the greater the probability of the above two behaviors,and the more obvious the effect.After the above behavior occurs,the liquid film(smearing)at the bottom of the droplet forms a neck wire on the hydrophobic area due to the difference in retraction speed between the hydrophilic area and the hydrophobic area,and the droplet continues to move downward.The neck wire will break.Satellite droplets are formed in hydrophilic regions.And on the slanted surface,due to the arrangement of the hydrophilic and hydrophobic regions,the droplet body undergoes transition behavior and retracts counterclockwise in a spiral shape in the horizontal direction.The pinning phenomenon and transition behavior make the transverse and longitudinal contact diameters change with the dimensionless time when the inclination angle of the inclined plane increases and the We number increases.