Research On The Motion Characteristics Of Droplet Impacting The Wettability-patterned Surface

The directional movement of droplets exists widely in nature and also has a wide range of applications in daily life and production.In recent years,the droplet control technology has been continuously developed.And the directional movement of the droplets on the surface can be realized by applying active fields and constructing wettability gradient on the surface.However,these methods have disadvantages such as complex control system,high energy consumption,strict processing technology requirements,high cost and so on.Based on this,this paper proposes to use the non-equilibrium force generated by the wettability-patterned surface,combined with the energy of the droplet impact to achieve the directional bounce of the impacted droplet.So that the droplet that impacts the wall vertically can obtain the ability of lateral movement.In this study,a hydrophilic-hydrophobic patterned surface was prepared by using a wettability photo-responsive surface,and then the directional bounce of the impact droplets was realized on the patterned surface.In addition,the effects of impact velocity,impact location and surface conditions on droplet directional bouncing were studied by visualization experiments.The main research contents of this paper are as follows:（1）The titanium dioxide nanoparticles are hydrophobically modified,and the wettability photo-responsive superhydrophobic surface is prepared by hydrophobic Ti O₂nanoparticles.The causes of surface wettability change are analyzed,and the influence of illumination time and illumination intensity on surface wettability is studied.（2）The droplet directional bouncing is realized by using the patterned surface.Through the visualization experiment,the movement process of the droplet was analyzed,and the reason for the directional bounce of the droplet on the patterned surface is clarified.At the same time,the effects of impact velocity,position and other factors on the droplet bouncing motion are studied by combining visualization experiments and numerical simulations.（3）The bounce of droplets on the inclined patterned surface is explored,and the influence of surface inclination,impact velocity and position on the bounce motion of droplets is analyzed.The bouncing motion of impinging droplet on uniform hydrophobic surface and patterned surface is compared.Research shows that the modified titanium dioxide particles have good hydrophobicity.The wettability response surface prepared by this material is superhydrophobic.The contact angle and rolling angle of the surface are 155°and 5°,respectively.The hydrophilicity of the surface increases with the increase of the illumination time.What’s more,the stronger the illumination intensity,the faster the surface hydrophilicity increases.Droplet impact experiment shows that the main reason for droplet directional bounce is that the radial force inside the droplet is not zero during the retracting process under the action of hydrophilic pattern on the surface.On the horizontal patterned surface,too small or too large offset distance of droplet impacting on the surface is not conducive to droplet splitting and bouncing and small hydrophilic stripe on the patterned surface is more conducive to the splitting and bouncing of impact droplet.In addition,both the splitting mass and the bouncing distance of the impact droplet increase with the increase of droplet velocity under certain conditions.On the inclined patterned surface,the larger the surface inclination angle,the shorter the upward bounce distance of the droplet,and the greater the downward bounce distance of the droplet.When the surface inclination is constant,the mass ratio of split droplet increases with the increase of the initial velocity of impact droplet.While the bouncing distance of the droplet increases first and then decreases,there is an initial velocity that is most favorable for the split and bouncing of the droplet.The research results in this paper provide some references for the study of droplet directional motion.