Study On Kinetics Of Droplets Impact On Micro/Nanostructure Surface

When a droplet impacts on a solid surface,it may deposit,rebound,splash and so on.Therefore,it is important to investigate the interaction mechanism between droplets and surfaces for applications such as inkjet printing,pesticide spraying and so forth.It is found that the micro/nano-structure and wettability of the surface have great influence on the impact process and outcome of droplet impact.In this thesis,the high-speed camera is used to record the whole impact process,and then the image processing is carried out with Matlab algorithm.Finally,the results are analyzed and discussed.For macro-droplet impacts with a diameter of about 1 mm on the superhydrophobic nanostructure surfaces,the results show that the impact phenomena on the inclined surface are consistent with those on the horizontal surface.Bubble entrapment and jetting only take place within a certain range of velocities.According to different generation mechanisms of jetting and the occurrence of bubble entrapment,the impact velocities can be devided into three regions.The relationship between jet velocity and radius conforms to different power law in different regime.The inclination angle of the surface does not affect the area of bubble capture,but it does affect the size of bubble capture.In addition,within a small velocity range in the bubble trapping regime on the inclined surface,it is found that bubbles in the droplet will break up at the droplet surface after rebound,resulting in a secondary jet.For micro-droplet impacts with a diameter of about 50 micron on the hydrophobic microstructure surfaces,the results show that the maximum spreading factor increases with the increase of droplet impact velocity,and is less affected by the morphological characteristics of surface microstructures.The existing theoretical models overestimate the maximum spreading factor.The oscillation process of droplets impacting on surfaces is equivalent to a single-degree-of-freedom damping spring system.The surface microstructures have an effect on the droplet vibration damping coefficient,but have little effect on the elastic constants.Compared with millimeter droplets,the oscillation damping coefficient is about three orders of magnitude smaller,while the elastic constant is independent of the size of droplets.