Study On The Rebound Characteristics Of Micro-nano Structure Surface Prepared By Femtosecond Laser

The dynamic behavior of droplets hitting a solid surface can be seen everywhere in daily life,and has played an important role in many applications: as large as anti-icing of aircraft,and as small as microfluidics in chip labs.Therefore,researchers have never stopped exploring and studying the dynamic behavior of liquid droplets hitting solid surfaces.One of the important research directions is how to effectively control the rebound behavior of the impacting droplets.The current research results show that according to the dynamic characteristics of the impact surface of liquid droplets,it is mainly divided into two important research directions: impact of liquid droplets on solid surfaces at normal temperature and hot solid surfaces.Different types of surfaces have different dynamics of impacting droplets.In this thesis,micro-nano structures are prepared on metal surfaces using femtosecond lasers,and the rebound characteristics of liquid droplets at normal temperature and thermal micro-nano structures are studied.The main contents are as follows:In the study of the dynamic behavior of droplets at normal temperature,researchers at home and abroad use surface chemical composition,microstructure,or their synergy to construct different wettable surfaces.The purpose is to perform the rebound dynamics of impacting droplets.control.In this paper,a new method is proposed and verified for the first time—the use of micro-nano structures with different adhesive properties to join surfaces can control the movement behavior of impacting droplets in the rebound process.The physical mechanism is the micro-nano structures prepared on the surface Will affect its adhesion,by changing the micro-nano structure of the solid surface,you can control the adhesion difference of the splicing surface,and then achieve precise regulation of the rebound behavior of the impact droplet.In the experimental results of this paper,the maximum offset distance that can be achieved is 9mm,and the minimum control accuracy is 0.2mm,and the adverse effects caused by the difference in spatial topography can be overcome.This research provides a new idea and development direction for the regulation of droplet rebound,and it is of great significance for the development of liquid transportation and microfluidic devices.In the study of the dynamic behavior of droplets hitting hot surfaces,there have been studies showing that when the surface temperature rises to a certain range,the droplets hitting the surface will be in a thermal state called Leidenfrost,and the droplets will appear Different from the dynamic behavior of the surface at room temperature.In this paper,the micro-nano structure surface prepared by the femtosecond laser is heated,and the droplet impact experiments are performed at different heating temperatures(20-260?).It was found that the morphology of the surface of the micro-nano structure will affect its Leidenfrost temperature.For surfaces with structural differences,when the surface temperature is low,the main factor affecting the directional rebound behavior of the impacting droplets is the difference in surface adhesion;and when the surface temperature rises to a certain range,the impacting droplets will be in a kind of A new thermal state called Janus.The droplets in the hot state have both Contact-boiling and Leidenfrost states,so that there is a curvature gradient in a single droplet to achieve directional rebound;as the surface temperature further increases,The impacting droplets completely changed to the Leidenfrost state,and the directional rebound of the droplets disappeared.This research is of great significance for understanding and controlling droplet dynamics,and provides new ideas for the application of high temperature multifunctional surfaces in the future.