The Mechanism And Experimental Research Of Rapid Rebound Of Droplets On Microstructure Surface

In nature,some strange phenomena often can be observed.For example,the surface of the lotus leaf after the rain is not soaked by rain and only leaves crystal clear dewdrops in the center of the leaves;the swan playing in the lake,and the feathers floating or sinking in the water but remains clean and tidy.After long-term exploration,various surface like the plants,or the wings or scales of animals are covered by the patterned array structures which exhibited various special wetting properties such as hydrophilicity,superhydrophobicity.Through the development of bionic engineering technology,researchers have done a lot of work on the surface of the biomimetic microstructure.However,most of the work is only for the static wetting behavior,the research for the dynamic wetting states of the droplet on the microstructure surface is not perfect enough.The microstructure surface which can realize the rapid rebound behavior of the droplets,whether it is on the anti-icing of the construction equipment which working in the low temperature environment,or the self-cleaning of people’s objects in the daily life,they all have good application value.Therefore,analyzing the rapid rebound behavior of droplets on the surface of materials will have important research significance for improving the safety,applicability and durability of equipment.This paper is based on the rapid pancake bouncing of the droplets on the surface of the superhydrophobic conical array,the microstructures’ size,morphology and the flexible of the substrate are used as the entry point,the dynamic wetting states of droplets are research from two aspect.The range of pancake bouncing,contact time and performance optimization of the microstructure surface were systematically studied,and a simple experimental design was made for the engineering application of droplets rebounding rapidly from the surface.The main research contents of this paper are as follows:(1)The wetting states and pancake bouncing of droplets on the superhydrophobic conical array surface were studied by thermodynamic theory and energy method,and the static wettability,energy of rebound and scale of contact time which limit the pancake bouncing of droplets are discussed.The pancake bouncing phase diagram and contact time of the droplets on the superhydrophobic conical array are be given by the theoretically calculated,and it is concluded that the rebound energy and contact time can be adjusted by adjusting the size of the microstructure.(2)From the experimental point of view,the superhydrophobic conical array surface with different spacing size was designed and prepared.The actual dynamic rebound behavior of the droplets was observed and analyzed to obtain the rebound law of the droplets on the surface of different microstructures,which proved the correctness of the previous theoretical derivation was verified.In addition,the influence of droplet size and conical microstructural spacing on droplet resilience is analyzed,and the quantitative relationship between droplet volume and conical microstructural spacing is given.(3)The effect of the flexibility of the conical microstructure surface material itself on the rebound of the droplet was investigated.Through the theoretical analysis of the rebound of the droplets on the surface of the flexible superhydrophobic cone array,it is discussed how to expand the range of the pancake bouncing and shorten the rebound time of the droplet by changing the flexibility of the tapered microstructure.In addition,microstructures with different modulus of elastic were prepared experimentally to verify the correctness of theoretical analysis.Studies have shown that changing the microstructure’s modulus of elastic can effectively shorten the contact time of droplets and the required rebound energy.(4)The rebound of droplets on the surface of a thin film structure with tapered array structures was studied.Firstly,gives several possible prediction scenarios though the theoretical analysis of the rebound behavior of droplets on this film structure.Then,the superhydrophobic film is fixed by a clamp to form a simple film structure with both ends fixed at the clamp and no support at the bottom for the rebound experiments of the droplets.Finally,an applied mechanical strain is applied to the film,thereby effectively regulating the contact time of pancake bouncing of the droplets.(5)The effects of parameters such as surface tension,viscosity and density on the rebound of droplets were analyzed.The surface of the superhydrophobic conical array,the common hydrophobic surface and the ordinary superhydrophobic surface were respectively subjected to liquid soaking experiment,droplet dropping experiment,fluid jet experiment and spraying experiment.Through experimental comparison,it is concluded that the superhydrophobic conical array surface has more excellent hydrophobicity and self-cleaning property than the other two surfaces.In summary,this thesis firstly combines theory and experiment to comprehensively analyze the rebound of droplets on the surface of tapered microstructures,and gives the phase diagram of the rapid rebound range of droplets under different microstructure spacings.The relationship between the droplet contact time and the microstructure spacing is accurately predicted.Then,the influence of the elastic modulus and support mode of the microstructure surface material on the rebound of the droplet is further considered.The expansion of the droplet shape and the shortening of the contact time are realized by the material flexibility and the fixing of the film structure..Finally,the experimental comparison of the surface with a common hydrophobic surface and an ordinary superhydrophobic surface proves that the surface has potential advantages in self-cleaning.The theoretical and experimental results of this thesis can play a good role in guiding and referencing the bionic microstructure surface in many fields such as self-cleaning,anti-icing and waterproofing.