Interfacial Phenomena And Regulation Mechanism Of Droplet Impact On Ridged Superhydrophobic Surfaces

The emerging anti-icing technology utilizing superhydrophobic surfaces has shown great potential in diverse fields such as energy and power engineering and aerospace industry,because superhydrophobic surfaces with excellent water repellency easily drive droplets to escape from surfaces.Structured superhydrophobic surfaces formed by constructing structures on superhydrophobic surfaces can further improve the performance of anti-icing and anti-frosting.However,surface structures complicate the interfacial phenomena caused by droplets impacting on solid surfaces,and the precise regulation of droplet behaviors becomes more challenging.Herein,for droplets impacting on superhydrophobic surfaces decorated with ridges(one of the most typical structures),from the two perspectives of weakening solid-liquid contact and strengthening droplet detachment,systematical studies are carried out on three aspects: droplet spreading characteristics,solid-liquid contact time and droplet rebound characteristics.This work aims to elucidate the underlying mechanism of complex interfacial phenomena of droplets impacting on ridged superhydrophobic surfaces,reveal effects of various parameters on droplet dynamics,and propose strategies to regulate droplet behaviors.The achieved findings can not only advance the understanding of droplet dynamics on structured superhydrophobic surfaces,but also provide valuable insights for the development of advanced anti-icing technology.Droplet dynamic behaviors on ridged superhydrophobic surfaces are experimentally observed,and droplet spreading is found to be anisotropic,where spreading length varies in different directions.By quantitatively analyzing the effects of the Weber number and the ridge-to-droplet size ratio on the maximum axial spreading coefficient,the inhibition effect of ridge structures on droplet axial spreading is elucidated,and the theoretical model is established for accurately predicting the maximum axial spreading coefficients.Under two practical but complex conditions of surfaces being obliquely placed and droplets eccentrically impacting on ridges,the features of droplet morphology evolutions are discussed,the influence of various factors on the contact time is clarified,and the prediction models of the contact time are developed.On inclined ridged superhydrophobic surfaces,the contact time can be reduced by elevating the Weber number or appropriately increasing the inclined angle.For droplet eccentric impacts,the eccentricity between the impacting droplet and the ridge should be minimized to achieve the minimum contact time.The splitting dynamics and rebound motions of droplets impacting on ridged superhydrophobic surfaces are reported.Regarding droplet splitting,the criterion for trigging droplet splitting is established,and the scaling law of the splitting time is proposed.Based on the discovered directional rebound of split droplets,an efficient strategy of droplet directional transport is proposed,which owns multiple advantages including high transport speed,long transport distance and fast response.Furthermore,the excellent performance of the proposed strategy is experimentally validated through application cases.Lastly,the pancake bouncing on ridge-textured superhydrophobic surfaces is investigated in detail,which shows superior performance in reducing contact time.The mechanism of the occurrence of pancake bouncing is revealed,and then the design criteria of ridge-textured superhydrophobic surfaces for inducing pancake bouncing is proposed,which simplifies all initial parameters into two parameters only related to properties of droplets and surfaces,respectively.The proposed design criteria diagram offers useful guidance for the optimal design of superhydrophobic surfaces with ridges.