Bouncing Mechanism Of Droplets On The Hierarchical Structure Surface With Antiicing Properties

Ice formation on critical parts of aircrafts usually brings tough issues.The traditional anti-icing and de-icing strategies still unavoidably face the fate of elimination in future owing to the complex design and high energy comsumption.Therefore,it is necessary to develop some new anti-icing strategies.Superhydrophobic materials have broad application prospects in passive anti-icing area since it can obviously delay the freezing of droplet and reduce the ice adhesion.The superhydrophobic surface with anti-icing properties was prepared by constructing microstructures and reducing surface energy through fluoridation modification on aluminium alloys.Then spontaneous jump of condensed droplets,icing delay property,ice adhesion strength and frosting process were investigated respectively.The main conclusions were as follows:(1)Based on the aluminium alloys,we constructed a layer of nanohairs by means of hydrothermal treatment on the microblock structures fabricated by electrochemical etching,and obtained the superhydrophobic surface after modifying the hierarchical microblock-nanohair structures with FAS-17.The comparative studies with the other microstructure surfaces revealed that the optimal hydrophobic performance was obtained under the conditions of 6 V voltage,2 h time,and 5 h hydrothermal treatment time.The resultant surface with hierarchical structure exhibited superior water repellency with the water contact angle reaching 164° and the sliding angle of 1.5°.(2)The impacting processes of the droplets were recorded to ascertain the dynamic water repellency of the superhydrophobic surfaces.The impacting droplets adhered to the smooth surface after retracting.However,the impacting droplets on the surface with microblock-nanohair structures would bounce off the surface within 9.8 ms after spreading and shrinking.The contact time of the impacting droplets on microstructured surface and nanostructured surface was 12.4 ms and 11.6 ms,respectively,caused by the microstructure of superhydrophobic surfaces,reducing the resistance during droplet spreading and shrining.(3)The superhydrophobic surfaces were all able to delay droplet freezing to some different degrees.Among them,the longest freezing time of droplet on microblock-nanohair structure surface was extended to 1697 s.The special microscopic structure can considerably reduce the actual solid/liquid contact area between solid surface and water droplet based on the synergistic action of the microstructure and the chemical composition.In this case,the extremely low thermal-transfer efficiency would cause the great icing delay performance.The ice adhesion on the surfaces was reduced to 35.7 k Pa,which was about 20 times lower than that on the smooth surface.According to the observation of the frosting processes on the three surfaces,it was found that on the nanoscale surface and the micronanoscale surfaces,the droplets spontaneously jumped off during the condensation process.The condensed microdroplets maintained high mobility on the low viscosity surface.The self-propelled movements were the intrinsic reason of frosting delay properties on superhydrophobic surfaces containing nanoscale structure,while the hierarchical structure surface exhibited a better anti-frosting performance due to the lower viscous resistance.