Supercooled Droplet Crystallization Process And Anti-Icing Mechanism Of The Superhydrophobic Aluminum Surfaces

The traditional active anti-icing/de-icing methods,based on the idea of melting ice and breaking ice,cannot solve the root problem.The passive anti-icing is an important development direction.Under ispiration of bio-inspired superhydrophobic surface technology,the dissertation constructed two kinds of typical micro-nanoscale hierarchical structures on the aluminum surface.The superhydrophobic surfaces were obtained after modifying with fluorosilane.The crystallization process of supercooled droplets and the anti-icing performance at low temperature on two typical surfaces were carried out to explore the mechanism of different rough structures on non-wettability and anti-icing performance,so as to do basic research and explorationwork for the application of superhydrophobic surface anti-icing technology.The main research results obtained are as follows:(1)Two typical micro-nanoscale structures,i.e.,sealed layered nanoporous structures and open nanocone structures were prepared by hydrothermal synthesis.As a consequence,the resultant surfaces exhibited great superhydrophobic properties and the impacting droplets could be rapidly rebounded off with shorter contact time of 11.2 ms and 10.4 ms,respectively.Meanwhile,the droplets showed ultra low adhesion on the both superhydrophobic surfaces(16 ?N and 4.1 ?N,respectively,and it is about two orders of magnitude smaller than that(317.3 ?N)of the flat aluminum surface).According to the analysis,the solid-liquid contact mode between the microstructure and the droplet was the main factor of affecting the adhesion of the droplet.The magnitude of adhesive force of a droplet on surface descends in the order area-contac(flat aluminum surface)> line-contact(layered nanoporous structures surface)> point-contact(open nanocone structures surface).Meanwhile,the negative pressure caused by capillary adhesion in the sealed layered nanoporous structures,causing the droplet adhesion larger than that of the open nanocone structures with great air flow.(2)Having stronger self-propellsion capability compared with the sealed layered nanoporous structures,the opend nanocone superhydrophobic surface could efficiently control the size of condensed droplets at the microscale,especially bellow 10 ?m with a more than 80% drop number distribution.The prominent property was ascribed to the extremely low solid-liquid adhesion,and the de-pinning ability at the microscopic scale of the opened nanoconical structures.The self-propelled phenomenon effectively reduced the nucleation position on the surface,and enhanced the anti-frost performance of the superhydrophobic surface.(3)The mechanism of ice nucleation and growth under special wetting interface model was analyzed on superhydrophobic surfaces,which exhibited great icing delay performance compared to the smooth substrate surface(~50 times of icing delay time at-10 °C,and ~ 8~12 °C reduction in icing temperature measured by DSC).The anti-icing mechanism of the droplet material surfaces was studied by establishing the heat transfer model.The superhydrophobic roughness structure could capture a large amount of air pockets to form a thermal-insulation layer.At the same time,the actual solid-liquid contact area f between the droplet and the superhydrophobic sample surface was small,which effectively reduced the ice nucleation rate and delayed the growth velocity.