Interface Mechanical Behavior Of Bioinspired Superhydrophobic Surfaces And Properties Control

Organisms in nature have created the unique functional surfaces to better adapt to their surroundings.Inspiration from nature,bio-inspired superhydrophobic surfaces have play an important role in industrial and agricultural production and people’s daily life,and have been a hot research topic at home and abroad.However,the current design and fabrication of bio-inspired superhydrophobic surfaces cannot yet meet the needs of functional surfaces in production and life.The lack of analysis of the interaction mechanism of the mechanical behavior of the solid-liquid interface of the bionic surface,lead to the failure to regulate effectively the surface properties such as interfacial hydrophobicity,physical adhesion,heat and mass transfer.Thus,this paper focuses on the interfacial mechanical behavior of bio-inspired superhydrophobic surfaces,based on the experimental characterization and Computational Fluid Dynamics（CFD）numerical simulation methods,with an emphasis on the analysis of the interfacial behavior of bionic superhydrophobic surfaces and the effective regulation of solid-liquid interface interactions.The dynamic droplet impacting behavior of bio-inspired surfaces have been resolved to reveal the mechanism of interfacial mechanical behavior of superhydrophobic surfaces.This will provide a new ideas for the properties regulation of the low-temperature surface desorption,high-temperature surface evaporation,and directional asymmetric driving of bionic superhydrophobic surfaces.The research results are summarized as follows:（1）The bionic microarray structured surface is designed by multi-coupled bionic theory,and the surfaces with similar structures but different chemical compositions were prepared using different processing.The numerical modeling of the interfacial mechanical behavior has been performed using CFD numerical simulation method,simulating the spreading state and impacting process of dynamic droplets on the bio-inspired surface.Compared with the untreated smooth surface,the stored air in the micro-nano structure of the bionic surface have leaded to a rapid shrinkage of droplets for desorption,which reduces the contact time by 15.6%.A quantitative mathematical model between the maximum spreading diameter(D_max)and the maximum spreading time(t_max)of the droplets on the bionic surface was established,which provides a basis for the mechanical properties regulation of the bio-inspired surface in the low-temperature surface desorption,high-temperature surface evaporation,and asymmetric surface directional driving.（2）Coupled Level Set-Volume of Fluid（CLSVOF）with solidification/melting model,a numerical simulation method applicable to low-temperature phase transition and interfacial heat transfer was established to resolve the interfacial heat transfer and droplet phase transition during low-temperature freezing on the bio-inspired low-adhesion surface.And it revealed the performance regulation mechanism of freezing adhesion on the low-temperature surface.The non-uniform heat transfer was blocked by the thermal barrier formed by the air stored between the convex pack structure and the static droplet,which prolongs the freezing nucleation time.The synergistic effect between the larger contact angle and the cavitation structure directly affected the solid-liquid contact area,and thus determine the adhesion force between the frozen droplets and the surface.The droplet freezing time of the bio-inspired surface was increased by a factor of 3 and the freezing delay rate was increased to 194%,while the adhesion strength of the frozen droplets was reduced by a factor of 4.（3）A 3D CFD numerical simulation method integrating Volume of Fluid（VOF）model,modified evaporation model and dynamic contact angle model has been applied to analyze the vapor dynamics and anisotropic heat and mass transfer on the bio-inspired high-adherent superhydrophobic surface.Combined with high speed thermal imaging experiments,the dynamic vapor generation behavior of droplets and the suppression mechanism of evaporation lift on a high temperature surface was resolved under the Leiden Frost effect.The results showed that the dynamic vapor generation behavior of liquid droplets under the Leydenfrost effect and the suppression mechanism of evaporation lift on the high-temperature surface have been investigated.The results show that the synergistic enhancement of heat transfer by the microcolumn height H and gap L and droplet impacting velocity v of the bio-inspired surface increases the Leydenfrost critical temperature point(T_Lmax)of the surface by 44.2%.A mechanical model of the high-temperature bionic surface was developed to predict the evaporative boiling state of the surface droplets,and can regulate the heat transfer efficiency of the high-temperature surface.（4）Using the CFD numerical computational method mentioned above,the mechanism of asymmetric bouncing behavior on the mixed wettability surface was computationally analyzed,and the asymmetric driving mechanical behavior of the interfacial transport process is investigated.The prepared bionic hybrid wetting surface can achieve the normal horizontal directional transport of vertical droplets.The regime map of the transport pattern is determined by the synergy between the wettability-controlled driving force and transport capability.Of all these effects,the maximum transport distance by up to 6.2D₀ and the initial desorption time of only 7.8 ms.This realized the precise regulation of the performance of the horizontal transport distance and throwing time of the droplets.In a word,the numerical simulation method coupling interface capture model,turbulence model,wall treatment method and gas-liquid-solid phase change model has been applied to investigated the interfacial mechanical behavior of the bio-inspired superhydrophobic surface.The dynamic droplet impacting on the bio-inspired surface under the different application scenarios are analyzed and to conduct the mechanical mechanisms of the microarray structure of the superhydrophobic surface.And this revealed the low-temperature surface phase transition,high-temperature surface evaporation and boiling,and asymmetric bouncing of the mixed wettability surface.Thus,a mapping relationship between surface microarray structure and mechanical properties regulation was established,to guide the typical application scenarios such as low-temperature surface desorption,high-temperature surface evaporation,and mixed wettability surface transport.