Research On Mechanism Of Interfacial Effect On Nucleation And Droplet Dynamics Behaviors

As a typical phase change process,vapor condensation is of great significance to the heat management of high-power systems and the improvement of water collection and desalination technology.As the beginning of the entire condensation process,the nucleation process determines the initial state of vapor condensation.In-depth understanding of the micro-mechanism of nucleation and revealing the effect of surface energy and surface microstructure on the nucleation process have become a research topic worthy of attention.For the nucleation process,the spatial scale of clusters and droplets is usually in the order of nanometers,and the time scale is usually in the order of femtoseconds,which brings great difficulties to the experimental observation and research of nucleation phenomena.Therefore,numerical simulation becomes an effective tool in this field.In this paper,molecular dynamics(MD)simulations are used to reveal the effects of surface energy and surface microstructure on cluster growth,nucleation site distribution,and initial droplet wetting status,as well as the resting mode and dynamics behavior of droplets controlled by the morphology and parameters of surfaces.First,the MD simulations are performed to investigate the effects of solid-liquid interfacial energies and anisotropic microstructures on the formation and growth of clusters,as well as wetting behaviors of droplets.The results show that surface energy plays a crucial role in the anisotropic wetting behavior of water droplets on all surfaces.The anisotropic wetting behavior of the droplet depends on the atomic potential barrier and the top area of the solid substrate.Due to the presence of a clear atomic potential energy barrier and a larger top area to support the water droplets,the droplets on the square surface have the most obvious anisotropic wetting behavior.The distribution of atomic potential energy determines the location where water molecules tend to nucleate,and water molecules tend to nucleate in the region with lower atomic potential energy.Furthermore,by reasonably designing the micro-nano structure or surface chemistry,and using the spontaneous condensation and agglomeration of the droplets to drive the transformation,the spontaneous dewetting of the droplets without external force is achieved.The influence of the volume ratio and height of the cylindrical array on the droplet dynamics behaviors was studied,and the results were compared with the square cylindrical array.The formation,growth and coalescence of nanodroplets were simulated and quantitatively recorded,and the wetting and dewetting transitions of the droplets were observed.The research results show that larger fraction volume and lower height are conducive to the emergence of dewetting.Finally,the simulation analysis reveals the internal physical mechanism of the effects of surface energy gradient and Laplace force on the dynamic migration of droplets.First,the Laplace pressure gradient is introduced to enhance the dewetting performance of the structure.The effect of the inclination angle of the conical structure on the vapor condensation and droplet dynamics is studied.The results show that the conical structure with a 100 inclination angle has the best dewetting performance.Based on the above,the surface energy gradient is introduced,and the influence of the proportion of the hydrophilic and hydrophobic regions on the tapered structure is studied.The structure shows that the proportion of 1/3 of the hydrophilic and hydrophobic regions is most conducive to the formation of the Cassie state of the droplet.