Molecular Dynamic Simulations Of Wetting Behaviors Of Nanodroplet Impacting On Solid Surface

Droplet impingement is the focu of basic research and engineering applications across nanoscopic,mesoscopic and continuum scales.At the macro-and mesoscopic scale,the researchers have summed up the criterion of droplet topology evolution through CFD simulations and experiments,which is attributed to the relationship between the dimensionless numbers of We,Re and Oh.However,when the interest is the nano/micro scale behavior of ensemble,inter-molecular interaction will play an important role in presenting flow performances and properties instead of constitutive relations.With the development of nanotechnology,physical mechanics of surfaces and interfaces on the deformation modes and flow features of nanodroplets has become increasingly prominent.In this thesis,the molecular dynamics simulation method is used to investigate the trajectory of atoms and the behavior evolution the molecular cluster during the nanodroplets impact process.The wetting dynamics of a single nanodroplet impact flat and curved surfaces as well as double nanodroplets impingement on flat wall was analyzed by molecular dynamics simulation software LAMMPS.The results indicated that:1)By specifying initial parameters of a single nanodroplet impingement on the flat surface,the influences of the initial droplet velocity,the L-J potential depth of the solid-liquid interaction and the initial droplet diameter are discussed.We summarized the evolution law of drop impact dynamics: splashing,spreading,receding and bouncing.The larger initial kinetic energy of the droplet is beneficial to the greater the deformation of the droplets.The depth of the solid-liquid can realize the transition of spreading,receding and bouncing.When the droplet diameter is less than 120?,the net suction of the droplet decreases and the surface energy is smaller.Therefore,it is necessary to consider the effect of the size factors on the spreading characteristics.2)The wall is not only the boundary of the movement of water molecules,but also relates to the total adhesion work of the wall when a single nanodroplet impact on the curved wall.With the increase of curvature,the droplet tends to completely wet the whole wall,and then dripped.3)The coupling property between the nanodroplets affects the behavioral evolution and spreading performance during nanodroplets impact.Observing the morphologicalevolution and configuration of the nanodroplets impingement,the influence of the relevant parameters on the spreading characteristics was quantitatively analyzed.In the case of large velocity or small central distance of droplets,the axial spreading factor is obviously increased because of jet flow produced by radial interference.For the vertical cascade impact of double nanodroplets,the former will form a transient adhesion film,and the later will be embedded into the former due to the impingement.The deeper the potential well between the solid and liquid is,the more favorable the rebound will be.