Research On Dynamic Wetting Of Mesoscopic Droplets Based On SDPD

In the dynamic wetting process of droplets,the contact angle quantifies the interaction between solids and liquids,which plays a key role in understanding chemical and physical processes in many industries.In recent years,there have been many research results on wetting at the micro-scale based on molecular dynamics and the macro-scale based on continuum mechanics.At the mesoscopic scale,due to the difference of experimental methods and the difference of the surface microstructure at the mesoscopic scale,There have been many controversies about the quantitative characterization of contact angles,and this mesoscopic mechanism of action has also become one of the main problems in the development and manufacture of bionic surfaces.Dynamic wetting at the mesoscopic scale involves problems such as free surface and large deformation of fluid structure,which coincides with the mesoscopic computing power of the smooth dissipative particle dynamics(SDPD)method and the advantages of the method itself.Therefore,the SDPD method is selected in this paper.According to the influence of boundary conditions on wetting,numerical simulation of the flow characteristics of droplet dynamic wetting behavior at the mesoscopic scale is carried out,the calculation results of droplet contact angle,particle density and pressure changes,and internal flow field under two boundary conditions are carried out.Based on the comparative analysis,the main important conclusions are as follows:The particles near the three-phase contact point under the mirror particle boundary will have a continuous acceleration state,and the particles near the three-phase contact point under the pressure boundary will not continue to accelerate,while the particle motion in the entire flow field reaches a dynamic equilibrium.Under the boundary of mirrored particles,due to the algorithm itself,in the superhydrophilic simulation,fluid particles and boundary particles become the same kind of particles in the vicinity of the three-phase contact point,which leads to the phenomenon of emptying of particles in local areas,and in the hydrophobicity simulation of more than 135°,gas phase particles will be adaptively involved in fluid phase particles,as the hydrophobicity increases,the higher the degree of involvement,the more turbulent the internal particle movement.The fluid particles are tightly distributed in the superhydrophilic and superhydrophobic simulations under the pressure boundary,and there is no emptying or entrapment phenomenon,while the pressure distribution in the calculation area is uniform.The contact angle between 30° and 135° under the boundary of mirrored particles can meet the calculation accuracy requirements,and the pressure boundary can accurately simulate the contact angle in a larger range from 30° to 150°.Under the two boundary conditions,the simulated superhydrophilic or superhydrophobic droplets cannot reach the theoretical angle.The superhydrophilic simulation under the pressure boundary cannot reach the simulation angle under the mirror particle boundary.