Numerical Study On Evaporative Sedimentation Characteristics Of Drops Containing Nanoparticles

The regulatory inhibition technologies for the deposition pattern during the evaporation of the droplets containing nanoparticles have been widely used in ink jet printing,coating technology and other fields.At present,a large amount of researches mainly focus on the experimental investigation to investigate the influence of surfactant,temperature field,electrowetting and the shape of solute particle on the sedimentary structure.However,the theoretical basis of its intrinsic evolution mechanism is still relatively deficient.In view of the challenge of complexity and observability in the microscale flow,the numerical simulation method plays a crucial role in the research progress.The research results can provide a theoretical direction for exploring the inherent evolution mechanism of particle deposition in the droplet evaporation process and proposing the advanced controlling measures.In this paper,the evolution characteristics of the droplets near the three-phase contact area are obtained by numerical simulation.And we discuss the influence of shape anisotropy of nanoparticles and the slipping scale on the deposition pattern and the evolutionary characteristics.The main contents are as follows:(1)Based on the lubrication theory,the mathematical model for the evaporation process of the droplets containing nanoparticles is established,in which the influence of particle shape on the viscosity of the liquid is considered.And the comprehensive relationship between the particle shape and solution viscosity is established.The evolution of the droplets in the late evaporation stage is numerically simulated by the numerical simulation software-FREEFEM.We explore the influence of shape anisotropy on the height of the deposition ring,the evolution of evaporation term,convection term and diffusion term and the receding speed of the three-phase contact line.(2)The Navier slipping boundary condition is adopted to establish the evolution model for the droplet evaporation under the weak slip scales.The evolution characteristics near the three-phase contact area are investigated by numerical simulation.We compare the droplet evaporation evolution and the state of the three-phase contact line at different slipping scales.Through analyzing the disjoining pressure and the pressure difference between the gas-liquid interface pressure and the vapor pressure in the evolutionary process,the mechanism of the effect of the slipping scale on the deposition pattern is examined,which contributes to put forward the method to control the deposition structure with more practical guide.