Numerical study of thermocapillary migration behaviors of droplets on a grooved surface with a three-dimensional color-gradient lattice Boltzmann model

Abstract

Thermocapillary actuation is used extensively in droplet-based microfluidic devices to manipulate the dynamic behaviors of droplets. In this study, a three-dimensional color-gradient lattice Boltzmann model is used to investigate the migration behaviors of droplets in the Wenzel state on a grooved surface that is subject to a uniform temperature gradient. On the solid surface, the wetting boundary condition is used to improve the accuracy of the simulations and to suppress spurious velocities at the contact line. The model is used to simulate the thermocapillary migration of a three-dimensional deformable droplet and the thermocapillary migration of a two-dimensional droplet on a solid substrate, and its accuracy is verified against theoretical predictions. The migration behavior of droplets on a smooth surface is investigated, and the flow field and corresponding temperature field around the droplets are analyzed. The experimental findings numerically confirm that a surface with micro-grooves parallel to the temperature gradient can accelerate thermocapillary migration to a greater extent than a smooth surface, indicating the influence of the grooves. The influence of the viscosity ratio is investigated, and it is found that the use of high-viscosity fluids is an effective means of obstructing migration. To determine the influence of surface roughness, a systematic and parametric study of groove depth and width is conducted. Finally, the influence of the orientation of the surface topography is investigated, and it is demonstrated that a surface with micro-grooves perpendicular to the temperature gradient can obstruct migration.