Detachment of particles from surfaces by thermocapillary flows induced by a moving laser beam

The thermocapillary flows produced by heating with the moving laser beam in a thin liquid layer on a light-absorbing solid surface have recently been recognized to be effective for the removal of particulate impurities from the surface. We performed the comparative analysis of adhesion and thermocapillary removal forces acting on particles attached to the solid surface. A simplified hydrodynamic model was used to evaluate the velocity field of the thermocapillary flow in the liquid layer covering particles. Hydrodynamic forces such as the drag force, the lifting force induced by the shear flow far away from the receding contact line and the maximal lifting force caused by the transversal velocity in the layer near the receding contact line were identified as the cleaning forces, which are determined by the temperature gradient along the surface. It was found out that the lifting force is not enough to overcome the adhesion force and detach particles from the solid surface. The drag and the maximal lifting forces were shown to be responsible for removal of particles by using the proposed method. A reasonable qualitative agreement between experimental results and the quantitative force analysis was observed.