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A droplet that moves on a solid substrate with a velocity higher than a certain critical velocity disintegrates, i.e., leaves behind residual droplets. Infrared laser illumination can be used to increase the droplet mobility and suppress the shedding of droplets. By means of two-dimensional numerical simulations, we studied the effect of a non-uniform temperature distribution on the dynamics of straight receding contact lines. A streamfunction-vorticity model is used to describe the liquid flow in the vicinity of the receding contact line. The model takes into account the thermocapillary shear stress and the temperature-dependent liquid viscosity and density. A second, coupled model describes the laser-induced displacement of the contact line. Our results show that the reduction of the liquid viscosity with increasing temperature is the dominant mechanism for the increase of the critical velocity. Thermocapillary shear stresses are important primarily for low substrate speeds. [ABSTRACT FROM AUTHOR]

The shape of a droplet moving on a solid substrate is largely determined by the mobility of its contact line. Above a certain critical velocity, the droplet typically disintegrates and leaves residual liquid behind. We studied experimentally how localized infrared laser illumination can stabilize it against the progressive loss of liquid. We systematically varied the substrate velocity, the laser power, and the laser spot position and found that the critical velocity of the droplet can be substantially increased. These results are potentially important for increasing throughput in immersion lithography systems. [ABSTRACT FROM AUTHOR]