Thermocapillary migration of a thin droplet on wettability-confined tracks

The thermocapillary migration of droplets on a solid surface is widely used in daily life and industrial fields. Regulating droplet thermocapillary migration by changing surface wettability have received extensive attention. Based on the lubrication theory and slip boundary conditions, we establish a mathematical model of the thermocapillary migration dynamics of a droplet on wettability-confined tracks subject to a uniform temperature gradient. Combined with the contact line dynamics, a method for determining the velocity of the contact line in different directions of the three-dimensional droplet is proposed, FreeFEM++ is employed for simulation coding. The evolution of droplet migration is examined, and the effects of track width and wettability on the droplet migration dynamics are emphatically investigated. The results show that the main part of the droplet moves from the high-temperature region to the low-temperature region, the trailing edge of the droplet forms a small bulge during the movement, and a thin liquid film is formed between the bulge and the main part of the droplet. The droplet spreading perpendicular to the track direction is inhibited and remains pinned after shrinking to the track edge. Negative correlation between the velocity of the advancing contact line and track width is observed. The velocity of the advancing line decreases rapidly at first and then slowly decrease to steady. The squeezing effect caused by the wettability confined in perpendicular to the track direction accelerates the thermocapillary migration of the droplet on the track at the initial short time. The enhanced track wettability increases the initial velocity of the receding contact line but has little effect on its stable value. The velocity of the advancing contact line is positively correlated with track wettability. Changing the track width is possibly easier to regulate the thermocapillary migration of a droplet than varying the track wettability.