By using the dimension-analysis method, the thermal diffusion time scale has been determined as the controlling one of the thermocapillary droplet migration system. During this time, the whole thermocapillary migration process is fully developed.

Steady and unsteady states as the terminal ones of thermocapillary migration of a planar droplet at moderate and large Marangoni numbers are captured in a longer time scale than the thermal diffusion one.

The physical mechanism of thermocapillary droplet migration can be described as the significance of the thermal convection around the droplet is higher than/just as the thermal conduction across the droplet at large/moderate Marangoni numbers.