Numerical study of thermocapillary migration of a droplet on an oleophilic track

The thermocapillary migration dynamics of a droplet with a non-circular footprint on an oleophilic track is studied numerically. Three-dimensional simulations showed that reducing the width of the oleophilic track improves the droplet migration velocity only upto a specific track width when compared to the change in velocity of a droplet with circular footprint. Further decrease in track width is seen to depreciate the enhancement in migration velocity. The spread length of the droplet on the oleophilic track is also observed to have a similar variation with track width. The two trends are related because the temperature difference in the droplet, which scales with spread length, determines the driving force governing the migration velocity characteristics. Further, a parametric study is performed to assess the migration behaviour on oleophilic tracks with change in substrate temperature gradient, droplet volume and contact angles within and outside the track. The influence of change in these parameters on the variation in enhancement in spread length and corresponding track width is also investigated. The study identified trends in the minimum track width that may be used to improve migration characteristics, as well as the order of enhancement that can be noticed with changes in each parameter.