Droplet dissolution driven by emerging thermal gradients and Marangoni flow

The lifetime τ of an isothermal and purely diffusively dissolving droplet in a host liquid scales as τ∼R02 with its initial radius R0 [Langmuir, Phys. Rev. 12, 368 (1918)0031-899X10.1103/PhysRev.12.368]. For a droplet dissolving due to natural convection driven by density differences, its lifetime scales as τ∼R05/4 [Dietrich, J. Fluid Mech. 794, 45 (2016)0022-112010.1017/jfm.2016.158]. In this paper we experimentally find and theoretically derive yet another droplet dissolution behavior, resulting in τ∼R04. It occurs when the dissolution dynamics is controlled by local heating of the liquid, leading to a modified solubility and a thermal Marangoni flow around the droplet. The thermal gradient is achieved by plasmonic heating of a gold nanoparticle decorated sample surface, on which a sessile water droplet immersed in water-saturated 1-butanol solution is sitting. The resulting off-wall thermal Marangoni flow and the temperature dependence of the solubility determine the droplet dissolution rate, resulting in a shrinkage R(t)∼(τ-t)1/4 of the droplet radius and thus in τ∼R04.