Droplet dissolution driven by emerging thermal gradients and Marangoni flow

The lifetime r of an isothermal and purely diffusively dissolving droplet in a host liquid scales as tau similar to R-2(0) with its initial radius R-0 [Langmuir, Phys. Rev. 12, 368 (1918)]. For a droplet dissolving due to natural convection driven by density differences, its lifetime scales as tau similar to R-0(5/4) [Dietrich et al., J. Fluid Mech. 794, 45 (2016)]. In this paper we experimentally find and theoretically derive yet another droplet dissolution behavior, resulting in tau similar to R-0(4). 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) similar to (tau - t)(1-4) of the droplet radius and thus in tau similar to R-2(0).

Automated summary

The paper presents a new droplet dissolution behavior, where the dissolution dynamics is controlled by local heating of the liquid, resulting in a thermal Marangoni flow around the droplet. By experimentally and theoretically studying the process, it is found that there is a relationship between the dissolution rate and the initial radius of the droplet.