Marangoni effects on oil droplets rising in a stratified fluid

There are many environmental examples of droplets and particles getting trapped in regions of high density gradients, including oil plumes in the ocean and smoke stack exhaust in thermal inversions. In the former case, the gradients are due to varying salt and temperature concentrations, and subsurface trapping happens despite the fact that oil is less dense than all salt water layers. Although this trapping is usually attributed to entrained fluid, interfacial tension gradients are also present. The resulting Marangoni force from the interfacial tension gradient generates additional flows that may influence droplet trapping, but this effect has received little experimental attention until recently. When a droplet of lower density rises through a stratified ambient fluid, it often gets trapped in regions with a high density gradient. We present experimental results that quantify the effect of interfacial tension gradients on droplet slowdown in stratified fluids at the intermediate Reynolds regime and low Froude number regime.