Marangoni Convection in Droplets on Ultrahydrophobic Surfaces
by Tam, D., von Arnim, V., McKinley, G.H. and Hosoi, A.E.

We consider a small droplet of water sitting on top of a heated superhydrophobic sur-
face. A toroidal convection pattern develops in which fluid is observed to rise along the
surface of the spherical droplet and to accelerate downwards in the interior towards the
liquid/solid contact point. The internal dynamics arise due to the presence of a vertical
temperature gradient; this leads to a gradient in surface tension which in turn drives
fluid away from the contact point along the interface. We develop a solution to this
thermocapillary-driven Marangoni flow analytically in terms of streamfunctions. Quan-
titative comparisons between analytical and experimental results are presented as well
as effective heat transfer coefficients.