  The Marangoni contraction of sessile droplets occurs when a binary mixture of
volatile liquids is placed on a high-energy surface. Although the surface is
wetted completely by the mixture and its components, a quasi-stationary
non-vanishing contact angle is observed. This seeming contradiction is caused
by Marangoni flows that are driven by evaporative depletion of the volatile
component near the edge of the droplet. Here we show that the composition of
such droplets is governed by Taylor dispersion, a consequence of diffusion and
strong internal shear flow. We demonstrate that Taylor dispersion naturally
arises in a self-consistent long wave expansion for volatile liquid mixtures.
Coupled to diffusion limited evaporation, this model quantitatively reproduces
not only the apparent shape of Marangoni-contracted droplets, but also their
internal flows.
