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Abstract

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 quasistationary nonvanishing 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 diffusionlimited evaporation, this model quantitatively reproduces not only the apparent shape of
Marangoni-contracted droplets, but also their internal flows.