Taylor Dispersion Governs the Compositional Evolution of Marangoni-Contracted Droplets
Fluids and Materials Seminar
18th February 2021, 2:00 pm – 3:00 pm
Online seminar, Zoom link is sent to the fluids and materials seminar mailing list on Mondays.
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. The phenomenon is widely used for drying and cleaning in
technological applications, for instance in semiconductor or printing
industries, but its physical explanation remains debated in literature.
Here we show that the compositional evolution of such droplets is
governed by Taylor dispersion. Breaking with precedent, we demonstrate
that Taylor dispersion can consistently be included in a long wave
expansion for the evolution of thin films. Coupled to a non-local
description of diffusion limited evaporation, this model quantitatively
reproduces not only the apparent shape of Marangoni contracted droplets,
but also their internal flows.