Stefan Karpitschka

Max Planck Institute for Dynamics and Self-Organization, Interfaces of Complex Fluids Group

” Taylor Dispersion Governs the Compositional Evolution of Marangoni-Contracted Droplets “

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.