Taylor Dispersion in Thin Liquid Films of Volatile Mixtures: A Quantitative Model for Marangoni Contraction

TL;DR

This paper develops a quantitative model based on Taylor dispersion to explain Marangoni contraction in volatile liquid droplets, capturing their shape and internal flows through a self-consistent long wave expansion.

Contribution

It introduces a novel application of Taylor dispersion in modeling the composition and flow dynamics of volatile droplet contractions.

Findings

Model accurately predicts droplet shape and flow patterns.

Taylor dispersion explains the internal composition distribution.

Coupled with evaporation, the model matches experimental observations.

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 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.