Evaporation-driven ring and film deposition from colloidal droplets

TL;DR

This paper models the evaporation-driven pattern formation in drying colloidal droplets, linking evaporation dynamics, internal flow, and particle deposition to predict various deposit patterns.

Contribution

It introduces a multiphase model that couples evaporation, flow, and deposition dynamics to explain pattern transitions in drying colloidal droplets.

Findings

A dimensionless parameter predicts pattern types.

The model explains transition from rings to uniform deposits.

Insights into controlling deposit patterns in applications.

Abstract

Evaporating suspensions of colloidal particles lead to the formation of a variety of patterns, ranging from a left-over ring of a dried coffee drop to uniformly distributed solid pigments left behind wet paint. To characterize the transition between single rings, multiple concentric rings, broad bands, and uniform deposits, we investigate the dynamics of a drying droplet via a multiphase model of colloidal particles in a solvent. Our theory couples the inhomogeneous evaporation at the evolving droplet interface to the dynamics inside the drop, i.e. the liquid flow, local variations of the particle concentration, and the propagation of the deposition front where the solute forms an incompressible porous medium at high concentrations. A dimensionless parameter combining the capillary number and the droplet aspect ratio captures the formation conditions of different pattern types.