Dynamics of evaporative colloidal patterning

TL;DR

This study investigates the formation of periodic bands and uniform films during the drying of colloidal suspensions on a vertical plate, combining experiments, minimal theory, and multiphase modeling to understand pattern dynamics.

Contribution

It introduces a coupled multiphase model and minimal theory to explain the transition from banding to filming based on evaporation and deposition rates.

Findings

Pattern formation depends on colloidal concentration and evaporation rate.

The model predicts bandwidth and deposition rate as functions of concentration.

Experimental observations confirm the transition dynamics between bands and films.

Abstract

Drying suspensions often leave behind complex patterns of particulates, as might be seen in the coffee stains on a table. Here we consider the dynamics of periodic band or uniform solid film formation on a vertical plate suspended partially in a drying colloidal solution. Direct observations allow us to visualize the dynamics of the band and film deposition, and the transition in between when the colloidal concentration is varied. A minimal theory of the liquid meniscus motion along the plate reveals the dynamics of the banding and its transition to the filming as a function of the ratio of deposition and evaporation rates. We also provide a complementary multiphase model of colloids dissolved in the liquid, which couples the inhomogeneous evaporation at the evolving meniscus to the fluid and particulate flows and the transition from a dilute suspension to a porous plug. This allows us to determine the concentration dependence of the bandwidth and the deposition rate. Together, our findings allow for the control of drying-induced patterning as a function of the colloidal concentration and evaporation rate.