Drying of complex suspensions

TL;DR

This study explores how complex suspensions of emulsion droplets and colloidal particles dry and collapse, revealing size-dependent behaviors and modeling the dynamics with a simple pressure-flow relationship, enabling the creation of hierarchical structures.

Contribution

It provides a detailed analysis of drying dynamics in complex suspensions and introduces a model predicting droplet collapse thresholds based on size and pressure.

Findings

Large droplets collapse rapidly, forcing contents into the surrounding pack.

Small droplets remain intact and only deform during drying.

A model accurately predicts the threshold size for droplet collapse.

Abstract

We investigate the 3D structure and drying dynamics of complex mixtures of emulsion droplets and colloidal particles, using confocal microscopy. Air invades and rapidly collapses large emulsion droplets, forcing their contents into the surrounding porous particle pack at a rate proportional to the square of the droplet radius. By contrast, small droplets do not collapse, but remain intact and are merely deformed. A simple model coupling the Laplace pressure to Darcy's law correctly estimates both the threshold radius separating these two behaviors, and the rate of large-droplet evacuation. Finally, we use these systems to make novel hierarchical structures.