Arrest of Fluid Demixing by Nanoparticles: A Computer Simulation Study

TL;DR

This study uses lattice Boltzmann simulations to explore how nanoparticles arrest fluid demixing, revealing a transition from bijel to droplet structures with increasing asymmetry and analyzing particle ejection dynamics at colloidal time scales.

Contribution

It provides new simulation insights into asymmetric quenches, crossover behavior, and detailed post-arrest dynamics of nanoparticle-stabilized fluid structures.

Findings

Crossover from bijel to droplet phase with increasing asymmetry.

Effective activation barrier for particle ejection is significantly reduced at fluid interfaces.

Post-arrest dynamics occur on colloidal time scales with lower energy barriers.

Abstract

We use lattice Boltzmann simulations to investigate the formation of arrested structures upon demixing of a binary solvent containing neutrally wetting colloidal particles. Previous simulations for symmetric fluid quenches pointed to the formation of `bijels': bicontinuous interfacially jammed emulsion gels. These should be created when a glassy monolayer of particles forms at the fluid-fluid interface, arresting further demixing, and rigidifying the structure. Experimental work has broadly confirmed this scenario, but shows that bijels can also be formed in volumetrically asymmetric quenches. Here we present new simulation results for such quenches, compare these to the symmetric case, and find a crossover to an arrested droplet phase at strong asymmetry. We then make extensive new analyses of the post-arrest dynamics in our simulated bijel and droplet structures, on time scales comparable to the Brownian time for colloid motion. Our results suggest that, on these intermediate time scales, the effective activation barrier to ejection of particles from the fluid-fluid interface is smaller by at least two orders of magnitude than the corresponding barrier for an isolated particle on a flat interface.