# Geometry and kinetics determine the microstructure in arrested coalescence of Pickering emulsion droplets

## TL;DR

This study investigates how the shape and rate of particle coverage influence the final microstructure of arrested coalescence in Pickering emulsions, revealing the importance of extrinsic geometry and kinetics.

## Contribution

It demonstrates that the microstructure depends on the ratio of area change rate to diffusion constant, highlighting the role of extrinsic geometry and arrest kinetics.

## Key findings

- Microstructure depends on the ratio of area change rate to diffusion constant.
- Extrinsic geometry influences the arrest process more than static packings.
- Negative Gaussian curvature regions can form around the neck during coalescence.

## Abstract

An important strategy to stabilize emulsions is to arrest coalescence of the constituent droplets with an opposing rheological force. Colloidal particles adsorbed on the surface of emulsion droplets in a Pickering emulsion become increasingly crowded during successive coalescence events because the combined surface area of coalescing droplets is less than that of the constituent droplets. Beyond a critical density, the particles form a rigid shell around the droplet and inhibit both relaxation of the droplet shape and further coalescence. The resulting droplets have a nonuniform distribution of curvature and, depending on the initial coverage, may incorporate a region with negative Gaussian curvature around the neck that bridges the two droplets. Here, we resolve the relative influence of the curvature and the kinetic process of arrest on the microstructure of the final state. Identifying the dimensionless ratio of the rate of area change \dot{A} to the diffusion constant D as a measure of the importance of kinetics in this system, we show that this depends on the extrinsic geometry of the surface as opposed to the static packings that depend solely on intrinsic geometry.