# Charged hydrophobic colloids at an oil/aqueous phase interface

## TL;DR

This study investigates how charged hydrophobic colloids interact at oil/aqueous interfaces, revealing that image charge effects dominate their binding and interactions, which can be modeled simply by particle charge as a key parameter.

## Contribution

The paper demonstrates that charged hydrophobic colloids in oil can be effectively modeled by an image-charge approach, isolating charge effects from wettability influences.

## Key findings

- Particles become highly charged in oil with high dielectric constant.
- Image charge effects cause strong binding to the interface.
- Interactions are well described by a simple image-charge model.

## Abstract

Hydrophobic PMMA colloidal particles, when dispersed in oil with a relatively high dielectric constant, can become highly charged. In the presence of an interface with a conducting aqueous phase, image charge effects lead to strong binding of colloidal particles to the interface, even though the particles are wetted very little by the aqueous phase. In this paper, we study both the behavior of individual colloidal particles as they approach the interface, and the interactions between particles that are already interfacially bound. We demonstrate that using particles which are minimally wetted by the aqueous phase allows us to isolate and study those interactions which are due solely to charging of the particle surface in oil. Finally, we show that these interactions can be understood by a simple image-charge model in which the particle charge $q$ is the sole fitting parameter.