# Colloid-oil-water-interface interactions in the presence of multiple salts: charge regulation and dynamics

## TL;DR

This study combines theoretical modeling and experiments to understand how multiple salts influence charge regulation and interaction dynamics of colloidal particles at oil-water interfaces, revealing tunable colloid-interface interactions.

## Contribution

It introduces a combined theoretical and experimental approach to analyze salt-dependent charge regulation and dynamics at colloid-oil-water interfaces.

## Key findings

- Salt concentrations significantly affect the sign and magnitude of the Donnan potential.
- The effective colloid-interface interactions can be highly tuned by salt partitioning.
- Theoretical predictions align well with experimental observations.

## Abstract

We theoretically and experimentally investigate colloid-oil-water-interface interactions of charged, sterically stabilized, poly(methyl-methacrylate) colloidal particles dispersed in a low-polar oil (dielectric constant $\epsilon=5-10$) that is in contact with an adjacent water phase. In this model system, the colloidal particles cannot penetrate the oil-water interface due to repulsive van der Waals forces with the interface whereas the multiple salts that are dissolved in the oil are free to partition into the water phase. The sign and magnitude of the Donnan potential and/or the particle charge is affected by these salt concentrations such that the effective interaction potential can be highly tuned. Both the equilibrium effective colloid-interface interactions and the ion dynamics are explored within a Poisson-Nernst-Planck theory, and compared to experimental observations.