# Interactions between Silica Particles in the Presence of Multivalent Coions

## TL;DR

This study measures electrostatic forces between charged silica particles in multivalent coion solutions, finding that DLVO theory accurately describes the interactions and revealing how potential and regulation depend on coion valence and concentration.

## Contribution

It demonstrates that DLVO theory applies to multivalent coion systems and uncovers how electrostatic properties depend on coion valence and concentration.

## Key findings

- DLVO theory accurately describes forces in multivalent coion solutions.
- Diffuse-layer potential shifts to lower concentration with higher coion valence.
- Force profiles collapse onto a master curve when plotted against monovalent counterion concentration.

## Abstract

Forces between charged silica particles in solutions of multivalent coions are measured with colloidal probe technique based on atomic force microscopy. The concentration of 1:z electrolytes is systematically varied to understand the behavior of electrostatic interactions and double-layer properties in these systems. Although the coions are multivalent the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory perfectly describes the measured force profiles. The diffuse-layer potentials and regulation properties are extracted from the forces profiles by using the DLVO theory. The dependencies of the diffuse-layer potential and regulation parameter shift to lower concentration with increasing coion valence when plotted as a function of concentration of 1:z salt. Interestingly, these profiles collapse to a master curve if plotted as a function of monovalent counterion concentration.