Charge regulation of colloidal particles in aqueous solutions

TL;DR

This paper develops a quantitative theory for charge regulation of colloidal particles in aqueous solutions, predicting their effective charge based on surface chemistry and chemical equilibrium, validated by simulations.

Contribution

It introduces a model that accurately predicts colloidal surface charge considering acidic and basic groups, extending to mixed surface chemistries.

Findings

The theory matches Monte Carlo simulation results with high accuracy.

It effectively predicts charge regulation for particles with mixed surface groups.

The model provides insights into colloidal stability mechanisms.

Abstract

We study charge regulation of colloidal particles inside aqueous electrolyte solutions. To stabilize colloidal suspension against precipitation, colloidal particles are synthesized with either acidic or basic groups on their surface. In contact with water these surface groups undergo proton transfer reaction, resulting in colloidal surface charge. The charge is determined by the condition of local chemical equilibrium between hydronium ions inside the solution and at the colloidal surface. We use a model of Baxter sticky spheres to explicitly calculate the equilibrium dissociation constants and to construct a theory which is able to quantitatively predict the effective charge of colloidal particles with either acidic or basic surface groups. The predictions of the theory for the model are found to be in excellent agreement with the results of Monte Carlo simulations. The theory is further extended to treat colloidal particles with a mixture of both acidic and basic surface groups.