Charge Regulation of Colloidal Particles: Theory and Simulations

TL;DR

This paper develops a new theoretical model for charge regulation in colloidal particles, improving upon existing theories by accurately matching simulation results and accounting for surface chemistry effects.

Contribution

The authors introduce a novel charge regulation theory based on the sticky length concept, resolving limitations of the Ninham and Parsegian approach and aligning well with simulations.

Findings

New charge regulation theory matches simulations without adjustable parameters

The model accurately predicts colloidal charge as a function of pH and salt concentration

Deviations of previous theories are explained and corrected

Abstract

To explore charge regulation (CR) in physicochemical and biophysical systems, we present a model of colloidal particles with sticky adsorption sites which account for the formation of covalent bonds between the hydronium ions and the surface functional groups. Using this model and Monte Carlo simulations, we find that the standard Ninham and Parsegian (NP) theory of CR leads to results which deviate significantly from computer simulations. The problem of NP approach is traced back to the use of bulk equilibrium constant to account for surface chemical reactions. To resolve this difficulty we present a new theory of CR. The fundamental ingredient of the new approach is the sticky length, which is non-trivially related with the bulk equilibrium constant. The theory is found to be in excellent agreement with computer simulations, without any adjustable parameters. As an application of the theory we calculate the effective charge of colloidal particles containing carboxyl groups, as a function of pH and salt concentration.