Effective interactions from ion-ion correlations: the case of Calcium-Silicate-Hydrates

The spatial organization of multivalent ions in solution can strongly affect the potential of mean force (PMF) between charged surfaces, which in turn affects the self-assembly of charged aggregates or particles. We combine Grand Canonical Monte Carlo and molecular dynamics simulations with a primitive model for a complex ionic solution between charged surfaces. By implementing an explicit dipolar model for the solvent, we investigate its effect on the electrostatic interactions in these systems and obtain the PMF in the case of divalent ions in water and a high surface charge. Depending on the ion concentration and spatial organization, the PMF can feature attractive wells, pure repulsion, or even competing attractive and repulsive parts. We apply this approach to compute the effective interactions that, due to the evolving ion concentration in the solvent, drive Calcium Silicate Hydrate (C-S-H) self-assembly into cement gels during cement hydration.