Interactions between colloidal particles in NaCl aqueous solutions: molecular dynamics simulations with an implicit solvent model

An implicit solvent model based on the potentials of mean force (PMFs) has been applied to the molecular dynamics simulations of charged macroparticle(s) immersed in NaCl aqueous solutions, where the ion concentration profiles around the macroparticle(s) and the interaction forces between two macroparticles and among three macroparticles are investigated. As a consequence, it is found that (i) the ion concentration profiles of the smaller Na+ ions near the macroparticle are in good agreement with the theoretical predictions base on the Poisson-Boltzmann equation, whereas those of the larger Cl- ions slightly deviate from the theoretical profiles, (ii) the interaction force between the unlike-charged macroparticles is more attractive than expected from the theory at a lower NaCl concentration of 0.001 M, although the force at a higher NaCl concentration of 0.1 M or the forces between the like-charged macroparticles agree with the theoretical force curves, and (iii) the threebody force among the like-charged macroparticles is less repulsive than the pairwise approximation using the two-body force at a lower NaCl concentration of 0.001 M. The present simulations demonstrate that the interactions between colloidal particles in aqueous electrolyte solutions can be computed by the implicit solvent model based on the PMFs.