Influence of solvation on the structure of highly charged nanoparticles in salt-free solutions

Abstract

We investigate the influence of ion and nanoparticle solvation on the structure of an aqueous salt-free solution of highly charged nanoparticles. In particular, we perform molecular dynamics simulations of a minimal model of highly charged nanoparticles with an explicit solvent and counter-ions, where the relative affinity of the counter-ions and the nanoparticle for the solvent is tunable through the variation of the relative strength of the dispersion interactions of both the nanoparticle and counter-ions. We show that the competitive solvation of the counter-ions and nanoparticles leads to significant changes in the structure of the nanoparticle solution, which ranges from relatively uncorrelated conformations to self-assembled string- and sheet-like structures. Based on our coarse-grained model, we construct a morphology diagram identifying the different structures that emerge in our model with the variation of the solvent affinity for the charged species. The emergence of these different heterogeneous structures arising from the differential solvation of the charged species demonstrates the essential role of the solvent in the description of charged nanoparticle solutions, and provides guidance for the development of a more predictive theory of the thermodynamic and transport properties of these complex fluids.