Formation of ion clusters in aqueous NaCl solutions at $25°\mathrm{C}$ is investigated with dynamics simulations in the $0.1–3\mathrm{M}$ concentration range. The medium is found to be highly structured even at moderate concentrations, and clusters of over 20 ions are observed above $\sim 2\mathrm{M}$. The medium can be viewed as a multicomponent fluid, composed of reacting particles with well-defined average populations, shapes, sizes, and charge distributions. Clusters show substantial morphological variations that are here characterized by their hydrodynamic radii and internal charge distributions. Clusters can be described as prolate spheroids in the subnanometer length scale. The hydrodynamic radius and the radius of gyration follow simple power laws with the number of ions in the cluster. Dipole moment distributions show characteristic peaks in the $\sim 10–60\text{debye}$ range that reflect conformational preferences modulated by electrostatic and liquid-structure forces.

• Received 6 December 2007

DOI:https://doi.org/10.1103/PhysRevE.77.031501