Figure : Schematics of the coarse grained approach used to determine the interaction energy in aqueous electrolyte solutions: The solution is separated into a central "observation volume" with radius, R d (black line) and its environment. All distances R = n R R h are measured in units of the hydrated electrolyte radius, R h (dashed circle at the center) so that n d = R d /R h identifies the droplet radius in this coordinate system. If we neglect ion-ion interactions, the charge distribution inside and outside the droplet is uniform. Upon ion-ion interaction, the charge distribution inside the central droplet produces an electrostatic potential outside the droplet which attracts charges of the opposite sign. At high concentration R d decreases and the interaction energy increases.