PAIR CONNECTEDNESS FUNCTIONS AND PERCOLATION IN HIGHLY-CHARGED ELECTROLYTE-SOLUTIONS

The structure of highly charged electrolyte solutions is investigated through a percolation approach. The systems, simulated by standard Mon te Carlo methods, include several 2:2 aqueous solutions with concentra tions ranging from 0.25 to 2 M and one 1:1 electrolyte at 1 M concentr ation. The ion-ion pair connectedness functions and related quantities have been computed. Two ions are considered connected if they are clo ser than a predefined distance. Besides this-geometric criterion, an e nergetic condition (i.e., only particles with unlike charge signs are allowed to form directly connected links) has also been employed. The clusters obtained via the geometric and the energetic conditions are s ubstantially different for the 1:1 electrolyte while the 2:2 solutions show a cluster structure almost independent on the criterion used. Th e percolation thresholds exhibit a nonmonotonic variation with concent ration. A minimum in the percolation threshold has been observed at th e higher concentrations investigated for the 2:2 systems; the shape of the curve and the limiting values for infinitely dilute solutions sug gest the appearance of a maximum at concentrations lower than those st udied in this paper. In addition, the critical exponents alpha, gamma, and tau have been computed. The result for alpha significantly differ s from the values reported for three dimensional lattices but it agree s with those obtained for the Lennard-Jones fluid. In contrast, the ga mma and tau exponents for 3D lattice systems and for our electrolyte s olutions seem to be coincident.