CLUSTER STRUCTURE IN MODEL ELECTROLYTE-SOLUTIONS

Brownian dynamics are used to simulate the behaviour of two model electrolyte solutions - 1:1 and 2:2 - at a 1 M concentration. The results for the ion-ion distribution functions are discussed in some detail in connection with the coordination numbers and the excess charge. Then, the computed configurations are analyzed within a cluster approach. Distances ranging from 4.5-8 angstrom are used a linking criterion. The overall study reveals completely different ordering in both models. In the 2:2 electrolyte there is a relatively "short-range" region containing very few ions: the mean number of unlike neighbours in a first coordination shell is about two. At the same time, the cluster analysis reveals chain-like (topological) structures involving a relevant proportion of the total number of ions. On the contrary, a classical "charge cloud" picture would adequately describe the structural features of the 1:1 model solution.