The Influence of Concentration and Ionic Strength
on the Cluster Structure of Highly Charged Electrolyte Solutions
J.L.F. Abascal and F. Bresme
ABSTRACT
The structure of 2:2 electrolyte solutions at several concentrations
-obtained through stochastic dynamics simulations- is investigated by
means of a cluster analysis. It is shown that most of the ions in the
systems at the higher concentrations studied (up to 2 M) are linked at
short distances forming large clusters even though the mean number of
neighbours is only about 2. As the concentration decreases there is a
distinct short and long range behaviour. The clustering observed at
short distances is similar to that obtained in the more concentrated
solutions. This means that within this region the charges of the nearby
ions are individually perceived. Conversely, at long distances the
effect of the surrounding charges becomes more diffuse; the properties
seem to be rather dependent on the mean field and are similar to those
of a 1:1 electrolyte at the same ionic strength. Although no neutral
pairs seem to be actually present in the more dilute solution
investigated in this paper (0.25 M), the concentration dependence of
our results suggests that the Bjerrum picture (and recent theories of
the ionic association) should accurately describe the clustering at
lower concentrations.
