Kavli Affiliate: Jos W. Zwanikken
| First 5 Authors: Chantal Valeriani, Philip J. Camp, Jos W. Zwanikken, René van Roij, Marjolein Dijkstra
| Summary:
The association of ions in electrolyte solutions at very low concentration
and low temperature is studied using computer simulations and quasi-chemical
ion-pairing theory. The specific case of the restricted primitive model
(charged hard spheres) is considered. Specialised simulation techniques are
employed that lead to efficient sampling of the arrangements and distributions
of clusters and free ions, even at conditions corresponding to nanomolar
solutions of simple salts in solvents with dielectric constants in the range
5-10, as used in recent experimental work on charged-colloid sus- pensions. A
direct comparison is effected between theory and simulation using a variety of
clustering criteria and theoretical approximations. It is shown that
conventional distance-based cluster criteria can give erroneous results. A
reliable set of theoretical and simulation estimators for the degree of
association is proposed. The ion-pairing theory is then compared to
experimental results for salt solutions in low-polarity solvents. The agreement
is excellent, and on this basis some calculations are made for the screening
lengths which will figure in the treatment of colloid-colloid interactions in
such solutions. The accord with available experimental results is complete.
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