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Photo Jan Forsman

Jan Forsman

Professor

Photo Jan Forsman

Cluster Formation Induced by Local Dielectric Saturation in Restricted Primitive Model Electrolytes

Author

  • David Ribar
  • Clifford E. Woodward
  • Sture Nordholm
  • Jan Forsman

Summary, in English

Experiments using the Surface Force Apparatus (SFA) have found anomalously long-ranged charge–charge underscreening in concentrated salt solutions. Meanwhile, theory and simulations have suggested ion clustering to be a possible origin of this behavior. The popular Restricted Primitive Model of electrolyte solutions, in which the solvent is represented by a uniform relative dielectric constant, εr, is unable to resolve the anomalous underscreening seen in experiments. In this work, we modify the Restricted Primitive Model to account for local dielectric saturation within the ion hydration shell. The dielectric “constant” in our model locally decreases from the bulk value to a lower saturated value at the ionic surface. The parameters for the model are deduced so that typical salt solubilities are obtained. Our simulations for both bulk and slit geometries show that our model displays strong cluster formation and these give rise to long-ranged density correlations between charged surfaces, at distances similar to what has been observed in SFA measurements. An electrolyte model wherein the dielectric constant remains uniform does not display similar clusters, even with εr equal to the low saturated value at ion contact. Hence, the observed behaviors are not simply due to an enhanced Coulomb interaction. In the latter case, cluster growth is counteracted by long-ranged repulsions between like-charged ions within clusters; this is an effect that is considerably reduced when the dielectric response drop is local. Our results imply that long-ranged interactions in these systems are mainly due to cluster–cluster correlations, rather than large electrostatic screening lengths.

Department/s

  • Computational Chemistry

Publishing year

2024-08-15

Language

English

Pages

8326-8333

Publication/Series

The Journal of Physical Chemistry Letters

Volume

15

Issue

32

Document type

Journal article

Publisher

The American Chemical Society (ACS)

Topic

  • Physical Chemistry (including Surface- and Colloid Chemistry)
  • Theoretical Chemistry (including Computational Chemistry)

Status

Published

ISBN/ISSN/Other

  • ISSN: 1948-7185