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

Ribar, David LU orcid ; Woodward, Clifford E. ; Nordholm, Sture and Forsman, Jan LU (2024) In The Journal of Physical Chemistry Letters 15(32). p.8326-8333
Abstract
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... (More)
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. (Less)
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author
; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
The Journal of Physical Chemistry Letters
volume
15
issue
32
pages
8 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • pmid:39109581
  • scopus:85200809754
ISSN
1948-7185
DOI
10.1021/acs.jpclett.4c01829
language
English
LU publication?
yes
id
22be3d7a-141b-4dd5-8b23-6c4145213983
date added to LUP
2024-08-15 12:04:50
date last changed
2025-04-04 15:26:31
@article{22be3d7a-141b-4dd5-8b23-6c4145213983,
  abstract     = {{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.}},
  author       = {{Ribar, David and Woodward, Clifford E. and Nordholm, Sture and Forsman, Jan}},
  issn         = {{1948-7185}},
  language     = {{eng}},
  month        = {{08}},
  number       = {{32}},
  pages        = {{8326--8333}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{The Journal of Physical Chemistry Letters}},
  title        = {{Cluster Formation Induced by Local Dielectric Saturation in Restricted Primitive Model Electrolytes}},
  url          = {{http://dx.doi.org/10.1021/acs.jpclett.4c01829}},
  doi          = {{10.1021/acs.jpclett.4c01829}},
  volume       = {{15}},
  year         = {{2024}},
}