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Exceptionally Strong Double-Layer Barriers Generated by Polyampholyte Salt

Ribar, David LU orcid ; Woodward, Clifford E. and Forsman, Jan LU (2025) In Journal of Physical Chemistry B 129(17). p.4241-4248
Abstract

Experiments using the surface force apparatus have found anomalously long-range interactions between charged surfaces in concentrated salt solutions. Ion clustering has been suggested as a possible origin of this behavior. In this work, we demonstrate that if such stable clusters indeed form, they are able to induce remarkably strong free energy barriers under conditions where a corresponding solution of simple salt provides negligible forces. Our cluster model is based on connected ions producing a polyampholyte salt containing a symmetric mixture of monovalent cationic and anionic polyampholytes. Ion distributions and surface interactions are evaluated utilizing statistical-mechanical (classical) polymer density functional theory,... (More)

Experiments using the surface force apparatus have found anomalously long-range interactions between charged surfaces in concentrated salt solutions. Ion clustering has been suggested as a possible origin of this behavior. In this work, we demonstrate that if such stable clusters indeed form, they are able to induce remarkably strong free energy barriers under conditions where a corresponding solution of simple salt provides negligible forces. Our cluster model is based on connected ions producing a polyampholyte salt containing a symmetric mixture of monovalent cationic and anionic polyampholytes. Ion distributions and surface interactions are evaluated utilizing statistical-mechanical (classical) polymer density functional theory, cDFT. In the Supporting Information, we briefly investigate a range of different polymer architectures (connectivities), but in the main part of the work, a polyampholyte ion is modeled as a linear chain with alternating charges, in which the ends carry an identical charge (hence, a monovalent net charge). These salts are able to generate repulsions, between similarly charged surfaces, of a remarkable strength, exceeding those from simple salts by orders of magnitude. The underlying mechanism for this is the formation of brush-like layers at the surfaces, i.e., the repulsion is strongly related to excluded volume effects, in a manner similar to the interaction between surfaces carrying grafted polymers. We believe our results are relevant not only to possible mechanisms underlying anomalously long-ranged underscreening in concentrated simple salt solutions but also for the potential use of synthesized polyampholyte salt as extremely efficient stabilizers of colloidal dispersions.

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author
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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Physical Chemistry B
volume
129
issue
17
pages
8 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • pmid:40178092
  • scopus:105002031575
ISSN
1520-6106
DOI
10.1021/acs.jpcb.5c00012
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2025 The Authors. Published by American Chemical Society.
id
972407c0-ce0b-407c-b623-258eb238f86f
date added to LUP
2025-05-01 11:12:48
date last changed
2025-10-14 13:04:02
@article{972407c0-ce0b-407c-b623-258eb238f86f,
  abstract     = {{<p>Experiments using the surface force apparatus have found anomalously long-range interactions between charged surfaces in concentrated salt solutions. Ion clustering has been suggested as a possible origin of this behavior. In this work, we demonstrate that if such stable clusters indeed form, they are able to induce remarkably strong free energy barriers under conditions where a corresponding solution of simple salt provides negligible forces. Our cluster model is based on connected ions producing a polyampholyte salt containing a symmetric mixture of monovalent cationic and anionic polyampholytes. Ion distributions and surface interactions are evaluated utilizing statistical-mechanical (classical) polymer density functional theory, cDFT. In the Supporting Information, we briefly investigate a range of different polymer architectures (connectivities), but in the main part of the work, a polyampholyte ion is modeled as a linear chain with alternating charges, in which the ends carry an identical charge (hence, a monovalent net charge). These salts are able to generate repulsions, between similarly charged surfaces, of a remarkable strength, exceeding those from simple salts by orders of magnitude. The underlying mechanism for this is the formation of brush-like layers at the surfaces, i.e., the repulsion is strongly related to excluded volume effects, in a manner similar to the interaction between surfaces carrying grafted polymers. We believe our results are relevant not only to possible mechanisms underlying anomalously long-ranged underscreening in concentrated simple salt solutions but also for the potential use of synthesized polyampholyte salt as extremely efficient stabilizers of colloidal dispersions.</p>}},
  author       = {{Ribar, David and Woodward, Clifford E. and Forsman, Jan}},
  issn         = {{1520-6106}},
  language     = {{eng}},
  month        = {{04}},
  number       = {{17}},
  pages        = {{4241--4248}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Journal of Physical Chemistry B}},
  title        = {{Exceptionally Strong Double-Layer Barriers Generated by Polyampholyte Salt}},
  url          = {{http://dx.doi.org/10.1021/acs.jpcb.5c00012}},
  doi          = {{10.1021/acs.jpcb.5c00012}},
  volume       = {{129}},
  year         = {{2025}},
}