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Ribar D, Woodward CE, Nordholm S, Forsman J. Cluster Formation Induced by Local Dielectric Saturation in Restricted Primitive Model Electrolytes. J Phys Chem Lett 2024; 15:8326-8333. [PMID: 39109581 PMCID: PMC11331514 DOI: 10.1021/acs.jpclett.4c01829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2024] [Revised: 07/24/2024] [Accepted: 07/31/2024] [Indexed: 08/16/2024]
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.
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Affiliation(s)
- David Ribar
- Computational
Chemistry, Lund University, P.O. Box 124, S-221 00 Lund, Sweden
| | - Clifford E. Woodward
- School
of Physical, Environmental and Mathematical Sciences, University College, University of New South Wales, ADFA Canberra ACT 2600, Australia
| | - Sture Nordholm
- Department
of Chemistry and Molecular Biology, The
University of Gothenburg, 412 96 Gothenburg, Sweden
| | - Jan Forsman
- Computational
Chemistry, Lund University, P.O. Box 124, S-221 00 Lund, Sweden
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2
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Forsman J, Ribar D, Woodward CE. An efficient method to establish electrostatic screening lengths of restricted primitive model electrolytes. Phys Chem Chem Phys 2024; 26:19921-19933. [PMID: 38990567 DOI: 10.1039/d4cp00546e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/12/2024]
Abstract
We present a novel, and computationally cheap, way to estimate electrostatic screening lengths from simulations of restricted primitive model (RPM) electrolytes. We demonstrate that the method is accurate by comparisons with simulated long-ranged parts of the charge density, at various Bjerrum lengths, salt concentrations and ion diameters. We find substantial underscreening in low dielectric solvent, but with an "aqueous" solvent, there is instead overscreening, the degree of which increases with ion size. Our method also offers a possible path to (future) more accurate classical density functional treatments of ionic fluids.
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Affiliation(s)
- Jan Forsman
- Computational Chemistry, Lund University, P.O. Box 124, S-221 00 Lund, Sweden.
| | - David Ribar
- Computational Chemistry, Lund University, P.O. Box 124, S-221 00 Lund, Sweden.
| | - Clifford E Woodward
- School of Physical, Environmental and Mathematical Sciences University College, University of New South Wales, ADFA Canberra ACT 2600, Australia
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3
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Fiuza T, Sarkar M, Riedl J, Cousin F, Demouchy G, Depeyrot J, Dubois E, Perzynski R, Peyre V. Dispersions of magnetic nanoparticles in water/ionic liquid mixtures. Faraday Discuss 2024. [PMID: 39044685 DOI: 10.1039/d4fd00028e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/25/2024]
Abstract
Nanoparticles (NPs) of iron oxide are dispersed in mixtures of water and ionic liquid, here ethylammonium nitrate (EAN), and the NP/NP and NP/solvent interactions are studied. They are analysed via small-angle X-ray scattering and dynamic light scattering coupled to forced Rayleigh scattering, from 22 °C to 80 °C. The NPs are well-dispersed as individual objects in the whole range of compositions and temperatures thanks to sufficient repulsion due to the organization of the solvents at the interface. The surface changes from hydrophilic to hydrophobic around a proportion of 50 vol% water : 50 vol% EAN, following the evolution of the bulk mixtures, which remain heterogeneous in the whole range of compositions.
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Affiliation(s)
- T Fiuza
- PHENIX UMR CNRS 8234, Sorbonne Université, Paris, France.
- Grupo Fluidos Complexos, Inst. de Fisica, Univ. de Brasilia, Brasilia (DF), Brazil
| | - M Sarkar
- PHENIX UMR CNRS 8234, Sorbonne Université, Paris, France.
| | - J Riedl
- PHENIX UMR CNRS 8234, Sorbonne Université, Paris, France.
| | - F Cousin
- Lab. Léon Brillouin, UMR CNRS 12, CE Saclay, Gif sur Yvette, France
| | - G Demouchy
- PHENIX UMR CNRS 8234, Sorbonne Université, Paris, France.
- Dpt de Physique, Univ. de Cergy Pontoise, Cergy-Pontoise, France
| | - J Depeyrot
- Grupo Fluidos Complexos, Inst. de Fisica, Univ. de Brasilia, Brasilia (DF), Brazil
| | - E Dubois
- PHENIX UMR CNRS 8234, Sorbonne Université, Paris, France.
| | - R Perzynski
- PHENIX UMR CNRS 8234, Sorbonne Université, Paris, France.
| | - V Peyre
- PHENIX UMR CNRS 8234, Sorbonne Université, Paris, France.
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Abstract
Experimental measurements of interactions in ionic liquids and concentrated electrolytes over the past decade or so have revealed simultaneous monotonic and oscillatory decay modes. These observations have been hard to interpret using classical theories, which typically allow for just one electrostatic decay mode in electrolytes. Meanwhile, substantial progress in the theoretical description of dielectric response and ion correlations in electrolytes has illuminated the deep connection between density and charge correlations and the multiplicity of decay modes characterising a liquid electrolyte. The challenge in front of us is to build connections between the theoretical expressions for a pair of correlation functions and the directly measured free energy of interaction between macroscopic surfaces in experiments. Towards this aim, we here present measurements and analysis of the interactions between macroscopic bodies across a fluid mixture of two ionic liquids of widely diverging ionic size. The measured oscillatory interaction forces in the liquid mixtures are significantly more complex than for either of the pure ionic liquids, but can be fitted to a superposition of two oscillatory and one monotonic mode with parameters matching those of the pure liquids. We discuss this empirical finding, which hints at a kind of wave mechanics for interactions in liquid matter.
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Affiliation(s)
- Timothy S Groves
- Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, UK.
| | - Susan Perkin
- Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, UK.
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Zhao R, Han T, Zhang C, Yu Q. Disparate External Electric Field Effect on the Adsorption and Shear Behavior of Monovalent and Trivalent Ions in Electrolyte Solution. NANO LETTERS 2024; 24:7941-7947. [PMID: 38912650 DOI: 10.1021/acs.nanolett.4c01312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/25/2024]
Abstract
Reducing friction is of great interest, and an external potential applied to the friction pair can regulate lubricity. Electrochemical atomic force microscopy (EC-AFM) is used to study the tribological and adsorption behavior of monovalent and trivalent ionic solutions between charged surfaces. An opposite trend of coefficient of friction (COF) and normal force that varies with the applied electric potential is witnessed. Direct force measurements and theoretical models have disclosed that, for the NaCl solution, the negative electric field reduces the COF by increasing cation adsorption. As for LaCl3 solution, the positive electric field promotes the primary adsorption of anions on HOPG, resulting in the disappearance of the attractive ion-ion correlation between the trivalent ions, thereby reducing the COF. The shear behavior of adsorbed ions in electrolyte solution is sensitive to their valence, because of their different surface force contribution. The study further provides a framework to optimize the design of hydration lubrication.
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Affiliation(s)
- Ruiqi Zhao
- State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, Beijing 100084, China
| | - Tianyi Han
- State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, Beijing 100084, China
| | - Chenhui Zhang
- State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, Beijing 100084, China
| | - Qingyuan Yu
- State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, Beijing 100084, China
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G Lopez C, Matsumoto A, Shen AQ. Dilute polyelectrolyte solutions: recent progress and open questions. SOFT MATTER 2024; 20:2635-2687. [PMID: 38427030 DOI: 10.1039/d3sm00468f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/02/2024]
Abstract
Polyelectrolytes are a class of polymers possessing ionic groups on their repeating units. Since counterions can dissociate from the polymer backbone, polyelectrolyte chains are strongly influenced by electrostatic interactions. As a result, the physical properties of polyelectrolyte solutions are significantly different from those of electrically neutral polymers. The aim of this article is to highlight key results and some outstanding questions in the polyelectrolyte research from recent literature. We focus on the influence of electrostatics on conformational and hydrodynamic properties of polyelectrolyte chains. A compilation of experimental results from the literature reveals significant disparities with theoretical predictions. We also discuss a new class of polyelectrolytes called poly(ionic liquid)s that exhibit unique physical properties in comparison to ordinary polyelectrolytes. We conclude this review by listing some key research challenges in order to fully understand the conformation and dynamics of polyelectrolytes in solutions.
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Affiliation(s)
- Carlos G Lopez
- Institute of Physical Chemistry, RWTH Aachen University, Aachen, 52056, Germany
| | - Atsushi Matsumoto
- Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui City, Fukui 910-8507, Japan.
| | - Amy Q Shen
- Micro/Bio/Nanofluidics Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan.
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Fiuza T, Sarkar M, Riedl JC, Beaughon M, Torres Bautista BE, Bhattacharya K, Cousin F, Barruet E, Demouchy G, Depeyrot J, Dubois E, Gélébart F, Geertsen V, Mériguet G, Michot L, Nakamae S, Perzynski R, Peyre V. Ion specific tuning of nanoparticle dispersion in an ionic liquid: a structural, thermoelectric and thermo-diffusive investigation. Phys Chem Chem Phys 2023; 25:28911-28924. [PMID: 37855156 DOI: 10.1039/d3cp02399k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2023]
Abstract
Dispersions of charged maghemite nanoparticles (NPs) in EAN (ethylammonium nitrate) a reference Ionic Liquid (IL) are studied here using a number of static and dynamical experimental techniques; small angle scattering (SAS) of X-rays and of neutrons, dynamical light scattering and forced Rayleigh scattering. Particular insight is provided regarding the importance of tuning the ionic species present at the NP/IL interface. In this work we compare the effect of Li+, Na+ or Rb+ ions. Here, the nature of these species has a clear influence on the short-range spatial organisation of the ions at the interface and thus on the colloidal stability of the dispersions, governing both the NP/NP and NP/IL interactions, which are both evaluated here. The overall NP/NP interaction is either attractive or repulsive. It is characterised by determining, thanks to the SAS techniques, the second virial coefficient A2, which is found to be independent of temperature. The NP/IL interaction is featured by the dynamical effective charge ξeff0 of the NPs and by their entropy of transfer ŜNP (or equivalently their heat of transport ) determined here thanks to thermoelectric and thermodiffusive measurements. For repulsive systems, an activated process rules the temperature dependence of these two latter quantities.
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Affiliation(s)
- T Fiuza
- Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France.
- Grupo de Fluidos Complexos, Inst. de Fisíca, Univ. de Brasília, Brasília (DF), Brazil
| | - M Sarkar
- Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France.
| | - J C Riedl
- Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France.
| | - M Beaughon
- Service de Physique de l'état condensé, SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette, CEDEX, France
| | - B E Torres Bautista
- Service de Physique de l'état condensé, SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette, CEDEX, France
| | - K Bhattacharya
- Service de Physique de l'état condensé, SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette, CEDEX, France
| | - F Cousin
- Lab. Léon Brillouin-UMR 12 CNRS-CEA CEA-Saclay, 91191 Gif-sur-Yvette, France
| | - E Barruet
- Univ. Paris-Saclay, CEA, CNRS, NIMBE-LIONS, 91191 Gif sur Yvette, CEDEX, France
| | - G Demouchy
- Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France.
- Univ. de Cergy Pontoise-Dpt de physique, 33 Bd du Port, 95011 Cergy-Pontoise, France
| | - J Depeyrot
- Grupo de Fluidos Complexos, Inst. de Fisíca, Univ. de Brasília, Brasília (DF), Brazil
| | - E Dubois
- Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France.
| | - F Gélébart
- Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France.
| | - V Geertsen
- Univ. Paris-Saclay, CEA, CNRS, NIMBE-LIONS, 91191 Gif sur Yvette, CEDEX, France
| | - G Mériguet
- Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France.
| | - L Michot
- Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France.
| | - S Nakamae
- Service de Physique de l'état condensé, SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette, CEDEX, France
| | - R Perzynski
- Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France.
| | - V Peyre
- Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France.
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Robertson H, Elliott GR, Nelson ARJ, Le Brun AP, Webber GB, Prescott SW, Craig VSJ, Wanless EJ, Willott JD. Underscreening in concentrated electrolytes: re-entrant swelling in polyelectrolyte brushes. Phys Chem Chem Phys 2023; 25:24770-24782. [PMID: 37671535 DOI: 10.1039/d3cp02206d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/07/2023]
Abstract
Hypersaline environments are ubiquitous in nature and are found in myriad technological processes. Recent empirical studies have revealed a significant discrepancy between predicted and observed screening lengths at high salt concentrations, a phenomenon referred to as underscreening. Herein we investigate underscreening using a cationic polyelectrolyte brush as an exemplar. Poly(2-(methacryloyloxy)ethyl)trimethylammonium (PMETAC) brushes were synthesised and their internal structural changes and swelling response was monitored with neutron reflectometry and spectroscopic ellipsometry. Both techniques revealed a monotonic brush collapse as the concentration of symmetric monovalent electrolyte increased. However, a non-monotonic change in brush thickness was observed in all multivalent electrolytes at higher concentrations, known as re-entrant swelling; indicative of underscreening. For all electrolytes, numerical self-consistent field theory predictions align with experimental studies in the low-to-moderate salt concentration regions. Analysis suggests that the classical theory of electrolytes is insufficient to describe the screening lengths observed at high salt concentrations and that the re-entrant polyelectrolyte brush swelling seen herein is consistent with the so-called regular underscreening phenomenon.
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Affiliation(s)
- Hayden Robertson
- College of Science, Engineering and Environment, University of Newcastle, Callaghan, NSW 2308, Australia.
| | - Gareth R Elliott
- College of Science, Engineering and Environment, University of Newcastle, Callaghan, NSW 2308, Australia.
| | - Andrew R J Nelson
- Australian Centre for Neutron Scattering, ANSTO, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia
| | - Anton P Le Brun
- Australian Centre for Neutron Scattering, ANSTO, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia
| | - Grant B Webber
- College of Science, Engineering and Environment, University of Newcastle, Callaghan, NSW 2308, Australia.
| | - Stuart W Prescott
- School of Chemical Engineering, UNSW Sydney, Sydney, NSW 2052, Australia
| | - Vincent S J Craig
- Department of Materials Physics, Research School of Physics, Australian National University, Canberra, ACT 0200, Australia
| | - Erica J Wanless
- College of Science, Engineering and Environment, University of Newcastle, Callaghan, NSW 2308, Australia.
| | - Joshua D Willott
- College of Science, Engineering and Environment, University of Newcastle, Callaghan, NSW 2308, Australia.
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