Electrostatic Correlation Induced Ion Condensation and Charge Inversion in Multivalent Electrolytes

Agrawal, Nikhil; Wang, Rui

doi:10.1021/acs.jctc.2c00607

Cited by 15 publications

(10 citation statements)

References 66 publications

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“…[23][24][25][26] Validation of these theories is, however, challenging due to limited experimental data giving insight into molecular level processes at interfaces. [22,26,27] Attempts to model EDL structures at high salinity are often validated against surface force apparatus (SFA) [26,[28][29][30] or electrophoresis data, [6,11,31] which unfortunately lack element-specific information. The development of more realistic modifications of EDL theories for overcharging regimes is further complicated by the common disparity of 'chemical' and 'physical' literature.…”

Section: Introductionmentioning

confidence: 99%

“…For example, state-of-the-art theories do not predict overcharging for monovalent ions in aqueous solutions due to their weak 'physical' ion correlations, and any 'chemical' effects related to surface-specificity are commonly ignored. [6,31,32] Muscovite mica, a phyllosilicate mineral, is one of the most widely used substrates to study EDL structures due to its atomically flat basal plane with a well-defined surface charge of ~1 e À /A UC (A UC : area of the muscovite (001) unit cell, 46.72 Å 2 ). The cleaved surface is decorated with K + ions that can have short-range ordering, as observed by low-temperature noncontact atomic force microscopy (AFM) under ultra-high vacuum (UHV) conditions.…”

Section: Introductionmentioning

confidence: 99%

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Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite‐Water Interface by Adsorption of Rb⁺ and Halides (Cl⁻, Br⁻, I⁻) at High Salinity

Neumann,

Lee,

Zhao

et al. 2023

ChemPhysChem

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Classical electric double layer (EDL) models have been widely used to describe ion distributions at charged solid‐water interfaces in dilute electrolytes. However, the chemistry of EDLs remains poorly constrained at high ionic strength where ion–ion correlations control non‐classical behavior such as overcharging, i.e., the accumulation of counter‐ions in amounts exceeding the substrate’s surface charge. Here, we provide direct experimental observations of correlated cation and anion distributions adsorbed at the muscovite (001)–aqueous electrolyte interface as a function of dissolved RbBr concentration ([RbBr] = 0.01–5.8 M) using resonant anomalous X‐ray reflectivity. Our results show alternating cation‐anion layers in the EDL when [RbBr] ≳ 100 mM, whose spatial extension (i.e., ~20 Å from the surface) far exceeds the dimension of the classical Stern layer. Comparison to RbCl and RbI electrolytes indicates that these behaviors are sensitive to the choice of co‐ion size. This new molecular‐scale understanding of the EDL structure during transition from classical to non‐classical regimes supports the development of realistic EDL models for technologies operating at high salinity such as water purification applications or modern electrochemical storage.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite‐Water Interface by Adsorption of Rb⁺ and Halides (Cl⁻, Br⁻, I⁻) at High Salinity

Neumann,

Lee,

Zhao

et al. 2023

ChemPhysChem

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“…The WKB approximation we used in our previous work overestimates the strength of the ion correlation and hence fails to capture the above moderate coupling regime and shows a discontinuous jump to the strong coupling regime (see Figure 1 in ref 69).…”

Section: The Journal Of Physical Chemistry Bmentioning

confidence: 97%

Nature of Overcharging and Charge Inversion in Electrical Double Layers

Agrawal,

Duan,

Wang

2023

J. Phys. Chem. B

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Understanding overcharging and charge inversion is one of the long-standing challenges in soft matter and biophysics.To study these phenomena, we employ the modified Gaussian renormalized fluctuation theory, which allows for the selfconsistent accounting of spatially varying ionic strength as well as the spatial variations in dielectric permittivity and excluded volume effects. The underlying dependence of overcharging on the electrostatic coupling is elucidated by varying the surface charge, counterion valency, and dielectric contrast. Consistent with simulations, three characteristic regimes corresponding to weak, moderate, and strong coupling are identified. Important features like the inversion of zeta potential, crowding, and ionic layering at the surface are successfully captured. For weak coupling, there is no overcharging. In the moderate coupling regime, overcharging increases with the surface charge. Finally, in the strong coupling regime, ionic crowding and saturation in overcharging are observed. Our theory predicts a nonmonotonic dependence of charge inversion on multivalent salt concentration as well as the addition of monovalent salt, in quantitative agreement with experiments.

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“…We set the excluded volumes

v_{\pm, s} = \frac{4}{3} π a_{\pm, s}^{3}

, where

a_{\pm, s}

denote the radius of ion and solvent molecules. The modified Gaussian renormalized fluctuation theory 62,65,66 yields the following self‐consistent equation for the spatial distribution of electrostatic potential

ψ

, ion concentrations

c_{\pm}

, self‐energy

u_{\pm}

, and correlation function

G

- \nabla . [ϵ (r) \nabla ψ (r)] = ρ_{fix} (r) + q_{+} c_{+} (r) - q_{-} c_{-} (r),

c_{\pm} (r) = \frac{e^{μ_{\pm}}}{v_{\pm}} \exp [\mp q_{\pm} ψ (r) - u_{\pm} (r) - v_{\pm} η (r)],

…”

Section: Modified Gaussian Renormalized Fluctuation Theorymentioning

confidence: 99%

“…When charge inversion occurs, the correlations are significantly enhanced at the surface, making it an extremely challenging task to model the steep change in correlations from the surface to the bulk. Previously, we developed the modified Gaussian renormalized fluctuation theory, 62,63 which self‐consistently includes the spatially varying ion correlations and excluded volume effects in a unified framework. Using the theory, we have successfully described the vapor–liquid interface in charged fluids 63 .…”

Section: Introductionmentioning

confidence: 99%

Non‐monotonic salt concentration dependence of inverted electrokinetic flow

Agrawal,

Wang

2023

AIChE Journal

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Modeling of electrokinetic flows is crucial to understand numerous phenomena associated with electrochemistry, biophysics, and colloidal science. Here, we incorporate the modified Gaussian renormalized fluctuation theory into transport equations for electrolyte solutions to study the ion‐correlation‐induced inversion of electrokinetic flows, also known as charge inversion. We are able to capture the non‐monotonic dependence of inverted streaming current and reversed electrophoretic mobility on salt concentration. By analyzing the double‐layer structure, we elucidate that this non‐monotonicity is a consequence of the competition between spatially varying ion correlations and the translational entropy of the ions. We find that for practical values of surface charge densities, the excluded volume effect does not play any significant role. In a significant improvement over existing theories, our theoretical predictions are in quantitative agreement with experimental measurements for charge inversion in trivalent salts.

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Electrostatic Correlation Induced Ion Condensation and Charge Inversion in Multivalent Electrolytes

Cited by 15 publications

References 66 publications

Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite‐Water Interface by Adsorption of Rb⁺ and Halides (Cl⁻, Br⁻, I⁻) at High Salinity

Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite‐Water Interface by Adsorption of Rb⁺ and Halides (Cl⁻, Br⁻, I⁻) at High Salinity

Nature of Overcharging and Charge Inversion in Electrical Double Layers

Non‐monotonic salt concentration dependence of inverted electrokinetic flow

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Electrostatic Correlation Induced Ion Condensation and Charge Inversion in Multivalent Electrolytes

Cited by 15 publications

References 66 publications

Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite‐Water Interface by Adsorption of Rb+ and Halides (Cl−, Br−, I−) at High Salinity

Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite‐Water Interface by Adsorption of Rb+ and Halides (Cl−, Br−, I−) at High Salinity

Nature of Overcharging and Charge Inversion in Electrical Double Layers

Non‐monotonic salt concentration dependence of inverted electrokinetic flow

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Product

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Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite‐Water Interface by Adsorption of Rb⁺ and Halides (Cl⁻, Br⁻, I⁻) at High Salinity

Direct Experimental Observations of Ion Distributions during Overcharging at the Muscovite‐Water Interface by Adsorption of Rb⁺ and Halides (Cl⁻, Br⁻, I⁻) at High Salinity