Ions confined in spherical dielectric cavities modeled by a splitting field-theory

Lue, Leo; Linse, Per

doi:10.1063/1.4917256

Cited by 7 publications

(6 citation statements)

References 28 publications

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“…We make the reasonable simplifying assumption that the dielectric exclusion near the nanopore surface is strong enough to keep finite size ions from approaching the pore wall (in fact there should be a distance of closest approach given by the ionic radius). This assumption leads to the absence of purely steric exclusion effects, which would become important for neutral particles, very large ions or inverted dielectric profiles (with a larger dielectric constant outside the nanopore than within, leading to ion accumulation at the nanopore surface [38]).…”

Section: Electrolyte With Hardcore Interactions Inside a Nanopore A V...mentioning

confidence: 99%

A variational approach to the liquid-vapor phase transition for hardcore ions in the bulk and in nanopores

Loubet

Manghi

Palmeri

2016

The Journal of Chemical Physics

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We employ a field-theoretical variational approach to study the behavior of ionic solutions in the grand canonical ensemble. To describe properly the hardcore interactions between ions, we use a cutoff in Fourier space for the electrostatic contribution of the grand potential and the CarnahanStarling equation of state with a modified chemical potential for the pressure one. We first calibrate our method by comparing its predictions at room temperature with Monte Carlo results for excess chemical potential and energy. We then validate our approach in the bulk phase by describing the classical "ionic liquid-vapor" phase transition induced by ionic correlations at low temperature, before applying it to electrolytes at room temperature confined to nanopores embedded in a low dielectric medium and coupled to an external reservoir of ions. The ionic concentration in the nanopore is then correctly described from very low bulk concentrations, where dielectric exclusion shifts the transition up to room temperature for sufficiently tight nanopores, to high concentrations where hardcore interactions dominate which, as expected, modify only slightly this ionic "capillary evaporation".

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Section: Electrolyte With Hardcore Interactions Inside a Nanopore A V...mentioning

confidence: 99%

A variational approach to the liquid-vapor phase transition for hardcore ions in the bulk and in nanopores

Loubet

Manghi

Palmeri

2016

The Journal of Chemical Physics

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“…This has been observed in previous models, which have shown no separation of anions from cations when confined in dielectric spheres with charged surfaces. 42,43 These models have provided accurate descriptions of microporous systems by using the Poisson equation for spherically symmetric distributions…”

Section: Introductionmentioning

confidence: 99%

Predicting Destabilization in Salt-Containing Aqueous Reverse Micellar Colloidal Systems

Ridley

Fathi-Kelly

Kelly

et al. 2021

ACS Earth Space Chem.

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Colloidal systems, including micellar and reverse micellar mixtures, are essential for a variety of natural transport processes, such as the flow of organic and inorganic contaminants in lakes, rivers, and underground fissures. Thus, an understanding of their structure and stability is important for prediction of their behavior in complex environments. Previous experiments have shown that the solvodynamic diameters (D) of reverse micelles contract linearly with increased concentrations of salts such as NaBH4, FeSO4, Mg(NO3)2, CuCl2, Al(NO3)3, Fe(NO3)3, and Y(NO3)3. It has also been previously determined that reverse micelle size is a function of cation valency, through the Debye screening length (κ–1), and of anion hydrated radius. Here, we present a new theoretical model for the aqueous reverse micelle core substructure in water/AOT/isooctane colloidal systems with added salts. Our model is based on electrical double layer (EDL) theory and assumes ions are evenly distributed within the reverse micelle water core. We further analyze reverse micelle size with respect to ion hydration, reverse micelle water dynamics, and ion distribution, to propose a mechanism for reverse micelle contraction and determine the cause of system instability at the critical destabilization concentration for each salt. We find that destabilization occurs when the interfacial core water and waters needed for complete ion hydration exceed the water contained within the reverse micelle at its stable size. This establishes ion hydration capacity a likely primary mechanism for reverse micelle destabilization.

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“…An open question in the theory of electrolytes concerns the relationship between the field theoretical variational method adopted here and the splitting field method [56] developed previously to study in an approximate way the subtle crossover between the mean-field Poisson-Boltzmann and strong-coupling limits. We have tried here to shed some (faint) light on this question and plan in the future to use the simplified setting of a spherical pore to further elucidate it.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

“…[49] the field theoretic variational theory method was used to study electrolytes excluded from, but not confined to, spherical regions (the focus here). A complementary splitting-field method was also used in conjunction with Monte Carlo simulations to study electrolytes inside spherical pores [56], although the focus was different from our own and the question of the ionic liquid-vapor phase transition was not addressed. It is crucial to underline that the field theoretic variational method developed here, unlike earlier methods [20], gives access to an approximate free energy (variational grand potential) functional that can be used to establish ionic liquid-vapor phase diagrams.…”

Section: Introductionmentioning

confidence: 99%

Competition between Born solvation, dielectric exclusion, and Coulomb attraction in spherical nanopores

2021

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The recent measurement of a very low dielectric constant, , of water confined in nanometric slit pores leads us to reconsider the physical basis of ion partitioning into nanopores. For confined ions in chemical equilibrium with a bulk of dielectric constant b > , three physical mechanisms, at the origin of ion exclusion in nanopores, are expected to be modified due to this dielectric mismatch: dielectric exclusion at the water-pore interface (with membrane dielectric constant, m < ), the solvation energy related to the difference in Debye-Hückel screening parameters in the pore, κ, and in the bulk κ b , and the classical Born solvation self-energy proportional to −1 − −1 b . Our goal is to clarify the interplay between these three mechanisms and investigate the role played by the Born contribution in ionic liquid-vapor (LV) phase separation in confined geometries. We first compute analytically the potential of mean force (PMF) of an ion of radius R i located at the center of a nanometric spherical pore of radius R. Computing the variational grand potential for a solution of confined ions, we then deduce the partition coefficients of ions in the pore versus R and the bulk electrolyte concentration ρ b . We show how the ionic LV transition, directly induced by the abrupt change of the dielectric contribution of the PMF with κ, is favored by the Born self-energy and explore the decrease of the concentration in the pore with both in the vapor and liquid states. Phase diagrams are established for various parameter values and we show that a signature of this phase transition can be detected by monitoring the total osmotic pressure as a function of R. For charged nanopores, these exclusion effects compete with the electrostatic attraction that imposes the entry of counterions into the pore to enforce electroneutrality. This study will therefore help in deciphering the respective roles of the Born self-energy and dielectric mismatch in experiments and simulations of ionic transport through nanopores.

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Ions confined in spherical dielectric cavities modeled by a splitting field-theory

Cited by 7 publications

References 28 publications

A variational approach to the liquid-vapor phase transition for hardcore ions in the bulk and in nanopores

A variational approach to the liquid-vapor phase transition for hardcore ions in the bulk and in nanopores

Predicting Destabilization in Salt-Containing Aqueous Reverse Micellar Colloidal Systems

Competition between Born solvation, dielectric exclusion, and Coulomb attraction in spherical nanopores

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