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Rezaei M, Sakong S, Groß A. Sodium Triflate Water-in-Salt Electrolytes in Advanced Battery Applications: A First-Principles-Based Molecular Dynamics Study. ACS APPLIED MATERIALS & INTERFACES 2024; 16:32169-32188. [PMID: 38862108 PMCID: PMC11212028 DOI: 10.1021/acsami.4c01449] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2024] [Revised: 04/03/2024] [Accepted: 05/29/2024] [Indexed: 06/13/2024]
Abstract
Offering a compelling combination of safety and cost-effectiveness, water-in-salt (WiS) electrolytes have emerged as promising frontiers in energy storage technology. Still, there is a strong demand for research and development efforts to make these electrolytes ripe for commercialization. Here, we present a first-principles-based molecular dynamics (MD) study addressing in detail the properties of a sodium triflate WiS electrolyte for Na-ion batteries. We have developed a workflow based on a machine learning (ML) potential derived from ab initio MD simulations. As ML potentials are typically restricted to the interpolation of the data points of the training set and have hardly any predictive properties, we subsequently optimize a classical force field based on physics principles to ensure broad applicability and high performance. Performing and analyzing detailed MD simulations, we identify several very promising properties of the sodium triflate as a WiS electrolyte but also indicate some potential stability challenges associated with its use as a battery electrolyte.
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Affiliation(s)
- Majid Rezaei
- Institute
of Theoretical Chemistry, Ulm University, Oberberghof 7, 89081 Ulm, Germany
| | - Sung Sakong
- Institute
of Theoretical Chemistry, Ulm University, Oberberghof 7, 89081 Ulm, Germany
| | - Axel Groß
- Institute
of Theoretical Chemistry, Ulm University, Oberberghof 7, 89081 Ulm, Germany
- Helmholtz
Institute Ulm (HIU) for Electrochemical Energy Storage, Helmholtzstraße 11, 89069 Ulm, Germany
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2
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Becker M, Loche P, Rezaei M, Wolde-Kidan A, Uematsu Y, Netz RR, Bonthuis DJ. Multiscale Modeling of Aqueous Electric Double Layers. Chem Rev 2024; 124:1-26. [PMID: 38118062 PMCID: PMC10785765 DOI: 10.1021/acs.chemrev.3c00307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Revised: 11/17/2023] [Accepted: 11/30/2023] [Indexed: 12/22/2023]
Abstract
From the stability of colloidal suspensions to the charging of electrodes, electric double layers play a pivotal role in aqueous systems. The interactions between interfaces, water molecules, ions and other solutes making up the electrical double layer span length scales from Ångströms to micrometers and are notoriously complex. Therefore, explaining experimental observations in terms of the double layer's molecular structure has been a long-standing challenge in physical chemistry, yet recent advances in simulations techniques and computational power have led to tremendous progress. In particular, the past decades have seen the development of a multiscale theoretical framework based on the combination of quantum density functional theory, force-field based simulations and continuum theory. In this Review, we discuss these theoretical developments and make quantitative comparisons to experimental results from, among other techniques, sum-frequency generation, atomic-force microscopy, and electrokinetics. Starting from the vapor/water interface, we treat a range of qualitatively different types of surfaces, varying from soft to solid, from hydrophilic to hydrophobic, and from charged to uncharged.
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Affiliation(s)
| | - Philip Loche
- Fachbereich
Physik, Freie Universität Berlin, 14195 Berlin, Germany
- Laboratory
of Computational Science and Modeling, IMX, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
| | - Majid Rezaei
- Fachbereich
Physik, Freie Universität Berlin, 14195 Berlin, Germany
- Institute
of Theoretical Chemistry, Ulm University, 89081 Ulm, Germany
| | | | - Yuki Uematsu
- Department
of Physics and Information Technology, Kyushu
Institute of Technology, 820-8502 Iizuka, Japan
- PRESTO,
Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Roland R. Netz
- Fachbereich
Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Douwe Jan Bonthuis
- Institute
of Theoretical and Computational Physics, Graz University of Technology, 8010 Graz, Austria
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3
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Gravelle S, Haber-Pohlmeier S, Mattea C, Stapf S, Holm C, Schlaich A. NMR Investigation of Water in Salt Crusts: Insights from Experiments and Molecular Simulations. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023. [PMID: 37207369 DOI: 10.1021/acs.langmuir.3c00036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The evaporation of water from bare soil is often accompanied by the formation of a layer of crystallized salt, a process that must be understood in order to address the issue of soil salinization. Here, we use nuclear magnetic relaxation dispersion measurements to better understand the dynamic properties of water within two types of salt crusts: sodium chloride (NaCl) and sodium sulfate (Na2SO4). Our experimental results display a stronger dispersion of the relaxation time T1 with frequency for the case of sodium sulfate as compared to sodium chloride salt crusts. To gain insight into these results, we perform molecular dynamics simulations of salt solutions confined within slit nanopores made of either NaCl or Na2SO4. We find a strong dependence of the value of the relaxation time T1 on pore size and salt concentration. Our simulations reveal the complex interplay between the adsorption of ions at the solid surface, the structure of water near the interface, and the dispersion of T1 at low frequency, which we attribute to adsorption-desorption events.
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Affiliation(s)
- Simon Gravelle
- Institute for Computational Physics, University of Stuttgart, D-70569 Stuttgart, Germany
| | - Sabina Haber-Pohlmeier
- Institut für Wasser und Umweltsystemmodellierung, University of Stuttgart, D-70569 Stuttgart, Germany
| | - Carlos Mattea
- Institute of Physics, Technische Universität Ilmenau, Ilmenau 98693, Germany
| | - Siegfried Stapf
- Institute of Physics, Technische Universität Ilmenau, Ilmenau 98693, Germany
| | - Christian Holm
- Institute for Computational Physics, University of Stuttgart, D-70569 Stuttgart, Germany
| | - Alexander Schlaich
- Institute for Computational Physics, University of Stuttgart, D-70569 Stuttgart, Germany
- Stuttgart Center for Simulation Science (SC SimTech), University of Stuttgart, 70569 Stuttgart, Germany
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4
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Siani P, Frigerio G, Donadoni E, Di Valentin C. Modeling Zeta Potential for Nanoparticles in Solution: Water Flexibility Matters. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2023; 127:9236-9247. [PMID: 37223652 PMCID: PMC10201526 DOI: 10.1021/acs.jpcc.2c08988] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 04/17/2023] [Indexed: 05/25/2023]
Abstract
Nonequilibrium molecular dynamics simulations were performed to study the electrokinetic properties of five mainstream TIPxP water models (namely, TIP3P-FB, TIP3Pm, TIP4P-FB, TIP4P-Ew, and TIP4P/2005) in NaCl aqueous solutions in the presence of a negatively charged TiO2 surface. The impact of solvent flexibility and system geometry on the electro-osmotic (EO) mobility and flow direction was systematically assessed and compared. We found that lack of water flexibility decelerates the forward EO flow of aqueous solutions at moderate (0.15 M) or high (0.30 M) NaCl concentrations, in some special cases to such an extent that EO flow reversal occurs. Zeta potential (ZP) values were then determined from the bulk EO mobilities using the Helmholtz-Smoluchowski formula. The straight comparison against available experimental data strongly suggests that water flexibility improves the ZP determination of NaCl solutions adjacent to a realistic TiO2 surface under neutral pH conditions.
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Affiliation(s)
- Paulo Siani
- Dipartimento
di Scienza dei Materiali, Università
di Milano Bicocca, via
R. Cozzi 55, 20125 Milano, Italy
- BioNanoMedicine
Center NANOMIB, University of Milano-Bicocca, 20126 Milano, Italy
| | - Giulia Frigerio
- Dipartimento
di Scienza dei Materiali, Università
di Milano Bicocca, via
R. Cozzi 55, 20125 Milano, Italy
- BioNanoMedicine
Center NANOMIB, University of Milano-Bicocca, 20126 Milano, Italy
| | - Edoardo Donadoni
- Dipartimento
di Scienza dei Materiali, Università
di Milano Bicocca, via
R. Cozzi 55, 20125 Milano, Italy
- BioNanoMedicine
Center NANOMIB, University of Milano-Bicocca, 20126 Milano, Italy
| | - Cristiana Di Valentin
- Dipartimento
di Scienza dei Materiali, Università
di Milano Bicocca, via
R. Cozzi 55, 20125 Milano, Italy
- BioNanoMedicine
Center NANOMIB, University of Milano-Bicocca, 20126 Milano, Italy
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5
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Gravelle S, Holm C, Schlaich A. Transport of thin water films: from thermally activated random walks to hydrodynamics. J Chem Phys 2022; 157:104702. [DOI: 10.1063/5.0099646] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Under ambient atmospheric conditions, a thin film of water wets many solid surfaces, including insulators, ice, and salt. The film thickness as well as its transport behavior sensitively depend on the surrounding humidity. Understanding this intricate interplay is of highest relevance for water transport through porous media, particularly in the context of soil salinization induced by evaporation. Here, we use molecular simulations to evaluate the transport properties of thin water films on prototypical salt and soil interfaces, namely NaCl and silica solid surfaces. Our results showtwo distinct regimes for water transport: at low water coverage, the film permeance scales linearly with the adsorbed amount, in agreement with the activated random walk model.For thicker water films, the permeance scales as the adsorbed amount to the power of 3, in line with the Stokes equation. By comparing results obtained for silica and NaCl surfaces, we find that, at low water coverage, water permeance at the silica surface is considerably lower than at the NaCl surface, which we attribute to difference in hydrogen bonding. We also investigate the effect of atomic surface defects on the transport properties. Finally, in the context of water transport through porous material, we determine the humidity-dependent crossover between a vapor dominated and a thin film dominated transport regimes depending on the pore size.
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Affiliation(s)
| | - Christian Holm
- Institute for Computational Physics, University of Stuttgart, Germany
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6
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Döpke MF, Westerbaan van der Meij F, Coasne B, Hartkamp R. Surface Protolysis and Its Kinetics Impact the Electrical Double Layer. PHYSICAL REVIEW LETTERS 2022; 128:056001. [PMID: 35179914 DOI: 10.1103/physrevlett.128.056001] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Revised: 12/08/2021] [Accepted: 01/05/2022] [Indexed: 06/14/2023]
Abstract
Surface conductivity in the electrical double layer (EDL) is known to be affected by proton hopping and diffusion at solid-liquid interfaces. Yet, the role of surface protolysis and its kinetics on the thermodynamic and transport properties of the EDL are usually ignored as physical models consider static surfaces. Here, using a novel molecular dynamics method mimicking surface protolysis, we unveil the impact of such chemical events on the system's response. Protolysis is found to strongly affect the EDL and electrokinetic aspects with major changes in ζ potential and electro-osmotic flow.
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Affiliation(s)
- Max F Döpke
- Process & Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, Netherlands
| | | | - Benoit Coasne
- Université Grenoble Alpes, CNRS, LIPhy, 38000 Grenoble, France
| | - Remco Hartkamp
- Process & Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, Netherlands
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7
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Rojano AE, Córdoba A, Walther JH, Zambrano HA. Effect of charge inversion on nanoconfined flow of multivalent ionic solutions. Phys Chem Chem Phys 2022; 24:4935-4943. [DOI: 10.1039/d1cp02102h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A comprehensive understanding of fluid dynamics of dilute electrolyte solutions in nanoconfinement is essential to develop more efficient nanofluidic devices. In nanoconduits, the electrical double layer can occupy a considerable...
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8
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Rezaei M, Mitterwallner BG, Loche P, Uematsu Y, Netz RR, Bonthuis DJ. Interfacial, Electroviscous, and Nonlinear Dielectric Effects on Electrokinetics at Highly Charged Surfaces. J Phys Chem B 2021; 125:4767-4778. [PMID: 33939436 PMCID: PMC8154604 DOI: 10.1021/acs.jpcb.0c11280] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
The dielectric constant
and the viscosity of water at the interface
of hydrophilic surfaces differ from their bulk values, and it has
been proposed that the deviation is caused by the strong electric
field and the high ion concentration in the interfacial layer. We
calculate the dependence of the dielectric constant and the viscosity
of bulk electrolytes on the electric field and the salt concentration.
Incorporating the concentration and field-dependent dielectric constant
and viscosity in the extended Poisson–Boltzmann and Stokes
equations, we calculate the electro-osmotic mobility. We compare the
results to literature experimental data and explicit molecular dynamics
simulations of OH-terminated surfaces and show that it is necessary
to additionally include the presence of a subnanometer wide interfacial
water layer, the properties of which are drastically transformed by
the sheer presence of the interface. We conclude that the origin of
the anomalous behavior of aqueous interfacial layers cannot be found
in electrostriction or electroviscous effects caused by the interfacial
electric field and ion concentration. Instead, it is primarily caused
by the intrinsic ordering and orientation of the interfacial water
layer.
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Affiliation(s)
- Majid Rezaei
- Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | | | - Philip Loche
- Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Yuki Uematsu
- Department of Physics, Kyushu University, 819-0395 Fukuoka, Japan
| | - Roland R Netz
- Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Douwe Jan Bonthuis
- Institute of Theoretical and Computational Physics, Graz University of Technology, 8010 Graz, Austria
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9
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Döpke MF, Hartkamp R. The importance of specifically adsorbed ions for electrokinetic phenomena: Bridging the gap between experiments and MD simulations. J Chem Phys 2021; 154:094701. [DOI: 10.1063/5.0038161] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Affiliation(s)
- Max F. Döpke
- Process & Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands
| | - Remco Hartkamp
- Process & Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands
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10
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Palaia I, Telles IM, Dos Santos AP, Trizac E. Electroosmosis as a probe for electrostatic correlations. SOFT MATTER 2020; 16:10688-10696. [PMID: 33089848 DOI: 10.1039/d0sm01523g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We study the role of ionic correlations on the electroosmotic flow in planar double-slit channels, without salt. We propose an analytical theory, based on recent advances in the understanding of correlated systems. We compare the theory with mean-field results and validate it by means of dissipative particle dynamics simulations. Interestingly, for some surface separations, correlated systems exhibit a larger flow than predicted by mean-field. We conclude that the electroosmotic properties of a charged system can be used, in general, to infer and weight the importance of electrostatic correlations therein.
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Affiliation(s)
- Ivan Palaia
- Department of Physics and Astronomy, Institute for the Physics of Living Systems, University College London, London WC1E 6BT, UK and MRC Laboratory for Molecular Cell Biology, University College London, London WC1E 6BT, UK
| | - Igor M Telles
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970, Porto Alegre, RS, Brazil
| | - Alexandre P Dos Santos
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970, Porto Alegre, RS, Brazil
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11
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Buyukdagli S. Nanofluidic Charge Transport under Strong Electrostatic Coupling Conditions. J Phys Chem B 2020; 124:11299-11309. [PMID: 33231451 DOI: 10.1021/acs.jpcb.0c09638] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The comprehensive depiction of the many-body effects governing nanoconfined electrolytes is an essential step for the conception of nanofluidic devices with optimized performance. By incorporating self-consistently multivalent charges into the Poisson-Boltzmann equation dressed by a background monovalent salt, we investigate the impact of strong-coupling electrostatics on the nanofluidic transport of electrolyte mixtures. We find that the experimentally observed negative streaming currents in anionic nanochannels originate from the collective effect of Cl- attraction by the interfacially adsorbed multivalent cations and the no-slip layer reducing the hydrodynamic contribution of these cations to the net current. The like-charge current condition emerging from this collective mechanism is shown to be the reversal of the average potential within the no-slip zone. Applying the formalism to surface-coated membrane nanoslits located in the giant dielectric permittivity regime, we reveal a new type of streaming current activated by attractive polarization forces. Under the effect of these forces, multivalent ions added to the KCl solution set a charge separation and generate a counterion current between the neutral slit walls where the pure KCl conductivity vanishes. The adjustability of the current characteristics solely via the valency and amount of the added multivalent ions identifies the underlying process as a promising mechanism for nanofluidic ion separation purposes.
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Sen T, Barisik M. Slip Effects on Ionic Current of Viscoelectric Electroviscous Flows through Different Length Nanofluidic Channels. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:9191-9203. [PMID: 32635731 DOI: 10.1021/acs.langmuir.0c01457] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The pressure driven slip flow of an electrolyte solution is studied through different nanofluidic channel lengths at varying salt concentrations. The viscous-thickening due to the electrostatic interactions within the electric double layer and the reverse ionic transport due to the streaming potential are developed. The influence of the Navier slip boundary condition is described under both electroviscous and viscoelectric effects with a surface charge regulation (CR) model while the observed behavior is compared and validated with molecular dynamic (MD) calculations from multiple studies. Results show that electroviscous and viscoelectric effects decrease transport. Earlier studies at the no slip boundary presented an increase of ionic current by increasing salt concentration and decreasing channel length. In contrast, our study found that the ionic current occurred almost independent of both salt concentration and channel length, except for very short channels and very low salt concentrations, when electroviscous and viscoelectric effects were considered. In the case of the constant slip length condition, ionic conduction was enhanced, but velocity slip developing on surfaces showed significant variation based on the salt concentration and channel length. This is due to the natural CR behavior enhancing the surface charge and consequential near surface electrohydrodynamics as a result of increase in salt concentration and/or decrease of channel length. Considering that the electroviscous effect alone creates up to 70% lower velocity slips than Poiseuille flow predictions, while further including the viscoelectric effect, results in an almost no-slip condition at high salt concentrations and/or short channels. As a result, the ionic current of a viscoelectric electroviscous slip flow is found to be equal to 1/3 of an electroviscous slip flow and to decrease with a decrease in the channel length.
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Affiliation(s)
- Tumcan Sen
- Department of Mechanical Engineering, Izmir Institute Of Technology, Izmir 35430, Turkey
| | - Murat Barisik
- Department of Mechanical Engineering, Izmir Institute Of Technology, Izmir 35430, Turkey
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Kundu D, Bhattacharyya S. Influence of slip velocity at the core of a diffuse soft particle and ion partition effects on mobility. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2020; 43:27. [PMID: 32447590 DOI: 10.1140/epje/i2020-11957-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Accepted: 05/04/2020] [Indexed: 06/11/2023]
Abstract
Nonlinear effects on the electrophoresis of a soft particle, consisting of a rigid hydrophobic core coated with a diffuse polymer layer (PEL) suspended in an electrolyte medium, are studied. The impact of the ion partitioning effect arising due to the Born energy difference between the PEL and the electrolyte is approximated based on the equilibrium Boltzmann equation, with which the ion distribution and hence, the charge density is modified. The equations describing the electrokinetic transport comprising the Darcy-Brinkman extended Navier-Stokes equations which includes the ion partitioning effect coupled with the modified Nernst-Planck equations and Poisson equations for electric field are solved numerically. The present numerical model for the soft particle compares well with the existing theoretical solutions and experimental results in the limiting cases. A deviation from existing simplified models based on the Boltzmann distribution of ions occurs when the Debye layer polarization, relaxation and the electroosmosis induced by the PEL immobile charge become significant. The hydrophobicity of the inner core strongly influences the nonlinear electrokinetic effects by modifying the Debye layer, electroosmotic flow in the PEL and surface conduction. The results indicate that the ion partitioning can significantly increase the electrophoretic mobility of the soft particle by attenuating the shielding effect. When the Debye layer is in the order of the particle size the hydrophobicity of the core surface and the ion partitioning effect manifest the surface conduction, which implies that the Boltzmann distribution of ions is no longer valid. The core hydrophobicity and ion partitioning effect have influence on the condensation of the PEL immobile charge, which creates a significant impact on the mobility.
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Affiliation(s)
- Dipankar Kundu
- Department of Mathematics, Indian Institute of Technology Kharagpur, 721302, Kharagpur, India
| | - Somnath Bhattacharyya
- Department of Mathematics, Indian Institute of Technology Kharagpur, 721302, Kharagpur, India.
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14
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Rezaei M, Azimian AR, Pishevar AR. Surface charge-dependent hydrodynamic properties of an electroosmotic slip flow. Phys Chem Chem Phys 2018; 20:30365-30375. [PMID: 30489580 DOI: 10.1039/c8cp06408c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The electroosmosis effects at the interface of an aqueous NaCl solution and a charged silicon surface are studied using a molecular dynamics (MD) method. Considering a plug-like electroosmotic flow, we identified a thin interfacial layer in the immediate vicinity of the charged surface, where the flow velocity experiences almost linear spatial variations. The thickness of this interfacial layer is found to be linearly dependent on the surface charge density, with a negative slope which slightly depends on the surface hydrophobicity while being independent of the salt concentration, electric field strength, and orientation of the surface lattice. It is also found that upon increasing the surface charge density, the effective slip length first increases up to a maximum amount and then follows an almost linear reduction. We found that increasing the salt concentration drastically reduces the surface charge at which the effective slip length reaches its maximum amount. For highly concentrated solutions, therefore, the effective slip length could be assumed to change linearly in the whole range of the surface charge density, with a slope which is proportional to the square root of the electric field strength divided by the depth of the potential well assigned to the surface atoms εwall. Also, in a wide range of the surface charge density, the slip velocity is found to be a constant fraction of the electroosmotic velocity, which could be measured experimentally. Finally, by comparing the electroosmotic velocities calculated from the Stokes equation (considering both the slip and no-slip boundary conditions) with our MD results, we found that the no-slip boundary condition, which is normally used in analytical calculations, leads to a very inaccurate result for the studied system.
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Affiliation(s)
- Majid Rezaei
- Mechanical Engineering Department, Isfahan University of Technology, Isfahan, Iran.
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