Influence of ion sterics on diffusiophoresis and electrophoresis in concentrated electrolytes

Stout, Robert F.; Khair, Aditya S.

doi:10.1103/physrevfluids.2.014201

Cited by 40 publications

(32 citation statements)

References 46 publications

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“…Thus, we also measured electrophoretic mobilities of the same particles (as a function of salt concentration) as well as the diffusion potential drop across a membrane separating two well-stirred solutions having different salt concentrations. These results are compared with predictions from the recent theory of Stout and Khair (36).…”

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confidence: 83%

Diffusiophoresis of charged colloidal particles in the limit of very high salinity

Prieve

Malone

Khair

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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Diffusiophoresis is the migration of a colloidal particle through a viscous fluid, caused by a gradient in concentration of some molecular solute; a long-range physical interaction between the particle and solute molecules is required. In the case of a charged particle and an ionic solute (e.g., table salt, NaCl), previous studies have predicted and experimentally verified the speed for very low salt concentrations at which the salt solution behaves ideally. The current study presents a study of diffusiophoresis at much higher salt concentrations (approaching the solubility limit). At such large salt concentrations, electrostatic interactions are almost completely screened, thus eliminating the long-range interaction required for diffusiophoresis; moreover, the high volume fraction occupied by ions makes the solution highly nonideal. Diffusiophoretic speeds were found to be measurable, albeit much smaller than for the same gradient at low salt concentrations.

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confidence: 83%

Diffusiophoresis of charged colloidal particles in the limit of very high salinity

Prieve

Malone

Khair

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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“…20,21 The differences between these different steric interaction models for the predicted electrophoretic mobility of spherical particles with fixed charge density have been found to be minor. 22 As an alternative to these adjustments, the PB equation has been modified by incorporating a potential of mean force in addition to the electrostatic potential. 9,23,24 For example, the potential of mean force between surfaces and hydrated ions has been extracted from classical molecular dynamics (MD) simulations, 24,25 taking into account the combined effects of ion-specific interactions, dielectric profile, steric interactions and image charge effects.…”

Section: Introductionmentioning

confidence: 99%

Analytical Interfacial Layer Model for the Capacitance and Electrokinetics of Charged Aqueous Interfaces

2018

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We construct an analytical model to account for the influence of the subnanometer-wide interfacial layer on the differential capacitance and the electro-osmotic mobility of solid-electrolyte interfaces. The interfacial layer is incorporated into the Poisson-Boltzmann and Stokes equations using a box model for the dielectric properties, the viscosity, and the ionic potential of mean force. We calculate the differential capacitance and the electro-osmotic mobility as a function of the surface charge density and the salt concentration, both with and without steric interactions between the ions. We compare the results from our theoretical model with experimental data on a variety of systems (graphite and metallic silver for capacitance and titanium oxide and silver iodide for electro-osmotic data). The differential capacitance of silver as a function of salinity and surface charge density is well reproduced by our theory, using either the width of the interfacial layer or the ionic potential of mean force as the only fitting parameter. The differential capacitance of graphite, however, needs an additional carbon capacitance to explain the experimental data. Our theory yields a power-law dependence of the electro-osmotic mobility on the surface charge density for high surface charges, reproducing the experimental data using both the interfacial parameters extracted from molecular dynamics simulations and fitted interfacial parameters. Finally, we examine different types of hydrodynamic boundary conditions for the power-law behavior of the electro-osmotic mobility, showing that a finite-viscosity layer explains the experimental data better than the usual hydrodynamic slip boundary condition. Our analytical model thus allows us to extract the properties of the subnanometer-wide interfacial layer by fitting to macroscopic experimental data.

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“…Diffusiophoresis, which has received recent interest because of experimental and theoretical advances [7][8][9][10][11][12][13][14][15][16][17], refers to the motion of colloidal particles induced by the solute gradients. The local solute gradient gives rise to the particle motion due to the osmotic pressure gradient developed along the particle surface (chemiphoresis) and the liquid junction potential generated by the diffusion of ions with different diffusivities (electrophoresis).…”

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Accumulation of Colloidal Particles in Flow Junctions Induced by Fluid Flow and Diffusiophoresis

et al. 2017

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The flow of solutions containing solutes and colloidal particles in porous media is widely found in systems including underground aquifers, hydraulic fractures, estuarine or coastal habitats, water filtration systems, etc. In such systems, solute gradients occur when there is a local change in the solute concentration. While the effects of solute gradients have been found to be important for many applications, we observe an unexpected colloidal behavior in porous media driven by the combination of solute gradients and the fluid flow. When two flows with different solute concentrations are in contact near a junction, a sharp solute gradient is formed at the interface, which may allow strong diffusiophoresis of the particles directed against the flow. Consequently, the particles accumulate near the pore entrance, rapidly approaching the packing limit. These colloidal dynamics have important implications for the clogging of a porous medium, where particles that are orders of magnitude smaller than the pore width can accumulate and block the pores within a short period of time. We also show that this effect can be exploited as a useful tool for preconcentrating biomolecules for rapid bioassays.

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Influence of ion sterics on diffusiophoresis and electrophoresis in concentrated electrolytes

Cited by 40 publications

References 46 publications

Diffusiophoresis of charged colloidal particles in the limit of very high salinity

Diffusiophoresis of charged colloidal particles in the limit of very high salinity

Analytical Interfacial Layer Model for the Capacitance and Electrokinetics of Charged Aqueous Interfaces

Accumulation of Colloidal Particles in Flow Junctions Induced by Fluid Flow and Diffusiophoresis

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