Numerical study supplemented with simplified model on electrophoresis of a hydrophobic colloid incorporating finite ion size effects and ion‐solvent interactions

Bhaskar, Babu; Bhattacharyya, S.

doi:10.1002/elps.202200232

Cited by 3 publications

(1 citation statement)

References 46 publications

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“…Enhanced viscosity may lead to the attenuation of μ D through increased hydrodynamic friction and lowering of the ionic mobility, which may create a better match with the experimental data. In the context of electrophoresis, Bhaskar and Bhattacharyya 49 considered the ion steric interactions and dependence of viscosity on the local ionic volume fraction, leading to a better agreement of the computed results with experimental analysis.…”

Section: Comparison Of Mobility With Existing Results and Validation ...mentioning

confidence: 99%

Diffusiophoresis of a Charged Droplet in Asymmetric as Well as Mixed Electrolytes through Numerical and Semianalytic Models

Majhi

Bhattacharyya

2023

Langmuir

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A numerical study on the diffusiophoresis of a droplet in an electrolyte medium is carried out by solving the full set of coupled governing equations, which are based on the conservation principle. Diffusiophoresis is considered for monovalent as well as non-z:z electrolytes and mixed electrolytes. The numerical model is supplemented with a semianalytic simplified model based on first-order perturbation analysis, which agrees with the numerical model for a low to moderate range of surface potential. The mobility for a low-viscosity fluid at a thinner Debye length is dominated by the chemiphoresis part, which creates the mobility to become an even function of the surface charge density for a monovalent electrolyte. Such a pattern in mobility does not appear in a non-z:z asymmetric electrolyte. At a thinner Debye length, diffusiophoresis becomes independent of the diffusion field, hence the mobility is independent of the composition of electrolytes in a mixed monovalent electrolyte solution. Our results show that the size-based sorting of droplets is efficient when a mixed electrolyte is considered. We have also addressed the finite ion size effects by considering a modified ion transport equation. One of the key features of the present study is the simplified semianalytical model for the diffusiophoresis of a droplet in a z:z electrolyte as well as in non-z:z and mixed electrolytes, which is shown to be valid up to a moderate range of surface potential for a finite Debye length.

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Section: Comparison Of Mobility With Existing Results and Validation ...mentioning

confidence: 99%

Diffusiophoresis of a Charged Droplet in Asymmetric as Well as Mixed Electrolytes through Numerical and Semianalytic Models

Majhi

Bhattacharyya

2023

Langmuir

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Numerical model supplemented by thin-layer analysis for diffusiophoresis of a particle incorporating finite ion size effects

Bhaskar

Bhattacharyya

2023

Physics of Fluids

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The impact of finite-sized ions on the diffusiophoresis of a charged colloid subjected to a concentration gradient of electrolyte solution consisting monovalent or multivalent ionic species, is studied. In diffusiophoresis, the ion concentration is of O(1M). In this non-dilute electrolyte solutions, the ion–ion steric interaction is important. We have adopted the Boublik–Mansoori–Carnahan–Starling–Leland (BMCSL) model to account for the ion steric interactions and the Batchelor–Green expression for the relative viscosity of suspension. We have solved the standard model numerically considering ions as point charge (PNP-model), the modified Nernst–Planck equations incorporating the ion steric interaction with constant viscosity (MNP-model), and modification of the MNP-model by incorporating the viscosity variation with the ionic volume fraction (MNPV-model). Semi-analytical expressions for mobility based on a linear perturbation technique under a thinner Debye length is presented for PNP- and MNP-models. In the MNP-model, counterion saturation in the Debye layer due to the ion steric interaction enhances the surface potential by attenuating the shielding effect, diminishes the surface conduction, and magnifies the induced electric field. These in combination create a larger mobility at a thinner Debye length compared with the PNP-model. This increment in mobility attenuates when the MNPV-model is considered. The MNPV-model is more appropriate to analyze the finite ion size effects, and it is found to yield the mobility values more close to the experimental data compared with the MNP- and PNP-model. The semi-analytical expressions for mobility based on the PNP- and MNP-models agree with the corresponding exact numerical solutions when the surface potential is in the order of thermal potential. However, a large discrepancy between the simplified expression and the exact numerical results is found for a concentrated electrolyte in which the induced electric field is large.

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Diffusiophoresis of a highly charged rigid colloid in a hydrogel incorporating ion steric interactions

Bhaskar,

Bhattacharyya

2023

Physics of Fluids

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Diffusiophoresis, mediated by an imposed ionic concentration gradient, is a useful technique in directed migration of colloids. Theoretical studies on diffusiophoresis in a polymer hydrogel medium are rather limited owing to the presence of nonlinear terms in the fluid transport equations. The hydrogel creates a hydrodynamic interaction and short-range steric interaction to the dispersing particle and macromolecules. The volume exclusion due to a finite ion size consideration is important in the context of a highly charged particle. In this study, we consider the finite ion size effects on diffusiophoresis of a charged particle with ζ≥1 in a hydrogel medium. The modified ion transport equations coupled with the Brinkman equation for fluid flow and the Poisson equation for electric field are solved numerically in a coupled manner through a control volume approach. Our results based on the Brinkman model incorporating only the hydrodynamic interactions deviate from the existing experimental results. A close comparison with this experimental data is established when the computed mobility is modified to incorporate the short-range steric factor. We have considered the impact of the hindered diffusivity of ions in the gel medium. Our results show that the modification in the ionic diffusivity is significant for low porosity and high charge density situations. The impact of the finite ion size effect is found to be significant when the bulk ionic concentration is large enough to create an electric double layer thinner than the particle size. We have analyzed the size dependency of the mobility in the gel medium. A simplified expression for the mobility in a hydrogel medium is proposed.

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Numerical study supplemented with simplified model on electrophoresis of a hydrophobic colloid incorporating finite ion size effects and ion‐solvent interactions

Cited by 3 publications

References 46 publications

Diffusiophoresis of a Charged Droplet in Asymmetric as Well as Mixed Electrolytes through Numerical and Semianalytic Models

Diffusiophoresis of a Charged Droplet in Asymmetric as Well as Mixed Electrolytes through Numerical and Semianalytic Models

Numerical model supplemented by thin-layer analysis for diffusiophoresis of a particle incorporating finite ion size effects

Diffusiophoresis of a highly charged rigid colloid in a hydrogel incorporating ion steric interactions

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