Slippery and mobile hydrophobic electrokinetics: From single walls to nanochannels

Vinogradova, Olga I.; Silkina, Elena F.; Asmolov, Evgeny S.

doi:10.1016/j.cocis.2023.101742

Current Opinion in Colloid & Interface Science

2023

DOI: 10.1016/j.cocis.2023.101742

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Slippery and mobile hydrophobic electrokinetics: From single walls to nanochannels

Olga I. Vinogradova

Elena F. Silkina

Evgeny S. Asmolov

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Cited by 5 publications

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Impact of laterally mobile surface charge on diffusiophoresis of hydrophobic rigid colloids

Majhi,

Bhattacharyya,

Gopmandal

2024

J. Fluid Mech.

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The diffusiophoresis of charged hydrophobic nanoparticles (NPs) governed by an imposed ionic concentration gradient is analysed. The main objective is to elucidate the impact of the laterally mobile adsorbed surface ions at the interface on the propulsion of the hydrophobic NPs in diffusiophoresis. In addition, the dielectric polarization due to the difference in dielectric constant between the NPs and the suspension medium is also considered. The mobile surface ions create a friction as well as an electric force at the hydrophobic surface, which leads to a modification of the slip velocity condition and the slip length. We obtain an exact numerical solution of the governing electrokinetic equations in their full form by adopting a control volume formulation. The numerical model is supplemented by analytical solutions derived based on the Debye–Hückel linearization. We find that the lateral mobility of the surface ions obstruct the coions to diffuse from the higher concentration side to the lower concentration side, which results in a repulsive force to the particle leading to the occurrence of a negative mobility. Based on the numerical results and analytical solutions, we have shown that for a fully mobile surface charge, the diffusiophoresis of a hydrophobic NP is identical to the diffusiophoresis of a liquid droplet whose viscosity is related to the slip length of the hydrophobic particle. We establish that the dielectric polarization enhances the velocity of a hydrophobic particle, which has potential applications in the practical context.

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Impact of laterally mobile surface charge on diffusiophoresis of hydrophobic rigid colloids

Majhi,

Bhattacharyya,

Gopmandal

2024

J. Fluid Mech.

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Electrophoresis of ions and electrolyte conductivity: From bulk to nanochannels

Vinogradova,

Silkina

2023

The Journal of Chemical Physics

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When electrolyte solutions are confined in micro- and nanochannels their conductivity is significantly different from those in a bulk phase. Here we revisit the theory of this phenomenon by focusing attention on the reduction in the ion mobility with the concentration of salt and a consequent impact to the conductivity of a monovalent solution, from bulk to confined in a narrow slit. We first give a systematic treatment of electrophoresis of ions and obtain equations for their zeta potentials and mobilities. The latter are then used to obtain a simple expression for a bulk conductivity, which is valid in a concentration range up to a few molars and more accurate than prior analytic theories. By extending the formalism to the electrolyte solution in the charged channel the equations describing the conductivity in different modes are presented. They can be regarded as a generalization of prior work on the channel conductivity to a more realistic case of a nonzero reduction of the electrophoretic mobility of ions with salt concentration. Our analysis provides a framework for interpreting measurements on the conductivity of electrolyte solutions in the bulk and in narrow channels.

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Surface potentials of conductors in electrolyte solutions

Vinogradova,

Silkina,

Asmolov

2024

The Journal of Chemical Physics

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When we place conducting bodies in electrolyte solutions, their surface potential Φs appears to be much smaller in magnitude than the applied one Φ0 and normally does not obey the classical electrostatic boundary condition of a constant potential expected for conductors. In this paper, we demonstrate that an explanation of these observations can be obtained by postulating that diffuse ions condense at the “wall” due to the reduced permittivity of a solvent. For small values of Φ0, the surface potential responds linearly. On increasing Φ0 further, Φs augments nonlinearly and then saturates to a constant value. Analytical approximations for Φs derived for these three distinct modes show that it always adjusts to salt concentration, which is equivalent to a violation of the constant potential condition. The latter would be appropriate for highly dilute solutions but only if Φ0 is small. Surprisingly, when the plateau with high Φs is reached, the conductor surface switches to a constant charge density condition normally expected for insulators. Our results are directly relevant for conducting electrodes, mercury drops, colloidal metallic particles, and more.

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Slippery and mobile hydrophobic electrokinetics: From single walls to nanochannels

Cited by 5 publications

References 54 publications

Impact of laterally mobile surface charge on diffusiophoresis of hydrophobic rigid colloids

Impact of laterally mobile surface charge on diffusiophoresis of hydrophobic rigid colloids

Electrophoresis of ions and electrolyte conductivity: From bulk to nanochannels

Surface potentials of conductors in electrolyte solutions

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