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14 pages, 2324 KB

Open AccessArticle

Diffusiophoresis of a Charged Dielectric Fluid Droplet in a Cylindrical Pore in the Presence of Diffusion Potential

by Lily Chuang and Eric Lee

Colloids Interfaces 2026, 10(3), 47; https://doi.org/10.3390/colloids10030047 - 15 Jun 2026

Viewed by 440

We conducted a theoretical analysis on the diffusiophoretic motion of a dielectric droplet in a cylindrical pore in the presence of an induced diffusion potential, such as that in a NaCl electrolyte solution. The fundamental electrokinetic governing equations are solved using a patched pseudo-spectral method based on Chebyshev polynomials, coupled with a geometric mapping scheme to handle the irregular solution domain. The impact of the boundary confinement effect on droplet mobility is examined in detail. Interesting electrokinetic phenomena are found in this work, such as mobility reversal in narrow cylindrical pores with the droplet moving against the direction expected based on the classical Coulomb electrostatic law due to the strong boundary confinement effect. Moreover, “solidification phenomenon” is also found at some specific pore radius where the droplets move as rigid particles with no interior recirculating vortex flows regardless of the droplet viscosities. Corresponding critical points of

R_{w}^{*}

, the ratio of droplet radius to the cylindrical radius are found where the spinning orientation on the droplet surface changes each time as it passes them. The profound boundary confinement effect, both electrostatically and hydrodynamically, is responsible for these peculiar phenomena. The results presented here have direct applications in microfluidic and nanofluidic operations as well as drug delivery applications. Full article

(This article belongs to the Special Issue State of the Art of Colloid and Interface Science in Asia: 2nd Edition)

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14 pages, 1307 KB

Open AccessArticle

Transient Gel Diffusiophoresis of a Spherical Colloidal Particle

by Hiroyuki Ohshima

Micromachines 2025, 16(3), 266; https://doi.org/10.3390/mi16030266 - 26 Feb 2025

Viewed by 1333

Abstract

A general theory is presented to analyze the time-dependent, transient diffusiophoresis of a charged spherical colloidal particle in an uncharged gel medium containing a symmetrical electrolyte when an electrolyte concentration gradient is suddenly applied. We derive the inverse Laplace transform of an approximate expression for the relaxation function R(t), which describes the time-course of the ratio of the diffusiophoretic mobility of a weakly charged spherical colloidal particle, possessing a thin electrical double layer, to its steady-state diffusiophoretic mobility. The relaxation function depends on the mass density ratio of the particle to the electrolyte solution, the particle radius, the Brinkman screening length, and the kinematic viscosity. However, it does not depend on the type of electrolyte (e.g., KCl or NaCl), which affects only the steady-state gel diffusiophoretic mobility. It is also found that the expression for the relaxation function in transient gel diffusiophoresis of a weakly charged spherical colloidal particle with a thin electrical double layer takes the same form as that for its transient gel electrophoresis. Full article

(This article belongs to the Special Issue Electrokinetic Particle and Fluid Transport Driven by Solute Concentration and Thermal Gradients)

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13 pages, 1177 KB

Open AccessArticle

Transient Diffusiophoresis of a Spherical Colloidal Particle

by Hiroyuki Ohshima

Colloids Interfaces 2025, 9(1), 7; https://doi.org/10.3390/colloids9010007 - 19 Jan 2025

Cited by 1 | Viewed by 2341

Abstract

A general theoretical approach is introduced to analyze the time-dependent, transient diffusiophoresis of a charged spherical colloidal particle in a symmetrical electrolyte solution when an electrolyte concentration gradient is suddenly applied. We derive a closed-form approximate expression for the relaxation function R(t), which describes the time course of the diffusiophoretic mobility of a weakly charged spherical colloidal particle possessing a thin electrical double layer. The relaxation function depends on the mass density ratio of the particle to the electrolyte solution and the kinematic viscosity. However, it does not depend on the type of electrolyte (e.g., KCl or NaCl). It is also found that the expression for the relaxation function in transient diffusiophoresis of a weakly charged spherical colloidal particle with a thin electrical double layer takes the same form as that for its transient electrophoresis. Full article

(This article belongs to the Special Issue Biocolloids and Biointerfaces: 2nd Edition)

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12 pages, 1539 KB

Open AccessArticle

Gel Diffusiophoresis of a Spherical Colloidal Particle

by Hiroyuki Ohshima

Fluids 2024, 9(9), 203; https://doi.org/10.3390/fluids9090203 - 1 Sep 2024

Cited by 1 | Viewed by 3004

Abstract

A theoretical framework is established for the gel diffusiophoresis of a spherical colloidal particle moving through an uncharged dilute porous polymer gel medium when an electrolyte concentration gradient field is applied. The network of cross-linked polymer segments is treated as a porous skeleton containing an electrolyte solution using the Brinkman–Debye–Bueche model. We derive a general expression for the gel-diffusiophoretic mobility of a charged spherical colloidal particle. Based on this general mobility expression, we farther derive a closed-form approximate expression for the gel-diffusiophoretic mobility of a weakly charged spherical particle correct to the second order of the particle’s zeta potential. The obtained mobility expression depends on the Debye–Hückel parameter and the Brinkmann parameter. Full article

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19 pages, 4210 KB

Open AccessArticle

Self-Diffusiophoresis and Symmetry-Breaking of a Janus Dimer: Analytic Solution

by Eldad J. Avital and Touvia Miloh

Symmetry 2023, 15(11), 2019; https://doi.org/10.3390/sym15112019 - 3 Nov 2023

Cited by 2 | Viewed by 1876

Abstract

A self-diffusiophoretic problem is considered for a chemically active dimer consisting of two equal touching spherical colloids that are exposed to different fixed-flux and fixed-rate surface reactions. A new analytic solution for the autophoretic mobility of such a catalytic Janus dimer is presented in the limit of a small Péclet number and linearization of the resulting Robin-type boundary value problem for the harmonic solute concentration. Explicit solutions in terms of the physical parameters are first obtained for the uncoupled electrostatic and hydrodynamic problems. The dimer mobility is then found by employing the reciprocal theorem depending on the surface slip velocity and on the normal component of the shear stress acting on the inert dimer. Special attention is given to the limiting case of a Janus dimer composed of an inert sphere and a chemically active sphere where the fixed-rate reaction (Damköhler number) is infinitely large. Examples are given, comparing the numerical and approximate analytic solutions of the newly developed theory. Singular points arising in the model are discussed for a dimer with a fixed-rate reaction, and the flow field around the dimer is also analysed. The new developed theory introduces a fast way to compute the mobility of a freely suspended dimer and the induced flow field around it, and thus can also serve as a sub grid scale model for a multi-scale flow simulation. Full article

(This article belongs to the Special Issue Symmetry in Magnetohydrodynamic Flows and Their Applications)

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11 pages, 1603 KB

Open AccessArticle

Diffusiophoresis of a Soft Particle as a Model for Biological Cells

by Hiroyuki Ohshima

Colloids Interfaces 2022, 6(2), 24; https://doi.org/10.3390/colloids6020024 - 14 Apr 2022

Cited by 11 | Viewed by 4344

Abstract

We derive the general expression for the diffusiophoretic mobility of a soft particle (i.e., polyelectrolyte-coated hard particle) in a concentration gradient of electrolytes for the case in which the particle’s core size is large enough compared with the Debye length. Therefore, the particle surface can be regarded as planar, and the electrolyte concentration gradient is parallel to the core surface. The obtained expression can be applied for arbitrary values of the fixed charge density of the polyelectrolyte layer and the surface charge density of the particle core. We derive approximate analytic mobility expressions for soft particles of three types, i.e., (i) weakly charged soft particles, (ii) soft particles with a thick polyelectrolyte layer, in which the equilibrium electric potential deep inside the polyelectrolyte layer is equal to the Donnan potential, and (iii) soft particles with an uncharged polymer layer of finite thickness. Full article

(This article belongs to the Special Issue Biocolloids and Biointerfaces)

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9 pages, 1003 KB

Open AccessArticle

Diffusiophoresis of a Colloidal Cylinder at Small Finite Péclet Numbers

by Yu C. Chang and Huan J. Keh

Colloids Interfaces 2019, 3(2), 44; https://doi.org/10.3390/colloids3020044 - 15 Apr 2019

Cited by 3 | Viewed by 3399

Abstract

The diffusiophoretic migration of a circular cylindrical particle in a nonelectrolyte solution with a solute concentration gradient normal to its axis is analytically studied for a small but finite Péclet number

P e

. The interfacial layer of interaction between the solute molecules [...] Read more.

P e

. The interfacial layer of interaction between the solute molecules and the particle is taken to be thin, but the polarization of its mobile molecules is allowed. Using a method of matched asymptotic expansions, we solve the governing equations of conservation of the system and obtain an explicit formula for the diffusiophoretic velocity of the cylinder correct to the order

P e^{2}

. It is found that the perturbed solute concentration and fluid velocity distributions have the order

P e

, but the leading correction to the particle velocity has the higher order

P e^{2} \ln P e

. The correction to the particle velocity to the order

P e^{2}

can be either positive or negative depending on the polarization parameter of the thin interfacial layer, establishing that the solute convection effect is complicated and can enhance or retard the diffusiophoretic motion. The particle velocity at

P e = 0.6

can be about 17% smaller or 0.2% greater than that at

P e = 0

. Under practical conditions, the solute convection effect on the diffusiophoretic velocity is much greater for a cylindrical particle than for a spherical particle, whose leading correction has the order

P e^{2}

. Full article

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