Diffusiophoresis of a charged porous shell in electrolyte gradients

Colloids and Interfaces

2020

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The diffusiophoresis in a suspension of charged soft particles in electrolyte solution is analyzed. Each soft particle is composed of a hard core of radius r0 and surface charge density σ and an adsorbed fluid-penetrable porous shell of thickness a−r0 and fixed charge density Q. The effect of particle interactions is considered by using a unit cell model. The ionic concentration, electric potential, and fluid velocity distributions in a unit cell are solved as power expansions in σ and Q, and an explicit formula for the diffusiophoretic velocity of the soft particle is derived from a balance between the hydrodynamic and electrostatic forces exerted on it. This formula is correct to the second orders of σ and Q and valid for arbitrary values of κa, λa, r0/a, and the particle volume fraction of the suspension, where κ is the Debye screening parameter and λ is the reciprocal of a length featuring the flow penetration into the porous shell. The effects of the physical characteristics and particle interactions on the diffusiophoresis (including electrophoresis and chemiphoresis) in a suspension of charged soft particles, which become those of hard particles and porous particles in the limits r0=a and r0=0, respectively, are significant and complicated.

Section: Resultsmentioning

confidence: 99%

Section: Velocity Of the Particlementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Diffusiophoresis in Suspensions of Charged Soft Particles

Lin

Colloids and Interfaces

2020

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“…In the past, some formulas for the steady electrophoretic mobility of a charged particle were derived analytically for the cases of hard sphere (impermeable to both the solvent and small ions) , porous sphere (permeable) , soft sphere (hard in the core but porous in the surface layer) , and porous spherical shell (e.g. microcapsule or vesicle) . The soft particle and porous shell approach to the full porous particle when the core shrinks to zero.…”

Section: Introductionmentioning

confidence: 99%

Transient electrophoresis of a charged porous particle

Lai

2020

Electrophoresis

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Transient electrophoresis of a charged porous particleThe starting electrophoretic motion of a porous, uniformly charged, spherical particle, which models a solvent-permeable and ion-penetrable polyelectrolyte coil or floc of nanoparticles, in an arbitrary electrolyte solution due to the sudden application of an electric field is studied for the first time. The unsteady Stokes/Brinkman equations with the electric force term governing the fluid velocity fields are solved by means of the Laplace transform. An analytical formula for the electrophoretic mobility of the porous sphere is obtained as a function of the dimensionless parameters κa, λa, ρ p /ρ, and νt/a 2 , where a is the radius of the particle, κ is the Debye screening parameter, λ is the reciprocal of the square root of the fluid permeability in the particle, ρ p and ρ are the mass densities of the particle and fluid, respectively, ν is the kinematic viscosity of the fluid, and t is the time. The electrophoretic mobility normalized by its steady-state value increases monotonically with increases in νt/a 2 and κa, but decreases monotonically with an increase in ρ p /ρ, keeping the other parameters unchanged. In general, a porous particle with a high fluid permeability trails behind an identical porous particle with a lower permeability and a corresponding hard particle in the growth of the normalized electrophoretic mobility The normalized electrophoretic acceleration of the porous sphere decreases monotonically with an increase in the time and increases with an increase in λa from zero at λa = 0.

“…A porous shell is often employed to model a permeable microcapsule or vesicle, − and the sedimentation and other electrokinetic phenomena of a charged porous shell are of interest. , Recently, analytical formulas of the electrophoretic mobility and diffusiophoretic mobility were derived for a charged spherical porous shell. , These formulas reduce to those obtained for an intact porous sphere ,− when the inner radius of the spherical shell equals zero. However, the sedimentation velocity and potential in solutions of charged porous shells have not been analyzed yet.…”

Section: Introductionmentioning

confidence: 99%

Sedimentation Velocity and Potential in Dilute Suspensions of Charged Porous Shells

Yeh

2018

J. Phys. Chem. B

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The sedimentation of a charged spherical porous shell with arbitrary inner and outer radii, which can model a permeable microcapsule or vesicle, in a general electrolyte solution is analytically examined. The relaxation effect in the electric double layers of arbitrary thickness around the porous shell is considered. The differential equations governing the electric potential profile, ionic electrochemical potential energy (or concentration) distributions, and fluid velocity field are linearized by taking the system to be only slightly distorted from equilibrium. These linearized equations are solved using a perturbation method with the density of the fixed charge of the porous shell as the small perturbation parameter. Closed-form formulas for the sedimentation velocity of a porous shell and sedimentation potential in a suspension of porous shells are obtained from a force balance and a zero current requirement, respectively. Both the charge-induced sedimentation velocity retardation and sedimentation potential are monotonic increasing functions of the relative shell thickness, and these increases are substantial if the shell is thin. The sedimentation velocity and potential are complex functions of the electrokinetic radius and normalized flow penetration length of the porous shell. In the limit of the porous shells with zero inner radius, our formulas for the sedimentation velocity and potential reduce to the results obtained for the intact porous spheres.