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Huan J Keh - One of the best experts on this subject based on the ideXlab platform.

  • Start-Up Electrophoresis of a Cylindrical Particle with Arbitrary Double Layer Thickness.
    The Journal of Physical Chemistry B, 2020
    Co-Authors: Huan J Keh
    Abstract:

    The start-up of electrophoretic motion of a charged circular cylindrical particle in an unbounded solution of arbitrary electrolytes is analytically investigated. The modified Stokes equation for the transient fluid flow field is solved by using the Laplace transform. Analytical formulas for the time-evolving electrophoretic velocities of the dielectric cylinder are determined for the transversely and axially imposed electric fields, and they can be superimposed linearly for an imposed electric field of arbitrary direction. The transient electrophoretic velocities normalized by their respective steady-state values increase monotonically with an increase in the ratio of the particle radius to the Debye screening length but decrease monotonically with an increase in the particle-to-fluid density ratio, keeping the other parameter unchanged. The normalized electrophoretic acceleration of the particle decreases monotonically with the elapsed time. In general, the electrophoretic velocity of the cylindrical particle is not collinear with the arbitrarily oriented imposed electric field. The effect of the relaxation time for the transient electrophoresis is much more important for a cylindrical particle than for a spherical particle.

  • start up electrophoresis of a cylindrical particle with arbitrary Double Layer Thickness
    Journal of Physical Chemistry B, 2020
    Co-Authors: Huan J Keh
    Abstract:

    The start-up of electrophoretic motion of a charged circular cylindrical particle in an unbounded solution of arbitrary electrolytes is analytically investigated. The modified Stokes equation for t...

  • Diffusiophoresis of a charged particle in a charged cavity with arbitrary electric Double Layer Thickness
    Microfluidics and Nanofluidics, 2018
    Co-Authors: Ya C. Chiu, Huan J Keh
    Abstract:

    An analysis is presented for the diffusiophoretic motion of a charged colloidal sphere located at the center of a charged spherical cavity filled with an electrolyte solution at the quasisteady state for the case of arbitrary electric Double Layers. The electrokinetic equations governing the ionic concentration, electric potential, and velocity distributions in the fluid are linearized with assumption that the system is slightly distorted from equilibrium. These linearized differential equations are solved using a perturbation method with the zeta potentials of the particle and cavity as the small perturbation parameters. An explicit formula for the diffusiophoretic velocity of the particle as a combination of the electrophoretic and chemiphoretic contributions valid for arbitrary values of $$\kappa a$$ and $$a/b$$ is obtained by balancing the electrostatic and hydrodynamic forces exerted on it, where $$\kappa$$ is the Debye screening parameter, $$a$$ is the radius of the particle, and $$b$$ is the radius of the cavity. The effect of the charged cavity wall on the diffusiophoresis of the particle is interesting and can be significant. The contributions from the diffusioosmotic (electroosmotic and chemiosmotic) flow taking place along the cavity wall and from the wall-corrected diffusiophoretic force to the particle velocity are comparably important, and this diffusioosmotic flow can reverse the direction of diffusiophoresis. The particle velocity in general increases with an increase in $$\kappa a$$ and decreases with an increase in $$a/b$$ , but exceptions exist.

  • Electrophoresis of a Charged Soft Particle in a Charged Cavity with Arbitrary Double-Layer Thickness
    The Journal of Physical Chemistry B, 2013
    Co-Authors: Wei J. Chen, Huan J Keh
    Abstract:

    An analysis for the quasi-steady electrophoretic motion of a soft particle composed of a charged spherical rigid core and an adsorbed porous Layer positioned at the center of a charged spherical cavity filled with an arbitrary electrolyte solution is presented. Within the porous Layer, frictional segments with fixed charges are assumed to distribute uniformly. Through the use of the linearized Poisson–Boltzmann equation and the Laplace equation, the equilibrium Double-Layer potential distribution and its perturbation caused by the applied electric field are separately determined. The modified Stokes and Brinkman equations governing the fluid flow fields outside and inside the porous Layer, respectively, are solved subsequently. An explicit formula for the electrokinetic migration velocity of the soft particle in terms of the fixed charge densities on the rigid core surface, in the porous Layer, and on the cavity wall is obtained from a balance between its electrostatic and hydrodynamic forces. This formul...

  • Magnetohydrodynamic effects on a charged colloidal sphere with arbitrary Double-Layer Thickness.
    The Journal of Chemical Physics, 2010
    Co-Authors: Tzu H. Hsieh, Huan J Keh
    Abstract:

    An analytical study is presented for the magnetohydrodynamic (MHD) effects on a translating and rotating colloidal sphere in an arbitrary electrolyte solution prescribed with a general flow field and a uniform magnetic field at a steady state. The electric Double Layer surrounding the charged particle may have an arbitrary Thickness relative to the particle radius. Through the use of a simple perturbation method, the Stokes equations modified with an electric force term, including the Lorentz force contribution, are dealt by using a generalized reciprocal theorem. Using the equilibrium Double-Layer potential distribution from solving the linearized Poisson–Boltzmann equation, we obtain closed-form formulas for the translational and angular velocities of the spherical particle induced by the MHD effects to the leading order. It is found that the MHD effects on the particle movement associated with the translation and rotation of the particle and the ambient fluid are monotonically increasing functions of κ...

Mitthan Lal Kansal - One of the best experts on this subject based on the ideXlab platform.

  • Estimation of the electric Double Layer Thickness in the presence of two types of ions in soil water
    Applied Clay Science, 2014
    Co-Authors: K. K. Mahanta, Govinda C. Mishra, Mitthan Lal Kansal
    Abstract:

    Abstract The deficit of charges on the clay surface is balanced by the cations in soil water forming the electric Double Layer (EDL). In sodic soil monovalent Na + ions are dominant and hence, Thickness of the EDL ( β ) is more than in the nonsodic soil where bivalent Ca 2 + ions are dominant. For reclaiming the sodic soil, gypsum is added as a source of Ca 2 + ions to replace the Na + ions from the EDL as well as for reducing β . In this paper, an analytical solution is derived to the nonlinear Poisson–Boltzman equation and the solution is used for computing β exactly. A comparison is made between β computed from the solutions of linearized and nonlinear Poisson–Boltzman equation. The solution to the linearized Poisson–Boltzman equation overestimates β . Therefore, it is appropriate to adopt the solution of the nonlinear Poisson–Boltzman equation for computing β .

  • estimation of electric Double Layer Thickness from linearized and nonlinear solutions of poisson boltzman equation for single type of ions
    Applied Clay Science, 2012
    Co-Authors: K. K. Mahanta, Govinda C. Mishra, Mitthan Lal Kansal
    Abstract:

    Abstract The electric Double Layer (EDL) plays an important role in the sodification and desodification processes. The Gouy (1910) and Chapman (1913) solution to the linearized Poisson–Boltzman equation is mostly used for quantification of the EDL. In this paper, a simplified analytical solution to the nonlinear Poisson–Boltzman equation is derived. The solution of the nonlinear Poisson–Boltzman equation given by Appelo and Postma (2005) is supplemented with a method for determining the EDL Thickness, β. It is found that the solution to the linearized equation overestimates β. However, at higher bulk concentrations, β computed from the solution of linearized Poisson–Boltzman equation closely matches with that computed from the solution to the nonlinear equation. The difference in β computed using the two solutions being significant for lower Cb, solution given by Appelo and Postma should be used for finding true value of β.

  • Estimation of electric Double Layer Thickness from linearized and nonlinear solutions of Poisson–Boltzman equation for single type of ions
    Applied Clay Science, 2012
    Co-Authors: K. K. Mahanta, Govinda C. Mishra, Mitthan Lal Kansal
    Abstract:

    Abstract The electric Double Layer (EDL) plays an important role in the sodification and desodification processes. The Gouy (1910) and Chapman (1913) solution to the linearized Poisson–Boltzman equation is mostly used for quantification of the EDL. In this paper, a simplified analytical solution to the nonlinear Poisson–Boltzman equation is derived. The solution of the nonlinear Poisson–Boltzman equation given by Appelo and Postma (2005) is supplemented with a method for determining the EDL Thickness, β. It is found that the solution to the linearized equation overestimates β. However, at higher bulk concentrations, β computed from the solution of linearized Poisson–Boltzman equation closely matches with that computed from the solution to the nonlinear equation. The difference in β computed using the two solutions being significant for lower Cb, solution given by Appelo and Postma should be used for finding true value of β.

Jyh-ping Hsu - One of the best experts on this subject based on the ideXlab platform.

  • Effect of eccentricity on the electroosmotic flow in an elliptic channel
    Journal of Colloid and Interface Science, 2015
    Co-Authors: Bo-tau Liu, Shiojenn Tseng, Jyh-ping Hsu
    Abstract:

    The electroosmotic flow in an elliptic channel having constant surface potential (CSP) or charge density (CSCD) is considered at low potential and arbitrary Double Layer Thickness. Analytical expressions for the flow velocity and the corresponding asymptotic results for thick Double Layers that are readily applicable to experimentalists are recovered. For the range of salt concentration usually encountered in practice, the mean flow velocity for the case of CSP differs both quantitatively and qualitatively from that for the case of CSCD. Using an equivalent circular channel to simulate an elliptic one is inappropriate, in general, neither is assuming electroneutrality on the channel axis even when Double Layer is ca. 1/3 of the equivalent channel radius.

  • Electrophoresis of a particle at an arbitrary surface potential and Double Layer Thickness: importance of nonuniformly charged conditions.
    Langmuir, 2012
    Co-Authors: Jyh-ping Hsu, Hsiao-ting Huang, Li-hsien Yeh, Shiojenn Tseng
    Abstract:

    Recent advances in material science and technology yield not only various kinds of nano- and sub-micro-scaled particles but also particles of various charged conditions such as Janus particles. The characterization of these particles can be challenging because conventional electrophoresis theory is usually based on drastic assumptions that are unable to realistically describe the actual situation. In this study, the influence of the nonuniform charged conditions on the surface of a particle at an arbitrary level of surface potential and Double Layer Thickness on its electrophoretic behavior is investigated for the first time in the literature taking account of the effect of Double-Layer polarization. Several important results are observed. For instance, for the same averaged surface potential, the mobility of a nonuniformly charged particle is generally smaller than that of a uniformly charged particle, and the difference between the two depends upon the Thickness of Double Layer. This implies that using the conventional electrophoresis theory may result in appreciable deviation, which can be on the order of ca. 20%. In addition, the nonuniform surface charge can yield Double vortex in the vicinity of a particle by breaking the symmetric of the flow field, which has potential applications in mixing and/or regulating the medium confined in a submicrometer-sized space, where conventional mixing devices are inapplicable.

  • Electrophoresis of an arbitrarily oriented toroid in an unbounded electrolyte solution.
    Colloids and Surfaces B: Biointerfaces, 2011
    Co-Authors: Jyh-ping Hsu, Chih-hao Chou, Chao-chung Kuo, Shiojenn Tseng
    Abstract:

    The electrophoresis of a non-conducting rigid toroid in an unbounded Newtonian electrolyte solution having an arbitrary orientation is modeled theoretically under the condition of low surface potential. In particular, the influence of the orientation angle, defined as the angle between the applied electric field and the center line of the toroid, on its electrophoretic behavior as the Thickness of Double Layer varies is investigated. The results of numerical simulation reveal that both the Thickness of Double Layer and the orientation angle can influence appreciably the mobility of the toroid. In general, for a fixed orientation, the mobility of the toroid increases with decreasing Double Layer Thickness, and for a fixed Double Layer Thickness, the scaled electrophoresis mobility increases with increasing orientation angle. If the Double Layer is infinitely thin, then the present result reduces to that predicted by Smoluchowski, that is, the scaled electrophoretic mobility of the toroid is unity, and is not influenced by its shape. On the other hand, if it is infinitely thick, then the present result follows the same trend as that predicted by Henry, that is, the electrophoretic mobility of the toroid depends highly on its form effect, and the thicker the Double Layer the smaller that mobility. If the Thickness of Double Layer is comparable to the radius of a toroid, the variation in the orientation angle can lead to as much as 40% difference in the mobility.

  • Diffusiophoresis of concentrated suspensions of spherical particles with distinct ionic diffusion velocities.
    The Journal of Physical Chemistry B, 2007
    Co-Authors: Jyh-ping Hsu, James Lou, Eric Lee
    Abstract:

    The diffusiophoresis of a concentrated spherical dispersion of colloidal particles subject to a small electrolyte gradient is analyzed theoretically for an arbitrary zeta potential and Double Layer Thickness. In particular, the influence of the difference in the diffusivities of cations and anions is discussed. A unit cell model is used to simulate a spherical dispersion, and a pseudospectral method is adopted to solve the equations governing the phenomenon under consideration. We show that, as in the case of an infinitely dilute dispersion, when the diffusivities of cations and anions are different, the diffusiophoretic mobility is no longer an even function of the zeta potential or Double Layer Thickness. In contrast to the case of identical diffusivity of cations and anions, a local electric field is induced in the present case due to an unbalanced charge distribution between higher and lower concentration regions. Depending upon the direction of this induced electric field, the diffusiophoretic mobility can be larger or smaller than that for the case of identical diffusivity. The diffusiophoretic mobility is influenced mainly by the induced electric field arising from the difference in the ionic diffusivities, the concentration gradient, and the effect of Double Layer polarization.

  • Effect of charged boundary on electrophoresis: Sphere in spherical cavity at arbitrary potential and Double-Layer Thickness.
    Journal of Colloid and Interface Science, 2007
    Co-Authors: Jyh-ping Hsu, Zheng-syun Chen, Li-hsien Yeh
    Abstract:

    The boundary effect on electrophoresis is investigated by considering a spherical particle at an arbitrary position in a spherical cavity. Our previous analysis is extended to the case where the effect of Double-Layer polarization can be significant. Also, the effect of a charged boundary, which yields an electroosmotic flow and a pressure gradient, thereby making the problem under consideration more complicated, is investigated. The influences of the level of the surface potential, the Thickness of Double Layer, the relative size of a sphere, and its position in a cavity on the electrophoretic behavior of the sphere are discussed. Some results that are of practical significance are observed. For example, if a positively charged sphere is placed in an uncharged cavity, its mobility may have a local minimum as the Thickness of the Double Layer varies. If an uncharged sphere is placed in a positively charged cavity, the mobility may have a local minimum as the position of the sphere varies. Also, if the size of a sphere is fixed, its mobility may have a local minimum as the size of a cavity varies. These provide useful information for the design of an electrophoresis apparatus.

Eric Lee - One of the best experts on this subject based on the ideXlab platform.

  • Electrophoresis of a soft particle within a cylindrical pore: polarization effect with the nonlinear Poisson-Boltzmann equation.
    The Journal of Physical Chemistry B, 2010
    Co-Authors: Cheng-hsuan Huang, Wen-li Cheng, Eric Lee
    Abstract:

    Electrophoresis of a soft particle along the centerline of a cylindrical pore is investigated theoretically in this study. The soft particle consists of an inner hard sphere covered by a concentric porous Layer with fixed charge uniformly distributed in it. The polarization effect, the deformation of ion clouds surrounding the particle due to convection flow, is taken into account properly by adopting the full nonlinear Poisson-Boltzmann equation. The study reveals that recent investigation in the literature without consideration of the polarization effect could severely overestimate the particle mobility up to nearly two times if the fixed charge in the porous Layer is high. The boundary effect in terms of the reduction of particle mobility is very significant when the Double Layer is thick and diminishes as it gets very thin. The effect of the highly charged cylindrical wall is analyzed, in particular, among other factors of electrokinetic interest. The presence of the cylindrical wall retards the particle motion in general, as compared with an isolated particle. With the generation of an electroosmotic flow, however, the charged wall can either enhance the particle motion or deter it, depending on the surface potential on the wall and the Double-Layer Thickness. The thinner the Double Layer, the more significant the influence of the osmotic flow on the particle motion in general. The direction of particle motion may even change twice as the reciprocal of the Double-Layer Thickness increases when both the wall and the particle are highly charged. This is due to the competition between the electric driving force of the charged particle and the hydrodynamic retarding force from the background electroosmotic flow. This has direct impact in practical applications of nanofluidics when a weak electric field is applied. Conducting operations near these critical Double-Layer Thicknesses should be avoided in practice.

  • Diffusiophoresis of a Spherical Particle Normal to a Plane
    The Journal of Physical Chemistry C, 2008
    Co-Authors: James Lou, Eric Lee
    Abstract:

    Diffusiophoresis of a spherical colloidal particle normal to a plane subject to a uniform electrolyte concentration gradient is investigated theoretically for arbitrary Double Layer Thickness and surface potential. The governing general electrokinetic equations are put in terms of bipolar spherical coordinates and solved numerically with a pseudospectral method based on Chebyshev polynomial. The effects of key parameters are examined such as the Double Layer Thickness, surface potential, and the distance between the particle and the plane. It is found, among other things, that the presence of the boundary has a retardation effect on the motion of the particle, provided that the Double Layer does not touch the planar boundary. If it does, however, the velocity of the particle will exhibit a maximum as the Double Layer just loses touch of the plane, thanks to the competitive force of the polarization effect. The planar boundary poses not only as a conventional hydrodynamic retarding force, but also may dist...

  • Electrophoresis in concentrated dispersions of charged porous spheres
    Chemical Engineering Science, 2008
    Co-Authors: Eric Lee
    Abstract:

    Abstract Electrophoresis in a concentrated suspension of charged porous spheres is investigated theoretically, taking into account of the polarization effect of Double Layer in particular. The Double Layer Thickness and fixed charge density of the porous spheres are arbitrary and Double Layer overlapping is considered as well. A pseudo-spectral method based on Chebyshev polynomial is used to solve the resulted general electrokinetic equations. Local extrema are observed in the mobility profile as the Double Layer Thickness varies, which is absent in previous theoretical studies neglecting polarization effect but agrees well with the experimental observations in the literature, indicating the importance of polarization effect in correctly interpreting the electrophoretic experimental results. A simple mutual transform of mobility predictions between Levine–Neale and Shilov–Zharkikh boundary conditions is established and confirmed by direct calculations, which facilitates the dialogue between theoretical and experimental researches. In general, the higher the fixed charge density, the more significant the polarization effect is.

  • Diffusiophoresis of concentrated suspensions of spherical particles with distinct ionic diffusion velocities.
    The Journal of Physical Chemistry B, 2007
    Co-Authors: Jyh-ping Hsu, James Lou, Eric Lee
    Abstract:

    The diffusiophoresis of a concentrated spherical dispersion of colloidal particles subject to a small electrolyte gradient is analyzed theoretically for an arbitrary zeta potential and Double Layer Thickness. In particular, the influence of the difference in the diffusivities of cations and anions is discussed. A unit cell model is used to simulate a spherical dispersion, and a pseudospectral method is adopted to solve the equations governing the phenomenon under consideration. We show that, as in the case of an infinitely dilute dispersion, when the diffusivities of cations and anions are different, the diffusiophoretic mobility is no longer an even function of the zeta potential or Double Layer Thickness. In contrast to the case of identical diffusivity of cations and anions, a local electric field is induced in the present case due to an unbalanced charge distribution between higher and lower concentration regions. Depending upon the direction of this induced electric field, the diffusiophoretic mobility can be larger or smaller than that for the case of identical diffusivity. The diffusiophoretic mobility is influenced mainly by the induced electric field arising from the difference in the ionic diffusivities, the concentration gradient, and the effect of Double Layer polarization.

  • Dynamic electrophoresis of droplet dispersions at low surface potentials
    Journal of Colloid and Interface Science, 2007
    Co-Authors: Jyh-ping Hsu, Wei-lun Min, Eric Lee
    Abstract:

    The dynamic electrophoresis of a dispersion of spherical droplets under conditions of low surface potential and arbitrary Double-Layer Thickness and droplet volume fraction is analyzed. A cell model with the Shilov-Zharkikh boundary condition for the electric potential is adopted to simulate a dispersion, and the governing equations and the associated boundary conditions are solved by a pseudo-spectral method based on Chebyshev polynomials. The influence of the frequency of the applied electric field, the volume fraction of the droplets, the Thickness of the Double Layer, and the relative magnitude of the viscosity of the droplet fluid on the electrophoretic behavior of a dispersion is discussed.

K. K. Mahanta - One of the best experts on this subject based on the ideXlab platform.

  • Estimation of the electric Double Layer Thickness in the presence of two types of ions in soil water
    Applied Clay Science, 2014
    Co-Authors: K. K. Mahanta, Govinda C. Mishra, Mitthan Lal Kansal
    Abstract:

    Abstract The deficit of charges on the clay surface is balanced by the cations in soil water forming the electric Double Layer (EDL). In sodic soil monovalent Na + ions are dominant and hence, Thickness of the EDL ( β ) is more than in the nonsodic soil where bivalent Ca 2 + ions are dominant. For reclaiming the sodic soil, gypsum is added as a source of Ca 2 + ions to replace the Na + ions from the EDL as well as for reducing β . In this paper, an analytical solution is derived to the nonlinear Poisson–Boltzman equation and the solution is used for computing β exactly. A comparison is made between β computed from the solutions of linearized and nonlinear Poisson–Boltzman equation. The solution to the linearized Poisson–Boltzman equation overestimates β . Therefore, it is appropriate to adopt the solution of the nonlinear Poisson–Boltzman equation for computing β .

  • estimation of electric Double Layer Thickness from linearized and nonlinear solutions of poisson boltzman equation for single type of ions
    Applied Clay Science, 2012
    Co-Authors: K. K. Mahanta, Govinda C. Mishra, Mitthan Lal Kansal
    Abstract:

    Abstract The electric Double Layer (EDL) plays an important role in the sodification and desodification processes. The Gouy (1910) and Chapman (1913) solution to the linearized Poisson–Boltzman equation is mostly used for quantification of the EDL. In this paper, a simplified analytical solution to the nonlinear Poisson–Boltzman equation is derived. The solution of the nonlinear Poisson–Boltzman equation given by Appelo and Postma (2005) is supplemented with a method for determining the EDL Thickness, β. It is found that the solution to the linearized equation overestimates β. However, at higher bulk concentrations, β computed from the solution of linearized Poisson–Boltzman equation closely matches with that computed from the solution to the nonlinear equation. The difference in β computed using the two solutions being significant for lower Cb, solution given by Appelo and Postma should be used for finding true value of β.

  • Estimation of electric Double Layer Thickness from linearized and nonlinear solutions of Poisson–Boltzman equation for single type of ions
    Applied Clay Science, 2012
    Co-Authors: K. K. Mahanta, Govinda C. Mishra, Mitthan Lal Kansal
    Abstract:

    Abstract The electric Double Layer (EDL) plays an important role in the sodification and desodification processes. The Gouy (1910) and Chapman (1913) solution to the linearized Poisson–Boltzman equation is mostly used for quantification of the EDL. In this paper, a simplified analytical solution to the nonlinear Poisson–Boltzman equation is derived. The solution of the nonlinear Poisson–Boltzman equation given by Appelo and Postma (2005) is supplemented with a method for determining the EDL Thickness, β. It is found that the solution to the linearized equation overestimates β. However, at higher bulk concentrations, β computed from the solution of linearized Poisson–Boltzman equation closely matches with that computed from the solution to the nonlinear equation. The difference in β computed using the two solutions being significant for lower Cb, solution given by Appelo and Postma should be used for finding true value of β.