The Experts below are selected from a list of 180 Experts worldwide ranked by ideXlab platform
Ángel V. Delgado - One of the best experts on this subject based on the ideXlab platform.
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Sedimentation velocity and potential in a concentrated colloidal suspension
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2001Co-Authors: Félix Carrique, Francisco J. Arroyo, Ángel V. DelgadoAbstract:Abstract The standard theory of the sedimentation velocity and potential of a concentrated suspension of charged spherical colloidal particles, developed by H. Ohshima on the basis of the Kuwabara cell model (J. Colloid Interf. Sci. 208 (1998) 295), has been numerically solved for the case of non-overlapping double layers and different conditions concerning volume fraction, and ζ-potential of the particles. The Onsager Relation between the sedimentation potential and the electrophoretic mobility of spherical colloidal particles in concentrated suspensions, derived by Ohshima for low ζ-potentials, is also analyzed as well as its appropriate range of validity. On the other hand, the above-mentioned Ohshima's theory has also been modified to include the presence of a dynamic Stern layer (DSL) on the particles’ surface. The starting point has been the theory that Mangelsdorf and White (J. Chem. Soc. Faraday Trans. 86 (1990) 2859) developed to calculate the electrophoretic mobility of a colloidal particle, allowing for the lateral motion of ions in the inner region of the double layer (DSL). The role of different Stern layer parameters on the sedimentation velocity and potential are discussed and compared with the case of no Stern layer present. For every volume fraction, the results show that the sedimentation velocity is lower when a Stern layer is present than that of Ohshima's prediction. Likewise, it is worth pointing out that the sedimentation field always decreases when a Stern layer is present, undergoing large changes in magnitude upon varying the different Stern layer parameters. In conclusion, the presence of a DSL causes the sedimentation velocity to increase and the sedimentation potential to decrease, in comparison with the standard case, for every volume fraction. Reasons for these behaviors are given in terms of the decrease in the magnitude of the induced electric dipole moment on the particles, and therefore on the relaxation effect, when a DSL is present. Finally, we have modified Ohshima's model of electrophoresis in concentrated suspensions, to fulfill the requirements of Shilov–Zharkhik's cell model. In doing so, the well-known Onsager Reciprocal Relation between sedimentation and electrophoresis previously obtained for the dilute case is again recovered but now for concentrated suspensions, being valid for every ζ-potential and volume fraction.
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Effect of a Dynamic Stern Layer on the Sedimentation Velocity and Potential in a Dilute Suspension of Colloidal Particles.
Journal of colloid and interface science, 2000Co-Authors: Félix Carrique, Francisco J. Arroyo, Ángel V. DelgadoAbstract:Abstract In this paper the theory of the sedimentation velocity and potential (gradient) in a dilute suspension of charged spherical colloidal particles developed by Ohshima et al. (H. Ohshima, T. W. Healy, L. R. White, and R. W. O'Brien, J. Chem. Soc., Faraday Trans. 2, 80, 1299 (1984)) has been modified to include the presence of a dynamic Stern layer on the particle surfaces. The starting point has been the theory that Mangelsdorf and White (C. S. Mangelsdorf, and L. R. White, J. Chem. Soc., Faraday Trans.86, 2859 (1990)) developed to calculate the electrophoretic mobility of a colloidal particle allowing for the lateral motion of ions in the inner region of the double layer (dynamic Stern layer). The effects of varying the different Stern layer parameters on the sedimentation velocity and potential are discussed and compared to the case when a Stern layer is absent. The influence of electrolyte concentration and ζ potential of the particles is also analyzed. The results show that regardless of the chosen set of Stern layer and solution parameters, the presence of a dynamic Stern layer causes the sedimentation velocity to increase and the sedimentation potential to decrease, in comparison with the standard case (no Stern layer present). These changes are almost negligible when sedimentation velocity is concerned, but they are very important when it comes to the sedimentation potential. A justification for this fact can be given in terms of an Onsager Reciprocal Relation, connecting the magnitudes of the sedimentation potential and the electrophoretic mobility. As previously reported, the presence of a dynamic Stern layer exerts a great influence on the electrophoretic mobility of a colloidal particle, and by means of the Onsager Relation, the same is confirmed to occur when the sedimentation potential is concerned.
Yung C. Liu - One of the best experts on this subject based on the ideXlab platform.
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Sedimentation Velocity and Potential in a Dilute Suspension of Charged Composite Spheres
Journal of colloid and interface science, 1997Co-Authors: Huan J. Keh, Yung C. LiuAbstract:Abstract The sedimentation of a charged composite particle composed of a solid core and a surrounding porous shell in an electrolyte solution is analytically studied. In the solvent-permeable and ion-penetrable porous surface layer of the particle, idealized hydrodynamic frictional segments with fixed charges are assumed to distribute at a uniform density. The equations which govern the ionic concentration distributions, the electric potential profile, and the fluid flow field inside and outside the surface layer of a charged composite particle migrating in an unbounded solution are linearized assuming that the system is only slightly distorted from equilibrium. Using a perturbation method, these linearized equations are solved for a composite sphere with the charge densities of the rigid core surface and of the surface layer as the small perturbation parameters. An analytical expression for the settling velocity of the composite sphere in closed form is obtained from a balance among its gravitational, electrostatic, and hydrodynamic forces. The result demonstrates that the presence of the fixed charges in the composite sphere slows down its settling velocity relative to that of an uncharged one. A closed-form formula for the sedimentation potential in a dilute suspension of identical charged composite spheres is also derived by using the requirement of zero net electric current. The Onsager Reciprocal Relation is found to be satisfied between sedimentation and electrophoresis. It is shown that spherically-symmetric “neutral” composite particles (bearing no net charge) can undergo electrophoresis, induce sedimentation potential, and experience a smaller settling velocity relative to corresponding uncharged particles. The direction of the electrophoretic velocity or the induced potential gradient is determined by the fixed charges in the porous surface layers of the particles. In the limiting cases, the analytical solutions describing the sedimentation velocity and sedimentation potential (or electrophoretic mobility) for charged composite spheres reduce to those for charged solid spheres and for charged porous spheres.
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Electrokinetic Flow in a Circular Capillary with a Surface Charge Layer
Journal of Colloid and Interface Science, 1995Co-Authors: Huan J. Keh, Yung C. LiuAbstract:Abstract An analytical study is presented of the steady electrokinetic flow in a long uniform circular capillary bearing a layer of adsorbed polyelectrolytes on its inside wall. In this solvent-permeable and ion-penetrable surface charge layer, idealized polyelectrolyte segments are assumed to distribute at a uniform density. The electrical potential and space charge density distributions on a cross section of the capillary are obtained by solving the linearized Poisson-Boltzmann equation. The fluid velocity profile due to the application of an electric field and a pressure gradient through the capillary is obtained from the analytical solution of a modified Navier-Stokes equation. Explicit formulas for the volumetric flow rate, the electro-osmotic velocity, the electric current and the streaming potential in the capillary are also derived. The results demonstrate that the structure of the surface charge layer can result in an augmented or a diminished electrokinetic flow relative to that in a capillary with bare walls, depending on the characteristics of the electrolyte solution, of the surface charge layer, and of the capillary. The Onsager Reciprocal Relation is found to be satisfied in the general case.
Masato Makino - One of the best experts on this subject based on the ideXlab platform.
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Electrokinetic boundary condition compatible with the Onsager Reciprocal Relation in the thin double layer approximation.
The Journal of chemical physics, 2008Co-Authors: Masao Doi, Masato MakinoAbstract:The boundary condition, which has been used in the conventional electrokinetic calculation in the thin double layer approximation, has a flaw that it does not give the Onsager Reciprocal Relation for the sedimentation of charged particle. We propose a new boundary condition, which satisfies the Reciprocal Relation, and derive a general form for the mobility matrix for the motion of a charged particle under the action of external force, torque, and electric field. We then calculate the mobility matrix explicitly for homogeneously charged spherical particle and discuss the effect of the surface slippage and the surface conductivity on the particle mobility and electric conductivity.
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Electrokinetic Boundary Condition Compatible with the Onsager Reciprocal Relation in the Thin Double Layer Approximation
AIP Conference Proceedings, 2008Co-Authors: Masao Doi, Masato MakinoAbstract:The boundary condition which has been used in the conventional electrokinetic calculation in the thin double layer approximation has a flaw that it does not give the Onsager Reciprocal Relation for the sedimentation of charged particle. We propose a new boundary condition which satisfies the Reciprocal Relation, and derive a general form for the mobility matrix for the motion of a charged particle under the action of external force, torque and electric field.
Félix Carrique - One of the best experts on this subject based on the ideXlab platform.
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Sedimentation velocity and potential in a concentrated colloidal suspension
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2001Co-Authors: Félix Carrique, Francisco J. Arroyo, Ángel V. DelgadoAbstract:Abstract The standard theory of the sedimentation velocity and potential of a concentrated suspension of charged spherical colloidal particles, developed by H. Ohshima on the basis of the Kuwabara cell model (J. Colloid Interf. Sci. 208 (1998) 295), has been numerically solved for the case of non-overlapping double layers and different conditions concerning volume fraction, and ζ-potential of the particles. The Onsager Relation between the sedimentation potential and the electrophoretic mobility of spherical colloidal particles in concentrated suspensions, derived by Ohshima for low ζ-potentials, is also analyzed as well as its appropriate range of validity. On the other hand, the above-mentioned Ohshima's theory has also been modified to include the presence of a dynamic Stern layer (DSL) on the particles’ surface. The starting point has been the theory that Mangelsdorf and White (J. Chem. Soc. Faraday Trans. 86 (1990) 2859) developed to calculate the electrophoretic mobility of a colloidal particle, allowing for the lateral motion of ions in the inner region of the double layer (DSL). The role of different Stern layer parameters on the sedimentation velocity and potential are discussed and compared with the case of no Stern layer present. For every volume fraction, the results show that the sedimentation velocity is lower when a Stern layer is present than that of Ohshima's prediction. Likewise, it is worth pointing out that the sedimentation field always decreases when a Stern layer is present, undergoing large changes in magnitude upon varying the different Stern layer parameters. In conclusion, the presence of a DSL causes the sedimentation velocity to increase and the sedimentation potential to decrease, in comparison with the standard case, for every volume fraction. Reasons for these behaviors are given in terms of the decrease in the magnitude of the induced electric dipole moment on the particles, and therefore on the relaxation effect, when a DSL is present. Finally, we have modified Ohshima's model of electrophoresis in concentrated suspensions, to fulfill the requirements of Shilov–Zharkhik's cell model. In doing so, the well-known Onsager Reciprocal Relation between sedimentation and electrophoresis previously obtained for the dilute case is again recovered but now for concentrated suspensions, being valid for every ζ-potential and volume fraction.
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Effect of a Dynamic Stern Layer on the Sedimentation Velocity and Potential in a Dilute Suspension of Colloidal Particles.
Journal of colloid and interface science, 2000Co-Authors: Félix Carrique, Francisco J. Arroyo, Ángel V. DelgadoAbstract:Abstract In this paper the theory of the sedimentation velocity and potential (gradient) in a dilute suspension of charged spherical colloidal particles developed by Ohshima et al. (H. Ohshima, T. W. Healy, L. R. White, and R. W. O'Brien, J. Chem. Soc., Faraday Trans. 2, 80, 1299 (1984)) has been modified to include the presence of a dynamic Stern layer on the particle surfaces. The starting point has been the theory that Mangelsdorf and White (C. S. Mangelsdorf, and L. R. White, J. Chem. Soc., Faraday Trans.86, 2859 (1990)) developed to calculate the electrophoretic mobility of a colloidal particle allowing for the lateral motion of ions in the inner region of the double layer (dynamic Stern layer). The effects of varying the different Stern layer parameters on the sedimentation velocity and potential are discussed and compared to the case when a Stern layer is absent. The influence of electrolyte concentration and ζ potential of the particles is also analyzed. The results show that regardless of the chosen set of Stern layer and solution parameters, the presence of a dynamic Stern layer causes the sedimentation velocity to increase and the sedimentation potential to decrease, in comparison with the standard case (no Stern layer present). These changes are almost negligible when sedimentation velocity is concerned, but they are very important when it comes to the sedimentation potential. A justification for this fact can be given in terms of an Onsager Reciprocal Relation, connecting the magnitudes of the sedimentation potential and the electrophoretic mobility. As previously reported, the presence of a dynamic Stern layer exerts a great influence on the electrophoretic mobility of a colloidal particle, and by means of the Onsager Relation, the same is confirmed to occur when the sedimentation potential is concerned.
Huan J. Keh - One of the best experts on this subject based on the ideXlab platform.
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Sedimentation Velocity and Potential in a Dilute Suspension of Charged Composite Spheres
Journal of colloid and interface science, 1997Co-Authors: Huan J. Keh, Yung C. LiuAbstract:Abstract The sedimentation of a charged composite particle composed of a solid core and a surrounding porous shell in an electrolyte solution is analytically studied. In the solvent-permeable and ion-penetrable porous surface layer of the particle, idealized hydrodynamic frictional segments with fixed charges are assumed to distribute at a uniform density. The equations which govern the ionic concentration distributions, the electric potential profile, and the fluid flow field inside and outside the surface layer of a charged composite particle migrating in an unbounded solution are linearized assuming that the system is only slightly distorted from equilibrium. Using a perturbation method, these linearized equations are solved for a composite sphere with the charge densities of the rigid core surface and of the surface layer as the small perturbation parameters. An analytical expression for the settling velocity of the composite sphere in closed form is obtained from a balance among its gravitational, electrostatic, and hydrodynamic forces. The result demonstrates that the presence of the fixed charges in the composite sphere slows down its settling velocity relative to that of an uncharged one. A closed-form formula for the sedimentation potential in a dilute suspension of identical charged composite spheres is also derived by using the requirement of zero net electric current. The Onsager Reciprocal Relation is found to be satisfied between sedimentation and electrophoresis. It is shown that spherically-symmetric “neutral” composite particles (bearing no net charge) can undergo electrophoresis, induce sedimentation potential, and experience a smaller settling velocity relative to corresponding uncharged particles. The direction of the electrophoretic velocity or the induced potential gradient is determined by the fixed charges in the porous surface layers of the particles. In the limiting cases, the analytical solutions describing the sedimentation velocity and sedimentation potential (or electrophoretic mobility) for charged composite spheres reduce to those for charged solid spheres and for charged porous spheres.
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Electrokinetic Flow in a Circular Capillary with a Surface Charge Layer
Journal of Colloid and Interface Science, 1995Co-Authors: Huan J. Keh, Yung C. LiuAbstract:Abstract An analytical study is presented of the steady electrokinetic flow in a long uniform circular capillary bearing a layer of adsorbed polyelectrolytes on its inside wall. In this solvent-permeable and ion-penetrable surface charge layer, idealized polyelectrolyte segments are assumed to distribute at a uniform density. The electrical potential and space charge density distributions on a cross section of the capillary are obtained by solving the linearized Poisson-Boltzmann equation. The fluid velocity profile due to the application of an electric field and a pressure gradient through the capillary is obtained from the analytical solution of a modified Navier-Stokes equation. Explicit formulas for the volumetric flow rate, the electro-osmotic velocity, the electric current and the streaming potential in the capillary are also derived. The results demonstrate that the structure of the surface charge layer can result in an augmented or a diminished electrokinetic flow relative to that in a capillary with bare walls, depending on the characteristics of the electrolyte solution, of the surface charge layer, and of the capillary. The Onsager Reciprocal Relation is found to be satisfied in the general case.
