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Sedimentation velocity and potential in concentrated suspensions of charged composite spheres
Date Issued
2010
Date
2010
Author(s)
Chiu, Yu-Si
Abstract
The body-force-driven migration in a homogeneous suspension of charged composite spherical particles, each with the structure of a solid core surrounded by a porous shell, in an electrolyte solution is analyzed. The porous shell of a particle is treated as a solvent-permeable and ion-penetrable surface polymer layer of finite thickness, in which idealized hydrodynamic frictional segments with fixed charges are assumed to distribute at a uniform density. The effects of particle interactions are taken into account by employing a unit cell model. The overlap of the electric double layers of adjacent particles is allowed and the relaxation effect in the double layer surrounding each particle is considered. The electrokinetic equations which govern the electrostatic potential profile, the ionic concentration (or electrochemical potential energy) distributions, and the fluid velocity field inside and outside the surface layer of the charged composite particle migrating in a unit cell are linearized by assuming that the system is only slightly distorted from equilibrium. Using a regular perturbation method, these linearized equations are solved for a symmetrically charged electrolyte with the fixed charge densities of the rigid core surface and surface layer of the composite sphere as the small perturbation parameters.
An analytical expression for the settling velocity of the composite sphere is obtained from a balance among its gravitational, electrostatic, and hydrodynamic forces. A closed-form formula for the sedimentation potential in a suspension of identical charged composite spheres is also derived by using the requirement of zero net electric current. The dependence of the sedimentation velocity and sedimentation potential of the suspension on the particle volume fraction and other properties of the particle-solution system is found to be quite complicated. In the limiting cases, the analytical solutions describing the sedimentation velocity and potential for charged composite spheres reduce to those for charged solid spheres and for charged porous spheres.
An analytical expression for the settling velocity of the composite sphere is obtained from a balance among its gravitational, electrostatic, and hydrodynamic forces. A closed-form formula for the sedimentation potential in a suspension of identical charged composite spheres is also derived by using the requirement of zero net electric current. The dependence of the sedimentation velocity and sedimentation potential of the suspension on the particle volume fraction and other properties of the particle-solution system is found to be quite complicated. In the limiting cases, the analytical solutions describing the sedimentation velocity and potential for charged composite spheres reduce to those for charged solid spheres and for charged porous spheres.
Subjects
composite spheres
Sedimentation
suspensions
Type
thesis
File(s)
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Name
ntu-99-R97524056-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):65b71102cc1a9ec745e7bb27eb32ddec