Effect of Charged Boundary on the Electrophoresis in Newtonian and Carreau Fluid: Non-Totally Symmetric Problems
Date Issued
2007
Date
2007
Author(s)
Yeh, Li-Hsien
DOI
en-US
Abstract
The effect of the presence of a charged boundary on the electrophoretic behavior of an entity in a Newtonian fluid and a non-Newtonian fluid are investigated in this study for various types of problems through solving numerically the governing electrokinetic equations by a finite element method. Previous analyses are modified by using a more realistic electrostatic force formula. This expression derived, which is based on Maxwell stress tensor, is applicable to both rigid and soft particles for various types of surface conditions and to both totally symmetric and asymmetric geometries. These analyses considered in this study include that, for example, problems of total symmetric nature such as an isolated sphere moving along the axis of a cylindrical pore and at the center of a spherical cavity, and those of not total symmetric nature such as two spheres moving along the axis of a cylindrical pore, a sphere moving toward to a large disk, and a sphere at an arbitrary position in a spherical cavity. All of the above eletrophoetic problems investigated in this study are under the conditions of low surface potential and weak applied electric field.
We shown that the qualitative behavior of a particle depends largely on how significant of the boundary effect is, the geometries of a particle and a boundary, the separation distance between a particle and a boundary or between two particles, the thickness of double layer, and the nature of a fluid. In addition to the fact that the effect of shear-thinning is advantageous to the movement of a sphere, several other results are also observed. For example, the presence of a boundary has the effect of increasing the conventional hydrodynamic drag on a particle through a non-slip condition on the former. Also, a decrease in the thickness of double layer surrounding a sphere has the effect of increasing the electrostatic force acting on its surface so that its mobility increases, and increases the effect of the shear-thinning for a Carreau fluid. However, this might not be the case when an uncharged particle is placed in a positively charged boundary, where the electroosmotic flow and/or osmotic pressure force plays a role, for example, the mobility can exhibit a local extreme and the direction of electrophoresis can change. Also, the effect of shear-thinning is important only if the thickness of double layer is either sufficiently thin or sufficiently thick.
Subjects
電泳
泳動度
帶電邊界效應
固定表面電位
固定表面電荷
非牛頓流體
卡羅模式
Electrophoresis
Mobility
Effect of charged boundary
Constant surface potential
Constant surface charge
Non-Newtonian fluid
Carreau model
Type
thesis