Electrophoresis Behavior of a Rigid Particles and Liquid Droplet Normal to a Charged Plane
Date Issued
2015
Date
2015
Author(s)
Wang, Tsung-Yu
Abstract
The electrophoretic behavior of a spherical rigid particle or a non-conducting liquid drop normal to a charged plane is investigated in this study. Due to the particular physical configurations, the systems were characterized by bipolar and sphere coordinates respectively. The coupled electrical potential, ion conservation and hydrodynamic equations, or the so-called electrokinetic equations, are linearized by assuming the applied external electric field is weak. A pseudo-spectral method based on Chebyshev polynomials and Newton-Raphson iteration scheme are adopted to solve the resulting electrokinetic equations numerically. When the particle is near a solid boundary, the presence of the boundary will affect the particle motion significantly. The electrophoretic mobility of the particle is affected by the distance to the charged plane. We conclude that the thinner the double layer and/or the larger the particle-surface distance, the greater the mobility of the particle. Moreover, a charged plane can exert electro-osmosis flow so dominant that sometimes it may even reverse the direction of the particle motion. This phenomenon can be enhanced by the effect of electro-osmotic buoyancy, and will affect the particle motion significantly. For the liquid drop, without considering the polarization effect, the magnitude of the scaled electrophoretic mobility increases with the decrease of viscosity ratio. This is because the flow inside the drop enhances the hydrodynamic drag on the liquid drop. It is also very interesting that the electrophoresis of the liquid drop will be very similar to the colloid particle if the viscosity ratio is very large. Besides, we find that the closer the particle to the plane, the more significant the distortion of electric double layer. The electrophoretic mobility becomes slow.
Subjects
liquid drop
electrophoresis
charged plane
boundary effect
double layer polarization
Type
thesis
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