Electrokinetic Effects and Electrostatic Interaction of Colloids in Electrolyte Solutions

• Main Authors: Kao Chen-Yuan, 高承遠
• Other Authors: Hsu Jyh-Ping
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/16808993661872605047

博士 === 國立臺灣大學 === 化學工程學研究所 === 90 === The basic properties of a colloidal dispersion depend largely on the electric property of the dispersed phase. When an external field such as electric field and pressure gradient is applied, a relative motion between the dispersed phase and the dispersion medium can be observed. This relative motion leads to the so-called electrokinetic effects, which include electrophoresis, electroosmosis, streaming potential, and sedimentation potential. These effects are often used to quantify the charged nature of the dispersed phase. Electrophoresis, for instance, is a powerful tool for the measurement of the surface potential of colloidal particles. Among various factors, which influence the behavior of a colloidal dispersion, boundary effect is an important yet often overlooked one. In practice, this effect becomes significant as the concentration of the dispersed phase is appreciable so that the interaction between neighboring entities plays a role, or as an entity is close to a boundary such as a wall. The latter must be considered, for example, in the discussion of the adsorption behavior of the entity where entity-surface interaction is the key factor. The former should be taken into account, for instance, in the analysis of the electrophoresis of a concentrated dispersion. The description of an electrokinetic phenomenon includes the governing equations for electric field, flow field, and concentration field. Because these equations are nonlinear and coupled differential equations, in general, solving them analytically is almost impossible. More often than not, drastic assumptions such as thin double layer, low electrical potential, and simple geometry are made so that mathematical treatment can be simplified. These assumptions, however, can be unrealistic in practice. For example, if electrolyte concentration is low, the double layer surrounding a particle can be on the order of its linear size, and particles can assume various shapes. In the present work, electrokinetic effects are investigated theoretically. The effects of aspect ratio of non-cylindrical microchannel, including elliptic and rectangular microchannel, on the electrokinetic properties, including volumetric flow rate, total electric current, streaming potential and electroviscous effect are discussed in Chapters 2 and 3. Chapter 4 considers the effects of the aspect ratio of a spheroidal particle and the distance between it and a spherical cavity on the electrostatic interactions between the particle and the cavity. The electrophoresis of a finite cylinder along the axis of a cylindrical pore is investigated in Chapter 5. In particular, the effects of the diameter of the pore, the aspect ratio of the particle, and the charged conditions on particle surface on the electrophoretic behavior of the particle are discussed.