Electrokinetic effects on the capillary electrophoresis of macromolecules and colloidal particles

Abstract

In this thesis, the movement of charged particles through a capillary under the action of an electric field was studied both theoretically and experimentally. The particles considered here were either spherical polystyrene particle covered with ionic surfactant or rigid rod-like xanthan molecules. When direct electric field is applied to the axial direction of the capillary, the effluent flow known as the electroosmosis takes place. In addition charged macromolecules or colloidal particles suspended in the effluent set into motion under the electric field via the electrophoresis. Thus, the overall motion of the particles are a superposition of the electroosmotic and electrophoretic motions, which are dependent upon the particle conformation in the capillary. The objective of this thesis is to demonstrate that the capillary electrophoresis can serve as a probe to the macromolecular conformation in an electric field. To do this, the present work is pursued by three-part studies, as outlined below. In the first part, the electroosmosis is examined both theoretically and empirically by taking the Smoluchowski equation as a cornerstone which has been developed under the condition of very thin double-layer thickness compared to the capillary diameter. The Poisson equation in conjunction with the Navier-Stokes equation was solved in order to express the electro-osmotic velocity distribution across the inner region of the capillary. That solution is more reliable and different from the classical expression derived previously in which the Debye-H(ckel approximation was used. Then, the Smoluchowski equation was modified to consider the nonuniform temperature effect caused by Joule heating effect. In order to calculate the nonuniform temperature distribution in the capillary,the Onsager equation was introduced considering the temperature dependence of all the relevant physical properties, such as dielectric constant, viscosity, and molar electric conductivities of existi...