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COLLOID LAB

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Research Area

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Overview

Our group is mainly interested in understanding and application of various electrokinetic phenomena that involve the fluid motion and transport of molecules and particles under the influence of external electric field. The interaction between the electrical double layer formed in the fluid near the charged surface and the external electric field causes various electrokinetic phenomena. Among others electrophoresis and electroosmosis are the most important electrokinetic phenomena that have many practical applications in colloidal science. In particular, novel applications of electrophoresis and electroosmosis in the design and operation of microfluidic systems are our major concern.

Microhydrodynamics : transport phenomena in micro-structured media

Hydrodynamic interaction between colloidal particles is of theoretical interest itself. And also it's a fundamental subject to understand macroscopic behaviors of a given suspension. Since the Reynold's number is very small for most suspension systems, the fluid motion is described by the Stokes equations. There are many analytical results due of the linearity of the problem.

1. Electrophoresis

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Electrophoresis is one of the most important techniques for the analysis and separation of molecules and particles. Electrophoresis has been widely used for determining the zeta potential or the net charge of molecules. In order to determine the zeta potential or the net charge of molecules it is necessary to have an appropriate theory that furnishes a relationship between the electrokinetic property and the electrophoretic mobility data of molecules. Although there are several theories available for this purpose, most theories are for molecules of simple shapes. Since such simple theories cannot be used to analyze electrophoretic mobility data of complex molecules, we are developing more general electrophoresis theories that can predict the zeta potential or charge distribution of complex molecules. In addition, we are investigating the utility of electrophoresis of molecules and particles in high order electric field. High order field electrophoresis has a possible application in analyzing electrokinetic properties of molecules that conventional electrophoresis analysis using constant electric field cannot investigate.

2. Electroosmosis

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lectroosmosis is widely used for transporting fluid samples in microfluidic systems. By manipulating the distribution of electrical charges in the electrical double layer and the external electric field we can effectively control the electroosmotic flow through a microchannel. We are devising various schemes for electroosmotic flow controls that can be implemented in microfluidic systems of particular purposes. Both analytical and numerical schemes are used to model electroosmotic flows under various complex boundary conditions. In addition, we are investigating the utility of complex electroosmotic flow for enhancing the transport and separation of complex molecules.

Electrostatics & Electrokinetics

For charged particles in electrolytes, the motions are described via electrostatic or electrokinetic interactions together with the hydrodynamic interactions. Ion transport equation and Poisson equation give the relation between the ion concentration, the electric potential, and the fluid velocity.

Transport Phenomena in Living Systems

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There are many suspension systems in a living organism. For example, blood contains many small organisms such as red-blood cells, white -blood cells, and blood-platelets. And cell itself also a suspension containing nuclei, rybosom, and so on. As an application above two topics, enzyme-substrate reaction is now began to analyzed considering Brownian motion of the substrate.