Measurements of Electric Field and Electrokinetic Phenomena Using Two Kinds of Tracer Particles with Different Mobilities

Abstract

In this study, we propose a novel technique to measure electric fields and electrokinetic phenomena in microchannels using two kinds of tracer particles with different electrophoretic mobilities. In the present technique, electric fields, whose precise measurement is quite difficult, is obtained from the velocity differences between two kinds of tracer particles. The principle of electric field measurement is based on the flow visualization and the mathematical analysis of the flow fields of different particles. Each tracer particle with different mobilities due to surface charge densities is mixed in a buffer solution to analyze the flow by particle image velocimetry (PIV). Experimental demonstrations are successfully conducted both in straight and T-shaped microchannels with rectangular cross sections. The experimental results of the electric field are compared with the roughly estimated values based on the numerical analysis of the Laplace equation. The comparison indicates the applicability of the proposed technique because they are in reasonable agreement. Moreover, the detailed electrokinetic phenomena, e.g., the electrophoresis and electro osmosis flow, are successfully investigated using the electric field obtained here. These results lead us to conclude that the proposed method can be used as a practical tool to access the details of electrokinetic phenomena in microchannels.