Measurement of Colloidal Mobility in the Vicinity of a Solid-Liquid Interface based on an Interference of Evanescent Waves

Abstract

We report on the performance of a measurement system based on laser Doppler principle using an interference of evanescent waves generated at total internal reflections of incident lasers at a solid wall. The system was developed for the velocity measurement of colloidal particles at an interfacial boundary of colloidal liquid and a solid wall. The system has a unique advantage of a high spatial resolution in the direction perpendicular to the boundary due to the short penetration depth of an evanescent wave in the range of a few hundred nanometers. The measurement performance of the system was investigated using a scanning probe in the measurement volume. The result quantitatively confirmed the measurement feasibility of the system. The system was further applied to the velocity measurement of the aqueous solution of alumina particles filled in a square cell induced with electric fields. The measurement result demonstrated the applicability of the measurement system for average velocity of colloidal particles in the vicinity of a solid wall.