Accuracy evaluation of zeta-potential measurement using current monitoring technique and closed electrokinetic cell technique

Abstract

The present study was performed to evaluate and to improve the measurement accuracies for zeta-potentials of particle and wall. Electric potentials near colloid particle surfaces and channel wall surfaces are defined as the zeta-potential of particle and wall, respectively. Their accurate measurements are important because both zeta-potentials are the key factors to control many microfluidic applications. Electroosmotic flow is used as a means of liquid transport, and its rate is determined by the zeta-potential of wall. In addition, the zeta-potential of particle is also an important parameter to control many properties of colloid particles. The previous studies developed the measurement techniques of zeta-potentials, which are called the current monitoring technique and the closed electrokinetic cell technique. However, the measurement accuracies of both techniques have not been well discussed, and thus, the present study compared the error ratios based on the measurement uncertainties of both techniques. For the measurements of negative zeta-potentials of wall using negatively charged particles, their error ratios of the current monitoring technique and the closed electrokinetic cell technique were 14.2% and 9.6%, respectively. However, when using positively charged particles, it was difficult to measure zeta-potentials due to the adsorption of positively charged particles on negatively charged channel wall surfaces. In order to reduce the adsorption, the surface modification technique was used to alter the electric charge on the channel wall surface. Then, for the measurements of positive zeta-potentials of particle and wall, their error ratios using the current monitoring technique were 31.9% and 31.6%, respectively, and those using the closed electrokinetic cell technique were 13.0% and 17.7%, respectively. It was revealed that the measurement uncertainties of the closed electrokinetic cell technique were superior to those of the current monitoring technique, even if negatively and positively charged particles were used.