James N. Groves

Alternating streaming current measurements

Abstract The streaming currents which result when a sinusoidally alternating fluid flow is forced through a cylindrical capillary allow the rapid and reproducible measurement of electrokinetic phenomena. An apparatus for measuring the currents can be constructed easily and inexpensively. The zeta potential of any material which can be formed as a capillary or can be produced as a homogeneous coating on a supporting capillary can be measured by this technique. The use of this apparatus does require that the system be calibrated using a capillary whose zeta potential has been determined by an absolute method.

The use of oscillating laminar flow streaming potential measurements to determine the zeta potential of a capillary surface

Abstract The determination of the electrokinetic properties of continuous surfaces has traditionally been accomplished by measuring the streaming potential or current during Hagen-Poiseuille flow, a procedure with inherent difficulties due to electrode potential drift and asymmetry. We have now developed an absolute method of measuring the streaming potential which avoids these difficulties. In this method a sinusoidally oscillating pressure was applied across the capillary and the resulting oscillating streaming potential was measured. The classical theory of electrokinetics and Uchidas solution for laminar oscillating viscous flow were used to derive an equation relating the oscillating streaming potential to the zeta potential. The zeta potential calculated from the streaming potential was demonstrated to be independent of frequency, capillary radius, and capillary length.

LAMINAR OSCILLATING FLOW STREAMING POTENTIAL MEASUREMENTS (I)

There exists a large class of materials whose electro-kinetic properties cannot be studied by measurement of their electrophoretic mobility. This experimental limitation may be due to inherent properties of the material, e.g., density, size distribution, or from the necessity of using a continuous surface rather than a particulate one. In such cases the measurement of either the streaming potential or current can be used to provide a method of surface characterization. Such measurements have usually been done under conditions of unidirectional Hagen-Poiseuille flow. In aqueous solutions only a small potential difference is produced which requires further amplification. In order to circumvent the experimental difficulties of the unidirectional flow system, e.g., noise, electrode rest potential drift, and D.C. amplification, we have developed an alternating laminar flow system to measure the zeta potential of any material which may be fabricated as a capillary or coated onto a supporting capillary. In this system the sinusoidally oscillating flow streaming potential is measured as a function of both frequency and applied pressure and the zeta potential is determined by using both classical electro-kinetic theory and the theory of oscillating laminar flow developed by Uchida. The reliability of this experimental procedure has been confirmed by measuring the streaming potential over a range of frequencies and computing the zeta potential.