Zeta Potential Measurements of Sedimentary Particles by the Microelectrophoretic Method

Abstract

   Department of Forest Products, Faculty of Agriculture, Kyushu University; Hakozaki, Higashi-ku, Fukuoka-shi 812 Japan The zeta potentials of sedimentary particles (clay) were measured in a flat electrophoresis cell in horizontal and lateral arrangements.
   When the cell was mounted horizontally, the distribution curves of electrophoretic velocities of the particles were asymmetrical about the cell center, because the bottom surface charge was changed by the settling of particles, which occurred gradually during the measurement. Therefore, the electroosmotic flow resulted in an asymmetry. Then it is very difficult to make accurate measurements. The larger the differences in electrical: character between cell walls and particles, the greater the errors of experiments became. The zeta potentials (A) obtained from the upper stationary level were always higher than those (B) from the lower one and the A/B ratios occasionally went up to over 4.
   When the cell was mounted laterally, reproducible measurements were carried out in a wide range of particle concentrations. However, if the microscope illumination was given in the ordinary way, even though a light blue heat filter was interposed in the illumination path, it was difficult to measure the electrophoretic velocities of particles because of rapid particles rising due to convection. Then, it became feasible to put a stop to the particles by balancing the particles rising and the particles falling under gravity, namely by covering an appropriate area of the illumination lens with an adiabatic body such as a water tank according to the degree of convective and settling disturbances. The zeta potentials at the two stationary levels were very close to each other.
   The zeta potential should be determined from the mean value of electrophoretic velocities at the two stationary levels obtained from the Komagata's equation or from the velocity that is obtained by substituting the coefficients of the quadratic equation derived from the observed velocities at several levels by the least-squares method into the Mori-Okamoto's equation.