Electrokinetic: Movement of settled spherical particles in fine capillaries

In certain soil remediation schemes using electrical fields, through the soil's porous network there may be transport of colloidal and larger-than-colloidal particles, which can affect remediation in several ways. In the first visual investigation of the electrokinetic motion of particles in fine capillaries, an experimental methodology is described for studying the effects of capillary diameter, ionic strength and pH. The technique is applied to the case of negatively charged spherical particles having a diameter of 6.76 mu m, after they have been allowed to settle inside cylindrical capillaries with diameters of 10, 110, and 700 mu m, respectively. Electrokinetic velocities are reported at several values of applied electric field. In most cases, the direction of the particles' movement is toward the cathode, implying that electroosmotic flow is dominant. At pH 4 and in the 10-mu m capillary, the direction of electrokinetic movement depends on the applied field. At low electric fields, the particles move toward the cathode, whereas above some critical value for the electric field, movement takes place toward the anode.