HYDRAULIC AND ELECTROOSMOTIC FLOW-THROUGH SILICA CAPILLARIES

Electrokinetic effects are of renewed interest since the emergence of new separation techniques such as micellar electrokinetic capillary chromatography and the prospects for a variety of soil decontamination technologies. In this study, hydraulic and electroosmotic flow through silica capillaries, 50-10 mum diameters, have been determined experimentally and analyzed theoretically. Hydraulic flow follows the Poiseuille relation very well; however, with increase of the ionic strength of the fluid, the rate of electroosmotic flow decreases. Particularly, the energy consumptions are compared for hydraulic and electroosmotic flow. Results show that, in general, hydraulic flow is much more energy efficient than electroosmotic flow because of bulk IR losses in the latter. The classical theory for electrokinetic phenomena possibly overestimates the transfer of electrical into mechanical energy since both irreversible thermal as well as ion migration energy losses occur in the conductance of double layer ions. The physical significance of the electrokinetic zeta potential based on classical theory, zeta, needs to be carefully reexamined.