Electroosmosis and electrolyte conductance in charged microcapillaries

Interactions between the electrostatic double layer and transport rates in long capillary pores were investigated experimentally. Track‐etched mica sheets with extremely narrow pore size distribution and large length‐toradius ratio were used as model membranes to examine the electrokinetic phenomena enhanced conduction and electroosmosis as a function of pore size and electrolyte (potassium chloride) concentration. Of experimental significance was that the capillary pores were of radius comparable to or even less than the solution Debye length parameter even at moderate (10 −4 – 10 −3 M) electrolyte concentrations. Heparin, a negatively charged polyelectrolyte, was adsorbed to the pore wall to augment electrostatic effects. The data were compared with numerical calculations based on a diffuse double‐layer model, and the unknown pore wall charge densities were computed for each experiment. The results show that the classical analysis is somehow deficient and also that adsorption of the potential determining ion (heparin) is dependent on electrostatic potential at the pore wall.