ELECTROCHEMISTRY OF CAPILLARY SYSTEMS WITH NARROW PORES V - STREAMINGPOTENTIAL - DONNAN HINDRANCE OF ELECTROLYTE TRANSPORT

The electrochemical theory of capillary systems with narrow pores outl ined in Part I of this series is applied to the streaming potential an d the electrical hindrance of electrolyte transport across ion selecti ve membranes (Donnan hindrance). Both phenomena are related to the fix ed ion concentration. Streaming potentials were measured while using c ollodion membranes of graded porosity and graded fixed ion concentrati on. The bulk phases consisted of aqueous KCl solutions with a concentr ation 2 x 10(-4) n. The streaming potentials were calculated theoretic ally by using the electrical conductivity data of the membranes given in Part III of this series. The agreement between the experimental res ults and the predictions of the theory is good. Theory also predicts t hat a volume flow across the membrane caused by a hydrostatic pressure difference generates a filtration effect the concentration c(s) of th e electrolyte in the solution leaving the membrane on the low pressure side is lower than the concentration c on the high pressure side. The concentration ratio (c(s)/c) is equal to the ratio (kappa/kappa(i)) o f the electrical conductivity of the high pressure phase kappa and tha t of the pore fluid kappa(i). The hindrance of the electrolyte transpo rt is a transient phenomenon. It disappears slowly if the experiment i s continued over a long period of time. This phenomenon, which is of i mportance in the understanding of ultrafiltration processes using memb ranes, is discussed in detail. It is compared with the observed change s in the streaming potential as a function of time. The influence of t he electrical convection conductivity (electrical surface conductivity ) on the streaming potential can be neglected under the chosen experim ental conditions. Its influence will be discussed in Part VI of this s eries. (C) 1998 Published by Elsevier Science B.V. All rights reserved .