A NEW METHOD FOR DETERMINING TRANSPORT NUMBERS OF CHARGED MEMBRANES FROM CONVECTIVE DIFFUSION EXPERIMENTS

We present a new method for determining transport numbers of charged m embranes from convective diffusion experiments. The development of con centration differences in the two bulk solutions due to the passage of an electric current (which is characteristic of conventional Hittorf methods in membrane systems) is avoided by using a convective flow opp osed to the electric current. A theoretical modelling based on the Ner nst-Planck equations gives both the membrane charge density and the tr ansport number from the experimental data. The proposed method is suit ed for membranes porous enough to allow a hydrodynamic flow through an d avoids the need for an accurate chemical analysis, since only conduc tometric determinations are required.