Filtration Potential across Membranes Containing Selective Layers

Abstract

The filtration potential in the membranes containing selective layers is studied both theoretically and experimentally. A general thermodynamic expression is obtained for the pressure-induced potential difference across a membrane with an arbitrary number of macroscopically homogeneous layers. That expression is specified for the model of straight cylindrical capillaries in each of the layers. The limiting cases of very wide and very fine pores are considered for the supports and active layers, respectively. In membranes containing selective layers, the dependencies of filtration potential on the transmembrane volume flow are usually nonlinear. That occurs because the concentration differences arising in the membrane depend nonlinearly on the transmembrane volume flow. The concentration gradients cause nonlinearities due to the occurrence of membrane potential and because the streaming potential coefficient in coarse-porous layers (e.g., membrane supports) depends on electrolyte concentration. The membran...