ELECTRICAL AND ELECTROOSMOTIC TRANSPORT BEHAVIOR OF ASYMMETRIC CELLULOSE-ACETATE MEMBRANES .1. TRANSPORT BEHAVIOR IN DIALYSIS-OSMOSIS EXPERIMENTS

Using an asymmetric cellulose acetate (CA) membrane annealed at 82.5oC and the linear relationships of the thermodynamics of irreversible processes, the electrical and electroosmotic transport coefficients such as Re, lep, and lpe as well as the hydrodynamic permeability, lp, have been determined as functions of the NaC1 concentration, cs. The electroosmotic coefficient, lpe, and the so called pressure-membrane potential (pmp) coefficient, lep, have been found to be strongly dependent on the external salt concentration. At larger NaC1 concentrations both coefficients even change their sign being positive for css > 0.07 mole/liter. The positive values of lep and lpe at concentrations csp, and the electrical resistance, Re, of the asymmetric cellulose acetate membrane have been measured. The sign reversal of leo and loe is discussed by applying the finely porous membrane model to the two-layer membrane and taking into account the weak cation-exchange character of cellulose acetate membranes. The discussion indicates that both the weak cationexchange character as well as the asymmetry of the cellulose acetate membrane are responsible for the significant sign reversal of the electrokinetic transport coefficients lpe and lep at larger concentrations. Moreover, the value of the measured electrical resistance supports the idea of the two-layer model for the asymmetric cellulose acetate membrane. © 1980 by Academic Press, Inc.