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Schlagwörter:
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Zusammenfassung:
Using an asymmetric cellulose acetate (CA) membrane annealed at 82.5°C 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 NaCl 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 NaCl concentrations both coefficients even change their sign being positive for cs < 0.07 mole/liter and negative for cs > 0.07 mole/liter. The positive values of lep and lpe at concentrations cs < 0.07 mole/liter are in agreement with the cation exchange property of CA membranes. Furthermore, the hydrodynamic permeability, lp, and the electrical resistance, Re, of the asymmetric cellulose acetate membrane have been measured. The sign reversal of lep and lpe 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 cation-exchange character as well as the asymmetry of the cellulose acetate membrane are responsible for the significant sign reversal of the electrokinetic transport coefficients lep and lpe 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.
