Temporal and local concentration changes in diffusion layers at cellulose membranes due to concentration differences between the solutions on both sides of the membrane.

By means of a laser-interferometrical method diffusion layers at the interface of a noncharged cellulose membrane are studied. These layers are induced by a concentration difference between the NaCl solutions separated by the membrane. The temporal and local shift of the NaCl concentration in the diffusion layers were measured. A steady-state concentration profile could be obtained for times of 121 sec less than or equal to to less than or equal to 484 sec. The concentration profiles at any time (to less than or equal to 900) are not a linear function of the membrane surface, but could be fitted to a quadratic function. The thickness of the diffusion layers is also a function of time and its stationary value in this system is (575 +/- 49) X 10(-6)m. The role of concentration polarization for the determination of phenomenological thermodynamic coefficients of membranes is discussed and a new method is suggested, which excludes the difficulties of the concentration polarization in the diffusion layers at the membrane.