NONLINEAR DYNAMICS OF MEMBRANE PROCESSES - BISTABILITY AND OSCILLATIONS IN ELECTROKINETIC PHENOMENA

Bistability and oscillations have been studied for a C-1/membrane\C-2 system, where C-1 and C-2 represent the concentrations of dilute and c oncentrated solutions of NaCl/KCl. In this context (i) hydrodynamic pe rmeability, (ii) electroosmotic permeability, (iii) streaming current, and (iv) diffusion current (current due to concentration difference o n the two sides of the membrane) have been measured to test the assump tions of existing theories, Bistability data do not support the existi ng theories, The ratio of the slopes does not correspond to C-1/C-2 as predicted by the theory of Kobatake et al. A semiempirical correlatio n has been proposed for the interpretation of data. Data on electrokin etic oscillations in (i) a Pyrex membrane-aqueous electrolyte system a nd (ii) a Millipore filter-aqueous electrolyte system have been report ed in order to test certain features of the existing theories. The res ults show that the time period depends on the geometrical factors desc ribing the system and is independent of the current strength, which is in conformity with the theory of Teorell et al. as well as that of Me ares et al. It has been shown that previous theory also leads to an eq uation of the Van der Pol type, An attempt has been made to examine th e correlation between bistability and oscillations. It is found that b istability can occur when electroosmotic permeability is a function of potential difference and conductance is a function of volume flux, On the other hand, oscillations can occur when conductance is a function of volume flux, provided certain dynamic conditions are satisfied. (C ) 1995 Academic Press, Inc.