Bistability and electrokinetic oscillations

Nonlinear dynamic behavior and electrokinetic oscillations have been investigated for the membrane systems (a) 0.1 N NaCl/KCl parallel to Millipore filter parallel to 0.01 N NaCl/KCl; (b) 0.1 N NaCl/KCl parallel to Whatman Inorganic filter parallel to 0.01 N NaCl/KCl; and (c) 0.1 N NaCl/KCl parallel to silver-coated filter parallel to 0.01 N NaCl/KCl, from the viewpoint of testing the theories for the phenomena and elucidating the mechanism. To achieve these objectives, studies on hydrodynamic permeability, electroosmotic permeability, bistability, and electrokinetic oscillations were undertaken. Relaxation time for buildup and decay of electroosmotic pressures was experimentally determined. Bistability was not observed showing that it is not a prerequisite for oscillations and nonlinear relations between (J(v))(Delta rho=0) and Delta phi involving cubic or higher-order terms are necessary for bistability. The oscillations were studied at different current strengths. The period is found to be independent of current, while amplitude A is found to be linearly related to current I which is the bifurcation parameter. The bifurcation point occurs at similar to 0.4 mA. Studies have also been made with membranes of different pore size that show that amplitude increases with increase in pore size of the membranes. The validity of the two-variable model of Teorell was examined by comparing the experimental results with computer simulation based on parameters determined experimentally. Theory does not meet expectation and the results suggest that modification of theory is needed. The weakness of the theory has been critically examined. (C) 1999 Academic Press.