THE USE OF FLICKER-NOISE SPECTROSCOPY FOR STUDYING THE MECHANISM OF THE OVERLIMITING CURRENT IN A SYSTEM WITH CATION-EXCHANGE MEMBRANE

Spectral analysis of low-frequency fluctuations of the membrane potent ial, which occur when electrical current passes through a polyamide ca tion-exchange membrane placed in a NaCl solution, is employed for stud ying the mechanism of ionic transport at overlimiting current densitie s. Spectra of noise density of the membrane potential, S-V, as a funct ion of the concentration and viscosity of electrolyte as well as their dependence on the current density are investigated in the frequency r egion 0.002-500 Hz. Fluctuations of the membrane potential are shown t o become discernible when the current density j is approaching the lim iting value j(lim). When j is approximately equal to j(lim) the fluctu ation spectra include reproducible, discrete lines at frequencies 20-2 50 Hz. At j much greater than j(lim) the S-V function becomes smooth a nd corresponds to the flicker noise. Parameters of the S-V spectra dep end on the electrolyte viscosity. The spectral regularities observed a re interpreted in terms of the model that suggests the appearance of h ydrodynamic instabilities in the delta(N)-Nernst layer, at the membran e boundary, at j greater than or equal to j(lim). The mechanism leadin g to turbulent pulsations and the role played by turbulence in the pro cess of ionic transport at overlimiting currents are discussed.