Spontaneous oscillation of electrical potential across organic liquid membranes

An artificial membrane was studied consisting of an oil layer, nitrobenzene containing picric acid, imposed between two aqueous phases, one of which contained 5 mM hexadecyltrimethylammonium bromide (CTAB) and 5% ethanol. It was found that this system shows rhythmic and sustained oscillation of the electrical potential within the range 150-300 mV with an interval of 2-3 min. In the absence of CTAB or ethanol, no oscillation was observed. It is indicated that in this experiment the concentrations of the solutes are far-from-equilibrium, i.e., the hydrophilic substance, picric acid, was dissolved in the organic phase and the hydrophobic substance, CTAB, was dissolved in the aqueous phase. In addition, the presence of an unstirred layer was suggested to be essential for generating such electrical oscillations.