Interactions of Surfactants with Biomimetic Membranes. 1. Ionic Surfactants

When impregnated with esters of fatty acids, nitrocellulose filters can be used as a biomimetic membrane. They are easy to make, cheap, and may be used not only as an imitation of biological membranes but also as a sensor to characterize surfactant interactions with dirty fabric. These impregnated filters when fixed in a thermostatically controlled chamber separated into two compartments that contain stirred aqueous solutions by the filter, may be considered as a simple model of a laundry machine. The results revealed that the addition of ionic surfactants into one of the solutions led to the formation of transmembrane electrical potential that is proportional to the logarithm of surfactant concentration. Thus, our biomimetic membranes can be used as electrochemical sensors to detect and measure surfactant concentration. When concentration is near the critical micelle concentration (CMC), a new phenomenon was observed, i.e., spontaneous oscillations of both transmembrane potential and transmembrane current, which mimics the opening and closing of aqueous channels in biological membranes. A further increase of surfactant concentration les to a sharp 100-fold decrease of transmembrane electrical resistance and the disappearance of any transmembrane voltage. This effect, explained by the washing out of fatty acids from the pores, may be used for screening and development of new detergents.