Electric field effects in systems of associating amphiphilic electrolytes

Abstract

The thermodynamic stability and the structure of selfassociated amphiphilic electrolytes have been studied as a function of electric fields, the strength of which is of the order of 10 4–10 5 V/cm, thus corresponding to the conditions in the lipidic part of biological membranes. The experiments have been done with cetylpyridinium iodide and pinacyanol chloride, because these systems show association dependent changes of their optical absorption. The results which have been obtained in a field jump apparatus with short square wave pulses and optical detection can be classified as chemical and physical effects. Three chemical effects can be resolved in the cetylpyridinium iodide system. The concentration dependent relaxation times are of the order of 50 nsec, 1 μsec and 50 μsec. The nature of these effects is discussed with regard to the “Second Wien Effect”, the dipole field effect, and entropic events in the water structure. At higher concentrations of cetylpyridinium iodide physical field effects predominate in the optical observation. These electrodichroitic processes are attributed to the orientation or rearrangement of large anisometric micelles. The electric field effects in the pinacyanol system resemble those of the cetylpyridinium iodide: chemical reequilibration at lower concentrations and a superposition of chemical and physical effects in solutions with large aggregates.