Carlos Drummond
CRPP, CNRS, Univ. Bordeaux
http://www.crpp-bordeaux.cnrs.fr/

“Ions in motion; Effect of Oscillatory Electric Fields”

The dynamic response of fluids to applied electrical potentials is a topic of fundamental significance in many systems, from supercapacitors and batteries, to the understanding of electrokinetics. Many electrokinetic systems of interest involve the application of alternating potentials. In this seminar I will discuss the dynamic response of monovalent salt solutions to an applied oscillatory electric field, investigated by using a modified Surface Forces Apparatus. In opposition to what could be anticipated from purely electrostatic considerations, we observed a strong, slowly evolving repulsive force between surfaces separated by an aqueous electrolyte upon application of an alternating potential difference. This long-range force increases with the ratio of diffusion coefficients of the ions in the medium and the square of the applied potential. We argue that the repulsive force is a consequence of the field-induced ionic excess in the gap, due to field-induced lateral transport from adjacent reservoirs.