ESPCI web site
Carlos Drummond
Centre de Recherche Paul Pascal (CRPP), UPR 8641-CNRS, Université de
Bordeaux, Pessac F-33600, France
Title : Ions in motion : Effect of Oscillatory Electric Fields
Abstract : The dynamic response 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 to an applied oscillatory
electric field of monovalent salt solutions confined between two walls,
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 between the walls. This long-range repulsive 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
ionic transport from adjacent reservoirs.