Séminaire de Susan Perkin (Univ. of Oxford) :
Surface forces generated by the action of electric fields across electrolyte films
le lundi 15 juillet 2019 à 14h, salle des conseils de l’UFR de Chimie (32-42.101).
Résumé
Surface forces generated by the action of electric fields across electrolyte films
Susan Perkin & Carla Perez-Martinez
Physical & Theoretical Chemistry Laboratory, University of Oxford, Oxford, UK
Electric fields act across liquid or soft films in many technological and natural contexts, such as in liquid crystal displays, touch screens, and biological cell membranes. For dielectric fluids, the field scales inversely with film thickness such that micro-scale films require only small voltages applied to create an electric field sufficient to compete with thermal forces and manipulate the fluid structure and interactions. With electrolytic films, however, the effect of field is more complex (and interesting).
In my laboratory we perform high-resolution measurements of the force between surfaces across liquids using a Surface Force Balance (SFB). With this approach we are able to confine liquids to thin films and study their structure and mechanical, electrochemical, optical, and other properties. In this talk I will present recent experiments with an SFB modified to incorporate two gold electrodes on the confining surfaces. An electric field is imposed perpendicular to an electrolyte film, and the resulting surface force is measured as a function of time (and voltage, frequency, etc). An alternating electric field induces a force which diverges substantially from the calculated static response of the electrolyte. The magnitude of the force is larger than predicted, and the approach to steady state in electrolyte is slow compared to both the electrochemical and viscous timescales of the system. The non-trivial electrolyte response in AC electric fields may be connected to several recent reports of unexpected and bifurcating forces driving colloids in AC fields.
