UMR 5672

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Underscreening and Casimir forces in confined ionic liquids

Jean-Pierre Hansen (Cambridge University, UK)
When Apr 27, 2018
from 10:45 AM to 12:00 PM
Where Amphi A
Attendees Jean-Pierre Hansen
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Recent experiments on highly confined ionic liquids, using a surface force apparatus, point to an unexpected and dramatic INCREASE of the electrostatic screening length with ion concentration, a behaviour opposite to that of the Debye length; the measured screening length exceeds the Debye length by as much as two orders of magnitude.
We will present a "first principles" theory of underscreening, based on simple models of ionic liquids and standard Statistical Mechanics tools in an attempt to understand underscreening beyond purely phenomenological explanations.

As a "by-product", an extension of our underscreening work leads to the prediction of a novel, OSCILLATORY decay of the classical Casimir force acting between the confining plates as a function of their separation. Casimir forces are traditionally associated with the "quantization" of the allowed Fourier components (or modes) of the local particle densities. We show that this unexpected oscillatory decay is due to the competition between electrostatic and excluded volume effects in dense ionic liquids.