Berlin 2018 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 53: Complex Fluids and Soft Matter (joint session DY/ CPP / BP)

DY 53.11: Talk

Wednesday, March 14, 2018, 18:15–18:30, BH-N 334

Screening in ionic liquids: an analytical approach — •Fabian Coupette and Andreas Härtel — University of Freiburg, Freiburg, Germany

Recent experiments report an unexpected increase of the electrostatic screening length in concentrated electrolytes [Faraday Discuss. 199, 239 (2017)] which, as yet, lacks a theoretical foundation. The screening length can be obtained from the exponential long-range decay of the total correlation between ionic species, which in turn can be extracted from (classical) density functional theory. We propose a new functional for the primitive model of charged hard spheres which accounts for the packing of ions and solvent particles. With this approach, we find a universal behavior of the screening length in three distinct scaling regimes, including a strong increase at high ion concentrations. This increase culminates in a divergence of the screening length above a certain threshold. We validate our predictions by also performing Molecular Dynamics simulations, where we further observe a structural transition relatable to ion clustering close to the divergent regime. The universal scaling behavior matches well the experimental findings, however, differences remain which we will discuss in detail. We conclude that accounting for excluded volume is already inducing a strong increase in the screening length for concentrated systems, but insufficient to utter quantitative expectations for more intricate solvents, for instance polar ones. In this context we finally sketch the incorporation of dipolar interactions into our theory.