Forschergruppe
Nonlinear response to probe vitrification

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Project Roling (Marburg)

Nonlinear transport in ionic liquids and in their mixtures with molecular liquids

Summary

The nonlinear ionic conductivity of supercooled ionic liquids and of their mixtures with molecular liquids shall be studied by measuring higher-harmonic currents after applying high ac electric fields. In order to generate fields above 100 kV/cm, different electrode configurations will be set up and tested. In mixtures with small amounts of ionic liquid, the nonlinear dynamics of quasi-independent ions will be probed. With increasing ion concentration, interactions between the probe ions will become more and more relevant. A detailed comparison will be drawn between our experimental results and the theoretical results obtained in other projects. In particular, theoretical predictions about the shrinkage of the linear response regime close to the glass transitions will be tested. The aim is to gain new insights into the force-dependent subdiffusive and diffusive ion dynamics during vitrification.

P7 Roling, Universität Münster

Nonlinear ion transport in glass-forming ionic liquids: Higher harmonic ac currents and electrical creep

Summary
In this project, the nonlinear ion transport in glass-forming ionic liquids will be studied by (i) applying
high ac electric fields and analyzing higher harmonics in the resulting current response
and by (ii) carrying out electrical creep experiments under a constant bias field. Ionic liquids will
be chosen, for which the frequency dependence of the conductivity is governed by subdiffusive
translational movements of the ions, whereas rotational movements play a minor role. These
are in particular: (a) Monocationic and monoanionic liquids with small or zero permanent dipole
moments of the ions. (b) Dicationic ionic liquids, for which we expect a dynamic decoupling of
the small monovalent anions from the larger divalent cations upon supercooling. (c) Systems
with oligomeric cations, for which we have already observed a pronounced dynamic decoupling
of the monovalent anions from the oligomeric cations. The frequency/time dependence
as well as the temperature dependence of the nonlinear conductivity will be analysed in detail and compared to solid electrolytes. The interpretation of the nonllinear conductivity will be supported by molecular dynamics simulations.