Berlin 2005 – wissenschaftliches Programm

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DF: Dielektrische Festkörper

DF 8: Gl
äser II (gemeinsam mit FV DY)

DF 8.12: Vortrag

Montag, 7. März 2005, 17:30–17:45, TU A060

Translational and reorientational dynamics in room temperature ionic liquids — •Alberto Rivera, Alex Brodin, and Ernst A. Rössler — Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth, Germany.

We present a study of the dynamics of molten salts, so called "room temperature ionic liquids", based on the 1-butyl-3-methylimidazolium cation with different anions, by means of dielectric spectroscopy and depolarized light scattering. Ionic liquids in general are easily supercooled, but the different anions determine the dynamics of the sample, changing the glass transition temperature (Tg) and eventually preventing supercooling. Two dynamic process can be accessed separately, the diffusion of ions and their reorientation. The electric spectra are dominated by the translational contribution, showing a typical ionic conductor behavior, a dc-plateau in the conductivity and, equivalently, a relaxation in the electric modulus representation. We find that both the conductivity characteristic times and the dc conductivity increase with the anion size. Below Tg diffusion of ions is still observed at sufficiently long times. To probe orientational dynamics, depolarized light scattering experiments were performed in a sample with a symmetric anion (PF6-). The time constants obtained correlate well with conductivity ones, indicating a strong rotational/translational coupling at high temperatures.