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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 33: Glasses and Glass Transition (joint session DY/CPP)

CPP 33.2: Vortrag

Montag, 16. März 2020, 15:30–15:45, ZEU 118

Nonlinear dielectric response: molecular reorientation models — •Gregor Diezemann — Institut für Physikalische Chemie, JGU Mainz, Duesbergweg 10-14, 55128 Mainz

The nonlinear dielectric response of supercooled liquids has been intensively studied, both experimentally and theoretically during the last decade. Since an analogue of the well known fluctuation dissipation theorem for nonlinear responses is missing, one has to rely on the results of model calculations. A number of different models have been used for the calculation of the nonlinear (third order) response and some of them exhibit features also observed experimentally.

I will present the results of calculations of the third order and the fifth order response for models of molecular reorientations. Sofar, one important point in the interpretation of the peaks observed in the modulus of the nonlinear response was that rotational Brownian motion does not give rise to such a peak. However, it is well known that this model of isotropic rotational diffusion is also not able to reproduce important features of the linear dielectric response of glassforming systems.

Here, I will show that very simple models like the model of random rotational jumps or anisotropic rotational diffusion also exhibit a so-called hump in the modulus of the nonlinear response functions. Also the relation between the third order response and the fifth order repsonse is obeyed to some extent. What is missing in this kind of models is a temperature dependence of the features observed. I will discuss the results in the context of recent experimental observations.