Dipole-dipole correlations and the Debye process in the dielectric response of non-associating glass forming liquids

TL;DR

This paper investigates how dipole-dipole correlations influence the dielectric response of non-associating glass-forming liquids, revealing an additional relaxation process similar to the Debye process, which can be modulated by solvent dilution.

Contribution

It demonstrates that dipole-dipole correlations cause an extra dielectric relaxation process in supercooled liquids, providing insight into the Debye process in glassy dynamics.

Findings

Dipole-dipole correlations produce an additional dielectric process.

The extra process is slightly slower than the alpha-relaxation.

Dilution with nonpolar solvent suppresses the additional peak.

Abstract

The non-exponential shape of the $\alpha$-process observed in supercooled liquids is considered as one of the hallmarks of glassy dynamics and has thus been under study for decades, but is still poorly understood. For a polar van der Waals liquid, we show here - in line with a recent theory - that dipole-dipole correlations give rise to an additional process in the dielectric spectrum slightly slower than the $\alpha$-relaxation, which renders the resulting combined peak narrower than observed by other experimental techniques. This is reminiscent of the Debye process found in monohydroxy alcohols. The additional peak can be suppressed by weakening the dipole-dipole interaction via dilution with a nonpolar solvent.