Ions in glass forming glycerol: Close correlation of alpha and fast beta relaxation

TL;DR

This study investigates how adding LiCl to glycerol affects both slow alpha and fast beta relaxation processes across a broad frequency spectrum, revealing a strong correlation between these dynamics consistent with mode-coupling theory.

Contribution

It provides new broadband dielectric spectra showing the influence of ions on both alpha and beta relaxations in glycerol, extending into the THz range and linking experimental results with mode-coupling theory.

Findings

Ion addition modifies alpha relaxation times

Fast beta relaxation minimum broadens with ions

Correlation between alpha relaxation rate and minimum position

Abstract

We provide broadband dielectric loss spectra of glass-forming glycerol with varying additions of LiCl. The measurements covering frequencies up to 10 THz extend well into the region of the fast beta process, commonly ascribed to caged molecule dynamics. Aside of the known variation of the structural alpha relaxation time and a modification of the excess wing with ion content, we also find a clear influence on the shallow loss minimum arising from the fast beta relaxation. Within the framework of mode-coupling theory, the detected significant broadening of this minimum is in reasonable accord with the found variation of the alpha-relaxation dynamics. A correlation between alpha-relaxation rate and minimum position holds for all ion concentrations and temperatures, even below the critical temperature defined by mode-coupling theory.