On the Nature of the Debye-Process in Monohydroxy Alcohols: 5-Methyl-2-Hexanol Investigated by Depolarized Light Scattering and Dielectric Spectroscopy

TL;DR

This study investigates the Debye relaxation process in monohydroxy alcohols, specifically 5-methyl-2-hexanol, using dielectric spectroscopy and depolarized light scattering, revealing new insights into its molecular origin and dynamics.

Contribution

First direct evidence of the Debye process in DDLS for a monoalcohol, linking dielectric and optical signatures to molecular chain dynamics.

Findings

Debye process observed in DDLS for the first time in a monoalcohol.

Dielectric Debye process relates to chain-end fluctuations.

DDLS Debye signal shows local residual correlations due to anisotropic relaxation.

Abstract

The slow Debye-like relaxation in the dielectric spectra of monohydroxy alcohols is a matter of long standing debate. In the present work, we probe reorientational dynamics of 5-methyl-2-hexanol with dielectric spectroscopy and depolarized light scattering (DDLS) in the supercooled regime. While in a previous study of a primary alcohol no indication of the Debye peak in the DDLS spectra was found, we now for the first time report clear evidence of a Debye contribution in a monoalcohol in DDLS. A quantitative comparison between the dielectric and DDLS manifestation of the Debye peak reveals that while the dielectric Debye process represents fluctuations in the end-to-end vector dipole moment of the transient chains, its occurrence in DDLS shows a more local signature and is related to residual correlations which occur due to a slight anisotropy of the $\alpha$-relaxation caused by the chain formation.