Molecular mechanism of the Debye relaxation in monohydroxy alcohols revealed from rheo-dielectric spectroscopy

TL;DR

This study uses rheo-dielectric spectroscopy to reveal that shear accelerates Debye relaxation in monohydroxy alcohols, indicating a hydrogen-bonding breakage mechanism distinct from traditional models.

Contribution

First application of rheo-dielectric spectroscopy to study shear effects on Debye relaxation, proposing a new molecular mechanism involving hydrogen-bond breakage.

Findings

Shear accelerates structural, Debye, and terminal relaxations.

Debye relaxation time scales quadratically with structural and terminal relaxation times.

Debye relaxation follows Arrhenius temperature dependence across various monohydroxy alcohols.

Abstract

Rheodielectric spectroscopy is employed, for the first time, to investigate the effect of external shear on the Debyelike relaxation of a model monohydroxy alcohol, i.e., the 2-ethyl-1-hexanol (2E1H). Shear deformation leads to strong acceleration in the structural relaxation, the Debye relaxation, and the terminal relaxation of 2E1H. Moreover, the shear-induced reduction in structural relaxation time, tau_alpha, scales quadratically with that of Debye time, tau_D, and the terminal flow time, tau_f, suggesting a relationship of tau_D*tau_D~tau_alpha. Further analyses reveal tau_D*tau_D/tau_alpha of 2E1H follows Arrhenius temperature dependence that applies remarkably well to many other monohydroxy alcohols with different molecular sizes, architectures, and alcohol types. These results cannot be understood by the prevailing transient chain model and suggest a H-bonding breakage facilitated sub-supramolecular reorientation as the origin of Debye relaxation of monohydroxy alcohols, akin to the molecular mechanism for the terminal relaxation of unentangled living polymers