Debye relaxation and 250 K anomaly in glass forming monohydroxy alcohols

TL;DR

This study investigates the dielectric, NIR, and NMR properties of various monohydroxy alcohols near 250 K, revealing a common anomaly likely due to hydrogen bond cooperativity, and identifies a Debye-like peak in most samples.

Contribution

It extends previous findings on 2-ethyl-1-hexanol to other monohydroxy alcohols, showing a universal behavior near 250 K and linking NIR cluster sizes with dielectric data.

Findings

All studied alcohols show a behavior change near 250 K.

Most alcohols exhibit a Debye-like peak in dielectric spectra.

Neat 2-ethyl-1-butanol shows a structural relaxation previously seen only in diluted samples.

Abstract

A previous dielectric, near-infrared (NIR), and nuclear magnetic resonance study on the hydrogen-bonded liquid 2-ethyl-1-hexanol [C. Gainaru et al., Phys. Rev. Lett. 107, 118304 (2011)] revealed anomalous behavior in various static quantities near 250 K. To check whether corresponding observations can be made for other monohydroxy alcohols as well, these experimental methods were applied to such substances with 5, 6, 7, 8, and 10 carbon atoms in their molecular backbone. All studied liquids exhibit a change of behavior near 250 K which is tentatively ascribed to effects of hydrogen bond cooperativity. By analyzing the NIR band intensities, a linear cluster size is derived that agrees with estimates from dielectric spectroscopy. All studied alcohols, except 4-methyl-3-heptanol, display a dominant Debye-like peak. Furthermore, neat 2-ethyl-1-butanol exhibits a well resolved structural relaxation in its dielectric loss spectrum which so far has only been observed for diluted monohydroxy alcohols.