Communication: Slow supramolecular mode in amine and thiol derivatives of 2-ethyl-1-hexanol revealed by combined dielectric and shear-mechanical studies

Abstract

In this paper, we present results of dielectric and shear-mechanical studies for amine (2-ethyl-1-hexylamine) and thiol (2-ethyl-1-hexanethiol) derivatives of the monohydroxy alcohol, 2-ethyl-1-hexanol. The amine and thiol can form hydrogen bonds weaker in strength than those of the alcohol. The combination of dielectric and shear-mechanical data enables us to reveal the presence of a relaxation mode slower than the α-relaxation. This mode is analogous to the Debye mode seen in monohydroxy alcohols and demonstrates that supramolecular structures are present for systems with lower hydrogen bonding strength. We report some key features accompanying the decrease in the strength of the hydrogen bonding interactions on the relaxation dynamics close to the glass-transition. This includes changes (i) in the amplitude of the Debye and α-relaxations and (ii) the separation between primary and secondary modes.

Communication: Linking the dielectric Debye process in mono-alcohols to density fluctuations

“…However, there were some indications of a mechanical signature of the Debye process in ultrasonic measurements [31,34], and it was recently established that the Debye process indeed has a weak shear mechanical counterpart [35]. The rheological response is similar to what is observed for short-chain polymers [24,[35][36][37]. The detection of a shear mechanical signature of the dielectric Debye process is difficult because the signal is smallespecially compared to how dominant the dielectric signal is -and thus requires good resolution and accurate measurements.…”

Slow rheological mode in glycerol and glycerol–water mixtures

“…Could it be that in the case of glycerol one encounters slow dynamics which is rheologically, yet not dielectrically active? A similar behavior was reported by some of us for 2-ethyl-1-hexylamine [39], and to address this question one has to understand in the first place what kind of structural foundation may support the emergence of the dielectric Debye mode. For monoalcohols a general agreement has been already established that they form quasilinear supramolecular structures with the backbone formed by the hydrogenbonded hydroxyl groups [25].…”

Interplay between the static ordering and dynamical heterogeneities determining the dynamics of rotation and ordinary liquid phases in 1,6-anhydro-β-D-glucose

“…The molecular origin of the glass transition phenomenon seems to be one of the most challenging issue of condensed matter physics. The special effort is put to understand the microscopic nature of this peculiar phase transition as well as to explain enormous increase of the viscosity or relaxation times in the close vicinity of the glass transition temperature, T g , probed by different spectroscopies, including mechanical, dielectric or dynamic light scattering ones 1 2 3 4 . To get deeper insight into nature of this characteristic feature of supercooled liquids, systematic theoretical and experimental studies on various kinds of materials characterized by different degree of disorder and intermolecular interactions have been performed 5 6 7 .…”