Direct Evidence of Relaxation Anisotropy Resolved by High Pressure in a Rigid and Planar Glass Former

Abstract

Rigid molecular glass-formers with no internal degrees of freedom nonetheless have a single secondary β-relaxation. For a rigid and planar molecule, 1-methylindole (1MID), although a secondary relaxation is resolved at ambient pressure, its properties do not conform to the rules established for rigid molecules reported in early studies. By applying pressure to the dielectric spectra of 1MID, we find the single secondary relaxation splits into two. The slower one is pressure sensitive showing connections to the α-relaxation as observed in other rigid molecules, while the faster one is almost pressure insensitive and dominate the loss at ambient pressure. The two secondary relaxations, identified to associate with the out-of-plane and in-plane rotations of the rigid and planar 1MID, are resolved and observed for the first time by increasing density via elevating pressure.

Inter-enantiomer conversion dynamics and Johari–Goldstein relaxation of benzophenones

“…Having assigned the slowest (α) and intermediate (β) dielectric relaxations of both compounds to the structural and Johari–Goldstein relaxation processes, respectively, the fastest relaxation (γ) can only have an intramolecular character. Indeed, the molecule is not flat as methylindole, the only known example of a rigid molecule with two secondary whole-molecule relaxations in the isotropic liquid state 20 .…”

“…In the low frequency region (up to tens of GHz), supercooled isotropic liquids of rigid molecules exhibit only the α relaxation and a single JG relaxation (with the notable exception of methylindole, which exhibits two distinct rigid-rotation modes in the liquid state 20 ). From a theoretical perspective, secondary relaxations that do not correspond to intramolecular degrees of freedom are predicted both by the Coupling Model 21 , 22 , according to which all glass formers should exhibit a “slow β relaxation” acting as “local precursor” of the α relaxation at higher frequency (shorter relaxation time), and by the mode-coupling theory 8 , 23 , which predicts the existence of a “fast β relaxation” at frequencies of hundreds of GHz, likely associated with the rattling motion of single molecules in the transient cage formed by its first neighbours.…”

Fundamental Link between β Relaxation, Excess Wings, and Cage-Breaking in Metallic Glasses

“…In some glass formers, the β relaxations manifest as distinct peaks as probed by mechanical or dielectric loss spectra; while in some other glasses, the β relaxations appear to be absent and, instead, excess contributions to the tails of α relaxations show up, which are the socalled excess wings [15][16][17][18][19] . Notably, the behaviors of β relaxations are sensitive to chemical compositions and processing histories [17][18][20][21][22][23][24][25][26][27][28] . There a few empirical rules or correlations 3,17,[21][22] and especially the coupling model 1,3,6 can rationalize the relationship between β relaxations some other properties.…”

Viscoelasticity of Cu- and La-based bulk metallic glasses: Interpretation based on the quasi-point defects theory

“…On the one hand, it is widely accepted that α relaxation is connected with the dynamic glass transition and the viscous flow behavior, which corresponds to the cooperative atomic movements. On the other hand, the β relaxation is closely related to local atomic motion, which appears at lower temperature or higher frequency [13][14][15]. It has been regarded that the relaxation acts as a precursor of the main relaxation [7,14,[16][17][18][19].…”