Breakdown of the Simple Arrhenius Law in the Normal Liquid State

Abstract

It is common practice to discuss the temperature effect on molecular dynamics of glass formers above the melting temperature in terms of the Arrhenius law. Using dielectric spectroscopy measurements of dc conductivity and structural relaxation time on the example of the typical glass former propylene carbonate, we provide experimental evidence that this practice is not justified. Our conclusions are supported by employing thermodynamic density scaling and the occurrence of inflection points in isothermal dynamic data measured at elevated pressure. Additionally, we propose a more suitable approach to describe the dynamics both above and below the inflection point based on a modified MYEGA model.

Polymer matrix ferroelectric composites under pressure: Negative electric capacitance and glassy dynamics

“…A nice resume of the most recent efforts in this fields, showing also new possibilities due to the simultaneous consideration of both the primary relaxation time and DCconductivity is given in ref. [46]. This picture can be supported by the well-known piezoelectricity of PVDF.…”

Inflection Point in Pressure Dependence of Ionic Conductivity as a Fingerprint of Local Structure Formation

“…Interestingly, over the years, only a limited number of glass-forming materials have been proven to reveal inflection points experimentally—that is, glycerol, propylene carbonate (PC), Error! Bookmark not defined , 52 2-butyl-1-octanol, 30 protic IL [C 8 HIm][NTf 2 ], 53 and recently [P 666,14 ][BOB]. 54 Casalini and Bair suggested that the origin of the inflection point in PC can be attributed to the pressure dependences of compressibility and the apparent activation energy at a constant volume.…”

Normal-to-Supercooled Liquid Transition in Molecular Glass-Formers: A Hidden Structural Transformation Fuelled by Conformational Interconversion

“…For centuries, supercooled liquids have played a vital role in science, industry, and the day-to-day life of human beings. − They develop when their chemical components fail to create crystallization nuclei below the freezing point. Consequently, the formation of supercooled liquids is often related to the manufacturing of glasses (including the molecular ones) via the vitrification process, in which progressive lowering of the temperature results in dramatic slowing down of molecular motions from nanoseconds to hundreds of seconds around the glass-transition temperature ( T g ). ,, This process takes place in both the nonergodic and ergodic dynamic domains of the ultraviscous liquid, which intersect at the crossover temperature T B . , However, well above T g and T B , there is another characteristic point at which intermolecular organization, molecular motion, and transport coefficients (e.g., diffusivity, viscosity) undergo significant changes. − These transformations delineate collectively the inflection point which is often referred to as the Arrhenius crossover. − …”

“… 6 , 7 However, well above T g and T B , there is another characteristic point at which intermolecular organization, molecular motion, and transport coefficients (e.g., diffusivity, viscosity) undergo significant changes. 8 − 10 These transformations delineate collectively the inflection point which is often referred to as the Arrhenius crossover. 11 − 15 …”

“… 17 , 18 The exceptional behavior was reported for, e.g., propylene carbonate or α-picoline. 10 , 18 Apart from that, numerous additional discontinuous changes at T A have been documented, e.g., changes in the inhomogeneous broadening of Raman lines, 19 , 20 or additional contribution to the Landau–Placzek ratio. 21 , 22 Finally, some universal relationships have been identified between T A , T g , and melting point T m .…”