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Abstract
Nonequilibrium processes, including physical aging, belong to the most challenging phenomena of glassy dynamics. One of the fundamental problems that needs clarification is the effect of material polarity on the time scale of the structural recovery of glass. The importance of this issue arises from practical applications and recent findings suggesting a substantial contribution of dipole–dipole interactions to the dielectric permittivity spectra of polar glass-formers. Herein, we use dielectric spectroscopy to investigate structural relaxation and aging dynamics of highly polar glass-former 4-[(4,4,5,5,5-pentafluoropentoxy)methyl]-1,3-dioxolan-2-one (FPC), a derivative of propylene carbonate with εs = 180 and μ = 5.1. We show that ε″(tage) data of FPC at Tage < Tg reveal complex behavior resulting from considerable cross-correlation effects. Namely, two characteristic aging time scales, reflecting the evolution of cross-correlation mode and generic structural relaxation toward equilibrium, are obtained at a given Tage. Furthermore, a single stretched exponential behavior of ε″(tage) has been received for weakly polar carvedilol with negligible dipole–dipole interactions.
Highlights
Nonequilibrium processes, including physical aging, belong to the most challenging phenomena of glassy dynamics
Been distinguished in the dielectric response of these compounds: (i) a slower Debye-like process identified with cross-correlations and (ii) a faster contribution with a high-frequency power law of −0.5 corresponding to the generic structural relaxation and revealing the same characteristics as relaxation processes monitored by a depolarized dynamic light scattering (DDLS) technique.[15]
A fundamental question arises: Do the diverse contributions to the permittivity spectrum ε′′(ω) display different dynamics regarding structural aging? to address this problem, we have chosen 4-[(4,4,5,5,5pentafluoropentoxy)methyl]-1,3-dioxolan-2-one, a room-temperature liquid supplied from SynQuest Lab (United States) and abbreviated as FPC
Summary
Nonequilibrium processes, including physical aging, belong to the most challenging phenomena of glassy dynamics. The results of our dielectric aging experiments demonstrate that structural relaxation and recovery time scales are not the same, i.e., τage ≠ τα for both studied compounds, which follows the suggestions made in the recent Perspective by Richert et al.[16] we show that structural recovery dynamics becomes more complex when cross-correlation effects dominate in polar systems.
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