The Johari–Goldstein β-relaxation of glass-forming binary mixtures

Capaccioli, S.; Kessairi, Khadra; Thayyil, Mohamed Shahin; Prevosto, D.; Lucchesi, M.

doi:10.1016/j.jnoncrysol.2010.08.007

Cited by 39 publications

(29 citation statements)

References 42 publications

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“…27 Ultimately, the studies of dielectric relaxations concerning rigid character of the molecules hold the fundamental interest in glass transition which falls into the special class of Johari-Goldstein (JG) secondary relaxations. [28][29][30][31][32][33][34] Apart from dielectric studies, NMR spectroscopy and mechanical relaxations also support the evidence of secondary relaxations. 10 Rossler and coworkers have noted that the glass formers in this class display a common pattern in thermal behavior of secondary relaxation times with activation energy of E a ≈ 24RT g .…”

Section: Introductionmentioning

confidence: 65%

Glass transition dynamics and conductivity scaling in ionic deep eutectic solvents: The case of (acetamide + lithium nitrate/sodium thiocyanate) melts

Tripathy

Wojnarowska

Knapik

et al. 2015

The Journal of Chemical Physics

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A detailed investigation on the molecular dynamics of ionic deep eutectic solvents (acetamide + lithium nitrate/sodium thiocyanate) is reported. The study was carried out employing dielectric relaxation spectroscopy covering seven decades in frequency (10(-1)-10(6) Hz) and in a wide temperature range from 373 K down to 173 K, accessing the dynamic observables both in liquid and glassy state. The dielectric response of the ionic system has been presented in the dynamic window of modulus formalism to understand the conductivity relaxation and its possible connection to the origin of localized motion. Two secondary relaxation processes appear below glass transition temperature. Our findings provide suitable interpretation on the nature of secondary Johari-Goldstein process describing the ion translation and orientation of dipoles in a combined approach using Ngai's coupling model. A nearly constant loss feature is witnessed at shorter times/lower temperatures. We also discuss the ac conductivity scaling behavior using Summerfield approach and random free energy barrier model which establish the time-temperature superposition principle. These experimental observations have fundamental importance on theoretical elucidation of the conductivity relaxation and glass transition phenomena in molten ionic conductors.

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Section: Introductionmentioning

confidence: 65%

Glass transition dynamics and conductivity scaling in ionic deep eutectic solvents: The case of (acetamide + lithium nitrate/sodium thiocyanate) melts

Tripathy

Wojnarowska

Knapik

et al. 2015

The Journal of Chemical Physics

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“…It is reasonable to expect a correlation of ξhet with the width of the frequency dispersion of the relaxation or the size of (1-K). Indeed the correlation was borne out by considering ξhet for glycerol, o-terphenyl, sorbitol, and poly(vinyl acetate) obtained by multidimensional 13 C solid-state exchange NMR experiments from Reinsberg et al [ 69 ] The values of ξhet are 1.3, 2.2, and 3.7 nm for glycerol, o-terphenyl, and poly(vinyl acetate), respectively, all determined uniformly at T = Tg + 9 K. These values of ξhet correlate with the corresponding values of (1-) from dielectric permittivity, which are 0.30, 0.50, and 0.55, all obtained by fitting dielectric measurements by the Fourier transform of the Kohlrausch function when τα  1 s for the three glass-formers. If the vaue of =0.70 were replaced by =0.44 or 0.40 of G(f) from Schröter and Donth [ 70 ] and Gabriel et al [ 43 ] respectively, the correlation no longer exists.…”

Section: Discussionmentioning

confidence: 99%

Is there Universality in the Dielectric Response of Polar Glass Formers?

Ngai

Wojnarowska

Paluch

2021

Preprint

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The frequency dispersion of structural α-relaxation obtained from broadband dielectric spectroscopy measurements is relatively narrow in many polar glass-formers. On the other hand, it becomes much broader when probed by other techniques, including photon correlation spectroscopy (PCS), nuclear magnetic resonance (NMR), and mechanical shear modulus. Therefore, the dynamics of glass-formers observed by dielectric permittivity spectroscopy (DS) is called into question. Herein we propose a way to resolve this problem. First, we point out an unresolved Johari-Goldstein (JG) β-relaxation is present nearby the α-relaxation in these polar glass-formers. The dielectric relaxation strength of the JG β-relaxation is sufficiently weak compared to the α-relaxation so that the narrow dielectric frequency dispersion faithfully represents the dynamic heterogeneity and cooperativity of the α-relaxation. However, when the other techniques are used to probe the same glass-former, there is a reduction of relaxation strength of α-relaxation relative to that of the JG β-relaxation. Additionally, the separation between the α and the JG β relaxations in dielectric permittivity) decreases when probed by mechanical shear modulus. These changes in relation of α- to JG β-relaxation, when examined by the other techniques, engender the non-negligible contribution of the latter to the former. Hence the apparent α-relaxation is broader than observed by the dielectric permittivity. The broadening is artificial because it is due to a confluence of the α and JG β relaxations with a disparity in their relaxation strengths much less when the other techniques than by dielectric permittivity are used. This explanation is supported by showing the α-relaxation of polar glass-formers becomes broader when the dielectric data are represented in terms of the electric modulus instead of permittivity. The broadening, in this case, is again due to a reduction of the relaxation strength of the α-relaxation relative to that of the JG β-relaxation in the electric modulus representation. A corollary of the explanation applicable to weakly polar glass-formers having JG β-relaxation widely separated from the α-relaxation is the prediction that the frequency dispersion of dielectric α-relaxation is nearly the same as that of the electric modulus, and there is no significant additional broadening when probed by the other techniques. A host of experimental data from the literature and our new measurements are given to support the explanation for polar glass-formers and the ancillary prediction for weakly polar glass-formers. Thus the narrow frequency dispersion of the intense relaxation in polar glass-formers observed by dielectric permittivity is real and genuinely represents the dynamically heterogeneous and cooperative dynamics of α-relaxation. By contrast, the broad dispersion found by the other techniques is artificial and misleading.

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“…The study of the dynamics of a component in binary mixtures of two glass-formers has been an active research effort in the past decades and continued till the present time .The binary systems studied include (1) molecular glass-former and polymer [1,6,29,79,84,85,88], (2) two amorphous polymers [2-5,7-28,30-67,80.86,87], and (3) two van der Waals molecular glassformers [68][69][70][71][72][73][74][75][76][77][78][81][82][83]85],. One particular area of pursuit and the focus of this paper is the dynamics of the component having glass transition temperature T g2 lower than T g1 of the other component, and the changes with the composition of the mixture.…”

Section: Introductionmentioning

confidence: 99%