Dipole-dipole correlations and the Debye process in the dielectric response of nonassociating glass forming liquids

Pabst, Florian; Helbling, Andreas; Gabriel, Jan Philipp; Weigl, Peter; Blochowicz, Thomas

doi:10.1103/physreve.102.010606

Cited by 48 publications

(45 citation statements)

References 38 publications

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“…In the lower panel of Fig. 5 we compare M(f) with the susceptibility (f) from PCS (or DLS) obtained by Pabst et al, which has =0.49 [ 46 ]. There is excellent agreement in frequency dependence between M(f) and (f), and hence the difference of the -relaxation when probed by DLS from (f) is explained in the same way as for M(f).…”

Section: Tributyl Phosphate (Tbp)supporting

confidence: 52%

“…[ 33,78,79,80,81,82,83 ] are critical in restoring the verity of the dynamics obtained by using dielectric permittivity spectroscopy of polar glass-formers. On the other hand, the presence of the JG -relaxation and its relations to the -relaxation were not recognized in the papers of Körber et al [ 19,84 ], Gabriel et al [ 43 ], and Pabst et al [ 46 ], and the consequence is that they were not able to reach the same conclusion.…”

Section: Discussionmentioning

confidence: 98%

“…A serious challenge to the verity of the dynamics of polar glass-formers obtained by dielectric permittivity spectroscopy (DS) was issued by the recent publications by Körber et al [19], Gabriel et al [43], and Pabst et al [46]. The basis of the challenge is the narrow frequency dispersion of the intense dielectric -loss peak in (f) becomes much broader when the same material is probed by other spectroscopies including PCS (depolarized light scattering) and NMR [19,46] and also shear mechanical modulus G(f) in the case of glycerol [43]. The exponent of the Kohlrausch fit to the dielectric loss peak in (f) is significantly larger than the exponents, , , and of the other spectroscopies.…”

Section: Discussionmentioning

confidence: 99%

“…S1 for TEP and Fig. S2 for TPP) [ 44,45,46 ]. This property is like KDE, PDE, aroclor, and glycerol, as well as the other highly polar glass-formers [ 16,17 ] conforming to the correlation of with  found [ 15 ].…”

Section: Tributyl Phosphate (Tbp)mentioning

confidence: 99%

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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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Section: Tributyl Phosphate (Tbp)supporting

confidence: 52%

Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Tributyl Phosphate (Tbp)mentioning

confidence: 99%

See 2 more Smart Citations

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

Ngai

Wojnarowska

Paluch

2021

Preprint

View full text Add to dashboard Cite

show abstract

“…To compare the DDLS field correlation function g 1 (t) with BDS, it is useful to calculate a generalized DDLS susceptibility, 28 w 00 ðoÞ / o Ð g 1 ðtÞ expðÀiotÞÞdt; which is proportional to the Fourier transform of g 1 (t) multiplied by o. This was previously established for ionic liquids, 19 glass-forming liquids, 37 and alcohols. 28 The resulting susceptibilities are shown in Fig.…”

Section: Ddls Resultsmentioning

confidence: 99%