Intermolecular cross-correlations in the dielectric response of glycerol

Gabriel, Jan Philipp; Zourchang, Parvaneh; Pabst, Florian; Helbling, Andreas; Weigl, Peter; Böhmer, Till; Blochowicz, Thomas

doi:10.1039/c9cp06344g

Cited by 47 publications

(61 citation statements)

References 49 publications

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“…Both are much broader than that of (f), with their K-exponents and having the value of 0.44. The agreement in the frequency dispersion of the -relaxation from M(f) and G(f) was also found by Gabriel et al [ 43 ] in glycerol at 200 K. They also compared data from PCS and DS. The comparison reproduced by the inset of Fig.…”

Section: Glycerolsupporting

confidence: 81%

“…[ 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%

“…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%

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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: Glycerolsupporting

confidence: 81%

Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

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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“…It was evidenced that slow Debye mode in the dielectric response of some materials (e.g. 1-propanol 40 , glycerol 41 ) may be due to additional contribution originated from the cross-correlation part of the response function. Based on this idea, the occurrence of Debye relaxation was rationalized for polar liquid tributyl phosphate lacking hydrogen-bonding interactions 42 .…”

Section: Resultsmentioning

confidence: 99%

The dielectric response of phenothiazine-based glass-formers with different molecular complexity

Rams-Baron

Jędrzejowska

Jurkiewicz

et al. 2021

Sci Rep

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We examined a series of structurally related glass-forming liquids in which a phenothiazine-based tricyclic core (PTZ) was modified by attaching n-alkyl chains of different lengths (n = 4, 8, 10). We systematically disentangled the impact of chemical structure modification on the intermolecular organization and molecular dynamics probed by broadband dielectric spectroscopy (BDS). X-ray diffraction (XRD) patterns evidenced that all PTZ-derivatives are not ‘ordinary’ liquids and form nanoscale clusters. The chain length has a decisive impact on properties, exerting a plasticizing effect on the dynamics. Its elongation decreases glass transition temperature with slight impact on fragility. The increase in the medium-range order was manifested as a broadening of the dielectric loss peak reflected in the lower value of stretching parameter βKWW. A disagreement with the behavior observed for non-associating liquids was found as a deviation from the anti-correlation between the value of βKWW and the relaxation strength of the α-process. Besides, to explain the broadening of loss peak in PTZ with the longest (decyl) chain a slow Debye process was postulated. In contrast, the sample with the shortest alkyl chain and a less complex structure with predominant supramolecular assembly through π–π stacking exhibits no clear Debye-mode fingerprints. The possible reasons are also discussed.

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