Change in molecular dynamics with structures of the trialkyl phosphates and in mixtures with ortho-terphenyl

Saini, Manoj K.; Ngai, K. L.; Xiao, Jin; Wang, Limin

doi:10.1016/j.jnoncrysol.2019.119804

Cited by 2 publications

(2 citation statements)

References 56 publications

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“…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%

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)mentioning

confidence: 99%

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

“…S1 for TEP and Fig. S2 for TPP) 21 , 22 , 44 , 45 . 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 Δε found 15 .…”

Section: Experimental Verificationsmentioning

confidence: 99%

Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids

Ngai

Wojnarowska

Paluch

2021

Sci Rep

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The studies of molecular dynamics in the vicinity of liquid–glass transition are an essential part of condensed matter physics. Various experimental techniques are usually applied to understand different aspects of molecular motions, i.e., nuclear magnetic resonance (NMR), photon correlation spectroscopy (PCS), mechanical shear relaxation (MR), and dielectric spectroscopy (DS). Universal behavior of molecular dynamics, reflected in the invariant distribution of relaxation times for different polar and weekly polar glass-formers, has been recently found when probed by NMR, PCS, and MR techniques. On the other hand, the narrow dielectric permittivity function ε*(f) of polar materials has been rationalized by postulating that it is a superposition of a Debye-like peak and a broader structural relaxation found in NMR, PCS, and MR. Herein, we show that dielectric permittivity representation ε*(f) reveals details of molecular motions being undetectable in the other experimental methods. 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 polar glass-former, there is reduction of relaxation strength of α-relaxation relative to that of the JG β relaxation as well as their separation. Consequently the α relaxation appears broader in frequency dispersion when observed by PCS, NMR and MR instead of DS. The explanation is supported by showing that the quasi-universal broadened α relaxation in PCS, NMR and MR is captured by the electric modulus M*(f) = 1/ε*(f) representation of the dielectric measurements of polar and weakly polar glass-formers, and also M*(f) compares favorably with the mechanical shear modulus data G*(f).

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Change in molecular dynamics with structures of the trialkyl phosphates and in mixtures with ortho-terphenyl

Cited by 2 publications

References 56 publications

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

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

Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids

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