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

Abstract 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 correlatio...

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Autores principales:	K. L. Ngai, Z. Wojnarowska, M. Paluch
Formato:	article
Lenguaje:	EN
Publicado:	Nature Portfolio 2021
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/7f274fce7b964fafa25299395e462d27
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spelling	oai:doaj.org-article:7f274fce7b964fafa25299395e462d272021-11-14T12:18:20ZComparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids10.1038/s41598-021-01191-92045-2322https://doaj.org/article/7f274fce7b964fafa25299395e462d272021-11-01T00:00:00Zhttps://doi.org/10.1038/s41598-021-01191-9https://doaj.org/toc/2045-2322Abstract 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).K. L. NgaiZ. WojnarowskaM. PaluchNature PortfolioarticleMedicineRScienceQENScientific Reports, Vol 11, Iss 1, Pp 1-15 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q K. L. Ngai Z. Wojnarowska M. Paluch Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids
description	Abstract 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).
format	article
author	K. L. Ngai Z. Wojnarowska M. Paluch
author_facet	K. L. Ngai Z. Wojnarowska M. Paluch
author_sort	K. L. Ngai
title	Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids
title_short	Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids
title_full	Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids
title_fullStr	Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids
title_full_unstemmed	Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids
title_sort	comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids
publisher	Nature Portfolio
publishDate	2021
url	https://doaj.org/article/7f274fce7b964fafa25299395e462d27
work_keys_str_mv	AT klngai comparativeanalysisofdielectricshearmechanicalandlightscatteringresponsefunctionsinpolarsupercooledliquids AT zwojnarowska comparativeanalysisofdielectricshearmechanicalandlightscatteringresponsefunctionsinpolarsupercooledliquids AT mpaluch comparativeanalysisofdielectricshearmechanicalandlightscatteringresponsefunctionsinpolarsupercooledliquids
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Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids

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