Interpreting the nonlinear dielectric response of glassformers in terms of the coupling model
Abstract
Nonlinear dielectric measurements at high electric fields of glassforming glycerol and propylene carbonate initially were carried out to elucidate the dynamic heterogeneous nature of the structural αrelaxation. Recently, the measurements were extended to sufficiently high frequencies to investigate the nonlinear dielectric response of faster processes including the socalled excess wing (EW), appearing as a second power law at high frequencies in the loss spectra of many glass formers without a resolved secondary relaxation. While a strong increase of dielectric constant and loss is found in the nonlinear dielectric response of the αrelaxation, there is a lack of significant change in the EW. A surprise to the experimentalists finding it, this difference in the nonlinear dielectric properties between the EW and the αrelaxation is explained in the framework of the coupling model by identifying the EW investigated with the nearly constant loss (NCL) of caged molecules, originating from the anharmonicity of the intermolecular potential. The NCL is terminated at longer times (lower frequencies) by the onset of the primitive relaxation, which is followed sequentially by relaxation processes involving increasing number of molecules until the terminal Kohlrausch αrelaxation is reached. These intermediate faster relaxations, combined to form the socalled JohariGoldstein (JG) βrelaxation,more »
 Authors:

 CNRIPCF, Largo Bruno Pontecorvo 3, I56127 Pisa, Italy and Dipartimento di Fisica, Università di Pisa, Largo B. Pontecorvo 3, I56127 Pisa (Italy)
 Publication Date:
 OSTI Identifier:
 22415541
 Resource Type:
 Journal Article
 Journal Name:
 Journal of Chemical Physics
 Additional Journal Information:
 Journal Volume: 142; Journal Issue: 11; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 00219606
 Country of Publication:
 United States
 Language:
 English
 Subject:
 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CARBONIC ACID ESTERS; CORRELATION FUNCTIONS; COUPLING; DIELECTRIC MATERIALS; ELECTRIC FIELDS; GLASS; GLYCEROL; MANYBODY PROBLEM; MOLECULAR DYNAMICS METHOD; MOLECULES; NONLINEAR PROBLEMS; PERMITTIVITY; RELAXATION TIME; SORBITOL
Citation Formats
Ngai, K. L. Interpreting the nonlinear dielectric response of glassformers in terms of the coupling model. United States: N. p., 2015.
Web. doi:10.1063/1.4913980.
Ngai, K. L. Interpreting the nonlinear dielectric response of glassformers in terms of the coupling model. United States. doi:10.1063/1.4913980.
Ngai, K. L. Sat .
"Interpreting the nonlinear dielectric response of glassformers in terms of the coupling model". United States. doi:10.1063/1.4913980.
@article{osti_22415541,
title = {Interpreting the nonlinear dielectric response of glassformers in terms of the coupling model},
author = {Ngai, K. L.},
abstractNote = {Nonlinear dielectric measurements at high electric fields of glassforming glycerol and propylene carbonate initially were carried out to elucidate the dynamic heterogeneous nature of the structural αrelaxation. Recently, the measurements were extended to sufficiently high frequencies to investigate the nonlinear dielectric response of faster processes including the socalled excess wing (EW), appearing as a second power law at high frequencies in the loss spectra of many glass formers without a resolved secondary relaxation. While a strong increase of dielectric constant and loss is found in the nonlinear dielectric response of the αrelaxation, there is a lack of significant change in the EW. A surprise to the experimentalists finding it, this difference in the nonlinear dielectric properties between the EW and the αrelaxation is explained in the framework of the coupling model by identifying the EW investigated with the nearly constant loss (NCL) of caged molecules, originating from the anharmonicity of the intermolecular potential. The NCL is terminated at longer times (lower frequencies) by the onset of the primitive relaxation, which is followed sequentially by relaxation processes involving increasing number of molecules until the terminal Kohlrausch αrelaxation is reached. These intermediate faster relaxations, combined to form the socalled JohariGoldstein (JG) βrelaxation, are spatially and dynamically heterogeneous, and hence exhibit nonlinear dielectric effects, as found in glycerol and propylene carbonate, where the JG βrelaxation is not resolved and in Dsorbitol where it is resolved. Like the linear susceptibility, χ{sub 1}(f), the frequency dispersion of the thirdorder dielectric susceptibility, χ{sub 3}(f), was found to depend primarily on the αrelaxation time, and independent of temperature T and pressure P. I show this property of the frequency dispersions of χ{sub 1}(f) and χ{sub 3}(f) is the characteristic of the manybody relaxation dynamics of interacting systems which are governed solely by the intermolecular potential, and thermodynamic condition plays no role in this respect. Although linked to χ{sub 3}(f), dynamic heterogeneity is one of the parallel consequences of the manybody dynamics, and it should not be considered as the principal control parameter for the other dynamic properties of glassforming systems. Results same as χ{sub 3}(f) at elevated pressures had been obtained before by molecular dynamics simulations from the fourpoints correlation function and the intermediate scattering function. Naturally all properties obtained from the computer experiment, including dynamics heterogeneity, frequency dispersion, the relation between the α and JG βrelaxation, and the breakdown of the StokesEinstein relation, are parallel consequences of the manybody relaxation dynamics governed by the intermolecular potential.},
doi = {10.1063/1.4913980},
journal = {Journal of Chemical Physics},
issn = {00219606},
number = 11,
volume = 142,
place = {United States},
year = {2015},
month = {3}
}