Secondary Johari–Goldstein relaxation in linear polymer melts represented by a simple bead-necklace model

Bedrov, Dmitry; Smith, Grant D.

doi:10.1016/j.jnoncrysol.2010.06.043

Cited by 48 publications

(95 citation statements)

References 26 publications

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“…The dielectric spectra of the polar component measured with different combinations of P and T at constant α-loss peak frequency show the approximate coinvariance of τ β , τ α , and (1 − n). Moreover, molecular dynamics simulations of linear polymer melts represented by simple bead-necklace models were performed at ambient and elevated pressure by Bedrov and Smith, showing the same trend [33]. The torsional autocorrelation function (TACF) shows the presence of the JG β-relaxation at shorter times to be followed by the α-relaxation.…”

Section: Johari-goldstein Relaxation Of Rigid Polar Probes In Apolar mentioning

confidence: 85%

“…In 1970, Johari and Goldstein shocked the research community by showing the existence of secondary relaxation in a totally rigid small molecular glass-former [1]. Starting from 1998, Ngai [2][3][4], Ngai and co-workers , and other workers [27][28][29][30][31][32][33] found secondary relaxations belonging to a special class have properties bearing strong connection to the α-relaxation in glass-formers of various chemical and physical compositions. For non-polymeric glass-formers in general that can be flexible or not totally rigid, the secondary relaxation in the special class has to involve the entire molecule or the basic relaxation unit.…”

Section: Introductionmentioning

confidence: 99%

“…This experimental advance is complemented by elegant molecular dynamics simulations of polymers [33]. Another research trend of recent years is the study of the modification of the relation between the JG β-relaxation and the α-relaxation of a glass-former by mixing with another glass-former having significantly different T g [14,25,32,43].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Revealing the rich dynamics of glass-forming systems by modification of composition and change of thermodynamic conditions

Thayyil

Ngai

Prevosto

et al. 2015

Journal of Non-Crystalline Solids

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Section: Johari-goldstein Relaxation Of Rigid Polar Probes In Apolar mentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Revealing the rich dynamics of glass-forming systems by modification of composition and change of thermodynamic conditions

Thayyil

Ngai

Prevosto

et al. 2015

Journal of Non-Crystalline Solids

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“…Similar molecules that are symmetric [19,20] or almost symmetric [21][22][23][24] undergo 180 degree flips, which have a signature in the correlation function different from that observed experimentally, but a possible connection to the JG-process has been noted. A Johari-Goldstein process has also been observed in simulations of bead-spring polymers [25,26], In this paper we discuss features of the a and fi relaxations measured by different orientational correlators, which in experiments are detected by different techniques (first-order correlation function by dielectric spectroscopy, second-order by dynamic light scattering and NMR). We also examine how characteristics such as the temporal separation and spectral breadths of the relaxations depend on the molecular asymmetry.…”

Section: Introductionmentioning

confidence: 82%

Rotational dynamics of simple asymmetric molecules

Fragiadakis

Roland

2015

Phys. Rev. E

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Molecular dynamic simulations were carried out on rigid diatomic molecules, which exhibit both α (structural) and β (secondary) dynamics. The relaxation scenarios range from onset behavior, in which a distinct α process emerges on cooling, to merging behavior, associated with two relaxation peaks that converge at higher temperature. These properties, as well as the manifestation of the β peak as an excess wing, depend not only on thermodynamic conditions, but also on both the symmetry of the molecule and the correlation function (odd or even) used to analyze its dynamics. These observations help to reconcile divergent results obtained from different experiments. For example, the β process is more intense and the α-relaxation peak is narrower in dielectric relaxation spectra than in dynamic light scattering or NMR measurements. In the simulations herein, this follows from the weaker contribution of the secondary relaxation to even-order correlation functions, related to the magnitude of the relevant angular jumps.

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“…[6][7][8][9][10] These experimental investigations might be motivated by the cumulated findings of the relevance of the faster processes to a fundamental solution of the glass transition problem. [16][17][18][19][20][21][22][23][24][25][26][27] For glass-formers without a resolved secondary relaxation such as glycerol and propylene carbonate, the immediate faster process is the excess wing (EW), [18][19][20][21][28][29][30][31][32] which shows up in the dielectric loss, ε ′′ ( f ), as a second power law of frequency f at the high frequency flank of the α-loss peak, i.e., ε ′′ ( f ) = A(T) f −c with c approximately about 0.5. By lowering temperature T to approach or to fall below the glass transition temperature T g , another power law with small value of the exponent c appears at even higher frequencies and is appropriately referred to as the nearly constant loss (NCL).…”

Section: Introductionmentioning

confidence: 99%

Interpreting the nonlinear dielectric response of glass-formers in terms of the coupling model

Ngai

2015

The Journal of Chemical Physics

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Nonlinear dielectric measurements at high electric fields of glass-forming glycerol and propylene carbonate initially were carried out to elucidate the dynamic heterogeneous nature of the structural α-relaxation. Recently, the measurements were extended to sufficiently high frequencies to investigate the nonlinear dielectric response of faster processes including the so-called 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 α-relaxation, 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 α-relaxation 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 α-relaxation is reached. These intermediate faster relaxations, combined to form the so-called Johari-Goldstein (JG) β-relaxation, are spatially and dynamically heterogeneous, and hence exhibit nonlinear dielectric effects, as found in glycerol and propylene carbonate, where the JG β-relaxation is not resolved and in D-sorbitol where it is resolved. Like the linear susceptibility, χ1(f), the frequency dispersion of the third-order dielectric susceptibility, χ3(f), was found to depend primarily on the α-relaxation time, and independent of temperature T and pressure P. I show this property of the frequency dispersions of χ1(f) and χ3(f) is the characteristic of the many-body 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 χ3(f), dynamic heterogeneity is one of the parallel consequences of the many-body dynamics, and it should not be considered as the principal control parameter for the other dynamic properties of glassforming systems. Results same as χ3(f) at elevated pressures had been obtained before by molecular dynamics simulations from the four-points 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 β-relaxation, and the breakdown of the Stokes-Einstein relation, are parallel consequences of the many-body relaxation dynamics governed by the intermolecular potential.

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Secondary Johari–Goldstein relaxation in linear polymer melts represented by a simple bead-necklace model

Cited by 48 publications

References 26 publications

Revealing the rich dynamics of glass-forming systems by modification of composition and change of thermodynamic conditions

Revealing the rich dynamics of glass-forming systems by modification of composition and change of thermodynamic conditions

Rotational dynamics of simple asymmetric molecules

Interpreting the nonlinear dielectric response of glass-formers in terms of the coupling model

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