Complex dielectric constant of dipolar compounds as a function of temperature, pressure and frequency. Part 1 .—General relations and a consideration of models for relaxation

Williams, Graham

doi:10.1039/tf9646001548

Cited by 116 publications

(73 citation statements)

References 3 publications

(5 reference statements)

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“…33,54,63,64 The general observation is that for van der Waals liquids neither temperature nor pressure is the dominant variable controlling τ. For polymers such as PVAc and poly(methyl acrylate), polar interactions may increase somewhat the role of temperature; however, it is only for the polyalcohols in Table 1, associated with extensive hydrogen bonding, that the effect of volume can be neglected.…”

Section: Summary and Concluding Remarksmentioning

confidence: 99%

Temperature and Volume Effects on Local Segmental Relaxation in Poly(vinyl acetate)

2003

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Dielectric data on the local segmental relaxation of amorphous poly(vinyl acetate) (PVAc) are analyzed. At atmospheric pressure, the fragility (Tg-normalized temperature dependence) is invariant to molecular weight. Since the fragility is also independent of pressure, the combined temperature and pressure dependences of the relaxation times can be analyzed using the Avramov model of structural relaxation. This entropy model gives a satisfactory description of the data and yields an expression for the pressure dependence of the dynamic glass transition identical to the empirical Andersson equation. Although in principle the Avramov model parameters can be deduced from measurable thermodynamic properties of the glass-former, the results are at odds with the values obtained from fitting the relaxation times for PVAc. Using pressure-volume-temperature data, the respective contributions of thermal energy and volume to the local dynamics in PVAc were assessed. Specifically, we calculate the ratio of the isochoric to isobaric apparent activation energies. The obtained value, ≈0.6 at atmospheric pressure just above T g, indicates that temperature and volume both govern to a significant degree the relaxation times. This result is supported by a comparison of the relative magnitude of the isobaric and isochronal thermal expansion coefficients. These properties of PVAc are similar to those of other nonassociated polymers and glass-forming liquids and can be shown to be weakly correlated with the degree of super-Arrhenius behavior.

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Section: Summary and Concluding Remarksmentioning

confidence: 99%

Temperature and Volume Effects on Local Segmental Relaxation in Poly(vinyl acetate)

2003

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“…The latter has the advantage of providing a broad frequency range (routinely ten decades and even more at ambient pressure), which is essential since relaxation times vary by many orders of magnitude in the supercooled regime. Although dielectric spectroscopy measurements at elevated pressure were carried out forty years ago 30,31,32,33,34,35,36,37,38,39 , there has been a bit of a lull until very recently. For a comprehensive review of high pressure measurements see ref.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic interpretation of the scaling of the dynamics of supercooled liquids

Casalini

Mohanty²,

Roland³

2006

The Journal of Chemical Physics

183

217

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“…To a lesser extent dielectric techniques have been used to study the effect of pressure on the relaxations of phase materials [2][3][4][5][6][7][8][9]. By varying pressure, temperature and frequency, one can separate the activation energy and activation volume contributions to the activation enthalpy [4].…”

Section: Introductionmentioning

confidence: 99%

The dependence of dielectric response of an elastomer on hydrostatic pressure

Pae

Questad

1983

J. Polym. Sci. Polym. Phys. Ed.

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Dielectric methods have been employed to study the high‐pressure behavior of a polyurethane elastomer (Solithane 113) in the vicinity of its α transition. The α‐loss peak is shifted to higher temperatures and broadened somewhat with the application of hydrostatic pressure up to 6.4 kbars. The slope of Tα vs. P, or dTα/dP, obtained at low frequencies was found to be equal to dTg/dP obtained by a volumetric method. Moreover, it attained a nonzero limiting value at high pressures for each frequency tested (3—30,000 Hz) and the limiting value itself increased with increasing frequency from 10.5°C/kbar at 3 Hz to 18°C/kbar at 30,000 Hz. The activation enthalpy ΔH* was found to be nearly constant over the pressure range tested, but the activation volume ΔV* decreased with increasing pressure. The relation dTα/dP = T (ΔV*/ΔH*) was shown to hold for the elastomer.

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Complex dielectric constant of dipolar compounds as a function of temperature, pressure and frequency. Part 1 .—General relations and a consideration of models for relaxation

Cited by 116 publications

References 3 publications

Temperature and Volume Effects on Local Segmental Relaxation in Poly(vinyl acetate)

Temperature and Volume Effects on Local Segmental Relaxation in Poly(vinyl acetate)

Thermodynamic interpretation of the scaling of the dynamics of supercooled liquids

The dependence of dielectric response of an elastomer on hydrostatic pressure

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