Dielectric Properties of Polymers

Williams, Graham

doi:10.1002/9783527603978.mst0142

Cited by 4 publications

(3 citation statements)

References 182 publications

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“…The mechanical compliance D* (ω) = D ‘ (ω) − iD ‘ ‘ (ω) is given by the one-sided Fourier or pure imaginary Laplace transform of the time derivative of the decay function φ( t ): where u and r designate unrelaxed (for ω → ∞ or t → 0) and relaxed compliance (for ω → 0 or t → ∞) values, respectively, and i 2 = −1.…”

Section: Resultsmentioning

confidence: 99%

Viscoelastic Behavior of Poly(methyl methacrylate) Networks with Different Cross-Linking Degrees

et al. 2004

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The influence of the cross-linking degree on the dynamics of the segmental motions close to the glass transition of poly(methyl methacrylate), PMMA, networks was investigated by three different mechanical spectroscopy techniques: thermally stimulated recovery (TSR), dynamic mechanical analysis (DMA), and creep. The application of the time-temperature superposition principle to isothermal DMA and creep results permitted to successfully construct master curves for PMMA networks with distinct cross-linking degrees. The former results were fitted to the KWW equation. The obtained variation of KWW for the distinct networks indicated that the relaxation curves tend to broaden as the cross-linking degree increases. TSR results clearly revealed a significant shift of the R-relaxation to longer times and a broader relaxation as the cross-linking degree increases, what was also observed by DMA and creep. A change from a Vogel to an Arrhenius behavior was detected by the three techniques with the decrease of temperature below T g. The temperature dependence of the apparent activation energies (Ea) was calculated from DMA, creep, and TSR experiments; above Tg a good agreement was seen between the Ea values for all the techniques. Furthermore, the effect of the cross-linking degree on the fragility of PMMA networks was evaluated. For these materials an increase of fragility with increasing cross-linking degree was observed.

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Section: Resultsmentioning

confidence: 99%

Viscoelastic Behavior of Poly(methyl methacrylate) Networks with Different Cross-Linking Degrees

et al. 2004

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“…The dielectric relaxation in polymer-LC composites is a rather complicated process to which various causes likely contribute, e.g., the dipole motions in the LC phase and the dipole motions in the host polymer matrix [76,89]. Even the slightly polar semi-crystalline polymer PEO itself exhibits multiple dielectric relaxations in the amorphous region; this is due to micro-Brownian motions of chains and due to the partial reorientation of chain segment dipoles [75,90,91]. In particular, the considered PEO/E8 and PEO/E8/NaIO 4 polymer-LC composites are extremely complex heterogeneous systems with complex geometries and morphologies, comprising LC nematic molecules confined in an amorphous (semi-crystalline) polymeric matrix (LC nematic molecules linked to molecular chains in a porous polymer network).…”

Section: Modelling Of Dielectric Behaviorsmentioning

confidence: 99%

Ion-Conducting Flexible Thin Films of Composites from Poly(ethylene oxide) and Nematic Liquid Crystals E8—Characterization by Impedance and Dielectric Relaxation Spectroscopy

et al. 2021

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Complex electrical impedance and dielectric spectroscopy were applied to study the dielectric relaxations and their thermal behavior in ion-conducting composites/complexes from polymer poly(ethylene oxide) (PEO) and E8 nematic liquid crystals (LCs), at the compositional ratio PEO:E8 = 70:30 wt%. Flexible thin films of PEO/E8 with a thickness of 150 μm were inspected, as well as such films from Na+ ion-conducting electrolyte PEO/E8/NaIO4 with the same PEO:E8 compositional ratio, but additionally containing 10 wt.% from the salt sodium metaperiodate (NaIO4) as a dopant of Na+ ions. The molecular dynamics, namely the dielectric relaxation of PEO/E8 and PEO/E8/NaIO4, were characterized through analyses of complex impedance and dielectric spectra measured in the frequency range of 1 Hz–1 MHz, under variation of temperature from below to above the glass-transition temperature of these composites. The relaxation and polarization of dipole formations in PEO/E8 and PEO/E8/NaIO4 were evidenced and compared in terms of both electrical impedance and dielectric response depending on temperature. The results obtained for molecular organization, molecular relaxation dynamics, and electric polarization in the studied ion-conducting polymer/LC composites/complexes can be helpful in the optimization of their structure and performance, and are attractive for applications in flexible organic electronics, energy storage devices, and mechatronics.

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“…[47,48] • Detailed accounts of our studies of the dielectric properties and alignment behaviour of SC-LCP materials were included in extensive reviews of the dielectric behaviour of liquid crystals [49] and amorphous, crystalline and liquid crystalline polymers. [50][51][52] …”

Section: Carbon-chain Sc-lcp Materialsmentioning

confidence: 99%

Alignment behaviour and molecular dynamics of liquid crystalline side-chain polymers

Williams

2015

liq cryst

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Studies made at Aberystwyth and Swansea of siloxane-chain liquid crystalline side-chain polymers (SC-LCP) provided by Professor George Gray at Hull University, together with those for certain carbon-chain SC-LCP are summarised briefly. Methods were developed to obtain materials homeotropically aligned (n||E), planarly/homogeneously aligned (n? E) or in any intermediate state of alignment through the use of ac electric fields of variable frequency. The molecular dynamics of the dipolar groups in these materials were studied over wide ranges of temperature and hydrostatic pressure using Broad Band Dielectric Spectroscopy covering 10 −4 to 10 5 Hz. Multiple relaxation processes were observed whose dielectric spectra changed markedly as the nature and degree of alignment were changed and the results were interpreted using macroscopic and molecular theories for the dielectric relaxation of such LCPs developed during these studies.

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Dielectric Properties of Polymers

Cited by 4 publications

References 182 publications

Viscoelastic Behavior of Poly(methyl methacrylate) Networks with Different Cross-Linking Degrees

Viscoelastic Behavior of Poly(methyl methacrylate) Networks with Different Cross-Linking Degrees

Ion-Conducting Flexible Thin Films of Composites from Poly(ethylene oxide) and Nematic Liquid Crystals E8—Characterization by Impedance and Dielectric Relaxation Spectroscopy

Alignment behaviour and molecular dynamics of liquid crystalline side-chain polymers

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