Thermally Stimulated Depolarization of Phase-Separated Polymer Systems

Vanderschueren, J.; Ladang, M.; Heuschen, J.

doi:10.1021/ma60076a041

Cited by 27 publications

(9 citation statements)

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“…The electrical properties of heterogeneous media are important in many branches of science, in colloid physics and chemistry [1][2][3][4][5][6], in the physics of metalinsulator composites and alloys [7][8][9][10][11][12][13][14], in geophysics [15,16], in photographical physics [17][18][19][20], and in the description of phase separated glasses [21][22][23][24][25], ceramics [26], and polymers [27][28][29][30][31][32][33]. As has been stressed in an earlier review [34] scientists dealing with these topics are frequently unaware of each other's work and results.…”

Section: Introductionmentioning

confidence: 99%

Comparison of electrical mixture rules for composites

Bánhegyi

1986

Colloid & Polymer Sci

196

139

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Firstly the basic theoretical methods of calculating the dielectric properties of heterogeneous mixtures are discussed. These are the mean field and effective medium theories and integral methods. Formulae are presented for systems containing parallel oriented ellipsoids and for randomly oriented ellipsoidal systems. Theoretical formulae are divided into two sub-groups: symmetric equations for statistical mixtures and asymmetric equations for matrix-inclusion type composites. In the former case only the relative amount of the components is important, in the second case phase inversion results in a change of the dielectric properties.Formulae are compared numerically using spherical and spheroidal systems with sharply different components (permittivity ratio is I : 100). In the case of asymmetric formulae the effect of phase inversion is studied as well. Percolation behaviour predicted by the equations is demonstrated and discussed. Functional shapes are compared in relation to the theoretical differences.Finally, experimental data are compared with the theoretical results, advantages and drawbacks of the various formulae are discussed. For spherical systems the simplest mean field formula yields somewhat worse values than effective medium or integral equations. The Looyenga equation does not work very well if the permittivity difference is high. For nonspherical systems the fit is better in general, even the simplest formula works satisfactorily. The shape independence predicted by the Looyenga theory for randomly oriented ellipsoids is in conflict with experimental data.

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Section: Introductionmentioning

confidence: 99%

Comparison of electrical mixture rules for composites

Bánhegyi

1986

Colloid & Polymer Sci

196

139

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“…In the TSDC case, these two peaks reflect essentially the two main relaxation ranges typical of diene elastomers (15). The ~ peak appears close to the glass transition temperature as determined by differential scanning calorimetry (Tg = 186 K) and can, thus, be related to microBrownian motions of Chain segments (~ relaxation) involving in particular rotation of cis and v.inYlbutadiene isomers (effective dipole moment --8.2 • 10 -~1 Cm) (16) while the/3 peak corresponds well to the low temperature complex peak observed in pure polybutadiene by dynamic mechanical measurements and can, thus, be ascribed to local chain motions (~ relaxation) (17).…”

Section: Resultsmentioning

confidence: 95%

Effect of Crosslinking and Doping on Thermoluminescence of U.V.‐Irradiated Polymers

Ladang¹,

Vanderschueren

Niézette

et al. 1983

J. Electrochem. Soc.

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The thermoluminescence (TL) of elastomeric materials modified by doping and chemical or ~-induced crosslinking was measured following irradiation with u.v. light at 77 K and compared with the thermally stimulated depolarization currents (TSDC) obtained during warmup of samples previously polarized from 298 to 77 K, stressing the comparison of luminescence and current peaks observed in the glass ~ransition range. Significant.shiftings of the TL peaks were found as a function of degree of crosslinking and nature of the dophnt, even though the glass transition temperature and the position of the TSDC peaks were not affected, showing that the kinetics of the light-emitting process is not only governed by the thermal motions of the polymer units but also critically depends on the nature of traps and luminescent species. Generally speaking, the TL method appears to be much more sensitive than the classical relaxation methods to any structural, morphological, or environmental change of the macromolecular chains and seems, thus, particularly attractive to obtain valuable information on new aspects of polymer relaxation.The thermoluminescence (TL), which involves measuring and analyzing light emitted during warmup of materials previously irradiated at low temperature, is generally considered as a useful means for studying molecular motion and structural transitions occurring in polymeric solids (1-5). On the basis of significant correlations observed between the TL glow curves and the relaxation peaks obtained by mechanical or dielectric loss measurements, it is usually assumed that the luminescence emission depends on the molecular mobility either because the macromolecular chains can act as effective carrier traps (e.g., Via formation of dielectric cavity traps defined by the chains themselves) or because the release of charge carriers from other traps (such as free radicals or neutral molecules with positive electron affinity) can only occur as a result of the onset of local motion involving molecules located in the immediate vicinity of the trap (1-5). As an alternative to the detrapping phenomenon, it has been sometimes postulated that charge recombination can occur by physical approach and reaction of a radical ion with the parent ion or any other neighboring positive ion (3). In principle, such a process should be also closely related to structural changes in the polymeric matrix because it is likely to arise only in a temperature range where large scale motion sets in, i.e., in the vicinity of the glass transition temperature Tg. Whatever the exact trapping and detrapping mechanisms involved and the nature of luminescence centers, the macromolecular motions are, thus, expected to contribute Significantly to the light-emitting processes in such a way that the TL glow curve could be considered as reflecting the relaxation itself and could be used to determine the transition temperatures.We have recently shown, however, that, at least in certain polymers, the type of impurity present in the matrix can atso play a pre...

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“…In TSC spectra of this acrylic polymer, which is analogous to PMMA, the first peak at -40~ is associated to the ~ relaxation [7,8] of the polymer which is due to localized movements. At the higher temperature, the e~ relaxation corresponding to the glass transition which can be the peak at around 120~…”

Section: Aging On Airplane Windowsmentioning

confidence: 97%

Characterization of polymers using the thermally stimulated current technique

Galop¹

1997

Journal of Thermal Analysis

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Thermally Stimulated Current (I'SC) technique is a relaxation technique, such as DMA, but works at very low equivalent frequency (10-3-10 -4 Hz) and thus clearly resolves the peaks related to the molecular mobility. The effect of orientation on Polypropylene fibers, the relaxation of internal stresses on Polycarbonate disks, and the effect of aging on acrylic airplane windows have been investigated using the TSC method.

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Thermally Stimulated Depolarization of Phase-Separated Polymer Systems

Cited by 27 publications

References 0 publications

Comparison of electrical mixture rules for composites

Comparison of electrical mixture rules for composites

Effect of Crosslinking and Doping on Thermoluminescence of U.V.‐Irradiated Polymers

Characterization of polymers using the thermally stimulated current technique

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