Electron trapping in polyethylene

Wang, Yang; Wu, Kai; Cubero, David; MacKernan, Donal; Coker, David F.; Quirke, N.

doi:10.1109/icsd.2013.6619710

Cited by 5 publications

(13 citation statements)

References 9 publications

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“…In order to explore their influence on excess electrons, nanometre sized voids were produced in the simulated amorphous phase by expanding a test particle [44]. By calculating the Gibbs free energy to create different radius of spherical voids in amorphous PE, a surface tension of 36 mN/M was obtained, in good agreement with the experimental value of 35.7 mN/M at 20 o C for linear HDPE [50].…”

Section: Pe Morphologies and Its Conformational Disordersmentioning

confidence: 80%

“…In the interfaces between lamellae and amorphous phases, the lowest atomic density values are found either in the amorphous regions or near the interface [45]. Figure 2 shows a typical ground state localized in that area.…”

Section: Electronic Properties Of Pementioning

confidence: 97%

“…More recently, multi-phase polyethylene morphologies including crystalline, amorphous, lamellae and interfacial regions have been studied using MD [44,45]. As discussed in reference [2], a polyethylene sample may contain amorphous, lamellae and crystalline regions of various sizes depending on the material processing details.…”

Section: Pe Morphologies and Its Conformational Disordersmentioning

confidence: 99%

“…As discussed in reference [2], a polyethylene sample may contain amorphous, lamellae and crystalline regions of various sizes depending on the material processing details. In reference [44], model crystalline and lamellae regions were created by geometry optimization using the all-atom COMPASS forcefield in Materials Studio 5.5 [46]. For the lamellae regions, gauche and anti-gauche defects were introduced into ten all-trans PE chains with 552 CH2 units in order to enable them to fold back and forth upon themselves, resulting in a lamellar thickness of around 5.0 nm.…”

Section: Pe Morphologies and Its Conformational Disordersmentioning

confidence: 99%

“…Very recently, the analysis of references [27,60] has been extended to larger systems and more representative regions of PE, including lamellae and interfaces between lamellae and amorphous [44,45]. A clear correlation between local atomic density (calculated as the number of CH2 united atoms per unit volume in a cube of side 0.5nm at a given position) and electron probability has been found in all PE phases, showing that the electron is more likely to localize in lower density regions.…”

Section: Electronic Properties Of Pementioning

confidence: 99%

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Molecular modeling and electron transport in polyethylene

Wang

Cubero

et al. 2014

IEEE Trans. Dielect. Electr. Insul.

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Polyethylene is commonly used as an insulator for AC power cables. However it is known to undergo chemical and physical change which can lead to dielectric breakdown. Despite almost eighty years of experimental characterization of its electrical properties, very little is known about the details of the electrical behaviour of this material at the molecular level. An understanding of the mechanisms of charge trapping and transport could help in the development of materials with better insulating properties required for the next generation of high voltage AC and DC cables. Molecular simulation techniques provide a unique tool with which to study dielectric processes at the atomic and electronic level. Here we summarise simulation methodologies which have been used to study the properties of PE at the molecular level, elucidating the role of morphology in the trapping of excess electrons. We find that polyethylene has localised states due to conformational trapping extending below the mobility edge (above which the excess electrons are delocalised), at -0.1±0.1eV with respect to the vacuum level. These trap states with localisation lengths between 0.3 and 1.2nm have energies as low as -0.4±0.1eV in the amorphous and interfacial regions of polyethylene with more positive values in lamella structures. Crystalline regions have a mobility edge at +0.46 ±0.1eV, so we would expect transport by electrons excited above the mobility edge to delocalised states to be predominantly through amorphous regions if they percolate the sample.

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Section: Pe Morphologies and Its Conformational Disordersmentioning

confidence: 80%

Section: Electronic Properties Of Pementioning

confidence: 97%

Section: Pe Morphologies and Its Conformational Disordersmentioning

confidence: 99%

Section: Pe Morphologies and Its Conformational Disordersmentioning

confidence: 99%

Section: Electronic Properties Of Pementioning

confidence: 99%

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Molecular modeling and electron transport in polyethylene

Wang

Cubero

et al. 2014

IEEE Trans. Dielect. Electr. Insul.

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A model and simulation of fast space charge pulses in polymers

Rowland

2017

J. Phys. D: Appl. Phys.

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The transport of space charge packets across polyethylene and epoxy resin in high electric fields has been characterized as fast or slow depending on packet mobility. Several explanations for the formation and transport of slow space charge packets have been proposed, but the origins of fast space charge pulses, with mobilities above 10−11 m2 V−1 s−1, are unclear. In one suggested model, it is assumed that the formation of fast charge pulses is due to discontinuous electromechanical compression and charge injection at the electrode-insulation interface, and their transport is related to corresponding relaxation processes. In that model, charges travel as a pulse because of group polarization. This paper provides an alternative model based on the reduction of charge carrier activation energy due to charge density triggered polymer chain movement and subsequent chain relaxation times. The generation and transport of fast charge pulses are readily simulated by a bipolar charge transport model with three additional parameters: reduced activation energy, charge density threshold, and chain relaxation time. Such a model is shown to reproduce key features of fast space charge pulses including speed, duration, repetition rate and pulse size. This model provides the basis for a deep understanding of the physical origins of fast space charge pulses in polymers.

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