Single electron states in polyethylene

Wang, Y.; MacKernan, Donal; Cubero, David; Coker, David F.; Quirke, N.

doi:10.1063/1.4869831

Cited by 49 publications

(55 citation statements)

References 30 publications

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“…There have been both experimental and computational efforts in tracing the origin of these traps and quantifying their density and energies, including traps due to the polaron effect 60 , structural disorder and cavities 61 , and chemical defects and impurities 15,16,62,63 . But a comprehensive picture of the relationship between the trapping parameters and the polymer chemistry, processing condition and the electrical ageing is still missing, posing difficulties for material design.…”

Section: Discussionmentioning

confidence: 99%

On the nature of high field charge transport in reinforced silicone dielectrics: Experiment and simulation

Huang

Schadler

2016

Journal of Applied Physics

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The high field charge injection and transport properties in reinforced silicone dielectrics were investigated by measuring the time-dependent space charge distribution and the current under dc conditions up to the breakdown field, and were compared with properties of other dielectric polymers. It is argued that the energy and spatial distribution of localized electronic states are crucial to determining these properties for polymer dielectrics. Tunneling to localized states likely dominates the charge injection process. A transient transport regime arises due to the relaxation of charge carriers into deep traps at the energy band tails, and is successfully verified by a Monte Carlo simulation using the multiple-hopping model. The charge carrier mobility is found to be highly heterogeneous due to non-uniform trapping. The slow moving electron packet exhibits a negative field dependent drift velocity possibly due to the spatial disorder of traps.

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Section: Discussionmentioning

confidence: 99%

On the nature of high field charge transport in reinforced silicone dielectrics: Experiment and simulation

Huang

Schadler

2016

Journal of Applied Physics

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“…At room temperature, PE is semicrystalline, consisting of both amorphous and crystalline regions. The semicrystalline state, which is significantly more complex to model than the isolated amorphous and crystalline states, has received some attention 9–14 . The complexity arises from the crystal-amorphous interface (interphase) and the fact that the packing of the stems in the crystalline phase is also affected by the structure of the amorphous phase 15 …”

Section: Introductionmentioning

confidence: 99%

“…In DFT simulations, PE is usually modeled as a single isolated oligomeric chain 30,31 or as a fully amorphous or fully crystalline polymer 25 . Only a few studies have previously examined the electronic structure of semicrystalline PE using DFT 14 or other theoretical approaches 9 …”

Section: Introductionmentioning

confidence: 99%

First-principle simulations of electronic structure in semicrystalline polyethylene

Moyassari

Unge

Hedenqvist

et al. 2017

The Journal of Chemical Physics

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In order to increase our fundamental knowledge about high-voltage cable insulation materials, realistic polyethylene (PE) structures, generated with a novel molecular modeling strategy, have been analyzed using first principle electronic structure simulations. The PE structures were constructed by first generating atomistic PE configurations with an off-lattice Monte Carlo method and then equilibrating the structures at the desired temperature and pressure using molecular dynamics simulations. Semicrystalline, fully crystalline and fully amorphous PE, in some cases including crosslinks and short-chain branches, were analyzed. The modeled PE had a structure in agreement with established experimental data. Linear-scaling density functional theory (LS-DFT) was used to examine the electronic structure (e.g., spatial distribution of molecular orbitals, bandgaps and mobility edges) on all the materials, whereas conventional DFT was used to validate the LS-DFT results on small systems. When hybrid functionals were used, the simulated bandgaps were close to the experimental values. The localization of valence and conduction band states was demonstrated. The localized states in the conduction band were primarily found in the free volume (result of gauche conformations) present in the amorphous regions. For branched and crosslinked structures, the localized electronic states closest to the valence band edge were positioned at branches and crosslinks, respectively. At 0 K, the activation energy for transport was lower for holes than for electrons. However, at room temperature, the effective activation energy was very low (∼0.1 eV) for both holes and electrons, which indicates that the mobility will be relatively high even below the mobility edges and suggests that charge carriers can be hot carriers above the mobility edges in the presence of a high electrical field.

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“…The input to the model is the electron contact density, the dimensions of the sample and the density of excess electron states (DoS), which we divide into two contributions; the low energy (shallow) physical traps where the DoS is taken from ab initio simulations of amorphous polyethylene [7] and the high energy (deep) chemical traps represented by a single trap [8]. The model solves a current-field equation together with the Poisson equation for the variation of charge density with field, in the absence of diffusion and polarization currents, and is based on a transport model involving electrons hopping from localized trap states to the mobility edge and then back down to a new localized state in a different position.…”

Section: Electrical Conductionmentioning

confidence: 99%

Dielectric breakdown strength and electrical conductivity of low density polyethylene octylnanosilica composite

Virtanen¹,

Vaughan²,

Yang³

et al. 2016

2016 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP)

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Abstract-One challenge in studying nanodielectric composites is to produce reliable, reproducible samples. A common strategy to suppress aggregation and make the particles more compatible with the polymer matrix is to modify the nanoparticle surface chemistry but, often, evaluation of the effectiveness of the chosen surface functionalization process can prove difficult. In this paper the emphasis is on feasible ways to monitor the production of silane coupled nanosilica low density polyethylene (LDPE) composites, using Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). The AC-breakdown properties of the resulting composites is studied and the field dependency of the DCconductivity is measured and also calculated using a space charge limited conduction (SCLC) model together with densities of states obtained from ab initio calculations. For composites containing 13 wt% of nanosilica, breakdown strengths some 18 % higher than that of the unfilled LDPE were obtained. However, the results are not stable over time. This appears to be related to how extensively the composite is dried at elevated temperatures under vacuum.

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Single electron states in polyethylene

Cited by 49 publications

References 30 publications

On the nature of high field charge transport in reinforced silicone dielectrics: Experiment and simulation

On the nature of high field charge transport in reinforced silicone dielectrics: Experiment and simulation

First-principle simulations of electronic structure in semicrystalline polyethylene

Dielectric breakdown strength and electrical conductivity of low density polyethylene octylnanosilica composite

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