| 1. |
- Gedde, Ulf W, et al.
(författare)
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Mass and charge transport in polyethylene – Structure, morphology and properties
- 2023
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 266
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Forskningsöversikt (refereegranskat)abstract
- Polyethylene is a model for semicrystalline polymers that provides the option to vary crystallinity within wide ranges and then to establish relationships between structure and mass and charge transport properties. Three different topics are covered: diffusion of n-hexane in polyethylene, extensive penetrant uptake kinetics, swelling and the design of a novel sensor, and finally electrical conduction in polyethylene, a field important to modern distribution of electric power (HVDC). This feature article presents past and ongoing studies at KTH Royal Institute of Technology using a variety of experimental methods and computer-aided simulation and modelling.
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| 2. |
- Unge, Mikael, et al.
(författare)
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Coarse-Grained Model for Prediction of Hole Mobility in Polyethylene
- 2023
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 19:21, s. 7882-7894
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Tidskriftsartikel (refereegranskat)abstract
- Electrical conductivity measurements of polyethylene indicate that the semicrystalline structure and morphology influence the conductivity. To include this effect in atomistic charge transport simulations, models that explicitly or implicitly take morphology into account are required. In the literature, charge transport simulations of amorphous polyethylene have been successfully performed using short oligomers to represent the polymer. However, a more realistic representation of the polymer structure is desired, requiring the development of fast and efficient charge transport algorithms that can handle large molecular systems through coarse-graining. Here, such a model for charge transport simulations in polyethylene is presented. Quantum chemistry calculations were used to define six segmentation rules on how to divide a polymer chain into shorter segments representing localized molecular orbitals. Applying the rules to amorphous systems yields distributions of segments with mode and median segment lengths relatively close to the persistence length of polyethylene. In an initial test, the segments of an amorphous polyethylene were used as hopping sites in kinetic Monte Carlo (KMC) simulations, which yielded simulated hole mobilities that were within the experimental range. The activation energy of the simulated system was lower compared to the experimental values reported in the literature. A conclusion may be that the experimental result can only be explained by a model containing chemical defects that generate deep traps.
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| 3. |
- Unge, Mikael, et al.
(författare)
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Hole mobility in amorphous polyethylene - Impact of intra-chain electronic coupling
- 2023
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Ingår i: 2023 IEEE Conference on Electrical Insulation and Dielectric Phenomena, CEIDP 2023. - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350335620
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Konferensbidrag (refereegranskat)abstract
- Experimental results indicate that electrical conductivity in polyethylene depend on the morphology. In order to simulate mobility in polyethylene the morphology need to be included implicitly or explicitly. To include the morphology explicitly in atomic scale simulation of mobility the charge transport along the chain need to described. Marcus theory can be used to describe the hopping process. Here a ghost atom model was used to calculate electronic coupling both along and between chains. A factor 10 difference was seen between intra-chain electronic coupling obtained here compared to previous results. However, the charge transport in amorphous polyethylene was primarily limited by the inter-chain electronic coupling.
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| 4. |
- Unge, Mikael, et al.
(författare)
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Electron traps in polyethylene due to water
- 2022
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Ingår i: ICD 2022 - IEEE 2022 4th International Conference on Dielectrics. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 210-213
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Konferensbidrag (refereegranskat)abstract
- Electron traps in polyethylene (PE) origin from water has been calculated using density functional theory. Atomistic structure has been simulated using molecular dynamics (MD) and used to calculate the electronic structure. Densities comparable with experimentally determined values are obtained. Both single water molecules and cluster of water molecules are considered. For a single water molecule both electron and hole states are within the bands from PE. The electron state is close to the conduction band minima (CBM) and may coincide with the CBM depending on the local atomic density. The absence of electron traps due to water is contradictory to previous simulation results but can be explained by atomic density and relaxation of conduction states of PE. Systems with 10 water molecules relaxed to two pentamers in the MD simulations. Calculation of trap levels of the pentamers result in trap levels in the order of 0.1-0.3 eV.
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| 5. |
- Unge, Mikael, et al.
(författare)
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Electronic conductivity of polymer electrolytes : electronic charge transport properties of LiTFSI-doped PEO
- 2020
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 22:15, s. 7680-7684
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of poly(ethyleneoxide) with and without a common electrolyte lithium bis(trifluoromethane)sulfonimide salt is calculated from first principles. Introducing the salt into the polymer electrolyte significantly reduces the band gap, down to 0.6 eV. Thus, this will have a significant impact on the leakage currents in polymer electrolytes used in all-solid-state batteries.
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