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Polymer degradation under oxidative conditions, particularly under accelerated stresses such as increased temperatures and irradiation, often exhibits spatially heterogeneous oxidation profiles. This well-known behavior is the result of diffusion-limited oxidation (DLO), which occurs when the oxidation rate is faster than the resupply of oxygen through diffusion into the material. So far most theoretical model descriptions have focused on DLO in equilibrium situations in which the underlying material properties do not change with increasing degradation levels or are constant (i.e. time-independent) variables. An extension of a previously developed finite element model is now presented, which accommodates time-dependent variables that are either explicitly time-dependent (i.e. changes homogeneously throughout the material), or through a feedback mechanism driven by the localized degree of oxidation, which results in spatial variations in the material properties responsible for specific DLO behavior. This model is realized in COMSOL Multiphysics and is capable of geometries in 1D up to 3D. Additionally, specific theoretical cases in 1D are shown which relate to known non-stationary phenomena in polymer degradation. They illustrate the effect on the resulting oxidation profile, when the oxygen diffusivity, solubility or oxidation rate properties change over time and in space. With COMSOL based FEM, it is now possible to model DLO for whatever material behavior may exist or could be envisaged.
Erik Linde; Fritjof Nilsson; Matija Barrett; Mikael S. Hedenqvist; Mathew C. Celina. Time- and Feedback-Dependent DLO Phenomena in Oxidative Polymer Aging. Polymer Degradation and Stability 2021, 189, 109598 .
AMA StyleErik Linde, Fritjof Nilsson, Matija Barrett, Mikael S. Hedenqvist, Mathew C. Celina. Time- and Feedback-Dependent DLO Phenomena in Oxidative Polymer Aging. Polymer Degradation and Stability. 2021; 189 ():109598.
Chicago/Turabian StyleErik Linde; Fritjof Nilsson; Matija Barrett; Mikael S. Hedenqvist; Mathew C. Celina. 2021. "Time- and Feedback-Dependent DLO Phenomena in Oxidative Polymer Aging." Polymer Degradation and Stability 189, no. : 109598.
Among the various requirements that high voltage direct current (HVDC) insulation materials need to satisfy, sufficiently low electrical conductivity is one of the most important. The leading commercial HVDC insulation material is currently an exceptionally clean cross-linked low-density polyethylene (XLPE). Previous studies have reported that the DC-conductivity of low-density polyethylene (LDPE) can be markedly reduced either by including a fraction of high-density polyethylene (HDPE) or by adding a small amount of a well dispersed, semiconducting nanofiller such as Al2O3 coated with a silane. This study demonstrates that by combining these two strategies a synergistic effect can be achieved, resulting in an insulation material with an ultra-low electrical conductivity. The addition of both HDPE and C8–Al2O3 nanoparticles to LDPE resulted in ultra-insulating nanocomposites with a conductivity around 500 times lower than of the neat LDPE at an electric field of 32 kV/mm and 60–90 °C. The new nanocomposite is thus a promising material regarding the electrical conductivity and it can be further optimized since the polyethylene blend and the nanoparticles can be improved independently.
Fritjof Nilsson; Mattias Karlsson; Ulf W. Gedde; Roland Kádár; Karolina Gaska; Christian Müller; Per-Ola Hagstrand; Richard T. Olsson; Mikael S. Hedenqvist; Thomas Gkourmpis. Nanocomposites and polyethylene blends: two potentially synergistic strategies for HVDC insulation materials with ultra-low electrical conductivity. Composites Part B: Engineering 2020, 204, 108498 .
AMA StyleFritjof Nilsson, Mattias Karlsson, Ulf W. Gedde, Roland Kádár, Karolina Gaska, Christian Müller, Per-Ola Hagstrand, Richard T. Olsson, Mikael S. Hedenqvist, Thomas Gkourmpis. Nanocomposites and polyethylene blends: two potentially synergistic strategies for HVDC insulation materials with ultra-low electrical conductivity. Composites Part B: Engineering. 2020; 204 ():108498.
Chicago/Turabian StyleFritjof Nilsson; Mattias Karlsson; Ulf W. Gedde; Roland Kádár; Karolina Gaska; Christian Müller; Per-Ola Hagstrand; Richard T. Olsson; Mikael S. Hedenqvist; Thomas Gkourmpis. 2020. "Nanocomposites and polyethylene blends: two potentially synergistic strategies for HVDC insulation materials with ultra-low electrical conductivity." Composites Part B: Engineering 204, no. : 108498.
The best commercial high-voltage insulation material of today is (crosslinked) ultra-pure low-density polyethylene (LDPE). A 100-fold decrease in electrical conductivity can be achieved by adding 1–3 wt.% of well-dispersed inorganic nanoparticles to the LDPE. One hypothesis is that the nanoparticle surfaces attract ions and polar molecules, thereby cleaning the surrounding polymer, and thus reducing the conductivity. LDPE-based nanocomposites with 1–12 wt.% octyl-coated aluminum oxide nanoparticles were prepared and the sorption and desorption of one polar compound (acetophenone, a crosslinking by-product) and one non-polar compound of a similar size (limonene) were examined. Since the uptake of acetophenone increased linearly with increasing filler content, whereas the uptake of limonene decreased, the surface attraction hypothesis was strengthened. The analytical functions for predicting composite solubility as a function of particle size and filler fraction were derived using experimental solubility measurements and Monte Carlo simulations.
Shima L. Holder; Mattias E. Karlsson; Richard T. Olsson; Mikael S. Hedenqvist; Fritjof Nilsson. Solubility and Diffusivity of Polar and Non-Polar Molecules in Polyethylene-Aluminum Oxide Nanocomposites for HVDC Applications. Energies 2020, 13, 722 .
AMA StyleShima L. Holder, Mattias E. Karlsson, Richard T. Olsson, Mikael S. Hedenqvist, Fritjof Nilsson. Solubility and Diffusivity of Polar and Non-Polar Molecules in Polyethylene-Aluminum Oxide Nanocomposites for HVDC Applications. Energies. 2020; 13 (3):722.
Chicago/Turabian StyleShima L. Holder; Mattias E. Karlsson; Richard T. Olsson; Mikael S. Hedenqvist; Fritjof Nilsson. 2020. "Solubility and Diffusivity of Polar and Non-Polar Molecules in Polyethylene-Aluminum Oxide Nanocomposites for HVDC Applications." Energies 13, no. 3: 722.
Hüsamettin Deniz Özeren; Richard T. Olsson; Fritjof Nilsson; Mikael S. Hedenqvist. Prediction of plasticization in a real biopolymer system (starch) using molecular dynamics simulations. Materials & Design 2020, 187, 1 .
AMA StyleHüsamettin Deniz Özeren, Richard T. Olsson, Fritjof Nilsson, Mikael S. Hedenqvist. Prediction of plasticization in a real biopolymer system (starch) using molecular dynamics simulations. Materials & Design. 2020; 187 ():1.
Chicago/Turabian StyleHüsamettin Deniz Özeren; Richard T. Olsson; Fritjof Nilsson; Mikael S. Hedenqvist. 2020. "Prediction of plasticization in a real biopolymer system (starch) using molecular dynamics simulations." Materials & Design 187, no. : 1.
Guanda Yang; Fritjof Nilsson; Dirk W. Schubert. A Study of Finite Size Effects and Periodic Boundary Conditions to Simulations of a Novel Theoretical Self‐Consistent Mean‐Field Approach. Macromolecular Theory and Simulations 2019, 28, 1 .
AMA StyleGuanda Yang, Fritjof Nilsson, Dirk W. Schubert. A Study of Finite Size Effects and Periodic Boundary Conditions to Simulations of a Novel Theoretical Self‐Consistent Mean‐Field Approach. Macromolecular Theory and Simulations. 2019; 28 (5):1.
Chicago/Turabian StyleGuanda Yang; Fritjof Nilsson; Dirk W. Schubert. 2019. "A Study of Finite Size Effects and Periodic Boundary Conditions to Simulations of a Novel Theoretical Self‐Consistent Mean‐Field Approach." Macromolecular Theory and Simulations 28, no. 5: 1.
Fritjof Nilsson; Mattias Karlsson; Love Pallon; Marco Giacinti; Richard T. Olsson; Davide Venturi; Ulf W. Gedde; Mikael S. Hedenqvist. Corrigendum to “Influence of water uptake on the electrical DC-conductivity of insulating LDPE/MgO nanocomposites” [Compos. Sci. Technol. 152 (2017) 11-19]. Composites Science and Technology 2019, 181, 107668 .
AMA StyleFritjof Nilsson, Mattias Karlsson, Love Pallon, Marco Giacinti, Richard T. Olsson, Davide Venturi, Ulf W. Gedde, Mikael S. Hedenqvist. Corrigendum to “Influence of water uptake on the electrical DC-conductivity of insulating LDPE/MgO nanocomposites” [Compos. Sci. Technol. 152 (2017) 11-19]. Composites Science and Technology. 2019; 181 ():107668.
Chicago/Turabian StyleFritjof Nilsson; Mattias Karlsson; Love Pallon; Marco Giacinti; Richard T. Olsson; Davide Venturi; Ulf W. Gedde; Mikael S. Hedenqvist. 2019. "Corrigendum to “Influence of water uptake on the electrical DC-conductivity of insulating LDPE/MgO nanocomposites” [Compos. Sci. Technol. 152 (2017) 11-19]." Composites Science and Technology 181, no. : 107668.
Promising electrical field grading materials (FGMs) for high-voltage direct-current (HVDC) applications have been designed by dispersing reduced graphene oxide (rGO) grafted with relatively short chains of poly (n-butyl methacrylate) (PBMA) in a poly(ethylene-co-butyl acrylate) (EBA) matrix. All rGO-PBMA composites with a filler fraction above 3 vol.% exhibited a distinct non-linear resistivity with increasing electric field; and it was confirmed that the resistivity could be tailored by changing the PBMA graft length or the rGO filler fraction. A combined image analysis- and Monte-Carlo simulation strategy revealed that the addition of PBMA grafts improved the enthalpic solubility of rGO in EBA; resulting in improved particle dispersion and more controlled flake-to-flake distances. The addition of rGO and rGO-PBMAs increased the modulus of the materials up to 200% and the strain did not vary significantly as compared to that of the reference matrix for the rGO-PBMA-2 vol.% composites; indicating that the interphase between the rGO and EBA was subsequently improved. The new composites have comparable electrical properties as today’s commercial FGMs; but are lighter and less brittle due to a lower filler fraction of semi-conductive particles (3 vol.% instead of 30–40 vol.%).
Carmen Cobo Sánchez; Martin Wåhlander; Mattias Karlsson; Diana C. Marin Quintero; Henrik Hillborg; Eva Malmström; Fritjof Nilsson. Characterization of Reduced and Surface-Modified Graphene Oxide in Poly(Ethylene-co-Butyl Acrylate) Composites for Electrical Applications. Polymers 2019, 11, 740 .
AMA StyleCarmen Cobo Sánchez, Martin Wåhlander, Mattias Karlsson, Diana C. Marin Quintero, Henrik Hillborg, Eva Malmström, Fritjof Nilsson. Characterization of Reduced and Surface-Modified Graphene Oxide in Poly(Ethylene-co-Butyl Acrylate) Composites for Electrical Applications. Polymers. 2019; 11 (4):740.
Chicago/Turabian StyleCarmen Cobo Sánchez; Martin Wåhlander; Mattias Karlsson; Diana C. Marin Quintero; Henrik Hillborg; Eva Malmström; Fritjof Nilsson. 2019. "Characterization of Reduced and Surface-Modified Graphene Oxide in Poly(Ethylene-co-Butyl Acrylate) Composites for Electrical Applications." Polymers 11, no. 4: 740.
Peroxides are widely used as crosslinkers in polyethylene (PE) drinking water pipes. Cross-linked polyethylene (PEX) has better mechanical properties than PE, but peroxide decomposition by-products can migrate from PEX water pipes into the drinking water unless sufficient preventive actions are undertaken. This work systematically examines the migration of tert-Butyl methyl ether (MTBE), a dominating crosslinking by-product from PEX water pipes, into tap water by utilizing both experimental techniques and finite element (FEM) diffusion modeling. The effects of pipe geometry, tap water temperature (23–80 °C), boundary conditions (air or water interface) and degasing (at 180 °C) were considered. The MTBE diffusivity increased strongly with increasing temperature and it was concluded that a desired water quality can be achieved with proper degasing of the PEX pipes. As the FEM simulations were in excellent agreement with the experimental results, the model can accurately predict the MTBE concentration as a function of time, water temperature and PEX pipe geometry, and enable the pipe manufacturers to aid in ensuring desirable drinking water quality.
Shima L. Holder; Mikael S. Hedenqvist; Fritjof Nilsson. Understanding and modelling the diffusion process of low molecular weight substances in polyethylene pipes. Water Research 2019, 157, 301 -309.
AMA StyleShima L. Holder, Mikael S. Hedenqvist, Fritjof Nilsson. Understanding and modelling the diffusion process of low molecular weight substances in polyethylene pipes. Water Research. 2019; 157 ():301-309.
Chicago/Turabian StyleShima L. Holder; Mikael S. Hedenqvist; Fritjof Nilsson. 2019. "Understanding and modelling the diffusion process of low molecular weight substances in polyethylene pipes." Water Research 157, no. : 301-309.
Guanda Yang; Dirk W. Schubert; Muchao Qu; Fritjof Nilsson. Macromol. Theory Simul. 4/2018. Macromolecular Theory and Simulations 2018, 27, 1 .
AMA StyleGuanda Yang, Dirk W. Schubert, Muchao Qu, Fritjof Nilsson. Macromol. Theory Simul. 4/2018. Macromolecular Theory and Simulations. 2018; 27 (4):1.
Chicago/Turabian StyleGuanda Yang; Dirk W. Schubert; Muchao Qu; Fritjof Nilsson. 2018. "Macromol. Theory Simul. 4/2018." Macromolecular Theory and Simulations 27, no. 4: 1.
The electrical conductivity of polymeric fiber composites is generally strongly dependent on the constituent conductivities, the fiber filler fraction, the fiber aspect ratio, and on the orientation of the fibers. Even though electrically conductive polymer composites are emerging materials of high scientific and commercial interest, accurate mathematical models for describing such materials are rare. A very promising mathematical model for predicting the electrical conductivity below the electrical percolation threshold, for both isotropic and anisotropic composites, is however recently published by Schubert. The shortcomings of that study are that the model includes so far only one predicted parameter and that it is not sufficiently validated. In the current study, finite element modeling is used to successfully validate the model of Schubert for isotropic fiber composites and to accurately determine the predicted parameter. These theoretical predictions are finally compared with experimental conductivity data for isotropic carbon fiber/poly(methyl methacrylate) (PMMA) composites with fiber filler fractions in the range 0–12 vol% and fiber aspect ratios from 5 to 30. The model forecasts, without any adjustable parameters, are satisfactory close to the experimental data.
Guanda Yang; Dirk W. Schubert; Muchao Qu; Fritjof Nilsson. Novel Theoretical Self-Consistent Mean-Field Approach to Describe the Conductivity of Carbon Fiber-Filled Thermoplastics: PART II. Validation by Computer Simulation. Macromolecular Theory and Simulations 2018, 27, 1 .
AMA StyleGuanda Yang, Dirk W. Schubert, Muchao Qu, Fritjof Nilsson. Novel Theoretical Self-Consistent Mean-Field Approach to Describe the Conductivity of Carbon Fiber-Filled Thermoplastics: PART II. Validation by Computer Simulation. Macromolecular Theory and Simulations. 2018; 27 (4):1.
Chicago/Turabian StyleGuanda Yang; Dirk W. Schubert; Muchao Qu; Fritjof Nilsson. 2018. "Novel Theoretical Self-Consistent Mean-Field Approach to Describe the Conductivity of Carbon Fiber-Filled Thermoplastics: PART II. Validation by Computer Simulation." Macromolecular Theory and Simulations 27, no. 4: 1.
The electrical conductivity of extruded carbon fiber (CF)/Polymethylmethacrylate (PMMA) composites with controlled CF aspect ratio and filler fractions ranging from 0 to 50 vol. % has been investigated and analyzed. The composites were extruded through a capillary rheometer, utilizing either 1-mm or 3-mm diameter extrusion dies, resulting in cylindrical composite filaments of two different diameters. Since the average CF orientation becomes more aligned with the extrusion flow when the diameter of the extrusion dies decreases, the relationship between conductivity and average fiber orientation could therefore be examined. The room temperature conductivities of the extruded filaments as a function of CF fractions were fitted to the McLachlan general effective medium (GEM) equation and the percolation thresholds were determined to 20.0 ± 2.5 vol. % and 32.0 ± 5.9 vol. % for the 3-mm (with CFs oriented less) and 1-mm (with CFs oriented more) filaments, respectively. It turned out that the oriented CFs in the composite shift the percolation threshold to a higher value, however, the conductivity above the percolation threshold is higher for composites with oriented CFs. A novel approach based on the Balberg excluded volume theory was proposed to explain this counterintuitive phenomenon.
Muchao Qu; Fritjof Nilsson; Dirk W. Schubert. Effect of Filler Orientation on the Electrical Conductivity of Carbon Fiber/PMMA Composites. Fibers 2018, 6, 3 .
AMA StyleMuchao Qu, Fritjof Nilsson, Dirk W. Schubert. Effect of Filler Orientation on the Electrical Conductivity of Carbon Fiber/PMMA Composites. Fibers. 2018; 6 (1):3.
Chicago/Turabian StyleMuchao Qu; Fritjof Nilsson; Dirk W. Schubert. 2018. "Effect of Filler Orientation on the Electrical Conductivity of Carbon Fiber/PMMA Composites." Fibers 6, no. 1: 3.
Guanda Yang; Muchao Qu; Fritjof Nilsson; Dirk W. Schubert. Universal and Anisotropic Simulation Platform for the Study of Electrical Properties of Conductive Polymer Composites. Journal of Materials Science and Engineering B 2017, 7, 1 .
AMA StyleGuanda Yang, Muchao Qu, Fritjof Nilsson, Dirk W. Schubert. Universal and Anisotropic Simulation Platform for the Study of Electrical Properties of Conductive Polymer Composites. Journal of Materials Science and Engineering B. 2017; 7 (6):1.
Chicago/Turabian StyleGuanda Yang; Muchao Qu; Fritjof Nilsson; Dirk W. Schubert. 2017. "Universal and Anisotropic Simulation Platform for the Study of Electrical Properties of Conductive Polymer Composites." Journal of Materials Science and Engineering B 7, no. 6: 1.
Fritjof Nilsson; Mattias Karlsson; Love Pallon; Marco Giacinti; Richard T. Olsson; Davide Venturi; Ulf W. Gedde; Mikael S. Hedenqvist. Influence of water uptake on the electrical DC-conductivity of insulating LDPE/MgO nanocomposites. Composites Science and Technology 2017, 152, 11 -19.
AMA StyleFritjof Nilsson, Mattias Karlsson, Love Pallon, Marco Giacinti, Richard T. Olsson, Davide Venturi, Ulf W. Gedde, Mikael S. Hedenqvist. Influence of water uptake on the electrical DC-conductivity of insulating LDPE/MgO nanocomposites. Composites Science and Technology. 2017; 152 ():11-19.
Chicago/Turabian StyleFritjof Nilsson; Mattias Karlsson; Love Pallon; Marco Giacinti; Richard T. Olsson; Davide Venturi; Ulf W. Gedde; Mikael S. Hedenqvist. 2017. "Influence of water uptake on the electrical DC-conductivity of insulating LDPE/MgO nanocomposites." Composites Science and Technology 152, no. : 11-19.
Muchao Qu; Fritjof Nilsson; Yijing Qin; Guanda Yang; Yamin Pan; Xianhu Liu; Gabriel Hernandez Rodriguez; Jianfan Chen; Chunhua Zhang; Dirk W. Schubert. Electrical conductivity and mechanical properties of melt-spun ternary composites comprising PMMA, carbon fibers and carbon black. Composites Science and Technology 2017, 150, 24 -31.
AMA StyleMuchao Qu, Fritjof Nilsson, Yijing Qin, Guanda Yang, Yamin Pan, Xianhu Liu, Gabriel Hernandez Rodriguez, Jianfan Chen, Chunhua Zhang, Dirk W. Schubert. Electrical conductivity and mechanical properties of melt-spun ternary composites comprising PMMA, carbon fibers and carbon black. Composites Science and Technology. 2017; 150 ():24-31.
Chicago/Turabian StyleMuchao Qu; Fritjof Nilsson; Yijing Qin; Guanda Yang; Yamin Pan; Xianhu Liu; Gabriel Hernandez Rodriguez; Jianfan Chen; Chunhua Zhang; Dirk W. Schubert. 2017. "Electrical conductivity and mechanical properties of melt-spun ternary composites comprising PMMA, carbon fibers and carbon black." Composites Science and Technology 150, no. : 24-31.
Front Cover: In article number 1700291, Eva Malmström and co-workers report the hopping of charge carriers between reduced graphene oxide flakes separated by polymer grafts. Nanocomposites containing polymer-grafted rGO exhibit tunable nonlinear resistivities and rapidly change from electrically insulating to conducting with increasing voltage. Such nanocomposites can distribute the electrical stresses and are therefore interesting as tunable field-grading materials for compact HVDC cable accessories, soft electronics, and wearables. Cover image design: Martin Wåhlander.
Martin Wåhlander; Fritjof Nilsson; Richard L. Andersson; Anna Carlmark; Henrik Hillborg; Eva Malmström. Macromol. Rapid Commun. 16/2017. Macromolecular Rapid Communications 2017, 38, 1 .
AMA StyleMartin Wåhlander, Fritjof Nilsson, Richard L. Andersson, Anna Carlmark, Henrik Hillborg, Eva Malmström. Macromol. Rapid Commun. 16/2017. Macromolecular Rapid Communications. 2017; 38 (16):1.
Chicago/Turabian StyleMartin Wåhlander; Fritjof Nilsson; Richard L. Andersson; Anna Carlmark; Henrik Hillborg; Eva Malmström. 2017. "Macromol. Rapid Commun. 16/2017." Macromolecular Rapid Communications 38, no. 16: 1.
Field-grading materials (FGMs) are used to reduce the probability for electrical breakdowns in critical regions of electrical components and are therefore of great importance. Usually, FGMs are heavily filled (40 vol.%) with semi-conducting or conducting particles. Here, polymer-grafted reduced graphene oxide (rGO) is used as a filler to accomplish percolated networks at very low filling ratios (<2 vol.%) in a semi-crystalline polymer matrix: poly(ethylene-co-butyl acrylate) (EBA). Various simulation models are used to predict the percolation threshold and the flake-to-flake distances, to complement the experimental results. A substantial increase in thermal stability of rGO is observed after surface modification, either by silanization or subsequent polymerizations. The non-linear DC resistivity of neat and silanized rGO and its trapping of charge-carriers in semi-crystalline EBA are demonstrated for the first time. It is shown that the polymer-grafted rGO improve the dispersibility in the EBA-matrix and that the graft length controls the inter-flake distances (i.e. charge-carrier hopping distances). By the appropriate selection of graft lengths, both highly resistive materials at 10 kV mm-1 and FGMs with a large and distinct drop in resistivity (six decades) are obtained, followed by saturation. The nonlinear drop in resistivity is attributed to narrow inter-flake distance distributions of grafted rGO.
Martin Wåhlander; Fritjof Nilsson; Richard L. Andersson; Anna Carlmark; Henrik Hillborg; Eva Malmström. Reduced and Surface‐Modified Graphene Oxide with Nonlinear Resistivity. Macromolecular Rapid Communications 2017, 38, 1700291 .
AMA StyleMartin Wåhlander, Fritjof Nilsson, Richard L. Andersson, Anna Carlmark, Henrik Hillborg, Eva Malmström. Reduced and Surface‐Modified Graphene Oxide with Nonlinear Resistivity. Macromolecular Rapid Communications. 2017; 38 (16):1700291.
Chicago/Turabian StyleMartin Wåhlander; Fritjof Nilsson; Richard L. Andersson; Anna Carlmark; Henrik Hillborg; Eva Malmström. 2017. "Reduced and Surface‐Modified Graphene Oxide with Nonlinear Resistivity." Macromolecular Rapid Communications 38, no. 16: 1700291.
Tuning of the dielectric properties of PDMS–ZnO nanocomposites by the control of inter-particle distances and self-assembled NP-morphologies via polymer grafting. Polymer grafts were used to tailor the interphases between ZnO nanoparticles (NPs) and silicone matrices. The final electrical properties of the nanocomposites were tuned by the grafted interphases, by controlling the inter-particle distance and the NP-morphology. The nanocomposites can be used in electrical applications where control of the resistivity is desired. Hansen's solubility parameters were used to select a semi-compatible polymer for grafting to obtain anisotropic NP morphologies in silicone, and the grafted NPs self-assembled into various morphologies inside the silicone matrices. The morphologies in the semi-compatible nanocomposites could be tuned by steering the graft length of poly( n -butyl methacrylate) via entropic matrix-graft wetting using surface-initiated atom-transfer radical polymerization. Image analysis models were developed to calculate the radius of primary NPs, the fraction of aggregates, the dispersion, and the face-to-face distance of NPs. The dielectric properties of the nanocomposites were related to the morphology and the face-to-face distance of the NPs. The dielectric losses, above 100 Hz, for nanocomposites with grafted NPs were approximately one decade lower than those of pristine NPs. The isotropic nanocomposites increased the resistivity up to 100 times compared to that of neat silicone rubber, due to the trapping of charge carriers by the interphase of dispersed NPs and nanoclusters. On the other hand, the resistivity of anisotropic nanocomposites decreased 10–100 times when the inter-particle distance in continuous agglomerates was close to the hopping distance of charge carriers. The electrical breakdown strength increased for compatible isotropic nanocomposites, and the temperature dependence of the resistivity and the activation energy were ∼50% lower in the nanocomposites with grafted NPs. These flexible dielectric nanocomposites are promising candidates for low-loss high-voltage transmission cable accessories, mobile electronic devices, wearables and sensors.
Martin Wåhlander; Fritjof Nilsson; Richard L. Andersson; Carmen Cobo Sanchez; Nathaniel Taylor; Anna Carlmark; Henrik Hillborg; Eva Malmström. Tailoring dielectric properties using designed polymer-grafted ZnO nanoparticles in silicone rubber. Journal of Materials Chemistry A 2017, 5, 14241 -14258.
AMA StyleMartin Wåhlander, Fritjof Nilsson, Richard L. Andersson, Carmen Cobo Sanchez, Nathaniel Taylor, Anna Carlmark, Henrik Hillborg, Eva Malmström. Tailoring dielectric properties using designed polymer-grafted ZnO nanoparticles in silicone rubber. Journal of Materials Chemistry A. 2017; 5 (27):14241-14258.
Chicago/Turabian StyleMartin Wåhlander; Fritjof Nilsson; Richard L. Andersson; Carmen Cobo Sanchez; Nathaniel Taylor; Anna Carlmark; Henrik Hillborg; Eva Malmström. 2017. "Tailoring dielectric properties using designed polymer-grafted ZnO nanoparticles in silicone rubber." Journal of Materials Chemistry A 5, no. 27: 14241-14258.
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.
A. Moyassari; M. Unge; M. S. Hedenqvist; U. W. Gedde; F. Nilsson. First-principle simulations of electronic structure in semicrystalline polyethylene. The Journal of Chemical Physics 2017, 146, 204901 .
AMA StyleA. Moyassari, M. Unge, M. S. Hedenqvist, U. W. Gedde, F. Nilsson. First-principle simulations of electronic structure in semicrystalline polyethylene. The Journal of Chemical Physics. 2017; 146 (20):204901.
Chicago/Turabian StyleA. Moyassari; M. Unge; M. S. Hedenqvist; U. W. Gedde; F. Nilsson. 2017. "First-principle simulations of electronic structure in semicrystalline polyethylene." The Journal of Chemical Physics 146, no. 20: 204901.
Conductive biofoams made from glycerol-plasticized wheat gluten (WGG) are presented as a potential substitute in electrical applications for conductive polymer foams from crude oil. Conductive biofoams made from glycerol-plasticized wheat gluten (WGG) are presented as a potential substitute in electrical applications for conductive polymer foams from crude oil. The soft plasticised foams were prepared by conventional freeze-drying of wheat gluten suspensions with carbon nanotubes (CNTs), carbon black (CB) or reduced graphene oxide (rGO) as the conductive filler phase. The change in conductivity upon compression was documented and the results show not only that the CNT-filled foams show a conductivity two orders of magnitude higher than foams filled with the CB particles, but also that there is a significantly lower percolation threshold with percolation occurring already at 0.18 vol%. The rGO-filled foams gave a conductivity inferior to that obtained with the CNTs or CB particles, which is explained as being related to the sheet-like morphology of the rGO flakes. An increasing amount of conductive filler resulted in smaller pore sizes for both CNTs and CB particles due to their interference with the ice crystal formation before the lyophilization process. The conductive WGG foams with CNTs were fully elastic with up to 10% compressive strain, but with increasing compression up to 50% strain the recovery gradually decreased. The data show that the conductivity strongly depends on the type as well as the concentration of the conductive filler, and the conductivity data with different compressions applied to these biofoams are presented for the first time.
Qiong Wu; Henrik Sundborg; Richard L. Andersson; Kevin Peuvot; Léonard Guex; Fritjof Nilsson; Mikael S. Hedenqvist; Richard T. Olsson. Conductive biofoams of wheat gluten containing carbon nanotubes, carbon black or reduced graphene oxide. RSC Advances 2017, 7, 18260 -18269.
AMA StyleQiong Wu, Henrik Sundborg, Richard L. Andersson, Kevin Peuvot, Léonard Guex, Fritjof Nilsson, Mikael S. Hedenqvist, Richard T. Olsson. Conductive biofoams of wheat gluten containing carbon nanotubes, carbon black or reduced graphene oxide. RSC Advances. 2017; 7 (30):18260-18269.
Chicago/Turabian StyleQiong Wu; Henrik Sundborg; Richard L. Andersson; Kevin Peuvot; Léonard Guex; Fritjof Nilsson; Mikael S. Hedenqvist; Richard T. Olsson. 2017. "Conductive biofoams of wheat gluten containing carbon nanotubes, carbon black or reduced graphene oxide." RSC Advances 7, no. 30: 18260-18269.
Electrical trees are one reason for the breakdown of insulating materials in electrical power systems. An understanding of the growth of electrical trees plays a crucial role in the development of reliable high voltage direct current (HVDC) power grid systems with transmission voltages up to 1 MV. A section that contained an electrical tree in low-density polyethylene (LDPE) has been visualized in three dimensions (3D) with a resolution of 92 nm by X-ray ptychographic tomography. The 3D imaging revealed prechannel-formations with a lower density with the width of a couple of hundred nanometers formed around the main branch of the electrical tree. The prechannel structures were partially connected with the main tree via paths through material with a lower density, proving that the tree had grown in a step-by-step manner via the prestep structures formed in front of the main channels. All the prechannel structures had a size well below the limit of the Paschen law and were thus not formed by partial discharges. Instead, it is suggested that the prechannel structures were formed by electro-mechanical stress and impact ionization, where the former was confirmed by simulations to be a potential explanation with electro-mechanical stress tensors being almost of the same order of magnitude as the short-term modulus of low-density polyethylene.
Love K. H. Pallon; Fritjof Nilsson; Shun Yu; Dongming Liu; Ana Diaz; Mirko Holler; Xiangrong Chen; Stanislaw Gubanski; Mikael S. Hedenqvist; Richard T. Olsson; Ulf W. Gedde. Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene. Nano Letters 2017, 17, 1402 -1408.
AMA StyleLove K. H. Pallon, Fritjof Nilsson, Shun Yu, Dongming Liu, Ana Diaz, Mirko Holler, Xiangrong Chen, Stanislaw Gubanski, Mikael S. Hedenqvist, Richard T. Olsson, Ulf W. Gedde. Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene. Nano Letters. 2017; 17 (3):1402-1408.
Chicago/Turabian StyleLove K. H. Pallon; Fritjof Nilsson; Shun Yu; Dongming Liu; Ana Diaz; Mirko Holler; Xiangrong Chen; Stanislaw Gubanski; Mikael S. Hedenqvist; Richard T. Olsson; Ulf W. Gedde. 2017. "Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene." Nano Letters 17, no. 3: 1402-1408.