Research

12 pages, 2425 KiB

Open AccessArticle

Percolation Effect on the Complex Permittivities of Polymer Blends

by Hsien-Wen Chao, Yun-Yu Lai and Tsun-Hsu Chang

Polymers 2023, 15(18), 3751; https://doi.org/10.3390/polym15183751 - 13 Sep 2023

Viewed by 909

This study focuses on the measurement and analysis of the complex permittivities of polymer blends using the field enhancement method (FEM). The blends, consisting of air-powder or solvent–solute mixtures, are placed in a Teflon holder and inserted into the FEM cavity to determine [...] Read more.

This study focuses on the measurement and analysis of the complex permittivities of polymer blends using the field enhancement method (FEM). The blends, consisting of air-powder or solvent–solute mixtures, are placed in a Teflon holder and inserted into the FEM cavity to determine the complex permittivity. The resonant frequency and quality factor of the FEM cavity coupled with the samples provide information on the blends’ dielectric constant and loss tangents. To extract the complex permittivities of three specific samples of DC-840, MCL-805, and MCL-Siloxane, we employ effective medium theories and the high-frequency structure simulator (HFSS) together with the measured data. The results reveal that when the volume fraction of the DC-840 solute in the xylene solvent surpasses a specific threshold, the dielectric constants and the loss tangents experience a notable increase. This phenomenon, known as percolation, strongly correlates with the viscosity of polymer blends. The observed percolation effect on the dielectric behavior is further elucidated using the generalized dielectric constant and the Debye model. By employing these models, the percolation effect and its impact on the dielectric properties of the blends can be explained. Full article

(This article belongs to the Special Issue Electric Properties, Characterization, and Simulation of Polymer Composites)

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15 pages, 4683 KiB

Open AccessArticle

Achieving Excellent Dielectric and Energy Storage Performance in Core-Double-Shell-Structured Polyetherimide Nanocomposites

by You Yuan, Jingyu Lin, Xinhua Wang, Jun Qian, Peiyuan Zuo and Qixin Zhuang

Polymers 2023, 15(14), 3088; https://doi.org/10.3390/polym15143088 - 19 Jul 2023

Cited by 2 | Viewed by 1540

Abstract

The development of pulse power systems and electric power transmission systems urgently require the innovation of dielectric materials possessing high-temperature durability, high energy storage density, and efficient charge–discharge performance. This study introduces a core-double-shell-structured iron(II,III) oxide@barium titanate@silicon dioxide/polyetherimide (Fe₃O₄@BaTiO [...] Read more.

The development of pulse power systems and electric power transmission systems urgently require the innovation of dielectric materials possessing high-temperature durability, high energy storage density, and efficient charge–discharge performance. This study introduces a core-double-shell-structured iron(II,III) oxide@barium titanate@silicon dioxide/polyetherimide (Fe₃O₄@BaTiO₃@SiO₂/PEI) nanocomposite, where the highly conductive Fe₃O₄ core provides the foundation for the formation of microcapacitor structures within the material. The inclusion of the ferroelectric ceramic BaTiO₃ shell enhances the composite’s polarization and interfacial polarization strength while impeding free charge transfer. The outer insulating SiO₂ shell contributes excellent interface compatibility and charge isolation effects. With a filler content of 9 wt%, the Fe₃O₄@BaTiO₃@SiO₂/PEI nanocomposite achieves a dielectric constant of 10.6, a dielectric loss of 0.017, a high energy density of 5.82 J cm⁻³, and a charge–discharge efficiency (η) of 72%. The innovative aspect of this research is the design of nanoparticles with a core-double-shell structure and their PEI-based nanocomposites, effectively enhancing the dielectric and energy storage performance. This study provides new insights and experimental evidence for the design and development of high-performance dielectric materials, offering significant implications for the fields of electronic devices and energy storage. Full article

(This article belongs to the Special Issue Electric Properties, Characterization, and Simulation of Polymer Composites)

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8 pages, 2511 KiB

Open AccessCommunication

Improvement in the Thermal Conductivity of Silver Epoxy Adhesive by Treating with Water Vapor

by Yiyang E, Zhaobo Tian, Keyu Chi, Renyao Jiang, You Lv, Qi Sun and Yuan Zhu

Polymers 2023, 15(10), 2338; https://doi.org/10.3390/polym15102338 - 17 May 2023

Viewed by 1399

Abstract

With the miniaturization of electronic devices, electronic packaging has become increasingly precise and complex, which presents a significant challenge in terms of heat dissipation. Electrically conductive adhesives (ECAs), particularly silver epoxy adhesives, have emerged as a new type of electronic packaging material, thanks [...] Read more.

With the miniaturization of electronic devices, electronic packaging has become increasingly precise and complex, which presents a significant challenge in terms of heat dissipation. Electrically conductive adhesives (ECAs), particularly silver epoxy adhesives, have emerged as a new type of electronic packaging material, thanks to their high conductivity and stable contact resistance. However, while there has been extensive research on silver epoxy adhesives, little attention has been paid to improving their thermal conductivity, which is a critical requirement in the ECA industry. In this paper, we propose a straightforward method for treating silver epoxy adhesive with water vapor, resulting in a remarkable improvement in thermal conductivity to 9.1 W/(m·K), three times higher than the sample cured using traditional methods (2.7 W/(m·K)). Through research and analysis, the study demonstrates that the introduction of H₂O into the gaps and holes of the silver epoxy adhesive increases the path of electron conduction, thereby improving thermal conductivity. Furthermore, this method has the potential to significantly improve the performance of packaging materials and meet the needs of high-performance ECAs. Full article

(This article belongs to the Special Issue Electric Properties, Characterization, and Simulation of Polymer Composites)

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13 pages, 5868 KiB

Open AccessArticle

Quantitative Evaluation of Thermal Ageing State of Cross-Linked Polyethylene Insulation Based on Polarization and Depolarization Current

by Ping Huang, Wenyao Yu, Chunhao Lu, Xinghua He, Yiyi Zhang, Yansong Liu, Jiaheng Zhou and Yuwang Liang

Polymers 2023, 15(5), 1272; https://doi.org/10.3390/polym15051272 - 02 Mar 2023

Viewed by 1066

Abstract

The widespread use of cross-linked polyethylene (XLPE) as insulation in cables may be attributed to its outstanding mechanical and dielectric properties. In order to quantitatively evaluate the insulation status of XLPE after thermal ageing, an accelerated thermal ageing experimental platform is established. Polarization [...] Read more.

The widespread use of cross-linked polyethylene (XLPE) as insulation in cables may be attributed to its outstanding mechanical and dielectric properties. In order to quantitatively evaluate the insulation status of XLPE after thermal ageing, an accelerated thermal ageing experimental platform is established. Polarization and depolarization current (PDC) as well as elongation at break of XLPE insulation under different ageing durations are measured. XLPE insulation state is determined by the elongation at break retention rate (ER%). Based on the extended Debye model, the paper proposed the stable relaxation charge quantity and the dissipation factor at 0.1 Hz to evaluate the insulation state of XLPE. The results show that the ER% of XLPE insulation decreases with the growth of ageing degree. The polarization and depolarization current of XLPE insulation will increase obviously with thermal ageing. Conductivity and trap level density will also increase. The number of branches of the extended Debye model increases, and new polarization types appear. Stable relaxation charge quantity and dissipation factor at 0.1 Hz proposed in this paper have a good fitting relationship with ER% of XLPE insulation, which can evaluate the thermal ageing state of XLPE insulation effectively. Full article

(This article belongs to the Special Issue Electric Properties, Characterization, and Simulation of Polymer Composites)

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10 pages, 2128 KiB

Open AccessArticle

A Reactive Molecular Dynamics Study on Crosslinked Epoxy Resin Decomposition under High Electric Field and Thermal Aging Conditions

by Wei-Feng Sun, Wen Kwang Chern, John Chok You Chan and Zhong Chen

Polymers 2023, 15(3), 765; https://doi.org/10.3390/polym15030765 - 02 Feb 2023

Cited by 3 | Viewed by 1721

Abstract

To reveal the microscopic mechanism of synergetic thermal–electrical degradation during a partial discharge process in epoxy insulation materials, the decomposition of crosslinked epoxy resin is investigated using reactive molecular dynamics simulations under high electric field and thermal degradation conditions. Bond-boost acceleration method is [...] Read more.

To reveal the microscopic mechanism of synergetic thermal–electrical degradation during a partial discharge process in epoxy insulation materials, the decomposition of crosslinked epoxy resin is investigated using reactive molecular dynamics simulations under high electric field and thermal degradation conditions. Bond-boost acceleration method is employed in reactive molecular dynamics simulations to successfully establish epoxy polymer models with a crosslink degree of 93%. Active molecular species derived from electrical partial discharges are considered in the current work. Small molecule products and decomposition temperature in the degradation process under an electric field are calculated to elucidate the effect of nitric acid and ozone molecules, being the active products generated by electrical partial discharges, on the synergetic thermal–electrical degradation of epoxy resin. Both nitric acid and ozone exacerbate thermal impact decomposition of crosslinked epoxy polymer by decreasing initial decomposition temperature from 1050 K to 940 K and 820 K, respectively. It is found that these active products can oxidize hydroxyl groups and carbon–nitrogen bridge bonds in epoxy molecular chains, leading to the aggravation of epoxy resin decomposition, as manifested by the significant increase in the decomposed molecular products. In contrast, thermal degradation of the epoxy resin without the active species is not expedited by increasing electric field. These strongly oxidative molecules are easily reduced to negative ions and able to obtain kinetic energies from electric field, which result in chemical corrosion and local temperature increase to accelerate decomposition of epoxy insulation materials. Full article

(This article belongs to the Special Issue Electric Properties, Characterization, and Simulation of Polymer Composites)

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13 pages, 3166 KiB

Open AccessArticle

Dielectric Characteristics of Crosslinked Polyethylene Modified by Grafting Polar-Group Molecules

by Jun-Guo Gao, Li-Wei Liu and Wei-Feng Sun

Polymers 2023, 15(1), 231; https://doi.org/10.3390/polym15010231 - 01 Jan 2023

Cited by 3 | Viewed by 2329

Abstract

Polar group-modified crosslinked polyethylene (XLPE) materials are developed with a peroxide thermochemical method of individually grafting chloroacetic acid allyl ester (CAAE) and maleic anhydride (MAH) to polyethylene molecular-chains, which are dedicated to ameliorating dielectric characteristics through charge-trapping mechanism. By free radical addition reactions, [...] Read more.

Polar group-modified crosslinked polyethylene (XLPE) materials are developed with a peroxide thermochemical method of individually grafting chloroacetic acid allyl ester (CAAE) and maleic anhydride (MAH) to polyethylene molecular-chains, which are dedicated to ameliorating dielectric characteristics through charge-trapping mechanism. By free radical addition reactions, the CAAE and MAH molecules are successfully grafted to polyethylene molecular chains of XLPE in crosslinking process, as verified by infrared spectroscopy molecular characterizations. Dielectric spectra, electric conductance, and dielectric breakdown strength are tested to evaluate the improved dielectric performances. Charge trap characteristics are investigated by analyzing thermal stimulation depolarization currents in combination with first-principles electronic-structure calculations to reveal the polar-group introduced mechanisms of contributing dipole dielectric polarization, impeding electric conduction, and promoting electrical breakdown field. The grafted polar-group molecules, especially for MAH, can introduce deep-level charge traps in XLPE materials to effectively restrict charge injections and hinder charge carrier transports, which accounts for the significant improvements in electric resistance and dielectric breakdown strength. Full article

(This article belongs to the Special Issue Electric Properties, Characterization, and Simulation of Polymer Composites)

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18 pages, 18261 KiB

Open AccessArticle

Mechanism Analysis of Ethanol Production from Cellulosic Insulating Paper Based on Reaction Molecular Dynamics

by Yufan Fan, Yi Li, Yiyi Zhang and Keshuo Shi

Polymers 2022, 14(22), 4918; https://doi.org/10.3390/polym14224918 - 14 Nov 2022

Cited by 1 | Viewed by 1175

Abstract

The paper/oil system is the main component of transformer insulation. Indicator plays a vital role in assessing the aging condition of local hot spots of transformer insulation paper. The cellulosic insulating paper is mainly composed of cellobiose. This study uses the molecular dynamics [...] Read more.

The paper/oil system is the main component of transformer insulation. Indicator plays a vital role in assessing the aging condition of local hot spots of transformer insulation paper. The cellulosic insulating paper is mainly composed of cellobiose. This study uses the molecular dynamics method based on reactive force field (ReaxFF) to pyrolyze the insulating paper. Various production paths of ethanol were studied at the atomic level through ReaxFF simulations. A model consisting of 40 cellobioses was established for repeated simulation at 500 K–3000 K. Besides, to explore the relationship between the intermediate products and ethanol, the combination model of intermediate products (levoglucosan, acetaldehyde, 2,2-dihydroxyacetaldehyde) was established for repeated simulation. The simulation results showed that the increase in temperature can accelerate the production of ethanol from insulating paper and its pyrolysis intermediate products, which matched the related experimental results. This study can provide an effective reference for the use of ethanol as an indicator to assess the aging condition of the local hot spots of transformers. Full article

(This article belongs to the Special Issue Electric Properties, Characterization, and Simulation of Polymer Composites)

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13 pages, 4240 KiB

Open AccessArticle

Direct Current Electrical Performances of Cable Accessory Insulation EPDM Modified by Grafting Polar-Group Compound

by Zhong-Yuan Li, Wei-Feng Sun, Jian Zhang, Jian-Quan Liang, Lei Wang and Ke-Xin Zhang

Polymers 2022, 14(21), 4625; https://doi.org/10.3390/polym14214625 - 31 Oct 2022

Cited by 2 | Viewed by 1341

Abstract

In order to improve electrical matching between ethylene-propylene-diene misch-polymere (EPDM) reinforce insulation and crosslinked polyethylene (XLPE) main insulation in direct current (DC) cable accessories, the glyceryl monooleate (GMO) organic compound composed of several polar-groups and one long carbon chain is employed for chemical [...] Read more.

In order to improve electrical matching between ethylene-propylene-diene misch-polymere (EPDM) reinforce insulation and crosslinked polyethylene (XLPE) main insulation in direct current (DC) cable accessories, the glyceryl monooleate (GMO) organic compound composed of several polar-groups and one long carbon chain is employed for chemical graft modification on EPDM to ameliorate DC electrical performances. Charge trap characteristics are analyzed by testing thermal stimulation current (TSC) and verified by calculating first-principles electronic properties to elucidate the GMO-graft-modified charge trapping mechanism accounting for DC electric conductance and dielectric breakdown. The grafted GMO molecules introduce substantial shallow charge traps that lead to nonlinear profiles of electric conduction versus electric field and cause hopping transports of percolation conductance. Electric conductance of EPDM is significantly improved by GMO graft for electrical matching with XLPE, while a high level of dielectric breakdown strength is retained sufficiently for reinforce insulation in cable accessories. Shallow charge traps introduced by GMO graft are capable of capturing charge carriers to form homocharge layers near electrodes which can scatter the transporting charge carriers and exclude further charge injections, thus to mitigate the dielectric breakdown strength reduction caused by electric conductivity improvement. Electric field finite-element simulations demonstrate that the electric field in DC cable terminals can be evidently homogenized by using GMO-grafted EPDM as reinforce insulation. Full article

(This article belongs to the Special Issue Electric Properties, Characterization, and Simulation of Polymer Composites)

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