Special Issue "Nano- and Microcomposites for Electrical Engineering Applications"

A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (31 January 2016).

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editor

Prof. Dr. Frank Wiesbrock
E-Mail Website
Guest Editor
PCCL - Polymer Competence Center Leoben GmbH, Roseggerstrasse 12, 8700 Leoben, Austria
Tel. +43 3842 42962 42; Fax: +43 3842 42962 6
Interests: functional polymers; ring-opening polymerizations; crosslinked polymers; biopolyesters; polymeranalogous modifications
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Special Issue Information

Dear Colleagues,

Nano- and Microcomposites for Electrical Engineering Applications Polymers aims to compile the current trends and research directions within the preparation, characterization and application of polymer-based composite materials in electrical engineering applications. This type of material has evolved to become one of the most thoroughly investigated materials these days, stimulated by the demand for resource-efficient assembly of generators, transformers, communication devices, etc. Novel composites are to be used as insulating materials with high thermal conductivity and excellent temperature stability, through which premature ageing and degradation of devices shall be avoided or at least reduced.

Aiming at a comprehensive representation of research activities in the field, contributions that describe one or multiple steps of the material research and development are invited to this Special Issue. Material research and development comprises the molecular structure of polymers, adequate processing technologies and the inner material structure, as well as material properties and the functionality of composites. Hence, potential topics for this Special Issue comprise the synthesis of functionalized polymers and/or the surface modification of particles in order to enhance compatibility, the processing of the materials, and the physico-chemical characterization of composite materials, with a special focus on thermal conductivity, ageing and electrical characterization.

Review articles, as well as original papers, will be considered for this Special Issue.

Prof. Dr. Frank Wiesbrock
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • functionalized polymers
  • surface functionalization of micro- and nanoparticles
  • curing of composites
  • composite processing
  • adhesion in multilayer composites
  • thermal conductivity
  • electrical characterization of composite materials
  • stability/reliability of devices and ageing phenomena

Published Papers (11 papers)

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Editorial

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Open AccessEditorial
Interdisciplinary Approaches towards Materials with Enhanced Properties for Electrical Engineering
Polymers 2016, 8(8), 307; https://doi.org/10.3390/polym8080307 - 16 Aug 2016
Abstract
The internationally growing demand for electrical energy is one of the most prominent triggers stimulating research these days.[...] Full article

Research

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Open AccessArticle
The Effects of in Situ-Formed Silver Nanoparticles on the Electrical Properties of Epoxy Resin Filled with Silver Nanowires
Polymers 2016, 8(4), 157; https://doi.org/10.3390/polym8040157 - 21 Apr 2016
Cited by 6
Abstract
A novel method for preparing epoxy/silver nanocomposites was developed via the in situ formation of silver nanoparticles (AgNPs) within the epoxy resin matrix while using silver nanowires (AgNWs) as a conductive filler. The silver–imidazole complex was synthesized from silver acetate (AgAc) and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole [...] Read more.
A novel method for preparing epoxy/silver nanocomposites was developed via the in situ formation of silver nanoparticles (AgNPs) within the epoxy resin matrix while using silver nanowires (AgNWs) as a conductive filler. The silver–imidazole complex was synthesized from silver acetate (AgAc) and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole (imidazole). AgNPs were generated in situ during the curing of the epoxy resin through the thermal decomposition of the AgAc–imidazole complex, which was capable of reducing Ag+ to Ag by itself. The released imidazole acted as a catalyst to cure the epoxy. Additionally, after the curing process, the in situ-generated AgNPs were stabilized by the formed epoxy network. Therefore, by using the thermal decomposition method, uniformly dispersed AgNPs of approximately 100 nm were formed in situ in the epoxy matrix filled with AgNWs. It was observed that the nanocomposites containing in situ-formed AgNPs exhibited isotropic electrical properties in the epoxy resins in the presence of AgNWs. Full article
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Open AccessArticle
On the Effect of Nanoparticle Surface Chemistry on the Electrical Characteristics of Epoxy-Based Nanocomposites
Polymers 2016, 8(4), 126; https://doi.org/10.3390/polym8040126 - 06 Apr 2016
Cited by 7
Abstract
The effect of nanosilica surface chemistry on the electrical behavior of epoxy-based nanocomposites is described. The nanosilica was reacted with different volumes of (3-glycidyloxypropyl)trimethoxysilane and the efficacy of the process was demonstrated by infrared spectroscopy and combustion analysis. Nanocomposites containing 2 wt % [...] Read more.
The effect of nanosilica surface chemistry on the electrical behavior of epoxy-based nanocomposites is described. The nanosilica was reacted with different volumes of (3-glycidyloxypropyl)trimethoxysilane and the efficacy of the process was demonstrated by infrared spectroscopy and combustion analysis. Nanocomposites containing 2 wt % of nanosilica were prepared and characterized by scanning electron microscopy (SEM), AC ramp electrical breakdown testing, differential scanning calorimetry (DSC) and dielectric spectroscopy. SEM examination indicated that, although the nanoparticle dispersion improved somewhat as the degree of surface functionalization increased, all samples nevertheless contained agglomerates. Despite the non-ideal nature of the samples, major improvements in breakdown strength (from 182 ± 5 kV·mm−1 to 268 ± 12 kV·mm−1) were observed in systems formulated from optimally treated nanosilicas. DSC studies of the glass transition revealed no evidence for any modified interphase regions between the nanosilica and the matrix, but interfacial effects were evident in the dielectric spectra. In particular, changes in the magnitude of the real part of the permittivity and variations in the interfacial α′-relaxation suggest that the observed changes in breakdown performance stem from variations in the polar character of the nanosilica surface, which may affect the local density of trapping states and, thereby, charge transport dynamics. Full article
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Open AccessArticle
Charge Transport in LDPE Nanocomposites Part II—Computational Approach
Polymers 2016, 8(4), 103; https://doi.org/10.3390/polym8040103 - 23 Mar 2016
Cited by 17
Abstract
A bipolar charge transport model is employed to investigate the remarkable reduction in dc conductivity of low-density polyethylene (LDPE) based material filled with uncoated nanofillers (reported in the first part of this work). The effect of temperature on charge transport is considered and [...] Read more.
A bipolar charge transport model is employed to investigate the remarkable reduction in dc conductivity of low-density polyethylene (LDPE) based material filled with uncoated nanofillers (reported in the first part of this work). The effect of temperature on charge transport is considered and the model outcomes are compared with measured conduction currents. The simulations reveal that the contribution of charge carrier recombination to the total transport process becomes more significant at elevated temperatures. Among the effects caused by the presence of nanoparticles, a reduced charge injection at electrodes has been found as the most essential one. Possible mechanisms for charge injection at different temperatures are therefore discussed. Full article
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Open AccessArticle
Charge Transport in LDPE Nanocomposites Part I—Experimental Approach
Polymers 2016, 8(3), 87; https://doi.org/10.3390/polym8030087 - 16 Mar 2016
Cited by 30
Abstract
This work presents results of bulk conductivity and surface potential decay measurements on low-density polyethylene and its nanocomposites filled with uncoated MgO and Al2O3, with the aim to highlight the effect of the nanofillers on charge transport processes. Material [...] Read more.
This work presents results of bulk conductivity and surface potential decay measurements on low-density polyethylene and its nanocomposites filled with uncoated MgO and Al2O3, with the aim to highlight the effect of the nanofillers on charge transport processes. Material samples at various filler contents, up to 9 wt %, were prepared in the form of thin films. The performed measurements show a significant impact of the nanofillers on reduction of material’s direct current (dc) conductivity. The investigations thus focused on the nanocomposites having the lowest dc conductivity. Various mechanisms of charge generation and transport in solids, including space charge limited current, Poole-Frenkel effect and Schottky injection, were utilized for examining the experimental results. The mobilities of charge carriers were deduced from the measured surface potential decay characteristics and were found to be at least two times lower for the nanocomposites. The temperature dependencies of the mobilities were compared for different materials. Full article
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Open AccessArticle
Structural and Spectroscopic Characterization of A Nanosized Sulfated TiO2 Filler and of Nanocomposite Nafion Membranes
Polymers 2016, 8(3), 68; https://doi.org/10.3390/polym8030068 - 01 Mar 2016
Cited by 8
Abstract
A large number of nano-sized oxides have been studied in the literature as fillers for polymeric membranes, such as Nafion®. Superacidic sulfated oxides have been proposed and characterized. Once incorporated into polymer matrices, their beneficial effect on peculiar membrane properties has [...] Read more.
A large number of nano-sized oxides have been studied in the literature as fillers for polymeric membranes, such as Nafion®. Superacidic sulfated oxides have been proposed and characterized. Once incorporated into polymer matrices, their beneficial effect on peculiar membrane properties has been demonstrated. The alteration of physical-chemical properties of composite membranes has roots in the intermolecular interaction between the inorganic filler surface groups and the polymer chains. In the attempt to tackle this fundamental issue, here we discuss, by a multi-technique approach, the properties of a nanosized sulfated titania material as a candidate filler for Nafion membranes. The results of a systematic study carried out by synchrotron X-ray diffraction, transmission electron microscopy, thermogravimetry, Raman and infrared spectroscopies are presented and discussed to get novel insights about the structural features, molecular properties, and morphological characteristics of sulphated TiO2 nanopowders and composite Nafion membranes containing different amount of sulfated TiO2 nanoparticles (2%, 5%, 7% w/w). Full article
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Open AccessArticle
Dielectric Properties and Energy Storage Densities of Poly(vinylidenefluoride) Nanocomposite with Surface Hydroxylated Cube Shaped Ba0.6Sr0.4TiO3 Nanoparticles
Polymers 2016, 8(2), 45; https://doi.org/10.3390/polym8020045 - 16 Feb 2016
Cited by 30
Abstract
Ceramic-polymer nanocomposites, consisting of surface hydroxylated cube-shaped Ba0.6Sr0.4TiO3 nanoparticles (BST–NPs) as fillers and poly(vinylidenefluoride) (PVDF) as matrix, have been fabricated by using a solution casting method. The nanocomposites exhibited increased dielectric constant and improved breakdown strength. Dielectric constants [...] Read more.
Ceramic-polymer nanocomposites, consisting of surface hydroxylated cube-shaped Ba0.6Sr0.4TiO3 nanoparticles (BST–NPs) as fillers and poly(vinylidenefluoride) (PVDF) as matrix, have been fabricated by using a solution casting method. The nanocomposites exhibited increased dielectric constant and improved breakdown strength. Dielectric constants of the nanocomposite with surface hydroxylated BST–NPs (BST–NPs–OH) were higher as compared with those of their untreated BST–NPs composites. The sample with 40 vol % BST–NPs–OH had a dielectric constant of 36 (1 kHz). Different theoretical models have been employed to predict the dielectric constants of the nanocomposites, in order to compare with the experimental data. The BST–NPs–OH/PVDF composites also exhibited higher breakdown strength than their BST–NP/PVDF counterparts. A maximal energy density of 3.9 J/cm3 was achieved in the composite with 5 vol % BST–NPs–OH. This hydroxylation strategy could be used as a reference to develop ceramic-polymer composite materials with enhanced dielectric properties and energy storage densities. Full article
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Open AccessFeature PaperArticle
Crosslinked Poly(2-oxazoline)s as “Green” Materials for Electronic Applications
Polymers 2016, 8(1), 6; https://doi.org/10.3390/polym8010006 - 30 Dec 2015
Cited by 5
Abstract
Poly(2-nonyl-2-oxazoline)80-stat-poly(2-dec-9′-enyl-2-oxazoline)20 and poly(2-dec-9′-enyl-2-oxazoline)100 can be synthesized from the cationic ring-opening polymerization of monomers that can be derived from fatty acids from renewable resources. These (co)poly(2-oxazoline)s can be crosslinked with di- and trifunctional mercapto compounds using the UV-induced [...] Read more.
Poly(2-nonyl-2-oxazoline)80-stat-poly(2-dec-9′-enyl-2-oxazoline)20 and poly(2-dec-9′-enyl-2-oxazoline)100 can be synthesized from the cationic ring-opening polymerization of monomers that can be derived from fatty acids from renewable resources. These (co)poly(2-oxazoline)s can be crosslinked with di- and trifunctional mercapto compounds using the UV-induced thiol-ene reaction. The complex permittivity of the corresponding networks increases with the temperature and decreases with the network density. In a frequency range from 10−2 to 106 Hz and at temperatures ranging from −20 to 40 °C, the changes of the real part of the complex permittivity as well as the loss factor can be explained by interfacial polarization within the material. At a temperature of 20 °C and a frequency of 50 Hz, the permittivity of the crosslinked (co)poly(2-oxazoline)s covers a range from 4.29 to 4.97, and the loss factors are in the range from 0.030 to 0.093. The electrical conductivities of these polymer networks span a range from 5 × 10−12 to 8 × 10−9 S/m, classifying these materials as medium insulators. Notably, the values for the permittivity, loss factor and conductivity of these copoly(2-oxazoline)s are in the same range as for polyamides, and, hence, these copoly(2-oxazoline)-based networks may be referred to as “green” alternatives for polyamides as insulators in electronic applications. Full article
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Review

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Open AccessReview
Mechanical Properties of Composites Used in High-Voltage Applications
Polymers 2016, 8(7), 260; https://doi.org/10.3390/polym8070260 - 14 Jul 2016
Cited by 6
Abstract
Materials used in high voltage applications have to meet a lot of regulations for their safety and functional usage during their lifetime. For high voltage applications the electrical properties are the most relevant designing criteria. However, the mechanical properties of such materials have [...] Read more.
Materials used in high voltage applications have to meet a lot of regulations for their safety and functional usage during their lifetime. For high voltage applications the electrical properties are the most relevant designing criteria. However, the mechanical properties of such materials have rarely been considered for application dimensioning over the last decades. This article gives an overview of composite materials used in high voltage applications and some basic mechanical and thermo-mechanical characterization methods of such materials, including a discussion of influences on practically used epoxy based thermosets. Full article
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Open AccessReview
Mica/Epoxy-Composites in the Electrical Industry: Applications, Composites for Insulation, and Investigations on Failure Mechanisms for Prospective Optimizations
Polymers 2016, 8(5), 201; https://doi.org/10.3390/polym8050201 - 20 May 2016
Cited by 8
Abstract
The investigation of mica and mica/epoxy-composites has always been of high importance and has gained increased attention in recent years due to their significant role as insulation material in the electrical industry. Electrical insulation represents a key factor regarding the reliability and lifespan [...] Read more.
The investigation of mica and mica/epoxy-composites has always been of high importance and has gained increased attention in recent years due to their significant role as insulation material in the electrical industry. Electrical insulation represents a key factor regarding the reliability and lifespan of high voltage rotating machines. As the demand for generating power plants is increasing, rotating machines are of intrinsic importance to the electrical energy supply. Therefore, impeccable functioning is of immense importance for both the producers of high voltage machines as well as the energy suppliers. Thus, cost reduction caused by shorter maintenance times and higher operational lifespan has become the focus of attention. Besides the electrical properties, composites should offer compatible chemical and mechanical, as well as thermal characteristics for their usage in insulating systems. Furthermore, knowledge of several occurring stresses leading to the final breakdown of the whole insulation is required. This review aims to give an overview of the properties of pure components, the composite, and the possible occurring failure mechanisms which can lead to a full understanding of insulation materials for high voltage rotating machines and therefore establish a basis for prospective optimizations. Full article
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Open AccessReview
Properties of Polymer Composites Used in High-Voltage Applications
Polymers 2016, 8(5), 173; https://doi.org/10.3390/polym8050173 - 28 Apr 2016
Cited by 80
Abstract
The present review article represents a comprehensive study on polymer micro/nanocomposites that are used in high-voltage applications. Particular focus is on the structure-property relationship of composite materials used in power engineering, by exploiting fundamental theory as well as numerical/analytical models and the influence [...] Read more.
The present review article represents a comprehensive study on polymer micro/nanocomposites that are used in high-voltage applications. Particular focus is on the structure-property relationship of composite materials used in power engineering, by exploiting fundamental theory as well as numerical/analytical models and the influence of material design on electrical, mechanical and thermal properties. In addition to describing the scientific development of micro/nanocomposites electrical features desired in power engineering, the study is mainly focused on the electrical properties of insulating materials, particularly cross-linked polyethylene (XLPE) and epoxy resins, unfilled and filled with different types of filler. Polymer micro/nanocomposites based on XLPE and epoxy resins are usually used as insulating systems for high-voltage applications, such as: cables, generators, motors, cast resin dry-type transformers, etc. Furthermore, this paper includes ample discussions regarding the advantages and disadvantages resulting in the electrical, mechanical and thermal properties by the addition of micro- and nanofillers into the base polymer. The study goals are to determine the impact of filler size, type and distribution of the particles into the polymer matrix on the electrical, mechanical and thermal properties of the polymer micro/nanocomposites compared to the neat polymer and traditionally materials used as insulation systems in high-voltage engineering. Properties such as electrical conductivity, relative permittivity, dielectric losses, partial discharges, erosion resistance, space charge behavior, electric breakdown, tracking and electrical tree resistance, thermal conductivity, tensile strength and modulus, elongation at break of micro- and nanocomposites based on epoxy resin and XLPE are analyzed. Finally, it was concluded that the use of polymer micro/nanocomposites in electrical engineering is very promising and further research work must be accomplished in order to diversify the polymer composites matrices and to improve their properties. Full article
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