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Dielectric Materials: Challenges and Prospects

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Materials Chemistry".

Deadline for manuscript submissions: closed (31 August 2020) | Viewed by 37845

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Prof. Dr. Georgios C. Psarras

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Smart Materials and Nanodielectrics Laboratory, Department of Materials Science, University of Patras, 26504 Patras, Greece
Interests: smart materials; polymer nanocomposites; polymers; nanodielectrics; dielectric behavior; conductivity; storing/retrieving energy; stimuli-responsive materials; active dielectrics
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Dear Colleagues,

Contemporary lifestyles and our technological civilization are based on the ability to distribute and use electrical power safely and easily. This can be achieved by employing all three electrical categories of materials, namely, conductors, semi-conductors, and insulators. Dielectrics or dielectric materials are non-conductive materials which can be polarized by an exerted electric field. Dielectrics can be natural or synthetic, ceramic, polymer, mineral, organic, or composite in nature. The role of dielectrics in emerging technologies is crucial, since the current and potential applications of dielectrics include, but are not limited to, integrated capacitors, acoustic emission sensors, solar cells, batteries, strain sensors, interlayer capacitors, self-current regulators, wireless personal digital assistance, electromagnetic shielding, energy storing devices, to name but a few. Moreover, in the era of nanomaterials, new perspectives are offered concerning dielectrics. Studying the interactions between polar molecules or groups, induced dipoles, and interfacial phenomena could lead to controlling and tailoring the electric performance of nanodielectrics, thus creating “personalized” materials for each application. The challenges and prospects of research in the field of dielectrics appear to be wide open and require, but also attract, scientific attention.

This Special Issue on “Dielectric Materials: Challenges and Prospects” welcomes original research and reviews on experimental or theoretical/computational studies of all kind of dielectrics. Development of novel dielectric materials, nanocomposites, hybrids, biological systems, electrical engineering devices, electroresponsive materials, smart materials, structure–property relationships and applications all comprise a short—and definitely not exhaustive—list of the possible subjects for this Special Issue.

Prof. Georgios C. Psarras
Guest Editor

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Keywords

dielectric permittivity
relaxations
molecular mobility
polarization
interfacial effects
conductivity mechanisms
phase transitions
electroresponsive materials
piezo/ferro/pyroelectrics
polar oxides
multifunctional materials
nanodielectrics
polymer composites
energy materials

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Published Papers (10 papers)

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Research

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21 pages, 2338 KiB

Open AccessArticle

The Study of Electrical and Electrochemical Properties of Magnesium Ion Conducting CS: PVA Based Polymer Blend Electrolytes: Role of Lattice Energy of Magnesium Salts on EDLC Performance

by Shujahadeen B. Aziz, Mohamad A. Brza, Elham M. A. Dannoun, Muhamad H. Hamsan, Jihad M. Hadi, Mohd F. Z. Kadir and Rebar T. Abdulwahid

Molecules 2020, 25(19), 4503; https://doi.org/10.3390/molecules25194503 - 1 Oct 2020

Cited by 43 | Viewed by 3523

Abstract

Plasticized magnesium ion conducting polymer blend electrolytes based on chitosan (CS): polyvinyl alcohol (PVA) was synthesized with a casting technique. The source of ions is magnesium triflate Mg(CF₃SO₃)₂, and glycerol was used as a plasticizer. The electrical and electrochemical characteristics were examined. The outcome from X-ray diffraction (XRD) examination illustrates that the electrolyte with highest conductivity exhibits the minimum degree of crystallinity. The study of the dielectric relaxation has shown that the peak appearance obeys the non-Debye type of relaxation process. An enhancement in conductivity of ions of the electrolyte system was achieved by insertion of glycerol. The total conductivity is essentially ascribed to ions instead of electrons. The maximum DC ionic conductivity was measured to be 1.016 × 10⁻⁵ S cm⁻¹ when 42 wt.% of plasticizer was added. Potential stability of the highest conducting electrolyte was found to be 2.4 V. The cyclic voltammetry (CV) response shows the behavior of the capacitor is non-Faradaic where no redox peaks appear. The shape of the CV response and EDLC specific capacitance are influenced by the scan rate. The specific capacitance values were 7.41 F/g and 32.69 F/g at 100 mV/s and 10 mV/s, respectively. Finally, the electrolyte with maximum conductivity value is obtained and used as electrodes separator in the electrochemical double-layer capacitor (EDLC) applications. The role of lattice energy of magnesium salts in energy storage performance is discussed in detail. Full article

(This article belongs to the Special Issue Dielectric Materials: Challenges and Prospects)

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14 pages, 4826 KiB

Open AccessArticle

Dielectric Relaxation Characteristics of Epoxy Resin Modified with Hydroxyl-Terminated Nitrile Rubber

by Chi Chen, Qing Sun, Chuang Wang, Yue Bu, Jiawei Zhang and Zongren Peng

Molecules 2020, 25(18), 4128; https://doi.org/10.3390/molecules25184128 - 10 Sep 2020

Cited by 8 | Viewed by 3282

Abstract

Utilizing liquid rubber to toughen epoxy resin is one of the most mature and promising methods. However, the dielectric relaxation characteristics of the epoxy/liquid rubber composites have not been studied systematically, while the relaxation behaviours are a critical factor for both micro and macro properties. In this paper, hydroxyl-terminated liquid nitrile rubber (HTBN) is employed to reinforce a kind of room-temperature-cured epoxy resin. The dielectric spectrum is measured and analysed. Results show that two relaxation processes are introduced in the binary composites. The α relaxation of HTBN shows a similar temperature dependence with the β relaxation of epoxy resin. The interfacial polarization leads to an increase of complex permittivity, which reaches its maximum at 70 °C. In addition, affected by interfacial polarization, the thermionic polarization is inhibited, and the samples with filler ratios of 15% and 25% show lower DC-conductivity below 150 °C. In addition, the α relaxation and thermionic polarization of epoxy resin obey the Vogel‒Fulcher‒Tammann law, while the interfacial polarization and DC-conductivity satisfy with the Arrhenius law. Furthermore, the fitting results of the Vogel temperature of α relaxation, glass transition temperature, apparent activation energy of interfacial polarization and DC-conductivity all decline with HTBN content. These results can provide a reference and theoretical guidance for the assessment of dielectric properties and the improvement of the formulation of liquid-rubber-toughened epoxy resin. Full article

(This article belongs to the Special Issue Dielectric Materials: Challenges and Prospects)

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13 pages, 7640 KiB

Open AccessArticle

Elevated-Temperature Space Charge Characteristics and Trapping Mechanism of Cross-Linked Polyethylene Modified by UV-Initiated Grafting MAH

by Hong Zhao, Chen Xi, Xin-Dong Zhao and Wei-Feng Sun

Molecules 2020, 25(17), 3973; https://doi.org/10.3390/molecules25173973 - 31 Aug 2020

Cited by 17 | Viewed by 2495

Abstract

Space charge characteristics of cross-linked polyethylene (XLPE) at elevated temperatures have been evidently improved by the graft modifications with ultraviolet (UV) initiation technique, which can be efficiently utilized in industrial cable manufactures. Maleic anhydride (MAH) of representative cyclic anhydride has been successfully grafted onto polyethylene molecules through UV irradiation process. Thermal stimulation currents and space charge characteristics at the elevated temperatures are coordinately analyzed to elucidate the trapping behavior of blocking charge injection and impeding carrier transport which is caused by grafting MAH. It is also verified from the first-principles calculations that the bound states as charge carrier traps can be introduced by grafting MAH onto polyethylene molecules. Compared with pure XLPE, the remarkably suppressed space charge accumulations at high temperatures have been achieved in XLPE-g-MAH. The polar groups on the grafted MAH can provide deep traps in XLPE-g-MAH, which will increase charge injection barrier by forming a charged layer of Coulomb-potential screening near electrodes and simultaneously reduce the electrical mobility of charge carriers by trap-carrier scattering, resulting in an appreciable suppression of space charge accumulations inside material. The exact consistence of experimental results with the quantum mechanics calculations demonstrates a promising routine for the modification strategy of grafting polar molecules with UV initiation technique in the development of high-voltage DC cable materials. Full article

(This article belongs to the Special Issue Dielectric Materials: Challenges and Prospects)

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11 pages, 2258 KiB

Open AccessFeature PaperArticle

Investigation on the Interaction between Cellulosic Paper and Organic Acids Based on Molecular Dynamics

by Mengzhao Zhu, Chao Gu and Wenbing Zhu

Molecules 2020, 25(17), 3938; https://doi.org/10.3390/molecules25173938 - 28 Aug 2020

Cited by 4 | Viewed by 2289

Abstract

Organic acid is an important factor that accelerates the aging of cellulosic insulation materials. In this study, the interactions between cellulose and five acids, representative of what may be found in an aging transformer, were studied using molecular dynamics. The adsorption process of the five acids onto the surface of crystalline cellulose shows that the three low molecular acids are more readily adsorbed onto cellulose than the two high molecular acids. The deformation and adsorption energies of the acids all increase with an increase in molecular weight when they are stably interacting with cellulose. However, the differences between adsorption energies and deformation energies are positive for the three low molecular acids, whereas they are negative for the two high molecular acids. This indicates that the attachments onto cellulose of low molecular acids are considerably more stabilized than those of the high molecular acids. This is consistent with the experimental results. Furthermore, based on the calculated solubility parameters of acids, the experimental result that the three low molecular acids are to a large degree absorbed onto the cellulose, whereas the two high molecular acids remain in the oil, was theoretically elucidated using the theory of similarity and intermiscibility. Full article

(This article belongs to the Special Issue Dielectric Materials: Challenges and Prospects)

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10 pages, 9752 KiB

Open AccessArticle

The Effect of Fe₃O₄ Nanoparticle Size on Electrical Properties of Nanofluid Impregnated Paper and Trapping Analysis

by Bin Du, Qian Liu, Yu Shi and Yushun Zhao

Molecules 2020, 25(16), 3566; https://doi.org/10.3390/molecules25163566 - 6 Aug 2020

Cited by 9 | Viewed by 2728

Abstract

This paper systematically studies the effect of Fe₃O₄ nanoparticle size on the insulation performance of nanofluid impregnated paper. Three kinds of Fe₃O₄ nanoparticles with different sizes and their nanofluid impregnated papers were prepared. Environmental scanning electron microscopy (ESEM) and infrared spectroscopy were used to analyze the combination of Fe₃O₄ nanoparticles and nanofluid impregnated paper. The effect of nanoparticle size on breakdown voltage and several dielectric characteristics, e.g., permittivity, dielectric loss, of the nanofluid impregnated paper were comparatively investigated. Studies show that the Fe₃O₄ nanoparticles were bound to impregnated paper fibers by O–H bonds, while the relative permittivity and dielectric loss of the nanofluid impregnated papers were increased. Meanwhile, the increase of trap depth, caused by the nanoparticles, can trap the electric charge and improve the breakdown strength. The test results show that the direct current (DC) and alternating current (AC) breakdown voltages of nanofluid impregnated paper increased by 9.1% and 10.0% compared to FR3 nanofluid impregnated paper, respectively. Full article

(This article belongs to the Special Issue Dielectric Materials: Challenges and Prospects)

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12 pages, 2548 KiB

Open AccessArticle

Ameliorated Mechanical and Dielectric Properties of Heat-Resistant Radome Cyanate Composites

by Hou-Yu Li, Chang-Ming Li, Jun-Guo Gao and Wei-Feng Sun

Molecules 2020, 25(14), 3117; https://doi.org/10.3390/molecules25143117 - 8 Jul 2020

Cited by 17 | Viewed by 3343

Abstract

In order to improve the mechanical and dielectric properties of radome cyanate, a synergistic reinforcement method is employed to develop a resin-based ternary-composite with high heat-resistance and preferable radar-band transmission, which is expected to be applied to fabricate radomes capable of resisting high temperature and strong electric field. According to copolymerization characteristics and self-curing mechanism, epoxy resin (EP) and bismaleimide (BMI) are employed as reinforcements mixed into a cyanate ester (CE) matrix to prepare CE/BMI/EP composites of a heat-resistant radome material by high-temperature viscous-flow blending methods under the catalysis of aluminum acetylpyruvate. The crystallization temperature, transition heat, and reaction rate of cured polymers were tested to analyze heat-resistance characteristics and evaluate material synthesis processes. Scanning electron microscopy was used to characterize the micro-morphology of tensile fracture, which was combined with the tensile strength test and dynamic thermomechanical analysis to investigate the composite modifications on tenacity and rigidity. Weibull statistics were performed to analyze the experimental results of the dielectric breakdown field, and the dielectric-polarization and wave-transmission performances were investigated according to alternative current dielectric spectra. Compared with the pure CE and the CE composites individually reinforced by EP or BMI, the CE/BMI/EP composite acquires the most significant amelioration in both the mechanical and electrical insulation performances as indicated by the breaking elongation and dielectric breakdown strength being simultaneously improved by 40%, which are consistently manifested by the obviously increased transverse lines uniformly distributed on the fracture cross-section. Furthermore, the glass-transition temperature of CE/BMI/EP composite reaches the highest values of nearly 300 °C, with the relative dielectric constant and dielectric loss being mostly reduced to less than 3.2 and 0.01, respectively. The experimental results demonstrate that the CE/BMI/EP composite is a highly-qualified wave-transmission material with preferences in mechanical, thermostability, and electrical insulation performances, suggesting its prospective applications in low-frequency transmittance radomes. Full article

(This article belongs to the Special Issue Dielectric Materials: Challenges and Prospects)

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15 pages, 3763 KiB

Open AccessArticle

On the Ferroelectric to Paraelectric Structural Transition of BaTiO₃ Micro-/Nanoparticles and Their Epoxy Nanocomposites

by Georgia C. Manika, Konstantinos S. Andrikopoulos and Georgios C. Psarras

Molecules 2020, 25(11), 2686; https://doi.org/10.3390/molecules25112686 - 9 Jun 2020

Cited by 15 | Viewed by 3343

Abstract

BaTiO₃ is one of the most widely used ceramic components in capacitor formulation due to its exceptional ferroelectric properties. The structural transition from the ferroelectric tetragonal to the paraelectric cubic phase has been studied in both nano- and micro-BaTiO₃ particles. Several experimental techniques were employed for characterization purposes (X-ray diffraction-XRD, laser Raman spectroscopy-LRS, differential scanning calorimetry-DSC and broadband dielectric spectroscopy-BDS). All gave evidence for the structural transition from the polar tetragonal to the non-polar cubic phase in both nano- and micro-BaTiO₃ particles. Variation of Full Width at Half Maximum (FWHM) with temperature in XRD peaks was employed for the determination of the critical Curie temperature (T_c). In micro-BaTiO₃ particles (T_c) lies close to 120 °C, while in nanoparticles the transition is complicated due to the influence of particles’ size. Below (T_c) both phases co-exist in nanoparticles. (T_c) was also determined via the temperature dependence of FWHM and found to be 115 °C. DSC, LRS and BDS provided direct results, indicating the transition in both nano- and micro-BaTiO₃ particles. Finally, the 15 parts per hundred resin per weight (phr) BaTiO₃/epoxy nanocomposite revealed also the transition through the peak formation at approximately 130 °C in the variation of FWHM with temperature. The present work introduces, for the first time, a qualitative tool for the determination and study of the ferroelectric to paraelectric structural transition in both nano- and micro-ferroelectric particles and in their nanocomposites. Moreover, its novelty lies on the effect of crystals’ size upon the ferroelectric to the paraelectric phase transition and its influence on physical properties of BaTiO₃. Full article

(This article belongs to the Special Issue Dielectric Materials: Challenges and Prospects)

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33 pages, 16278 KiB

Open AccessReview

Energy Storage and Electrocaloric Cooling Performance of Advanced Dielectrics

by Yalong Zhang, Jie Chen, Huiyu Dan, Mudassar Maraj, Biaolin Peng and Wenhong Sun

Molecules 2021, 26(2), 481; https://doi.org/10.3390/molecules26020481 - 18 Jan 2021

Cited by 11 | Viewed by 4185

Abstract

Dielectric capacitors are widely used in pulse power systems, electric vehicles, aerospace, and defense technology as they are crucial for electronic components. Compact, lightweight, and diversified designs of electronic components are prerequisites for dielectric capacitors. Additionally, wide temperature stability and high energy storage density are equally important for dielectric materials. Ferroelectric materials, as special (spontaneously polarized) dielectric materials, show great potential in the field of pulse power capacitors having high dielectric breakdown strength, high polarization, low-temperature dependence and high energy storage density. The first part of this review briefly introduces dielectric materials and their energy storage performance. The second part elaborates performance characteristics of various ferroelectric materials in energy storage and refrigeration based on electrocaloric effect and briefly shed light on advantages and disadvantages of various common ferroelectric materials. Especially, we summarize the polarization effects of underlying substrates (such as GaN and Si) on the performance characteristics of ferroelectric materials. Finally, the review will be concluded with an outlook, discussing current challenges in the field of dielectric materials and prospective opportunities to assess their future progress. Full article

(This article belongs to the Special Issue Dielectric Materials: Challenges and Prospects)

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23 pages, 3811 KiB

Open AccessReview

The Electric Field Responses of Inorganic Ionogels and Poly(ionic liquid)s

by Zhenjie Zhao, Guangchen Zhang, Yuting Yin, Chenjie Dong and Ying Dan Liu

Molecules 2020, 25(19), 4547; https://doi.org/10.3390/molecules25194547 - 4 Oct 2020

Cited by 16 | Viewed by 3788

Abstract

Ionic liquids (ILs) are a class of pure ions with melting points lower than 100 °C. They are getting more and more attention because of their high thermal stability, high ionic conductivity and dielectric properties. The unique dielectric properties aroused by the ion motion of ILs makes ILs-contained inorganics or organics responsive to electric field and have great application potential in smart electrorheological (ER) fluids which can be used as the electro-mechanical interface in engineering devices. In this review, we summarized the recent work of various kinds of ILs-contained inorganic ionogels and poly(ionic liquid)s (PILs) as ER materials including their synthesis methods, ER responses and dielectric analysis. The aim of this work is to highlight the advantage of ILs in the synthesis of dielectric materials and their effects in improving ER responses of the materials in a wide temperature range. It is expected to provide valuable suggestions for the development of ILs-contained inorganics and PILs as electric field responsive materials. Full article

(This article belongs to the Special Issue Dielectric Materials: Challenges and Prospects)

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43 pages, 3211 KiB

Open AccessReview

Sustainable, Renewable and Environmental-Friendly Insulation Systems for High Voltages Applications

by Muhammad Rafiq, Muhammad Shafique, Anam Azam, Muhammad Ateeq, Israr Ahmad Khan and Abid Hussain

Molecules 2020, 25(17), 3901; https://doi.org/10.3390/molecules25173901 - 27 Aug 2020

Cited by 64 | Viewed by 7581

Abstract

With the inception of high voltage (HV), requisites on the insulating permanence of HV equipment is becoming increasingly crucial. Mineral/synthetic oil liquid insulation—together with solid insulation materials (paper, pressboard)—is the fundamental insulation constituent in HV apparatuses; their insulation attributes perform a substantial part in a reliable and steady performance. Meanwhile, implications on the environment, scarcity of petroleum oil supplies and discarding complications with waste oil have stimulated investigators to steer their attention towards sustainable, renewable, biodegradable and environmentally friendly insulating substances. The contemporary insulating constituent’s evolution is driven by numerous dynamics—in particular, environmental obligations and other security and economic issues. Consequently, HV equipment manufacturers must address novel specifications concerning to these new standards. Renewable, sustainable and environmentally friendly insulating materials are continuously substituting conventional insulating items in the market place. These are favorable to traditional insulating materials, due to their superior functionality. The also offer explicit security and eco-friendly advantages. This article discusses cutting-edge technology of environmentally friendly insulating materials, including their fabrication, processing and characterization. The new renewable, insulating systems used in HV equipment are submitted and their fundamental gains stated in comparison with conventional insulating materials. Several experimental efforts carried out in various parts of the world are presented, offering an outline of the existing research conducted on renewable insulating systems. The significance of this article lies in summarizing prior investigations, classifying research essence, inducements and predicting forthcoming research trends. Furthermore, opportunities and constraints being experienced in the field of exploration are evidently reported. Last but not least, imminent research proposals and applications are recommended. Full article

(This article belongs to the Special Issue Dielectric Materials: Challenges and Prospects)

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