Fabrication, performance and applications of

Composite Interfaces

ISSN: 0927-6440 (Print) 1568-5543 (Online) Journal homepage: http://www.tandfonline.com/loi/tcoi20

Fabrication, performance and applications of integrated nanodielectric properties of materials – a review J. Anandraj & Girish M. Joshi To cite this article: J. Anandraj & Girish M. Joshi (2017): Fabrication, performance and applications of integrated nanodielectric properties of materials – a review, Composite Interfaces, DOI: 10.1080/09276440.2017.1361717 To link to this article: http://dx.doi.org/10.1080/09276440.2017.1361717

Published online: 08 Aug 2017.

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Date: 08 August 2017, At: 07:25

Composite Interfaces, 2017 https://doi.org/10.1080/09276440.2017.1361717

Fabrication, performance and applications of integrated nanodielectric properties of materials – a review J. Anandraj and Girish M. Joshi Polymer Nanocomposite Laboratory, Center for Crystal Growth, VIT University, Vellore, India

Downloaded by [GIRISH JOSHI] at 07:25 08 August 2017

ABSTRACT

The design and development of modern technological composites for the electrical and electronic applications are highly crucial. The minitualization, performance and durability of nanocomposites are achieved by integrating the nanodielectric properties of materials. In this review article, the entire upcoming trends in the domain of nanodielectric illustrated with important applications co-related to the various fabrication techniques of integrated nanodielectric composites are provided. The factors affecting the nanodielectric due to operating electric field and material interface which exhibit the high dielectric constant, low loss and moderate breakdown voltage. The complete sketch from concept, fabrication, factors co-related and applications of nanodielectric properties with the future scope are taken into consideration for further developments.

ARTICLE HISTORY

Received 11 March 2017 Accepted 27 May 2017 KEYWORDS

Nanodielectric; interfacial role; interfacial properties; dielectric constant; loss; applications

Introduction Material properties are highly critical to obtain the desirable performance, durability and sustainability under external stimuli for worthwhile engineering applications. Researchers in the area of dielectrics overcome the various challenges related to the properties of nanodielectric and its practical feasibility for applications and devices [1]. The new generation of materials has highly optimized dielectric and electrical insulating properties are integrated

CONTACT Girish M. Joshi

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© 2017 Informa UK Limited, trading as Taylor & Francis Group


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J. ANANDRAJ AND G. M. JOSHI

altogether [2–5]. The term ‘Nanodielectric’ was defined as a multi-component dielectric and has the nanostructures that lead to changes in one or several dielectric properties. These materials are usually associated with the incorporation of nanoparticles in the polymer matrix in order to improve their performances. Nanodielectrics properties are mainly observed in two types of materials namely ceramics and nanocomposites. In the case of ceramics, nanostructures are obtained to a larger extent. In the recent years, it was noted that substantial benefit could be obtained if nanocrystalline powders are to be utilized as starting materials in the solid product. In the case of nanocomposites, preparation of nanostructure needs novel approaches and concepts. These novel approaches consist of more than merely adding nanoparticles into polymer matrix [6–9]. Nanodielectrics can be fabricated using inorganic oxide particles having diameters less than 20 nm. This will bring its own problems since such finely divided particles have a natural tendency to agglomerate. The fundamental principle of nanodielectric depends on very large internal surface area displayed. Nanodielectric research interest had increased tremendously and various electrical properties are compared with their unfilled and micro filled counterparts. The vast published research papers and reports in the domain of nanodielectric show the great interest in nanodielectric field. To engineer these materials, we need to apply interfacial modifications, select particular aspect ratio and change in morphology. Nanodielectric deals with the dielectric process of spontaneous polarization as a function of the applied external field across a nanoscale. The first experimental evidence of increased polarization in polymer nanodielectric composites was reported by Henk et al. [10]. A fluid diglycidyl ether of bisphenol A (DGEBA)/methyl hydride epoxy system filled with inorganic particles cast in bubble-free plates. The investigation on the pure network polymer and polymer/particle composites withstands the partial electrical discharges. The high endurance was obtained by dispersion of silicon dioxide aerosol nanoparticles in the epoxy system. Nano scale structure ceramics demonstrated the nanodielectric behaviour [10–15]. Frechette determined the performance of the dielectric surface exposed to partial discharge is compared to the epoxy-containing only the silicon dioxide (SiO2) loading. Low-density discharges are produced along a gap formed by the interface between compressed air and the bulk sample. The materials contained a low density of nanoparticles would stop the present discharge conditions and show the improved performance in epoxy without nanoclay [16–20]. Michael explained the presence of nanoscale objects and the existence of process with characteristics length consisting of nanoscale affects in dielectrics. Some analogy between crystalline dielectrics and dendrimers are developed to argue that grains and interfaces in a high degree self-assembly polymer nanodielectric could play each role. The report reveals that wave surrounded nanodielectric and formed a spiral shape [21–24].

Present trend of nanodielectrics Nanodielectric domain has been developed in recent years to improve the dielectric properties such as dielectric constant, dielectric strength and voltage endurance. Nanodielectric belongs to the new type of materials and related to the dielectric phenomena of nanoscale materials having the unique morphology of particles, sheets, wires and tubes. These materials have enormous applications in power electronics industry, gate electrodes, capacitors, sensors, electrochemical transducers, fuel injectors for automobiles and engines. There are some methods to be used to prepare nanodielectric such as polyethylene (PE), polyamide


COMPOSITE INTERFACES

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Figure 1. Published reports in the field of nanodielectrics.

(PI), silicone, epoxy resin (EP) and polyimide (PI). The vast published research papers and reports in the domain of nanodielectric are shown in Figure 1. Nano fillers also become a major focus in nanodielectric research. Nano fillers can improve the different properties of materials in which they are incorporated such as optical, electrical, thermal and mechanical properties. Nano fillers can be classified into three types. Zero-dimensional, one-dimensional, two-dimensional and three-dimensional nanofillers. Zero-dimensional may be particles of quantum range such as quantum dots. Onedimensional nano filler may be in the form of plates, laminas and shells. Two-dimensional nanofillers are in the form of nanotubes and nano fiber having diameter contains different aspect ratio. Three-dimensional nano filler are in the form of isodimensional particles such as nanometric silica. Some nano filler such as layered silicate, silicon dioxide and titanium dioxide are used as resins in the industry. The major research was done in the domain of polymer nanocomposites since last three decade. Polymer nanocomposites are found to improve the partial discharge resistance, space charge formation and effects of charge relaxation. The properties of polymer nanocomposites are changed simultaneously by adding the filler. The survey of polymer host system based on properties and applications are shown in Table 1.

The interface between polymer system and nano entity In nanodielectric, interface phenomena occur between the two immiscible phases. The physics and chemistry of nanodielectric interface using spherical inorganic nanoparticles and exfoliated layered inorganic or synthetic clays. The highlighted the progress in the understanding of the interface role but also had some contradictory results [25]. This process

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Table 1. Survey of polymer nanocomposites properties and applications. Host system Polyethylene


Diglycidyl ether of bisphenol A (DGEBA) Polypropylene

Filler system Properties Silicon dioxide (SiO2), Tin Dielectric relaxation Oxide (TiO2), Aluminium oxide (Al2O3) SiO2 Insulating system Montmorillonite (MMT)

Polymethyl methacrylate (PMMA) Epon58034 (EEW: 325–375)

Barium Fluoride (BaF2)

Hyperbranched aromatic polyamide (HBP)/PMMA Diglycidyl ether of bisphenol-A (DGEBA) Low density polyethylene (LDPE) Polypropylene PVDF

Barium Titanate (BaTiO3)

Silver

Nanoalumina Bismuth Ferrite (BiFeO3)

Nanosilica Copper nanowire/ Multiwalled carbon nanotube (MWCT) 2-Ethyl-4methylimidazole BaTiO3 (2E-4MI) Polyaniline (PANI) Calcium copper titanate oxide (CCTO) LDPE Al2O3 Polyamide Zirconia Polyethylenimine BaTiO3 Cross linked polyethylene Silica (XLPE)

Applications Engineering applications [6] Electro technical applications [16] Industrial and academic fields [68] High voltage application [72]

Mechanical properties, direct injection molding Agglomeration of particles and electrical insulation properties Dielectric constant (εr~100) and Capacitor application [79] dielectric loss (Tanδ = 0.02). (Mechanical properties) High dielectric constant, low loss Energy storage devices [85] and high energy density Thermal stability Water absorption [86]

Controlling the spontaneous Waste water treatment technolmagnetization by electric field ogy [87] Surface degradation is increased Capacitor [88] Polarization mechanism Communication devices, charge-storage capacitors systems [89] Dielectric constant ε = 20 and Microelectronics [90] dielectric loss 0.01 Improved electrical conductivity Light emitting diodes, lightweight battery electrodes [91] Reduction of nano effect Power engineering [92] Increase in thermal properties High voltage applications [107] High energy density, high power Capacitor and electrical density insulation application [108] Increase in partial discharge Electrical power industry [126] resistance

does not include electrical, mechanical, physical or thermal ageing effects. Nanodielectric interface emphasizes a lot of interface in chemistry which involved in making nanocomposites. The process needs synthesis steps enable for synergic effect on voltage endurance and partial discharge resistance properties. Researchers found that measurements in polymer nanodielectric of glass transition temperature, free volume, and broadband frequency, dielectric measurements of the real and imaginary components of permittivity, morphology, infrared and electron paramagnetic resonance (EPR) measurements demonstrated the significant effect and challenge of modeling the interface in composites. The effect of nanoparticles on melting point and glass transition temperature (Tg) was reported in the review addressed the theoretical and experimental issues [26]. It was demonstrated the dynamic, thermodynamic and pseudo thermodynamic measurements reported for Tg in confined geometries for both small molecules in nonporous in ultrathin films. The trend of Tg increases, decreases, remains unchanged or even disappears depending on the experimental conditions. For the same material, different values of Tg had been observed. Many experiments are carried out and results are evaluated. It was concluded that existing theories of Tg are able to explain the range of behavior at the nanometric size scale. A quantitative analysis proved the experimental results on the nanoconfinement of the glass transition temperature can be explained by a defect diffusion model. This model gives the defect-defect interaction enthalpy, defect concentrations, defect lattice geometry,



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correlation length and percolation fraction to determine Tg and provides a quantitative relationship between the percolation fractions of rigid to mobile regions [27]. Different spherical inorganic nanoparticles in bisphenol-A epoxy as a function of filler concentration illustrates a strong unusual sensitivity of Tg. The trend was dropped sharply as the concentration increases to 0.5% and then steadily increases as concentration increased to 20%. This concept will help us to improve our understanding of the nano interface and developing an interface model can be related to physical and electrical properties [28]. Lewis and Tanaka represented the structure of the interface in a diffuse double layer and 4-layer electrical structure in polymer properties [29,30]. Some features lead to dramatic improvements in the non-polar bonding of nanoparticles. However, there are also some differences in interface characteristics can be related to the chemical nature of the nanoparticles surface, polymer matrix types (e.g., amorphous or semi-crystalline thermoplastic polymer, crosslinked polymer and thermoset polymer), molecular weight and stereo-regularity qualities. The influence of water on electrical properties such as broadband dielectric and infrared measurements, low and high field electrical measurements, short and long term hydrolysis of the nanoparticle surface and another ageing effect cannot be over emphasized. Primarily it deals with the intercalated and exfoliated nanocomposites and the subsequent undesirable effect upon the properties [31]. Jeschke demonstrated the structure and dynamics of the surfactant layer in nano clays prepared from synthetic clays and their composites are studied to understand the influence of interfacial layer on composite properties. EPR methodology is used for probing different aspects for polymer surfactant clay interface layer. It characterizes the intercalation, exfoliation process and properties of polymer clay nanocomposites [32]. The dynamic properties of interface play the crucial role in macroscopic dynamics of multiphase soft condensed matter systems [33]. These properties affect the dynamics of emulsions, biological fluids, coatings, free surface flows, immiscible polymer blends and many other complex systems [34]. The study of interfacial dynamic properties and surface rheology is a major discipline in physics, chemistry, biology and life sciences [35]. In the past three to four decades a vast amount of literature has been produced dealing with the properties of interfaces stabilized by low molecular weight surfactants [36–40].

Interfacial issue of materials The material scientific community well addressed the interfacial issue of composite materials. The unique surface properties of interfacial materials are used to develop the effective solutions for challenging integration of materials suitable for various applications. The report on mechanisms and fabrication techniques of interfacial materials have lot of scope with special wettability and environmental applications implemented for the oil-water separation, membrane-based water purification, desalination, bio-fouling control, high-performance vapor condensation and atmospheric water collection. A wide range of applications based on a principle of interface materials has been proved in practice. Some of them include self-cleaning textile, oil-water separation, anti-icing, anti-fogging glass, atmospheric water collection, chemical shielding, corrosion control and biological adhesion mitigation [41]. Interfacial phenomena play a crucial role in many environmental processes includes membrane-based separations, adsorption, biological fouling, corrosion, interfacial phase transition and catalytic surface reaction. The properties of the interfacial material are based on the lanthanide di-(2-ethylhexyl) phosphate. It reported the local vibration at the interface

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of the heterogeneous liquid system changes the properties of the material [42]. In cellulose and pectin localization there was continuity between host cell wall and the interfacial material. The report concluded that in order to verify the interfacial material there are some techniques allows the identification of cell wall components are used [43]. The glass/ epoxy composite demonstrated the consistency in interfacial materials properties. These materials constant are proved with the help of experimental results and made finite element calculations on interface elements [44]. The material interface is important in interfacial issues because it determines the mechanical, fracture and functional properties. In the present review, the nano entity reinforced composites are highly crucial to demonstrate the nanodielectric properties.


Interfacial issue of external field The evolution of interfacial field was monitored by probe beam through an electric field induced second harmonic generation. By tracking the evolution of different interfacial fields we are able to study the redistribution of carriers between the layers due to electron transport across the interfaces. Glinka observed the complicated evolution of interfacial fields originating from the redistribution of carriers between the interfaces [45]. Peng reported the strong interfacial field in the graphene/model magnetic insulator hetero structure. Using graphene as a prototypical 2D system it was demonstrated the coupling to the magnetic insulator produces the substantial magnetic exchange field (MES) leads to enhancement of Zeeman spin Hall Effect. The MES effect shows in graphene/EuS heterostructure provides future spin logic and memory devices based on emerging 2D materials in classical and quantum information processing [46]. The nitrile group is stretched frequency in red shifts and improved the dielectric constant was proved in experimental model. In the theoretical model, Onsager reaction field plays a vital role in predicting vibrational frequency shifts in bulk dielectric media. But due to the asymmetric environment, the Onsager reaction field is not applicable for the interface. This model successfully explains the red shift of nitrile group stretch as a function of dielectric constant which used to estimate the reaction field near the interface [47].

Nano filler and polymer host system an interfacial mechanism Basically interfacial between the fillers (nanoscale) and the host system demonstrated interesting electrostatic, electrical and dielectric properties. It may be due to small size fillers having discrete energy states compared to the bulk filler. We observed the several examples of improved dielectric properties under the domain of nanofillers such as organic, inorganic carbon nanotubes (CNT’s), graphene, metal precursor and piezo-ceramics in the host system. However, the process of permanent dipole displacement optimized by high voltage poling treatment. It was suitable for the applications to obtain the device like hydrophone and variety of sensor and communication applications. The internal material nanostructure demonstrates the effect of dielectric properties such as external stimuli in the form of poling. However, a variety of application such as battery electrolytes, super capacitors, smart polymer phones, piezo and pyroelectric composites, dielectric barrier as polymer electrets may be the future prospect of nanodielectric based on selection of appropriate nano entity [48].



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Basically, electrostatic model playing a crucial role in nanodielectric polymer composites. The factors affecting were spherical nature of nano filler, a surface area surrounded by three layer interface attributes the dipole types, concentration, permittivity and charge distribution were disclosed [49]. The computational techniques and models proposed to demonstrate the nanodielectric property co-related to charge distribution permittivity deals with the electrostatic, numerical interface charge models related to effective volume. It is also based on capacitor in and out plane interconnection of the elementary unit cell. In principle interface electrostatic numeric model dependent interface charge used to modify the structure feasible to identify the nanodielectric properties. The Electrostatic force is converted to amplitude modulation to determine the microstructure of materials at the subatomic level. Furthermore, optimization of the property has a lot of scopes to develop from microscope to communication level. In the domain of nano science and technology, morphology of nanocomposites identified by using microscope specially the electron force microscope. This obeys the principle of nanodielectric spectroscopy. The sample is biased with some potential. The sharp cantilever made of silicon is metal coated interact with the sample. The electrostatic force between tip and sample follows the precision of phase loop criteria. The force gradient provides cantilever motion variation which is correlated to the electrostatic component of cantilever frequency. The dc bias and dielectric relaxation induces a spontaneous polarization and optimizes a dielectric loss known as polarization noise co-related to the dielectric susceptibility which provides the dynamic time-dependent information of nanostructure [50].

Interfacial properties in nanodielectric Interfacial properties in nanodielectric can dominate the overall performance of materials. For example, atomic level interfacial features such as multiple oxidation states and impurities are considered to be less important in large scale systems due to smaller volume fraction occupied by the interfacial region. These effects can be seen on the electrical properties in the nanoscale systems. It is important to characterize the electronic and dielectric properties of the interface containing materials in the nanostructure. The relationship between the interface structure, polarization, dielectric response and electronic structure are co-related. This theory deals with the interface effects modify the static and optical local dielectric permittivity and the evolution of the local electronic structure. For e.g., valence band and conduction band as the function of position across interfaces are explained by density functional theory (DFT) based computational methods. It includes the interface between Silicon (Si) and inorganic oxides silicon dioxide (SiO2) and the interface between the polymers (polyvinylidene fluoride or polyethylene). Silicon-hafnium oxide (Si-HfO2) and SiO2 polymer interface used to capture the bending, band offsets and creation of trap states at interfaces. Their application used to detect the interfaces and atomic level on dielectric and electronic properties of the wide area in nanostructured systems [30]. Interfacial issues deal with the restricted polarization based on the mixed phase of the polymers. It disclosed the interfacial performance, properties and utility of engineering polymer blends. In this author performed a DFT aimed at interfacial properties very close to dielectric applications. The atomic level interface made possible by DFT. The stability of interfaces and atomic level interface are described [51].

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Engineering properties of materials co-related to dielectrics


Ferroelectric Ferroelectric is the property of materials which exhibit the spontaneous electric polarization was observed in cubic barium titanate (BaTiO3) and lead titanate (PbTiO3) structures. It can be reversed by application of the external electric field. BaTiO3 and PbTiO3 show a permanent dipole moment. It was demonstrated the surface charge density expressed by a ferroelectric polymeric thin film matches the density of charges in polyelectrolyte. The combination of ferroelectric and polyelectrolyte provides large specific capacitance; fast polarization response times and high semiconductor surface charge density resulted in non-volatile memory devices [52]. The electrode interface plays the key role in controlling the macroscopic electrical properties of ferroelectric capacitors was based on thin films. In epitaxial ferroelectrics, electrode interface was important in controlling the leakage current and polarization switching. The results suggest that the depolarization occurs during the polarization switching and almost independent to the metals [53]. Paraelectric property of materials Paraelectric is the ability of materials to become temporarily polarized under an external electric field. This can happen if there is no permanent electric dipole present in the material and removal of electric field results in the polarization of the material which returns to zero. Paraelectric occurs in crystal phases in which electric dipoles is unaligned and have the potential to align with an external electric field and strengthen it. Yoshiyuki demonstrated the kinetics of phase transition between ferroelectric to paraelectric phase in copolymers of vinylidene fluoride and trifluoroethylene. It studied by measuring the time development of dielectric permittivity during the phase transition with temperature [54]. Barium strontium titanate paraelectric ceramics with various grain sizes are synthesized by oxalate co-precipitation method and prepared by conventional solid state sintering process. By decreasing grain sizes the dielectric breakdown strength increases gradually. Based on the conductivity activation energy analysis, it was found that the large grain boundary density plays a dominant role in controlling dielectric breakdown strength for samples with smaller grain size around 0.6–1.0 μm. If the growth of grain size was above 1.0 μm there was a decrease in dielectric breakdown strength induced by the combined effect of lower grain boundary density and more interface polarization [55]. Pyroelectric Pyroelectric is the property of certain crystals such as gallium nitride that are electrically polarized and results contain large electric fields. In other ways pyroelectric was interpreted in such a way that ability of certain materials (gallium nitride) generated a temporary voltage when they are heated or cooled. Martin LW demonstrated that piezoelectric transducer heterostructure can be controlled to show the low dielectric permittivity due to the presence of built-in potentials. It diminishes the dielectric permittivity and large values of the pyroelectric coefficient are obtained. They are used in infrared sensors and pyroelectric energy conversion of waste heat [56]. Jiang Lu presented a multi-human tracking system with sensor selection and calibration based on distributed binary pyroelectric infrared


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sensors (PIR). This sensor has been developed to select sensor nodes [57]. The improved enhanced ionization using a pyroelectric lithium niobate crystal for use in a smaller level ion mobility gas sensor. It was achieved by increasing the power system by using folded copper electrodes on the crystal surface to amplify the electric field. The author reported by reducing the distance between the copper electrodes was possible to achieve the ionization events at much lower temperature shifts [58].


Piezoelectric Piezoelectric is the ability (of certain solid materials such as crystals and ceramics) to generate the electric charge in response to applied mechanical stress. The piezoelectric effect is well understood by the linear electromechanical interaction between a mechanical and electrical state in crystalline materials. It is the reversible process and exhibits the direct piezoelectric effect. The behavior of piezoelectricity used in various applications such as micro and nanomaterials in sensors, electromechanical actuators and energy conversion. The piezoelectric polymers such as polyvinylidene fluoride (PVDF) and its copolymers are being developed for use in flexible electronic components due to intrinsic features of low weight, charming flexibility and electroactive properties [59]. Piezoelectric materials are considered to be smart materials and can convert any kind of strain into electricity and vice versa. Examples of piezoelectric materials are lead zirconium titanate (PZT) and barium titanate. PZT is common filler for piezoelectric composites. Dielectric and piezoelectric can be modified by the addition of suitable dopant [60].

Electrical properties of polymer Electrical properties of polymers widely used in industrial and domestic applications such as automotive, aerospace, marine packaging and consumer goods. Electrical tests are the measurements of resistance, conductivity and capacitance on the surface. Organic and polymer materials have unique electrical properties due to higher volume ratio and can be done by experimental techniques such as spin coating, electrostatic spraying. These two techniques used in a large number of optoelectronic devices such as interfacial layer [61,62]. This material used in metal organic/polymer semiconductor in terms of electrical and optical characteristics having the structure of solar cells and LEDs. Many researchers worked tirelessly for the development of electrical properties and cause the general improvement in polymer behavior and had a great application in large scale electronic and optoelectronic devices [63,64]. The schematic diagram for the electrical properties of the polymer was shown in Figure 2. Electrical hysteresis loop The electrical hysteresis loop is a characteristic of the electric field (E) and electric displacement field (D). This electrical hysteresis loop occurs in the ferroelectric material. When electric field E is increased, the electric displacement D also increases slowly at first and then increases more rapidly. The rate of electric displacement slows down again and reaches the saturation value (Es). With further increase in the electric field E, there is no increase in the electric displacement D. If the electric field is reversed the electric


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Figure 2. Electrical properties of polymer.

displacement decreases slowly at first and reaches the residual value Dr at zero fields. If the electric field is continued in the opposite direction, the domain leads to reverse their alignment. So the remaining value of electric displacement is lost at the certain value of the reverse electric field is called the coercive field (Ec). The process of reversal of domain continues to give a net electric field in the opposite direction. After the saturation occurs in this direction, it restores the original field which completes the hysteresis loop. Polarization and dielectric studies of ceramic show the better dielectric material at 1200 °C. It shows the dielectric constant at 16.4 and loss at 0.4 [65]. Similarly dielectric and hysteresis study of bismuth sodium titanate and barium zirconate samples demonstrates the hysteresis loop at temperature 423 K [66]. The ferroelectric characteristics of nanostructured zinc oxide and magnesium oxide bilayer metal capacitor have high resistivity and low leakage current density. Based on ferroelectric characteristics, it shows the polarization and electric field hysteresis gives the symmetry loop and maintains the hysteresis for external voltage by adding polyvinylidene fluoride and trifluoroethylene in the capacitor configuration [67,68]. The numeric solution of nonlinear equation describes the hysteresis behavior of coupling capacitance among silicon via three-dimensional integrated circuits. It resulted in developing a behavioral capacitance model matches the coupling capacitance measurement among three silicon vias [69].

Various fabrication techniques of nanodielectric composites and blends Melt blending method In order to melt the polymer granules to form a viscous liquid melt blending method was used. To evaluate this, consider the nanoparticle can be separated into polymer matrix with high temperature. So sample can be prepared by compression molding and injection molding.



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Melt blending method is an extrusion melt compounding of dispersive nanofillers with the polymer host material. It was considered to be the productive and cost-effective process [70]. The major advantage of melt blending is to allow the nanocomposites to be produced using ordinary compounding devices such as extruders. Some advanced polymer technologies used in melt blending method in a very attractive manner of large-scale production of nanocomposite materials. The mixing parameters have an influence on the morphology of the nanocomposite. Some of the variables are taken into account are balancing the dispersion, distributive mixing, melting temperature, time spent for a particular place for melting and shear elongation forces [71]. The extruder type and screw configuration are the important parameters to achieve good nano filler dispersion [72]. Furthermore, if the extruder remains in longer times it has a better dispersion. In most cases having a melt viscosity in maximum will helpful in achieving better dispersion because of the higher strain can be forced on the nano filler particles [73]. The conditions under which dispersive mixing can be balanced between the cohesive force and hydrodynamic forces [74]. There are some steps for liquid-solid dispersive mixing. Some of them are incorporating the filler into the liquid matrix, wetting of solid phase by the liquid one, fragmenting the solid agglomerates and limited agglomeration dispersed particles produced by a particle-particle collision. All the parameters are controlled but the still complete dispersion of nano particle are difficult. The advantages of melt blending method are that nanocomposite can be made by using thermoplastic resins. This method was mainly used for producing clay nanocomposites and has been improved for industrial materials. Melt blending was a huge disadvantage because thermoplastic polymers are used. Sol-gel method Sol-gel is a wet-chemical process used for fabrication of both glass and ceramic materials. It has a solid and liquid phase in which solution forms the gel-like network. The sol-gel method has the formation of inorganic networks through colloidal suspension (sol) and gelation of the sol to form a network in a continuous liquid phase (gel). The sol-gel method is a process used for producing solid materials from smaller molecules. The main advantage of a sol-gel method was used in the preparation process for organic and inorganic nanocomposites. It consists of hydrolysis of molecular precursors of desired nanoparticles and polycondensation of a particle in a glass-like form [75]. Organic polymers are introduced at the initial stage authorized by the homogeneous dispersion of particles on the nanometric scale [76]. In the sol-gel method, the reactions formed the base polymer and nanofiller occurred simultaneously. The latter one was formed by the hydrolysis and condensation reactions of alkoxides. This method was unsuitable for industrial manufacture. However, it has been improved recently and now widely accepted in the industry. Electro spinning Electro spinning (ES) is a process to obtain continuous polymeric or inorganic fibres having dimensions that range from tens of nanometers to few micrometers by electro statistically charged molten polymer [77]. The jet of polymer solution electro statistically charged by


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high voltage (HV) source comes out of the needle tip in the form of hanging drop. The high electric field between the needle and grounded electrode causes a distortion of the drop until it takes a conical shape called Taylor cone. When the electrostatic force acting on the charged drop it exceeds the surface tension and critical value of electric potential resulted in a thin jet of the fluid polymer was formed and attracted towards the metal collector. The charged jet was stretched and accelerated by the electric field and undergoes to the process of instability called whipping instability. The fibres run through the spiral path increases the stretching process resulting in fibres to be thinner and the solvent evaporates. During this instability process, the formation of fibres occurs in the order of a few hundred nanometers. The chaotic movement produces the jet from the random deposition of the fibres on the collector in the form of nonporous. The electro spinning was simple, cheap and industrially scalable and used to obtain highly porous nonmaterial’s and nanocomposites with good dispersion having inorganic nanoparticles. For example, high performance of polymeric nanocomposites for lithium ion batteries was developed by means of electro spinning [78]. Bian has used an electro spinning to disperse nano silica into silicone rubber to reduce the particle agglomeration. Silicone fibres are coated with electro spun with nanosilica incorporates into rubber matrix. It was shown that large volume of nanosilica could be dispersed into silicone rubber by means of electro spinning is compared with high-shear melt compounding [79]. Intercalation method Intercalation method is widely used for the synthesis of polymer nanocomposites. It depends upon the intercalated and exfoliated hybrid methods. This process involves the combining polymers within the layers of clay. When intercalate was required, organic materials immersed within the layers of clay expands within the component mixtures. When it is in the exfoliated mixture the entire layers of clay materials are separated from each other but tied within the matrix of the organic component. Intercalation method is a reversible state included within a group of compounds with layered structures. Intercalation method is used for preparing nanocomposite clay. Nylon-6 clay hybrid is the first nanocomposite produced by the Toyota group was prepared by intercalation method and polymerization. Polymerization required a chemical plant to polymerize the monomer dispersed with organically modified clays. Direct dispersion method Direct dispersion method is used for producing nanocomposites by chemically modifying nanoparticles. It also used to increase the compatibility with polymers. The advantage of this method is total homogeneity achieved without porosity of a given form of sediment is decreased. For example, zinc oxide nanoparticles are prepared by combining the zinc sulphate and ammonium bicarbonate. The direct dispersion method is the simplest methods and its difficult to disperse the nanofillers homogeneously. However, a recent improvement of mixing devices and surface treatment techniques has helped in many cases for direct dispersion method. The various fabrication and techniques of nanodielectric with examples are shown in Figure 3.



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Figure 3. Various fabrication and techniques of nanodielectrics.

High dielectric constant High dielectric constant has the tremendous applications in energy storage solution for electronic equipment [80–82]. The innovation of new dielectric materials leads to a new generation of capacitors. Nowadays there was a growing demand for capacitors can store a lot amount of charges. This charge storage depends on the high dielectric constant and electrical permittivity of nanodielectric. These properties are increased by adding nanoparticles fillers into the polymer matrix material. The electrical properties of nanodielectric can be improved by the nanoparticles are properly dispersed in the polymer matrix. Since nanoparticles agglomerate easily due to high surface energy and doing well dispersed discrete nanoparticles in polymer films. These are the key factor to achieve the high dielectric performance. Polymers have a lot of advantages such as high processing capacity, mechanical moldability, electrical breakdown strength and compatibility with several electronic technologies. However, they have a low electrical permittivity. This problem was overcome by using polymer-ceramic composites because they combine the processing ability of the polymer with the high permittivity of the ceramics. If permittivity of the polymer-ceramic composite was high it is to be loaded with ceramic fillers. However, if the polymer was loaded to a higher level, there was a problem with poor adhesion [83]. Even with the ceramic-filled polymer technology achieving k value was greater. Relative k values are experimentally proved and it was considered excellent for polymer and ferroelectric composites with ferroelectric ceramics of volume fraction which is less than 50%. Embedded metal nanoparticles in polymer matrices seem also to be a very effective way to increase the dielectric performance of the nanocomposite [84–87]. In order to have high permittivity particles, the concept of metal nanoparticles is used. To increase the capacitance of the nanocomposite we need core-shell capacitors to be distributed uniformly in the host polymer system. This mechanism should allow a large amount of high energy density can be released rapidly the high power density. Badi proposed that nanodielectric materials made up of core-shell metal nanoparticles into polymers were a

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powerful concept for producing high permittivity polymer films with minimum dielectric loss can be made part of a standard capacitor manufacturing process. The other name for high permittivity nanodielectric was high-k refers to a material having high dielectric permittivity (k) as compared to SiO2 used in semiconductor manufacturing process. The use of high-k materials has extended beyond electronics and has triggered the development of other-k materials.


Low dielectric loss Nanocomposite exhibits the nanodielectric properties with the low dielectric loss and higher dielectric constant as potential applications in energy storage devices. The technique core-double shell barium titanate (BaTiO3) are successfully prepared by in situ polarization techniques in which BaTiO3 nanoparticles are used as a core and the two shells hyper branched aromatic polyamide (HMP) and poly(methylmethacrylate) (PMMA). It was proved the low dielectric loss because of poor nanoparticles dispersion and the interfacial adhesion between barium titanate and PMMA [88]. The dielectric properties of Polyethylene nanocomposites exhibit low-frequency loss as a function of nano alumina loading [89]. Dielectric loss of Bismuth Ferrite (BiFeO3) and low-density polyethylene (LDPE) nanocomposites indicated a low dielectric loss in the range of 100–105 Hz and the variation of dielectric loss was small with 3wt% BiFeO3, 1wt% LDPE and dielectric loss were increased by adding 2wt% of BiFeO3. The dielectric loss of BiFeO3/LDPE nanocomposites was derived from the polarization loss which has a large number of polar groups of BiFeO3 nanoparticles generated. Similarly, conductivity and structure loss are derived from the microheterogeneity of nanocomposite [90]. The loss factor measurements with the function of temperature at high voltage laboratories resulted in a low dielectric loss by using low nanofiller concentrations. So the large volume fraction of interfaces and polymer chain entanglements decrease the motion of charge carriers reducing the dielectric losses [91]. The PVDF/copper nanowires composites are prepared by precipitation techniques well exhibit the low dielectric loss property. The result concluded that increase in ohmic and polarization losses arises from the conductive network formation and developed the interfacial polarization [92]. The barium titanate (BaTiO3)/epoxy nanocomposites are proved the good dielectric properties. This method proved the broadband response of capacitor in structure directly co-related to the dielectric properties and has the low dielectric loss. By increasing BT contents the dielectric loss does not change remarkably. In this case slow mobility of epoxy chain plays an important role on this stable dielectric loss [93]. Polyaniline and calcium copper titanate nanocrystal composites are frequency dependent characteristics of dielectric loss are studied for PANI and composites. Dielectric loss shows two times lesser than the value obtained for pure PANI at 100 Hz. This loss would help to design and fabrication of PANI based materials for the potential applications such as light emitting diodes, information storage, frequency converters, modulators, dielectric amplifiers, sensors, anti-corrosion coatings, light weight battery electrodes and electromagnetic shielding devices. The composites also very useful in tailoring super capacitors as devices [94]. The factors affecting the nanodielectric are shown in the Figure 4. The process of dielectric loss I-V plot was shown in Figure 5. We discussed the input signal as in the form of sine wave, square wave and triangular wave in ac bias. Basic polarisation process under


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Figure 4. Factors affecting the nanodielectrics.

Figure 5. Process of dielectric loss I-V plot.

external electrical field was shown in Figure 6. The varying external signal response may be good control over the desired dielectric properties.

Issues of dielectric polarization in view of nanodielectric Dielectric polarization is the separation of charge centres (the nucleus being the positive charge centre and electron cloud being the negative charge centre) within the atoms of a material by applying the electric field across the material. When the DC field was applied across the dielectric it pushes the electron cloud opposite to the field direction separating out the coincident charge centres called an induced dipole. The separation of the charge


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Figure 6. Basic polarization process under external electric field.

continues up to the point where the force due to the field was balanced out by attractive Coulomb force between the electron cloud and the nucleus. This induced dipole gives rise to a surface charge density on dielectric and volume charge density within the bulk of the dielectric. The process was known as dielectric polarization. The effective permittivity and polarization properties of polyethylene nanodielectric reported that permittivity reduction was closely related to the molecular chain movements, physical and chemical interactions and polarization effects in interfacial region. It stimulates the effective permittivity and polarization properties of (LDPE)/aluminium oxide nanoparticles (Al2O3) nanodielectrics based on interphase power law model (IPL). It indicates that the IPL model was well fitted into experimental results of reduced permittivity in LDPE/Al2O3 at low loadings [95]. Dielectric polarization and conductivity of new metal-containing polymer thin film structure suggested that measurements of the dielectric properties exhibited by the metal containing polymer structures based on copper (II) complexes in the frequency range of 102–106 Hz are reported [96]. The charging behaviour of electrode/LDPE and fluorinated ethylene propylene (FEP)/electrode and LDPE/FEP interfaces are done by using pulsed electroacostic technique. The time dependence of space charge distribution was recorded at room temperature under polarization and depolarization. In the experimental results demonstrated that the space charge accumulations at the dielectric interfaces are studied at test specimens. The magnitude and dynamics of the charge are not well described by the Maxwell–Wagner theory for the interfacial polarization. It means that electrode materials have the largest influence on the polarization at the interface [97]. Dielectric polarizations of C60 in electric fields are high because of hydrogen atoms directly attached to the carbon nanoparticles [98]. Dielectric polarization has the temperature and the effects of the capacitive across radio frequency played a role of micro-electromechanical switches. Generally,


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Figure 7. Issues of dielectric polarization.

dielectric charging formed by charge injection under the voltage stress was observed. These results are confirmed that dielectric charging was complicated the process known as a stretched exponential relaxation. This whole mechanism was done by activation energy which was calculated from the temperature dependence of capacitance transient response [99]. The dielectric polymerization and molecular association of hydrogen fluoride were measured as a function of pressure at various temperatures. At ambient temperature and pressure region, there was no molecular association occurs a dipole moment value has been obtained [100]. The issues of dielectric polarization in view of nanodielectric shown in Figure 7.

Experimental evidence of nanodielectric properties Energy storage capacitance of future demand would be fulfilled by the giant dielectrics property possess the high permittivity. Hence it is a challenge to the material community to deliver nanodielectric composites. The variety of engineering treatments on the nanoparticles has applications of nanodielectric. These particles embedded to obtain the giant dielectric permittivity [101]. Reports on giant dielectric constant as a function of the metal precursor, piezo-ceramic and graphite sheets are reported and it was demonstrated the improved nanodielectric properties. In Figure 8 shows the variation of dielectric constant of polycarbonate and polystyrene blend of 5, 10, 15% of aluminium oxide (Al2O3) under external DC bias potential. Inset is the variation of dielectric loss with respect to the loading of aluminium oxide (Al2O3) [102]. It shows the higher dielectric constant and DC-bias conduction mechanism was evaluated. Figure 9 shows the overall performance of polycarbonate composite as the function of calcium copper titanate (CaCu3T14O12) loading exhibit the higher permittivity [103]. Figure 10 shows the variation of dielectric constant and dielectric loss of polyvinyl alcohol (PVA)/copper bismuth sulphide (CuBi2S3) composites exhibit the role of filler on dielectric constant [104]. It shows the low dielectric constant and high dielectric loss and has a tremendous growth in electrical and electronics domain as capacitor and sensor applications. Figure 11 shows the discrete plot of dielectric constant and dielectric loss of isophthalic polyester (IP) resin/styrene composed of strontium titanate nanoparticles (STONP)


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Figure 8. Variation of dielectric constant of polycarbonate/polystyrene blend of 5, 10, 15% of aluminium oxide (Al2O3) as a dopant with respect to DC bias in volts. Inset is variation of dielectric loss with respect to loading of aluminium oxide (Al2O3).

Figure 9. Variation of dielectric constant and dielectric loss of polycarbonate/calcium copper titanate (CaCu3T14O12) with respect to loading of CaCu3T14O12.

[105]. It concluded that dielectric constant was proportional to STONP loading. Figure 12 shows the variation of dielectric constant and dielectric loss of virgin graphite flakes as a function of temperature [106]. It shows the high dielectric constant and dielectric loss used



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Figure 10. Variation of dielectric constant and dielectric loss of polyvinyl alcohol (PVA)/copper bismuth sulphide (CuBi2S3) composites with respect to loading of CuBi2S3.

Figure 11. Variation of dielectric constant and dielectric loss of Isophthalic polyester (IP) resin/styrene/ strontium titanate nanoparticles (STONP) with respect to loading of STONP.

in industrial areas and automobile industries. Figure 13 shows the discrete plots of dielectric constant and dielectric loss of polyvinylidene fluoride (PVDF)/trifluoroethylene (TrFE) as a loading of calcium copper titanate (CCTO) [107]. The dense structure of the composites and the uniform distribution of CCTO particles in the matrix region played the key role in the dielectric enhancement. It is feasible for the fuel cells and supercapacitors applications.


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Figure 12. Variation of dielectric constant and dielectric loss of virgin graphite flakes as a function of temperature.

Figure 13. Variation of dielectric constant and dielectric loss of polyvinylidene fluoride (PVDF)/ trifluoroethylene (TrFE) as a loading of calcium copper titanate (CCTO).

The recent trend shows the composition of nano entity enables to obtain the nanostructures in the form of nanocomposites follows the criteria of percolation threshold. It was co-related to the conductivity or dielectric percolation may be due to carbon allotropes such as CNT, graphene [108].


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The basic mechanism observed in the modification of the structure of virgin polymer system as a function of nano filler loading. It was observed that the phase changes occurs from amorphous to the crystalline induced thickness of interfacial grain boundary layers which demonstrated the nature of phase change from amorphous to crystalline for the virgin polymer systems. It was tested to obtain the desired integrated performance of polymer composite under external stimuli.

Applications and future prospects of nanodielectric science


High voltage dielectric Optimized efficiency with minimum thickness with improved dielectric constant was suitable for the high voltage applications. In order to minimize electric stress with an adequate reliability under high potential operation was the speciality of nanodielectric materials [109]. High voltage in alternating and direct current brings new challenges in terms of dielectric materials. It needs a growth to develop materials with controlled electrical resistivity, space charge accumulation, high thermal conductivity, high dielectric strength and longer endurance lifetime. The unique properties effective for the power systems withstand power densities, more reliable and have a longer lifetime and durable [110]. Dielectric capacitor Nanodielectric has high breakdown field strength with high dielectric constant. It will develop the performance of storage density of capacitor and miniaturize the capacitor. The excellent anti-ageing properties can ensure the stable performance of the capacitor. Increasing the dielectric break down strength and reliable films are one of the challenges and goals in modern day dielectrics research in dielectric applications [111]. Capacitors are known as energy storage components in electrical and electronic engineering applications. Capacitors having different types such as ceramic film, aluminium electrolytic, laminated ceramic, tantium electrolytic and supercapacitors. Electrolytic and supercapacitors are the largest capacities. They are manufactured worldwide and some of the largest producers are panasonic, vishay, kemet and murata [112]. Some energy storage capacitors have great demand in military applications include vehicles, airplanes and ships. In order to improve the energy storage capability of the capacitor should increase the energy density of the dielectric materials [113]. Capacitors are important components in power conditioning applications. The main purpose of a capacitor was to mediate current fluctuations in the electrical circuit to provide a load with the constant flow of current. These capacitors are widely used in electrical power conditioning systems. In power, conditioning was concluded that capacitors have stable dielectric properties across the temperature range and wide range of frequencies [114]. Capacitors are considered to be important elements used for DC-link filters, AC filters and energy storages in power electronic systems. Some capacitors such as aluminium electrolytic and metallized polypropylene film are widely used in DC-link applications due to the wide range of capacitances and voltages. The advantages of capacitors are energy density, reliability, capacitance stability and voltage capability [115]. The advantages of the dielectric capacitor are shown in Figure 14.

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Figure 14. Advantages of dielectric capacitor.

High voltage direct current (HVDC) cable The excellent space charge properties of nanodielectric can moderate the internal electric field. The operating voltage level and reliability of high voltage direct current (HVDC) cable will increase the breakdown performance and anti-electrical ageing properties of nanodielectric. An HVDC electric power transmission system uses direct current for the electrical power system. For long distance transmission lines, HVDC cables are used for less expensive and low electrical losses. When it comes in underwater power cables HVDC avoids the heavy currents and discharge the cable capacitance. It allows the power transmission between unsynchronized AC transmission systems. HVDC allows the transferring the power between grid systems at different frequencies such as 50–60 Hz. It improves the stability and economy of each grid by allowing the exchange of power between incompatible networks. HVDC cable generates both electric and magnetic fields. An electric field was created when sea water containing ions moves through the magnetic field [116]. To analysis of HVDC submarine cables done by using the harmonic analysis method. HVDC cables are buried at about 1.5 m under the seabed surface. There are three categories of HVDC cables are mass-impregnated (MI), self-contained fluid-filled (SCFF) and extruded. These masses saturated with a substance insulated with paper and soaked with high viscosity compound. These SCFF insulated with paper soaked with low viscosity oil. In extruded it insulated with a polyethylene based compound. MI cables are widely used for many years was highly reliable. SCFF cables are used for the high voltages. Extruded cables for HVDC applications are still under development. Nowadays they are used for relatively low voltage levels up to 2000 kV DC was mainly associated with voltage source converters [117]. The performance of HVDC was shown in Figure 15. Dielectric in power supply The application of nanodielectric materials will reduce the size and increase the reliability of generator and reduce the cost. In addition, a generator will be extended for the corona-resistant property of nanodielectric. We demonstrated the application of dielectric in power supply in Figure 16.


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Figure 15. Performance of high voltage direct current cable.

Figure 16. Application of dielectric in power supply.

Dielectric paint Dielectric paints have a wide range of spectrum coated with thermal reflection was applied to a specific type of microspheres to block the heat radiation in a much larger or broader range of thermal energy to disappear heat rapidly. This coating has a thermally reflective material reduces the heat transfer through the coating with 90% of solar infrared radiations and 85% of ultraviolet radiations from the coated surface. Dielectric paint works bi-directionally. For example, the external wall of building dielectric paint has been applied. A direct sunlight was reflected from the surface as well as heat is migrating through the wall outward towards the colder outside air. The infrared photograph will clearly show the reduction of wintertime heat loss from a home through the areas that have been painted with a dielectric paint. Dielectric paints will improve the temperature distribution within a room without any energy inputs and ceramic paint was applied to the interior surface of a room [118]. This dielectric paint was characterized by the emission of far-infrared radiation and its physiological impact on the human body. This dielectric paint was compared to the conventional material through the test application similar to spaces in an actual building [119]. Nanodielectric preferred as the best dielectric coating paint due to waterproof, fire resistance and flashover properties. The advantage of dielectric paint is illustrated in Figure 17.

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Figure 17. Advantages of dielectric paint.

Dielectric materials for the rotating machine systems When electric motors and generators were invented, commercially known as the rotating machine system. Rotating machine helps to run the smaller machines. This can be accomplished when the machine was capable of withstanding higher electrical and thermal stress and has a better thermal conductivity. The advantages of rotating machine systems are good mechanical strength and environmental friendly [120]. The rotation machine system was one of the very first applications of nanodielectric and the driving thrust for improvements in motor systems and used in inverter-fed drives in fast-rise-time pulses. Some developed with great improvements in resistance to partial discharges. Some of them are random-wound wire enamel and form-wound strand wire enamel. Research in rotating machine has been carried out for a number of years with the materials like mica, epoxy resin and fibreglass [121]. In this, mica can split into the thin flat laminate. It has great advantages such as high dielectric strength, low dielectric losses, resistance to high temperatures and good mechanical properties [122]. The high voltage rotating machines was subjected to a combination of different stresses such as thermal, electrical and mechanical. The electrical stress was related to the electrode geometry. The thermal stress was determined by the losses within the conductors. It often plays the dominant role in the aging process of materials and has an influence on the interface between metallic and insulating parts. The mechanical stress was done by a combination of thermal and mechanical stress due to expansion or contraction of the material depends upon the function of temperature. The mechanical stress contributes the aging performance of the materials and failure of the mechanical performance due to fatigue of the material leads to electrical failure [123]. The role of dielectric materials for the rotating machine systems was shown in Figure 18. Random-wound wire enamel A typical low voltage generator was built with multi-turn stator coils, ranging from 1 to 16 turns per coil. These coils can either form wound or random wound. Consider the units less than 1500 kW the size of the stator and the minimum wire thickness does not allow the form-wound coils. In some cases, form-wound or random wound coils can be used. Random-wound coils generators can be made at a reduced cost and their capability



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Figure 18. Role of dielectric materials for the rotating machine system.

to withstand severe environmental conditions can be improved through the use of vacuum-pressure impregnation. Consider the low voltage motors are random-wound with round wire and coated with polyamide-imide provides the suitable abrasion resistance for winding at high operating temperatures. Multiple layers are applied to four passes with dipping and drying of each layer to obtain the total thickness of about 50 μm. For improved resistance to partial discharge, the center layers contain the various nanosize oxide fillers such as tin oxide was considered to be most common filler. Normally there was a trade-off between resistance to partial discharge increases with filler loading and manufacturing with increased filler loading reduces with wire flexibility leads to cracks in the enamel. In low filler loading, the resistance to partial discharges was greatly improved [124–126]. The random wound wire enamel was shown in Figure 19. Wound coils are preferred for electrical appliances basically need good dielectric enamels to maintain the power performance.

Figure 19. Random wound wire enamel.

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Form-wound strand wire enamel The coils for medium to high voltage motors are wounded by rectangular-shaped magnet wire called strands. During the enameling process of magnet wire, it was done to expand the required thickness to meet the electrical, thermal and abrasion resistance. The magnetic wire passes through the coating had a number of times depending on the wire type and its application. This layer-by-layer coating was oven-cured and resulted in multiple polymers to polymer interfaces. Under pulse-width modulation waveforms from resistance to partial discharge the outer layer contain nano-sized oxide fillers resulted in complex multi-layer enamel. The application of form wound strand wire enamel was shown in Figure 20.

Future applications


Increased stress applications All practical applications of solid dielectrics are concerned with electrical treeing that originates from defects within extrusions, mouldings and castings. For example, it was used in gas-insulated equipment and moulded bushings. It was the reason that average stress was kept at relatively low level. However nano-sized fillers will improve the resistance of the materials to electrical treeing by acting as barriers delayed the growth of trees [127]. This property improvement leads the way of higher stress and reduction in thickness. This made be possible to epoxy polymer resin and cross-linked polyethylene cable. For that above reason, an ultra-clean cable was used. Charge injection, trapping, space charge accumulation and HVDC played an important role in dielectric strength [128]. Nano-sized fillers tend to increase the electrical conductivity and reducing the tendency of materials to trap the charge [129]. High temperature applications Dielectric materials have low thermal conductivity and for the application requirements need high thermal conductivity to remove heat. In industry epoxy composites containing

Figure 20. Application of wound coil wire enamel.



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Figure 21. Application of high temperature in dielectric.

~50 wt% of micron-sized silica are currently used as packaging material for power electronic devices like an Insulated-gate bipolar transistor and silica has high electrical resistivity and low dielectric constant. The low thermal conductivity was a limitation of having high thermal conductivity packaging whatever the limited it’s in the application in dielectric materials. Nano-sized fillers improved the thermal conductivity of nanodielectric at low volume fractions [130]. Most studies are limited to knowing the thermal conductivity of nanodielectric. But thermal expansion and breakdown strength are other important properties are critical to microelectronic packaging. High thermal conductivity can be achieved by forming a thermally conductive pathway in the matrix whereas the thermal conductivity of the nanodielectric depends on the types of filler, a number of pathways formed and thermal resistance of the contact points. Some of them used to form conductive paths such as whiskers and filaments. However, it was often very difficult to the processing of nanodielectric with filler level above the percolation threshold. In future, high thermal conductivity nanodielectric applications in power electronic devices and rotating machine systems would be evolved around the mixtures such as micro and nano sized fillers. Mixtures can improve the packing fraction of fillers and achieved the low percolation threshold as the conductivity pathway increases resulted in high thermal conductivity at a lower cost of processing [131]. The application of a high temperature in dielectric was shown in Figure 21. Electric stress control applications In this trend to control the electric stress in medium voltage, cable accessories and rotating machine systems was largely accomplished with silicon carbide nonlinear resistive

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compositions. Silicon carbide has a modest nonlinear coefficient, but in future, it will be done by using zinc oxide filler has the greater nonlinear coefficient having the properties of reducing the physical size of the grading device, high voltage applications and grading of high voltage (HV) bushings consider to be a new application [132]. Silicon carbide and zinc oxide are based on percolated materials and zinc oxide was nano size in nature. In order to increase the thermal conductivity of nanodielectric and electric stress applications combine with nano size particles and micron-sized zinc oxide fillers to improve the packing fraction reduces the percolation threshold with increased pathways resulting in improved processability [133].


Nanostructure dielectric surface applications Nanostructure dielectric surface suitable for the industrial applications and outdoor insulation having the great advantage of easy to clean surface. Such surface shows a high static contact angle and creating a non-wetting surface. Water droplets away from the surface and sweeping contaminants along their path and improving the performance of outdoor insulators in polluted and wet environments. A nanostructure surface was created by nano size silica in the surface layer of the materials. Natural weathering gradually destroys the nanostructure and made performance was very low. In silicones, the lower molecular weight species are migrated to the surface and gives the hydrophobicity to silicones destroyed the nanostructure within the short time. The dielectric application based on performance was shown in Figure 22.

Figure 22. Dielectric applications based on performance.


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Future development of nanodielectric domain In this review article, we introduced some of the important better features of nanocomposite research related to application and development of engineering applications. Nanocomposite appears to offer a variety of advantages over their micron-filled counterparts. However, there are many unanswered questions to overcome. Certain aspects of dielectric properties such as electrical erosion and dielectric spectroscopic characteristics are well understood. But still to have a little understanding of the physics the charge dynamics and electrical breakdown behaviour of these systems should be well disclosed. One can visualize that understanding of the aging mechanisms and behaviour of nanocomposites are critical importance to use in practical high voltage plant. Finally, we understood little about the long-term toxicity of nanocomposites. It should not assume that the nanoparticles are harmless to health as their macroscopic counterparts. Firstly, largely increased surface area has greater chemical activity and may be catalysts for the production of damaging radicals [134]. Secondly, if they enter the body they can penetrate deeper into biological systems accumulating in individual cells. Soto studied the toxicity of a range of nanoparticles, including TiO2, Fe2O3, Al2O3, ZrO2 and crysotile asbestos commented on ‘it would seem unrealistic to repeat the failures of the asbestos industry largely ignored the product dangers for more than 2000 years’ [135]. In 1990s Toyota group reported their preparation of nylon-6/clay hybrids, academic and industrial interest. The domain of nanocomposites has grown exponentially using this term in the literal mathematical sense. Many novel materials are developed having a great interest to the electrical insulation engineer brings great advantage in increased mechanical strength, reduced mechanical and electrical erosion, and improved electrical breakdown/ endurance behavior and space charge mitigation. However, the field was still in infancy. For example, the review of Tanaka describes the reports of contradictory effects needs to be understood nanodielectric, potentially appears great and we would suggest that it was important to temper our enthusiasm by remembering there was still much to understand in this fascinating class of materials [136,137].

Conclusions We have consolidated the overall issues of nanodielectric properties. In the present trend of nanodielectric, research demonstrates the scientific excellence was made a great progress in domestic and industrial applications. In order to execute in the industry, the production cost and processing may be a drawback. In interfacial concept has grown rapidly to the practical applications. Interfacial issue related to the materials and electrical field are discussed in connection with nanodielectric. The correlated terms of nanodielectric process enable to know the better nanodielectric engineering, electrical properties and electrical hysteresis characteristics are feasible to improve the performance, properties and development of relevant applications. Dielectrics have been regarded as the mature science, but there are real opportunities to provide substantial performance improvement and cost effective. Many applications are not limited by electrical properties but explained by mechanical and thermal damping too. It was put forward the new and improved nanodielectric properties with great capabilities and electro-technical potential would be found among the nanostructure ceramics and leads to wide applications. The new class of materials and the nanodielectric properties will be the fact of an emerging technology and devices.

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Disclosure statement No potential conflict of interest was reported by the authors.

ORCID Girish M. Joshi

http://orcid.org/0000-0002-0959-0268


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