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In this study, hybrid boron nitride (BN)/titanium carbide (TiC)/epoxy resin composite nanodielectrics were manufactured and characterized. Their morphological and structural characterization was conducted via scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns, whereas the dielectric behavior was studied by means of broadband dielectric spectroscopy (BDS). Dielectric measurements were carried out from 30 to 160 °C and from 10−1 to 106 Hz, respectively. The dielectric results revealed the existence of three relaxation mechanisms, which from high to low frequencies, at constant temperature, refer to re-arrangement of polar-side groups (β-relaxation) of the macromolecular chains, transition from glassy to rubbery state of the amorphous polymer matrix (α-relaxation) and interfacial polarization (IP) between the polymer matrix and the nanofillers. It was found that, in general, nanodielectrics exhibited enhanced dielectric properties mainly due to the high dielectric permittivity of TiC and the fine dispersion of the fillers, confirmed also by the SEM images. Dynamic analysis conducted for the α-relaxation showed a Vogel–Fulcher–Tammann dependence on temperature. The ability of energy storing of the nanocomposites was examined via their energy density. Optimum performance is exhibited by the 5 phr TiC/1 phr BN/epoxy nanocomposite, reaching an energy storing ability nine times greater than the unfilled matrix.

The presented thesis aims at developing of new types of insulation dielectric materials based on polymer nanocomposites for high-voltage DC cables. The DC grid network is rapidly developing across Europe and China, and this necessitates the design of new insulation polymer nanocomposites withstanding specific DC properties that vary significantly from common AC. Driven by the environmental pressure, green approach encourages us to find innovative solutions for the scientific and practical challenges in polymeric nanocomposites development. In this research work, polypropylene/elastomer blend is used as an insulation matrix due to its recyclability in opposition to commonly used cross-linked polyethylene. In addition, the plasma and solvent-free methods were successfully applied to modify the nanosilica filler surface, eliminating the environmental impact of waste solvent commonly used in suspension type of modifications. Nanodielectric polymer composites draw a lot of attention from both, industry and academia. It is reported that the polymer blend selection and the interface between a nanofiller surface and polymer matrix play an important role in improving the dielectric performance. This study focuses on the influence of the nanosilica surface functionalization on the micromorphology, dynamic and dielectric properties of the polypropylene based dielectric nanocomposites.

From a novel empirical power law between the DC breakdown field and DC conductivity, an analysis of the trapping characteristics in polyimide/boron nitride (PI/BN) nanocomposites is presented based on space-charge-limited current (SCLC) measurements. The impact of the total trap density H t enhancement (increasing up to 1.1×1017 cm−3) induced by the BN nanoparticles on the space charge attenuation, the DC conductivity reduction and the DC breakdown field increase is clearly reported. This work proves that an efficient control of the trapping parameters allows huge enhancement of the insulating properties of PI nanocomposites. High temperature thermal breakdown can be delayed by free carrier reduction through deep trap formation caused by nanofiller addition.

The purpose of this present study is to prepare a stable mineral-oil (MO)-based nanofluid (NF) for usage as a coolant in a transformer. Nanoparticles (NPs) such as hexagonal boron nitride (h-BN) and titanium oxide (TiO2) have superior thermal and electrical characteristics. Their dispersion into MO is likely to elevate the electrothermal properties of NFs. Therefore, different batches of NFs are prepared by uniformly dispersing the insulating h-BN and semiconducting TiO2 NP of different concentrations in MO. Bulk h-BN NP of size 1μm is exfoliated into 2D nanosheets of size 150–200 nm, subsequently enhancing the surface area of exfoliated h-BN (Eh-BN). However, from the zeta-potential analysis, NP concentration of 0.01 and 0.1 wt.% are chosen for further study. The thermal conductivity and ACBDV studies of the prepared NF are performed to investigate the cooling and insulation characteristics. The charging-dynamics study verifies the enhancement in ACBDV of the Eh-BN NF. Weibull statistical analysis is carried out to obtain the maximum probability of ACBDV failure, and it is observed that 0.01 wt.% based NF has superior cooling and insulation properties than MO and remaining batches of NFs.

Compact capacitive energy storing/harvesting systems could play a key role in the urgent need for more energy-efficient technologies to address both energy and environmental issues. Therein, the purpose of the present work is to develop and investigate epoxy/BaMnO4 nanocomposites at various filler concentrations, which could be applicable as compact materials systems for energy storage and harvesting. Broadband dielectric spectroscopy was used for studying the dielectric properties and the relaxation processes of the examined nanodielectrics. The energy storing/retrieving ability of the nanocomposites was also evaluated via DC charge–discharge experiments. The coefficient of energy efficiency (neff) was found for all prepared nanocomposites to evaluate the energy performance of the systems. Dielectric data divulge the existence of two matrix-related relaxations, i.e., α-mode and β-mode, attributed to the glass-to-rubber transition of the polymer matrix and re-orientation of polar side groups, respectively. Interfacial polarization was also identified in the low-frequency and high-temperature region. The 7 phr BaMnO4 nanocomposite exhibits the best performance in terms of the stored and harvested energies compared to all systems. On the other hand, the 5 phr, 3 phr and 1 phr nanocomposites display optimum energy performance, reaching high values of neff.

Trimethylolpropane triacrylate (TMPTA) as a photoactive crosslinker is grafted onto hydrophobic nanosilica surface through click chemical reactions of mercapto double bonds to prepare the functionalized nanoparticles (TMPTA-s-SiO2), which are used to develop TMPTA-s-SiO2/XLPE nanocomposites with improvements in mechanical strength and electrical resistance. The expedited aging experiments of water-tree growth are performed with a water-knife electrode and analyzed in consistence with the mechanical performances evaluated by means of dynamic thermo-mechanical analysis (DMA) and tensile stress–strain characteristics. Due to the dense cross-linking network of polyethylene molecular chains formed on the TMPTA-modified surfaces of SiO2 nanofillers, TMPTA-s-SiO2 nanofillers are chemically introduced into XLPE matrix to acquire higher crosslinking degree and connection strength in the amorphous regions between polyethylene lamellae, accounting for the higher water-tree resistance and ameliorated mechanical performances, compared with pure XLPE and neat-SiO2/XLPE nanocomposite. Hydrophilic TMPTA molecules grafted on the nano-SiO2 surface can inhibit the condensation of water molecules into water micro-beads at insulation defects, thus attenuating the damage of water micro-beads to polyethylene configurations under alternating electric fields and thus restricting water-tree growth in amorphous regions. The intensified interfaces between TMPTA-s-SiO2 nanofillers and XLPE matrix limit the segment motions of polyethylene molecular chains and resist the diffusion of water molecules in XLPE amorphous regions, which further contributes to the excellent water-tree resistance of TMPTA-s-SiO2/XLPE nanocomposites.

The development of high-performance multifunctional polymer-based electronic circuits is a major step toward future flexible electronics. Here, we demonstrate a tunable approach to fabricate such devices based on rationally designed dielectric super-lattice structures with photochromic azobenzene molecules. These nanodielectrics possessing ionic, molecular, and atomic polarization are utilized in polymer thin-film transistors (TFTs) to realize high-performance electronics with a p-type field-effect mobility (μFET) exceeding 2 cm2 V-1 s-1. A crossover in the transport mechanism from electrostatic dipolar disorder to ionic-induced disorder is observed in the transistor characteristics over a range of temperatures. The facile supramolecular design allows the possibility to optically control the extent of molecular and ionic polarization in the ultrathin nanodielectric. Thus, we demonstrate a 3-fold increase in the capacitance from 0.1 to 0.34 μF/cm2, which results in a 200% increase in TFT channel current.

International audience; Interphases are commonly believed to be responsible for the physical properties of nanodielectrics unexplainable by general mixture laws. For instance, the prediction of the dielectric permittivity of these materials supposes to include the intrinsic permittivity and the volume of the interphase. Despite the need for a local characterization of these nanometric regions, no sufficiently reliable proof of its existence has been reported yet. Electrostatic Force Microscopy (EFM) constitutes a promising technique to accomplish this objective. However, the study of interphases with EFM has never been completely and accurately established yet, and the interpretation of EFM signals can be misleading. The aim of this work is to set up a first accurate method and signal analysis to examine interphases in nanodielectrics. Model samples of sufficiently known and mastered properties have been designed and synthesized to "calibrate" the technique for future interphase study. EFM proved good sensitivity to thin alumina interphase model layers between polystyrene spheres and polyvinyl acetate matrix. Consistent permittivity values have been also deduced after confrontation to numerical simulations.

The performance of polymeric insulation will be distorted by the accumulation of space charge. This will lead to local electric field enhancement within the insulation material that can cause degradation and electrical breakdown. The introduction of nanofillers in the insulation material is expected to reduce the space charge effect. However, there is a need to analyze potential nanofillers to determine the best option. Therefore, the objective of this research work is to examine two types of nanofillers for Cross-Linked Polyethylene (XLPE); Zinc Oxide (ZnO) and Acrylic (PA40). The effects of these nanofillers were measured using the Pulsed-Electro Acoustic (PEA) method. The development of space charge is observed at three different DC voltage levels in room temperature. The results show that hetero charge distribution is dominant in pure XLPE materials. The use of both nanofiller types have significant effect in decreasing the space charge accumulation. With nanofillers, the charge profile changed to homo-charge distribution, suppressing the space charge formation. Comparison between both the nanofillers show that PA40 has better suppression performance than ZnO.

The complex permittivity characteristics of epoxy nanocomposite systems were examined and an attempt has been made to understand the underlying physics governing some of the unique macroscopic dielectric behaviors. The experimental investigations were performed using two different nanocomposite systems with low filler concentrations over the frequency range of 10(-2)-400 Hz, but for some cases, the data has been reported upto 10(6) Hz for a better understanding of the behaviors. Results demonstrate that nanocomposites do possess unique permittivity behaviors as compared to those already known for unfilled polymer and microcomposite systems. The nanocomposite real permittivity and tan delta values are found to be lower than that of unfilled epoxy. In addition, results show that interfacial polarization and charge carrier mobilities are suppressed in epoxy nanocomposite systems. The complex permittivity spectra coupled with the ac conductivity characteristics with respect to frequency was found to be sufficient to identify several of the nanocomposite characteristics like the reduction in permittivity values, reduction in the interfacial polarization mechanisms and the electrical conduction behaviors. Analysis of the results are also performed using electric modulus formalisms and it has been seen that the nanocomposite dielectric behaviors at low frequencies can also be explained clearly using this formalism.

An important prerequisite for the design of digital integrated circuits is the ability to control the threshold voltage of the individual transistors during manufacturing. To address the problem of controlling the threshold voltage of low-voltage organic transistors we have synthesized a fluoroalkylphosphonic acid that forms self-assembled monolayers on patterned, plasma-oxidized aluminum gate electrodes for use as high-capacitance, low-temperature gate dielectrics in p-channel and n-channel organic transistors. Compared with alkyl phosphonic acid-based monolayers, the strong electron-withdrawing character of the fluoroalkyl monolayers causes a change in the threshold voltage of the transistors by about 1 V, i.e. almost half of the supply voltage.