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The uprising demands for electrical power and electrification requires advanced dielectric functionalities including high capacitance density, high energy density, high current handling capability, high voltage, high temperature, high thermal conductivity, light weight, and environmental reliability. Nanodielectric engineering emerges and attracts extensive efforts from many countries as a result. Unlike prior reviews focusing on lab scale nanocomposite study, this review focuses on recent innovations in polymerbased nanodielectric design on a large scale and their film scale-up efforts for advanced capacitors. The unconventional polymer-nanofiller engineering and their process in the last two decades are discussed. The nanofunctionalized polymers on a molecular level for high dielectric constants and high dielectric strength are briefly described. The challenge associated with film scale-up and retention of nanodielectric properties are then pointed out to be crucial toward a transfer of dielectric and capacitor technology. Several important attempts at scaling up dielectric films and capacitors recently supported by the US government and industry are reviewed. An alternative strategic approach to achieving high performance polymer films is introduced by leveraging 2D surface coating on commercially mature large-scale polymer films. Future pathways for high quality scalable dielectric films exhibiting desirable dielectric properties and feasibility for capacitor manufacturing are suggested.to develop a more compact pulse-forming network for a pulsed high power microwave (HPM), a laser source, aircraft ignition systems, and high-power electrical systems. [1] The US NAVY strove to develop an all-electric warship for advancing its future combat capability (lethality and survivability). This warship required high-power weapons such as electromagnetic railguns for obtaining pin-point accuracy at a very long range electromagnetic launch systems for rapid aircraft and missile deployment and higher-power radar and sonar systems for "seeing" farther through both air and water. The US Army funded the development of the high-energy-density biaxially oriented polypropylene (BOPP) capacitor and the high-temperature polyetherimide dielectric for ground vehicles to realize better serviceability, higher power, and lower mass of the equipment that ground troops carry. [2,3] Although the energy density has been improved up to 3 J cm −3 via metallization control, the performance, and lifetime of BOPP capacitors degrade rapidly with increasing temperature (the ripple current handing capability decreases as the temperature increases from 85 to 105 °C).Improvements in the fault resistance and the reliability of dielectric materials will enable capacitors to withstand higher electrical current and heat without being excessively derated under extreme stress conditions. A large gap remains between the technology availability and the desired properties, such as combined high temperature and energy density and a low dissipation factor. Fa...

Abstract

Abstract-The objective of the present study was to investigate changes in the structural, textural, and surface properties of tubular halloysite under heating, which are significant in the applications of halloysite as functional materials but have received scant attention in comparison with kaolinite. Samples of a purified halloysite were heated at various temperatures up to 1400ºC, and then characterized by X-ray diffraction, electron microscopy, Fourier-transform infrared spectroscopy, thermal analysis, and nitrogen adsorption. The thermal decomposition of halloysite involved three major steps. During dehydroxylation at 500À900ºC, the silica and alumina originally in the tetrahedral and octahedral sheets, respectively, were increasingly separated, resulting in a loss of long-range order. Nanosized (5À40 nm) g-Al 2 O 3 was formed in the second step at 1000À1100ºC. The third step was the formation of a mullite-like phase from 1200 to 1400ºC and cristobalite at 1400ºC. The rough tubular morphology and the mesoporosity of halloysite remained largely intact as long as the heating temperature was <900ºC. Calcination at 1000ºC led to distortion of the tubular nanoparticles. Calcination at higher temperatures caused further distortion and then destruction of the tubular structure. The formation of hydroxyl groups on the outer surfaces of the tubes during the disconnection and disordering of the original tetrahedral and octahedral sheets was revealed for the first time. These hydroxyl groups were active for grafting modification by an organosilane (g-aminopropyltriethoxysilane), pointing to some very promising potential uses of halloysite for ceramic materials or as fillers for novel clay-polymer nanocomposites.

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