Poly(vinylidene fluoride) (PVDF) has generated interest for use in electrical energy storage, mostly due to its high dielectric constant compared to other polymers. There still exist challenges, such as its high energy losses, that have prevented large scale commercialization of PVDF-based capacitors, but progress is continuously being made. In this paper we explore a promising route to improve the energy storage performance of PVDF, through a synergy of HFP comonomers and of kaolinite clay nanofillers. This study shows that the addition of these high aspect ratio fillers to poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] copolymers does not increase the polar phase and, consequently, these composites exhibit markedly enhanced dielectric properties at high electric fields. Specifically, strained films of these composites exhibit reduced high field losses, markedly increased breakdown strength and, thus, large recoverable energy density values, in the range of 19 J/cm3.

Nanocomposite formation, through the incorporation of high aspect ratio nanoparticles, has been proven to enhance the dielectric properties of thermoplastic polymers, when the mitigation of internal charges and the nature of the interfacial regions are properly adjusted. Here, we explore polyethylene/montmorillonite nanocomposites, and we specifically investigate how to impart desirable dielectric behavior through controlled nanoscale texturing, i.e., through control of the spatial arrangement of the high aspect ratio nanofiller platelets. In particular, it is shown that filler alignment can be used to improve the high electric-field breakdown strength and the recoverable energy density. The origins of the improved high field performance were traced to improved charge-trapping by a synergy of nanofillers and polar maleic anhydride (MAH) groups—introduced via polyethylene-MAH copolymers—as templated by the inorganic nanofillers. Further, it is conclusively demonstrated that the alignment of the two-dimensional nanoparticles has a measurable positive effect on the breakdown strength of the materials and, consequently, on the maximum recoverable energy density.

Quantum dynamics of ultrafast charge transfer at an oligothiophene-fullerene heterojunction J. Chem. Phys. 137, 22A540 (2012) Electrostatic correlations in inhomogeneous charged fluids beyond loop expansion J. Chem. Phys. 137, 104902 (2012) Interfacial electronic properties of the heterojunctions C60/rubrene/Au and rubrene/C60/Au J. Appl. Phys. 112, 023711 (2012) Band offset measurements of the GaN/dielectric interfaces J. Appl. Phys. 112, 024508 (2012) Laterally confined two-dimensional electron gases in self-patterned LaAlO3/SrTiO3 interfaces Appl.Polymer nanocomposites prepared by epoxy reinforced with high permittivity barium titanate ͑BT͒ fillers or high aspect ratio montmorillonite ͑MMT͒ fillers exhibited marked changes in their high electric field properties and their relaxation dynamics, depending on the nanoparticle type and concentration, the nanoparticle size, and the epoxy matrix conversion. We investigated epoxy resin composites based on organically modified montmorillonite ͑oMMT͒ or BT ͑BaTiO 3 ͒ nanoparticles in order to delineate the effects of the high aspect ratio of the MMT and the high permittivity of the BT particles. We also explored the potential benefits of the synergy between the two fillers in systems consisting of epoxy and both oMMT and BT particles. It was observed that the nature of the organic-inorganic interfaces dominate the glass transition temperature and the dielectric properties of these composites. Specifically, using dielectric relaxation spectroscopy, we probed the local dynamics of the polymer at the interfaces. The MMT systems had approximately three orders of magnitude slower interfacial dynamics than those at the BT interfaces, indicating more robust interfaces in the MMT composites than in the BT-based composites; the corresponding energy barriers ͑activation energies͒ associated with these motions were also doubled for the MMT systems. Furthermore, we investigated the effect of the decreased glass transition, interfacial area, polymer-phase at the organic-inorganic interface, and of the dielectric breakdown on the electrical energy storage capabilities of these composites.

Polymer/ceramic composites with controlled spatial distribution of fillers are synthesized, and the corresponding changes in their properties are studied. Using dielectrophoretic assembly, we create anisotropic composites of aligned BaTiO 3 particles in silicone elastomer and study their electrical properties as a function of ceramic volume fraction and composite morphology. These structured composites show an increase in the permittivity compared to composites with the same composition and randomly dispersed ͑0-3͒ fillers. This study emphasizes the important role of conductivity, permittivity, and, particularly, local cluster distribution in controlling high-field dielectric behavior. Designed anisotropy in dielectric properties can provide unexampled paradigms for the development of high energy density materials and gain important insights into the mechanisms that control dielectric breakdown strengths and nonlinear conduction at high fields in polymer/ceramic composites.

Using dielectrophoretic assembly, we create anisotropic composites of BaTiO3 particles in a silicone elastomer thermoset polymer. We study a variety of electrical properties in these composites, i.e., permittivity, dielectric breakdown, and energy density as function of ceramic volume fraction and connectivity. The recoverable energy density of these electric-field-structured composites is found to be highly dependent on the anisotropy present in the system. Our results indicate that x-y-aligned composites exhibit higher breakdown strengths along with large recoverable energy densities when compared to 0-3 composites. This demonstrates that engineered anisotropy can be employed to control dielectric breakdown strengths and nonlinear conduction at high fields in heterogeneous systems. Consequently, manipulation of anisotropy in high-field dielectric properties can be exploited for the development of high energy density polymer-ceramic systems.

Barium titanate ͑BT͒ and montmorillonite ͑MMT͒ nanoparticles were covalently-bonded by organically modifying the particle surfaces and chemically reacting them in solution. These integrated two-material hybrid inorganic nanofillers were subsequently dispersed in epoxy resin and nanocomposites were obtained at several weight fractions. The inorganic component consisted of well dispersed BT spherical nanoparticles that are surrounded by attached layered MMT nanoplatelets, with the latter having the ability to react with the epoxy matrix. The thermodynamic properties of the glass transition process, the macroscopic mechanical properties of the nanocomposites, and the dynamics of the polymer segments at the inorganic interfaces, all indicate that this filler configuration enhances the polymer-ceramic interfaces. Polarization as a function of electric field and dielectric breakdown show improvements in the electrical properties of these composites, compared to the corresponding unfilled epoxy, despite the expected reduction in crosslinking density. The resulting nanocomposites have a property set which can be utilized in energy storage and power system applications.

Emerging technologies in the areas of electronics and energy storage require the design of next-generation dielectric-component materials with welldefined structure and properties with higher performance under voltage and temperature. Polymers filled with inorganic nanoparticles are potential CONTENTS

Emerging technologies in the areas of electronics and energy storage require the design of next-generation dielectric-component materials with welldefined structure and properties with higher performance under voltage and temperature. Polymers filled with inorganic nanoparticles are potential CONTENTS