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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. [ABSTRACT FROM AUTHOR]

Barium titanate (BT) and montmorillonite (MMT) 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. [ABSTRACT FROM AUTHOR]

Polymer nanocomposites prepared by epoxy reinforced with high permittivity barium titanate (BT) fillers or high aspect ratio montmorillonite (MMT) 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 (oMMT) or BT (BaTiO3) 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 energies) 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. [ABSTRACT FROM AUTHOR]

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 BaTiO3 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 (0–3) 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. [ABSTRACT FROM AUTHOR]

Molecular Dynamics simulations are used to explore the effect of severe -1 nanometerconfinement on the short-time dynamics of poly(ethylene oxide) (PEO). Bulk and intercalated systems have been atomistically modeled to comparatively illustrate their differences. In particular, we aim to trace the molecular level mechanisms responsible for the counter intuitive distribution of relaxation times recorded by solid state ²H NMR for the C-H bond reorientations in confinements. Computer simulations complement the experiments and reveal that factors such as local density inhomogeneities, proximity of Li[sup +], and disorder in the system, combine to determine the PEO segmental dynamics. In contrast with the respective bulk PEO systems, where a clear transition from distinct solid to liquid like dynamics takes place with increasing temperatures, for the nanoscopically confined chains there persists a coexistence of fast and slow segmental relaxations over the same temperature range. [ABSTRACT FROM AUTHOR]

Bitsanis et al. J. Chem. Phys. 99, 5520 (1993) found that in nanoscopically confined films between strongly physisorbing surfaces chains with many contacts with the walls are irreversibly adsorbed. When shear is imposed to these systems molecular dynamics (MD) simulations show that the majority of the adsorbed oligomers adopts flat conformations on top of the walls. Although these conformations are characterized by high molecular adsorption energies, the same MD simulations show that desorption is strongly promoted by shear. The underlying mechanism is discussed. [ABSTRACT FROM AUTHOR]

Examines the static and dynamic properties of organically modified layered silicates through molecular dynamics simulations. Description of simulation model used; Relationships between simulated and experimental d-spacing; Analysis of silicate segment density profiles and configurations.

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. [ABSTRACT FROM AUTHOR]

Fluids in nanoscopic confinements possess a variety of unusual properties, and in particular, remarkable dynamical heterogeneities which vary on length scales as short as a fraction of a nanometer. While the surface forces apparatus provides an experimental probe of macroscopic properties of fluids in contact with atomically smooth solid surfaces, few experimental probes are available which test the microscopic origins of these heterogeneities. In this article we describe our recent efforts to apply nuclear magnetic resonance spectroscopy to nanoscopically confined poly(styrene) (PS) created by intercalation into a surface-modified fluorohectorite. A comparison between surface-sensitive cross polarization experiments with spin-echo experiments which probe the entire organic layer suggests that PS in the center of the nanopores is more mobile than the bulk at comparable temperatures, while chain segments which interact with the surface are dynamically inhibited. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present a microstereolithographic technique that enables the manufacturing of polymeric components for microelectromechanical systems. Model microstructures were fabricated in the form of end-supported microbeams (10 μm in diameter), in order to characterize the mechanical properties of the produced structures at the micron scale. The flexural modulus of these microbeams was measured by atomic force microscopy, using cantilevers with attached metal spheres, and employed in a three-point bending geometry. Postfabrication treatment of the microstructures allows for the tailoring of their stiffness. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]