Study of flexible nanodielectric materials (FNDMs) with high permittivity is one of the most active academic research areas in advanced functional materials. FNDMs with excellent dielectric properties are demonstrated to show great promise as energy-storage dielectric layers in high-performance capacitors. These materials, in common, consist of nanoscale particles dispersed into a flexible polymer matrix so that both the physical/chemical characteristics of the nanoparticles and the interaction between the nanoparticles and the polymers have crucial effects on the microstructures and final properties. This review first outlines the crucial issues in the nanodielectric field and then focuses on recent remarkable research developments in the fabrication of FNDMs with special constitutents, molecular structures, and microstructures. Possible reasons for several persistent issues are analyzed and the general strategies to realize FNDMs with excellent integral properties are summarized. The review further highlights some exciting examples of these FNDMs for power-energy-storage applications.

Flexible Nanodielectric Materials with High Permittivity for Power Energy Storage

A multi-core model, i.e. a simplified term of a multi-layered core model, is proposed as a working hypothesis to understand various properties and phenomena that polymer nanocomposites exhibit as dielectrics and electrical insulation. It gives fine structures to what are called "interaction zones". An interfacial layer of several tens nm is multi-layered, which consists of a bonded layer, a bound layer, and a loose layer. In addition, the Gouy-Chapman diffuse layer with the Debye shielding length of several tens to 100 nm is superimposed in the interfacial layer to cause a far-field effect. Nano-particles may interact electrically with the nearest neighbors each other due to this effect, resulting in possible collaborative effect. Such a multi-core model with the far-field effect is discussed, for example, to explain partial discharge (PD) resistance of polyamide layered silicate nanocomposites, and is verified to demonstrate its effectiveness.

Proposal of a multi-core model for polymer nanocomposite dielectrics

Perovskite lead-free dielectrics for energy storage applications

Polymer nanocomposites possess promising high performances as engineering materials, if they are prepared and fabricated properly. Some work has been recently done on such polymer nanocomposites as dielectrics and electrical insulation. This was reviewed in 2004 based on the literatures published up to 2003. New significant findings have been added since then. Furthermore, a multi-core model with the far-distance effect, which is closely related to an "interaction zones", has been proposed from consideration of mesoscopic analysis of electrical and chemical structures of an existing interface with finite thickness. It is speculatively examined in the paper how the model works for various properties and phenomena already found in nanocomposites as dielectrics focusing on electrical characteristics, resistance to high voltage environment, and thermal properties.

Dielectric nanocomposites with insulating properties

Polymer nanocomposites are defined as polymers in which small amounts of nanometer size fillers are homogeneously dispersed by only several weight percentages. Addition of just a few weight percent of the nanofillers has profound impact on the physical, chemical, mechanical and electrical properties of polymers. Such change is often favorable for engineering purpose. This nanocomposite technology has emerged from the field of engineering plastics, and potentially expanded its application to structural materials, coatings, and packaging to medical/biomedical products, and electronic and photonic devices. Recently these 'hi-tech' materials with excellent properties have begun to attract research people in the field of dielectrics and electrical insulation. Since new properties are brought about from the interactions of nanofillers with polymer matrices, mesoscopic properties are expected to come out, which would be interesting to both scientists and engineers. Improved characteristics are. expected as dielectrics and electrical insulation. Several interesting results to indicate the foreseeable future have been revealed, some of which are described on materials and processing in the paper together with basic concepts and future direction.

Polymer nanocomposites as dielectrics and electrical insulation-perspectives for processing technologies, material characterization and future applications

There is a growing demand for the production of a DNA biosensor with applications in medicine, the food industry, agriculture, veterinary science and environmental science. In this paper we describe methods for the optical and electrochemical detection of DNA using the enzyme horseradish peroxidase (EC 1.11.1.7) and glucose oxidase (EC 1.1.3.4). We have used bis-methylacridinium nitrate and luminol for the optical detection of DNA using a purpose built, inexpensive luminometer. Using this system detection limits of 10−11g of plasmid DNA have been observed. Electrochemical detection of DNA was carried out by the use of a fluoride ion selective electrode and stripping voltametry. DNA was detected down to 1 (10−9 − 10−10g of DNA by the enzymatic release of halogen ions from organohalogen compounds.

Optical and electrochemical detection of DNA

Some early models of breakdown in polymers are reviewed. The proposal of H.R. Zeller et al. (1984) of electrofracture as an aging mechanism in which the growth of a filamentary (i.e. tubular) crack through a dielectric is caused by electrostatic forces is discussed, and the nature of filamentary electromechanical breakdown is examined. Experimental results in support of the filamentary model are summarized. It is concluded that electromechanical breakdown at least contributes to breakdown in many polymeric systems, particularly those involving thin films where a small deformation gives rise to a sharp increase in electric field. >

Filamentary electromechanical breakdown in polymers

The directly observed growth of individual water trees has been used to examine analytically the applicability of a number of field-dependent growth models. Aqueous electrodes with different radii of curvature have been used to investigate the influence of the inception geometry upon tree growth. Measurements of growth rate have been made over a range of frequencies and the rate constants and compared with the results of dynamic dielectric and mechanical responses, in an attempt to elucidate the material factors that are involved in treeing. It is shown that the frequency dependence of the growth rate cannot be attributed to a modification of the dielectric by the tree, causing a frequency-dependent change of field strength for large enough trees. The rate constants obtained are frequency dependent and the analytical results are consistent with a mechanism of electrical origin, which causes microvoids and crazes to nucleate and grow. In general, the propagation rate of the damage seems to be rate limiting, but in a few cases generally characterized by a sharp inception geometry and thus possibly mechanical strain, it is the nucleation rate that is the slowest. >

An analysis of field-dependent water tree growth models

The dielectric response of two bisphenol-A epoxy resin systems Araldite CY1301 (T g ∼ 50°C) and Araldite CY1311 (T g ∼0°C) was studied at different levels of absorbed moisture. The dielectric measurements were carried out over the frequency range 1 mHz to 100 kHz and the results were characterised in terms of dc bulk electrical conduction and dielectric processes. The characteristic parameters (frequency and magnitude) of all processes have been found to be moisture dependent. In both resins above the glass transition temperature, absorbed moisture was found to be implicated in the formation of a bulk quasi-dc dielectric response consistent with cluster formation of the absorbed water molecules.

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Influence of absorbed moisture on the dielectric properties of epoxy resins

Complex geometry structures, such as produced by imperfections, cause the electric field to reach a very high local value even at low applied voltages. These are often the initiators of breakdown. Though direct measurement methods for space charge and electric field can be used only for planar or coaxial geometry, the authors propose to apply the pulsed-electro-acoustic (PEA) method to such complex geometry structures by using a simulation technique. The physical background of the simulation is presented. Comparisons between simulated and experimental signals are shown to be in good agreement meaning that simulations can be used as a tool for signal analysis.

http://iopscience.iop.org/article/10.1088/0022-3727/35/1/305/pdf

John C. Fothergill

Papers

Optical and electrochemical detection of DNA

Filamentary electromechanical breakdown in polymers

An analysis of field-dependent water tree growth models

Influence of absorbed moisture on the dielectric properties of epoxy resins

Improvement of PEA signal analysis using simulations for complex geometry samples