T.J. Lewis

Bio: T.J. Lewis is an academic researcher from Bangor University. The author has contributed to research in topics: Space charge & Electron mobility. The author has an hindex of 6, co-authored 6 publications receiving 1437 citations.

Interfaces are the dominant feature of dielectrics at the nanometric level

Abstract: It is argued that the behavior of dielectric particles as they shrink in size through micrometric to nanometric scales will be increasingly dominated by the properties of their interfaces with the environment. The various interatomic and intermolecular forces that determine the structure of these interfaces are reviewed with special emphasis on their electrical nature. A number of situations in which passive and dynamic dielectric properties are traceable to nanometric interfacial properties are considered. It is also demonstrated that such interfaces are nanometric electromechanical (NEM) systems which acting collectively also explain piezoelectricity in macroscopic systems. Interfaces are naturally nanometric entities and must have a major role in the future development of nanotechnology. Their ubiquitous employment in living systems is noted and comparison suggests synergistic opportunities.

Nanometric dielectrics

Abstract: It is suggested that a major field of study in the future development of dielectrics will concern their properties when relatively few molecules are involved. Such smallness arises naturally at interfaces of nanometric thickness and will occur also when dielectrics are employed in the nano-technical devices of the future. It already occurs in living systems where the dielectric and conductive properties of biomaterials are vital in sustaining activity. The transverse and lateral properties of interfaces, including the effects of molecular ordering, are considered and it is suggested that the advent of scanning tunneling and atomic force microscopies provides a significant opportunity for nanometric dielectric studies. An important feature, suggested for future exploitation, is the cross-coupling in interfaces of force fields arising from electrical, mechanical, chemical and entropic potential gradients. Application of these concepts to biology and to the behavior of polymer gels which may lead to development of muscle-like actuators and transducers are considered. Finally, attention is drawn to the likely role of nanometric interfacial processes in the initiation of electrical breakdown in insulating materials. >

The contribution of field-induced morphological change to the electrical aging and breakdown of polyethylene

Abstract: A brief review of the early literature is given which provides evidence that electrically-induced mechanical stresses make an important contribution to the electrical breakdown of solid dielectrics. Special attention is given to polyethylene and the manner in which this semi-crystalline polymer yields under mechanical stress by microvoid, crack and craze development in the amorphous phase between the lamellar crystallites. The nature of the forces induced by an electrical field is considered and it is shown that a significant component of tensile stress is generated in a direction orthogonal to the field and can become large as breakdown is approached. This suggests a correlation between the responses of the polymer to mechanical and electrical stresses and consequently the importance of morphology in determining the latter. The likely effect of field-induced morphological change on charge transport and electrode processes is described and its underlying contribution to possible aging markers for polyethylene, such as high field conduction, electroluminescence, space charge and charge packets is considered.

Breakdown initiating mechanisms at electrode interfaces in liquids

Abstract: Two hitherto neglected mechanisms, which occur at the interface between insulating liquids and metal electrodes under high electrical fields, are considered and shown to be significant for the initiation of breakdown. One involves the Lippmann effect in which the electrical fields of the double layers at the electrodes reduce the interfacial tension and lead to the generation of low-density microcavities on the electrode surfaces. The other is the Auger effect in which non-radiative recombination of electrons and positive holes across the large energy gap between these states leads to secondary electrons of high energy. The coupling between these two mechanisms is expected to be highly conducive to streamer initiation at the electrodes.

A model for bilayer membrane electroporation based on resultant electromechanical stress

Abstract: Reconsideration of the effect of an electrical field applied across a phospholipid bilayer membrane shows that, in addition to a compressive stress normal to the membrane plane, transverse traction stresses are generated in the lateral plane of the membrane. In the fields usually employed for electroporation these transverse stresses are likely to be sufficient to reduce the membrane tension considerably, causing electroporation and rupture. This mode of field-induced change in the membrane provides a natural model for the various forms of electroporation.

Recent Progress on Ferroelectric Polymer-Based Nanocomposites for High Energy Density Capacitors: Synthesis, Dielectric Properties, and Future Aspects.

Abstract: Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers...

Flexible Nanodielectric Materials with High Permittivity for Power Energy Storage

Abstract: 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.

Non-thermal plasmas in and in contact with liquids

Abstract: During the last two decades atmospheric (or high) pressure non-thermal plasmas in and in contact with liquids have received a lot of attention in view of their considerable environmental and medical applications. The simultaneous generation of intense UV radiation, shock waves and active radicals makes these discharges particularly suitable for decontamination, sterilization and purification purposes. This paper reviews the current status of research on atmospheric pressure non-thermal discharges in and in contact with liquids. The emphasis is on their generation mechanisms and their physical characteristics.

Proposal of a multi-core model for polymer nanocomposite dielectrics

Abstract: 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.