Thomas Andritsch

Bio: Thomas Andritsch is an academic researcher from University of Southampton. The author has contributed to research in topics: Epoxy & Dielectric. The author has an hindex of 22, co-authored 143 publications receiving 1600 citations. Previous affiliations of Thomas Andritsch include Delft University of Technology.

Properties of Mineral Oil based Silica Nanofluids

Abstract: A nanofluid as intended for use in high voltage engineering is a heat transfer fluid, containing a small fraction of nano-sized filler materials. These nanoparticles exhibit unique properties, compared to those of the same material at the bulk scale. The term "nanofluid" was coined by Choi et al. at Argonne National Laboratory and refers to a colloid fluid, composed of a liquid phase and dispersed nanoparticles in suspension. Nowadays, nanofluids are considered the next generation of heat transfer fluids due to their improved heat transfer properties, compared to conventional fluids. In HV applications nanofluids based on mineral oil are being studied, to determine if they are a suitable replacement for conventional transformer oil or vegetable oil. In this study, mineral oil based silica nanofluids with different concentrations were prepared. The AC breakdown voltage of the nanofluids was tested at different moisture content levels. Silica nanofluids exhibit improved breakdown strength, especially at high moisture content level. The thermal conductivity was measured in the temperature range 10°C to 80°C, with up to 0.1% silica nanoparticles. Despite the reputation of nanofluids of being superior heat transfer fluids, only a negligible effect on the thermal conductivity of mineral oil could be found.

Anomalous behaviour of the dielectric spectroscopy response of nanocomposites

Abstract: A study on the dielectric spectroscopy of epoxy-based nanocomposites filled with different types of particles, such as Al2O3, AlN, MgO, SiO2 and BN, is presented. The surface of the nanoparticles was modified with a silane coupling agent, in order to make them compatible with the organic host and create a system with homogeneously dispersed filler material. Morphological characterizations of individual particles and fabricated composites were performed by means of transmission and scanning electron microscopy. The present research addresses an analysis of the complex permittivity. The relative permittivity of nanocomposites shows an unusual behaviour. Introduction of a low percentage of high permittivity filler results in a decrease of the permittivity of the bulk polymer material. We propose a qualitative explanation for the reduction of the relative permittivity, compared to the reference samples. The interface layer of surface modified particles plays a more important role than the nature of the particles themselves. The immobilization caused by the surface treatment of the nanoparticles seems to be the main factor determining the relative permittivity of the composites with fillgrade below 5 wt.%. The imaginary part of the complex permittivity, which represents the dielectric losses in the system, does not change significantly with addition of nanofiller up to 5 wt.%.

Modelling of the thermal conductivity in polymer nanocomposites and the impact of the interface between filler and matrix

Abstract: In this paper the thermal conductivity of epoxy-based composite materials is analysed. Two and three-phase Lewis–Nielsen models are proposed for fitting the experimental values of the thermal conductivity of epoxy-based polymer composites. Various inorganic nano- and microparticles were used, namely aluminium oxide, aluminium nitride, magnesium oxide and silicon dioxide with average particle size between 20 nm and 20?m. It is shown that the filler–matrix interface plays a dominant role in the thermal conduction process of the nanocomposites. The two-phase model was proposed as an initial step for describing systems containing 2 constituents, i.e. an epoxy matrix and an inorganic filler. The three-phase model was introduced to specifically address the properties of the interfacial zone between the host polymer and the surface modified nanoparticles.

Characterization of epoxy microcomposite and nanocomposite materials for power engineering applications

Abstract: This article presents the results from round-robin tests performed on epoxy composite materials. These results show the potential of these materials for use as electrical insulation in some specific applications. A small section of the article addresses the health and safety issues related to the use of nanoparticles in the electrical power engineering industry. We define epoxy nanocomposites as epoxy-based materials containing exclusively nanosized filler particles. Epoxy microcomposites are defined as epoxy materials containing exclusively microsized filler particles, and epoxy micro+nano composites are materials containing both microsized and nanosized particles.

Epoxy Based Nanodielectrics for High Voltage DC Applications: Synthesis, Dielectric Properties and Space Charge Dynamics

Abstract: Main goal of the research described in this PhD thesis was to determine the influences of filler size, material and distribution on the DC breakdown strength, permittivity and space charge behaviour of nanocomposites. This should lay the groundwork for tailored insulation materials for HVDC applications. Examples for this are medical and industrial X-ray imaging, radar and cable terminations. In the course of this project a manufacturing process was devised, which enabled the fabrication of epoxy based nanocomposites with a good dispersion of different types of nanoparticles. Models from literature, which explain the behaviour nanodielectrics exhibit, are discussed: electric double-layer model, intensity model, multi-core model and the interphase volume model. Based on these theories, a new model was devised for explaining the behaviour of epoxy based nanocomposites: the polymer chain alignment model. The underlying idea of this model is that the restructuring of the base polymer on the molecular scale, due to the presence of surface modified nanoparticles, plays a fundamental part in the properties of the bulk material. Each modified particle will act as centre for crosslinking of the polymer, leading to a rigid layer of polymer chains around each particle. These rigid layers have a much lower permittivity than both host and filler material, thus their presence can easily be identified by dielectric spectroscopy, since the relative permittivity of the bulk material decreases. In literature it is shown, that the strong bonding of particles and host material due to the surface modification gives rise to improved resistance to partial discharges and electrical treeing. More energy is needed to break these bonds than it would be the case in unmodified polymers. The particles themselves can also act as recombination centres for electrons and holes, which travel between or along polymer chains. This has an effect on the space charge dynamics. Agglomerations of nanoparticles can nullify these effects however: it is explained how agglomerations can act as charge traps, lead to field enhancements and cause interfacial polarization. Claims from theory are tested with three measurement methods: short term DC breakdown tests, dielectric spectroscopy and space charge measurement. It is shown that nanocomposites exhibit improved DC breakdown strength for very low fillgrades of 0.5 to 2 % by weight. Compared to the unmodified base material improvements of up to 80 % could be measured. Dielectric spectroscopy reveals that the relative permittivity in nanocomposites is lower than of the host and filler materials, with a minimum at a fillgrade of approximately 2 % by weight. For higher fillgrades the permittivity of the composite increases depending on the ratio between the permittivity values of filler and host material. Above 2 wt.% the permittivity of the filler material starts to overshadow the low permittivity of the rigid layers around the particles. Results from space charge measurement with the pulsed electro-acoustic method show that the quality of particle dispersion has an impact on the charge intake. Based on these measurements it is concluded that particle agglomerations act as charge traps, while the amount of charges in nanocomposites with good particle dispersion is lower than in the unmodified epoxy. This confirms that the particles indeed act as recombination centres, actively mitigating charge buildup inside the material. These results show why nanocomposites are very interesting for HVDC equipment. Space charges are a limiting factor for DC applications. Their reduction improves the reliability of the insulation system. The increased DC breakdown strength enables more compact high voltage equipment, respectively the utilization at higher field strengths. The work presented here is a stepping stone on the way to industrial applications of nanostructured insulation material and fundament for further investigations on topics like nanofluids.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Introduction to Spectroscopy

Abstract: Spectroscopy is the study of matter interacting with electromagnetic radiation (e.g., light). The electromagnetic spectrum in Figure 1 illustrates the many different types of electromagnetic radiation, including gamma rays (γ-rays), X-rays, ultraviolet (UV) radiation, visible light, infrared (IR) radiation, microwaves, and radio waves. The frequency (ν) and wavelength (λ) ranges associated with each form of radiant energy are also indicated in Figure 1.

25th Anniversary Article: A Soft Future: From Robots and Sensor Skin to Energy Harvesters

Abstract: Scientists are exploring elastic and soft forms of robots, electronic skin and energy harvesters, dreaming to mimic nature and to enable novel applications in wide fields, from consumer and mobile appliances to biomedical systems, sports and healthcare. All conceivable classes of materials with a wide range of mechanical, physical and chemical properties are employed, from liquids and gels to organic and inorganic solids. Functionalities never seen before are achieved. In this review we discuss soft robots which allow actuation with several degrees of freedom. We show that different actuation mechanisms lead to similar actuators, capable of complex and smooth movements in 3d space. We introduce latest research examples in sensor skin development and discuss ultraflexible electronic circuits, light emitting diodes and solar cells as examples. Additional functionalities of sensor skin, such as visual sensors inspired by animal eyes, camouflage, self-cleaning and healing and on-skin energy storage and generation are briefly reviewed. Finally, we discuss a paradigm change in energy harvesting, away from hard energy generators to soft ones based on dielectric elastomers. Such systems are shown to work with high energy of conversion, making them potentially interesting for harvesting mechanical energy from human gait, winds and ocean waves.