Matthew Praeger

Bio: Matthew Praeger is an academic researcher from University of Southampton. The author has contributed to research in topics: High harmonic generation & Dielectric. The author has an hindex of 12, co-authored 64 publications receiving 419 citations.

Soft-x-ray wavelength shift induced by ionization effects in a capillary.

Abstract: Coherent soft x rays are produced by high-harmonic generation in a capillary filled with Ar gas. We demonstrate that the tuning of the harmonic wavelengths with intensity and chirp arises from changes in the Ar ionization level. Control over the tuning can be achieved either by changing the average intensity of the laser pulse or by varying the quadratic spectral phase of the laser pulse. We observe an ionization-dependent blueshift of the fundamental wavelength that is directly imprinted on the harmonic wavelengths. The harmonic tuning is shown to depend on nonlinear spectral shifts of the fundamental laser pulse that are due to the plasma created by ionization, rather than directly on any chirp imposed on the fundamental wavelength.

The Effects of Water on the Dielectric Properties of Silicon-Based Nanocomposites

Abstract: A series of polyethylene-based nanocomposites was prepared, utilizing silicon nitride or silicon dioxide (silica) nanopowders, and the effect of filler loading and conditioning (i.e., water content) on their morphology and electrical properties was examined. The addition of nanosilicon nitride led to systems that were free of obvious nanoparticle aggregates, whereas the nanosilica-based systems showed evidence of aggregation up to the micrometer scale. While the nanosilicon nitride composites remained essentially dry under ambient conditions, the nanosilica-based composites absorbed appreciable quantities of water from the ambient environment, indicating that interactions with water are dependent on the nanoparticle surface chemistry. Dielectric spectroscopy showed a broad relaxation peak due to adsorbed water at nanoparticle surfaces, which shifted to higher frequencies with increased water content. Similarly, the electrical conductivity was found to be highly sensitive to the presence of absorbed water, particularly for systems containing well-dispersed nanoparticles. We conclude that, in nanodielectric applications, nanoparticle surface chemistry is important in determining macroscopic properties, and not just as a means of compatibilizing the filler and the matrix. Additional factors can be critical, here, as exemplified by interactions with water.

On the effect of functionalizer chain length and water content in polyethylene/silica nanocomposites: Part I — Dielectric properties and breakdown strength

Abstract: A series of nanoparticles was prepared by functionalizing a commercial nanosilica with alkylsilanes of varying alkyl tail length, from propyl to octadecyl. By using a constant molar concentration of silane, the density of alkyl groups attached to each system should be comparable. The effect of chain length on the structure of the resulting nanosilica/polyethylene nanocomposites was examined and comparison with an unfilled reference system revealed that, other than through a weak nucleating effect, the inclusion of the nanosilica does not affect the matrix structure. Since water interacts strongly with applied electric fields, water was used as a dielectric probe in conjunction with dielectric spectroscopy to examine the effect of the nanofiller and its surface chemistry on the system. Sets of samples were prepared through equilibrating under ambient conditions, vacuum drying and water immersion. While the water content of the unfilled polymer was not greatly affected, the water content of the nanocomposites varied over a wide range as a result of water accumulation, in a range of states, at nanoparticle interfaces. The effect of water content on breakdown behavior was also explored and, in the unfilled polymer, the breakdown strength was found to depend little on exposure to water (∼13% reduction). In all the nanocomposites, the increased propensity for these systems to absorb water meant that the breakdown strength was dramatically affected (>66% reduction).

Effect of water absorption on dielectric properties of nano-silica/polyethylene composites

Abstract: The effect of moisture content on the dielectric properties of polymer/nano-silica blends was investigated. It was found that the DC breakdown strength, electrical conductivity and complex permittivity were all strongly influenced by absorbed water. However, a control sample without nano-silica was largely unaffected by changes in moisture content. This has important implications for researchers and cable designers.

Preparation of nanoparticles

Abstract: Innovative developments of science and engineering have progressed very fast toward the synthesis of nanomaterials to achieve unique properties that are not the same as the properties of the bulk materials. The particle reveals interesting properties at the dimension below 100 nm, mostly from two physical effects. The two physical effects are the quantization of electronic states apparent leading to very sensitive size-dependent effects such as optical and magnetic properties and the high surface-to-volume ratio modifies the thermal, mechanical, and chemical properties of materials. The nanoparticles’ unique physical and chemical properties render them most appropriate for a number of specialist applications.

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 …

Mechanisms, Capabilities, and Applications of High-Resolution Electrohydrodynamic Jet Printing.

Abstract: This review gives an overview of techniques used for high-resolution jet printing that rely on electrohydrodynamically induced flows. Such methods enable the direct, additive patterning of materials with a resolution that can extend below 100 nm to provide unique opportunities not only in scientific studies but also in a range of applications that includes printed electronics, tissue engineering, and photonic and plasmonic devices. Following a brief historical perspective, this review presents descriptions of the underlying processes involved in the formation of liquid cones and jets to establish critical factors in the printing process. Different printing systems that share similar principles are then described, along with key advances that have been made in the last decade. Capabilities in terms of printable materials and levels of resolution are reviewed, with a strong emphasis on areas of potential application.

Materials Science 高分子の材料科学

Abstract: Materials science is the study of processing-structure-property relationships in materials of importance to society, such as metals, ceramics, polymers, semiconductors, biomaterials, nanomaterials, and their combinations (composites). Materials scientists pay special attention to “microstructure”—i.e., how materials are constructed on the microscopic, submicroscopic, and even the nanometer levels, and how this affects their properties. Given the wide range of uses for materials, their properties of interest are similarly broad, from mechanical (e.g., strength) to electrical (e.g., semiconduction) to biological (e.g., biocompatibility).