Dielectric dispersion has been observed in the symmetric-top molecules CHF₃ and CH₃­F in the gas phase over a density range from 10­³ to 40 amagats at a temperature of 309°K and a frequency of 30 MHz. The absorption (related to the dispersion by the Kramers-Kronig relations) has been expressed in terms of a simple correlation function of the permanent electric dipole moment which is the product of the correlation function for free motion and an exponentially decaying "reduced" correlation function. The effects of molecular collisions were described by a single correlation time which measures the apparent molecular diameter. The results were compared with microwave nonresonant absorption and nuclear spin relaxation experiments done on the same molecules. At low densities (<.l amagats) a dispersion curve of the Debye type was observed. At high densities (>1 amagat) the dependence of the dielectric susceptibility on density deviated from that expected from the Clausius-Mossotti equation. The origin of this effect is not understood at present. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The frequency dependence and temperature dependence of the complex dielectric constant of water is of great interest. The temperature dependence of the physical properties of water given in the literature, specific heat, thermal conductivity, electric conductivity, pH, etc. are compared to the a. c. (microwave) and d. c. conductivity of water with a variety of concentration of different substances such as HC1, NaCl, HaS04, etc. When each of these properties is plotted versus inverse absolute temperature, it can be seen that each sample shows "transition temperatures". In this work, Slater's perturbation equations for a resonant microwave cavity were used to analyze the experimental results for the microwave data.

Approved for public release / This research was part of an ongoing program studying the concept of multi-material dielectrics (MMD) with dielectric constants much higher than homogenous materials. MMD described in this study have dielectric constants six orders of magnitude greater than the best single materials. This is achieved by mixing conductive particles with an insulating surface layer into a composite matrix phase composed of high surface area ceramic powder and aqueous electrolyte. Specifically examined in this study was micron-scale nickel powder treated in hydrogen peroxide (H2O2) loaded into high surface area alumina powder and aqueous boric acid solution. This new class of dielectric, composite electrolyte dielectrics (CED), is employed in an electrostatic capacitor configuration and demonstrated dielectric constant of order 10 [raised to the 10th power] at approximately 1 Volt. Additionally, it is demonstrated that treated nickel can be loaded in high volume fractions in the CED configuration. Prior studies of composite capacitors indicated a general limitation due to shorting. This results from the onset of percolation due to excess loading of conductive phases. Insulated particles described herein are successfully loaded up to 40% by volume, far above typical percolation thresholds. Simple models are presented to explain results. / Lieutenant, United States Navy

Dielectric permittivity measurements provide important input to engineering and scientific disciplines due to the effects of permittivity on the interactions between electromagnetic energy and materials. A novel ring resonator design is presented for the measurement of permittivity of low dielectric constant foams. A review of dielectric material properties and currently available measurement methods is included. Measurements of expanded polystyrene are reported and compared with results from the literature; good agreement between measurements and published results is shown.

No description available.

No description available.

Call number: LD2668 .T4 1949 O4 / Master of Science

Call number: LD2668 .T4 1952 U5 / Master of Science

Dielectrophoresis (DEP) is a term which describes the motion of polarisable particles induced by a non-uniform electric field. It has been the subject of research into a variety of fields including nanoassembly, particle filtration and biomedicine. The application of DEP to the latter has gained significant interest in recent years, driven by the development of microfluidic “Lab-on-a-chip” devices designed to perform sophisticated biochemical processes. It provides the ability to characterise and selectively manipulate cells based on their distinct dielectric properties in a manner which is non-invasive and label free, by using electrodes which can be readily integrated with microfluidic channels. Under appropriate conditions a biological cell will experience a DEP force directing it either towards or away from concentrations in the electric field. At a so-called “crossover frequency” the cell is effectively invisible to the field resulting in no DEP force, a response typically observed in the 1 kHz to 1 MHz range. Its value is a function of cell membrane dielectric properties and has been the subject of research directed at devices capable of using it to both characterise and sort cells. The aim of this work was to investigate the behaviour of a higher frequency crossover referred to as fxo2, predicted to occur in the 1 MHz to 1 GHz range. At these frequencies the electric field is expected to penetrate the cell membrane and behave as a function of intracellular dielectric properties. Standard lithography techniques have been used to fabricate electrodes carefully designed to operate at these frequencies. The existence of fxo2 was then confirmed in murine myeloma cells, in good agreement with dielectric models derived from impedance spectroscopy. A temperature dependent decrease in its value was observed with respect to the time that cells were suspended in a DEP solution. This decrease is consistent with previous studies which indicated an efflux of intracellular ions under similar conditions. An analytical derivation of fxo2 demonstrates its direct proportionality to intracellular conductivity. Direct control of the crossover was achieved by using osmotic stress to dilute the intracellular compartment and thereby alter its conductivity. By using a fluorophore which selectively binds to potassium, a strong relationship has been demonstrated between the value of fxo2 and the concentration of intracellular potassium. Measurements of fxo2 for an unfed culture demonstrated a correlation with viability and subtle shifts in its distribution were caused by the early stages of chemically induced apoptosis.

Epoxy res~ a major component of solid electrical insulation systems, degrades when subjected to electrical discharges. Identification of the epoxy resin degradation mechanism might indicate improvements which can be made in the chemical formulation of the resin to enhance the insulation systems. Samples of a commonly used epoxy res~ bisphenol-A epoxy crosslinked with phthalic anhydride, were manufactured and then aged by applying lOkV AC to an electrode 2mm above the resin surface. The following experimental conditions were altered: manufacturing system: (i) moulded slab and (ii) slice cut from moulded cylinder; atmosphere: (i) nitrogen, (ii) dry, (iii) normal and (iv) moist air; high voltage electrode:(i) brass and (ii) copper. In addition, ageing due to chemical, thermal and radiative stressing was also examined. The changes in the stressed resin samples were determined using the following techniques: diffuse reflectance Fourier Transform infrared spectroscopy (DRIFT), attenuated total reflectance FTIR (ATR-FTIR), thermogravimetric analysis (TGA), thermogravimetric FTIR (TG-FTIR) and atomic force microscopy (AFM). The changes in the electrode materials were determined using X-ray diffratometry (XRD) and Fourier Transform infrared (FTIR) techniques. The method of production of the specimens was shown to affect the degradation. Silicone release agent, used in the moulding of the resin slabs, was found on the surface of degraded moulded resin slabs: the contamination of the moulded samples was not detectable prior to partial discharge stressing. Crazing and flaking of the stressed resin surface were found on the moulded slabs but not on the slices of resin. Anhydride, acid and amine species were identified on the surface of the electrically stresses resin slices. Chemical reactions accounting for the changes found on the surface of the stressed resin slices are given. The radical species formed by methyl group dissociation, reacting with hydroxyl and activated oxygen species, lead to the formation of linear anhydrides, acids and peracids on the resin surface. Reactive nitrous oxide species in the discharge atmosphere react with the resin to form amines. Zinc formate dihydrate was identified on brass electrodes after the resin ageing process, whilst basic copper nitrate was identified on copper electrodes. The difference in deposit found on the electrode indicates that zinc reacts with carbon species from the discharge environment; copper reacts, not with carbon species, but with nitrogen species. The variation in chemical interaction at the high voltage electrode, dependant upon electrode material, has been found to correlate with changes on the resin surface. Correlations are made between the effects of partial discharge and other stresses applied. None of the applied stresses generated the anhydride structure found in partial discharge stressed resin samples. However, in common with p.d. stress, UV radiation increases the level of crosslinking in the epoxy resin and produces carbonyl structures, nitric acid fumes produce acid, peracid and nitroso structures.