This thesis describes a study of electrical conduction in polyvinylchloride compounds. By way of an introduction the first chapter outlines mechanism of absorption and conduction in polymeric systems, reviews the principles of formulation of polyvinylchloride compiounds for use in electrical insulation applications, and gives a review of previous measurements on such compounds. In the second chapter a description of the experimental techniques employed in the present study is given. The experimental results are presented in the third chapter, and in the final chapter the results are discussed and conclusions drawn. The research described is the original work of the author and has not been submitted for any other degree. Additional information has been gathered from various literary sources which are listed at the end of the thesis.

In the present investigation, measurements were made at liquid-helium temperatures on single-crystal bismuth samples which had a stair-step geometry in order to study several thicknesses during one helium run. These samples were also thinned to extend the thickness range of the steps to a thinner region. In addition J.E. Parrott's theory is extended to include a diagonal anisotropic relaxation-time tensor and the effect of holes on the size effect. A discussion of the theory of Parrott, and the extension of Parrott's theory in connection with the experimental results is presented.

The four-electrode method modified for laboratory use was employed for electrical conductivity measurements of eight Scottish and two Greek Ca-saturated soils (< 2 mm fraction) over a range of soil solution conductivities (0.5 - 10 dS m^-1 as CaCℓ2) and for a range of tensions (saturation to 8 bars). Soil bulk conductivity, κb(dS m^-1), was linearly related with the soil solution conductivity κw (dS m^-1) for the tensions used, the relationship being of the form, κb = 1/F_f κw + κs, where κs (dS m^-1) is the adsorbed Ca conductivity and 1/F_f accounts for tortuosity and available pore volume fraction for conductance. For each soil, 1/F_f was linearly related with the volumetric moisture content θ. It was found that for the type of the soils used, non-montmorillonitic soils and mean organic matter content 5% for the Scottish soils, the adsorbed Ca molar conductivity is only a small fraction (1 - 4%) of its infinite dilution value. Also κs was related to soil properties like clay content, total surface area, CEC and organic matter. Diffusion coefficients for Ca and Cℓ for the soil solution and for adsorbed Ca were calculated by the Nernst-Einstein relationship from the measured solution conductivities and from the κs values. For θ= 0.57 to 0.15 and soil solution concentration of 0.0025 - 0.0045M as CaCℓ2, Ca diffusion coefficients ranged from 2.67 to 0.062 x 10^-10m²s^-1 and Cℓ diffusion coefficients from 6.9 to 0.16 x 10^-10m^2s^-1. A concentration correction was applied. Adsorbed Ca diffusion coefficients ranged from 11.8 to 0.045 x 10^-12m^2s^-1 for θ= 0.52 tp 0.14. A bulk density effect was introduced by consolidating and compacting four of the soils with a static load of 0.45 kg cm^-2. Soil bulk conductivities were measured at the same range of soil solution conductivities and for a tension range of 40 cm to 2 bars. Diffusion coefficients for Ca and Cℓ in the soil solution calculated using the Nernst-Einstein relationship were higher than the non-compressed soils on a tension basis, while for each soil on a common θ basis diffusion coefficients for Ca and Cℓ tended to increase slightly as bulk density was increased.

Thesis (Ph.D.)--University of Texas at Dallas, 2008. / Includes vita. Includes bibliographical references (leaves 77-79)

Polymer nanocomposites are prepared by appropriately dispersing nanoscale fillers into polymer matrices. Graphene, a two-dimensional nano-carbon material with outstanding physical properties, has been widely studied as a conductive filler for nanocomposites. In this work, a gum Arabic aqueous solution was proposed as a new media to exfoliate graphite into few-layer graphene by liquid-phase sonication. Successful exfoliation was confirmed by Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. Four types of graphene nanoplatelets were used to study the effects of the filler's aspect ratio. The one with the largest aspect ratio showed the best performance, where the conductivity of neat epoxy was increased by five orders of magnitude at 10 wt.%. Using a hot sonication technique and adding a small amount of second fillers further improved the electrical conductivities. The highest conductivity obtained in this study was 0.025 S/cm, which met the requirements of electromagnetic shielding material.

Orientador: Darcy Hiroe Fujii Kanda / Coorientador: Haroldo Naoyuki Nagashima / Banca: Fernando Rogerio de Paula / Banca: Roberto Mendonça Faria / Resumo: Neste trabalho, estudamos os processos de condução envolvidos na condutividade elétrica de nanocompósitos de polianilina com óxido de índio e estanho (PANI/ITO) e de poliuretano com negro de fumo (PU/NF), a partir da aplicação de um modelo estatístico de rede de resistores e da análise da condutividade dc próximo ao limiar de percolação. O modelo estatístico foi desenvolvido em linguagem Fortran 90 para gerar a estrutura morfológica desses nanocompósitos e calcular a condutividade elétrica alternada pela aplicação de uma técnica de matriz de transferência. O modelo levou em consideração a estrutura desordenada da PANI não dopada, a formação de segmentos moles e duros no PU e a distribuição aleatória de nanopartículas e agregados de ITO e NF em suas respectivas matrizes. A impedância entre dois sítios vizinhos da matriz polimérica, tanto para PANI quanto para PU, foi calculada pelo modelo de Dyre, enquanto que a impedância entre dois sítios vizinhos que compõem a fase condutora de ambos nanocompósitos foi calculada pelo modelo de Drude. Foram realizadas medidas de espectroscopia de impedância e de condutividade dc para ambos os compósitos, com diferentes concentrações da fase condutora. Os objetivos foram analisar os processos de condução, determinar o limiar de percolação e os expoentes críticos da condutividade. De acordo com os resultados das simulações e dos resultados experimentais, o processo de condução entre dois sítios da matriz polimérica obedece ao modelo de distribuição aleatória de barreiras de energia livre de Dyre (RFEB), ao passo que a condução nos domínios condutores é descrita pelo modelo de Drude. A análise das medidas de condutividade dc realizadas abaixo do limiar de percolação de ambos os compósitos indica que o processo de condução... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this paper, we study the conducting processes involved in electrical conductivity of polyaniline/indium tin oxide nanocomposites (PANI/ITO) and polyurethane/carbon black nanocomposites (PU/CB), from the application of a statistical model of network resistors and the analysis of the dc conductivity near the percolation threshold. The statistical model was developed in Fortran 90 to generate the morphological structure of these nanocomposites and calculate the alternating electrical conductivity by applying a transfer matrix technique. The model took into account the disordered structure of undoped PANI, the formation of soft and hard segments in PU and random distribution of nanoparticles and aggregates of ITO and NF in their respective matrix. The impedance between two neighboring sites of the polymeric matrix, for both PANI and PU, was calculated by the model of Dyre, while the impedance between two neighboring sites from conductive phase was calculated by the Drude model. Were measured impedance spectroscopy and dc conductivity for both composites, with different concentrations of the phase conductor. The objectives were to analyze the processes of conduction, determine the percolation threshold and critical exponents of conductivity. According to the simulations and experimental results, the conduction process, between two sites of the polymeric matrix, is in agreement with random free energy barriers model proposed by Dyre (RFEB), while the conduction in the conductive phase is described by the Drude model. The analysis of the dc conductivity measurements obtained below the percolation threshold on both the composites indicates that the process of conduction occurs via hopping between sites of the polymeric matrix. In the region of percolation, both the hopping and tunneling can contribute to the conduction process. However, for samples with concentrations... (Complete abstract click electronic access below) / Mestre

Self-assembly is an astonishing phenomenon at the base of organized structures’ formation from disordered systems. It occurs in nature from atomic and molecular lengths to galactic distances. Nowadays self-assembly of colloidal solutions can be used to fabricate photonic crystals and metamaterials. This paper analyses the self-assembly and its effect on the electric conductivity of a colloid made up of carbon nanotubes and magnetite microparticles controlled by electrostatic potentials and magnetic fields. Alignment of the carbon nanotubes and creation of sparks and short-circuits are observed when the electrostatic field is applied. The magnetic field induces time-dependent and memory effects in the sample’s structure and conductivity. At constant potential, the electric current through the sample is reported to increase four times during and after the application of the magnetic fields.

This thesis is a study of the phenomenon of superconductivity.

No description available.

The work presented here is an experimental investigation of the effect of cylindrical geometry on electrical conductivity, in which single-crystal samples of cadmium at the temperature of liquid helium are used, with the diameter on the order of the electron mean free path.