In this dissertation, we determine how the dispersion, network formation and alignment of carbon nanotubes in polymer nanocomposites affect the electrical properties of two different polymer composite systems: high temperature bismaleimide (BMI) and polyethylene. The knowledge gained from this study will facilitate optimization of the above mentioned parameters, which would further enhance the electrical properties of polymer nanocomposites. BMI carbon fiber composites filled with nickel-coated single walled carbon nanotubes (Ni-SWNTs) were processed using high temperature vacuum assisted resin transfer molding (VARTM) to study the effect of lightning strike mitigation. Coating the SWNTs with nickel resulted in enhanced dispersions confirmed by atomic force microscopy (AFM) and dynamic light scattering (DLS). An improved interface between the carbon fiber and Ni-SWNTs resulted in better surface coverage on the carbon plies. These hybrid composites were tested for Zone 2A lightning strike mitigation. The electrical resistivity of the composite system was reduced by ten orders of magnitude with the addition of 4 weight percent Ni-SWNTs (calculated with respect to the weight of a single carbon ply). The Ni-SWNTs - filled composites showed a reduced amount of damage to simulated lightning strike compared to their unfilled counterparts indicated by the minimal carbon fiber pull out. Methods to reduce the electrical resistivity of 10 weight percent SWNTs -- medium density polyethylene (MDPE) composites were studied. The composites processed by hot coagulation method were subjected to low DC electric fields (10 V) at polymer melt temperatures to study the effect of viscosity, nanotube welding, dispersion and, resultant changes in electrical resistivity. The electrical resistivity of the composites was reduced by two orders of magnitude compared to 10 wt% CNT-MDPE baseline. For effective alignment of SWNTs, a new process called Electric field Vacuum Spray was devised to overcome viscosity within the dispersed nanotube polymer system, and produce conductive MDPE-SWNT thin films. Polarized Raman spectroscopy and scanning electron microscopy (SEM) analysis on the samples showed an improvement in SWNT -- SWNT contacts and alignment in the polymer matrix. The resistivity of the samples processed by this new method was two order magnitudes lower than the samples processed by hot coagulation method subjected to electric field.

Delineating the extent of brine contamination in shallow groundwater systems using piezometers is costly and does not provide adequate data resolution. Direct-push (D-P) electrical conductivity (EC) profiling enables rapid in situ measurements of bulk soil EC (ECa) at the cm scale. Previous studies using D-P EC profiling to detect contaminant plumes have solely relied on ECa measurements, and where attempts were made to isolate pore-water salinity variations from changes in ECa they were accomplished using simple linear methods. In this study D-P EC profiling was used to define groundwater salinity distributions using an established soil conductance model and estimate the timing of groundwater contamination at a long-term potash mine in south-central Saskatchewan, Canada. The site was dominated by fine-grained postglacial and glacial sediments with known Na-K-Cl brine impacts resulting from mining activities. Coreholes (n=22) were drilled to 7.6-12.2 m below ground (mbg) to obtain continuous cores for detailed geologic descriptions and measurements of index parameters (n=522) below the water table. Pore-water EC (ECw) and Cl- results from squeezed core samples (n=142) at 12 locations were compared to ECa measurements collected using a D-P probe adjacent to each corehole. Measured ECw and pore-water Cl- results ranged from 1.94-55.1 mS/cm and 87-20,700 mg/L, respectively. In situ D-P EC values from logs collected adjacent to all 22 coreholes ranged from 2-8 mS/cm within the oxidized zone (5-6 mbg) and decreased to background values of 0.3-2 mS/cm within the underlying unoxidized zone. Significant linear ECa–ECw regressions established for four lithological groups (r2=0.78-0.95) were used with porosity and dry density measurements to generate high-resolution depth profiles of ECw from D-P EC measurements. A significant linear ECw–Cl regression (r2=0.92) further enabled the generation of pore-water Cldepth profiles from ECw predictions. Observed 1D vertical profiles of Cl-, ECw, and ECa at three locations were modeled. Results suggested solute transport can be described as diffusion-dominated below depths of 3-5 mbg and that groundwater contamination began shortly after the onset of mining. Based on the results attained, this method can generate high-resolution depth profiles of pore-water salinity that can be used to define the lateral and vertical extent of brine contamination, dominant solute transport mechanisms, and timing of groundwater contamination.

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Piezoresistivity in conductive polymer nanocomposites occurs because of the disturbance of particle networks in the polymer matrix. The piezoresistance effect becomes more prominent if the matrix material is compliant making these materials attractive for applications that require flexible force and displacement sensors such as e-textiles and biomechanical measurement devices. However, the exact mechanisms of piezoresistivity including the relationship between the matrix polymer, conductive particle, internal structure and the composite’s piezoresistance need to be better understood before it can be applied for such applications. The objective of this thesis is to report on the development of conductive polymer nanocomposites for use as flexible sensors and electrodes. Electrically conductive and piezoresistive nanocomposites were fabricated by a scalable melt compounding process. Particular attention was given to elucidating the role of matrix and filler materials, plastic deformation and porosity on the electrical conduction and piezoresistance. These effects were parametrically investigated through characterizing the morphology, electrical properties, rheological properties, and piezoresistivity of the polymer nanocomposites. The electrical and rheological behavior of the nanocomposites was modeled by the percolation-power law. Furthermore, a model was developed to describe the piezoresistance behavior during plastic deformation in relation to the stress and filler concentration.

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-02-13Bitstream added on 2014-06-13T20:33:15Z : No. of bitstreams: 1 cardoso_ls_me_ilha.pdf: 1695440 bytes, checksum: a405a9de67a38bab365400a8a0d01ec9 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / 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... / 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)

Orientador: Wanda Cecília Las / Banca: Marian Rosaly Davolos / Banca: Sidnei Antônio Pianaro / Resumo: A influência do Cr na condutividade elétrica e propriedades microestruturais de cerâmicas à base de SnO2-Mn-Nb foi investigada. Também foi estudada a influência do método de preparação nas características dos pós precursores cerâmicos e nas propriedades e características das cerâmicas resultantes. Sistemas SnO2-Mn-Nb com concentrações variadas de Cr foram preparados pelo método convencional de mistura de óxidos e pelo método Pechini (rota orgânica). Foram utilizadas medidas de área superficial (método BET), difração de raios X, espectroscopia vibracional no infravermelho e microscopia eletrônica de varredura a fim de caracterizar os pós preparados. Análises de condutividade elétrica e impedância complexa confirmaram uma diminuição da condutividade em função do aumento da concentração de Cr também relacionado a esta segregação que limita a passagem de corrente pelo contorno de grão. Os sistemas preparados pelo método Pechini mostraram-se mais resistivos nas curvas I-V em relação aos sistemas preparados por mistura de óxidos. A adição de Cr levou a uma diminuição do coeficiente de não-linearidade uma vez que o Cr parece segregar no contorno de grão, diminuindo o tamanho de grão, levando a uma microestrutura porosa e conseqüentemente degradando as propriedades varistoras dos sistemas. / Abstract: The influence of Cr in the electrical conductivity and in microstuctural properties of SnO2-based ceramics was studied. In addition, the influence of preparation method in the characteristics of ceramics precursor powders and in the characteristics and properties of the resultant ceramics was investigated. SnO2-Mn-Nb systems with varied Cr concentration were prepared by the conventional method of mixture of oxides and by Pechini method (organic route). Surface area measurements (BET method), X-ray diffraction, infrared spectroscopy and scanning electronic microscopy were utilized to characterize the prepared powders. Analysis of electrical conductivity and complex impedance confirm a decrease of conductivity as a function of the increase of Cr concentration also related to this segregation that limits the current passage by the grain boundary. The systems prepared by Pechini method turned out to be more resistive in the I-V curves than systems prepared by mixture of oxides. The Cr addition led to a decrease of non-linear coefficient since the Cr seem to segregate on grain boundary, decreasing the grain size, leading to a porous microstructure and, consequently, degraded of varistors properties of systems. / Mestre

This investigation is a theoretical study of the influence of defects of finite volume on the electrical conductivity in the quantum size effect regime. Correction terms to existing equations are derived, and a physical explanation of the results is given. Many macroscopic properties of films exhibit an oscillatory dependence on thickness when the thickness is comparable to the de Broglie wavelength of an electron at the Fermi surface. This behavior is called the quantum size effect. In very thin films, scattering from surfaces, phonons, and crystal defects plays an increasingly important role. In this investigation the influence of scattering centers (defects) in semimetal films on the electrical conductivity is explored by extending existing work to include scattering centers of finite range. The purpose of this study is to determine the overall change in the conductivity and the alteration of the amplitude of the oscillations. The Boltzmann transport equation is the starting point for the calculation. An equation for the vector mean free path is derived, and a solution is obtained by the iterative process. The relaxation approximation need not be made since the vector mean free path is determined. The sample is a thin slab that is infinite in two dimensions. The assumption is made that the electron wave function is zero at the walls of the sample. It is further assumed that there is a known number of randomly located defects within the slab. The noninteracting electrons are considered free except in the vicinity of the scattering centers. The defects are characterized by a potential that is constant within a small cube and zero outside of it. This approach allows the potential matrix elements to be evaluated by expanding in a power series. The electrical conductivity is calculated for three defect sizes, and a comparison is made to 3-function (infinitely small) scattering centers. An overall decrease in the conductivity is found in each case, and the absolute magnitude of the oscillations is decreased. The percentage of oscillation, however, is increased. The general conductivity decrease is attributed to the increase in the scattering range. The change in the amplitude of the oscillations is explained by analyzing the transition probabilities to available energy states at critical film thicknesses. The oscillations are found to be a result of transitions from states with large energies in the plane of the film to states with small energies in the plane of the film. The number of electrons occupying the various states is determined at critical film thicknesses, and a comparison with the conductivity equation shows excellent agreement.

Riparian buffers have been created as a sustainable and effective way to combat the harmful effects of excess nitrogen and soil salinity in riparian settings. The goal of this research was to determine what species will I) germinate in saline environments and II) establish and produce sufficient biomass while being exposed to increased nitrogen. Incubation of eight native riparian graminoid species were evaluated for their ability to germinate in MgSO4-induced salinity. In a greenhouse study, seven riparian graminoid species were evaluated to quantify their ability to survive and take up nitrogen, mimicking buffer strips exposed to high inputs of runoff nitrogen. Slender wheatgrass and green needlegrass were able to germinate successfully when exposed to MgSO4 with EC levels up to 16 dS m-1 and 8 dS m-1, respectively. Of the graminoid species tested, smooth brome yielded sufficient biomass and nitrogen uptake percentages in a controlled setting.

Nitrogen is required by plants in large quantities and its deficiency is mostly related to reduction in crop production. A study was conducted to assess the importance of nitrogen in tomato (Lycopersicon esculentum Mill.) transplant production. Transplants were propagated at 0, 30, 60, 90, and 120 mg∙L-1 N applied as NH4NO3 while 30 mg∙L-1 P applied as NaH2PO4 and 30 mg∙L-1 K as KCl were used. Fergitation was done by floating cavity trays in nutrient solution until the medium reached field capacity. The experiment was arranged in a randomized complete block design (RCBD) with four replications. Sampling was initiated at 21 days after sowing and was done weekly until the transplants were ready for transplanting (when transplants could be pulled out of the cavity easily without breaking) at 42 days after sowing. Nitrogen supply had a pronounce influence on the transplant root and shoot growth. Observations throughout the experiment indicated that increased nitrogen application favoured shoot growth which is an indication that most of the assimilates were partitioned to shoots rather than to roots. Nitrogen application of 120 mg∙L-1increased fresh shoot mass and subsequently enhanced dry shoot mass. As nitrogen was increased from 0 to 120 mg∙L-1, it further promoted relative growth rate, specific leaf area, leaf mass ratio, leaf area ratio, plant chlorophyll content, leaf tissue nitrogen and improved the pulling success. At 42 days after sowing, a quality transplant that was produced with 90 mg∙L-1 N, had a root to shoot ratio of 0.16, leaf mass ratio of 0.86, root mass ratio of 0.13, leaf area of 594 cm2, plant chlorophyll content of 33, leaf tissue nitrogen of 32 g∙kg-1, specific leaf area of 194 cm2∙mg-1, leaf area ratio of 167.7 cm2∙mg-1, relative growth ratio of 0.31 cm∙mg-1∙wk-1 and 100% pulling success. This transplant proved to be ideal for the production of tomato as compared to other treatment combinations that were employed. Another glasshouse experiment was conducted to determine the influence of electrical conductivity (EC) and or nutrient solution composition on growth, yield and quality parameters in tomato. The pots were arranged in a randomized complete block design (RCBD). One plant per pot represented an experimental unit. Four EC treatments were used that consisted of 1.12, 2.24, 4.48 and 6.72 mS∙cm-1. Each treatment was replicated six times. Distilled water was used for irrigation water to maintain the required pH, which was 5.5 to 6.2 throughout the duration of the study, and cocopeat was used as substrate. Salinity inhibited growth (shoot length) and yield (average fruit mass, fruit diameter and fruit circumference) at the highest concentration of 6.72 mS∙cm-1. However, it did not significantly affect number of trusses, number of fruits and stem diameter, rather tomato quality was improved in terms of total soluble solids. Although tomato fruits grown at 6.72 mS∙cm-1 were relatively smaller than fruits grown at 1.12, 2.24 and 4.48 mS∙cm-1 treatments respectively, they had higher acidity, increased soluble solids and higher sugar content which are all qualities required by the tomato processing industry. Increasing the concentration of the solution from 1.12 to 6.72 mS∙cm-1 increased the %Brix from 3.9 to 6.1% while titratable acidity was also increased from 3.3 to 5.7%, respectively. The incidents of blossom end rot were higher (6.3%) at concentration of 6.72 mS∙cm-1 as compared to 1.12 mS∙cm-1 concentration, which was 0.5%. / Dissertation (MScAgric)--University of Pretoria, 2014. / tm2015 / Plant Production and Soil Science / MScAgric / Unrestricted

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21443号 / 理博第4436号 / 新制||理||1637(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 北川 宏, 教授 竹腰 清乃理, 教授 吉村 一良 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM