Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Digitized by Kansas State University Libraries

A substantial amount of research has already been undertaken towards creating commercially viable organic photovoltaics (OPVs). This is due to the potential use of OPV cells as an inexpensive source of renewable energy. There are many factors to consider in OPV cell design, including photo-active materials, cell architecture and electrode selection. However, additional interlayers for use between the photo-active materials and the electrodes were identified to be as important and need to be developed to optimise cell performance. The work presented here focuses on the influence of various metal oxide hole extracting layers in different OPV systems. Metal oxides such as molybdenum oxide (MoOx) have shown great promise in polymer cells as a hole extracting layer, and here we investigate their use in small molecule cells. An optimised MoOx layer thickness of 5 nm provides a ~ 60 % increase in overall power conversion efficiency (ηp) for chloroaluminium phthalocyanine (ClAlPc) / fullerene (C60) cells in comparison to those fabricated on bare ITO. A similar improvement of ηp is reported when using the MoOx layer in a boron subphthalocyanine chloride (SubPc) / C60 system. For both high ionisation potential donor materials, the cells containing MoOx achieve a significantly higher open circuit voltage (Voc). Conversely, cells utilising the lower ionisation potential donor materials such as copper phthalocyanine (CuPc) and pentacene produce similar Voc values when deposited on both ITO and MoOx. Hence, the ηp is marginally reduced with the MoOx layer. To attain a deeper understanding, the factors behind these performance differences were explored by UV-vis absorption spectroscopy, ultra-violet photoemission spectroscopy (UPS), X-ray diffraction (XRD) and atomic force microscopy (AFM). Thermally evaporated vanadium oxide (V2Ox) was used as an alternative hole extracting layer to MoOx, achieving analogous performance to MoOx when used in SubPc / C60 and CuPc / C60 cells. The electronic properties of the V2Ox layer are investigated using UPS, and it is demonstrated to have substoichiometric n-type character in contrast to the p-type behaviour previously reported. Additionally, the in-situ fabrication and characterisation of organic layers using UPS indicate Fermi level pinning of the organic to the metal oxide. A solution processed vanadium oxide (V2Ox(sol)) layer was developed and characterised as an alternative method of layer fabrication. The atmospheric processing conditions are found to have a dramatic effect on cell performance, and are studied using x-ray photoelectron spectroscopy (XPS). Layers spin-coated under a nitrogen atmosphere exhibit a larger composition of V4+ states. Kelvin probe and UPS experiments indicate the V2Ox(sol) is also a high work function, n-type layer, with the V2Ox(sol) hole extracting layer producing similar cell performance to the thermally evaporated metal oxide layers. Cells deposited on the V2Ox(sol) layer demonstrate good operational stability characteristics, outperforming a commonly used solution processable hole extracting layer.

The study of electronic noses has been an active area of research for over 25 years. Commercial instruments have been successfully deployed within niche application areas, for example, the food, beverage and pharmaceutical industries. However, these instruments are still inferior to their human counterparts and have not achieved mainstream success. Humans can distinguish and identify many thousands of different aromas, even at very low concentration levels, with relative ease. The human olfactory system is extremely sophisticated, which allows it to out-­perform artificial instruments. Though limited, artificial instruments can provide a lower cost option to specific problems and can be an alternative to the use of organoleptic panels. Most existing commercial electronic nose (e-­nose) instruments are expensive, bulky, desktop units, requiring a PC to operate. In addition, these instruments usually require a trained operator to gather and analyse the data. Motivated to improve the performance, size and cost of e-­nose instruments, this research aims to extract biological principles from the mammalian olfactory system to aid the implementation of a portable e-­nose instrument. This study has focused on several features of the biological system that may provide the key to its superior performance. Specifically, the large number of different olfactory receptors and the diversity of these receptors; the nasal chromatograph effect; stereo olfaction; sniff rate and odour conditioning. Based on these features, a novel, portable, cost effective instrument, called the Portable e-­Mucosa (PeM), has been designed, implemented and tested. The main components of the PeM are three sensor arrays each containing 200 carbon black composite chemoresistive sensors (totalling 600 sensors with 24 different tunings) mimicking the large number of olfactory receptors and two gas chromatographic columns (coated with non-­polar and polar compounds to maximise the discrimination) emulating the “nasal chromatograph” effect of the human mucus. A preconcentrator based on thermal desorption is also included as an odour collection system to further improve the instrument. The PeM provides USB and Multimedia Memory Card support for easy communication with a PC. The instrument weighs 700g and, with dimensions of 110 x 210 x 110 mm, is slightly larger than the commercial Cyranose 320 (produced by Smiths Detection). This novel instrument generates ‘spatio-­temporal’ data and when coupled with an appropriate pattern recognition algorithm, has shown an enhanced ability to discriminate between odours. The instrument successfully discriminates between simple odours (ethanol, ethyl acetate and acetone) and more complex odours (lavender, ylang ylang, cinnamon and lemon grass essential oils). This system can perhaps be seen as a foundation for a new generation of e-noses.

The term extractives defines chemical compounds of different classes that can be extracted from wood or bark by means of polar or non-polar solvents. Extractives are derived mostly from the metabolic processes of the tree, particularly the sapwood to heartwood transformation. The first objective of the research was to study the distribution of extractives within Sitka spruce trees at different heights in the trunk, as well as the distribution between bark, rootwood, knotwood, heartwood and sapwood. The second aim of the work was to learn about the influence of yield class, site elevation, North/East location and thinning on the extractives content and composition of Sitka spruce across Scotland. The samples were sawdust obtained in different ways from either discs, knots or roots sawn from Sitka spruce trees freshly cut in the forest, or collected during the coring of trees from 64 sites all around Scotland and northern England. The extraction was carried out on Soxhlet extractors using acetone as solvent. Two analytical techniques were used: gas chromatography and Fourier transform infrared spectroscopy. The results of the research showed that the extractive content and composition of Sitka spruce differed according to the type of wood studied with the largest amount detected in bark and the lowest in heartwood and sapwood. The last two types of wood were studied in more detail, showing that the difference in extractive content between heartwood and sapwood was consistent at all heights in the trunk. The chromatographic analysis of heartwood, sapwood, knotwood, rootwood and bark showed that their compositions differed slightly from published data on Norway spruce.

This thesis aims to describe the ultra-rapid synthesis of a number of important transition metal carbides as well as investigating their reaction mechanisms. 4 binary systems are discussed; Nb-C, Mo-C, Ta-C and W-C, and work carried out on the ternary system, Nb-Ta-C, is also evaluated. Carbide production was investigated from both the oxide and elemental precursors. Ultra-rapid synthesis has been achieved through the development of a reproducible experimental technique and the investigation into a plethora of reaction variables as well as microwave applicators and powers. This resulted in, specifically within the single mode cavity, the completion of the majority of reactions within 20 s. Further development was then built upon the direct relationship observed between phase fraction results (obtained from Powder X-ray Diffraction (PXD) data), in-situ temperature and ex-situ dielectric property measurements; allowing reaction profiles of the various carbides to be mapped, as well as a crucial understanding of the effects of microwave energy on materials at various temperatures. Powder Neutron Diffraction (PND) was also used to evaluate product purity and the C occupancy of the final products, revealing non-stoichiometry which relates directly to the Tc onset observed for the superconducting transition metal carbides. This, in turn, allowed the trends observed for the ternary carbides to be explained, a linear trend does not exist between Tc and C occupancy. In an effort to develop on the understanding of solid state microwave heating, in-situ reaction monitoring techniques were investigated. Through the use of thermal imaging and high speed photography, the W-C system was observed during the crucial initial stages of the reaction process. The information obtained both corroborated previously collected data and allowed a possible reaction mechanism to be alluded to. The observation of localised heating, prior to the beginning of carbide formation, suggests possible high temperatures far exceeding those observed by optical pyrometry. This could well explain the rapid reaction times as well as suggest an interaction mechanism between carbon, an efficient microwave absorber, and tungsten, a low dielectric loss metal.

In recent years the industrial application of advanced control techniques for the process industries has become more demanding, mainly due to the increasing complexity of the processes themselves as well as to enhanced requirements in terms of product quality and environmental factors. Therefore the process industries require more reliable, accurate, robust, efficient and flexible control systems for the operation of process plant. In order to fulfil the above requirements there is a continuing need for research on improved forms of control. There is also a need, for a variety of purposes including control system design, for improved process models to represent the types of plant commonly used in industry. Advanced technology has had a significant impact on industrial control engineering. The new trend in terms of advanced control technology is increasingly towards the use of a control approach known as an “intelligent” control strategy. Intelligent control can be described as a control approach or solution that tries to imitate important characteristics of the human way of thinking, especially in terms of decision making processes and uncertainty. It is also a term that is commonly used to describe most forms of control systems that are based on artificial neural networks or fuzzy logic. The first aspect of the research described in the thesis concerns the development of a mathematical model of a specific chemical process, a pH neutralization process. It was intended that this model would then provide an opportunity for the development, implementation, testing and evaluation of an advanced form of controller. It was also intended that this controller should be consistent in form with the generally accepted definition of an “intelligent” controller. The research has been based entirely around a specific pH neutralization process pilot plant installed at the University Teknologi Petronas, in Malaysia. The main feature of interest in this pilot plant is that it was built using instrumentation and actuators that are currently used in the process industries. The dynamic model of the pilot plant has been compared in detail with the results of experiments on the plant itself and the model has been assessed in terms of its suitability for the intended control system design application. The second stage of this research concerns the implementation and testing of advanced forms of controller on the pH neutralization pilot plant. The research was also concerned with the feasibility of using a feedback/feedforward control structure for the pH neutralization process application. Thus the study has utilised this control scheme as a backbone of the overall control structure. The main advantage of this structure is that it provides two important control actions, with the feedback control scheme reacting to unmeasured disturbances and the feedforward control scheme reacting immediately to any measured disturbance and set-point changes. A non-model-based form of controller algorithm involving fuzzy logic has been developed within the context of this combined feedforward and feedback control structure. The fuzzy logic controller with the feedback/feedforward control approach was implemented and a wide range of tests and experiments were carried out successfully on the pilot plant with this type of controller installed. Results from this feedback/feedforward control structure are extremely encouraging and the controlled responses of the plant with the fuzzy logic controller show interesting characteristics. Results obtained from tests of these closed-loop system configurations involving the real pilot plant are broadly similar to results found using computer-based simulation. Due to limitations in terms of access to the pilot plant the investigation of the feedback/feedforward control scheme with other type of controllers such as Proportional plus Integral (PI) controller could not be implemented. However, extensive computer-based simulation work was carried out using the same control scheme with PI controller and the control performances are also encouraging. The emphasis on implementation of advanced forms of control with a feedback/feedforward control scheme and the use of the pilot plant in these investigations are important aspects of the work and it is hoped that the favourable outcome of this research activity may contribute in some way to reducing the gap between theory and practice in the process control field.

The work in this thesis had two main aims. The first aim was to study the use of a number of precipitation methods to control the size and morphology of precursor phosphor materials for potential applications in a new generation of high definition and field emission displays. The morphological and luminescent characteristics of these precursor phosphor materials were studied after they were annealed to form their respective luminescent oxides using electron microscopy and light measuring techniques. The first set of experiments presented describes the development of a range of spherical submicron europium-doped yttrium oxide phosphor particles and their optimisation for use in the aforementioned applications. A homogeneous precipitation technique exploiting a hydrothermal decomposition of urea that provides hydroxycarbonate phosphor precursor ligands is at the centre of this work. In the presence of rare earth element nitrates the hydroxycarbonate ligands form spherical phosphor precursor particles that after annealing yield the luminescent oxides. This is followed by the presentation of a novel synthetic method using a micellar phase of rare earth element chlorides, after annealing, yielding europium-doped yttrium oxide. This method produces a variety of morphologies with crystallites as small as a few nanometres and up to hundreds of nanometres. Next is described a new precipitation method using ammonia and carbon dioxide gases that are introduced in a controlled manner into a solution of rare earth element chlorides at room temperature. Rare earth element hydroxycarbonates rapidly precipitate upon supersaturation, yielding a range of morphologies and particles sizes. The second aim of the thesis was to prepare a novel range of three-dimensional photonic band gap materials composed of conventional phosphor materials.

This project was aimed at developing an understanding of the issues faced by the power generation industry in the area of handling of coal/biomass mixes for co-firing. This project looked into two types of coals (Russian and Dawmill) and two types of biomasses (cereal co products (CCP) and milled palm nuts (MPN)) that are being extensively co-fired (as a mix) in the UK coal power plants and are known to cause a wide range of handling issues. The key objectives of the project included: Identifying a cost effective method of flow property measurement: Developing an understanding of the flow of coal/biomass mixes, and Identifying the handling problems in bunkers and design of bunker units to suit coal/biomass mixes flow. The main contribution of the project was the determination that caking due to mould growth over time, is a key handling issue and that different biomasses behave differently when added to coal in different mix ratios as far as caking it concerned. Another contribution is the Best Practice Guide that was prepared at the completion of the work as a recommendation to industry (which are using co-firing as method of power generation) and also for academia in the field.

Tissues constituting mammalian organisms are finitely organised 3-D multicellular structures where cell-cell and cell-matrix interactions are important modulators of functionality. The liver, being the site of metabolism in mammals, is extensively employed in in-vitro studies such as toxicology, drug testing and liver replacement. Most existing liver models have been static, homogenous 2-D models which have shown limited morphological and functional characteristics of in-vivo liver. With the improved understanding of the liver, these models became more sophisticated to comprise various liver and non-liver cell types, various configurations of extracellular matrix and complex scaffold supports, including fluidic systems. Fluidic supports for liver cells in-vitro are reported in this work and two different types were investigated. The first one was a glass based micro fluidic system with hexagonal structure to mimic the liver lobule. The second one was a standard flatplate fluidic chamber made of plastic (Ibidi channel). For the purpose of improving the attachment of the cells and the performance of the bioreactors examined, various substrate coating procedures were evaluated. The main coating techniques employed were collagen in two forms, adsorbed and gel, and plasma polymerised allylamine (ppAAm). The plasma coating procedures utilised in this work changed the surface properties of the substrate used by increasing the levels of nitrogen and improving hydrophilicity as demonstrated by x-ray photoelectron spectroscopy and contact angle measurements. The ppAAm penetrated both etched glass channels of the hexagonal bioreactor and the flat-plate chamber. The ppAAm films on etched glass channels had similar properties to the films produced on the glass surrounding the channels and coverslips. The ppAAm films obtained in the flat-plate chamber were different and they were characterised with a gradient of chemicals and hydrophilicity. This was because the Ibidi chamber is a closed environment and the plasma vapour infiltrated through the inlet and outlet at the ends of the channel. The attachment and functionality of primary rat hepatocytes seeded onto ppAAm films were evaluated using ppAAm coated coverslips and compared to coverslips coated with collagen gel. This demonstrated that both collagen gel and ppAAm improved the attachment, albumin secretion and 7-Ethoxyresorufin-O-deethylase (EROD) activity of the cells compared to uncoated glass. The hexagonal glass bioreactor showed poor attachment of liver cells and this was enhanced with ppAAm coating. The Huh-7 cells incubated into ppAAm coated hexagonal bioreactor died and detached after incubation with media flow. One of the reasons for this was poor cellular attachment. An improved attachment, but not viability, was observed when the cells were seeded using the biotin-avidin technique. The ppAAm coated flat-plate chamber demonstrated low adhesion of primary rat hepatocytes. However, these channels showed good attachment when collagen type I was adsorbed onto the surface. The viability and functionality, when measured using albumin secretion and EROD, of primary rat hepatocytes were maintained for 5 days in closed fluidic circuit in mono-culture and co-culture with 3T3 cells. These promising results could be exploited to further develop these systems for in-vitro culture of liver cells.