A process has been developed to make the dielectric layer for organic thin-film transistors (OTFTs) in a roll-to-roll vacuum web coater environment. This dielectric layer combined with an organic semiconductor layer and metal layer deposited in vacuum allows a solvent-free process to make organic/inorganic multilayer structures for thin-film electronic devices on a flexible substrate at, potentially, high speed. The polymeric gate dielectric layers were fabricated by flash evaporation of acrylic monomers onto a polymer film with pre-patterned metal gates followed by radiation curing by electron beam, ultra-violent light (UV) or plasma. With a non-polar dielectric surface, charge carrier mobility (μ) of 1 cm²-V^-1s^-1; on/off curren ratio of 10⁸, sub-threshold swing (SS) of 0.3 V/decade and saturated output curve were routinely achieved in dinaphtho-[2,3-b:2'3'-f]thieno[3,2-b]thiophene (DNTT) transistors with dielectric layer of tripropylene glycol diacrylate (TPGDA) of ~400 nm. Apart from the TPGDA, monomer formulas including 1,6-Hexanediol diacrylate (HDDA) as well as several commercial acrylic resins have been used to make the dielectric layer. The highest areal capacitance of 41nF-cm^-2 was achieved with a pin-hole free film of less than 100 nm made of an acrylate mixture resin. A non-polar dielectric surface treatment layer has been developed based on flash evaporation of lauryl acrylate and HDDA mixture. The transistors with the buffer layer showed constant performance and a mobility fivefold greater than those of untreated samples. The effect of humidity, oxygen, and light during switching cycles of both pentacene and DNTT transistors were studied. Water and oxygen/illumination had a distinct effect on both pentacene and DNTT transistors. Oxygen leads to acceptor-like charge traps under illumination, which shifted the turn-on voltage (V_to) to more positive values. In contrast, water in transistors gave rise to donor-like charge traps, which shifted the V_to and the threshold voltage (V_T) more negatively. The DNTT devices showed good stability in dry air without encapsulation, while pentacene transistors degraded with either repeating measurement or long term storage. A DNTT transistor with a PS-coated TPGDA dielectric layer showed stable drain current (I_d) of ~105A under bias stress of the gate voltage (em>V_g) of -20V and the drain voltage (em>V_d) of -20V for at least 144 hours. The V_to shift after the stress was less than 5 V and was recoverable when the device was kept in dry air for a few days. Possible reasons for the V_to shift have been discussed.

A 25% niobium substituted sitinakite was exchanged with strontium as time resolved X-ray diffraction data was collected. The structural modeling of this data by Rietveld method1 has lead to the determination of the atomic positions of the ions and unit cell parameters as strontium occupancy increases. The starting material of the exchange experiment is the protonated phase, H2Nb0.67Ti1.33SiO7·1.9 H2O, with space group P42/mcm2,3. Once strontium (Sr2+) enters the unit cell, extra-framework H2O molecules shift to provide the necessary hydration coordination. These new positions of H2O result in a lowering of symmetry to the P-42m space group, and it is thought that the new hydrogen bonding network serves to enhance strontium ion diffusion into the channels of sitinakite. Exchange of strontium into the microporous material reaches a maximum fractional occupancy of 21% when a 10.0 mM strontium ion solution is forced over the powdered material. Sequestration of strontium into this material has contributed valuable information to the study of microporous materials and ion exchange chemistries.

Imaging membrane potential is a promising technique in the elucidation of the interactions of large networks of neurons. The membrane potential in a neuron varies as an action potential, the basic electrical signal of neuronal communication, travels along the length of the cell. Voltage sensitive dyes play a key role by providing an optical readout of the electric field generated across a neuron membrane by the action potential. However, none of the dyes reviewed in Chapter 1 generate sufficient signal change with changes in membrane potential; this sensitivity problem limits the ability of the imaging membrane potential technique to allow the high spatial and temporal resolution necessary for neuronal networks to be better understood. This thesis features two avenues of research that are expected to result in the necessary enhancements to voltage sensitive dyes to improve the signal change. The first avenue is based on the effect of an electric field upon the non-linear optical properties of a porphyrin macromolecule. The encouraging field sensitivity of a previous porphyrin monomer voltage sensor inspired an investigation which identified optimisations to enhance the voltage sensitivity (Chapter 2). The design, synthesis and initial characterisation of optimised porphyrin voltage sensors is detailed in Chapter 3. The second avenue is based on the effect of an electric field upon the rate of intermolecular electron transfer. In a suitably designed dye, the competition between electron transfer and fluorescence, following excitation by incoming light, allows the fluorescence intensity to act as an optical indicator of the electron transfer rate. New dyes were rationally designed and synthesised, as this effect had not been applied to voltage sensitive imaging before the research detailed in Chapter 4. The challenging purification of the new amphiphilic dyes synthesised also inspired research into a novel testing method which does not require amphiphilic dyes (Chapter 5).

This thesis investigates the mechanisms behind natural silk spinning by integrating rheology, spectroscopy and small angle scattering to better understand this process and to guide our efforts towards mimicking Nature’s ways of producing high performance fibres. As a result of natural selection, arthropods such as spiders and moths have evolved the ability to excrete silk proteins in a highly controlled manner. Spun from liquid feedstocks, silk fibres are used ex vivo to build structures with mechanical properties currently unmatched by industrial filaments. As yet, relatively little attention has been directed to the investigation of spinning under biologically relevant conditions. To better understand how and why silk is spun, this thesis bridges the gap between liquid silk flow properties and structure development. To directly connect the two, I have developed and deployed novel experimental platforms that combine infrared spectroscopy and small angle scattering with rheology. This approach has clarified long-standing ambiguities on the structural root of silk’s apparently complex flow properties. Small angle scattering revealed the length scales involved in the flow induced solidification under a range of spinning conditions. Mo reover, infrared spectroscopy offered a unique perspective into silk’s formation process immediately after excretion. In a similar manner to the post-extrusion tuning of the properties of partly solidified spider silk filaments, this thesis has revealed that silkworm silk fibres are far from completely formed once excreted. One might describe the filaments of mulberry silkworm as seeded molten polymers that form its hydrogen bonding network and crystallises slowly on site. Consequently, it enlightens that post-spinning conditions are equally paramount for silkworm silk, giving an explanation for the relatively poorer mechanical properties. The comparison of silks from a range of species, allowed this hypothesis to be extended to wild silkworm silk. My insights into spinning had the fortuitous repercussion of facilitating silk fibre solubilisation leading to the development of better artificial silk feedstocks flowing like native silks. With these findings, I believe we are now in an improved position to conceive artificial fibres with properties rivalling those of Nature.

The thesis reports improvements in the characterization techniques for stress and texture in crystalline materials by x-ray and neutron powder diffraction. Furthermore, advances are made in texture evolution modelling and validation against experimental observations. In the beginning, the fundamental assumption of diffraction strain analysis is numerically examined and verified, namely, that the lattice parameter value determined from fitting the diffraction pattern is equal to the average lattice parameter within the gauge volume. Next, the task of shear strain determination from powder diffraction measurements is addressed. A method is developed and implemented for the complete 2D strain tensor determination from the multi-directional energy-dispersive x-ray diffraction patterns. The method not only offers a way to evaluate the shear strain, but also provides a better overall strain averaging approach. Rotation and translation of sample and/or detectors in powder diffraction mode can effectively increase the pole figure coverage and thus the accuracy of texture determination. However, the movements also introduce uncertainties and aberrations into data analysis due to the changes in the diffraction volume and transmitted intensity. In order to overcome these problems, accurate <strong>single exposure</strong> texture characterization techniques are proposed based on several different powder diffraction setups. Numerical analyses are carried out to prove that any simple texture in cubic polycrystals can be effectively determined using single exposure Debye-Scherrer diffraction pattern analysis. Several experiments are reported on collecting Debye-Scherrer diffraction patterns, multi-directional energy-dispersive x-ray diffraction patterns and multi-directional TOF neutron setup. Efficient data processing procedures of the diffraction patterns for ODF determination are presented. Crystal plasticity finite element models are developed to model the texture evolution in polycrystalline engineering samples during manufacturing. In the present thesis, quantitative measures extracted from orientation distribution function are employed to make precise comparison between the model and experiment. Unlike the simple uni-axial compression and tension considered in the literature, in the present thesis the complex texture evolution during linear friction welding is modelled as a sequence of different shear deformations.

The development of a vasculature within a tissue-engineered construct is one of the largest hurdles to successful bone regeneration. This thesis investigates methods to increase vasculature of such transplanted constructs, based on in vivo transplant studies and in vitro analysis of cell behaviors. A syngeneic mouse model in immunocompetent mice was developed and analyzed for both osteogenesis and hematopoiesis. This study demonstrates that syngeneic bone marrow stromal cells (BMSCs) are not rejected by the host, provided the strain of mice is sufficiently inbred. Additionally, an effective protocol was developed for the isolation of endothelial cells (ECs) from the bone marrow of mice. Two different sets of materials for this study were analyzed, both collagen based, and the GelfoamTM scaffold was found to possess advantages over synthesized collagen or collagen/hydroxyapatite composites, although only for mouse and not human bone transplantation. In order to gain rapid and integrated vasculature formation within the transplant, attempts were made to increase both (de novo) vasculogenesis and angiogenesis (ingrowth) from the surrounding tissue. For the former, transplant studies were combined with in vitro osteogenic calcification studies. Direct co-culture of the BMSCs and ECs increased osteogenic calcification and was monitored by using both alizarin red S quantification and quantitative polymerase chain reaction. Angiogenesis (as assessed by cell migration) was studied by various motility and chemotaxis assays in vitro, as well as through use of a directed in vivo angiogenesis assay. Growth factors, particularly TGF-β1 and BMP-4, were found to increase cell movement in these systems. In conclusion, we show that although much work remains to be done in order to increase the vasculature in bone transplants, systematic combination of in vivo and in vitro assays can elucidate the nature behind this crucial process in this context.

Human dental tissues are fascinating nano-structured hierarchical materials that combine organic and mineral phases in an intricate and ingenious way to obtain remarkable combinations of mechanical strength, thermal endurance, wear resistance and chemical stability. Attempts to imitate and emulate this performance have been made since time immemorial, in order to provide replacement (e.g. in dental prosthodontics) or to develop artificial materials with similar characteristics (e.g. light armour). The key objectives of the present project are to understand the structure-property relationships that underlie the integrity of natural materials, human dental tissues in particular, and the multi-scale architecture of mineralized tissues and its evolution under thermal treatment and mechanical loading. The final objective is to derive ideas for designing and manufacturing novel artificial materials serving biomimetic purposes. The objectives are achieved using the combination of a range of characterization techniques, with particular attention paid to the synchrotron X-ray scattering (Small- and Wide-Angle X-ray Scattering, SAXS and WAXS) and imaging techniques (Micro Computed Tomography), as well as microscopy techniques such as Environmental Scanning Electron Microscopy (ESEM), Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). Mechanical properties were characterized by nanoindentation and photoelasticity; and thermal analysis was carried out via thermogravimetric analysis (TGA). Experimental observations were critically examined and matched by advanced numerical simulation of the tissue under thermal-mechanical loading. SAXS and WAXS provided the initial basis for elucidating the structure-property relationships in human dentine and enamel through in situ experimentation. Four principal types of experiment were used to examine the thermal and mechanical behaviour of the hierarchical structure of human dental tissue and contributed to the Chapters of this thesis: (i) In situ elastic strain evolution under loading within the hydroxyapatite (HAp) in both dentine and enamel. An improved multi-scale Eshelby inclusion model was proposed taking into account the two-level hierarchical structure, and was validated against the experimental strain evaluation data. The achieved agreement indicates that the multi-scale model accurately reflects the structural arrangement of human dental tissue and its response to applied forces. (ii) The morphology of the dentine-enamel junction (DEJ) was examined by a range of techniques, including X-ray imaging and diffraction. The transition of mechanical properties across the DEJ was evaluated by the high resolution mapping and in situ compression measurement, followed by a brief description of the thermal behaviour of DEJ. The results show that DEJ is a narrow band of material with graded structure and mechanical properties, rather than a discrete interface. (iii) Further investigation regarding the thermo-mechanical structure-property relationships in human dental tissues was carried out by nanoindentation mapping of the nano-mechanical properties in ex situ thermally treated dental tissues. (iv) In order to understand the details of the thermal behaviour, in situ heat treatment was carried out on both human dental tissues and synthetic HAp crystallites. For the first time the in situ ultrastructural alteration of natural and synthetic HAp crystallites was captured in these experiments. The results presented in this thesis contribute to the fundamental understanding of the structure-property integrity mechanisms of natural materials, human dental tissues in particular. These results were reported in several first author publications in peer-reviewed journals, conference proceedings, and a book chapter.

This thesis reports the investigation of molecular materials for hydrogen storage applications with a particular emphasis on alkali-metal amidoboranes. I have developed new routes for the synthesis of $alpha$-LiNH$_{2}$BH$_{3}$ and NaNH$_{2}$BH$_{3}$, and have studied their hydrogen storage properties by thermogravimetric analysis, variable temperature X-ray and neutron diffraction and inelastic neutron scattering. I report the synthesis and full structural characterization of two new materials, KNH$_{2}$BH$_{3}$ and $beta$-LiNH$_{2}$BH$_{3}$, and have performed initial studies on a tetragonal phase of a variant of LiNH$_{2}$BH$_{3}$ with a preliminary structure solution. I have also performed variable temperature neutron diffraction on ammonium borodeuteride, ND$_{4}$BD$_{4}$, and report the full structural characterisation of the three phases identified as a result of these measurements. Furthermore, variable temperature inelastic neutron scatting (INS) measurements were performed on ammonia borane, NH$_{3}$BH$_{3}$, and the results are discussed in terms of crystallographic phase changes.

This thesis is devoted to the numerical and experimental investigation of residual stress and deformation in polycrystalline metallic alloys at different scales. The emphasis in the current study is placed on establishing the connection between the simulation of deformation by the Finite Element (FE) method and experimental characterisation by synchrotron X-Ray Diffraction (XRD). Of particular importance is the interpretation of modelling results and their validation by careful comparison with experimental data. The concept of eigenstrain was used extensively throughout the report to study the residual elastic strain distributions and their sources. A pseudo-thermal strain FE procedure was used systematically to simulate the residual stress states in samples and engineering components of different shape and dimensionality. The case of 1-D strain variation was considered using the example of a plastically bent bar. The direct and inverse problems of eigenstrain analysis were solved, and validated experimentally by the use of XRD and EDM slitting methods. A novel 2-D discrete inverse eigenstrain algorithm was proposed and implemented to reconstruct the residual stress distribution in a worn rail head. The link between the residual stress and deformation history was studied via thermo-mechanical modelling of the Linear Friction Welding (LFW) process. To advance the understanding of polycrystalline deformation behaviour across the scales, a crystal plasticity model was employed to simulate the elastic-plastic deformation behaviour of Ti-6Al-4V alloy. A post-processor was developed to extract the average elastic strains for orientation-specific grain groups and to compare them with XRD data. A “peak constructor” post-processor was developed that utilised the knowledge of both the elastic strain and dislocation density. In a further development step, a strain gradient crystal plasticity formulation was adopted to account for the local dislocation evolution. Intra-granular deformation analysis was carried out and micro-beam Laue experimental diffraction technique was used for validation. Thus, local lattice arrangement was studied at the microscopic, intragranular scale. Special attention was paid to the phenomenon of Laue spot “streaking”, indicative of the local lattice misorientation caused by dislocation activity during deformation. The results presented in this thesis contributed to the fundamental understanding of the residual stress and deformation in polycrystalline metallic alloys and lead to more than 20 publications in peer-reviewed journals and conference proceedings, which are listed in the Appendix.

Reduced-activation ferritic steels are considered as the primary candidate materials for structural applications within nuclear fusion power plants. It is known that by mechanically alloying ferritic steel powder with Y (usually in the form of Y₂O₃) then consolidating the material by hot isostatic pressing, a nanoscale dispersion of oxygen rich nanoclusters as small as ~2nm is introduced into the microstructure. This vastly improves high temperature strength and creep resistance, and the nanoclusters also act as trapping sites for helium and point defects produced under irradiation. In this thesis, the evolution of the oxide nanoclusters in a Fe-14Cr-2W-0.3Ti & 0.3Y₂O₃ ODS alloy was investigated primarily using atom probe tomography. The microstructure was characterised at various points during processing to give an insight into the factors influencing the formation of the nanoclusters. It was found that the nanoclusters nucleated during the mechanical alloying stage, then followed near classical nucleation and growth mechanisms keeping the same composition of ~8%Y, ~12%Ti,~25%O and ~45%Cr throughout. The formation and evolution of 5-15nm grain boundary oxides was also observed, and these were shown to form first as Cr₂O₃ particles that subsequently transform into a Y-Ti-O based oxide on further processing. The influence of mechanical alloying with 0.5wt.%Fe₂Y rather than 0.3wt.%Y₂O₃ was also investigated, and this showed that there was no difference in the final microstructure produced provided the level of Ti in the starting powder was tightly controlled. Without sufficient Ti, the nanoclusters were Y-O based and ~6nm diameter. Both the Y-O and Y-Ti-O nanoclusters were moderately stable on annealing at 1200°C for up to 100 hours, with only minimal coarsening observed. Ti was found not to influence the coarsening rate of the nanoclusters significantly. The stability of the oxide nanoclusters under irradiation was investigated by using Fe²⁺ ion irradiation to simulate displacement cascade damage in the ODS-Eurofer material (the official European candidate material for testing in the ITER fusion test reactor). Doses up to ~6 dpa at 400°C were used, and there was no significant change to the nanocluster distribution. However segregation of Mn to dislocations was observed after irradiation. These results indicate that ODS steels are good candidate structural materials, as the microstructure is stable at high temperature and under irradiation. The starting powders, and processing parameters need to be tightly controlled in order to produce the optimal material for use in service.