A study of InGaAs channel heterostructure field effect transistors (HFETs) on GaAs substrates was undertaken utilizing the low pressure organometallic chemical vapor phase epitaxial (OMVPE) growth technique. Excellent quality HFET material properties were obtained for a split level donor structure, in which the Schottky gate was placed on an undoped AlGaAs layer grown on top of the doped AlGaAs donor layer. A one micron gate length fabrication process was developed to examine the device properties of these materials. A very strong correlation between material characterization results and device performance was observed in all cases. After demonstrating the consistency of the growth and fabrication processes using an $\rm In\sb{0.15}Ga\sb{0.85}As$ channel as a baseline, improvements to the device were undertaken. A delta doping technique was successfully developed and optimized using SIMS and Hall measurements to study the diffusion of the dopant spike. The sheet charge density and device transconductance increased for delta doped material. Increasing the channel indium content reduced the 2DEG mobility, but the expected improvements in transconductance and RF performance were observed. Critical layer thickness (CLT) issues were examined using $\rm In\sb{0.33}Ga\sb{0.67}As$ channel HFETs. Lightly dislocated material still exhibited superior device performance. An asymmetry in dislocation formation was observed, with dislocations forming preferentially in the (011) direction. Devices with a 50 A well width displayed a sharp drop in current in the (0-11) direction. The transconductance and RF properties were not as strongly affected. As the CLT was further exceeded the dislocation network became more symmetric and dense and device performance was severely degraded. A linear channel indium grading methodology was developed to delay the onset of misfit dislocations. Grading from 25-33% produced device properties commensurate with the ungraded 33% indium channel structure, without the asymmetry effects due to dislocation formation. Efforts at developing lattice constant engineered substrates were undertaken. Linear grading to 53% indium at a low growth temperature of 575$\sp\circ$C reduced the amount of three dimensional growth compared to other techniques.

Block copolymer (BCP) nanocomposites are an important class of hybrid materials in which the BCP guides the spatial location and the periodic assembly of the additives. High loadings of well-dispersed nanofillers are generally important for many applications including mechanical reinforcing of polymers. In particular the composites shown in this work might find use as etch masks in nanolithography, or for enabling various phase selective reactions for new materials development. This work explores the use of hydrogen bonding interactions between various additives (such as homopolymers and non-polymeric additives) and small, disordered BCPs to cause the formation of well-ordered morphologies with small domains. A detailed study of the organization of homopolymer chains and the evolution of structure during the process of ordering is performed. The results demonstrate that by tuning the selective interaction of the additive with the incorporating phase of the BCP, composites with significantly high loadings of additives can be formed while maintaining order in the BCP morphology. The possibility of high and selective loading of additives in one of the phases of the ordered BCP composite opens new avenues due to high degree of functionalization and the proximity of the additives within the incorporating phase. This aspect is utilized in one case for the formation of a network structure between adjoining additive cores to derive mesoporous inorganic materials with their structures templated by the BCP. The concept of additive-driven assembly is extended to formulate BCPadditive blends with an ability to undergo photo-induced ordering. Underlying this strategy is the ability to transition a weakly interacting additive to its strongly interacting form. This strategy provides an on-demand, non-intrusive route for formation of well-ordered nanostructures in arbitrarily defined regions of an otherwise disordered material. The second area explored in this dissertation deals with the incorporation of additives into photoresists for next generation extreme ultra violet (EUV) photolithography applications. The concept of hydrogen bonding between the additives and the polymeric photoresist was utilized to cause formation of a physical network that is expected to slow down the diffusion of photoacid leading to better photolithographic performance (25-30 nm resolution obtained).

Lyotropic liquid crystalline polymer solutions containing rod-like polymer can be oriented changing the concentration and/or applying a shear field. These solutions can be processed into fibers and films with well-developed, nearly uniaxial orientation providing high stiffness and rigidity. The solutions studied in this dissertation were comprised of rod-like poly-$p$-phenylene benzobisthiazole (PBZT) and coil-like Zytel${\sp{\circler}}$330 (Z33) in methane sulfonic acid and a methane sulfonic acid/poly-phosphoric acid blend. The isotropic-nematic phase boundary for the binary, ternary and quaternary systems was determined from the concentrations corresponding to the maxima in zero-shear viscosity. These "critical concentrations" were found to be in close proximity to the concentrations corresponding to the appearance of a nematic phase as determined by optical microscopy. For the binary and ternary solutions (in addition to many case studies), the theory of Flory for the prediction of the isotropic-nematic phase boundary based on thermodynamics provided an adequate fit of the concentrations corresponding to the viscosity maxima in addition to the critical concentrations observed by microscopy. For quaternary solutions, the aspect ratio of the PBZT component corresponding to the theoretical fit was significantly lower than that expected based on molecular structure. The unique structure of the PPA solvent component is believed to be attributed to this observation (non-negligible energies of interaction). For all of the solutions, a partitioning of the phases was found to occur in which the addition of the coil-like Z33 decreased the amount of rod-like PBZT necessary for the appearance of a biphasic region. The zero-shear viscosity for the isotropic solutions was determined almost entirely by the concentration of the PBZT component and not significantly influenced by the concentration of the Z33 component. However, the critical concentration was significantly reduced by the addition of the Z33. The Doi theory did not provide an adequate fit of the concentration dependence of the zero-shear viscosity for binary and ternary solutions while it was quite successful for the quaternary solutions. The viscosity for solutions of higher total polymer concentration were found to be predominantly dependent on deformational history. This suggests that molecular ordering attained by the concentrated solutions through shearing does not relax significantly to result in a system that is independent of deformational history. The zero-shear viscosity for a concentrated solution is therefore an "apparent" one since it cannot be entirely retained after being subjected to higher shear rates.

This thesis consists of two closely related parts: Microstructure characterization and homogenization. Homogenization is a procedure to determine the effective properties of a material on macroscopic scale based on its heterogeneity on microscopic scale. The effective properties of a material are dependent on the spacial distribution of heterogeneity such as the distributions of material phases, the shapes of the continents, the distribution of microcracks, etc. The determination of the distribution of this geometrical heterogeneity is the task of microstructure characterization. The originality of the following work is claimed by the author: (1) Microstructure characterization: (a) Revealed a simple and useful relationship between volume fraction and mean chord-length. Volume fraction is the most important statistical property in homogenization and many other fields. Mean chord-length of a phase is mean size of the continents of that phase, which is easy to measure from the profile of material cross-sections. (b) Developed a method to obtain the two-point probability function for general anisotropic random material based on chord-length distribution and chord-center distribution. The two-point probability is the probability of finding the g-th phase at point P and finding the h-th phase at point Q simultaneously. Two-point probability has been identified as the basic function for characterizing the microstructures of random materials for the purpose of homogenization. (c) Introduced the concept of subphase which enables us to characterize the microstructure as detailed as one wishes without lazy higher order probabilities but more and more subphases. Materials are conventionally considered as multi-phase in terms of the difference of the mechanical properties of the continents such as elastic moduli and permeabilities. These multi-phase materials can be subdivided into more phases in terms of the geometrical differences (size, orientation of continents neighbor continents). Generally, to characterize the microstructure with n-point probabilities, higher-point probabilities are necessary in order to determine the microstructures in detailed. However, this will cause difficulties in two aspects. Firstly, for n $>$ 3, the n-point probabilities are usually very complex and difficult to obtain. Secondly, the complexity of the n-point probabilities will further cause difficulties in homogenization. These difficulties are overcome at a large degree by making subphases and combining the linear model of two-point probability. (2) Homogenization: (a) Developed a homogenization method for general anisotropic random materials with a probability approach. With this method, the effective moduli of n-phase anisotropic random elastic materials can be found. (b) Developed a homogenization method for conductivity problems for general anisotropic random materials with approach. The method can be used to calculate the effective permeabilities of n-phase anisotropic random materials. (c) Developed a homogenization method for randomly microcracking materials. With this method, the effective moduli of randomly cracking materials can found. The cracks under consideration can be any shape, any orientation distribution and dry or fluid-filled. It should be emphasized that the interaction between phases or cracks is fully considered in all these three methods. The effects of microstructures on effective properties are brought to the lights. In particular, the following effects are demonstrated: effects of microstructures on effective Young's moduli, effects of microcrack distributions on effective Young moduli, and effects of microstructures on effective permeabilities.

<p> Polymer blending facilitates the combination of the attractive attributes of two or more polymers while compensating for the unfavorable ones. Most polymers are thermodynamically incompatible with one another, and their blending yields a two-phase microstructure. This morphology generally determines the mechanical and rheological properties of the blend system which then determine its applications. Morphology development typically involves deformation of the dispersed phase followed by drop breakup. However, drop coalescence competes with this process, and ultimately a balance must be reached between these two competing processes. Extensional flow fields are known to promote drop breakup and are especially important for blends with high viscosity ratios, that is for blends where the viscosity of the dispersed phase is at least about 3.8 times greater than that of the matrix phase. Coalescence may be attenuated by compatibilizers that modify the interface between the polymer phases. Nanoparticles with tuned surface chemistry may also be used as compatibilizers. A combination of extensional flow and nanoparticle stabilization should, therefore, result in a fine, stable morphology. </p><p> To begin the investigation toward the effects of extensional flow blending with and without the incorporation of nanoparticles, preliminary results were obtained using two different polymer blend systems: polycarbonate (PC)/styrene acrylonitrile (SAN) and polystyrene (PS)/linear low-density polyethylene (LLDPE). However, the majority of the presented results involve blends of high-density polyethylene (HDPE) dispersed in PS. With this blend system, with the material grades selected, the viscosity ratio exceeded 3.8 over the entire domain of deformation rates anticipated in the processing used. Coarse blends of various compositions were formulated using shear flow in an internal mixer or in a twin-screw extruder. These blends were subjected to extensional flow in converging dies of different geometries and where more than one stretching episode was possible; the temperature, total strain, and flow rate were varied, among other factors, in a systematic manner. Experiments were repeated in the presence of various grades of fumed nanosilica of different sizes and surface treatments, which imparted different surface tension and relative surface polarity (hydrophilic versus hydrophobic) for the nanoparticles. The mixing sequence was varied including premixing the nanosilica into the thermodynamically non-preferred polymer phase. </p><p> Scanning electron microscopy (SEM) was used to determine the size and size distribution of the dispersed polymer phase. The material was typically sectioned in the flow direction, but sectioning in the direction perpendicular to flow and etching, or selectively dissolving, one phase or the other was also investigated. The primary effect of extensional flow blending was to reduce the volume-average diameter of the dispersed polymer phase, especially with increasing strains and flow rates, or strain rates, which is directly dependent on both. Finding suitable conditions for the nanoparticles to selectively localize at the HDPE/PS interface was challenging, but relatively small amounts of nanoparticles dispersed in the PS matrix decreased the volume-average diameter of HDPE drops. When the nanosilica was preloaded into the HDPE dispersed phase, very coarse initial blends were produced which then exhibited dramatic decreases in phase size with extensional flow. These and other results are properly organized and presented.</p>

Multidisciplinary design optimisation incorporates several disciplines in one integrated optimisation problem. The benefi t of considering all requirements at once rather than in individual optimisations is that synergies between disciplines can be exploited to fi nd superior designs to what would otherwise be possible. The main obstacle for the use of multidisciplinary design optimisation in an industrial setting is the related computational cost which may become prohibitively large. This work is focused on the development of a multidisciplinary design optimisation framework that extends the existing trust-region based optimisation method known as the mid-range approximation method. The main novel contribution is an approach to solving multidisciplinary design optimisation problems using metamodels built in sub-spaces of the design variable space. Each metamodel is built in the sub-space relevant to the corresponding discipline while the optimisation problem is solved in the full design variable space. Since the metamodels are built in a space of reduced dimensionality, the computational budget for building them can be reduced without compromising their quality. Furthermore, a method for efficiently building kriging metamodels is proposed. This is done by means of a two-step hyper parameter tuning strategy. The fi rst step is a line search where the set of tuning parameters is treated as a single variable. The solution of the fi rst step is used in the second step, a gradient based hyper parameter optimisation where partial derivatives are obtained using the adjoint method. The framework is demonstrated on two examples, a multidisciplinary design optimisation of a thin-walled beam section subject to static and impact requirements, and a multidisciplinary design optimisation of an aircraft wing subject to static and bird strike requirements. In both cases the developed technique demonstrates a reduced computational effort compared to what would typically be achieved by existing methods.

During normal activity, tendons are subjected to dynamic tensile strains of approximately 1-10%, whilst mechanical overload can lead to damage and degradation and the development of tendinopathy. The tenocytes within tendon respond to this mechanical environment although the mechanisms are poorly understood. Primary cilia consist of a slender axoneme composed of acetylated α-tubulin and are known to regulate a variety of signalling pathways including mechanosignalling. In various cell types, mechanical loading also influences primary cilia length. However relatively little is known about tendon primary cilia structure and function. This thesis set out to examine the structure and organisation of primary cilia in tendon cells and the effect of mechanical loading, both in situ and in isolated cells cultured in monolayer. Studies analysed cilia expression using confocal immunofluorescence microscopy in tendon fascicles from rat tail and isolated human tenocytes. Results demonstrated that the prevalence and orientation of primary cilia was different in the fascicular matrix (FM) and interfascicular matrix (IFM) regions of the tendon. Stress deprivation caused differential cilia elongation between the FM and IFM, associated with disruption of the surrounding extracellular matrix and alterations in tissue biomechanics. In isolated tenocytes, primary cilia were significantly longer with a greater prevalence than in situ. Cyclic tensile loading applied using the Flexcell system resulted in cilia disassembly within 8 hours with a dramatic reduction in prevalence and length. This effect was completely reversible on removal of strain. A similar response was observed in situ within both FM and IFM regions of the tendon. This mechanically-induced cilia disassembly was shown to be mediated, at least in part, by the release of TGFβ and activation of HDAC6 which causes tubulin deacetylation. These results in this thesis suggest a novel feedback mechanism through which physiological and pathological mechanical loading may regulate primary cilia signalling.

The effects of surface curvature and slope-of-curvature on the performance of aerofoils used in small wind turbines are studied experimentally and numerically. A symmetric aerofoil NACA0012 and an asymmetric aerofoil E387 are judiciously selected as an example of an aerofoil with a surface curvature discontinuity and an example of an aerofoil with slope-of-curvature discontinuities respectively. The prescribed surface curvature distribution blade design (CIRCLE) method is applied to both aerofoils to remove the curvature and slope-ofcurvature discontinuities. The newly designed aerofoils have continuous curvature and slope-of-curvature distributions and have nearly identical geometry compared to the original aerofoils, denoted as QM13F and A7. Low-speed wind tunnel experiments, together with two numerical methods, are conducted to aerofoil E387 and A7 to investigate the effects of slope-of-curvature. The slope-of-curvature discontinuities of E387 result in a larger LSB, which causes higher drag at low angles of attack, and result in premature LSB bursting process at higher angles of attack, causing earlier stall. The impact of the slope-ofcurvature distribution on aerodynamic performance is more profound at higher angles of attack and lower Reynolds number. The aerodynamic improvements are estimated over a 3 kW small HAWT, resulting in up to 10% increase in instantaneous power and 1.6% increase in annual energy production. In terms of the effects of surface curvature, the curvature discontinuity at the leading edge affects aerofoil lift and drag performance near the stalling angle in the steady flow, and it is estimated in a 5 kW small VAWT that the power coefficient can be increased by 9.7% by removing the curvature discontinuity. Acoustic experimental measurements were performed on aerofoil E387 and A7 in an anechoic wind tunnel to investigate effects of slope-of-curvature on aerofoil acoustic performance. The in-house CFD code Cgles was modified to perform large eddy simulation (LES) the 3D aerofoil sections to further investigate the experimental phenomenon. The tonal noise of E387 at different angles of attack is reduced by removing slope-of-curvature discontinuities. It is experimentally and numerically concluded that continuous curvature and slope-of-curvature distributions can result in better aerodynamic performance of the aerofoil used in small wind turbines, leading to lower aerofoil self-noise and higher energy output efficiency.

In recent years, polymeric microcarriers have drawn great attention because of their potential applications in medical, cosmetic and some other industries. A variety of materials, preparation techniques have been explored to endow these microcarriers the desired properties. In spite of encouraging improvements in other properties, the low permeability of microcarriers remains a challenge which results in massive amount of cargo loss due to fast release. This work aimed to develop microcarriers with reduced permeability by coating with biocompatible and hydrophobic polymers via different techniques such as Layer-by-Layer, surface-initiated atom transfer radical polymerization and emulsion methods. This thesis starts with an introduction and literature review, which present the background of this work, followed by the description of materials as well as methods used in this work in chapter 3. Chapter 4 studied various parameters for fabricating structurally intact Poly(lactic acid) stereocomplex microcapsules, and demonstrated that heat treatment could significantly reduce the permeability of PLA microcapsules. In chapter 5, Layer-by-Layer and surface-initiated atom transfer radical polymerization techniques were combined to fabricate PMMA coated microparticles with low permeability. A polyelectrolyte macroinitiator and Poly(sodium 4-styrenesulfonate) were first deposited onto CaCO3 particles through LbL process, followed by growing PMMA brush layer via ATRP from the polyelectrolyte precursor. Chapter 6 introduced a simple emulsion method to prepare PLA coated CaCO3 microparticles with low permeability, which can retain bioactive molecules within the particles. It was found that 0.8 was the optimal CaCO3/PLA mass ratio in terms of the low permeability of microparticles as well as high-usage of polymers. In chapter 7, PLA films were synthesized from two different types of macroinitiators, with one being polyelectrolyte based and the other one being Poly(2-hydroxyethyl methacrylate) polymer brush precursor. The kinetics of PLA film growth from different precursors was compared whilst degradation of PLA films was also studied.

Polyvinylidene fluoride (PVDF) and its copolymer with trifluoethylene (PVDF-TrFE) have been widely investigated. This is largely attributed to their ferroelectric properties, which are present in a limited number of polymers. In comparison with the more widely used ferroelectric ceramics, the ease of their fabrication makes them attractive in flexible electronic devices. Despite many advances in their application, we are still lacking a complete fundamental understanding of the relationship between their structure and the functional properties. The melt-extrusion of PVDF revealed that the α-phase is predominantly formed in films. The ferroelectric β-phase PVDF was obtained by high temperature drawing of the α-phase of as-extruded films. It was observed that a minimum draw ratio of 3 is required to generate the β-phase. Chain mobility is crucial to the formation of β-phase. Too high chain mobility when drawing at temperatures above 100 °C can only orientate the pre-existing α-crystals without making the chain conformation change to form the β-crystals. Furthermore, the comparison between the produced α- and β-PVDF films is summarized. The α-PVDF films crystallized into spherulites with random orientation, while β-PVDF films displayed fibriliar structure showing preferred orientation of the polymer chains along the drawing direction. The overall crystallinity obtained from DSC data hardly varied, however, the drawn β-PVDF films had a lower melting temperature, which was also confirmed from the dielectric temperature spectra. The drawn β-PVDF films showed higher dielectric constant and larger remnant polarization compared with the as-extruded α-PVDF films, which is mainly ascribed to their higher β-phase content and preferred orientation. Highly aligned PVDF-TrFE films were processed using a melt extrusion processing route. Crystalline structure and orientation were optimized by controlling the melt extrusion conditions. XRD patterns suggested that there was nearly perfect alignment of the c-axis (polymer chain direction) along the extrusion direction in the optimized as-extruded films. SEM analysis confirmed the morphology of the crystalline phase, showing edge-on lamellae stacked perpendicular to the extrusion direction. DSC data indicated high crystallinity and well-ordered ferroelectric structure of the extruded films. FTIR spectroscopy revealed strong intermolecular dipole-dipole interaction in the extruded films. Accordingly, the optimized as-extruded PVDF-TrFE films exhibited a coercive field of 24 kV/mm, half of the commonly reported values for bulk films (~ 50 kV/mm) and a remnant polarization of 0.078 C/m2 which further increased to 0.099 C/m2 after annealing. This value is close to the theoretical limit (0.102 C/m2) assuming perfect in-plane c-axis orientation and 100% crystallinity. The typical limitations of PVDF - low crystallinity and indirect ferroelectric β-phase crystallization - and PVDF-TrFE - higher materials and processing costs and a low Curie point - are tackled by a simple and industrially viable melt blending approach. Despite the immiscible nature of PVDF and PVDF-TrFE, strong interactions exist between the two polymers when co-melt processed, which substantially affect the morphology and texture of the blends as well as their dielectric and ferroelectric properties. Surprisingly, minor amounts of PVDF-TrFE led to a significant increase in the β-phase content and preferred orientation of PVDF, well beyond the rule-of-mixtures. Moreover, the blends exhibited maximum increases in the dielectric constant of 80% and 30%, respectively compared with pure PVDF and PVDF-TrFE. The ferroelectric remnant polarization increased from 0.040 to 0.077 C/m2, while the coercive field decreased from 75 to 32 kV/mm with increasing PVDF-TrFE from 0 to 40 wt. %. The enhancement of properties is explained by the strong interactions at the interfaces between PVDF and PVDF-TrFE, which also suppresses the Curie transition of PVDF-TrFE, providing a potentially increased working temperature range for blended films, which is important in applications like non-volatile energy storage devices, ferroelectric field-effect transistors and touch sensors. Ferroelectric composites, integrating dielectric ceramic fillers with mechanically flexible polymers, are promising materials for flexible electronic applications. Numerous research works have demonstrated enhanced dielectric and ferroelectric properties of composite materials. However, the mechanisms responsible for these enhancements are not completely understood. Herein, PVDF and BaTiO3 (BTO) were used to study the effect of dielectric filler on the crystallization, phase transformation and dielectric properties of PVDF. The crystallization of α-PVDF was not affected by the presence of BTO particles, but small amounts of BTO (< 3 vol. %) made PVDF crystallize into larger spherulites. This is linked to crystallization kinetic studies, which showed that BTO acted as a nucleation agent for large full ring banded spherulites when its content was less than 1 vol. %. Furthermore, solid state drawing in the presence of BTO particles promoted the formation of β-PVDF with more pronounced crystalline orientation at high drawing temperatures (120 °C). The dielectric and ferroelectric properties were enhanced with BTO filling. The 100 °C oriented drawn PVDF tape exhibited a dielectric permittivity of 14 (100 Hz) and remnant polarization of 0.080 C/m2 (10 Hz), which increased to 20 and 0.095 C/m2, respectively, after filling with 5 vol. % BTO; neither resulting in high dielectric loss tangent (~ 0.02) nor obvious current leakage. Moreover, the coercive field decreased from 80 to 50 kV/mm with increasing BTO content from 0 to 5 vol. %.