In recent decades, scientific research giving more attention to the development of bio-based polymer composites due to the extensive usage of petroleum based fillers as well as polymer matrices for the generation of polymer composites. It is a well-known fact that the petroleum derived polymer composites raise inevitable issues such as environmental pollution, waste management and depletion of petroleum resources etc. So it is important to develop fully or partially biodegradable polymer composites without compromising the mechanical, physical and thermal properties which are required for the end use applications. In this investigation, two different types of filler materials such as sisal fibres and halloysite nanotubes were used to prepare PLA polymer composites and their morphology, physical, mechanical, dynamic mechanical, thermal, water absorption and biodegradable properties were studied. This work also involves the preparation and properties of polypropylene composites reinforced with sisal fibres and halloysite nanotubes to compare the mechanical and thermal properties with PLA composites. First, surface treatment was performed for sisal fibres in order to remove the amorphous materials such as hemicellulose, lignin and pectin from the surface of the fibres which enhances the fibre-matrix interfacial strength and mechanical properties of the fibres and their polymer composites. Sisal fibres were subjected to different surface treatments such as alkali, high intensity ultrasound (HIU), and the combination of alkali and HIU and their effects on the morphology, fibre diameter, moisture absorption, mechanical and thermal properties of untreated and surface treated sisal fibres were studied. Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FE-SEM) results confirmed the removal of amorphous materials after the combined treatments of alkali and ultrasound. Moisture absorption and diameter of the sisal fibres were significantly reduced by 40 and 200% respectively after the combination of alkali and HIU treatment as compared to untreated sisal fibres. TGA results revealed that the thermal stability of sisal fibres obtained with the combination of alkali and HIU treatment significantly increased by 38.5 oC as compared to the untreated fibres. Tensile properties of single fibre showed a reduction in the tensile strength and modulus by 25% and 26% respectively as compared to the untreated sisal fibre owing to surface treatments. A reduction in the tensile properties is mainly due to the removal of amorphous materials from the surface of sisal fibres which act as binding materials for cellulose. Second, the effect of different surface treatments on the morphology, mechanical, thermal, water absorption and biodegradable properties of sisal fibres reinforced PLA (SF/PLA) composites has been investigated. For this, different ratio of untreated and surface treated sisal fibres was mixed with PLA polymer matrix by using an internal mixer. Compounded materials from the internal mixer were subjected to compression moulding to prepare the test specimens. FE-SEM analysis confirmed the good dispersion of different surface treated SF in the PLA composites. The tensile strength and modulus increased by 10 and 75.4% for 15 wt% and 30 wt% of fibre loading respectively with the combined treatment of alkali and HIU PLA composites as compared to the untreated fibre reinforced PLA composites. Young’s modulus of the composites has also been predicted by using the theoretical models which fit well to the obtained experimental values. Dynamic-mechanical analysis (DMA) revealed that the combination of alkali and HIU treated SF/PLA composites showed an increase in the storage modulus by 15% and 30% as compared to the untreated fibre composites and pure PLA respectively. TGA and DSC analysis revealed that the thermal stability and crystallinity increased significantly for the PLA composites reinforced with sisal fibres of combined treatment of alkali and HIU. Water absorption study showed a considerable reduction in the water absorption and coefficient of diffusion by 136% and 130% respectively for the combination of alkali and HIU treated SF/PLA composites as compared to untreated SF/PLA composites. The degradation of SF/PLA composites was studied by composting the samples into the soil. A significant weight loss of 17.87% could be observed for the addition of 30 wt% of untreated SF/PLA composites after soil composting for 120 days. Apart from sisal fibres, halloysite (Hal) nanotubes were also used as reinforcement fillers to study their effectiveness in improving the mechanical and thermal properties of PLA nanocomposites. Hal nanotubes were surface modified with 3-aminopropyltriethoxysilane (APTES) to enhance the surface interaction of Hal nanotubes with PLA and to achieve good dispersion of Hal nanotubes across the PLA matrix. Nitrogen adsorption-desorption, FTIR and TGA analysis results were confirmed the successful modification of Hal nanotubes surface with APTES. The different wt% of unmodified and APTES modified Hal-PLA nanocomposites were prepared by using internal mixer and compression moulding machine. The resultant Hal-PLA nanocomposites were characterized for their morphology, thermal, mechanical and dynamic-mechanical properties. Tensile strength increased to 62.6 MPa with the addition of 4 wt% of APTES modified Hal-PLA nanocomposites which is 26.5% higher than pure PLA and 15% higher than unmodified (4 wt%) Hal-PLA nanocomposites. Impact strength of 4 wt% APTES modified Hal-PLA nanocomposites increased by 20% and 40% as compared to unmodified Hal-PLA nanocomposites and the pure PLA respectively. TGA analysis revealed that the thermal stability increased significantly by 17 oC with the addition of 4 wt % of APTES modified Hal nanotubes onto PLA. Storage modulus increased by more than 10% with the addition of 4 wt% of APTES modified Hal nanotubes as compared to pure PLA. To compare the PLA composites with conventional polymer matrix composites, composites of polypropylene (PP) were prepared by reinforcing with sisal fibres and Hal nanotubes and the effect of surface treatment of sisal fibres and surface modification of Hal nanotubes on the mechanical and thermal properties of SF/PP and Hal-PP nanocomposites were studied. Tensile properties were increased for the combined treated SF/PP composites as compared to the untreated and pure PP. Tensile modulus and strength increased by more than 50% and 10% respectively as compared to the untreated SF/PP composites. TGA and DSC results revealed that the combination of alkali and HIU treatments increased the thermal stability and crystallinity by 8 oC and 8% respectively as compared to untreated SF/PP composites. DMA analysis confirmed the significant enhancement of storage modulus for the combined treated SF/PP composites by 50% as compared to pure PP. Mechanical and thermal properties were studied for unmodified and APTES modified Hal nanotubes reinforced PP nanocomposites. The investigations suggest that the mechanical properties of APTES modified Hal-PP nanocomposites were found to be superior to the unmodified Hal-PP nanocomposites. The tensile strength and modulus increased by 31 and 72% with the addition of 6 wt% of APTES modified Hal-PP nanocomposites as compared to pure PP. Impact strength also increased by 44% than pure PP with 6 wt% loading of APTES modified Hal nanotubes. Thermal analysis revealed that the thermal stability and percentage crystallinity increased by 15 oC and 22% respectively for the Hal-PP nanocomposites with surface modification by APTES. DMA analysis shows the improved storage modulus by 28% as compared to pure PP. Based on the present work, it can be said that the sisal fibres and Hal nanotubes have potential as reinforcing materials in the generation of fully bio-based polymer composites. / However, surface treatments and/or modification were playing an important role in order to tune the required mechanical and thermal properties of the polymer composites. This study also proved that in comparison to the conventional polymer matrix materials such as PP, PLA is a strong competitor with respect to its good mechanical properties and improved thermal stability apart from the fact that PLA is one of the best known biodegradable and biocompatible polymer matrices in the current market to use not only in medical application, but also in various commercial applications such as packaging, automotive and home appliances.

This Thesis describes the use of supercritical carbon dioxide as both a reaction solvent and processing medium for synthesis new polymeric materials. Chapter 2 details the high pressure equipment used for this body of work, as well as the analytical techniques employed. This includes equipment details for a new high pressure cell designed for measuring small angle x-ray scattering of polymers in situ. Chapter 3 describes the homopolymerisation of both methyl methacrylate and styrene in a supercritical carbon dioxide expanded phase system. Effects of molecular weight and viscosity on the final reaction product are probed in order to ascertain the most suitable types of polymers to be synthesised by this method. This is then extended to create low molecular weight block copolymers in the absence of any volatile organic solvents, with comparable properties to those produced by conventional methods. The development of the high pressure cell for measuring small angle x-ray scattering of block copolymers synthesised in a supercritical carbon dioxide dispersion polymerisation in situ is described in Chapter 4. Initial investigations showed problems with the synthesis in this new vessel, with different products obtained compared to a conventional autoclave. However, data is presented to display the suitability of certain aspects of the design and that scattering patterns can be acquire in situ during a polymerisation. Details of a second modified design are presented, with construction currently in progress. Finally, a green synthetic route to producing renewable, biodegradable and biocompatible polymers is presented in Chapter 5. By using supercritical carbon dioxide to lower the melting temperatures of the monomers, polymerisations usually conducted at temperatures in excess of 130 °C were successfully conducted at 80 °C. Through the use of a novel zirconium catalyst the tacticity of poly(lactic acid) was controlled, opening up a route to functional materials.

The work presented in this thesis deals with two important low dimensional nanostructures: carbon nanotubes (CNTs) and quantum dots (QDs). In the part of the work related to CNTs a novel method for growing CNTs without the need of metal catalyst is presented. The as produced CNTs were grown by means of chemical vapour deposition on Si-Ge islands and on Ge dots grown with the Stransky — Krastanow method on top of silicon substrates. Through rigorous characterisation products of the method were identified as single wall carbon nanotubes (SWCNTs) with diameters of 1.6 and 2.1 nm. Acquired Raman spectra showed very low intensity or none D — band while the G’ band was of high intensity indicating that the as produced CNTs may be of high quality. A by-product of this method is amorphous fibres which can be easily eliminated when exposed to HF vapour. As this method does not employ metal particles it is fully compatible with the front end silicon processing and therefore opens up the prospect of merging carbon nanotubes with silicon technology. Furthermore CNTs were utilised as probes for atomic force microscopy (AFM). For the fabrication of the CNT probes two methods were applied successfully: the surface growth method and the pick up method. The latter was found to be substantially more efficient than the former and although not proper for mass production it is ideal for laboratory use as it can potentially generate thousands of CNT probes. The as fabricated CNT probes, had diameters in the range of 4 to 7 nm. Using CNT probes the surface of a mesoporous material with pore diameter of 7 to 12 nm and repeated distance of 15 to 18 nm was imaged, proving the high resolution that can be achieved with such probes and that AFM can be applied successfully to mesoporous materials. The latter has the potential to considerably expand the knowledge and the control of such materials to the nanoscale. In the part of the work related to QDs a time resolved two colour pump photoluminescence (PL) technique was applied, with the aim to probe the coherent properties of the excitonic ground state of a single Stransky-Krastanow InGaAs QD. The method comprises of two pulses of different energy; a delayed blue pulse that pumps the GaAs barrier and an infrared (IR) pulse that pumps the excitonic ground state of the QD. The PL of the 1st excitonic excited state of the QD is used in order to probe the occupancy of the ground state. The detection is carried out at zero laser background and thus having a considerably higher signal to noise ratio than other pump and probe methods. A PL intensity variation and a red shift in the energy of the I excitonic excited state were observed, with both effects being dependant upon the intensity of the JR pulse but independent of the time delay and its energy. Further investigations showed that the IR excitation causes all PL and absorption lines of the QD to red shift, induces broadening of the absorption lines and increases the background absorption. Comparison with temperature dependent PL measurements showed that although heating might contribute to the above effects it cannot be the sole reason for their occurrence. Because of the above effects the time resolved two colour pump method cannot be applied as such for probing the coherence of QD ground excitonic state and needs to be modified further.

In this thesis we describe the complex array of behaviours of a homogeneous thermotropic nematic liquid crystal in the context of a Landau-de Gennes theory. There exist two parameters that control the behaviour of the system: the temperature and the shear rate, and by employing continuation and bifurcation theory we describe the different time dependent states for the two and three dimensional cases. For the two dimensional case we compute the steady state solution branches finding that the flow favours an in-plane nematic state at higher temperatures, while at lower temperatures it favours a nematic state with preferred direction of alignment perpendicular to the shear plane, the so-called log-rolling state. We have found excellent agreement between the numerical calculations and analytical results in the limit of very low and very large values of the shear rate. The existence of a Takens-Bogdanov bifurcation in the underlying bifurcation diagram organises the steady and the time dependent solutions in the state diagram. The periodic orbits can be either of the wagging type, at intermediate values of the shear rate or of the tumbling type at lower shear rates. We complete the analysis of the two dimensional case, by considering a general planar flow and studying the influences of strain and vorticity in the system. We provide a very detailed account of the behaviour of the liquid crystal in the three dimensional case, when the direction of alignment of the molecules that constitute the liquid crystal is allowed out of the shear plane. We establish that the only out-of-plane steady solution of the system is an anomalous continuum of equilibria, and therefore the Landau-de Gennes model that we are employing is structurally unstable. The time dependent solutions of the liquid crystal fall into one of the following categories: in plane periodic orbits, which are the tumbling and wagging solutions and out-of-plane periodic orbits, the so-called kayaking state. The use of bifurcation theory in the context of nematodynamics allows us to give a complete summary of the nonlinear behaviour of a nematic liquid crystal in a shear flow, for the two and three dimensional cases.

This thesis describes investigations into the design and evaluation of novel ultrasonic methods for 3-dimensional ionising radiation dose verification. Pulse-echo ultrasound methods were investigated for the measurement and analysis of complex radiation therapy dose delivery. The physical properties of MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) polymer gel dosimeters have been characterized. The variations of speed of sound, ultrasonic attenuation coefficient and density of MAGIC gel with radiation dose and temperature have been quantified. This extends work that has previously been reported for the properties of this gel to the effect of measurement temperature on the results. The facilities to perform these measurements were specified, constructed and evaluated as part of the project. The measurement of radiation dose using ultrasound back scatter from an interface between the polymer gel dosimeter and an inert reflector is demonstrated. To enable the measurement of radiation dose using pulse-echo ultrasound methods a novel inert material has been specified, manufactured and characterised. This material is matched to the acoustic impedance of MAGIC gel to produce the most dose-sensitive reflections. The reflections from the interface between the inert reflector and dose-dependent MAGIC gel have been analysed using both a single element transducer and a commercial ultrasound scanner. Both measurement systems demonstrate the same dose and temperature dependence of the ultrasonic reflection. A methodology has been developed to relate pixel values from the ultrasound scanner to the amplitude of the reflected ultrasound signal. A phantom consisting of an array of threads formed from the inert backscattering material has been designed and constructed and a method of extracting pixel data from images of the array acquired using a commercial ultrasound scanner has been developed, so that multiple imaging positions could be used to perform a 3-dimensional assessment of radiation dose distributions. It has been demonstrated that a pulse-echo technique using a commercial ultrasound scanner shows promise for radiation gel dosimetry. Further investigation and alternative polymer gel and inert reflector combinations may improve these techniques.

This thesis describes the preparation and characterisation of environmentally friendly and low-cost nanocrystalline Ni-Co coatings and Co-Ni-P coatings to replace hard chromium coatings for anti-wear and anti-corrosion applications. nanocrystalline Ni–Co coatings with different cobalt contents were electrodeposited.The investigation on the role of tribofilms and wear debris in the tribological behavior sliding against AISI-52100 stainless steel under unlubricated conditions shows that the tribofilms containing iron from the counterparts were formed on the worn surface of the coatings (less than 60 at.% Co), which exhibited high coefficients of friction and wear rates. In contrast, no tribofilm or iron transfer from the pin was found on the Co-rich coatings (more than 70 at.% Co), which exhibited a dramatic friction reduction of 50 % and improved wear resistance. The wear debris contains a mixture of face-centred cubic (fcc) metallic phase and fcc oxidised phase, irrespective of the coating composition. The oxidised debris cannot form an efficient lubricative film to promote separation of the sliding surfaces. Ni-Co coatings exhibited the active-passive polarisation behaviour in 3.5 % NaCl solution. The corrosion resistance of Ni-Co coatings needs to be further improved in order to replace hard chromium for anti-corrosion applications. A new approach to fabricate single-layer Ni-Co coatings with high cobalt content onto mild steel substrates has been developed by optimising of additives (saccharin and 2- butin-1,4-diol (BD)). The present method is more feasible in industry with a competitive cost compared to other techniques, e.g. developing graded coatings and applying pulse current waveforms. The effect of saccharin and BD on the properties of the coatings were investigated, including surface morphology, grain size, crystalline texture, hardness and tribological performance against a steel counterpart. The coating microstrain could be manipulated from tensile to compressive and the fibre texture could be modified from the (10¯10) for hexagonal close-packed (hcp) structure to (0002)hcp / (111)fcc. The inhibition effect of absorbed species on electrodeposited nanocrystalline coatings is explained via grain size and texture analyses. The coating from the bath with an optimised additive content had high hardness (500 HV) due to its reduced grain size (11±2 nm) and improved tribological properties due to the high proportion of hcp structure. The Hall-Petch relationship can fail when the grain size is below a critical value of tens of nanometres. This occurs particularly for coatings having porous surfaces. In this study, electrodeposited nanostructured Ni-Co coatings with different porosities were obtained by controlling the concentration of nickel sulphate and nickel chloride within electroplating baths. The coatings with the grain size in the range of 11-23 nm had varying surface morphologies and different porosities. A cluster-pore mixture model has been proposed by considering no contribution from pores to the hardness. As the porosity effect is taken into consideration, the calculated pore-free hardness is in agreement with the ordinary Hall-Petch relationship even when the grain size is reduced to 11 nm for the Ni-Co coatings with 77±2 at% cobalt. The present model has been applied to other porous nanocrystalline coatings, and the Hall-Petch relationship is maintained. In order to further improve the microhardness, wear resistance and corrosion resistance of Ni-Co coatings to match the properties of hard chromium, a new Co-Ni-P coating has been developed by combining the precipitation hardening of Ni-P alloys with the lubricity of cobalt-rich Ni-Co coatings. The evolution of composition and microstructure, hardness, thermal stability and tribological properties have been investigated. The local pH near the cathode played an important role in the change of the microstructure from nanocrystalline to amorphous along the growth direction as the phosphorus content increased from 7 at.% to 26 at.%. The highest microhardness (980 HV) and the lowest wear rate (an order of magnitude lower than that of hard chrome coatings under the same dry sliding conditions) were achieved by annealing the coatings at 400 °C facilitating precipitation hardening. Furthermore, the coefficients of friction of both the as-deposited Co-Ni-P coating and the heat-treated samples were approximately 0.3, only half of that of hard chrome coatings. The roll-like debris found on the worn surfaces of the coating annealed at 500 °C were oriented perpendicularly to the sliding direction. The Co-Ni-P coating annealed at 400 °C exhibited improved anti-corrosion properties, which can be attributed to the formation of a protective oxide layer.

The major aim of this project was development of novel covalently modified glassy carbon electrodes for application in NADH-dependent biosensors using combinatorial and high-throughput methods. Studies on transition metal complexes containing redox active 1,1-phenanthroline-5,6-dione (phendione) ligand(s) showed they are effective electrocatalysts for oxidation of NADH. In order to covalently tether the metal complexes at the GC surface, the design of GC electrodes modified with novel metal complexes bearing phendione ligand(s) was proposed based on sequential electrochemical and solid-phase synthesis methods. Initial work involved optimisation of the process for modification of individual GC electrodes. Firstly, following earlier work, the GC electrodes were electrochemically functionalised by primary amines or a diazonium salt bearing Boc-protected amine groups, which allowed introduction of chelating ligands at the GC surface under solid-phase coupling conditions. The final step involved coordination of the bidentate ligand at the GC surface to the metal centre and formation of novel metal complexes under solid-phase coupling conditions. The successfully modified individual electrodes were applied in the design of a library of GC electrodes modified with different linkers, ligands and metal complexes and prepared in a combinatorial and parallel way. The library was electrochemically screened in a high-throughput way using a multichannel potentiostat, which allowed instant comparison of electrochemical and electrocatalytic properties between different members of the library. The experimental data extracted from HTP screening of the library were used for evaluation of a) the surface coverage obtained for different library members; b) the catalytic activity towards NADH oxidation and c) the kinetics parameters kcat and KM for the electrocatalytic oxidation of NADH for all members of the library.

This thesis describes a study into the optical properties of nano-structured metallic films. Structures are produced by electrochemically depositing metal through a self-assembled template of polymer micro-spheres. This versatile technique allows nano-structured surface made from almost any metal to be produced quickly and cheaply. Geometries ranging from array of shallow dishes, to sharp metallic spikes and encapsulated spherical cavities can all be produced on the same sample. This thesis presents an in-depth study into the properties delocalised and localised surface plasmon polaritons. These plasmons can be tuned in energy by controlling the sample geometry and angle of the incident light. The coupling between these two types of plasmon is also investigated and theories are put forward to understand the observed results. These findings could prove useful in the design of plasmon guiding and computing devices. With an understanding into the plasmonic properties of the metallic nanostructures, research is undertaken to explore how the associate local electric field couples to molecules adsorbed onto a samples surface. A strong correlation between surface plasmons and enhanced Raman scattering is found, leading the observation of the beaming of the Raman scattered light. The nano-structured substrates are also shown to have excellent reproducibility as well as enhancement of the Raman signals, leading to applications such as high sensitivity molecular sensors. Finally, the interaction between organic semiconductor molecules and surface plasmons is explored. A strong interaction between the different states is found and plasmon enhanced fluorescence is also observed. These studies open the way for greater control over the exciton states, which have potential for the use in novel laser systems.

This thesis describes experimental and theoretical studies of interrogation systems for determining fluorescent decays of order a few microseconds. The studies have enabled optimised design of interrogators for sensing oxygen using a fluorescent polymerencapsulated ruthenium complex. Two basic interrogation methods were explored, using blue LED excitation. The Rapid Lifetime Detection (RLD) scheme, a fluorescence interrogation method based on direct interrogation of the decay curve following pulsed excitation was generalised, and a novel method for optimising measurement precision derived. The effect of background light on the optimum was quantified. Dissolved (aqueous) oxygen concentration was measured to a precision of 1 part per billion using a 1 second response time (the peak fluorescence power was only 12.5±0.5pW). A second interrogation method, where the phase delay between an intensity modulated excitation source and the resultant fluorescence is processed to make measurements, was for the first time, fully analysed for measurement of exponential decays. When measuring fluorescence lifetimes in the range 2.9-3.3μs, a precision of 2.3 x 10-10 s Hz-0.5 was achieved. (The peak fluorescence power was 500±25pW). A novel combination of ruby optical temperature sensor insert and oxygen sensing layer was demonstrated as a simultaneous temperature and oxygen sensor. A new fluorescence calibration standard consisting of thermally stabilised titanium-dopedsapphire sample was constructed to calibrate and test the indicators. This work was sponsored by a BRITE EuRam European project, which helped determine the priorities of the research.

Current questions concerning the safety of industrial chemicals requires that many substances be re-evaluated to quantify the significance of their environmental and occupational hazards. A large number of epoxides have been found mutagenic and carcinogenic. However, for many of these epoxides the stereochemical requirements are still undefined. After a general introduction into the toxicology of epoxides (Chapter 1), Chapter 2 reviews the general methods developed, and adopted in the syntheses of chiral epoxides and their precursors. In Chapter 3, the materials, methods and instruments used in this project are outlined. A new synthetic route to optically active epoxides is described in Chapter 4. The acid catalysed ketalisation of D-camphorquinone with racemic 1,2-diols is shown to afford a kinetic resolution from which one diastereoisomer is formed predominantly. This dioxolane was hydrolysed to yield an optically active diol or converted into an epoxide. A general route to chiral 1,2-diols is described. The reaction of the enantiomers of methyloxirane with biological nucleophiles (protected N-acetyl esters of amino-acids containing reactive nitrogens [ histidine imidazole nitrogens ] or sulphur [ cysteine ] and the amino ester of valine) is described in Chapter 5. This chapter determines the structure and stereochemistry of the products, along with enantio- selectivities and kinetic data. This data was used to ascertain the relative rates of nucleophilic attack upon the enantiomeric pairs. For ambifunctional nucleophiles identification of the preferred site of alkylation and the regioselectivity of nucleophilic attack was deduced. A method for deducing the enantioselectivity of nucleophilic groups in peptides using specifically deuterated epoxide racemates is described (Chapter 6). Product mixtures are determined by m.s. The use of this method to deduce enantioselectivities in peptides and proteins is outlined.