In order to characterise deformation as completely and unambiguously as possible it is desirable to eliminate the possibility of sample relaxation by performing measurements <I>in-situ</I>, during deformation. The bulk of the thesis describes a comprehensive series of investigations into the mechanical behaviour of a range of oriented and unoriented commercial grade polyethylenes deformed in tension and compression over a range of temperatures. High intensity synchrotron X-rays and fast electronic area detectors were used to enable the two-dimensional wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) patterns, which reveal information about the molecular and lamellar deformation respectively, to be measured simultaneously during deformation. In addition, the load-extension curve was measured at the same time as the X-ray scattering patterns. Sample relaxation was completely eliminated and for the first time the micro- and macroscopic deformation was precisely and unambiguously correlated. The use of a range of samples, with varying molecular weights, branch densities, branch types, lamellar thicknesses and percentage crystallinities, enabled a study to be made of the influence of microstructural variables (as well as experimental conditions such as deformation temperature) on the mechanical properties. A study was also performed on the mechanical properties of thin solution-cast PE films made from the same commercial grades used for the bulk samples. Crazing mechanisms were observed using optical and transmission electron microscopy. It was found that that results could be rationalised in terms of the degree of entanglement of the chains and the ease by which these entanglements were overcome during deformation. Increasing the entanglement density by increasing the molecular weight or by the incorporation of short chain branches increased the toughness of the films. As for the bulk samples, branch length was unimportant.

Recently, advances have been made in the design, manufacture and application of composite materials. A great deal of this progress has been made in the field of Fibre-Reinforced-Plastics (FRP). FRP often have greater strength to weight and stiffness to weight ratios than traditional materials such as metals, which makes them ideal for use in many application especially in aeronautical and aerospace sectors. For example Carbon-Fibre-Reinforced-Plastics (CFRP) are becoming more common in civil and military aircraft structures. However, there remain many unanswered questions regarding the behaviour of these materials especially under in-service conditions such as fatigue. There is an increasingly urgent need to gain an understanding of how FRPs behave. To fully understand the fatigue of a material it is necessary to gain an understanding of how damage initiates and accumulates and how the damage will affect the materials properties. It is also clear that to fully utilise FRPs it is necessary to be able to model the relationship between microstructural damage and the materials mechanical properties. This work has characterised the fatigue life of a quasi-isotropic carbon fibre reinforced composite, HS/919, at four R ratios. These are R=0.1 (tension-tension), R=+10 (compression-compression), R = -0.3 and R=-3.3 (both tension-compression). Those R ratios with a majority compression loading cycle experienced lower fatigue lives than those with a mainly tensile loading cycle. The work also highlighted the delaminations were a major damage mechanism. Post failure analysis of the fatigue specimens showed that the primary delamination, was occurring at different interfaces dependent on the loading cycle. With a mainly tensile loading cycle the delamination was occurring at the 0°/90° interface. While the mainly compressive loading cycle showed delaminations at the 0°/45° interface. This phenomenon was investigated using a modified mixed-mode bending technique developed by Reeder and Crews at Nasa. Static and fatigue tests were carried out on both the highlighted interfaces at three mixed-modes, M_I/M_II of 1/3, 1/1 and 3/1. Static tests showed that the 0°/45° interface was the weaker. In the fatigue tests two phenomena were observed, 1) that the strain energy release rate steadily decreased with crack length, 2) the strain energy release rate initially increased and then decreased. This is due to fibre bridging which was seen in both interface but was more apparent for the tests at the 0°/90° interface. There was a large amount of scatter in the fatigue data, especially at the 0°/45° interface. This made fitting a Paris type law to crack growth rates impossible for this interface. A Paris law was fitted to the 0°/90° data. It was hoped to transfer this knowledge to fatigue coupons with inserts.

My research has focused on the effects of reflective surfaces such as metals and dielectric stacks on the light emission from conjugated polymers. Conjugated polymers have semiconducting properties which arise from the delocalisation of electrons along the polymer backbone. These plastics are efficient light-emitters both in photoluminscence (PL) and Electroluminescence (EL). One of the unique features of these materials is their broad emission spectrum. Proximity to reflective surfaces alters the radiative rate of an emitter because of interference effects. This modification to the radiative rate is a function of the dielectric properties of the mirror, the orientation of the dipole, the distance between the dipole and the mirror, the emission angle, and the emission wavelength. In addition, non-radiative energy transfer from the emitter to excitations in a metal film efficiently quench luminescence at separations less than 60 nm. I have investigated the effects of interference and non-radiative energy transfer on the emission spectra and the PL and EL quantum efficiencies of conjugated polymer structures. The PL from thin films of conjugated polymers spin-coated onto Al and Au films, with and without SiO<SUB>2</SUB> spacer layers in between, was investigated. PL was found to be quenched close to the metal films. Experiments on double-layer LEDs where the distance between the emissive region can be controlled by altering the film thicknesses of the polymer layers extended those results from PL to EL. In addition, changes in the PL spectra and PL efficiency with increasing polymer-metal separation could be explained by computer-modelling the radiative power of oscillating dipoles. The results allowed design rules to be formulated which could improve the efficiency of LEDs, photovoltaic cells and microcavity devices in which the polymer film is sandwiched between two mirrors. Comparison between experiment and modelling revealed some information about the photophysics of conjugated polymers. Microcavities (Fabry-Perot resonators containing a light-emitter) modify the radiative rate of an emitter more strongly than single mirror devices. I have investigated the role of the dielectric properties of metals on the resonance wavelengths of a microcavity. It is shown that the metal film thickness influences the cavity resonances and that the angular dependence of the microcavity emission can be reduced exploiting specific properties of the metal.

Polyelectrolyte brushes are polymer brushes with charged units on polymer chains. Due to the responsive properties of polyelectrolyte brushes, they have large applications in many fields. This thesis describes the synthetic approaches of growing polyelectrolyte brushes in a controlled way. The majority of this thesis focuses on the study of applying controlled living radical polymerisation methods on surface-initiated polymerisation, aiming to achieve controlled growth of polyelectrolyte brush, <i>e.g. </i>controlled brush thickness, grafting density, and internal structure of the brush. Atom transfer radical polymerisation (ATRP), activators (re)generated electron transfer (A(R)GET) ATRP and single electron-transfer living radical polymerisation (SET-LRP) have been studied systematically on the synthesis of polyelectrolyte brushes from surface. These polyelectrolyte brushes are studied using ellipsometry, atomic force microscopy (AFM) and contact angle goniometry. During the study, a unique property of the polyzwitterionic brush is found and explored. Furthermore, considering the future applications of these polyelectrolyte brushes, the brush stability is also studied.

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In this thesis we investigated three different aspects of polymer dynamics using molecular dynamics simulations: orientation relaxation in equilibrium, shear flows and possible ways of coarse-graining. In the first part, we studied the orientation relaxation function of monodisperse and bidisperse melts of linear polymers. A universal time- dependent coupling parameter was derived to build the bridge between the monodisperse and bidisperse melts, which facilitates application of the theory of mono disperse melts to polydisperse samples. In the second part, non-equilibrium molecular dynamics simulations were used to investigate start-up shear of polymer melts. Shear stress, first and second normal stresses were measured in both transient and steady states. A possible shear banding was observed in mildly entangled system, which is in contradiction with experimental observation. We also tried to map our simulation results to PI experimental results according to the same number of entanglements and a qualitative agreement was obtained. In the last part, a systematic method was developed to derive the effective interaction forces between polymer chains in the melts. If we apply the pair-wise interaction obtained from vacuum to the melts, a reasonable agreement between the original MD simulations and the coarse- grained simulations can be achieved. However, if many-body effects were introduced, the agreement became worse.

Diblock copolymers (DBCs) are fascinating materials which, under the correct conditions, self-assemble into periodically ordered structures with nanometre sized domains. The majority of theoretical and experimental studies of DBCs have concentrated on the monodisperse melt, where all of the polymers are identical. Although these ideal molecules have allowed for detailed understanding of the phase behaviour of the materials by removing the effects of polydispersity, they are costly and time consuming to manufacture. More recently, however, a range of techniques have emerged that allow chemists to synthesise DBCs more cheaply, albeit with higher levels of polydispersity. These methods will be more attractive to industry providing that the novel material properties remain. Self consistent field theory (SCFT) has made good progress in predicting the effects of polydispersity in DBC melts, such as increasing domain size and shifting of order-order phase boundaries - effects which are observed in experiments. However, whereas SCFT predicts that polydispersity shifts the order-disorder transition (ODT) to higher temperatures, recent experiments have found that this is not always the case and we suspect that this failure is due to the lack of fluctuation effects in the theory. In this study, Monte Carlo simulations are used to investigate DBC melts since the technique includes fluctuation effects. A detailed study of the monodisperse system is performed, providing a benchmark to which the results from polydisperse melts are compared. The simulations are also contrasted with SCFT and experiments in order to resolve the disagreement between them.

Synthetic polymers obtained from acrylates and methacrylates have found wide spread use in medicine as drug carriers, functional colloidal particles, biomedical applications, synthesis of polypeptide vesicles and micelles. 2-aminoethyl methacrylate (AMA) is a commercially available amine- based methacrylic polymer from which a series of copolymers were prepared. In this study 2-aminoethyl methacrylate (AMA) was homopolymerised to different degrees of polymerisation using atom transfer radical polymerisation (ATRP) and free radical polymerisation (FRP) to afford a series of different molecular weight polyamines. The polymers were characterised using lH NMR spectroscopy and gel permeation chromatography. The intrinsic viscosities for the polymers synthesised by ATRP and FRP were determined and viscometric constants (Mark Hauwink constants) were calculated. Modification of the polymers was done by conjugating hydrophobic side moieties (cetyl chains) with their primary amino groups to achieve amphiphilies polymers with the ability to self-assemble in aqueous media into supramolecular structures. Characterisation of the modified polymers was done by lH NMR, 13C NMR, IR spectroscopy, and elemental analysis. The ability of the hydrophobically-modified polymers (HMP) to self-assemble in aqueous media was studied using dynamic light scattering (DLS), and it was found that these polymers have the ability to form polymeric micelles, the size was found to depend on solution pH. To investigate the solution properties of these novels HMP, cetylated PAMAs with different degrees of modifications were prepa red. The effect of increasing the molecular weight and degree of hydrophobic substitution on the aggregation behavior of these amphiphliles in aqueous solutions was studied using DLS, and transmission electron microscopy (TEM). The aggregation behavior and critical association concentration were studied using surface tension measurements, and fluorescent spectroscopy using pyrene as a polarity probe. The biocompatibility of the unmodified polymers was assessed using the haemolytic activity assay, and the slug mucosal irritation test (SMIT). It was found that PAMA did not induce detectable haemolysis and the irritancy potential of these polymers