The quenching characteristics of a range of concentrations of sodium polyacrylate, a commercially available polymer quenchant, have been studied. These solutions showed a stable film boiling stage the duration of which increased with increasing concentration. The maximum surface heat transfer coefficients were significantly below those recorded in water or polyalkylene glycol solutions and decreased with increasing concentration. Just after the passage of this maximum the surface heat transfer coefficient declined rapidly to reach values, at a surface temperature of about 300 C, equivalent to those recorded in the film boiling stage. Photography showed that this was associated with a decline in the mobility of the vapour bubbles formed in this stage. The surface heat transfer coefficients were used to calculate the stress and strain generated during quenching using a visco-elasticplastic model of an infinite plate of a low alloy steel. Comparisons of the predicted residual stresses in the case of the sodium polyacrylate solutions with residual stresses predicted in the case of other quenchants indicated that sodium polyacrylate solutions were capable of producing residual stress distributions similar to that produced by a medium speed quenching oil and greatly below those produced in the case of polyalkylene glycol solutions. This was achieved by a decline in the temperature gradient in the specimen before transformation to martensite began associated with the rapid reduction in surface heat transfer coefficient caused by the loss of mobility of the vapour at these surface temperatures. The predicted residual stresses and strains were also compared to experimentally measured residual stresses and strains to validate the model used. Three boundary layer theory models of film boiling were evaluated in the case of quenching in both water and a sodium polyacrylate solution and the predicted surface heat transfer coefficients compared to experimentally obtained values. None of the models produced a close agreement therefore a modification has been proposed to allow the inclusion of a turbulent interface in the models.

Biaxial orientation of PET for the production of high strength films for demanding applications, such as slot liners for electrical motors and sound and audio visual tapes, is a well established process. More recently biaxial orientation of PET has been utilised for the production of carbonated beverages, bottles and cans for processed food packaging to achieve high strength and impact resistance. These containers, however, are not suitable for hot filling and high temperature sterilization purposes owing to the lack of dimensional stability.

Highly organised structures have been well-known to be part of the complex neuronal network presented in the nervous system, where thousands of neuronal connections are arranged to give rise to critical physiological functions. Conventional in vitro culture methods are useful to represent simplistic neuronal behaviour, however, the lack of such organisation results in random and uncontrolled neurite spreading, leading to a lack of cell directionality and in turn, resulting in inaccurate neuronal in vitro models. Neurons are highly specialised cells, known to be greatly dependent on interactions with their surroundings. Therefore, when surface material is modified, drastic changes in neuronal behaviour can be achieved. The use of chemically modified surfaces in vitro has opened new avenues in cell culture, where the chaotic environment found in conventional culture methods can be controlled by the combination of surface modification methods with surface engineering techniques. Polymer brushes and self-assembled monolayers (SAMs) display a wide range of advantages as a surface modification tool for cell culture applications, since their properties can be finely tuned to promote or inhibit cellular adhesion, differentiation and proliferation. Therefore, when precisely combined with patterning techniques, a control over neuronal behaviour can be achieved. Neuronal patterning presents a system with instructive cues that can be used to study neuron-neuron communication by directing single neurites in specific locations to initiate synapses. Furthermore, although this area has not been much explored, the use of these patterned brushes could also be used in co-culture systems as a platform to closely monitor cell heterotypical communication. This research demonstrates the behaviour of SH-SY5Y neurons on a variety of SAMs and polymer brushes, both in isolation and combination to promote cellular spatial control. APTES and BIBB coatings promoted the highest cell viability, proliferation, metabolic activity and neuronal maturation, whilst low cell adhesion was seen on PKSPMA and PMETAC surfaces. Thereafter, PKSPMA brushes were used as a potential cell repulsive coating and its combination with micro- patterning techniques (photolithography and soft lithography) resulted in a system with instructive cues for neuronal guidance, where neuronal directionality was obtained. In the final chapter of this thesis, a chimeric co-culture system was developed where the patterned SH-SY5Y cells were co-cultured with C2C12 myoblasts in an attempt to obtain an organised neuronal-muscle co-culture system. Whilst preliminary observations showed first stages of a patterned neuronal-muscle co-culture, future work is necessary to refine and improve the patterned co-culture process.

Polyethoxy-silanes are of considerable commercial interest in Brake Fluid formulations. The synthesis of a polymeric Brake Fluid base material, known industrially as Silane Racing Fluid (SRF) isreported, along with the preparation of a series of reference compounds. The fluid contained a mixture of polymeric glycol silanes with theformula andn = 0,1,2, etc. The molecular weights of these compounds weredistributed over a range from 164 to at least 1200. The referencecompounds synthesised were monomeric, with the structure MenSi(OR1 where n = 0,1 ,2 and -OR1 represents varying chain length glycol units, including. The compounds prepared were characterised using a variety of analytical techniques including Si NMR, Size Exclusion Chromatography (SEC) and Mass Spectrometry. The partial hydrolysis of SRF and several of the reference compounds, including is also described. Reactions were monitored qualitatively by Si NMR spectroscopy. Molar ratios of water to si lane were in the range of 2:1 to ~14:1. The technique allowed the identification 'in situ' of labile partial hydrolysis products, before they condensed to more stable siloxanes. In further studies the hydrolysis of several polyethoxy-silanes is reported, in dilute aqueous solution. The reactions were monitored quantitatively by two techniques, ultra-violet spectrophotometry and an extraction method. In the spectrophotometric experiment the hydrolysis of was studied. Pseudo first order kinetics was observed, which was found to be specific Acid/Base catalysed over the pH range studied (4-9). The extraction method relied upon n-hexane specifically extracting the starting material. An Infra-red spectrometer was used to determine the quantity of starting material present after extraction, by monitoring the Si-O-C stretching frequency ~1100 cm. Pseudo first order rate constants were obtained for the hydrolysis of and (0Me)3 . The results indicated specific Acid/Base catalysis over the pH range studied (5-9). The kinetic results described are in good agreement with recent studies reported using Trialkoxysilanes.

With the rapid spread in use of polymers the study of diffusion in them is becoming increasingly important. For a number of industrial processes diffusion coefficients and elemental distributions need to be quantified precisely. From a more scientific approach accurate models need to be devised to describe the various diffusion mechanisms involved as well as the concentration and temperature dependencies of the diffusion coefficients. Using ion beam analysis techniques (Rutherford Backscattering and Nuclear Reaction Analysis) three systems were studied. The first was an industrially relevant system of relatively small dye molecules diffusing into a number of different polymer matrices. For fixed diffusion settings, diffusion coefficients were measured and found to correlate with the matrix glass transition temperatures. Surface dye concentrations, on the other hand, were independent of matrix properties. The other two systems studied involved polymer interdiffusion. Based on different assumptions, two contradictory theories have been developed to describe the concentration dependence of the mutual diffusion coefficient; the 'slow' and 'fast' theories. In one system, blends of low molecular weight (unentangled) polystyrene and poly(methyl methacrylate) our data followed the 'slow' theory at low temperatures and the 'fast' theory at high temperatures. An equation describing the concentration dependence of the mutual diffusion coefficient at all intermediate annealing temperatures (hence linking the 'slow' and 'fast' theories) was developed and found to describe the data accurately. In the second system, blends of entangled poly(methyl methacrylate) of several molecular weights, the mutual diffusion coefficient was found to follow the 'fast' theory at all studied temperatures. In all three systems the temperature dependence of the tracer diffusion coefficients of the various components were accurately described by the semi-empirical equations of the Free Volume theory.

The use of stereolithography tools for injection moulding allows plastic parts to be produced in a very short time due to the speed of mould production. The process's greatest advantage is that it can provide a low volume of parts that are produced in the same material and process as parts that would be produced by the conventional hard tooling, but in a fraction of the time and cost. However, this work has demonstrated different rates of polymer shrinkage are developed by parts produced by stereolithography tools and conventional tooling methods. These revelations defy the greatest advantages of the stereolithography injection moulding tooling process—the moulded parts do not replicate parts that would be produced by conventional hard tooling. The aim of this work is to acquire an understanding of the mechanisms in stereolithography tooling that induce these different part properties and develop a modification of the process that could change these, which would allow the moulded parts to demonstrate characteristics like those produced by conventional means.

Commercial polymers are typically classified according to their melt flow indices, measures of their viscosities. These properties are known to depend on a material’s molar mass distribution, on its averages and its degree of polydispersity. In determining a polymer’s performance, both the molar mass distribution and the process employed to produce the part are highly relevant, since the balance in the mass fractions from its distribution will determine the flow characteristics in the mould, and influence the material’s performance. The compromise polymer manufacturers have to make is to maintain the mechanical properties known to improve with increased molar mass at the same time as a sufficiently low viscosity, known to reduce with decreasing molar mass, to enable part production. This is often achieved by judicious blending of homopolymers. This thesis examines how varying molar mass and distribution in blends leads to changes in the thermal, rheological, and mechanical properties in polystyrene, and discusses and develops physical models to capturing the observed experimental responses. Chromatographic and calorimetric studies were carried out on monodisperse, bimodal blends of monodisperse, polydisperse, and blends of polydisperse polystyrenes. They revealed that changes in molar mass distributions and glass transition temperatures, Tg, could be directly attributed to the blending procedure of choice. In polydisperse blends, higher contents of low molar mass fractions, and corresponding lower Tgs were observed in the blends produced using a melt mixing method compared with solution-blended equivalents. Thermal degradation, accelerated by the large number of chain ends, was suggested as the cause for the increase in low molar mass fractions in the melt-mixed blends. The filtration and precipitation stages characteristic of solution blending instead promoted oligomer loss and evaporation, resulting in reductions in the low molar mass tails of the distributions. Craze initiation stress was measured in 3-point bending isochronal creep tests on the same polymers and blends, and was found to in-crease rapidly with additions of a higher molar mass component, reaching a plateau at 20 wt%. A simple model based on a weighted addition of the crazing stress contributions of individual weight fractions was developed from an established piecewise linear crazing law in order to enable predictions of the crazing stress in the blends, using a power law exponent of 2.59 (90% CI [1.75 17.34]). In highly poly-disperse systems, where short unentangled chains dilute the polymer, it was necessary to include dynamic tube dilution theory. Dilution leads to a change in the entanglement length and hence in the molar mass at which transitions in the crazing mechanisms (disentanglement and chain scission) occur. With the improved model, crazing stress could be predicted even for highly polydisperse blends with wide and bimodal distributions. Linear and non-linear rheological measurements were carried out in shear and extensions on the same materials. Existing rheological models for linear viscoelasticity including Likhtman-McLeish (L-M), Rubinstein-Colby (R-C) and polydisperse double reptation (pDR) theory were applied to the linear experimental data, exposing some of the fundamental difficulties of modelling the structure of systems where multiple chain-lengths interact. R-C was found applicable to bi-modal blends of monodisperse, whereas pDR was better able to model broad polydisperse blends. New non-linear shear and extensional rheology was recorded experimentally on all polymers and blends, and should enable future non-linear theories to be compared to experiment.

The enteric nervous system (ENS) is commonly referred to as the ‘second brain’ due to its complex networks of neuronal cells. The abnormality of these neurons and/or their absence has been shown to play a fundamental role in diseases of both the ENS and the central nervous system. Accordingly, electrophysiological studies of the ENS and general understanding of how enteric neurons behave in the gastrointestinal tract are critical in the characterization of the pathophysiology of enteric and neurodevelopmental diseases. To date, studies on these aspects have been limited by the difficulty of culturing enteric neurons in-vitro, as well as by their poor adhesion properties. The primary objectives of this thesis are to develop strategies to investigate electrodynamics processes of enteric neurons and close in on their interactions with polymeric substrates, aiming at optimizing conventional experimental approaches and expanding the current knowledge and critical understanding of this elusive cell type. By capitalizing on a rapid and efficient culturing method developed by our group, different polymers were tested in order to assess their ability to promote adhesion of enteric neurons, as confirmed by immunofluorescence analysis. The most effective polymer resulting from this initial screening was then applied as a coating onto the glass surface of multichannel electrode arrays (MEAs) allowing for the analysis of neuron dynamics. While Matrigel® was the most effective at promoting both neuron adhesion and neurite outgrowth, it acted as an insulating material which prevented the MEA electrodes from picking up electrical signals. Therefore, we opted instead for laminin protein and poly-d-lysine immobilized on glass by polydopamine, to study the electrophysiology of the neurons. Of note, polydopamine was found to be critical in enhancing the stability of the protein coating and ensuring cellular viability. The same protein coating was also used to functionalize the surface of blends of poly(styrene) and poly(methyl methacrylate), which segregate when mixed to give rise to varying topographical features. These surfaces aimed at elucidating fundamental processes that dictate how neurons interact with surfaces when compared to smooth rigid surfaces (i.e. glass). Finally, the most effective surface for neuron adhesion was applied to study how chemotaxis influences neurite elongation and directionality. Enteric neurons were cultured onto both a linear concentration gradient of protein created using a microfluidic system and a uniform concentration profile to compare their response to chemical signals. In general, their motion was random and lacked directionality on the uniform protein surface. The neuronal response to the chemical gradient could not be evaluated to completion; however, this analysis still provided meaningful insight as a starting point for future studies. The results presented in this thesis serve as a significant stepping-stone for the improvement of the in-vitro study of the ENS and will be used to gain a deeper understanding of enteric diseases, ultimately contributing to the development of novel polymeric scaffolds for tissue-engineering applications.

No description available.

No description available.