<p> Temperature sensitive microgel latexes of poly (N-isopropylacrylamide) cross-linked with N-N'methylene bisacrylamide (BA) were prepared and characterized by Dynamic Light Scattering, Titration and Electrophoresis. The study of gels, including temperature sensitive gels, is limited by the large size of traditional bulk gels which are slow to respond to changes and are difficult to measure. An alternative system, which may be easier to study, is a microgel latex which would constitute small particles of gel which would respond quickly to changes in their environment and could also be measured using colloidal measuring techniques like dynamic light scattering and particle electrophoresis.</p> <p> Monodisperse and stable microgel latex particles were prepared by reacting Nisopropylacrylamide (NIPAM) monomer with a cross-linking agent BA in water at 70°C with a surfactant (sodium dodecylsulfate) present. Latexes prepared without surfactant were polydisperse.</p> <p> Characterization of the poly (NIPAM) particles by dynamic light scattering at several different temperatures showed that the particles go through a transition from a water swollen gel at low temperature to a shrunken gel with a low water content at high temperature. The transition occurs about 32°C. The degree of swelling of the poly (NIPAM) particles can be expressed by the Flory-Huggins Interaction parameter c and is dependent upon the level of cross-linking agent included.</p> <p> Titration and electrophoresis results indicate that the particles contain about 0.39 Coulombs per gram of polymer of carboxylic and sulfuric charged end groups which are distributed throughout the particle.</p> / Thesis / Master of Engineering (MEngr)

<p> Part One deals with thin films of SnO₂ which were prepared by ion-beam sputtering, reactive sputtering and anodic oxidation. The films were found to be either amorphous or crystalline in their prepared state. </p> <p> The structure of the as-deposited amorphous films, as revealed by transmission electron microscopy, presented interesting features: there was a continuous structure in the case of high-temperature deposition, whereas an "island structure" was revealed in the case of low-temperature deposition. Furthermore, heat treatment of films having an "island structure" showed this structure to be maintained provided the heating was done with unsupported films, while the structure became continuous when heat treatment was performed on supported specimens. </p> <p> The crystalline form of the films has been worked out, and found to generally be cassiterite; nevertheless a phase different from cassiterite has been occasionally noticed during this work. In some cases it could be tentatively identified as SnO, while other cases it remains unidentified. Crystallization temperatures found here are somewhat different from those indicated in the literature, namely: 500, 300, 225ºC according to substrate temperature and nature and type of heat treatment. Anodic oxidation of tin has been performed(apparently for the first time) in a non-solvent electrolyte, the films being consistently crystalline. </p> <p> The results obtained in the case of films deposited on water-cooled substrates, have revealed a dependence of film structure on film thickness and this effect has been confirmed in supplementary experiments. Thus thick films appear to crystallize spontaneously at room temperature. </p> <p> Part Two deals with radiation damage studies. Our experiments on krypton-ion bombarded SnO₂ films show that amorphous specimens remain amorphous following ion bombardment. The electron-microscope evidence of whether crystalline SnO₂ is amorphized by ion bombardment was tentatively negative, while the gas-release evidence was strongly negative. </p> Part Three deals with diffusion in inert-gas implanted SnO₂. In the first section we give the theoretical background that enabled us to deduce from our experiments rough estimates of the melting temperature, self-diffusion temperature. and activation-energy for self-diffusion of the less mobile ion in SnO₂. In particular, we obtain the following results: </p> <p> T_melting = 2600 - 3000ºK </p> <p> T_self-diffusion = 1480 - 1870ºK for a 2 min. time scale and 134±44Å distance scale. </p> <p> ∆H_self-diffusion = 87,200 - 131,00 cal/mole </p> <p> Note that the melting point for tine oxide is variously reported in different handbooks to lie between 1400 and 2200ºK. From a comparison with other work we have concluded that our value for ∆H is very likely that for oxygen-ion diffusion. </p> / Thesis / Master of Science (MSc)

<p> The goal of this research project was the development of a protocol for preparation of optically clear organic/inorganic hybrid materials that was amenable to entrapment of lipophilic biomolecules. The protocol involved the acid-catalyzed hydrolysis of mixtures of tetraethylorthosilicate (TEOS) with organosilane precursors, including methyltriethoxysilane (MTES), dimethyldimethoxysilane (DMDMS) and propyltrimethoxysilane (PTMS) in the presence and absence of the polymer additives poly(ethylene glycol) or poly(vinyl alcohol).</p> <p> The effect of organosilane precursors and polymer additives on the optical clarity, hardness and hydration stability of the resulting materials was characterized. It was determined that there was a limit to the amount of organosilane that could be added before the materials exhibited unacceptable characteristics. These limits were 20.0% (v/v) for MTES, 10.0% (v/v) for PTMS, and 5.0% (v/v) for DMDMS. Addition of PEG to these materials at levels up to 10.0% (w/v) resulted in good material characteristics. However, addition of PVA produced opaque materials with poor material properties. The internal environment of the materials was also probed using the environmentally sensitive fluorescent probes 7-azaindole (7AI) and prodan. These studies showed that the method of hydrolysis of the silane precursors and the aging conditions had a dramatic effect on the resulting material.</p> <p> The hybrid materials were used to entrap human serum albumin (HSA) and lipase to determine the effect of organic content on the biological function of these biomolecules. Both biomolecules retained a portion of their native function when entrapped in sol-gel-derived materials, and it was found that both proteins showed enhanced function in the presence of MTES. In the case of lipase, it was also determined that addition of PEG 600 at 10.0% (w/v in the gelation buffer) provided a dramatic increase in activity compared to materials without this additive, likely owing to a direct effect of the PEG on the stability of the entrapped protein.</p> <p> Following studies using bulk glasses, a protocol was developed for the preparation of optically clear sol-gel-derived thin films that was amenable to entrapment of biomolecules. The optimal method involved dipcasting of co-hydrolyzed materials containing 1.0 to 3.0% PEG. By careful control of the viscosity of the casting solution and the rate of film deposition, it was possible to form very stable thin films with excellent physical characteristics. These films were used to entrap the pH-sensitive, ratiometric fluorescent probe dextran-SNARF-1, resulting in a prototype of a fluorimetric pH sensor. Co-entrapment of the probe and lipase into sol-gel-derived thin films resulted in a rapid, reagentless biosensor prototype that could monitor changes in pH due to the enzyme-catalyzed hydrolysis of triglycerides. These results demonstrate that species entrapped in sol-gel derived thin films are suitable for biosensor development.</p> / Thesis / Master of Science (MSc)

<p> Two methods for preparing semiconductor grade copper sulfide films, to be used in low cost thin film solar cells,have been investigated. The sulfurization method involves the controlled chemical conversion of copper films into the desired copper sulfide phase. The other method of evaporating Cu2S pellets is more adaptable for an all evaporated thin film solar cell. The copper sulfide films obtained by these methods were characterized using x-rays, cathodoluminescence, electrical and optical methods. The use of optical method in monitoring the stoichiometry of thin copper sulfide films has been illustrated. The photovoltaic properties of thin copper sulfide films obtained by these methods, were also investigated using Cu2S - Si heterojunctions. The behaviour of these junctions indicates that 900 Ȧ thick copper sulfide film is required for optimum photovoltaic conversion. This result may be of some importance in Cu2S - CdS solar cells in further reducing their thickness. Cu2S - Si heterojunctions can also be used to monitor the properties of copper sulfide, as silicon is a well characterized substrate.</p> / Thesis / Master of Science (MSc)