The growing interest towards polysiloxane-based radiation detection systems is related with the several advantages that polysiloxanes offer in comparison with other state-of-the-art plastic materials used in scintillation, like polyvinyltoluene and polystyrene. In this respect, polysiloxane elastomers offer higher thermal stability, flexibility and radiation hardness than the traditional plastic counterpart. For this reason, the study of polysiloxane-based systems for the detection of several types of radiation such as neutrons, high-energy photons and charged particles has recently received increasing attention by the scientific community. In this thesis, we report the current advances on both organic and hybrid polysiloxane-based radiation detection systems for scintillation and passive dosimetry applications. In this framework, we will start from the recent advances on organic polysiloxane-based scintillators for the detection of fast neutrons, with particular emphasis on their pulse-shape discrimination capabilities, allowing for the distinction of neutrons from the γ-ray background. The other and main part of the thesis will be then dedicated to hybrid nanostructured polysiloxane-based radiation detection systems. In this context, latest progress on polysiloxane scintillators embedding 6LiF nanocrystals for thermal neutron detection will be presented, with particular focus on the role of the nanocrystal size and dispersion in the detection performances. Subsequently, polysiloxane/quantum dots nanocomposites will be investigated for their possible use in both scintillation and passive dosimetry. In this latter application, the optical properties of the samples are analyzed after irradiation, with the aim to correlate the radiation-induced effects with the radiation dose. Lastly, the role of the polymer matrix in the post-irradiation optical response of the nanocrystals will be investigated.

Though the past two decades have seen a dramatic increase in research toward self-cleaning repellent surfaces, multiple challenges exist in the creation of biorepellent surfaces for everyday use. Environmental concerns persist with many of the chemicals utilized in this field and the need for scalable, low-cost alternatives remains. Spread of pathogens including bacteria and viruses in healthcare and public settings also presents a need for stable surfaces. In the work presented here, we report on the current status of antimicrobial nanomaterials and coatings toward virus repellency, followed by an investigation into the application of polysiloxane nanostructures in creation of flexible hierarchical surfaces. Using n-propyltrichlorosilane (n-PTCS) coated on activated polyolefin (PO) we were able to demonstrate superhydrophobicity, reporting water contact angles above 153° paired with <1° sliding angles on hierarchical surfaces. A transfer assay, that closely mimics contact with high-touch surfaces, using Escherichia coli K-12 transfected with green fluorescent protein (GFP) reported a 1.6-log (97.5%) reduction in fluorescence on surfaces compared to planar PO controls, paired with a 1.2-log (93%) reduction in CFU/mL in comparison to control groups. Additionally, surfaces demonstrated a contact angle of 140.8° with citrated whole blood. Droplets of blood incubated on our surfaces for 15 min showed a 93% reduction in visible staining, while submersion in citrated whole blood for 20 minutes revealed an 87% reduction in blood adhered to the surfaces. The applications for these biorepellent surfaces have widespread potential, including the demonstrated need for prevention of surface contamination to minimize spread of hospital acquired infections (HAIs) within the healthcare system. / Thesis / Master of Applied Science (MASc) / The goal of creating a surface capable of repelling biological samples continues to present challenges due to surface stability, scalability, and cost of manufacturing techniques. Beyond this, many of the existing solutions use fluorine-based chemicals that present a risk to the environment due to the difficulty in breaking down these molecules. This thesis aims to understand the current state of repellent surfaces used for biological applications, including prevention of surface contamination by bacteria and viruses, then investigates the use of more environmentally friendly methods to produce repellent surfaces. Using a silicone-based coating combined with heat induced shrinking of shape memory polymers (SMPs), we have created a flexible surface with multiscale roughness that demonstrates repellency to bacteria and whole blood.

Copolymer-cobalt complexes have been formed by thermolysis of dicobalt octacarbonyl in solutions of copolysiloxanes. The copolysiloxane-cobalt complexes formed from toluene solutions of PDMS-b-[PMVS-co-PMTMS] block copolymers were annealed at 600-700 °C under nitrogen to form protective siliceous shells around the nanoparticles. Magnetic measurements after aging for several months in both air and in water suggest that the ceramic coatings do protect the cobalt against oxidation. However, after mechanical grinding, oxidation occurs. The specific saturation magnetization of the siliceous-cobalt nanoparticles increased substantially as a function of annealing temperature, and they have high magnetic moments for particles of this size of 60 emu g⁻¹ Co after heat-treatment at temperatures above 600 °C. The siliceous-cobalt nanoparticles can be re-functionalized with aminopropyltrimethoxysilane by condensing the coupling agent onto the nanoparticle surfaces in anhydrous, refluxing toluene. The concentration of primary amine obtained on the surfaces is in reasonable agreement with the charged concentrations. The surface amine groups can initiate L-lactide and the biodegradable polymer, poly(L-lactide), can be polymerized directly from the surface. The protected cobalt surface can also be re-functionalized with poly(dimethylsiloxane) and poly(ethylene oxide-co-propylene oxide) providing increased versatility for reacting polymers and functional groups onto the siliceous-cobalt nanoparticles.Phthalonitrile containing graft copolysiloxanes were synthesized and investigated as enhanced oxygen impermeable shell precursors for cobalt nanoparticles. The siloxane provided a silica precursor whereas the phthalonitrile provided a graphitic precursor. After pyrolysis, the surfaces were silicon rich and the complexes exhibited a substantial increase in Ms. Early aging data suggests that these complexes are oxidatively stable in air after mechanical grinding. Aqueous dispersions of macromolecule-magnetite complexes are desirable for biomedical applications. A series of vinylsilylpropanol initiators, where the vinyl groups vary from one to three, were prepared and utilized for the synthesis of heterobifunctional poly(ethylene oxide) oligomers with a free hydroxy group on one end and one to three vinylsilyl groups on the other end. The oligomers were further modified with carboxylic acids via ene-thiol addition reactions while preserving the hydroxyl functionality at the opposite terminus. The resulting carboxylic acid heterobifunctional PEO are currently being investigated as possible dispersion stabilizers for magnetite in aqueous media. / Ph. D.

Poly(dimethylsiloxane-b-methylvinylsiloxane) (PDMS-b-PMVS) diblock copolymers were synthesized via anionic living polymerization with controlled molecular weights and narrow molecular weight distributions. Targeted molecular weights agreed well with experimental values determined by 1H NMR, 29Si NMR, and GPC. Morphologies were investigated by DSC to analyze glass transition temperatures. Only one Tg was observed for each PDMS-b-PMVS block copolymer suggesting that the blocks were miscible in bulk. Tg's ranged from approximately -126 to -128 °C and were between the Tg's of the PDMS (-123 °C) and PMVS (-137 °C) homopolymers. The PMVS blocks were functionalized with trimethoxysilethyl or triethoxysilethyl pendent groups via hydrosilations to yield poly(dimethylsiloxane-b-[poly(methylvinyl)-co-(methyl-(2-trimethoxysilethyl)siloxane)] (PDMS-b-[PMVS-co-PMTMS]) or poly(dimethylsiloxane-b-[poly(methylvinyl)-co-(methyl-(2-triethoxysilethyl)siloxane)] (PDMS-b-[PMVS-co-PMTES]) copolymers, respectively. The PMVS blocks were either derivatized with the functional groups or half of the repeat units were functionalized. The fully hydrosilated materials were diblock copolymers, and the materials that were 50% hydrosilated had a random sequence of methylvinylsiloxy units and methyl-(trialkoxysilethyl)siloxy units. The PDMS-b-[PMVS-co-PMTES] block copolymers had Tg's ranging from -124 to -126 °C and only one Tg was observed. Surface tension measurements suggested that PDMS-b-[PMVS-co-PMTES] copolymers formed aggregates in toluene. Stable suspensions of superparamagnetic cobalt nanoparticles were prepared in toluene in the presence of PDMS-b-[PMVS-co-PMTMS] or PDMS-b-[PMVS-co-PMTES] copolymers via thermolysis of Co2(CO)8. It is hypothesized that the block copolymers functioned as micellar templates for the cobalt nanoparticles. TEM micrographs showed non-aggregated cobalt nanoparticles coated with copolymers that had mean particle diameters ranging from ≥10-15 nm. Specific saturation magnetizations of these cobalt-copolymer complexes ranged from 90-110 emu g-1 Co, comparable to literature values for this particle size. / Master of Science

Polylactide-siloxane triblock copolymers with pendent carboxylic acid functional groups have been designed and synthesized for study as magnetite nanoparticle dispersion stabilizers. Magnetic nanoparticles are of interest in a variety of biomedical applications, including magnetic field-directed drug delivery and magnetic cell separations. Small magnetite nanoparticles are desirable due to their established biocompatibility and superparamagnetic (lack of magnetic hysteresis) behavior. For in-vivo applications it is important that the magnetic material be coated with biocompatible organic materials to afford dispersion characteristics or to further modify the surfaces of the complexes with biospecific moieties. The synthesis of the triblock copolymers is comprised of three reactions. Difunctional, controlled molecular weight polymethylvinylsiloxane oligomers with either aminopropyl or hydroxybutyl endgroups were prepared in ring-opening redistribution reactions. These oligomers were utilized as macroinitiators for ring-opening L-lactide to provide triblock materials with polymethylvinylsiloxane central blocks and poly(L-lactide) endblocks. The molecular weights of the poly(L-lactide) endblocks were controlled by the mass of L-lactide relative to the moles of macroinitiator. The vinyl groups on the polysiloxane center block were further functionalized with carboxylic acid groups by adding mercaptoacetic acid across the pendent double bonds in an ene-thiol free radical reaction. The carboxylic acid functional siloxane central block was designed to bind to the surfaces of magnetite nanoparticles, while the poly(L-lactide)s served as tailblocks to provide dispersion stabilization in solvents for the poly(L-lactide). The copolymers were complexed with magnetite nanoparticles by electrostatic adsorption of the carboxylates onto the iron oxide surfaces and these complexes were dispersible in dichloromethane. The poly(L-lactide) tailblocks extended into the dichloromethane and provided steric repulsion between the magnetite-polymer complexes. / Master of Science

Fuel cell technologies have developed high interest due to their ability to provide energy in an environmentally friendly method. Proton exchange membrane fuel cells (PEM-FCs) require a PEM for use, where the most accepted PEM used today is Nafion. Nafion is ideal due to its chemical durability and high proton conductivity however it is highly expensive and limited to 80˚C during operation. To target these issues two methods have been developed. One was to synthesize a new membrane material to replace Nafion based upon sulphonated polysiloxanes and the other was to improve Nafion by synthesizing a composite. Both of these methods involved the sulphonated silane 2-4-chlorosulphonylphenethyltrimethoxysilane. Methods to characterize membranes to observe their properties compared to Nafion were thermogravimetric analysis (TGA), Fourier transmission infrared spectroscopy (FT-IR), electrochemical impedance spectroscopy (used to determine proton conductivity) and fuel cell performance. / UOIT

Surface modification is an extensively researched approach in order to overcomethe limitations, and improve the performance of orthopedic and dental implants. It is atthe surface of the implant materials that the initial interactions of tissues or body fluidstake place. Therefore, surface properties of biomaterials are the important factors that cancontrol these biological responses. Molecular imprinting is a surface modificationtechnique that creates specific recognition sites on the surface of biomaterials. Todevelop the recognition sites, a functional monomer is assembled with templatebiomolecule and then crosslinked. After removal of the template, the surface can rebindthe molecules. Therefore, desired reactions can be initiated at the interface between tissueand implants by modifying surfaces to selectively bind certain types of biomolecules,such as proteins. The objective of this project was to observe the potential of molecularimprinting technique for creating biomaterials that can recognize specific biomolecules.Fluorescently labeled lysozyme or RNase A was used as a template biomolecule and theprotein-imprinted scaffolds were fabricated by sol-gel processing. To interpret the densityof binding sites created, the quantity of surface-accessible protein was determined. Theamount of protein available on the surface was proportional to the amount loaded.Protein-imprinted scaffolds were evaluated for their ability to selectively recognize thetemplate biomolecule. Further, for these selectivity studies, a combination of theimprinted protein and a competitor protein were rebound to the polysiloxane scaffolds.The template protein rebound to the surface was measured more than twice as much ascompetitor. These scaffolds were then tested to understand their interaction with cells.The results of DNA and alkaline phosphatase activities indicate that the scaffolds thusdeveloped support growth and adhesion of osteoblastic cells. These initial selectivity andcytocompatibility studies show the potential of molecular-imprinted polysiloxanescaffolds to be used as tissue engineered materials for stable and controlled interactions atthe tissue-implant interface.

Molecular imprinting, a common method used in separations and chromatography to isolate specific molecules via surface binding, has been adapted for applications in biomaterials and related sciences. The objective of this study was to determine the effectiveness of different approaches to molecular imprinting by testing for preferential binding of protein on polysiloxane scaffold surfaces. To test preferential rebinding, the scaffolds were exposed to a mixture of the template protein and a competitor protein with similar size but different chemistry. Lysozyme-imprinted polymers rebound 8.13 0.99% of lysozyme without any competition and 5.1 0.3% of the protein during competition. Lysozyme C peptide was imprinted into polysiloxane scaffolds to investigate the epitope approach to molecular imprinting. Without competition, 8.95 11.53% of the lysozyme preferentially bound to the scaffolds, while under competition 1.85 9.47% bound to the scaffolds. Lastly, bone morphogenetic protein 2 (BMP-2) was imprinted into the polymer scaffolds. Results revealed that BMP-2 imprinted scaffolds bound 10.09 6.625% under noncompetitive conditions and a very small 0.65 4.55% during competition. Trends of preferential binding via peptide imprinting and BMP-2 imprinting can be seen, and show promise in future tissue engineering material applications and biomaterial compatibility.

No description available.

<p>The thermal azide-alkyne cycloaddition using electron deficient alkynes was used to functionalize polysiloxanes at low temperatures and without the need of a metal catalyst. We observed that the temperature at which cycloaddition began can be attributed to the identity of the alkyne's substituents (Chapter 2). We propose that the location of functionalization can be controlled by the specific introduction of electron deficient alkynes on terminal or pendant points on the polysiloxane. Polysiloxanes, each containing two electronically different alkynes, were prepared to show preferential functionalization of the more reactive alkyne without consuming the less reactive alkyne. The alkyne's reactivity can be modified by our choice of substituents. The extension of these results led to polysiloxane difunctionalization where the more reactive alkyne was consumed by a small azide followed by consumption of the less reactive alkyne with a bisazide siloxane. Thermal cycloaddition was used to introduce carbohydrates onto polysiloxanes without complicated protection/deprotection schemes and without catalysts (Chapter 3). The process was successful as propiolate-functionalized siloxane and azide-functionalized gluconamide reacted to produce a trisiloxane-functionalized gluconamide. Trisiloxane-functionalized gluconamide gelled diethyl ether at 3.0% gelator/solvent volume ratio becoming one of the few siloxane-based gelling agents.</p> / Master of Science (MSc)