No description available.

This thesis documents a study of bonding stress and the reliability of GaAs-based lasers for high-power applications. GaAs-based lasers were bonded to oxygen-free high- conductivity (OFHC) copper heat sinks using a eutectic PbSn solder or a silver-filled conductive epoxy, and life tested. Epoxy-bonded devices were observed to have a larger failure rate on life test than solder-bonded devices. Bonding stress, as measured by the degree of polarization (DOP) of photoluminescence, was found to be the largest in epoxy-bonded devices. As well, the type of heat sink and bonding adhesive affected the stress in the laser material, with bonding stress increasing when there was a larger mismatch of coefficients of thermal expansion between the laser material, adhesive and heat sink. The reliability of the lasers was affected by the amount of force applied to unbonded laser chips. As the applied force increased on a chip centred on a groove, the rate of degradation in the output power increased. A limit in stress tolerance was observed in the lasers, which meant that larger amounts of stress would lead to increased rates of degradation in the output power. As well, the performance of lasers selected from a batch showing poor reliability degraded at an accelerated rate after several hours of operation under applied strain. / Thesis / Master of Engineering (ME)

Chalcogen bonding (ChB) is a particular case of secondary bonding centred on heavy group-16 elements. It is almost exclusively identified through crystallography by measuring interatomic distances intermediate between single-bond averages and the sum of van der Waals radii. However, there is significant recent progress in discerning its signatures using spectroscopic techniques such as multinuclear NMR. This M.Sc. thesis describes progress in two research projects on chalcogen bonding. The first examined the effect of halogenation on the aggregation of 3-methyl-5-phenyl 1-2-tellurazole 2-oxide. The second examined the strengthening of ChB interaction between molecules of benzo-1,2-chalcogenazole 2-oxides by chlorination. The bromination of 3-methyl-5-phenyl 1-2-tellurazole 2-oxide yielded 3,3,3-tri-bromo-3-methyl-5-phenyl-1,2-tellurazole-2-anole. Four unique crystal structures were obtained with the most promising being the dimeric structure. Deprotonation was unsuccessfully attempted although yielded 2 unique crystal structures co-crystallized with proton-sponge. Iodination of 3-methyl-5-phenyl 1-2-tellurazole 2-oxide was also performed, resulting in a mixed tetrameric aggregate containing two molecules of 3-methyl-5-phenyl 1-2-tellurazole 2-oxide and two 1,1-di-iodo-3-methyl-5-phenyl 1-2-tellurazole 2-oxide molecules. DFT investigations into the electronic properties, thermodynamics of aggregation, and basicity were performed. Similar to the chlorinated derivative, the most favourable aggregate to form is the hetero-tetramer with two brominated or iodinated molecules and 2 non-halogenated molecules. The reaction of benzo 1,2-sellenazole 2-oxide with SO2Cl2 and benzo 1,2-tellurazole 2-oxide with HCl followed by SO2Cl2 yielded halogenated derivatives of each molecule in which the chalcogen was oxidized from Ch(II) to Ch(IV). In the selenium derivative, an unexpected chlorination occurred on the heterocycle of the molecule. Crystal structures were obtained for each chlorinated product where dimeric interactions were observed. DFT calculations show how the electronic and orbital mixing contributions to the ChB interactions are enhanced upon halogenation. Gibbs free energy of aggregation is most negative for a mixed structure in which two chlorinated molecules and two unchlorinated molecules are linked. / Thesis / Master of Science (MSc)

Non-covalent interactions including nucleobase hydrogen bonding and ionic aggregation were studied in block and end-functional polymers synthesized via living polymerization techniques such as nitroxide mediated polymerization and anionic polymerization. The influence of non-covalent association on the structure/property relationships of these materials were studied in terms of physical properties (tensile, DMA, rheology) as well as morphological studies (AFM, SAXS). Hydrogen bonding, a dynamic interaction with intermediate enthalpies (10-40 kJ/mol) was introduced through complementary heterocyclic DNA nucleobases such as adenine, thymine and uracil. Hydrogen bonding uracil end-functionalized polystyrenes and poly(alkyl acrylate)s were synthesized via nitroxide mediated polymerization from novel uracil-functionalized alkoxyamine unimolecular initiators. Terminal functionalization of poly(alkyl acrylate)s with hydrogen bonding groups increased the melt viscosity, and as expected, the viscosity approached that of nonfunctional analogs as temperature increased. A novel difunctional alkoxyamine, DEPN2, was synthesized and utilized as an efficient initiator in nitroxide-mediated controlled radical polymerization of triblock copolymers. Complementary hydrogen bonding triblock copolymers containing adenine (A) and thymine (T) nucleobase-functionalized outer blocks were synthesized. Hydrogen bonding interactions were observed for blends of the complementary nucleobase-functionalized block copolymers in terms of increased specific viscosity as well as higher scaling exponents for viscosity with solution concentration. Multiple hydrogen bonding interactions were utilized to attach nucleobase-functional quaternary phosphonium ionic guests to complementary adenine-functionalized triblock copolymers. Ionic interactions, which possess stronger interaction energies than hydrogen bonds (~150 kJ/mol) were studied in the context of sulfonated poly(styrene-b-ethylene-co-propylene-b-styrene) block copolymers. Strong ionic interactions resulted in the development of a microphase separated physical network and greater extents for the rubbery plateau in DMA analysis compared to sulfonic acid groups, which exhibit weak hydrogen bonnding interactions. In contrast to the physical networks consisting of sulfonated or hydrogen bonding block copolymers, covalent networks were synthesized using carbon-Michael addition chemistry of acetoacetate functionalized telechelic oligomers to diacrylate Michael acceptors. The thermomechanical properties of the networks based on poly(propylene glycol) oligomers were analyzed with respect to the molecular weight between crosslink points (Mc) and the critical molecular weight for entanglement (Me). / Ph. D.

Theoretical tensions between theories of saturation, bonding and leisure were explored from feminist perspectives. Saturation defined by Gergen as a state of relational overload, may cause I of connection between family members. Leisure scholars suggets that bonding occurs during leisure, and a feminist perspective emphasizes that leisure includes conflict and inequality families. Participants were primarily White, and all were upper-middle class married couples with children aged 6 to 12. Individual and family interviews were held with parents and children. Data was analyzed qualitatively according to Strauss and Corbin's (1990) grounded theory procedures. Saturation, as a metaphor, does not capture the dynamic nature of how people grappled with time use. Being saturated reflects being filled up, but the experience described by participants may be closer to feeling drained, and more useful may be a concept that attends to both. Parents demonstrated four kinds of orientations to saturation: resistant, reformed, absorbent, and saturated. The persons who defined their experience as saturated were two men, both breadwinners with homemaker wives. Women took time-stress for granted, and were the main organizers and monitors of family leisure. Technology did not seem to add to time-stress, but TV in most households was restricted to weekends. Parents did not clearly associate bonding with leisure time. Bonding was defined as building connections and trust, showing warmth and caring, and being involved in each other lives. While bonding required attentiveness, leisure was an event where parents were free of responsibility for others. Parents discussed ideal vs. actual employment arrangements. Female homemakers were interested not in leisure, but in finding part-time work. Male breadwinners were wedded to their provider roles. Many adults would make changes in their employment situations, but felt stymied by gendered workplace culture. Children could describe times they felt time pressured, but mostly were content, and asked for parents not to rush them from one activity to the next. Children's leisure preferences were free time and family time, as opposed to organized activities, chores, and TV. / Ph. D.

Current research efforts have focused on the synthesis of novel, segmented, cross-linked networks and thermoplastics for emerging technologies. Tailoring macromolecular structures for improved mechanical performance can be accomplished through a variety of synthetic strategies using step-growth polymerization. The synthesis and characterization of novel Michael addition networks, ionene families, and ion-containing polyurethanes are described, with the underlying theme of fundamentally investigating the structure-property relationships of novel, segmented macromolecular architectures. In addition, it was discovered that both covalent and electrostatic crosslinking play an important role in the mechanical properties of all types of polymers described herein. Novel cross-linked networks were synthesized using quantitative base-catalyzed Michael chemistry with acetoacetate and acrylate functionalities. These novel synthetic strategies offer unique thermo-mechanical performance due to the formation of a multiphase morphology. In order to fundamentally elucidate the factors that influence the kinetics of the Michael addition reaction a detailed analyses of model compounds were conducted in the presence of an in-situ IR spectrometer to optimize reaction conditions using statistical design of experiments. Networks were then prepared based on these optimized conditions. The mechanical performance was evaluated as a function of molecular weight between crosslink points. Furthermore, the incorporation of hydrogen bonding within the monomer structure enhanced mechanical performance. The changes in morphological, thermal, and mechanical properties evaluated using dynamic mechanical analysis (DMA) and tensile behavior are described. In addition, the use of preformed urethane segments provides a safer method for incorporating hydrogen bonding functional groups into macromolecules. In order to compare the thermomechanical and morphological properties of ion-containing polyurethanes to non-charged polyurethanes, poly(tetramethylene oxide)-based polyurethanes containing either a novel phosphonium diol or 1,4-butanediol chain extenders were prepared using a prepolymer method. The novel phosphonium polyurethane was more crystalline, and it was presumed that hydrogen bonding in the non-charged polyurethane restricted polymer mobility, and reduced PTMO crystallinity, and hydrogen bonding interactions were significantly reduced due to the presence of phosphonium cations. These results correlated well with mechanical property analysis. The phase separation and ionic aggregation were demonstrated via wide-angle X-ray scattering, small-angle X-ray scattering, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy during STEM imaging, as described herein. In addition, a novel polyurethane containing imidazolium cations in the hard segment was synthesized and behaved very similarly to the phosphonium cation-containing polyurethane. Ammonium ionenes, which contain quaternary nitrogen in the macromolecular repeating unit, have many potential uses in biomedical applications. They offer interesting coulombic properties, and the charge density is easily controlled through synthetic design. This property makes ionenes ideal polyelectrolyte models to investigate the influence of ionic aggregation on many physical properties. Ammonium ionenes were prepared via the Menshutkin reaction from 1,12-dibromododecane and 1,12-bis(N,N-dimethylamino)dodecane. The absolute molecular weights were determined for the first time using an on-line multi-angle laser light scattering (MALLS) in aqueous size exclusion chromatography (SEC). Tensile testing and DMA were used to establish structure-property relationships between molecular weight and mechanical properties for a series of 12,12-ammonium ionenes. Furthermore, degradation studies in the presence of base support the possibility for water-soluble coatings with excellent mechanical durability that are amenable to triggered depolymerization. A novel synthetic strategy was utilized to prepare chain extended 12,12-ammonium ionenes containing cinnamate functional groups. In the presence of UV light, the polymers chain extended, and the resulting ionenes possessed enhanced thermomechanical properties and increased molecular weight. In addition, the novel synthesis of imidazolium ionenes was demonstrated, and the charge density was tuned for appropriate applications using either low molecular weight segments or oligomeric precursors. The change in charge density had a profound role in imidazolium ionene thermal and mechanical behavior. / Ph. D.

In an effort to synthesize macromolecules comprising both covalent and non-covalent bonding to tune ultimate physical properties, a variety of methodologies and functionalization strategies were employed. First, protected functional initiation, namely 3-[(N-benzyl-N-methyl)amino]-1-propyllithium and 3-(t-butyldimethylsilyloxy)-1-propyllithium, in living anionic polymerization of isoprene was used to yield well-defined chain end functional macromolecules. Using both initiating systems, polymers with good molar mass control and narrow molar mass distributions were obtained and well-defined chain end functionality was observed. There was no observed effect on the polymer microstructure from the polar functionality in the initiator, with ~92% 1,4- and 8% 3,4-enchainment observed in each case. Further investigation of the 3-[(N-benzyl-N-methyl)amino]-1-propyllithium initiated polyisoprenes proved that facile deprotection was not possible and residual catalyst was not removable from the polymer. However, polymers initiated with 3-(t-butyldimethylsilyloxy)-1-propyllithium were quantitatively hydrogenated and deprotected under relatively mild conditions to yield hydroxyl functional macromolecules in several architectures, including linear and star-shaped. Excellent conversion from arm polymer to star polymer was observed and well-defined macromolecules were obtained. Subsequently, a series of non-functional, hydroxyl functional, and 2-ureido-4[1H]-pyrimidone (UPy) chain end functional linear and star-shaped poly(ethylene-co-propylene)s were synthesized and characterized. The melt phase properties were investigated using melt rheology and the effect of macromolecular topology and multiple hydrogen bond functionality was investigated. Linear UPy functional poly(ethylene-co-propylene)s exhibited increased viscosity and shear thinning onset at lower frequencies than non-functional polymers of similar molar mass due to interaction of the multiple hydrogen bonding groups. Star-shaped UPy functional poly(ethylene-co-propylene)s showed inhibition to terminal flow and the absence of a zero shear viscosity in melt rheological characterization, indicative of a network like structure imparted from the multiple hydrogen bonding interactions. In addition, the living anionic polymerization of D3 was controlled using the functionalized initiators3-[(N-benzyl-N-methyl)amino]-1-propyllithium and 3-(t-butyldimethylsilyloxy)-1-propyllithium. Good molar mass control and narrow molar mass distributions were observed. In contrast to the polyisoprene homopolymers, facile deprotection of the 3-(t-butyldimethylsilyloxy)-1-propyllithium was not possible due to the acid sensitivity of the poly(dimethylsiloxane) backbone. However, facile deprotection of the protected secondary amine was achieved through hydrogenolysis and well-defined terminal amine functionalized poly(dimethylsiloxane) was synthesized, which are then amenable to further functionalization reactions. In contrast to the well-defined polymers synthesized using living anionic polymerization, free radical polymerizations was used to synthesize free radical copolymers with broader polydispersities and pendant UPy groups. These copolymers were compared with a simple dimeric hydrogen bonding carboxylic acid containing copolymer. Melt rheological characterization revealed that, at similar concentrations, the effect of the UPy group was much greater than the carboxylic acid, and broadened plateau moduli and increased viscosity for the UPy containing polymers were observed, while the acid containing polymer exhibited similar results to a non-functional control. The dynamic viscosity was observed to increase systematically with increasing UPyMA incorporation and the quadruple hydrogen bonding interactions were observed to dissociate between ~80-150 °C. / Ph. D.

The implications of chain topology and intermolecular interactions on the electrospinning process were investigated for linear and randomly branched polymers. Empirical correlations were developed based on solution rheological measurements that predict the onset of electrospun fiber formation and average fiber diameter. In particular, for neutral, non-associating polymer solutions, the minimum concentration required for fiber formation was the entanglement concentration (Ce), and uniform, bead-free fibers were formed at 2 to 2.5 Ce. This was attributed to entanglement couplings stabilizing the electrospinning jet and preventing the Raleigh instability. Moreover, the influence of molar mass and degree of branching on electrospun fiber diameter was eliminated when the polymer concentration was normalized with Ce, and the fiber diameter universally scaled with C/Ce to the 2.7 power. Polymers modified with quadruple hydrogen bonding groups were investigated to determine the role of intermolecular interactions on the solution rheological behavior and the electrospinning process. In nonpolar solvents, the hydrogen bonding functionalized polymers displayed significant deviation from the electrospinning behavior for neutral solutions due to the strong intermolecular associations of the multiple hydrogen bonding groups. The predicted electrospinning behavior was recovered when the hydrogen bonding interactions were screened with a polar solvent. Moreover, it was observed that branching and multiple hydrogen bonding afforded significant processing advantages compared to functionalized, linear analogs of equal molar mass. For example, branched chains in the unassociated state possessed a larger Ce compared to the linear chains, which indicated a lower entanglement density of the former. However, in the associated state the linear and branched chains possessed nearly equivalent Ce values, suggesting a similar entanglement density. Thus, the branched polymers displayed significantly lower viscosities in the unassociated state compared to linear polymers, while still retaining sufficient entanglements in the associated state due to the reversible network structure of the multiple hydrogen bond sites. The solution rheological and processing behavior of polyelectrolyte solutions was also investigated to discern the role of electrostatic interactions on electrospun fiber formation. In particular, the polyelectrolyte solutions formed nano-scale electrospun fibers with an average fiber diameter 2 to 3 orders of magnitude smaller than neutral polymer solutions of equivalent viscosity and C/Ce. This was attributed to the very high electrical conductivity of the polyelectrolyte solutions, which imparted a high degree of charge repulsion in the electrospinning jet and increased the extent of plastic stretching in the polymer filament. In fact, the average diameter of the polyelectrolyte fibers under certain conditions was less than 100 nm, which makes them good candidates for protective clothing applications due to their high specific surface area. Moreover, the neutral polymer solution electrospinning behavior was recovered after the addition of NaCl, which screened the electrostatic charge repulsions along the polyelectrolyte main chain. Finally, electrospun, biocompatible phospholipid membranes were produced from solutions of entangled worm-like lecithin micelles. This is the first example of successfully electrospinning low molar mass, amphiphilic compounds into uniform fibers. Electrospinning the phospholipid worm-like micelles into nonwoven fibrous mats will afford direct engineering of bio-functional, high surface area membranes without the use of multiple synthetic steps, complicated electrospinning setups, or post processing surface treatments. / Ph. D.

Changes in pretreated 5182, 6061 and 7075 aluminum surfaces on exposure to moisture for short times was studied. The pretreatment used was the standard ASTM method for FPL etching of aluminum. The moisture treatment used was either immersion in water at 81° C or exposure to water vapor at 81° C. The experimental techniques used to analyze the pretreated aluminum surfaces before and after exposure to moisture were ESCA or XPS, AES, high resolution SEM, and specular reflectance FTIR. There was a change in the surface topography on exposure of the aluminum surfaces to water as determined using high resolution SEM. Stoichiometric calculations based on XPS analysis were made to estimate the amount of excess water present on the surface. Water was present on the surface before exposure to moisture, for all three alloys. The amount of water present on the surface was found to decrease with increasing times of exposure to water for all three alloys. This result was consistent with the model that pseudoboehmite formed on the surface was being converted into boehmite at longer times of exposure to water. The thickness of the oxide layer was found to increase with time of exposure to water based on ESCA results. The same conclusion was reached by depth profiling the oxide layer using AES. The rate of increase in the concentration of pseudoboehmite on the surfaces as calculated from FTIR data went in the order 7075 < 5182 < 6061. The activation energy for the third step (transport of soluble species to the surface) in the conversion of surface Al₂O₃ to AlOOH was calculated from FTIR results to be 3.5 kcal mol⁻¹. / Master of Science

Numerous researchers have argued early adolescent behavior patterns are among the best predictors of later achievement and social-psychological adjustment outcomes. In the current study, a secondary data analysis was conducted to determine the extent to which four prosocial behaviors (cooperation, assertiveness, self-control and prosocial behaviors toward peers) and two forms of aggression (overt and relational) influence academic performance (as indexed by GPA and standardized achievement scores). Additionally, the potential moderating role of two school environment variables (perception of school climate and teacher bonding) were also considered in order to further examine the social-emotional environment of middle schools. Examining concurrent relations between grade 5 social behaviors and academic performance revealed all four forms of prosocial behavior were positively related to higher academic performance. Predictive relations between grade 6 social behaviors and academic outcomes at grade 9 indicated that of the four prosocial behaviors and two forms of aggression, cooperation alone predicted the likelihood of later academic achievement. Finally, it was hypothesized that prosocial behaviors, perception of school climate and teacher bonding would serve as moderators between aggression and academic performance; however, this prediction was unsupported. By drawing attention to the limited typology employed in studying prosocial behavior, as well as the methodological challenges that arise when examining these behaviors during adolescence, the hope is to spur research geared towards a more comprehensive understanding of prosocial development. / Master of Science