The relaxation characteristics of rubbery poly(ethylene oxide) [PEO] networks have been investigated as a function of network composition and architecture via dynamic mechanical analysis and broadband dielectric spectroscopy. A series of model networks were prepared via UV photopolymerization using poly(ethylene glycol) diacrylate [PEGDA] as crosslinker: variations in crosslink density were achieved either by the introduction of water in the prepolymerization reaction mixture, or by the inclusion of mono-functional acrylate such as poly(ethylene glycol) methyl ether acrylate [PEGMEA] or poly(ethylene glycol) acrylate [PEGA]. Copolymerization with mono-functional acrylate led to the insertion of flexible branches along the network backbone, and the corresponding glass-rubber relaxation properties of the copolymers (i.e., Tg, relaxation breadth, fragility) were a sensitive function of network architecture and corresponding fractional free volume. Relatively subtle variations in network structure led to significant differences in relaxation characteristics, and a systematic series of studies was undertaken to examine the influence of branch length, branch end-group, and crosslinker flexibility on viscoelastic response. Dielectric spectroscopy was especially useful for the elucidation of localized, sub-glass relaxations in the polymer networks: the imposition of local constraint in the vicinity of the crosslink junctions led to the detection of a distinctive fast relaxation process in the networks that was similar to a comparable sub-glass relaxation observed in crystalline PEO and in the confined regions of PEO nanocomposites. Gas permeation studies on the model PEGDA networks confirmed their utility as highly-permeable, reverse-selective membrane materials, and strategic control of the network architecture could be used to optimize gas separation performance. Dynamic mechanical and dielectric measurements have also been performed on a semicrystalline polyester, poly(trimethylene terephthalate) [PTT], in order to assess the influence of processing history on the resultant morphology and corresponding viscoelastic relaxation characteristics. Studies on both quenched and annealed PTT revealed the presence of a substantial fraction of rigid amorphous phase (RAP) material in the crystalline samples: dielectric measurements showed a strong increase in relaxation intensity above the glass transition indicating a progressive mobilization of the rigid amorphous phase with increasing temperature prior to crystalline melting.

The dynamic relaxation characteristics of Matrimid® (BTDA-DAPI) polyimide and several functionalized aromatic polyimides have been investigated using dynamic mechanical and dielectric methods. The functionalized polyimides were thermally rearranged to generate polybenzoxazole membranes with controlled free volume characteristics. All polyimides have application in membrane separations and exhibit three motional processes with increasing temperature: two sub-glass relaxations (ƴ and β transitions), and the glass-rubber (α) transition. For Matrimid, the low-temperature ƴ transition is purely non-cooperative, while the β sub-glass transition shows a more cooperative character as assessed via the Starkweather method. For the thermally rearranged polyimides, the ƴ transition is a function of the polymer synthesis method, thermal history, and ambient moisture. The β relaxation shows a dual character with increasing thermal rearrangement, the emerging lower-temperature component reflecting motions encompassing a more compact backbone contour. For the glass-rubber (α) transition, dynamic mechanical studies reveal a strong shift in Tα to higher temperatures and a progressive reduction in relaxation intensity with increasing degree of thermal rearrangement. The dynamic relaxation characteristics of poly(ether imide) and poly(methyl methacrylate) nanocomposites were investigated by dynamic mechanical analysis and dielectric spectroscopy. The nanoparticles used were native and surface-modified fumed silicas. The nanocomposites display a dual glass transition behavior encompassing a bulk polymer glass transition, and a second, higher-temperature transition reflecting relaxation of polymer chain segments constrained owing to their proximity to the particle surface. The position and intensity of the higher-temperature transition varies with particle loading and surface chemistry, and reflects the relative populations of segments constrained or immobilized at the particle-polymer interface. Dielectric measurements, which were used to probe the time-temperature response across the local sub-glass relaxations, indicate no variation in relaxation characteristics with particle loading. Nanocomposite studies were also conducted on rubbery poly(ethylene oxide) networks crosslinked in the presence of MgO or SiO2 nanoparticles. The inclusion of nanoparticles led to a systematic increase in rubbery modulus and a modest positive offset in the measured glass transition temperature (Tα) for both systems. The sizeable increases in gas transport with particle loading reported for certain other rubbery nanocomposite systems were not realized in these crosslinked networks.

Orientador: Maria da Consolação Fonseca de Albuquerque / Resumo: Inúmeros problemas sociais e ambientais são causados pela impermeabilização dos solos em decorrência da urbanização descontrolada e sem planejamento. O pavimento em concreto permeável aparece como uma forma de mitigação de enchentes, devido à sua característica de permitir a infiltração total ou parcial de água proveniente de precipitações. O objetivo deste trabalho foi estudar um traço eficiente e empregá-lo de maneira efetiva em uma calçada, para promover a captação total de eventos pluviométricos ocorridos no local e observar, com o decorrer do tempo, a eficiência de manutenção periódica na superfície do pavimento permeável quanto à colmatação. Foram experimentadas três proporções de misturas: 1:3,5; 1:5 e 1:6,5, sendo que em nenhuma foi utilizado agregado miúdo. Também foi observado o comportamento das misturas com duas granulometrias de agregados graúdos de 9,5/25,0 e 4,75/12,5. Ensaios destrutivos e não destrutivos foram realizados, entre eles: resistência à compressão axial, tração por compressão diametral, tração na flexão e taxa de infiltração. A mistura mais eficiente e escolhida para a construção da calçada foi a de teor 1:5, com a utilização do agregado de faixa granulométrica 4,75/12,5. Testes estatísticos ―t Student” foram utilizados para comparar os resultados obtidos na presente pesquisa com trabalhos semelhantes. A calçada foi dimensionada para ter eficiência de caráter pluviométrico, de acordo com incidência pluviométrica regional e mecânico através de análi... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Uncounted social and environmental problems are caused by the waterproofing of soils as a result of uncontrolled and unplanned urbanization. The pervious concrete pavement appears as a form of flood mitigation due to its characteristic of allowing total or partial infiltration of water from rainfall. The aim of this work was to study an efficient mixture and to use it effectively on a sidewalk, to promote the total retention of rainfall events occurring locally and to observe the efficiency of periodic maintenance on the pervious pavement surface, regarding clogging over time. Three proportions of mixtures were tested: 1:3.5; 1:5 and 1:6.5, in which none fine aggregates was used. Furthermore, the behavior in the mixtures of two coarse aggregates gradations of 9.5/25.0 and 4.75/12.5 was observed. Destructive and non-destructive tests were performed, such as: compressive strength, splitting tensile strength, flexural strength and infiltration rate. The most efficient and chosen mixture for the construction of the sidewalk was 1:5, with the use of the aggregate size 4.75/12.5. ―Student’s t‖ statistical tests were used to compare the results obtained in the present research with similar works. The sidewalk was dimensioned to have rainfall efficiency, according to regional rainfall incidence, and mechanical efficiency, through analysis in the EverFE computational program, followed by calculation of fatigue life. The permeability rate of the pavement was monitored weekly over time,... (Complete abstract click electronic access below) / Mestre

Neste trabalho foi estudada a influência da adição de quitosana e sílica a monômeros dimetacrílicos, BisEMA e TEGDMA, por meio das técnicas de fotocalorimetria, termogravimetria e análise dinâmico mecânica. Os resultados dos experimentos de fotocalorimetria demonstraram que a quitosana pode aumentar a velocidade de polimerização e o máximo de conversão para alguns sistemas em determinadas concentrações da mesma, já a sílica tem pouco efeito nas reações de fotopolimerização das amostras. Para os experimentos de termogravimetria, a quitosana tem pouca influência na degradação das amostras não alterando significativamente as curvas TGA/DTG, por outro lado a sílica acelerou a degradação térmica das amostras. A avaliação das propriedades mecânicas demonstrou que a quitosana diminui a temperatura de transição vítrea e a resposta elástica dos sistemas não afetando os valores dos módulos de armazenamento e módulos de perda. A sílica apresentou a tendência de aumento de temperatura de transição vítrea e não alteração da resposta elástica das amostras. / In this work we studied the influence of the addition of chitosan and silica in dimethacrylic monomers, BisEMA and TEGDMA, by photocalorimetry, thermogravimetric analysis and dynamic mechanical analysis. The results of photocalorimetry experiments demonstrated that chitosan can increase the polymerization rate and the degree of conversion for some concentrations. Silica has little effect on photopolymerization reactions of samples. For thermogravimetric experiments, chitosan has little influence on the degradation of samples and does a slightly change the TGA / DTG curves, on the other hand silica accelerated thermal degradation of the samples. The evaluation of mechanical properties showed that chitosan reduces the glass transition temperature and elastic response of the samples but does not affect the values of the storage modulus and loss modulus. Silica showed an effect of increasing glass transition temperature and almost no change in the elastic response of the samples.

Neste trabalho foi estudada a influência da adição de quitosana e sílica a monômeros dimetacrílicos, BisEMA e TEGDMA, por meio das técnicas de fotocalorimetria, termogravimetria e análise dinâmico mecânica. Os resultados dos experimentos de fotocalorimetria demonstraram que a quitosana pode aumentar a velocidade de polimerização e o máximo de conversão para alguns sistemas em determinadas concentrações da mesma, já a sílica tem pouco efeito nas reações de fotopolimerização das amostras. Para os experimentos de termogravimetria, a quitosana tem pouca influência na degradação das amostras não alterando significativamente as curvas TGA/DTG, por outro lado a sílica acelerou a degradação térmica das amostras. A avaliação das propriedades mecânicas demonstrou que a quitosana diminui a temperatura de transição vítrea e a resposta elástica dos sistemas não afetando os valores dos módulos de armazenamento e módulos de perda. A sílica apresentou a tendência de aumento de temperatura de transição vítrea e não alteração da resposta elástica das amostras. / In this work we studied the influence of the addition of chitosan and silica in dimethacrylic monomers, BisEMA and TEGDMA, by photocalorimetry, thermogravimetric analysis and dynamic mechanical analysis. The results of photocalorimetry experiments demonstrated that chitosan can increase the polymerization rate and the degree of conversion for some concentrations. Silica has little effect on photopolymerization reactions of samples. For thermogravimetric experiments, chitosan has little influence on the degradation of samples and does a slightly change the TGA / DTG curves, on the other hand silica accelerated thermal degradation of the samples. The evaluation of mechanical properties showed that chitosan reduces the glass transition temperature and elastic response of the samples but does not affect the values of the storage modulus and loss modulus. Silica showed an effect of increasing glass transition temperature and almost no change in the elastic response of the samples.

This thesis is a pilot study, designed to test and develop methods suitable for the study of Scandinavian flint spearhead functionality. The functionality of projectile and lithic point armament has not been studied for almost 30 years in Scandinavia. Meanwhile, methods used to analyse lithic projectiles have developed considerably. However, few of these methods are precise enough to be used in conjunction with Scandinavian stone technological analyses that emphasize the societal aspect of lithic points. Consequently, two methods were chosen that could provide data for Scandinavian research issues: 3D-scanning/continuum mechanical simulations and organic residue analysis. The methods were tested on 6 experimental spearheads. The continuum mechanical simulation generated both visual and numerical data that could be used to create precise functional-morphological descriptions. The data could also potentially be used for projectile point classification. The organic residue analysis revealed promising results for the use of an artefact and activity specific analysis, with a sequential extraction protocol. In unison, the results from both analyses could be used to reveal how spearheads were functionally designed and used in Stone Age Scandinavia, even though there are methodological and technological issues that need solving.

A melhoria nos aspectos de eficiência e de segurança dos reatores nucleares compactos está diretamente ligada às inovações nos combustíveis e na geometria dos Elementos Combustíveis - ou E.C. - como é o caso do tipo Placa, em comparação com o do tipo Vareta. Do ponto de vista mecânico, garantir que a estrutura de um E.C. está segura para funcionar em um reator PWR compacto é afirmar que esta cumpre os requisitos funcionais de projeto para estruturas deste tipo e aplicação, presentes na norma ANSI/ANS-57.5-1996; e também que as tensões resultantes dos carregamentos impostos sobre si são menores do que os limites mecânicos admissíveis para os seus materiais estruturais, de acordo com a norma ASME III, divisão 1, subseção NB. Para desenvolver uma metodologia de análise mecânica buscando verificar o atendimento aos critérios das normas citadas, foi proposto um modelo conceitual computacional de E.C. placa e, posteriormente, este modelo foi submetido a uma série de análises computacionais que simularam a aplicação das combinações dos principais carregamentos atuantes. Os resultados extraídos das análises revelaram que os valores das tensões resultantes da aplicação dos carregamentos foram inferiores aos valores dos limites admissíveis dos materiais que compõem os seus componentes. Foi observado, também, que os deslocamentos resultantes não ultrapassaram os limites funcionais, que são o contato entre estruturas semelhantes vizinhas e/ou o contato da região superior desta estrutura com as estruturas de suporte do vaso de pressão que o contém. / The improvement in the efficiency and safety aspects of compact nuclear reactors is directly linked to innovations in fuels and the geometry of Fuel Elements - F.E. - as is the case of the Plate type, as compared to the Rod type. From a mechanical point of view, to ensure that the structure of an F.E. is safe to operate in a compact PWR reactor is necessary to state that it meets the functional design requirements for structures of this type and application, present in ANSI / ANS-57.5-1996; and also that the stresses resulting from the loads imposed on them are less than the permissible mechanical limits for their structural materials in accordance with ASME III, division 1, subsection NB. In order to develop a methodology of mechanical analysis to verify compliance with the criteria of the cited standards, a computational conceptual model of F.E. Plate structure was proposed and later this model was submitted to a series of computational analyzes that simulated the application of the combinations of the main active loads. The results obtained from the analyzes revealed that the values of the stresses resulting from the application of the loads were lower than the values of the allowable limits of the materials that make up their components. It was also observed that the resulting displacements did not exceed the functional limits, which are the contact between neighboring similar structures i.e. the contact of the upper region of this structure with the supporting structures of the pressure vessel containing it.

The viscoelastic relaxation dynamics of a series of poly(methyl methacrylate) [PMMA] based nanocomposites filled with carbon nanotubes have been studied using dynamic mechanical analysis and broadband dielectric spectroscopy. The networks were prepared using four methods: (i) melt mixing, (ii) solution processing, (iii) in-situ polymerization, and (iv) polymer grafting. Nanotube modifications included surface oxidation via acid exposure and surface functionalization for polymer grafting. The effect of variations in processing method and nanotube modification on glass transition temperature (Tg) and relaxation dynamics was investigated. The relaxation behavior of the nanocomposites was sensitive to processing method and nanotube functionalization. Nanotube loading (to 5 wt%) led to a progressive increase in rubbery modulus, with the increase more pronounced in the solution-processed samples owing to enhanced nanotube dispersion. In the case of the oxidized nanotubes, loading led to an increase in modulus, but also a systematic decrease in Tg of ~ 15°C with 3 wt% nanotubes. For in-situ polymerized (PMMA/MWNT-ox) nanocomposites, there was no readily discernable trend in Tg. Composites prepared via in-situ polymerization in the presence of methyl methacrylate functionalized tubes (i.e., polymer grafting) displayed a positive shift in Tg of nearly 20°C at 1 wt% loading. Investigation of the dielectric relaxation of the PMMA/MWNT composites indicated a percolation threshold between 0.3 and 0.4 wt% MWNT.

The structural adhesives widely used in structural strengthening applications are thermoset ambient cure adhesive polymers. At ambient temperatures, these polymers are in a relatively hard and inflexible state. At higher temperatures, the material becomes soft and flexible. The region where the molecular mobility changes dramatically is known as the glass transition temperature Tg and often is presented as a single value. Epoxy polymers exhibit a significant reduction in mechanical properties near glass transition temperature Tg when they are exposed to elevated temperatures. Glass transition temperature Tg is used to characterise the change in epoxy adhesive properties with changing temperature. The mechanical properties of epoxies tend to improve with curing temperature. This is because the crosslink density between the adhesive molecular structures increases during the curing process consequently the Tg improves. The aims of this work are first to demonstrate the importance of curing temperature. Second, to investigate the influence of glass transition temperature !! improvement on the performance of EB-FRP strengthened steel structures in flexure at ambient and elevated temperatures. Third, to compare analytical results with experimental results from the flexure tests results. Finally, to compare the current design guideline recommendations with the flexure tests results. The most commonly used methods to evaluate Tg Dynamic Mechanical Analysis (DMA) and Differential Scanning Calorimetry (DSC) were used to study Tg. Two off-shelf structural adhesives were investigated to understand their property variation with temperature. Epoxy coupons were cured at different elevated temperature and humidity environments up to 28 days. A combination of two extreme relative humidity of 0 and 100% and variable curing temperatures between 15 to 80°C were considered. From a test matrix of 300 DMA and over 250 DSC coupons these conclusions were drawn. First, ambient cured thermosets have a linear relationship between Tg and curing temperature, but Tg is reduced if a certain temperature is reached. Second, a fully cured adhesive requires heating treatment. Without a curing regime, designed Tg may never be achieved. Finally, curing time is crucial at the low curing temperatures while it is less significant at the higher curing temperature. The results of Tg investigation were used to select appropriate curing temperature that the adhesives resistance to temperature can be maximised without damaging the mechanical properties. The study helps designs to understand and assess the behaviour of these two adhesives when they are exposed to extreme temperatures. The study increases the awareness that a fully cured adhesive may never be achieved at ambient or low temperatures. It is important to find the mechanical properties and Tg when the coupons are exposed to the same curing temperature. To investigate the influence of glass transition temperature Tg improvement on the performance of EB-FRP strengthened steel structures in flexure at ambient and elevated temperature, nine three metre length beams were designed to behave as a concrete-steel composite bridge deck. The beams were tested in four-point bending. Lap shear, DMA test, and pull-off adhesion samples were prepared and cured at the same conditions and tested at ambient temperature. Six beams were tested under only mechanically loading at ambient temperature, including the control specimen. Five beams were tested at ambient temperature to show the effects of adhesive curing on FRP strengthened sections. A significant increase of load capacity of the adhesive joints was achieved due to the curing of the joints at elevated temperature. The failure occurred was in the same manner. An increase in the load capacity was observed with increasing curing temperature. An increase of approximately 25% was noticed in the ultimate load capacity of the specimens cured at 50°C compared to the specimens cured at 30°C. The load capacity of lap-shear specimens cured at 50°C was 28% higher than the specimens cured at 30°C. Three specimens were tested under mechanical and thermal loading. A bespoke thermal chamber was designed and fabricated to apply a controlled thermal loading. The beams were loaded mechanically up to 350kN, first. The temperature of the specimens was then increased at a rate of 0.8°C/min. The sustained load 350kN remained constant during the heating phase. Digital Image Correlation (DIC) technique was used to detect the slippage of the tip of the FRP plates. The only specimen cured at 30°C showed relatively poor performance compared to the two specimens cured at 50°C. The plate ends started to slip when the adhesive storage modulus from the DMA runs reduced approximately by 15 and 18% for the beams cured at 30 and 50°C respectively. Pull-off adhesion tests confirmed that adequate surface preparation of over 25 MPa was achieved The flexural model for the composite steel section represented to predicate load-deflection behaviour of the specimens using semi-experimental constitutive material law. The model successfully predicts the load-deflection behaviour of specimens, considering the strain hardening contribution. A bond stress analysis is also presented, which counts for the effect of FRP plate moment effect. The experimental and theoretical FRP plate slippage assuming only adhesive degradation with temperature are compared. The analytical bond models cannot predict the experimental failure because the linear elastic material properties were assumed and the failure was adhesion.

In this work differential scanning calorimetry, dynamic mechanical analysis, Fourier-Transformed Infrared Spectroscopy [FT-IR] and polarized light microscopy will be employed to characterize polymeric systems. The first chapter broadly covers polymer synthesis and important characterization methods. In the second chapter, a polyamide (PA12) will be sintered via a novel additive manufacturing (AM) technology developed here at USF termed LAPS (Large Area Projection Sintering). LAPS uses extended sintering timespans to ensure complete melting and densification of the polymer powder over the entire two-dimensional area of the part’s footprint. Further, it allows for the printed layer to crystallize and shrink in its entirety as the temperature falls below the crystallization temperature prior to the next layer being added. The printed parts (termed coupons) will be assayed by DSC and polarized light microscopy to determine sintering efficacy. Additionally, the parts will be compared to coupons printed with conventional methods to show that the USF AM technology shows superior elongation at break (EaB), with comparable ultimate tensile strength (UTS) and Young’s Modulus to laser sintered coupons. This is notable as conventional AM methods produce parts which usually compromise between EaB and modulus. The EaB of LAPS-printed parts is comparable to injection molding (IM) grade PA12, which is remarkable as IM grade PA12 powder normally has higher molecular weight and limited crystallinity. The reduced crystallinity of IM grade PA12 parts is thought to be due to the high shear rates during injection and fast cooling rates post-fabrication. Further, the USF LAPS parts show minimal or no detectable porosity. Porosity is an artifact of the sintering process which conventional techniques like laser sintering (LS) have little ability to mitigate, as higher energy wattages simply burn and degrade the polymer surface with insufficient time available for heat transfer and bulk melt flow. Porosity is documented as one of the leading causes of part failure and decreased mechanical properties in the literature, and as such the USF AM technology is in the process of being patented as of March, 2018. Chapters three through six will explore a phenomenon first noticed by clinicians at the James A. Haley Veterans Hospital. They observed that starch-thickened drinks for patients suffering from dysphagia became dangerously thinned down upon addition of the osmotic drug polyethylene glycol (PEG) 3350, marketed as Miralax®. Starch-based hydrocolloids are common thickeners used for patients with dysphagia, and so any incompatibility with such a ubiquitous drug as PEG 3350 poses an immediate danger. Patients with the disorder can suffer increased rates of aspiration-related pneumonia, incurring up to nearly a 60% fatality rate within a year. Chances for aspiration greatly increase for food items which are too inviscid to safely swallow. Rheology and FT-IR spectroscopy will be used to show that the breakdown of the starch network in aqueous solution is dependent upon the molecular weight of PEG. As the molecular weight of PEG is reduced to that of a small molecule (~300MW) from its large drug form (3350MW), the structure stabilizes and can resist shearing forces in a steady shear rheological experiment. Spectroscopy will show that PEG molecular weight also influences syneresis and the crystallinity of the starch hydrocolloid solutions. It is postulated that the molecular weight of PEG influences its miscibility in starch solutions, and its ability to interrupt the hydrogen bonding and entanglements which maintain the elastic framework which allow starch thickeners to impart viscosity and resist shearing forces. When this framework collapses, absorbed water is expelled as evidenced as a biphasic separation where water collects on top of the starch suspension. This was the phenomenon observed by the clinicians at the Veterans’ Hospital.