M.S.

No description available.

Semicrystalline ionomers are an important class of polymers that are utilized in a wide range of applications. The particular end-use applications of these materials are determined by their chemical, physical, and thermomechanical properties which are directly related to their crystallization behavior. It is therefore critical to identify structure-property relationships for these materials. Sulfonated syndiotactic polystyrene (SsPS) is used as a model semicrystalline ionomer and two approaches are utilized to control the rate of crystallization of the SsPS ionomer in the presence of ionic aggregates. The first approach investigates the effect of the incorporation of nanoscale particles, montmorillonite clay, on the crystallization behavior of SsPS. The morphology of the ionomer clay hybrids were studies via TEM and WAXD while the crystallization behavior of SsPS in the presence of the clay was evaluated using DSC. It was found that the SsPS matrix containing 5 wt.% organically-modified clay crystallized more rapidly than the sPS homopolymer containing the same clay content. This behavior is attributed to the presence of homogenously dispersed nanoscale clay platelets that act as nucleation sites distributed throughout the ionomer matrix. The second approach that employed involved the manipulation of SsPS ionomer architecture via a controlled placement of the ionic sulfonate groups along the polymer backbone. A post-polymerization sulfonation technique was developed to place the sulfonate groups along the homopolymer backbone in a non-random fashion leading to a pseudo-block ionomer architecture. The crystallization behavior of the non-randomly sulfonated SsPS ionomer is compared to randomly sulfonated SsPS using differential scanning calorimetry. The morphologies of the two ionomers were studied using SALLS and SAXS. We have found that the non-randomly sulfonated SsPS ionomer crystallizes much more rapidly than the randomly sulfonated ionomer. The more rapid crystallization behavior of the non-random ionomer to the presence of longer sequences of unsulfonated homopolymer that are able to readily organize into crystalline structures than the random SsPS ionomer containing the same ionic content. / Ph. D.

M.S.

The detection and identification of particles within fluid samples is key in the prevention of the spreading of disease. This has created a growing need for devices able to successfully separate and identify multiple particles for this purpose while operating at a high enough throughput to be applicable in the field. A well investigated method of manipulating particles in this way is Dielectrophoresis (DEP), which is the use of varied electric fields gradients to generate a force on small particles. The strength of DEP depends of the properties of the particle medium, the signal generating the electric field, and the properties of the particles themselves. This method and its interaction with all small particles, including biological particles such as blood and cancer cells, has allowed devices utilizing this idea to be investigated for various biological purposes. This thesis investigates methods to increase the throughput of these types of devices in order to increase their ability to process large amounts of samples in reasonable amounts of time. This is done in primarily two methods. One approach uses the application of chromatographic methods to DEP devices to separate particles by altering their individual transit time through a device, allowing identification during constant flow. Another method is through mass parallel channels which each individually operate as a standard DEP particle trapping device. This allows for the summation of the maximum flow through the device due to its design layout. / Master of Science / Micrometer scale devices are popular for the identification, separation, and characterization of micron scale particles. This includes uses in biological fields for the manipulation of particles such as blood cells, cancer cells, and bacteria. A common method of manipulating these particles is Dielectrophoresis, a force that causes particles to be repelled or attracted to geometric designs within the device generated by an applied electric field. The strength and direction of this force on the particles is dependent on the properties of the electrical signal applied to the device, the physical properties of the particles, such as size and shape, and the properties of the medium the particles are suspended in within the device. Biological devices utilizing this force have been tested before, allowing for particles to be separated out of mixed particle solutions. Most of these devices operate by moving through very little material at one time, somewhere in the microliter per hour range. This thesis explores attempts to increase the rate at which samples can be processed by these devices in multiple ways. Chapter 2 explores methods of DEP by applying Chromatography principles, which is to constantly move samples through the device at a high rate and slow the target particles, so they exit the device at a different time than other particles. Chapter 3 investigates increasing device throughput by replicating a standard DEP channel multiple times on one device so that several may operate all at once.

No description available.

A Tioxantona (TX) e a Benzofenona (BP) são cetonas frequentemente utilizadas como sensibilizadores em reações fotoquímicas. Assim, foi investigada a degradação de filmes de poliestireno (PS) contendo TX e BP como fotossensibilizadores. Os filmes foram irradiados em λ > 350 nm, em condições e tempos diferentes. As mudanças espectrais dos filmes foram acompanhadas por espectroscopia de infravermelho e UV-Vis e as mudanças no peso molecular foram acompanhadas por cromatografia de exclusão por tamanho (SEC). Os espectros UV-Vis mostraram que TX sofre fotobranqueamento após 5 h, ao contrário de BP que é fotoestável. Simultaneamente, os polímeros contendo grupos cromóforos são formados e a luz é absorvida. Os fotoprodutos nos filmes contendo TX e BP mostraram um aumento de absorbância entre 280-360 nm e 310-370 nm, respectivamente. Os picos de IV em torno de 3645 e 1740 cm-1 indicam a geração de hidroperóxidos e espécies carbonílicas, respectivamente. Os resultados mostraram que TX gerou mais fotoprodutos do que a BP. Os filmes de PS irradiados apresentaram uma diminuição no peso molecular indicando que ocorreu a cisão na cadeia polimérica. A fotofísica dos estados excitados de TX e TX quimicamente incorporada no poliestireno (PS-TX I e PS-TX II) foi estudada, com a finalidade de estudar o comportamento como fotossensibilizador na fotodegradação do PS. O triplete-triplete (T-T) e transientes de TX e TX contendo poliestireno foram estudados em diferentes solventes, para verificar o efeito de polaridade do solvente. Uma boa correlação foi encontrada entre o solvente ET(30) e parâmetro de energia do T-T. A constante de velocidade de supressão para a desativação do triplete de TX por trietanolamina diminuiu quando aumentou-se a polaridade do solvente. Essa variação é representada pela escala de polaridade do solvente através dos parâmetros π*, α e β. / Many ketones, quinones and peroxides are initiators of different reactions such as polymerization, degradation, chemical modification that occur in organic compounds. Thioxanthone (TX) and Benzophenone (BP) are ketones often used as photosensitizers in photochemical reactions. The degradation of polystyrene films containing TX and BP was investigated. Films were irradiated at λ > 350 nmin different conditions at different times. The changes were investigated by infrared and UV-Vis spectroscopies and the molecular weight were determined by gel permeation chromatography (GPC). The UV-Vis spectra showed that TX is photobleached after 5 h, unlike BP which is photostable. Simultaneously, polymers containing chromoforic groups are formed and the light is absorbed by them. The formation of photoproducts films containing TX and BP showed an increase of absorbance between 280-360 nm and 310-370 nm, respectively. The IR peaks around 3645 and 1740 cm-1 indicated the generation of hydroperoxide and carbonyl species, respectively. The results showed that thioxanthone has generated more photoproducts than benzophenone. The UV-Vis irradiation of PS films in both samples presented a decrease in the molecular weight after irradiation, indicating that polymer chain scission occurs. The photophysics of the excited states of thioxanthone (TX) and thioxanthone which was chemically incorporated in polystyrene (PS-TX I and PS-TX II) have been studied in order to be able to predict their behavior as photoinitiator in photodegradation of PS. The triplet-triplet (TT) and transient absorptions of thioxanthone and thioxanthone-containing polystyrene (PS-TX I and PS-TX II) has been studied in different solvents in order to ascertain the effect of the solvent. A good correlation is found between the solvent ET(30) parameter and the energy of the triplet-triplet. The quenching rate constants for the deactivation of triplet thioxanthone by triethanolamine decreases when the solvent polarity increases. This variation is represented by the π*, α and β scale of solvent polarity.

O estudo do comportamento de materiais em relação a intempérie, esforços, tempo, temperatura é fundamental para a escolha de materiais para uma dada aplicação. O poliestireno é uma resina polimérica muito aplicada no mercado, pois é transparente e relativamente econômica, mas não é indicada para aplicações com muita exposição a radiações luminosas, já que é muito susceptível a intemperismos, não sendo recomendada para aplicações com excessiva exposição. A adição de borracha (copolímero de estireno e butadieno) melhora algumas de suas propriedades, como resistência ao impacto e ductilidade, mas piora outras características, como a resistência à tração. Em relação ao intemperismo, apesar da borracha degradar-se rapidamente, ela protege o poliestireno da radiação ultravioleta. Este estudo visa comparar as conseqüências da degradação por envelhecimento natural com o envelhecimento artificial acelerado do poliestireno e do poliestireno de alto impacto e a determinação da possível correlação entre eles. Foram utilizados equipamentos de envelhecimento artificial, de ensaio de tração, impacto IZOD, índice de fluidez, uma estação de envelhecimento natural e equipamento de análise térmica (DSC). Os resultados obtidos permitiram correlacionar os envelhecimentos natural e artificial em relação às propriedades medidas, sendo que para o poliestireno comum, o envelhecimento artificial acelerou a degradação em cerca de 4 vezes, enquanto que para o poliestireno de alto impacto, o fator de aceleração foi de cerca de 2 vezes. / The study of weathering materials regarding to climate, stresses, time, temperature, is essential to choose the materials for a purpose. Polystyrene is a polymeric resin with much usage in the market as it is transparent and relatively cheap, but it is not indicated for outdoor purposes with much actinic radiation exposure, as it is very sensitive to weathering, tough not recommended to purposes with much exposure. The addition of rubber (styrene-butadiene copolymer) improves some of its properties, like impact resistance and ductility, but decreases other properties, like tensile strength. Regarding the weathering, although the rubber degrades very quickly, it protects the polystyrene from the ultraviolet radiation. This study aims to compare the consequences of the degradation by natural weathering and accelerated artificial weathering and try to correlate their results. Equipments for artificial weathering, tensile strength, IZOD impact, melt flow, a natural weathering station and DSC thermal analysis equipment were used. The results allowed the correlation between the natural and artificial weathering regarding the measured properties, as for the common polystyrene the artificial weathering accelerated the degradation in approximately 4 times, while for the high impact polystyrene the acceleration factor resulted in approximately 2 times.

Polystyrene behaviour in reversed phase high performance liquid chromatography was influenced mainly by the solvent system, but secondary affects were observed depending on the stationary phase. A variety of reversed phase columns were investigated using mobile phase combinations of dichlorom ethane-methanol, dichloromethane-acetonitrile, ethyl acetate-methanol and ethyl acetate-acetonitrile. Several different modes of behaviour were observed depending on the polymer solubility in the solvent system. In the dichloromethane-methanol solvent system, polymer-stationary phase interactions only occurred when the molecules had pore access. Retention of excluded polystyrene depended on the kinetics of precipitation and redissolution of the polymer. Peak splitting and band broadening occurred when the kinetics were slow and molecular weight separations were limited !o oligomers and polystyrenes lower than 5-10(4) dalton. Excellent molecular weight separations of polystyrenes were obtained using gradient elution reversed phase chromatography with a dichloromethane-acetonitrile mobile phase on C18 columns. The retention was based on polymer-stationary phase interactions regardless of the column pore size. Separations were obtained on large diameter pellicular adsorbents that were almost as good as those obtained on porous adsorbents, showing that pore access was not essential for the retention of high molecular weight polystyrenes. In the best example, the separation ranged from the monomer to 10(6) dalton in a single analysis. Very little adsorption of excluded polymers was observed on C8 or phenyl columns. Polystyrene molecular weight separations to 7-10(5) dalton were obtained in an ethyl acetate-acetonitrile solvent system on C18 columns. Adsorption was responsible for retention. When an ethyl acetate-methanol solvent system was used, no molecular weight separations were obtained because of complex peak splitting. Reversed phase chromatography was compared to size exclusion chromatography for the analysis of polydisperse polystyrenes. Similar results were obtained using both methods. However, the reversed phase method was less sensitive to concentration effects and gave better resolution.

Fracture mechanics is applied to study the behavior of concrete containing expanded polystyrene (EPS) aggregate replacement. The EPS replaces a portion of the normal weight fine aggregate. Previous research has shown EPS aggregate replacement changes the failure mode in compression from a typical instantaneous failure, as in normal weight concrete (NWC), to a more gradual dissipation of load carrying capacity. This behavior is investigated through the use of fracture mechanics. The fracture energy, critical stress intensity factor and characteristic length of EPS concrete, NWC and fiber reinforced concrete (FRC) are experimentally determined. The two types of tests used to study these properties are the three point bending test recommended by the RILEM technical committee and a wedge splitting test developed recently. The conclusions derived from this research demonstrate that EPS aggregate replacement increases the size of the fracture process zone in front of the crack tip. This increase in size changes the failure mode of concrete allowing it to maintain load after reaching peak load and absorb more energy during the fracture process.