This thesis research focuses on the characterization of thinfilms made of poly(vinylidene fluoride) (PVDF) using an atomic force microscope. Thinfilms of PVDF were fabricated by a spin coating method with different conditions and characterized using the Atomic Force Microscopy (AFM) for morphological changes. Phase and conformational changes of PVDF were investigated using both wide angle X-ray diffraction (WAXD) and Fourier Transform Infrared Spectroscopy (FTIR). From this analysis, in-situ corona poling with annealing of spin-cast PVDF enabled a phase change from α to the mixture of β and γ phases. This process can decrease the complexity of the conventional method which requires mechanical stretching before poling PVDF in addition to thermal annealing for β phase transformation. This thesis describes some materials and surface properties of solution-cast PVDF thinfilms with various conditions such as topography and phase image, adhesion force, friction force, and roughness. Through the AFM topography and phase images, polymeric behavior and spherulites are discussed in the later part of the thesis.

This thesis research focuses on the characterization of thinfilms made of poly(vinylidene fluoride) (PVDF) using an atomic force microscope. Thinfilms of PVDF were fabricated by a spin coating method with different conditions and characterized using the Atomic Force Microscopy (AFM) for morphological changes. Phase and conformational changes of PVDF were investigated using both wide angle X-ray diffraction (WAXD) and Fourier Transform Infrared Spectroscopy (FTIR). From this analysis, in-situ corona poling with annealing of spin-cast PVDF enabled a phase change from α to the mixture of β and γ phases. This process can decrease the complexity of the conventional method which requires mechanical stretching before poling PVDF in addition to thermal annealing for β phase transformation. This thesis describes some materials and surface properties of solution-cast PVDF thinfilms with various conditions such as topography and phase image, adhesion force, friction force, and roughness. Through the AFM topography and phase images, polymeric behavior and spherulites are discussed in the later part of the thesis.

Yes / The isotactic polypropylene (iPP) usually shows a unique parent-daughter lamellae structure in which the parent and daughter lamellae are against each other with a near perpendicular angle (80° or 100°). Inducing a high fraction of oriented cross-hatched structure in iPP during processing is desirable for designing the bi-oriented iPP products. We processed a commercial iPP via tensile-stretching and die-drawing to evaluate the structural evolution of oriented parent-daughter lamellae. It turned out that the die-drawing process had an advantage in attaining a high fraction of oriented cross-hatched structure of iPP, as compared to the free tensile stretching. Besides, the presence of α-nucleating agents affected the formation of oriented parent-daughter lamellae in the die-drawn samples whereas such influence diminished in the free stretched ones. It was found that the confined deformation inside the die led to the well-preserved oriented cross-hatched structure in the die-drawn iPP. / This work was financially supported by the National Natural Science Foundation of China (Nos. 21704102, U1832186, and 51525305), Newton Advanced Fellowship of the Royal Society, United Kingdom (No. NA150222) and ExxonMobil Asia Pacific Research & Development Co., Ltd.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The enthalpy of fusion of a perfect crystal of cellulose acetate was calculated in this thesis. In order to do so, cellulose samples from different sources were acetylated through the heterogenous acetilation methodology. The cellulose acetate samples were characterized by differencial scanning calorimetry (DSC) and by wide angle X-ray diffraction (WAXD). The X-ray diffractograms were deconvoluted into halos and peaks using the Pseudo-Voigt peak function of program Origin® 7.0. Two hypotheses were proposed in order to fit the deconvolution patterns into the two-phase model. In the first, the amorphous regions of the material was considered to be represented by the area of the halo located at 21º and the crystalline area by the maxima at 8º, 11º, 13º and 16º. In the second hypothesis, the amorphous region was considered to be represented by the areas of the maxima at 11º and 21º, and the crystalline region by the maxima at 8º, 13º and 16º. The WAXD crystallinities of the samples were then calculated from these values. The first hypothesis was ignored for presenting a very high crystallinity value for a sample that did not present an enthalpy of fusion. The second hypothesis was used, but the linear regression that defined the relationship between the enthalpy of fusion and the crystallinity of the materials was forced through zero. Through this relationship, the enthalpy of fusion of a perfect crystal of cellulose acetate was calculated to be 58.8 J/g. / A entalpia de fusão de um cristal perfeito de acetato de celulose foi calculada nessa dissertação. Para isso, amostras de celulose de diferentes origens foram acetiladas através do método de acetilação heterogêneo. As amostras de acetato de celulose foram caracterizadas por calorimetria diferencial de varredura (DSC) e difração de raios-X a alto ângulo (WAXD). Os difratogramas de raios-X foram deconvoluídos em halos e picos utilizando a função pico Pseudo-Voigt do programa Origin® 7.0. Duas hipóteses foram propostas para que as deconvoluções estivessem de acordo com o modelo de duas fases. Na primeira, foi considerado que a parte amorfa do material era representada pela área do halo localizado em 21º e a área cristalina pela soma das áreas dos máximos em 8º, 11º, 13º e 16º. Na segunda hipótese, a região amorfa foi considerada como sendo representada pelas áreas dos máximos em 11º e 21º, e a região cristalina pelos máximos em 8º, 13º e 16º. A partir desses valores se calculou a cristalinidade das amostras de acetato de celulose via WAXD. A primeira hipótese foi desconsiderada por apresentar um valor muito alto de cristalinidade para uma amostra que não apresentou entalpia de fusão. A segunda hipótese foi utilizada, porém a regressão linear que definiu a relação entre a entalpia de fusão e cristalinidade dos materiais foi forçada a passar pela origem. Através dessa relação, calculou-se a entalpia de fusão de um cristal perfeito de acetato de celulose como sendo 58,8 J/g. / Mestre em Química

RNA tetraloop is the smallest, simplest and the most frequent motif which is involved in numerous important biological functions. A local deviation from the RNA standard tetraloop, d2 tetraloop, has been identified with high abundance in 5S, 16S and 23S rRNAs. The presence of d2 tetraloops in highly conserved regions of 16S and 23S rRNAs suggests their functional importance. With one less residue in the loop, d2 tetraloops are considered more energetically restrained and less stable than standard tetraloops. The deletion at position j+2 in the loop is always correlated with adjacent stem distortion. MD simulations of 314-d2-tetraloop (a sample structure of d2 tetraloops) and cutd2-tetraloop (an artificially built perfect d2 tetraloop with no stem defects) have shown that stem defects are the stabilizing factor of d2 tetraloops. Simulations have also revealed that the insertion residue 318C (an example of stem defect) is stabilizing 314-d2-tetraloop by forming hydrogen bonding interactions with both the loop and the stem. When these two hydrogen bonding interactions are eliminated, the structure remained relatively stable compared to cutd2-tetraloop where the insertion residue was completely removed from the stem. This suggests the insertion residue is also stabilizing 314-d2-tetraloop by providing some conformational relaxation in the stem. Investigation of RNA standard tetraloop high temperature unfolding has revealed that the d2 tetraloop is possibly a kinetically trapped intermediate state during the folding of the standard tetraloop. High temperature unfolding simulations of standard tetraloop have shown a three-state folding behavior: a folded state, an intermediate state and an unfolded state. The folding of standard tetraloop starts with the formation of the loop. The closing base pair forms first, followed by the loop and the stem which form critical interactions such as base pairing and stacking that make a tetraloop. ROMP PNB has been investigated as supports to immobilize homogeneous catalysts to achieve both high reactivity and selectivity and easy separation. Polymers with intermediate conformational order can increase the accessibility of tethered homogeneous catalysts. Simulations of ROMP PNBDC_UD have shown the importance of bulky side groups in enabling the polymer to adopt a helical conformation. Such helical conformations have been associated with intermediate structural order in similar polymers such as PNB made by non-ROMP mechanisms. This intermediate order manifests itself as a split in the amorphous halo of WAXD pattern. Bulk simulations generated WAXD patterns that are close to the experimentally generated WAXD patterns where there are two split peaks: lower angle peak representing intermolecular interaction and higher angle peak representing intramolecular interaction.

No / An experimental configuration that combines the powerful capabilities of a short-term shearing apparatus with simultaneous optical and X-ray scattering techniques is demonstrated, connecting the earliest events that occur during shear-induced crystallization of a polymer melt with the subsequent kinetics and morphology development. Oriented precursors are at the heart of the great effects that flow can produce on polymer crystallization (strongly enhanced kinetics and formation of highly oriented crystallites), and their creation is highly dependent on material properties and the level of stress applied. The sensitivity of rheo-optics enables the detection of these dilute shear-induced precursors as they form during flow, before X-ray techniques are able to reveal them. Then, as crystallization occurs from these precursors, X-ray scattering allows detailed quantification of the characteristics and kinetics of growth of the crystallites nucleated by the flow-induced precursors. This simultaneous combination of techniques allows unambiguous correlation between the early events that occur during shear and the evolution of crystallization after flow has stopped, eliminating uncertainties that result from the extreme sensitivity of flow-induced crystallization to small changes in the imposed stress and the material. Experimental data on a bimodal blend of isotactic polypropylenes are presented.

Neste trabalho, foram estudadas blendas de poliésteres sintéticos e de fonte renovável - poli(tereftalato de butileno-co-adipato de butileno) - PBAT e poli(ácido láctico) - PLA, respectivamente, utilizados em sacolas de supermercado. Amostras destes materiais foram pesadas e enterradas em solo simulado por quatro meses para simular uma compostagem tradicional. As amostras foram então analisadas por Calorimetria Exploratória Diferencial (DSC), Termogravimetria e Termogravimetria Derivada (TG e DTG, incluindo uma Análise Cinética não isotérmica comparativa com sacolas de PE aditivadas com agente pró-degradante, Espectroscopia Vibracional Raman com Transformada de Fourier (FT-Raman), Difração de Raios X e Cromatografia de exclusão por tamanho. Embora não tenha havido perda de massa significativa no período do envelhecimento por compostagem tradicional, foram constatadas importantes alterações estruturais nas amostras, tais como a redução nas energias de ativação (Ea) para os processos de decomposição térmica, a redução na intensidade da banda relativa ao estiramento da carbonila presente nos poliésteres e também uma drástica redução da massa molecular dos polímeros. Em paralelo, a aceleração do processo de biodegradação com Vermicompostagem foi investigado, com resultados bastante promissores, incluindo a degradação total da amostra após um tratamento prévio de exposição à luz solar. / In this study, blends of the synthetic polyester poly(butylene adipate-cotherephtalate) - PBAT - and the natural one poly(lactic acid) - PLA - used as biodegradable plastic shopping bags were studied. Samples of these materials were weighed and buried in simulated soil for four months to simulate domestic composting. These samples were then studied by Differential Scanning Calorimetry (DSC), Thermogravimetry (TG, including a comparative non-isothermal Kinetic Analysis with PE shopping bags containing prodegradation agents), Transformed Fourier Raman Vibrational Spectroscopy (FT-Raman), Wide Angle X-Ray Diffraction (WAXD) and Gel Permeation Chromatography (GPC). It was observed that even though there was no significant mass loss in the period of the ageing when using conventional home composting, important structural changes were detected in the samples, such as the reduction of activation energies (Ea) for the thermal decomposition processes, the reduction of intensity of the peak associated with the stretching of the carbonyl present in both polyesters and also a dramatic decrease in molecular weights. In parallel, the acceleration of the biodegradation process with vermicomposting was investigated, with very promising results, including the total disintegration of the samples when submitted to a previous treatment of sun light exposure.

Neste trabalho, foram estudadas blendas de poliésteres sintéticos e de fonte renovável - poli(tereftalato de butileno-co-adipato de butileno) - PBAT e poli(ácido láctico) - PLA, respectivamente, utilizados em sacolas de supermercado. Amostras destes materiais foram pesadas e enterradas em solo simulado por quatro meses para simular uma compostagem tradicional. As amostras foram então analisadas por Calorimetria Exploratória Diferencial (DSC), Termogravimetria e Termogravimetria Derivada (TG e DTG, incluindo uma Análise Cinética não isotérmica comparativa com sacolas de PE aditivadas com agente pró-degradante, Espectroscopia Vibracional Raman com Transformada de Fourier (FT-Raman), Difração de Raios X e Cromatografia de exclusão por tamanho. Embora não tenha havido perda de massa significativa no período do envelhecimento por compostagem tradicional, foram constatadas importantes alterações estruturais nas amostras, tais como a redução nas energias de ativação (Ea) para os processos de decomposição térmica, a redução na intensidade da banda relativa ao estiramento da carbonila presente nos poliésteres e também uma drástica redução da massa molecular dos polímeros. Em paralelo, a aceleração do processo de biodegradação com Vermicompostagem foi investigado, com resultados bastante promissores, incluindo a degradação total da amostra após um tratamento prévio de exposição à luz solar. / In this study, blends of the synthetic polyester poly(butylene adipate-cotherephtalate) - PBAT - and the natural one poly(lactic acid) - PLA - used as biodegradable plastic shopping bags were studied. Samples of these materials were weighed and buried in simulated soil for four months to simulate domestic composting. These samples were then studied by Differential Scanning Calorimetry (DSC), Thermogravimetry (TG, including a comparative non-isothermal Kinetic Analysis with PE shopping bags containing prodegradation agents), Transformed Fourier Raman Vibrational Spectroscopy (FT-Raman), Wide Angle X-Ray Diffraction (WAXD) and Gel Permeation Chromatography (GPC). It was observed that even though there was no significant mass loss in the period of the ageing when using conventional home composting, important structural changes were detected in the samples, such as the reduction of activation energies (Ea) for the thermal decomposition processes, the reduction of intensity of the peak associated with the stretching of the carbonyl present in both polyesters and also a dramatic decrease in molecular weights. In parallel, the acceleration of the biodegradation process with vermicomposting was investigated, with very promising results, including the total disintegration of the samples when submitted to a previous treatment of sun light exposure.

No description available.

The ability to quickly develop predictions of the time-to-failure under different loading levels allows designers to choose the best polymeric material for a specific application. Additionally, it helps material producers to design, manufacture, test, and modify a polymeric material more rapidly. In the case of polymeric pipes, previous studies have shown that there are two possible time-dependent failure mechanisms corresponding to ductile and brittle failure. The ductile mechanism is evident at shorter times-to-failure and results from the stretching of the amorphous region under loading and the subsequent plastic deformation. Empirical results show that many high-performance polyethylene (PE) materials do not exhibit the brittle failure mechanism. Hence, it is critical to understand the ductile mechanism and find an approach to predict the corresponding times-to-failure using accelerated means. The aim of this study is to develop an innovative rupture lifetime acceleration protocol for PE pipes which is sensitive to the structure, orientation, and morphology changes introduced by changing processing conditions. To accomplish this task, custom fixtures are developed to admit tensile and hoop burst tests on PE pipes. A pressure modified Eyring flow equation is used to predict the rupture lifetime of PE pipes using the measured mechanical properties under axial tensile and hydrostatic pressure loading in different temperatures and strain rates. In total, the experimental method takes approximately one week to be completed and allows the prediction of pipe lifetimes for service lifetime in excess of 50 years. / Master of Science