Orientador: Liliane Maria Ferrareso Lona / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-20T08:34:25Z (GMT). No. of bitstreams: 1 Goncalves_NuriaAngelo_M.pdf: 1743980 bytes, checksum: 9b3510495b5ac6cd3d024e2e39b172fa (MD5) Previous issue date: 2012 / Resumo: Ao longo dos últimos anos, com as fortes pressões ambientais e o aumento do preço do petróleo, os biopolímeros vêm recebendo especial atenção como substitutos para os polímeros convencionais. Para ampliar a faixa de utilização destes materiais, têm-se produzido os chamados nanocompósitos poliméricos, que são materiais híbridos consistindo de dois ou mais componentes, apresentando ao menos um destes em escala nanométrica. Com o acréscimo de uma pequena quantidade de agente de reforço, podem-se obter grandes melhoras nas propriedades destes materiais. Dentre as quais, podemos citar as propriedades térmicas e de barreira. Neste trabalho foram sintetizados o poli (L-lactídeo) (PLLA) e os hidróxidos duplos lamelares (HDLs) compostos pelos cátions divalentes/trivalentes cálcio/alumínio, cálcio/ferro, e magnésio/ferro intercalados com o ânion dodecil sulfato (DDS), a partir dos quais foram sintetizados três tipos de nanocompósitos poliméricos com matriz de PLLA e como agente de reforço os HDLs, com as frações mássicas de 1 e 2 %. Os HDLs foram caracterizados pelas técnicas de difração de raios X e espectroscopia de absorção no infravermelho. O PLLA e os nanocompósitos foram caracterizados pelas técnicas de difração de raios X, espectroscopia de absorção no infravermelho, termogravimetria, calorimetria exploratória diferencial e espectroscopia de absorção no UV-VIS. Os resultados obtidos nesse trabalho mostram que a maioria dos nanocompósitos teve uma boa dispersão do agente de reforço na matriz polimérica, bem como, melhoras significantes em suas propriedades quando comparados ao PLLA puro. O aumento da estabilidade térmica dos nanocompósitos foi condizente com uma melhor dispersão do HDL. Com a análise de UV-VIS, observaram-se menores valores de transmitância para os nanocompósitos. Essa melhora nas propriedades dos nanocompósitos pode ampliar a faixa de aplicações deste material em diversas áreas / Abstract: Over the years with strong environmental pressures and rising oil prices, the biopolymers are receiving special attention as substitutes for conventional polymers. To extend the range of use these materials, it has been produced the polymeric nanocomposites, that are hybrid materials consisting of two or more components, presenting at least one, dimensions in nanometer scale. It is shown that an addition of a lower amount of reinforcing agent can enhance the properties those material, such as thermal and barrier properties. In this work, were synthesized three type of nanocomposites of poli (L-lactide) (PLLA) and layered double hydroxide (LDH), with the divalent/trivalent cations calcium/aluminum, calcium/iron and magnesium/iron, intercalated with the dodecyl sulfate anion. The nanocomposites were synthesized using two different concentration (1 and 2 %) of LDH as reinforcing agent. The synthesized HDLs were characterized by X-ray diffraction and infrared spectroscopy analyses and the nanocomposites were characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric, differential scanning calorimetry and UV-VIS spectroscopy analyses.The results obtained in this work show that most of the nanocomposites exhibit a good dispersion of the reinforcement agent in the polymeric matrix as well as significant improvements on their properties compared with neat PLLA. The enhancement on thermal stability of nanocomposites can be attributed to higher dispersion of reinforcement agent. UV-VIS analysis, it was observed lower transmittance values of all nanocomposites. This improvement in properties of nanocomposites can widen the range of applications this material in several areas / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

Magister Scientiae Dentium - MSc(Dent) / Despite the phenomenal strides in research of dental resin composites regarding their physical and mechanical properties, discolouration, either intrinsic or extrinsic still remains a major drawback and is one of the main reasons for the replacement of these restorations. Toothbrushing and polishing procedures have been attempted to eliminate extrinsic staining without optimal results. Vital tooth bleaching has over 90% success rates in whitening discoloured teeth and this may be an alternative treatment modality for discoloured composite resins. Aim: The aim of this study was to determine whether tooth bleaching agents alter the colour of stained direct composite resins. Material and Method: 60 disc shaped specimens (9 x 2mm) of Filtek Supreme XT were prepared. They were randomly divided into 3 groups (n = 20) and exposed to either one of two experimental staining agents, tea or red wine, or artificial saliva (control) continuously over a 7-day period. They were all then bleached with Opalescence Xtra Boost, a chemically activated in-office whitening agent for 3, weekly sessions of a half hour each, broken into 2, fifteen minute cycles. Colour determinations were made using a reflectance spectrophotometer, from baseline, after each day of staining, after the bleaching treatments and after a 1 week rehydration period. The CIE Lab colour space was used and colour changes were monitored using ΔE, that was calculated during intervals between the experimental episodes using L, a and b values. A ΔE ≥ 3.3 represented colour changes that were deemed clinically noticeable. Data analysis was carried out using Microsoft excel and a non-parametric test (Wilcoxon Signed Sum Rank Test) with a significance level set at ≤ 0.05 for colour differences that are statistically significant. Results: Both staining solutions discoloured the composite resin samples, but red wine produced greater colour changes than tea. After bleaching, the specimens in the tea group reverted to baseline colour with a ΔE ≤ 3.3 but those in the red wine group did not revert to baseline values with a ΔE ≥ 3.3. Conclusion: Filtek Supreme XT, a nanocomposite, is susceptible to discolouration by chromogenic beverages. Red wine produced deeper staining than tea. Opalescence Xtra Boost was effective in removing tea stains but not red wine stains. / South Africa

Malaria is still the most important parasitic disease in humans with most cases occurring in Sub-Saharan Africa (90% cases). It is transmitted via anopheles mosquitoes. Several vector control methods are available, e.g. long lasting insecticidal mosquito nets (LLINs), insecticide-treated nets (ITNs) and indoor residual spraying (IRS). However, they are effective only when a person is in-doors. Outdoor protection can be obtained for short periods (48-72 hours) using topical repellents. This preliminary study investigated the possibility to develop longer acting delivery forms based on polymer technology. The viability of two different approaches were considered for the controlled release of the natural repellent 3,7-dimethyloct-6-en-1-al (citronellal). The first idea was to dissolve the repellent in the polymer while controlling the rate of release by clay nanoplatelets dispersed in the matrix. Towards this, ethylene vinyl acetate (EVA) copolymer (18% VA) was modified with organically modified nanoclay. Release tests showed that this approach was not viable as only a small amount of repellent could be incorporated and it was lost within a day or two from thin polymer strands. The second approach targeted the use of a polymer in which the repellent is not soluble at ordinary temperature but where solubility is achieved at high temperatures. In this case polyethylene was used as host polymer. It was shown that large quantities of repellent can be trapped inside the polymer matrix using the temperature induced phase separation method (TIPS). Scanning electron microscopy revealed that a microporous co-continuous phase structure was obtained by shock cooling homogeneous mixtures to temperatures well below the spinodal phase boundary curve. The phase behaviour of the LLDPE-citronellal system was studied using cloud point determinations in a microscope fitted with a hot stage and by differential scanning calorimetry. The experimental data points on the bimodal phase envelope were used to fix parameter values of the Flory-Huggins equation. The latter was then used to predict the location of the spinodal lines. At 40 wt.% polymer the spinodal boundary is located at 96 C. However, experiments showed that quenching temperature of 5°C (i.e. the temperature of typical cooling baths used during filament extrusion) is sufficient to generate the desired microporous structure. / Dissertation (MSc)--University of Pretoria, 2014. / tm2015 / Chemical Engineering / MSc / Unrestricted

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17891号 / 工博第3800号 / 新制||工||1581(附属図書館) / 30711 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 秋吉 一成, 教授 金谷 利治, 准教授 竹中 幹人 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

No description available.

The introduction of composition gradients into the already hierarchical structure of martensitic steel leads to difficulties in modeling that arise from events occurring in the material at different length scales. In this thesis we isolate the features that are important to describing the mechanical properties of martensite and constitutively couple them through their respective length scales. The idea of a representative volume element is rigorously explored in which the microstructure is represented through a Masing model as well as more advanced structures akin to a nanocomposite. As such, we are able to keep track of microscopic yielding and internal stress evolution at the smallest scales (nanoscale through microscale). With the use of representative volume elements, we are able to track events at the largest scale as well by freely being able to change scale. As such, macroscopic phenomenon such as: thermal fields, composition fields, macroscopic loads, and the associated macroscopic phase distributions and stress distributions are evaluated. We conclude by demonstrating the power of this modelling technique in the design and optimization of compositionally graded steel structures via virtual prototyping. / Dissertation / Doctor of Philosophy (PhD)

<p>Nanocomposite thin films are materials that have the potential to improve and tune many properties for various applications in electronics, sensors, memory storage, and optics. Materials properties are a consequence of their structure, so being able to manipulate the nanostructure of nanocomposite thin films is important for modifying them for device purposes. One structure that has gained a lot of attention is vertically aligned nanocomposites (VANs) due to the increased vertical coupling between two or more phases of materials and the unique nanostructures achievable through controlling deposition factors. </p> <p>VAN thin film growth involves many factors: diffusion, substrate surface conditions, source material composition, and deposition temperature and rate. The two main approaches to thin film fabrication are bottom-up and top-down. Bottom-up growth focuses on the self-assembly of the nanostructure. This work focuses on the self-assembly of VAN thin film materials through controlling the thermodynamic and kinetic factors involved in thin film growth. The main factors being considered in this work are substrate manipulation, oxygen gas flow during deposition, deposition rate, and composition. The effectiveness of each of these methods is evaluated in comparison to each other and their growth of VAN thin film materials along with the future work needed to refine each nanostructure manipulation method. </p>

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.

Nature creates high performance materials under modest conditions, i.e., neutral pH and ambient temperature and pressure. One of the most significant materials is the plant cell wall. The plant cell wall is a composite of oriented cellulose microfibrils reinforcing a lignin/hemicellulose matrix. In principle, the plant cell wall composite is designed much like a synthetic fiber-reinforced polymer composite. Unlike synthetic composites, the plant cell wall has an excellent combination of high modulus, strength, toughness and low density that originates in the optimal interactions between the biopolymers. Therefore, to produce high performance composites, a unique route may be to mimic a biological system like the plant cell wall. The present work focuses on understanding the thermodynamics of biopolymer assembly to exploit the process in vitro. In our system, we use an already polymerized nanocellulose template and polymerize phenolic monomers on the template using a peroxidase enzyme. In the first part, we have polymerized phenol using horseradish peroxidase (HRP) in the presence of TEMPO-oxidized nanocellulose. Similar to native plant cell wall structures, the polyphenol-nanocellulose composite had intimate mixing of polyphenol and cellulose at the nanoscale with the presence of cellulose promoting a uniquely organized structure. The obtained composite material showed synergy that enhanced the thermal stability, hydrophobicity, and possibly mechanical properties. In the second part, monolignol coniferyl alcohol was polymerized in the presence of nanocellulose by the same procedure. A comparison between the polyphenol composite and poly(coniferyl alcohol) (PCA) composite revealed that the propanyl substitution imparted flexibility to the PCA molecules so that they could bend and form a hollow globule structure to envelope nanocellulose inside. Polyphenol could not do this because of its rigidity. / Master of Science

<p>Understanding how light interacts with the matter is essential for developing future opto-electronic devices. Furthermore, tuning such light-matter interaction requires designing new material platforms that is essential for developing devices which are functional in different light wavelength regimes. Among these designs, particle-in-matrix, multilayer or nanowire morphology, consisting of metal and dielectric materials, have been demonstrated for achieving improved physical and optical properties, such as ferroelectricity, ferromagnetism and negative refraction. For example, Au-TiO₂ two phase nanocomposite has been explored in this dissertation as a way of achieving enhanced photocatalysis. However, due to the availability of a limited range of structures in terms of crystallinity and morphology in the two-phase nanocomposites, a greater design flexibility and structural complexity along with versatile growth techniques are needed for developing next generation integrated photonic and electronic devices. This can be achieved by incorporating a third phase through the three phase nanocomposite designs by judicious selection of materials and functionalities. </p> <p>In this dissertation, a new nanocomposite design having three different phases has been introduced: Au, BaTiO₃ and ZnO, which grow in a highly ordered ‘nanoman’-like structure. More interestingly, the three phases in the novel ‘nanoman’-like structure combine to give an emergent new property which are not found individually in the three phases. The ordered ‘nanoman’-like structures enable a high degree of tunability in their optical and electrical properties, including the hyperbolic dispersion in the visible and near infrared regime, in addition to the prominent ferroelectric/piezoelectric properties. Moreover, the growth kinetics and the thermal stability (using in-situ Transmission Electron Microscopy) of the ‘nanoman’ structures has also been studied. This study introduces a new growth paradigm of fabricating three-phase nanocomposite that will surely generate wide interests with potential applications to different systems. The ordered three-phase ‘nanoman’ structures present enormous opportunities for novel complex nanocomposite designs towards future optical, electrical and magnetic property tuning.</p>