Nesse trabalho, foi investigada a obtenção de novos materiais a partir de reações de hidrólise e condensação ácida do (3-aminopropil)trimetoxisilano, que resultaram na formação de nanoestruturas híbridas com grupos amônios e contraíons cloreto (POSS-NH3Cl). As nanoestruturas posteriormente foram submetidas a trocas iônicas durante 0,5, 2, 12 e 48 h, para remoção dos íons cloreto. As análises titulométricas mostraram que a troca iônica ocorreu parcialmente. As partículas de POSS-NH2 formadas apresentam predominância de estruturas em forma de gaiola (T8) octafuncionalizadas. Após a troca iônica, as nanoestruturas possuem capacidade de se autoassociar por meio de interações eletrostáticas formando estruturas do tipo blackberry com aproximadamente 100 nm. Os aglomerados de POSS-NH2 são formados por partículas primárias com tamanho de 1,4 nm em forma de fractal de massa e tamanho de correlação () dependente da quantidade do tempo de troca iônica. Devido à característica eletrostática das partículas foi possível obter filmes híbridos opticamente transparentes com elevado grau de hidrofilicidade. As nanopartículas de POSS-NH2 foram utilizadas como aditivo de lubrificantes de fontes renováveis (ácidos graxos) por meio de reações de amidação direta assistida por micro-ondas, sem o uso de catalisadores. A formação das ligações amidas foi constatada por meio das técnicas FTIR e RMN de 1H, onde observaram-se bandas de deformação angular do NH em 1550 cm-1 e 1120 cm-1 e o aparecimento de um singleto alargado em 6,50 ppm (N-H). Em termos estruturais, para o biolubrificante foi constatado que uma molécula de ácido graxo liga com uma molécula de POSS-NH2, entretanto foi notada ainda a existência de aglomerados após a amidação, conforme resultados de MET dos lubrificantes. O uso de POSS-NH2 reduziu a taxa de oxidação dos biolubrificantes com dependência do tempo de troca iônica das partículas. Todos os biolubrificantes apresentaram comportamento reológico newtoniano, e a viscosidade a 25ºC mostrou-se dependente da quantidade de partículas e não do tempo de troca iônica. A adição de nanopartículas de POSS-NH2 melhorou o desempenho dos biolubrificantes aplicados em superfícies metálicas, visto que tribossistema estudado apresentou valores inferiores e mais estáveis de coeficiente de atrito em comparação com o óleo base. Além disso, os biolubrificantes apresentaram uma elevada capacidade do suporte de carga, que representa a carga crítica para a ocorrência de engripamento (scuffing) do sistema. A resistência ao desgaste das superfícies metálicas variou com a adição de partículas no óleo lubrificante e com os tempos de troca iônica adotados para a síntese das partículas. / Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul, FAPERGS / In this work, was investigated the obtaining of new materials from the hydrolysis and acid condensation reactions of (3-aminopropyl) trimethoxysilane, which resulted in the formation of hybrid nanostructures with ammoniums groups and counter ions chloride (POSS-NH3Cl). The nanostructures were subjected to ion exchange procedures for 0.5, 2, 12 and 48 h for the removal of chloride ions. The titrimetric and volumetric results showed that the ion exchange occurred partially. The synthesized particles are predominantly POSS-NH2 cage-shaped structures (T8). After the ion exchange, the nanostructures have ability to selfassembly through electrostatic interactions forming the blackberry-like structures with approximately 100 nm. The POSS-NH2 cluster are formed by primary particles with a size of 1.4nm structured in form of a mass fractal with correlation length () dependent on the ion exchange time. Due to the electrostatic characteristic of the particles was possible obtained hybrid films optically transparent with a high degree of hydrophilicity. POSS-NH2 nanoparticles were used as additive of lubricants of renewable sources (fatty acids) by means of microwave-assisted direct reactions of amidation, without the use of catalysts. The formation of amide bonds were confirmed through the FTIR and 1H NMR techniques, where angular deformation bands in NH in 1550 cm-1 and 1120 cm-1 and the appearance of an enlarged singlet in 6.50 ppm (NH) were observed. The biolubricants was found that an alloy fatty acid molecule with a POSS, but has not yet noticed the existence of agglomerates after amidation, as TEM results of biolubricants. The POSS-NH2 are bonded individually to only one fatty acid molecule, however it was noted the existence of cluster after amidation reactions, as observed in TEM results of the biolubricants. The addition of POSS-NH2 nanoparticles reduced the oxidation rate of the biolubricants and has dependence on the ion exchange time. All the biolubricants showed a Newtonian rheological behavior and the viscosity at 25°C dependent on the amount of particles and not the exchange time. The addition of POSS-NH2, improved the performance of the biolubricants applied on metallic surfaces, since the studied sliding pair showed lower and more stable values of coefficient of friction, as compared to the base oil. Moreover, the biolubricants showed a high load support capacity, which represents the critical load for the scuffing occurrence of the system. The wear resistance of the metallic surfaces changed with the addition of POSS particles in the lubricant oil and with the ionic exchange time adopted for the synthesis of the particles.

Orientador: José de Alencar Simoni / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-25T07:32:13Z (GMT). No. of bitstreams: 1 Riaz_Ali_D.pdf: 5855772 bytes, checksum: b17d5626ad22333e3c2a8cff516ddc1a (MD5) Previous issue date: 2014 / Resumo: Este trabalho apresenta a síntese e caracterização de compostos silsesquioxanos gaiola cúbica (POSS) com cadeias orgânicas pendentes. O projeto foi iniciado com a idéia de sintetizar os silsesquioxanos cúbicos com cadeias organofuncionalizadas ancoradas, capazes de capturar os metais pesados, corantes e CO2. Mas foram enfrentadas algumas dificuldades como baixo rendimento (30-37%) e longo tempo de reação (5-35 dias). As reações foram investigadas para melhorar o rendimento, bem como para reduzir o tempo de reação. Algumas modificações em rotas de reação foram introduzidas, o que trouxe melhorias notáveis nos resultados, onde o rendimento aumentou cerca de 64 % e o tempo de reação foi reduzido para 24 horas em média. Na sequência, os produtos sintetizados foram caracterizados para elucidar suas estruturas, utilizando diferentes técnicas físicas tais como FTIR, CHN, XRD, MEV, TGA, 13CNMR e 29SiNMR no estado sólido, onde as gaiolas Si-O de todos os compostos foram evidenciadas por meio de 29SiRMN e dos seus espectros de FTIR, enquanto as cadeias ancorados às gaiolas de POSS foram confirmadas utilizando os resultados de 13CRMN, juntamente com seus respectivos espectros de FTIR. Os compostos sintetizados também foram testados quanto à sua estabilidade térmica utilizando a técnica de TGA. Após a otimização da síntese de silsesquioxanos cúbicos, os híbridos PAA-13-3, PAA-MTC e PAA-Ph foram avaliados por suas habilidades de captação de cátions bivalentes, tais como Cu2+, Cd2+ e Pb2+ de suas soluções aquosas, sendo que o Cu2+ apresentou maior afinidade de sorção em relação aos dois metais. Estes sistemas de sorção foram analisados através ICP-OES. Para explicar o comportamento de sorção destas amostras alguns modelos estatísticos como Langmuir, Freundlich, Temkin e Redlich-Peterson foram aplicadas, onde os dados de sorção de Cu2+ em PAA-13-3 foram melhor ajustados pelo modelo Langmuir, mostrando ser uma sorção monocamada, enquanto que no caso do PAA-MTC e PAA-Ph modelo de melhor ajuste foi o Freundlich, confirmando a sorção de múlti camadas. Um dos materiais sintetizados (PAA-13-3) foi avaliado quanto à sua capacidade de adsorver CO2 gasoso, mostrando-se promissor na remoção de CO2, mesmo a baixas pressões (máx. 100 mm Hg). A adsorção de CO2 no material também foi estudada por calorimetria de adsorção gás-sólido, em um calorímetro especialmente desenvolvido para tal, observando-se valores de entalpia de adsorção entre -36 e -7 kJ mol-1 / Abstract: This report presents the synthesis and characterization of POSS compounds having cubic silsesquioxane cage to which the organic pendant chains are anchored. The project was started with the idea to synthesize the cubic silsesquioxanes with organofunctionalized pendant chains, which are able to capture heavy metals, dyes and some acids like CO2. But in the beginning the hurdles like low % yields (30-37 %) and long reaction times (5-35 days) were to be faced. The reactions were worked out to enhance the % yields as well as to reduce the reaction time. Some modifications in reaction routes have been introduced, which brought up remarkable improvements in the results, where yield was increased upto 64 % and reaction time was reduced to 1 day. All the synthesized products were then characterized for their structure elucidations using different physical techniques like FTIR, CHN, TGA, 13CNMR & 29SiNMR in solid state, where Si¿O cages of all compounds were elaborated through 29Si-NMR in solid state as well as through their respective FTIR patterns, while the pendant chains anchored to the POSS cages were confirmed using 13C-NMR results along with their respective FTIR spectra. The synthesized compounds were then tested for their thermal stability using the TGA technique. After optimizing the synthesis of cubic silsesquioxanes, hybrids PAA-13-3, PAA-MTC and PAA-Ph were worked out for their abilities of capturing divalent cations like Cu2+, Cd2+ and Pb2+ from their aqueous solutions, where Cu2+ showed higher affinity of sorption than other two bivalent metals. These sorption systems were analyzed using the ICP-OES. To explain the sorption behaviour of these samples some statistical models like Langmuir, Freundlich, Sips, Temkin and Redlich-Peterson were applied to the sorption data, where the data for Cu2+ on to PAA-13-3 was best fitted by Langmuir adsorption isotherm model showing the sorption to be monolayer, while in case of PAA-MTC and PAA-Ph Freundlich model was found to be a best fit, confirming multilayer sorption. One of the synthesized materials (PAA-13-3) was also evaluated for its ability to adsorb gaseous CO2 and was proved to be promising in removing CO2, even at low pressures (max. 100 mmHg). The adsorption of CO2 in the material is also studied by solid-gas adsorption calorimetry through a calorimeter especially developed for this system, where enthalpy of adsorption values were found to be between -7 and -36 kJ mol-1 / Doutorado / Quimica Inorganica / Doutor em Ciências

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Molecular dynamics simulations were carried out on traditional polymers copolymerized with POSS (Polyhedral Oligomeric Silsesquioxanes) derivatives to identify the reason behind improved properties imparted to the conventional polymers with the chemical incorporation of POSS. Two classes of systems are used in the present study, namely the polystyrene and polymethyl methacrylate systems. Seven systems are studied in the polystyrene class. The effect of corner substituent groups of the POSS cage on the properties of the polymer nanocomposites was studied using the polystyrene. In addition, the effect of the type of cage structure on the properties was studied using T8, T10 and T12 POSS cage structures containing phenyl substituents on each POSS cage. Systems with polymethyl methacrylate were studied to analyze the effect of mole percent of POSS on the polymer properties, holding the corner substituents on the POSS unit constant. The corner function used was the isobutyl group. The properties analyzed using simulations include glass transition temperature, volumetric thermal expansion coefficient, X-ray scattering data, solubility parameter and mechanical properties. In both polystyrene and polymethyl methacrylate systems, simulations were also carried out on the pure parent polymers for the sake of comparison. The effect of forcefield on the predicted properties was studied using both COMPASS and PCFF forcefields. Performance analysis of the code used in the present simulation was done by analyzing the parallel run time of simulations involving pure atactic polystyrene.

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Over the past two decades one class of oligomers, polyhedral oligomeric silsesquioxanes (POSS), has attracted considerable attention because of their unique hybrid organic/inorganic molecular structures and nanoscopic sizes. While surface and interfacial properties may play a key role in many potential POSS applications, relatively little is actually known about the surface properties of POSS. This dissertation provides studies of the interfacial aspects of both POSS molecules and POSS/polymer blends at the air/water interface (A/W) through surface pressure-area per molecule (π-<i>A</i>) isotherm, Brewster angle microscopy (BAM), and interfacial stress rheometry (ISR) studies. Results for POSS Langmuir thin films at A/W show that trisilanol-POSS derivatives are a new class of amphiphiles, that exhibit multiple phase transitions in going from traditional 2D Langmuir monolayers (1 POSS molecule thick) to various 3D multilayer films upon compression. With small length/diameter ratios and bulky shapes, the monolayer phase behavior and packing states of different POSS are simpler than the traditional rod-like lipids. Meanwhile trisilanol-POSS derivatives have very different collapse behavior and multilayer organization showing strong substituent effects even though they have similar molecular sizes. While trisilanolisobutyl-POSS (TiBuP) monolayers undergo collapse around π ≈ 18 mNm⁻¹ and form various ordered or disordered solid-like 3D aggregates at different compression rates, trisilanolcyclohexyl-POSS (TCyP) monolayers collapse into trilayers via instantaneous nucleation with hemispherical edge growth around π ≈ 3.7 mNm⁻¹. ISR results reveal three different non-Newtonian flow regimes that correlate with phase transitions in the Pi-A isotherms. Further symmetric compression after trilayer formation induces TCyP thin films to self-assemble into highly ordered crystalline-like hydrophobic multilayers (≈8 POSS molecule thick) with unique rod-like morphologies, which are dramatically different from –collapsed– morphologies seen in other systems. By treating POSS derivatives as ideal nanofiller for studying confinement effects on filled polymer systems, amphiphilic poly(dimethylsiloxane) (PDMS) derivatives with different polar functional groups are studied as blends with TiBuP and octaisobutyl-POSS at A/W to resolve one of the key challenges for current nanocomposite applications: How to control nanofiller dispersion in polymer matrices? The results in this dissertation reveal that introducing polar groups into polymeric matrix polymers is a good way to control dispersion. / Ph. D.

La maladie d'Alzheimer est la maladie neurodégénérative la plus fréquente dont la prévalence augmente avec l'âge. Elle résulte d'un excès de peptide β-amyloïde (Aβ) capable de s'agréger, de s'insérer dans la membrane plasmique des cellules et de s'organiser en pores perméables au calcium. Cette insertion est modulée par la composition lipidique de la membrane dont le cholestérol. Alors que plusieurs études indiquent que le cholestérol interagit avec le peptide Aβ et module sa toxicité, les mécanismes moléculaires sous-jacents demeurent mal compris.A l'aide d'approches expérimentales multiples nous avons évalué le rôle du cholestérol dans l'insertion du peptide Aβ à la membrane ainsi que dans le processus d'oligomérisation responsable de la formation de pore. Notre étude identifie le domaine 22-35 du peptide Aβ comme domaine d'interaction avec le cholestérol au sein duquel deux acides aminés sont essentiels : la Val24 et la Lys28. Ce petit fragment s'organise en pore dans la membrane plasmique et déclenche une entrée massive de calcium dans les cellules. Cet effet n'est plus observé lorsque les cellules ont moins de cholestérol dans leur membrane ou en présence de zinc, un inhibiteur des pores amyloïdes. Le cholestérol maintient le peptide de façon oblique et en hélice α. Cette orientation favorise l'établissement d'une liaison hydrogène entre l'Asp27 d'un peptide et la Lys28 d'un peptide voisin, qui stabilise le pore. Enfin, notre étude montre que le bexarotène, un composé anti-Alzheimer dont le mécanisme d'action est controversé, prévient l'insertion du peptide dans des membranes et empêche la formation de pores dans la membrane plasmique des cellules nerveuses. / Alzheimer's disease is the most common neurodegenerative disease whose prevalence increases with age. It is the result of excess β-amyloid peptide (Aß), which self-organizes. This peptide is able to insert into the plasma membrane of cells where their organization in calcium permeable pores triggers the early stages of toxicity. This insertion is directly modulated by the lipid composition of the membrane especially cholesterol. Whereas several studies indicate that cholesterol interacts with and modulates Aß toxicity, the underlying molecular mechanisms remain poorly understood.Using computational, physico-chemical and cellular approaches, we evaluated the role of cholesterol in the insertion of the Aß peptide in the membrane and in the oligomerization process responsible for pore formation. Our study identifies the 22-35 fragment of Aβ as a functional cholesterol-binding domain in which two amino acids are essential: Val24 and Lys28. When incubated with SH-SY5Y cells, the minimal Aβ22-35 peptide caused an increase of Ca2+ entry. This effect was no longer observed in cholesterol-depleted cells and was inhibited by zinc, a classical blocker of amyloid channels. Cholesterol specifically induced a tilted alpha-helical topology of Aβ22-35 which appeared to facilitate the oligomerization process through the establishment of a hydrogen bond network involving Asn27 and Lys28. Finally, our study showed that bexarotene, an anti-Alzheimer compound whose mechanism of action is still under debate, competitively inhibited Aβ insertion into cholesterol-containing membranes and prevented calcium-permeable amyloid pore formation in the plasma membrane of neural cells.