Two different interfaces were the focus of study: 1) the interface between disordered amorphous carbon and inorganic materials (metal nanostructures and silicon), and 2) the interface between partially ordered graphene (graphene oxide) and synthetic polymer matrix. Specifically, the uniqueness of this study can be summarized through the following novel findings, fabrication processes, and characterization techniques: • A simple and efficient process for faster, greener, less-expensive, and highly localized transformation of amorphous carbon nanostructures into graphitic nanostructures using low temperature heat and light treatments was developed for the fabrication of low-resistance interfaces between carbon nanomaterials and inorganic metal surfaces. • A new protocol for high resolution mapping the charge distribution and electronic properties of nanoscale chemically heterogeneous domains on non-homogeneous surfaces such as graphene oxide was established. • High strength laminated mechanical nanocomposites based on high interfacial stress transfer between polymer matrices and large area, flat, and non-wrinkled graphene oxide sheets were suggested and demonstrated. • Scanning Thermal Twist Microscopy – a thermal microscopy based technique was developed and demonstrated for characterizing the thermal properties of homogeneous and heterogeneous interfaces with nanoscale spatial resolution and high thermal sensitivity unachievable using traditional techniques.

Conventional energetic materials which are based on monomolecular compounds such as trinitrotoluene (TNT) have relatively low volumetric energy density. The energy density can be significantly enhanced by the addition of metal particulates. Among all metals, aluminum is popular because of its high oxidation enthalpy, low cost, and relative safety. Micron-sized aluminum particles, which have relatively high ignition temperatures and burning times, have been most commonly employed. Ignition of micron-sized aluminum particles is typically achieved only upon melting of the oxide shell at 2350 K, thereby resulting in fairly high ignition delay. Novel approaches to reduce the ignition temperatures and burning times and enhance the energy content of the particle are necessary. Recently, there has been an enormous interest in nano-materials due to their unique physicochemical properties such as lower melting and ignition temperatures and shorter burning times. Favorably, tremendous developments in the synthesis technology of nano-materials have also been made in the recent past. Several metal-based energetic materials with nano-sized particles such as nano-thermites, nano-fluids, and metalized solid propellants are being actively studied. The “green” reactive mixture of nano-aluminum particles and water/ice mixture (ALICE) is being explored for various applications such as space and underwater propulsion, hydrogen generation, and fuel-cell technology. Strand burning experiments indicate that the burning rates of nano-aluminum and water mixtures surpass those of common energetic materials such as ammonium dinitramide (ADN), hydrazinium nitroformate (HNF), and cyclotetramethylene tetranitramine (HMX). Sufficient understanding of key physicochemical phenomena is, however, not present. Furthermore, the most critical parameters that dictate the burning rate have not been identified. A multi-zone theoretical framework is established to predict the burning properties and flame structure by solving conservation equations in each zone and enforcing the mass and energy continuities at the interfacial boundaries. An analytical expression for the burning rate is derived and physicochemical parameters that dictate the flame behavior are identified. An attempt is made to elucidate the rate-controlling combustion mechanism. The effect of bi-modal particle size distribution on the burning rate and flame structure are investigated. The results are compared with the experimental data and favorable agreement is achieved. The ignition and combustion characteristics of micron-sized aluminum particles can also be enhanced by replacing the inert alumina layer with favorable metallic coatings such as nickel. Experiments indicate that nickel-coated aluminum particles ignite at temperatures significantly lower than the melting point of the oxide film, 2350 K due to the presence of inter-metallic reactions. Nickel coating is also attractive for nano-sized aluminum particles due to its ability to maximize the active aluminum content. Understanding the thermo-chemical behavior of nickel-aluminum core-shell structured particles is of key importance to both propulsion and material synthesis applications. The current understanding is, however, far from complete. In the present study, molecular dynamics simulations are performed to investigate the melting behavior, diffusion characteristics, and inter-metallic reactions in nickel-coated nano-aluminum particles. Particular emphasis is on the effects of core size and shell thickness on all important phenomena. The properties of nickel-coated aluminum particles and aluminum-coated nickel particles are also compared. Considerable uncertainties pertaining to the ignition characteristics of nano-aluminum particles exist. Aluminum particles can spontaneously burn at room temperature, a phenomenon known as pyrophoricity. This is a major safety issue during particle synthesis, handling, and storage. The critical particle size below which nascent particles are pyrophoric is not well known. Energy balance analysis with accurate evaluation of material properties (including size dependent properties) is performed to estimate the critical particle size for nascent particles. The effect of oxide layer thickness on pyrophoricity of aluminum particles is studied. The ignition delay and ignition temperature of passivated aluminum particles are also calculated. Specific focus is placed on the effect of particle size. An attempt is made to explain the weak dependence of the ignition delay on particle size at nano-scales.

Thesis (M. S.)--Chemical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Nair, Sankar; Committee Member: Koros, William; Committee Member: Ludovice, Peter; Committee Member: Meredith, Carson; Committee Member: Thio, Yonathan; Committee Member: Zhou, Min.

It is common knowledge that water is one of the basic needs for human beings. However, the consumption of contaminated water can lead to waterborne diseases and fatalities. It is, therefore imperative to constantly monitor the quality of potable water. There are numerous technologies used for water quality monitoring. These technologies are relatively effective however these tests are expensive and complex to use, which then require experienced technicians to operate them. Other tests are not rapid, making consumers of water susceptible to waterborne diseases. In this study, dye-doped, surface functionalized silica nanoparticles (SiNPs) and surface-functionalized magnetic nanocomposites (MNCs) were proposed as materials that can be applied in order to reduce the time taken to get results as well as to make the processes less complex and portable. The aim of this study was to synthesize and characterize surface functionalized dye-doped SiNPs and surface functionalized MNCs for detection and preconcentration of in water. Additionally, proof of concept had to be shown using the synthesized materials. SiNPs were the materials of choice due to their easily functionalized surfaces and their strong optical properties. SiNPs are photostable and they do not leach in solution due to the inert nature of the silica matrix in aqueous media. MNCs were chosen as materials of choice for preconcentration of E. coli in water because they are easy to synthesize and they can be applied in various biological applications due to their functional groups. SiNPs were synthesized using the water-in-oil microemulsion. The SiNPs were further functionalized with amine and carboxyl groups and avidin. Thereafter, they were bioconjugated with biotinylated anti-E. coli antibodies. The pure and surface functionalized SiNPs were characterized using ATR-FTIR spectroscopy, FE-SEM, HR-TEM, Zeta Sizer, UV-vis spectroscopy and spectrofluorometry. The application of the dye—doped surface functionalized SiNPs in E. coli detection was characterized using the fluorescence plate reader. The SiNPs were spherical and uniform in size. They increased in size as they were being functionalized, ranging from 21.20 nm to 75.06 nm. The SiNPs were successfully functionalized with amine and carboxyl groups as well as with avidin and antibodies. Two methods were investigated for carboxyl group attachment (direct and indirect attachment) and the direct attachment method yielded the best results with a surface charge of -31.9 mV compared to -23.3 mV of the indirect method. The dye loading was found to be 1% after particle synthesis. The optical properties of the Ru(Bpy) dye were enhanced 3 fold when they were encapsulated in the Si matrix. The SiNPs were binding to the E. coli cells and enabled detection. MNCs were synthesized through in-situ polymerization. The MNCs were characterized using ATR-FTIR spectroscopy, SEM, TEM and XRD. The MNCs were successfully functionalized with carboxyl groups. The increase in size of the nanocomposites as seen in SEM images proved that the Fe3O4 was successfully encapsulated in the polymer matrix. The MNCs were proven to be magnetic by a simple magnetism test whereby they were separated in an aqueous solution using an external magnetic field. The antibody-labelled MNCs were binding to the E. coli cells as shown in TEM images. E. coli cells were removed from water at varying concentrations of 1x106 CFU/mL to 1x109 CFU/mL at 10 mL volumes. This study has demonstrated that dye-doped SiNPs amplify the signal of E. coli cells using fluorescence. The study has also demonstrated that the MNCs can be applied in sample preconcentration and enrichment for E. coli detection. However, further studies should investigate and optimize the combination of the two techniques in a point of use device for water quality testing of 100 mL-samples as per the requirement of the SANS 241 standard. / Civil and Chemical Engineering / M. Tech. (Chemical Engineering)

Dentre os métodos empregados para a proteção à corrosão de materiais metálicos os revestimentos orgânicos vêm sendo muito utilizados devido a sua facilidade de aplicação e custos razoáveis. A propriedade de barreira dos revestimentos orgânicos pode ser melhorada com a incorporação de cargas adequadas, tais como nanocargas que, mesmo em baixas concentrações, apresentam propriedades de barreira superiores às cargas convencionais. A montmorilonita (MMT) é a fase inorgânica mais utilizada na obtenção de nanocompósitos poliméricos. Para melhorar a compatibilidade e dispersão da argila na resina polimérica, muitos pesquisadores têm realizado o processo de funcionalização da argila utilizando silano. O presente trabalho tem como objetivo desenvolver e caracterizar uma tinta em pó base poliéster contendo diferentes teores da argila montmorilonita sódica (MMT-Na+) modificada com o silano 3-aminopropiltrietoxisilano (γ-APS). A argila modificada com silano (S-MMT) ou a MMT-Na+ foi incorporada numa formulação padrão de tinta em pó base poliéster nas proporções de 2, 4 e 8% (m/m). A incorporação da argila na tinta ocorreu no estado fundido (extrusão). As argilas, a tinta em pó e o revestimento após a cura foram analisados empregando diferentes técnicas de caracterização, tais como difração de raios X (DRX), espectroscopia de infravermelho por transformada de Fourier (FTIR), análise termogravimétrica (TGA), calorimetria exploratória diferencial (DSC), microscopia eletrônica de varredura (MEV), microscopia óptica (MO). As tintas em pó foram aplicadas sobre painéis de aço carbono por pulverização eletrostática. O efeito da incorporação de diferentes teores da argila modificada e não modificada nas propriedades físicas e de proteção à corrosão das tintas foram avaliadas empregando ensaios de medida de brilho, aderência, flexibilidade, resistência ao impacto, potencial de circuito aberto (OCP), imersão, impedância eletroquímica (EIS) e exposição à névoa salina. Através do DRX foi confirmada a modificação e a intercalação de uma bicamada de moléculas de aminopropil no espaçamento interlamelar da argila. A S-MMT apresentou uma maior perda de massa do que a MMT-Na+ devido à presença de silano na sua estrutura. A MMT-Na+ se apresentou na forma de grandes aglomerados irregulares que se tornaram menores e mais finos após sua modificação com silano. Nas tintas contendo os diferentes teores de argila (MMT-Na+ ou S-MMT) não foi constatada a esfoliação da argila, sendo obtido um microcompósito. A partir da caracterização térmica da tinta em pó constatou-se que os revestimentos contendo a S-MMT apresentaram menor estabilidade térmica que os demais revestimentos devido à presença do modificador orgânico. A presença da argila MMT-Na+ ou S-MMT (com exceção de 4% (m/m) da S-MMT) reduziu a energia liberada no processo de reticulação. Para todos os revestimentos contendo argila foi constatado o aumento da dureza superficial do revestimento e a redução de brilho com o aumento do teor de argila, sendo este efeito mais pronunciado com a adição de 8% (m/m) de MMT-Na+. A aderência do revestimento ao substrato e a flexibilidade do revestimento não foram alteradas pela presença da argila, porém os revestimentos contendo a S-MMT apresentaram melhores resultados quanto à resistência ao impacto que os revestimentos contendo a argila MMT-Na+. Tanto nos ensaios eletroquímicos como no de exposição à névoa salina a modificação da argila com o silano resultou em revestimentos com melhor desempenho à corrosão que os revestimentos contendo a argila não modificada. Contudo, a propriedade de proteção à corrosão dos revestimentos contendo argila não foi superior ao revestimento isento de argila. / Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2014-08-25T19:29:58Z No. of bitstreams: 1 Dissertacao Paula Tibola Bertuoli.pdf: 5722201 bytes, checksum: cbb4f785db0e5a8566d49614c04b7264 (MD5) / Made available in DSpace on 2014-08-25T19:29:58Z (GMT). No. of bitstreams: 1 Dissertacao Paula Tibola Bertuoli.pdf: 5722201 bytes, checksum: cbb4f785db0e5a8566d49614c04b7264 (MD5) / Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul, FAPERGS / Among the methods used for corrosion protection of metal materials the organics coatings have been widely used due to their ease of application and reasonable costs. The barrier property of the organic coatings can be improved by incorporation of appropriate fillers such as nanofillers that even in low concentrations show superior barrier properties to conventional fillers. The montmorillonite (MMT) is the inorganic phase more used to prepare polymer nanocomposites. To improve the compatibility and dispersion of the clay in a polymer resin, many researchers have performed the functionalization process of the clay using silane. This study aims to develop and characterize a polyester based powder coating containing different amounts of sodium montmorillonite (MMT-Na+) modified with the silane 3-aminopropyltriethoxysilane (γ-APS). The clay modified with silane (S-MMT) or MMT-Na+ clay were incorporated into a standard commercial formulation of a polyester based powder coating on the ratios of 2, 4 and 8 wt%. The incorporation of clay into the paint was in the molten state (extrusion). The clays, the powder coating and coating after curing were analyzed using different characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and optical microscopy (MO). The powder coatings were applied on carbon steel panels by electrostatic method. The effect of incorporating different amounts of modified and unmodified clay on the physical properties and corrosion protection of the coatings obtained were evaluated using techniques such as gloss measurement, adhesion, flexibility, impact resistance, open circuit potential (OCP), immersion and electrochemical impedance spectroscopy (EIS) in sodium chloride solution and exposure to salt spray. XRD results confirmed the modification and intercalation of a bilayer of aminopropyl molecules in the interlayer spacing of the clay. By thermal analysis the S-MMT clay showed greater loss greater than the MMT-Na+ clay due to the presence of silane in their structure. The MMT-Na+ are presented in the form of large irregular agglomerates that have become smaller and thinner after its modification with silane. In the coatings obtained by incorporating different concentrations of MMT-Na+ or S-MMT it was not detected the exfoliation of clay, characterizing a microcomposite. Through of the thermal characterization of the powder paint it was found that the coatings containing S-MMT clay showed lower thermal stability than other coatings due to the presence of the organic modifier. The presence of MMT-Na+ or S-MMT clay (except 4 wt% of S-MMT clay) reduced the energy released in the process of crosslinking. The surface hardness of the coating was increased and the brightness was decreased with increasing clay content and this effect was most pronounced with the addition of 8 wt% of MMT-Na+. The adhesion of the coating to the substrate and the flexibility of the coating were not changed by the presence of clay, but the clay coatings containing S-MMT showed better results than coatings containing MMT-Na+ regarding the impact resistance. Both electrochemical and exposure to salt spray tests the silane modified clay resulted in coatings with better corrosion performance than those coatings containing the unmodified clay. However, the corrosion protection of the coatings containing montmorillonite was not superior to the coating free of clay.

Materiais híbridos, como poliedros oligoméricos silsesquioxanos (POSS), têm recebido especial atenção nos últimos anos pois são materiais que possuem uma combinação sinérgica de propriedades de materiais orgânicos e inorgânicos. Sua preparação necessita de elevados tempos de síntese e o uso de aquecimento dielétrico se apresenta promissor. Entretanto, reatores comerciais são caros e uma alternativa passa a ser a adaptação de fornos de uso domésticos. Neste contexto, este trabalho busca adaptar um forno de micro-ondas doméstico para a síntese de POSS, comparando materiais obtidos via aquecimento por microondas e convencional (banho em óleo). O POSS foi sintetizado através da condensação hidrolítica do viniltrietoxisilano (VTES) e da mistura VTES e tetraetil ortosilicato (TEOS). As amostras sintetizadas foram caracterizadas por FTIR, RMN de 1H, TGA, GPC, MEV, MET e DRX. O uso de micro-ondas possibilitou a obtenção de POSS com maior rendimento para os sistemas VTES e VTES/TEOS, apresentando taxas de reação respectivas de 47 e 59 vezes maior que a síntese convencional. Todas as amostras apresentaram bandas FTIR intensas em ~1090 e ~568 cm-1, ambas relacionadas a formação de gaiolas de silsesquixanos. Não foram observadas vibrações -O-CH2CH3 mostrando que a reação de hidrólise foi totalmente completa. A presença de deformações OH nas amostras VTES/TEOS indica a formação de estruturas não totalmente condensadas, confirmada pelos espectros de RMN de H1 onde é observada a presença de silanóis não condensados. Análises GPC para o POSS VTES apresentaram a maior fração (96,5%) de estruturas T8 via convencional, e (93,93%) via micro-ondas. A adição de TEOS reduziu a fração de estruturas T8 obtidas, (78,0%) via dielétrico e (33,0%) convencional. A análise TGA de todas as amostras mostraram uma única etapa de degradação, onde diferenças observadas no sistema VTES/TEOS são associadas ao tamanho da estrutura do POSS conforme a análise de GPC. Imagens de MEV mostraram a presença de estruturas cúbicas e esféricas em todas as amostras, e a adição de TEOS indicou uma tendência a redução de tamanho. Imagens por MET para o POSS VTES mostrou morfologia similar as observadas por MEV, e para VTES/TEOS, a presença de aglomerados esféricos regulares nanométricos. O DRX para o POSS VTES micro-ondas, convencional e VTES/TEOS micro-ondas, indicou a presença de uma rede cristalina de estrutura romboédrica, típica de POSS T8. O POSS VTES/TEOS via convencional apresentou um padrão de DRX de uma amostra amorfa. As nanopartículas híbridas de POSS VTES, via aquecimento convencional e dielétrico em refluxo, mostrou possuírem características químicas muito semelhantes, confirmadas pelas técnicas de análise realizadas. Entretanto, a mesma comparação entre o POSS obtido via mistura VTES/TEOS, a mesma semelhança não é observada. Isto se deve ao precursor VTES ser trifuncional e ao TEOS ser tetrafuncional, ou seja, possuem momentos dipolares diferentes, induzindo estruturas irregulares orientadas aleatoriamente e de diferentes tamanhos, principalmente no aquecimento convencional, onde a reação apresentada é mais lenta. / Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2015-09-14T18:28:06Z No. of bitstreams: 1 Dissertacao Igor Luiz Penso.pdf: 3673859 bytes, checksum: f0f80b6c32267df60b2b04fa4df6d307 (MD5) / Made available in DSpace on 2015-09-14T18:28:06Z (GMT). No. of bitstreams: 1 Dissertacao Igor Luiz Penso.pdf: 3673859 bytes, checksum: f0f80b6c32267df60b2b04fa4df6d307 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior. / Hybrid materials, such as polyhedral oligomeric silsesquioxanes (POSS), nowadays have received special attention because they are materials that have a synergistic combination of organic and inorganic materials properties. Their preparation requires high time of synthesis and the use of dielectric heating appears promising. However, commercial reactors are expensive and the adaptation of domestic microwave ovens becomes an alternative. In this context, this work aims to adapt a domestic microwave oven for the synthesis of POSS, comparing materials obtained by microwave and conventional (oil bath) heating. The POSS was synthesized by the hydrolytic condensation of vinyltriethoxysilane (VTES) and tetraethyl orthosilicate (TEOS) in different proportions. The synthesized samples were characterized by FTIR, 1H-NMR, TGA, GPC, SEM, TEM and XRD. The use of microwaves enable the manufacture of POSS with increased yield for VTES and VTES/TEOS systems, respectively with rates of 47 to 59 times higher than conventional synthesis. All samples showed intense FTIR bands at ~ 1090 and ~ 568 cm-1, both related to formation of silsesquioxane cages. It was not observed -O-CH2CH3 vibrations showing the hydrolysis reaction has been fully completed. The presence of OH deformations in the VTES/TEOS samples indicate the formation of non-fully condensed structures, confirmed by 1H NMR spectra, where it is observed the presence of non-condensing silanol. GPC analysis for the POSS VTES exhibited a major fraction (96.5%) of T8 structures via conventional, and (93.9%) via microwave synthesis. The addition of TEOS decreased the fraction of T8 structures, (78.0%) via dielectric and (33.0%) for conventional synthesis. TGA analysis of all samples showed a single stage of degradation, differences between VTES/TEOS samples are associated with the size of the POSS structure according to GPC analysis. SEM images showed the presence of spherical and cubic structures in all samples, and the addition of TEOS indicated a tendency to increase the size of these structures. TEM images for POSS VTES showed similar morphology to those observed by SEM. The presence of nanometric regular spherical agglomerates was observed in VTES/TEOS samples. The XRD for POSS VTES microwave, conventional and VTES/TEOS microwave synthesis, indicated the presence of rhombohedral lattice structure, typical POSS T8. The POSS VTES/TEOS conventional route showed a XRD pattern of an amorphous sample. The hybrid nanoparticles of POSS VTES, prepared via conventional and dielectric heating using reflux system, showed a very similar chemical properties as confirmed by the analytical techniques performed. However, the same comparison between the POSS obtained via mixing of VTES/TEOS, the same behavior is not observed. This is due to the VTES precursors be trifunctional and TEOS tetrafunctional, i.e. have different dipole moments, inducing randomly oriented irregular structures and different sizes, especially in the conventional heating where reaction is slower.

A resina epóxi é uma das matrizes mais empregadas na produção de compósitos e revestimentos. Destaca-se no grupo dos materiais termorrígidos devido à facilidade de processamento, suas propriedades mecânicas e à estabilidade térmica. Propriedades como resistência à temperatura e flexibilidade têm sido sistematicamente modificadas pelo uso de diferentes materiais, como argilominerais e, mais recentemente, oligômeros poliédricos de silsesquioxano – POSS, aplicados em matrizes epóxi. Os oligômeros poliédricos de silsesquioxano (POSS) usados na preparação de nanocompósitos termorrígidos têm sido estudados na obtenção de materiais híbridos capazes de suportar temperaturas mais elevadas, promover aumento de propriedades mecânicas e melhorar propriedades de superfície como, por exemplo, a hidrofobicidade do polímero. Os grupos funcionais mais comuns utilizados na preparação de nanocompósitos com resina epóxi são aminas, álcoois e grupos epóxi. A funcionalidade da nanogaiola é importante, uma vez que um termorrígido formado por uma microestrutura reticulada apresente uma microestrutura tridimensional que pode interagir em qualquer direção formando ligações ou interagindo na interface das gaiolas inseridas. Nesse contexto, foi avaliado a influência da adição de três diferentes oligômeros poliédricos de silsesquioxano – POSS (Glicidilisobutil-POSS, Triglicidilisobutil-POSS e Glicidil-POSS), em duas diferentes concentrações 2,5% e 5% (m/m), em resina epoxídica, no comportamento morfológico, mecânico e eletroquímico quando aplicados em aço de baixa liga. Com adição de POSS à resina epóxi, observou-se um aumento na rugosidade e hidrofobicidade do revestimento, além de se obter uma maior resistência à termoxidação e um aumento nos valores de temperatura de transição vítrea do material em comparação com a amostra de resina epóxi. Dentre os sistemas estudados, a amostra contendo Glicidilisobutil-POSS (POSSmono) apresentou os melhores resultados em relação à resistência à corrosão, promovendo um aumento nos valores de ângulo de contato e na impedância eletroquímica. No quesito dispersão na matriz polimérica, o Glicidil-POSS (POSSocta) apresentou uma dispersão ineficiente com a formação de aglomerados, o que hipoteticamente influenciou no seu baixo desempenho no comportamento eletroquímico em relação aos demais sistemas. / Submitted by Ana Guimarães Pereira (agpereir@ucs.br) on 2016-07-05T14:13:46Z No. of bitstreams: 1 Dissertacao Marielen Longhi.pdf: 4767210 bytes, checksum: 8b9878a37cbc71de5a4cf9d89a1553a5 (MD5) / Made available in DSpace on 2016-07-05T14:13:46Z (GMT). No. of bitstreams: 1 Dissertacao Marielen Longhi.pdf: 4767210 bytes, checksum: 8b9878a37cbc71de5a4cf9d89a1553a5 (MD5) Previous issue date: 2016-07-05 / The epoxy resin is one of the matrices most used in manufacturing composites and coatings. It is highlighted in the group of thermosetting materials due to good processability, mechanic behavior and thermal stability. Properties as thermal resistance and flexibility have been systematically modified by the use of different materials, as clays and, more recently, polyhedral oligomeric silsesquioxanes – POSS, applied in epoxy matrices. The polyhedral oligomeric silsesquioxanes (POSS) in thermosetting nanocomposites have been studied in hybrid materials able to support higher temperatures, promoting increase of mechanic properties and improving surface properties such as, for example, the hydrophobicity of the polymer. The most common functional groups used to preparing nanocomposites with epoxy resin are amines, alcohols and epoxy groups. The nanocage functionality is important, once a thermosetting formed by a reticulated microstructure presents a three-dimensional microstructure that can interact in any direction, making bonds or interacting on the interface of the inserted cages. In this context, it was evaluated the influence of three different polyhedral oligomeric silsesquioxanes – POSS (Glycidylisobutyl-POSS, Triglycidylisobutyl-POSS and Glycidyl-POSS), at two different contents 2.5% and 5% (w/w), in epoxy resin, in the morphological, mechanic and electrochemical behavior when applied on low alloy steel. Adding POSS in the epoxy resin, it was observed an increase in roughness and hydrophobicity of the coating. Moreover, it was reached a higher thermal oxidation resistance and an increase in the values of glass transition temperature of the material, regarding the epoxy resin sample. Among the studied systems, the sample containing Glycidylisobutyl-POSS (POSSmono) showed the best results, regarding the corrosion resistance. The addition of POSSmono in the epoxy resin promoted an increase of contact angle and electrochemical impedance values. Regarding the dispersion in the polymeric matrix, the Glycidyl-POSS (POSSocta) presented an inefficient dispersion, with formation of agglomerates, which hypothetically influenced in its low performance in the electrochemical behavior, regarding the other systems.

Thesis submitted in fulfilment of the requirements for the degree Magister of Technology: Dental Technology In the Faculty of Health and Wellness Sciences At the Cape Peninsula University of Technology, 2012 / A study of the modification of dental nanocomposites with nanosized fillers is presented. The incorporation of TiO2 (titania) nanoparticles, via a silane chemical bond, to a standard dental acrylic resin matrix was explored to determine whether there was an increase in the wear resistance, flexural strength and surface hardness properties of the dental nanocomposites. The principal aim of this study was to synthesize dental nanocomposites with different sizes, treated, nano-TiO2 fillers in urethane dimethacrylate (UDMA) for potential application in posterior restoration and to evaluate their mechanical properties. Treatment of the nano-TiO2 particles was carried out with a silane coupling agent, 3-(methacryloyloxy)propyltrimethoxysilane (MPTMS), to improve bonding between the nano-TiO2 particles and acrylic matrix (UDMA), and reduce agglomeration of the nano-TiO2. Characterisation of products was carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FTIR). TEM results were used to compare the particle size distributions of untreated TiO2 and treated TiO2 under various experimental conditions in an ethanol solvent, while SEM images showed the adhesion between the matrix (UDMA) and the nano-TiO2. FTIR was used to show the qualitative composition of untreated TiO2 and treated TiO2. Eighteen groups of experimental dental nanocomposites were evaluated. Each group contained different average particle sizes of nano-TiO2 (filler): 5 nm, 21 nm and 80 nm. Each particle size category was treated with three different concentrations of the silane, (MPTMS): 2.5, 10 and 30 wt %. Samples were prepared by mixing the monomer resin matrix of UDMA and nano-TiO2 particles. For comparison, a commercially available dental resin was reinforced with untreated and treated nano-TiO2 particle sizes 5, 21 and 80 nm. Wear resistance, flexural strength and surface hardness of TiO2 nanocomposites treated with 2.5 wt % MPTMS were significantly higher compared to those treated with 10 and 30 wt% MPTMS. The nanocomposites with 5 nm TiO2 had higher wear loss, lower flexural strength and lower surface hardness values compared to those with 21 nm and 80 nm TiO2. Statistical analysis showed that the effect of the concentrations of MPTMS on wear resistance and surface hardness of specimens was significant (p<0.001), which is less than 0.05, while the effect of the concentration of MPTMS on flexural strength was statistically not significant, (p=0.02). Control composites reinforced with treated 80 nm TiO2 particles had much better mechanical properties than any of the other specimens. It was concluded that the most available commercial product for dental restorations could be improved by the addition of nano-TiO2 with relatively large particle size.

Dentre os métodos empregados para a proteção à corrosão de materiais metálicos os revestimentos orgânicos vêm sendo muito utilizados devido a sua facilidade de aplicação e custos razoáveis. A propriedade de barreira dos revestimentos orgânicos pode ser melhorada com a incorporação de cargas adequadas, tais como nanocargas que, mesmo em baixas concentrações, apresentam propriedades de barreira superiores às cargas convencionais. A montmorilonita (MMT) é a fase inorgânica mais utilizada na obtenção de nanocompósitos poliméricos. Para melhorar a compatibilidade e dispersão da argila na resina polimérica, muitos pesquisadores têm realizado o processo de funcionalização da argila utilizando silano. O presente trabalho tem como objetivo desenvolver e caracterizar uma tinta em pó base poliéster contendo diferentes teores da argila montmorilonita sódica (MMT-Na+) modificada com o silano 3-aminopropiltrietoxisilano (γ-APS). A argila modificada com silano (S-MMT) ou a MMT-Na+ foi incorporada numa formulação padrão de tinta em pó base poliéster nas proporções de 2, 4 e 8% (m/m). A incorporação da argila na tinta ocorreu no estado fundido (extrusão). As argilas, a tinta em pó e o revestimento após a cura foram analisados empregando diferentes técnicas de caracterização, tais como difração de raios X (DRX), espectroscopia de infravermelho por transformada de Fourier (FTIR), análise termogravimétrica (TGA), calorimetria exploratória diferencial (DSC), microscopia eletrônica de varredura (MEV), microscopia óptica (MO). As tintas em pó foram aplicadas sobre painéis de aço carbono por pulverização eletrostática. O efeito da incorporação de diferentes teores da argila modificada e não modificada nas propriedades físicas e de proteção à corrosão das tintas foram avaliadas empregando ensaios de medida de brilho, aderência, flexibilidade, resistência ao impacto, potencial de circuito aberto (OCP), imersão, impedância eletroquímica (EIS) e exposição à névoa salina. Através do DRX foi confirmada a modificação e a intercalação de uma bicamada de moléculas de aminopropil no espaçamento interlamelar da argila. A S-MMT apresentou uma maior perda de massa do que a MMT-Na+ devido à presença de silano na sua estrutura. A MMT-Na+ se apresentou na forma de grandes aglomerados irregulares que se tornaram menores e mais finos após sua modificação com silano. Nas tintas contendo os diferentes teores de argila (MMT-Na+ ou S-MMT) não foi constatada a esfoliação da argila, sendo obtido um microcompósito. A partir da caracterização térmica da tinta em pó constatou-se que os revestimentos contendo a S-MMT apresentaram menor estabilidade térmica que os demais revestimentos devido à presença do modificador orgânico. A presença da argila MMT-Na+ ou S-MMT (com exceção de 4% (m/m) da S-MMT) reduziu a energia liberada no processo de reticulação. Para todos os revestimentos contendo argila foi constatado o aumento da dureza superficial do revestimento e a redução de brilho com o aumento do teor de argila, sendo este efeito mais pronunciado com a adição de 8% (m/m) de MMT-Na+. A aderência do revestimento ao substrato e a flexibilidade do revestimento não foram alteradas pela presença da argila, porém os revestimentos contendo a S-MMT apresentaram melhores resultados quanto à resistência ao impacto que os revestimentos contendo a argila MMT-Na+. Tanto nos ensaios eletroquímicos como no de exposição à névoa salina a modificação da argila com o silano resultou em revestimentos com melhor desempenho à corrosão que os revestimentos contendo a argila não modificada. Contudo, a propriedade de proteção à corrosão dos revestimentos contendo argila não foi superior ao revestimento isento de argila. / Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul, FAPERGS / Among the methods used for corrosion protection of metal materials the organics coatings have been widely used due to their ease of application and reasonable costs. The barrier property of the organic coatings can be improved by incorporation of appropriate fillers such as nanofillers that even in low concentrations show superior barrier properties to conventional fillers. The montmorillonite (MMT) is the inorganic phase more used to prepare polymer nanocomposites. To improve the compatibility and dispersion of the clay in a polymer resin, many researchers have performed the functionalization process of the clay using silane. This study aims to develop and characterize a polyester based powder coating containing different amounts of sodium montmorillonite (MMT-Na+) modified with the silane 3-aminopropyltriethoxysilane (γ-APS). The clay modified with silane (S-MMT) or MMT-Na+ clay were incorporated into a standard commercial formulation of a polyester based powder coating on the ratios of 2, 4 and 8 wt%. The incorporation of clay into the paint was in the molten state (extrusion). The clays, the powder coating and coating after curing were analyzed using different characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and optical microscopy (MO). The powder coatings were applied on carbon steel panels by electrostatic method. The effect of incorporating different amounts of modified and unmodified clay on the physical properties and corrosion protection of the coatings obtained were evaluated using techniques such as gloss measurement, adhesion, flexibility, impact resistance, open circuit potential (OCP), immersion and electrochemical impedance spectroscopy (EIS) in sodium chloride solution and exposure to salt spray. XRD results confirmed the modification and intercalation of a bilayer of aminopropyl molecules in the interlayer spacing of the clay. By thermal analysis the S-MMT clay showed greater loss greater than the MMT-Na+ clay due to the presence of silane in their structure. The MMT-Na+ are presented in the form of large irregular agglomerates that have become smaller and thinner after its modification with silane. In the coatings obtained by incorporating different concentrations of MMT-Na+ or S-MMT it was not detected the exfoliation of clay, characterizing a microcomposite. Through of the thermal characterization of the powder paint it was found that the coatings containing S-MMT clay showed lower thermal stability than other coatings due to the presence of the organic modifier. The presence of MMT-Na+ or S-MMT clay (except 4 wt% of S-MMT clay) reduced the energy released in the process of crosslinking. The surface hardness of the coating was increased and the brightness was decreased with increasing clay content and this effect was most pronounced with the addition of 8 wt% of MMT-Na+. The adhesion of the coating to the substrate and the flexibility of the coating were not changed by the presence of clay, but the clay coatings containing S-MMT showed better results than coatings containing MMT-Na+ regarding the impact resistance. Both electrochemical and exposure to salt spray tests the silane modified clay resulted in coatings with better corrosion performance than those coatings containing the unmodified clay. However, the corrosion protection of the coatings containing montmorillonite was not superior to the coating free of clay.

Materiais híbridos, como poliedros oligoméricos silsesquioxanos (POSS), têm recebido especial atenção nos últimos anos pois são materiais que possuem uma combinação sinérgica de propriedades de materiais orgânicos e inorgânicos. Sua preparação necessita de elevados tempos de síntese e o uso de aquecimento dielétrico se apresenta promissor. Entretanto, reatores comerciais são caros e uma alternativa passa a ser a adaptação de fornos de uso domésticos. Neste contexto, este trabalho busca adaptar um forno de micro-ondas doméstico para a síntese de POSS, comparando materiais obtidos via aquecimento por microondas e convencional (banho em óleo). O POSS foi sintetizado através da condensação hidrolítica do viniltrietoxisilano (VTES) e da mistura VTES e tetraetil ortosilicato (TEOS). As amostras sintetizadas foram caracterizadas por FTIR, RMN de 1H, TGA, GPC, MEV, MET e DRX. O uso de micro-ondas possibilitou a obtenção de POSS com maior rendimento para os sistemas VTES e VTES/TEOS, apresentando taxas de reação respectivas de 47 e 59 vezes maior que a síntese convencional. Todas as amostras apresentaram bandas FTIR intensas em ~1090 e ~568 cm-1, ambas relacionadas a formação de gaiolas de silsesquixanos. Não foram observadas vibrações -O-CH2CH3 mostrando que a reação de hidrólise foi totalmente completa. A presença de deformações OH nas amostras VTES/TEOS indica a formação de estruturas não totalmente condensadas, confirmada pelos espectros de RMN de H1 onde é observada a presença de silanóis não condensados. Análises GPC para o POSS VTES apresentaram a maior fração (96,5%) de estruturas T8 via convencional, e (93,93%) via micro-ondas. A adição de TEOS reduziu a fração de estruturas T8 obtidas, (78,0%) via dielétrico e (33,0%) convencional. A análise TGA de todas as amostras mostraram uma única etapa de degradação, onde diferenças observadas no sistema VTES/TEOS são associadas ao tamanho da estrutura do POSS conforme a análise de GPC. Imagens de MEV mostraram a presença de estruturas cúbicas e esféricas em todas as amostras, e a adição de TEOS indicou uma tendência a redução de tamanho. Imagens por MET para o POSS VTES mostrou morfologia similar as observadas por MEV, e para VTES/TEOS, a presença de aglomerados esféricos regulares nanométricos. O DRX para o POSS VTES micro-ondas, convencional e VTES/TEOS micro-ondas, indicou a presença de uma rede cristalina de estrutura romboédrica, típica de POSS T8. O POSS VTES/TEOS via convencional apresentou um padrão de DRX de uma amostra amorfa. As nanopartículas híbridas de POSS VTES, via aquecimento convencional e dielétrico em refluxo, mostrou possuírem características químicas muito semelhantes, confirmadas pelas técnicas de análise realizadas. Entretanto, a mesma comparação entre o POSS obtido via mistura VTES/TEOS, a mesma semelhança não é observada. Isto se deve ao precursor VTES ser trifuncional e ao TEOS ser tetrafuncional, ou seja, possuem momentos dipolares diferentes, induzindo estruturas irregulares orientadas aleatoriamente e de diferentes tamanhos, principalmente no aquecimento convencional, onde a reação apresentada é mais lenta. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior. / Hybrid materials, such as polyhedral oligomeric silsesquioxanes (POSS), nowadays have received special attention because they are materials that have a synergistic combination of organic and inorganic materials properties. Their preparation requires high time of synthesis and the use of dielectric heating appears promising. However, commercial reactors are expensive and the adaptation of domestic microwave ovens becomes an alternative. In this context, this work aims to adapt a domestic microwave oven for the synthesis of POSS, comparing materials obtained by microwave and conventional (oil bath) heating. The POSS was synthesized by the hydrolytic condensation of vinyltriethoxysilane (VTES) and tetraethyl orthosilicate (TEOS) in different proportions. The synthesized samples were characterized by FTIR, 1H-NMR, TGA, GPC, SEM, TEM and XRD. The use of microwaves enable the manufacture of POSS with increased yield for VTES and VTES/TEOS systems, respectively with rates of 47 to 59 times higher than conventional synthesis. All samples showed intense FTIR bands at ~ 1090 and ~ 568 cm-1, both related to formation of silsesquioxane cages. It was not observed -O-CH2CH3 vibrations showing the hydrolysis reaction has been fully completed. The presence of OH deformations in the VTES/TEOS samples indicate the formation of non-fully condensed structures, confirmed by 1H NMR spectra, where it is observed the presence of non-condensing silanol. GPC analysis for the POSS VTES exhibited a major fraction (96.5%) of T8 structures via conventional, and (93.9%) via microwave synthesis. The addition of TEOS decreased the fraction of T8 structures, (78.0%) via dielectric and (33.0%) for conventional synthesis. TGA analysis of all samples showed a single stage of degradation, differences between VTES/TEOS samples are associated with the size of the POSS structure according to GPC analysis. SEM images showed the presence of spherical and cubic structures in all samples, and the addition of TEOS indicated a tendency to increase the size of these structures. TEM images for POSS VTES showed similar morphology to those observed by SEM. The presence of nanometric regular spherical agglomerates was observed in VTES/TEOS samples. The XRD for POSS VTES microwave, conventional and VTES/TEOS microwave synthesis, indicated the presence of rhombohedral lattice structure, typical POSS T8. The POSS VTES/TEOS conventional route showed a XRD pattern of an amorphous sample. The hybrid nanoparticles of POSS VTES, prepared via conventional and dielectric heating using reflux system, showed a very similar chemical properties as confirmed by the analytical techniques performed. However, the same comparison between the POSS obtained via mixing of VTES/TEOS, the same behavior is not observed. This is due to the VTES precursors be trifunctional and TEOS tetrafunctional, i.e. have different dipole moments, inducing randomly oriented irregular structures and different sizes, especially in the conventional heating where reaction is slower.