A radiopacidade dos materiais restauradores deve permitir distinguí-los da estrutura dental. Os adesivos dentinários normalmente, não possuem radiopacidade satisfatória a qual pode ser buscada com o acréscimo de substâncias que apresentem essa característica. Entretanto, esses materiais não devem interferir negativamente nas propriedades do polímero formado. O objetivo deste estudo foi avaliar a influência da adição de substâncias radiopacificantes em uma resina adesiva experimental nas propriedades do polímero. Uma resina adesiva experimental foi formulada com 50 % de Bis- GMA, 25 % TEGDMA, e 25 % HEMA, em peso, acrescido de Canforoquinona e EDAB (1% /mol). Para formar os grupos experimentais seis substâncias foram adicionadas à resina base: dióxido de titânio, óxido de bismuto, sulfato de bário, quartzo, dióxido de zircônio e trifluoreto de itérbio, em diferentes concentrações. A radiopacidade foi avaliada utilizando um sistema digital com placas de fósforo VistaScan (Dürr Dental GmbH & CO. KG, Bietigheim- Bissingen, Alemanha) sendo analisadas através do software DBSWIN 4.5, quanto a densidade radiográfica. As demais propriedades avaliadas foram: grau de conversão através de FTIR; resistência à flexão, baseada na normatização da ISO 4049/2010. Radiopacidade de resinas adesivas experimentais com ao menos 30% sulfato de bário ou óxido de bismuto ou 40% de zircônia apresentaram radiopacidade semelhante a 2mm de alumínio. Resinas adesivas com ao menos 20% de fluoreto de itérbio apresentaram radiopacidade satisfatória (2mm de Al) sem influenciar outras propriedades. / The radiopacity of restorative materials should be sufficient to allow the clinician to distinguish the material from normal and demineralized tissues. It is recognized that unfilled resin adhesives are radiolucent which could be reached with radiopaquing agents’ addition. The aim of this study is to evaluate, in an experimental adhesive resin, the influence of radiopaquing agents at polymer properties. A model adhesive resin was formulated with 50% of Bis-GMA, 25% of TEGDMA, 25% of HEMA in weight, and camphorquinone and EDAB (1%mol). The experimental groups were formed with addition of six radiopaquing agents: titanium dioxide, bismuth oxide, barium sulfate, quartz, zirconium, and ytterbium trifluoride at different concentration. The radiopacity was evaluated using an aluminum step-wedge and VistaScan (Dürr Dental GmbH & CO. KG, Bietigheim-Bissingen, Alemanha) phosphorous plates radiographs digital system and DBSWIN 4.5 software. The other properties evaluated were degree of conversion with FTIR and flexural strength, based at ISO 4049/2010. Radiopacity of model adhesive resins with at least 30% of barium sulfate or bismuth oxide or 40% of zircon showed no significant differences to 2mm of aluminum. Adhesive resin with at least 20% addition of ytterbium trifluoride presented satisfactory radiopacity (Al 2mm) without influencing other properties.

As células a combustível de etanol direto (DEFCs, Direct Ethanol Fuel Cells) são baseadas na eletro-oxidação do etanol à baixa temperatura e necessitam catalisadores à base de metais nobres, devido à cinética mais lenta para as reações de oxi-redução. Entre os catalisadores, a platina e as ligas de platina são os mais utilizados. Materiais para suportar os catalisadores são necessários a fim de reduzir a carga do mesmo empregada. Um dos suportes de catalisadores mais versáteis é o carvão ativado, e um dos mais utilizados tem sido o carvão mineral Vulcan. Recentemente, estudos têm sido realizados sobre a madeira como material precursor de carvão ativado, devido à sua sustentabilidade e também porque os materiais carbonosos obtidos têm excelentes propriedades finais. No presente trabalho, estudou-se a reação de eletro-oxidação do etanol, de catalisadores à base de Pt e PtSn suportados em biocarvões obtidos a partir da madeira Eucalyptus grandis. No início desse trabalho não havia relatos na literatura sobre o uso de carvões ativados obtidos a partir de madeira de Eucalyptus grandis como precursor. Foram utilizados dois métodos de ativação nos suportes, ativação física com CO2 e ativação química com ZnCl2. Os suportes de catalisadores foram caracterizados por análise textural, análise elementar, análise termogravimétrica e por espectroscopia de infravermelho. As técnicas empregadas para a caracterização dos catalisadores foram espectrometria de retroespalhamento de Rutherford (RBS), difração de raios-X (DRX), análise termogravimétrica (TGA), microscopia eletrônica de transmissão (MET), voltametria cíclica (VC) e caracterização espectroeletroquímica (ATR-FTIR in-situ). Os biocarvões apresentaram áreas superficiais maiores e tamanhos de poros menores do que o carvão Vulcan, independente do tratamento. A natureza do suporte influenciou nas características morfológicas dos eletrocatalisadores preparados. Com base nos resultados obtidos os catalisadores suportados nos suportes com ativação química apresentaram os melhores resultados de densidade de corrente para eletro-oxidação do etanol, com exceção do catalisador PtSn suportado no biocarvão ativado fisicamente (PtSn/BCAF). Pode-se dizer que os biocarvões são adequados para aplicações em células de combustível, podendo substituir o uso de suportes baseados em carvões minerais. A eletro-oxidação do etanol nos eletrocataliadores de PtSn nos carvões ativados ocorre principalmente através da produção de acetaldeído e ácido acético. / Direct ethanol fuel cells (DEFC) are based on ethanol electrooxidation at low-temperature and they require noble metal based catalysts, due to the slower kinetic of redox reactions. Among the catalysts, platinum and its alloys have been the most widely used. Catalysts support materials have been employed with the intent to reduce loading catalyst. One of the most versatile catalyst supports is activated carbon, and one of the most widely used is the Vulcan®, a mineral carbon. Currently, different studies have been conducted concerning wood as activated carbon precursor, because of its sustainability and its properties, like suitable porous texture, surface area and surface chemistry. In this work, it was studied ethanol electrooxidation reaction on Pt and PSn catalysts supported on biocarbon. Biocarbons were obtained from Eucalyptus grandis. Literature reports the use of carbon materials as catalyst support, however focused on carbon fibers and carbon nanotubes, without any precedent on the use of activated carbon obtained from Eucalyptus grandis until the start of this work. The carbon supports were obtained by physical activation using CO2, and chemical activation with ZnCl2. Catalyst support characterization boarded elemental analysis, texture analysis, thermogravimetric analysis and infrared spectroscopy. Techniques employed for the catalyst characterization were Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), cyclic voltammetry (CV) and spectroelectrochemical characterization (ATR-FTIR in situ). Biocarbons presended the higher surface areas and smallest pore size than the Vulcan ones, independent of the treatment. The support nature influenced on the catalyst morphology. Results showed that the catalyst on the chemically activated supports presented the best current density for ethanol electro-oxidation, except for the PtSn on the physically activated biocarbon (PtSn/BCAF). Biocarbons resulted adequate for fuel cell applications and are capable of substituting the conventional supports based on mineral carbon. Ethanol electro-oxidation on PtSn catalysts takes place through the production of acetaldehyde and acetic acid reaction mechanism.

abstract: Alkali-activated aluminosilicates, commonly known as "geopolymers", are being increasingly studied as a potential replacement for Portland cement. These binders use an alkaline activator, typically alkali silicates, alkali hydroxides or a combination of both along with a silica-and-alumina rich material, such as fly ash or slag, to form a final product with properties comparable to or better than those of ordinary Portland cement. The kinetics of alkali activation is highly dependent on the chemical composition of the binder material and the activator concentration. The influence of binder composition (slag, fly ash or both), different levels of alkalinity, expressed using the ratios of Na2O-to-binders (n) and activator SiO2-to-Na2O ratios (Ms), on the early age behavior in sodium silicate solution (waterglass) activated fly ash-slag blended systems is discussed in this thesis. Optimal binder composition and the n values are selected based on the setting times. Higher activator alkalinity (n value) is required when the amount of slag in the fly ash-slag blended mixtures is reduced. Isothermal calorimetry is performed to evaluate the early age hydration process and to understand the reaction kinetics of the alkali activated systems. The differences in the calorimetric signatures between waterglass activated slag and fly ash-slag blends facilitate an understanding of the impact of the binder composition on the reaction rates. Kinetic modeling is used to quantify the differences in reaction kinetics using the Exponential as well as the Knudsen method. The influence of temperature on the reaction kinetics of activated slag and fly ash-slag blends based on the hydration parameters are discussed. Very high compressive strengths can be obtained both at early ages as well as later ages (more than 70 MPa) with waterglass activated slag mortars. Compressive strength decreases with the increase in the fly ash content. A qualitative evidence of leaching is presented through the electrical conductivity changes in the saturating solution. The impact of leaching and the strength loss is found to be generally higher for the mixtures made using a higher activator Ms and a higher n value. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) is used to obtain information about the reaction products. / Dissertation/Thesis / M.S. Civil Engineering 2012

A conformação de dispositivos médicos implantáveis a partir de uma blenda exige o desenvolvimento de um produto com propriedades próximas do comportamento ideal, combinando propriedades térmicas e mecânicas e boa resposta tecidual. O Poli (ácido láctico-co-glicólico) (PLGA) e o Poli (isopreno) (IR) foram escolhidos como componentes da blenda com finalidade de promover boa biocompatibilidade e características mecânicas especificas. As blendas foram obtidas por dissolução dos polímeros em solvente orgânico, seguida de secagem. Para determinar a influência do teor de IR sobre as propriedades da blenda, foram realizados ensaios de espectroscopia na região de infravermelho por transformada de Fourier (FTIR), calorimetria diferencial de varredura (DSC), análise dinâmico-mecânica (DMA), microscopia óptica por luz polarizada (POM), análise de dureza, ensaio de tração e análise de viabilidade celular. A presença de IR na blenda provocou alteração na estrutura molecular semi-cristalina do PLGA, bem como influenciou o comportamento mecânico analisado a partir da curva tensão-deformação do material. A blenda se mostrou biocompativel em ambiente celular e em ensaios preliminares em animais, apresentando potencial para aplicação como biomaterial. / The conformation of an implantable medical device from a polymeric blend requires the development of a product with properties as close as possible of ideal behavior with the combination between thermal and mechanical properties and good tissue response. The poly (lactic-co-glycolic acid) (PLGA) and the poly (isoprene) (IR) were chosen as the blend components to promote good biocompatibility and specific mechanical characteristics. The blends were obtained by dissolution of polymers in organic solvent, followed by drying. In order to determine the IR content influence over the blend properties, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), polarized light optical microscopy (POM), hardness analysis, tensile test and cell viability test were carried out. The IR presence caused changes in semi-crystalline molecular structure of PLGA, as well as actuated over the mechanical response analyzed on material’s stress-strain curve. The blend showed itself biocompatible at cellular environment and at preliminary animal tests, presenting potential for application as biomaterial.

O objetivo deste estudo é caracterizar a influência da relação dos componentes hidrófilos de uma resina adesiva experimental em suas propriedades intrínsecas. Para isso, foram adicionados a um sistema polimérico (BisGMA, BisEMA e TEGDMA), diferentes concentrações de HEMA totalizando quatro grupos: 0%, 15%, 30% e 50% de HEMA. As misturas foram caracterizadas quanto à cinética de polimerização através de Fourier Transformed Infrared (FTIR) em tempo real e a taxa de polimerização (RP) foi calculada através da análise de regressão não-linear; resistência coesiva à tração utilizando-se uma máquina de ensaios mecânicos com corpos de prova em forma de ampulheta com área de constrição de 1mm2; e, sorção e solubilidade baseada na normatização ISO 4049. Houve correlação entre o tempo de fotoativação e o grau de conversão para todos os grupos (r2>0.98). O grupo 0% apresentou RPMÁX elevada nos segundos iniciais de fotoativação com, no entanto, uma brusca redução. As adições de 30% e 50% de HEMA determinaram uma RPMÁX do copolímero menor que em 15% e 0%. Não houve diferença entre o grau de conversão final (60s) entre os grupos de 0, 15 e 30%, sendo 59,7%, 61,4% e 55,2% respectivamente. As adições de 30% e 50% de HEMA determinaram a redução da resistência coesiva dos polímeros (p<0,05) quando comparado aos grupos 0% e 15%. Grupos com maiores adições de HEMA apresentaram maiores graus de sorção e solubilidade (p<0,05). Maiores adições de HEMA resultaram em polímeros mais propensos à degradação. / The aim of this study was to characterize the influence of hydrophilic monomers ratios on an experimental adhesive resin properties. Four groups, with 0, 15, 30 and 50% (wt) addiction of HEMA were prepared. Comonomer blends (BisGMA, BisEMA, TEGDMA and HEMA) were analyzed with kinetics of polimerization real time FTIR and the rate of polymerization was calculated by non-linear regression analysis. Ultimate tensile strength was tested using a universal testing machine (Emic) with hour-glass shaped specimens with cross-sectional area 1mm2. Water sorption and solubility tests were based on ISO 4049. For All groups was a positive and strong correlation between light-activation time and degree of conversion (r2>0,98). Group 0% of HEMA showed higher RPMÁX in early seconds with a suddenly decrease. Additions of 30% and 50% of HEMA determined a RPMÁX lower than the comonomer blends with 15% and 0% of HEMA. There was no statistical difference of final degree of conversion of the tested groups, varying from 63% to 67% . The additions of 30% and 50% of HEMA determined reduction of ultimate tensile strength of the polymers formed (p<0,05) when compared to 0% and 15 % of HEMA. Groups with higher additions of HEMA showed higher water sorption and solubility (p<0,05). Higher additions of HEMA resulted in polymers more prone to degradation.

A radiopacidade dos materiais restauradores deve permitir distinguí-los da estrutura dental. Os adesivos dentinários normalmente, não possuem radiopacidade satisfatória a qual pode ser buscada com o acréscimo de substâncias que apresentem essa característica. Entretanto, esses materiais não devem interferir negativamente nas propriedades do polímero formado. O objetivo deste estudo foi avaliar a influência da adição de substâncias radiopacificantes em uma resina adesiva experimental nas propriedades do polímero. Uma resina adesiva experimental foi formulada com 50 % de Bis- GMA, 25 % TEGDMA, e 25 % HEMA, em peso, acrescido de Canforoquinona e EDAB (1% /mol). Para formar os grupos experimentais seis substâncias foram adicionadas à resina base: dióxido de titânio, óxido de bismuto, sulfato de bário, quartzo, dióxido de zircônio e trifluoreto de itérbio, em diferentes concentrações. A radiopacidade foi avaliada utilizando um sistema digital com placas de fósforo VistaScan (Dürr Dental GmbH & CO. KG, Bietigheim- Bissingen, Alemanha) sendo analisadas através do software DBSWIN 4.5, quanto a densidade radiográfica. As demais propriedades avaliadas foram: grau de conversão através de FTIR; resistência à flexão, baseada na normatização da ISO 4049/2010. Radiopacidade de resinas adesivas experimentais com ao menos 30% sulfato de bário ou óxido de bismuto ou 40% de zircônia apresentaram radiopacidade semelhante a 2mm de alumínio. Resinas adesivas com ao menos 20% de fluoreto de itérbio apresentaram radiopacidade satisfatória (2mm de Al) sem influenciar outras propriedades. / The radiopacity of restorative materials should be sufficient to allow the clinician to distinguish the material from normal and demineralized tissues. It is recognized that unfilled resin adhesives are radiolucent which could be reached with radiopaquing agents’ addition. The aim of this study is to evaluate, in an experimental adhesive resin, the influence of radiopaquing agents at polymer properties. A model adhesive resin was formulated with 50% of Bis-GMA, 25% of TEGDMA, 25% of HEMA in weight, and camphorquinone and EDAB (1%mol). The experimental groups were formed with addition of six radiopaquing agents: titanium dioxide, bismuth oxide, barium sulfate, quartz, zirconium, and ytterbium trifluoride at different concentration. The radiopacity was evaluated using an aluminum step-wedge and VistaScan (Dürr Dental GmbH & CO. KG, Bietigheim-Bissingen, Alemanha) phosphorous plates radiographs digital system and DBSWIN 4.5 software. The other properties evaluated were degree of conversion with FTIR and flexural strength, based at ISO 4049/2010. Radiopacity of model adhesive resins with at least 30% of barium sulfate or bismuth oxide or 40% of zircon showed no significant differences to 2mm of aluminum. Adhesive resin with at least 20% addition of ytterbium trifluoride presented satisfactory radiopacity (Al 2mm) without influencing other properties.

Os nitro-hidrocarbonetos policíclicos aromáticos (NPAHs – nitro-polycyclic aromatic hydrocarbons) são compostos orgânicos constituídos de dois ou mais anéis benzênicos ligados ao grupo nitro (NO2). Tais compostos são amplamente distribuídos no meio ambiente e associados a partículas atmosféricas. O objetivo do presente estudo foi identificar os grupos funcionais dos NPAHs associados ao PM1.0 por espectroscopia de infravermelho termal com transformada de Fourier (FTIR – Fourier Transform Infrared Spectroscopy), determinar a concentração de tais compostos e avaliar a sazonalidade em uma área de influência veicular na região Metropolitana de Porto Alegre (MAPA – Metropolitan Area of Porto Alegre). Além disso, estudaram-se variáveis meteorológicas e outros poluentes (NO, NO2, NOx, O3) com a finalidade de relacioná-los com os NPAHs. Partículas atmosféricas (PM1.0) foram coletadas usando filtros de PTFE (polytetrafluorethylene) no amostrador automático PM162M. Após, o espectrorradiômetro FTIR portátil, da Designs & Prototypes, modelo 102, foi utilizado para realizar medidas espectrais de transmitância e emissividade dos padrões sólidos dos NPAHs: 1-NP e 2-NF e das amostras de partículas atmosféricas. As análises por cromatografia gasosa com detecção por captura de elétrons (GC-ECD - gas chromatography with electron capture detector) foram precedidas por isolamento/derivação, sendo essas as técnicas de determinação e extração, respectivamente, de NHPAs (1-NNa, 2-NF, 3-NFl, 1-NP e 6-NChr) associados a PM1.0. Para validar o método analítico foi usado o Material de Referência Padrão – SRM 1649b – do National Institute of Standards and Technology (NIST, USA). As análises espectrais resultantes de transmitância e emissividade apresentaram bons resultados, possibilitando identificar as ligações C-N e grupo NO2, assim como alguns grupos funcionais orgânicos característicos dos padrões 1-NP e 2-NF, indicando que este método pode ser aplicado no material particulado atmosférico. Com o método empregado foi possível identificar o 1-NP em todas as amostras, enquanto que 2-NF foi identificado apenas em Canoas 1 e Sapucaia do Sul 1 e 2. As concentrações de NPAHs foram mais elevadas no inverno e Sapucaia do Sul foi o local que apresentou maiores níveis destes compostos, exceto o 6-NChr. Os NPAHs associados a PM1.0 mostraram correlações com os poluentes óxidos de nitrogênio (NO e NOx), assim como NPAHs com as variáveis meteorológicas: temperatura e velocidade do vento. Os resultados indicaram a contribuição dos veículos com motores a diesel. Isto foi confirmado pelo estudo das razões NPAHs/PAHs, 1-NP/Py, 6-NChr/Chr. / The nitro-polycyclic aromatic hydrocarbons (NPAHs) are organic compounds that consisting of two or more benzene rings linked by a nitro group (NO2). These compounds are widely distributed in the environment and are mainly found associated with atmospheric particles. The objective of this study was to identify the functional groups of NPAHs associated with PM1.0 by Fourier Transform Infrared Spectroscopy (FTIR), determine the concentration of these compounds and evaluate the seasonality in an area of vehicular influence in the Metropolitan area of Porto Alegre (MAPA). Summed to that, meteorological variables and other pollutants (NO, NO2, NOx, O3) were studied in order to relate them with the NPAHs. Atmospheric particles (PM1.0) were collected using PTFE (polytetrafluorethylene) filters in autosampler PM162M. After that, the portable spectroradiometer FTIR, model 102 of Designs & Prototypes, was used for spectral measurements of transmittance and emissivity of solid standards of NPAHs: 1-NP and 2-NF and the atmospheric particles samples. Analyses by gas chromatography with electron capture detector (GC-ECD) were preceded by isolation / derivation, those being the determination and extraction techniques, respectively, of NHPAs (1-NNa, 2-NF, 3-NFl, 1-NP and 6-NChr) associated with PM1.0. To validate the analytical method it was used the Standard Reference Material - SRM 1649b - of National Institute of Standards and Technology (NIST, USA). The spectral analysis resulting of transmittance and emissivity showed good results, allowing to identify the CN bands and NO2 group, as well as some characteristic organic functional groups of 1-NP and 2-NF standards, indicating that this method can be applied in atmospheric particulate matter. With the employed method it was possible to identify the 1-NP in all samples, while the 2-NF was identified only in Canoas 1 and Sapucaia do Sul 1 and 2. The NPAHs concentrations were higher in winter and Sapucaia do Sul was the place that had the highest levels of these compounds, except to 6-NChr. The NPAHs associated with the PM1.0 showed correlations with the nitrogen oxides (NO and NOx) pollutants, as the NPAHs with the meteorological variables: temperature and wind speed. The results indicated the contribution of vehicles with diesel engines. It was confirmed by the reasons study of NPAHs/PAHs, 1-NP/Py, 6-NChr/Chr.

Localized drug delivery systems have been widely studied as potential replacements for conventional chemotherapy with the capability of providing sustained and controlled drug release in specific targeted sites. They offer numerous benefits over conventional chemotherapy such as enhancing the stability of embedded drugs and preserving their anticancer activity, providing sustained and controlled drug release in the tumor site, reducing toxicity and diminishing subsequent side effects, minimizing the drug loss, averting the need for frequent administrations, and minimizing the cost of therapy. The aim of this study is to develop a localized drug delivery system with niosomes embedded in a chitosan hydrogel with targeting capabilities. The incorporation of niosomes into a chitosan hydrogel has several advantages over each individually being used. First, embedding niosomes in a chitosan hydrogel can yield control over drug release especially for small molecule drugs. Second, chitosan hydrogel may improve the release time and dosage of drugs from niosomes by protecting them with an extra barrier, resulting in tunable release rates. Third, as a localized delivery system, chitosan hydrogels can prevent the migration of niosomes away from the targeted tumor sites. Finally, chitosan has mucoadhesive property which can be used in the targeting of the tumor cells with the mucin over expression. To enhance the specific targeting, the capacity of chitosan to target MUC1 overexpression in cancer cells will be analyzed. Similarly, the incorporation of chlorotoxin in this system will be achieved and evaluated. Chlorotoxin, a 36-amino acid peptide, is purified from Leiurus quinquestriatus scorpion venom with a distinct characteristic of binding preferentially to neuroectoderma tumors such as glioma, but not to normal tissue. The overexpression of MUC1, a mucin antigen, in certain cancer cells has been used as an attractive therapeutic target in the design of a drug delivery system consisting of chitosan with a distinct mucoadhesive property. To determine the level of MUC1expression in different cell lines, Cell based Enzyme Linked Immunosorbent Assay (Cell ELISA) was developed for the first time. Attenuated Total Reflectance- Fourier Transform Infra-Red (ATR-FTIR) Spectroscopy is used to investigate the possible molecular interaction between chlorotoxin and glioma cells. This study presents a new approach in monitoring the biochemical and biophysical changes in glioma cells after being exposed to CTX. In addition to characterizing the signature spectra of CTX and glioma cells, we evaluated the differences in biochemical compositions of the spectra of the glioma cells treated with and without CTX over different incubation time periods. The results indicate that the proposed localized drug delivery system with the distinct tumor targeting features and extended release profiles would tune and control the specific delivery of chemotherapeutics in tumor sites.

A partir de l'étude en matrice de gaz rare des produits de la réaction de Ti, Ti2 + N2O par spectroscopie d'absorption infrarouge, nous avons pu identifier trois espèces pour la réaction Ti + N2O (complexe de vdW, complexe e-o et molécule s-o), et deux pour la réaction 3Ti2 + N2O = 1[OTi2(?1 - NN)] ou 1[OTiNTiN]. Nous avons montré que le titane atomique ne réagit pas avec N2O dans son état fondamental, alors que le dimère de titane s'insère spontanément dans la liaison N-O du protoxyde d'azote et conduit à la formation d'un intermédiaire 1[OTi2(?1 - NN)]. La rupture de la liaison N-N pourrait ensuite être obtenue seulement par la voie de la photochimie, conduisant au produit final 1[OTiNTiN]. Face à la pléthore de fonctionnelles de la densité et leurs difficultés vis-à-vis de corrélation non-dynamique et de contribution de dispersion, nous avons mis en ¿uvre une stratégie pour choisir la fonctionnelle la mieux adaptée à la description électronique, structurale, énergétique et vibrationnelle des composés comprenant des métaux de transition. Elle consiste à construire tout d'abord un jeu de données de référence (expérimentales et/ou théoriques obtenues à partir des méthodes ab initio de type CCSD(T) et CASPT2). Le choix de la fonctionnelle la plus pertinente sera ensuite faite sur sa capacité à reproduire au mieux les données du jeu de référence. / From the spectroscopic study of the Ti, Ti2 + N2O reaction products trapped in rare gas matrices, we were able to identify three products for the reaction Ti + N2O (a simple van der Waals adduct, an end-on complex and a side-on molecule), and two for the 3Ti2 + N2O = 1[OTi2(η1 - NN)] or 1[OTiNTiN] reaction. We showed that the atomic titanium is unreactive with respect to N2O in its ground state, while the titanium dimer spontaneously reacts with N2O leading to the N-O bond scission and yielding to an intermediate adduct 1[OTi2(η1 - NN)]. A second bond breaking, the N-N bond cleavage, could be achieved by means of photochemistry, leading to the final product 1[OTiNTiN]. Over all the available functionals, none of them has been shown to systematically overshadow all the others. However, difficulties lie in choosing, from the plethora of density functionals, the one to apply. The selection of the functional to use depends on the problem at hand, i.e., on both the dispersion and static correlations. In this thesis, a strategy has been suggested in order to select the most adequate functional. It consists of a validation of calculation method for a given system by reproducing a set of reference data, obtained either by experiment or at the CCSD(T) or CASPT2 levels on the structural, energetic and vibrational properties.

Proprietary mixtures of amines and carboxylic acids are used as volatile corrosion inhibitors (VCIs) for the protection of steel and iron components against atmospheric corrosion during storage and transportation. Interactions between amines and carboxylic acids have been comprehensively reported in the literature. However, little is known about the nature of the vapours these mixtures emit. The present study focused on the development of the evolved gas analysis method which will help in the characterisation of the vapours released by VCIs. In the method, the evaporation of various amine-carboxylic acid binary mixtures was monitored by thermogravimetric analysis (TGA). The nature and the composition of the released vapours was followed by Fourier transform infrared (FTIR) spectroscopy. Mixtures consisting of triethylamine (TEA) and acetic acid were studied as a model compound using TGA-FTIR at 50 °C to validate the TGA-FTIR method. As vaporisation progressed, the composition of the remaining liquid and the emitted vapour converged to a fixed amine content of ca. 27 mol %. This is just above the composition expected for the 1:3 amine: carboxylic acid complex. Mixtures close to this composition also featured the lowest volatility. TGA-FTIR proved to be a convenient method for studying the evaporation of TEA-acetic acid mixtures, and the nature and composition of the released vapours. Amine addition leads to the dissociation of carboxylic acid dimers in favour salt formation. The formation of an ion pair between the amine and carboxylic acid was confirmed by the FTIR spectra of the liquid phase. The resulting amine-carboxylic acid mixtures showed a slow mass loss rate on TGA when compared with the pure amines and pure carboxylic acids. This indicated that the mixtures have low volatility, hence low vapour pressure compared with the pure components. The low vapour pressure of the mixtures was confirmed by the calculated gas permeability values. These values were much higher for the pure amines and the pure carboxylic acids. However, they dropped significantly on amine addition. The strong amine-carboxylic acid interaction is responsible for the suppressed volatility of the mixtures. No interaction is observed between amine and carboxylic acid molecules in the vapour phase at 230 °C. The method developed was applied to characterise the model compounds simulating the amine-carboxylic acid-based volatile corrosion inhibitors. These model systems contained the primary, secondary and tertiary amines (hexylamine, morpholine and triethylamine), as well as carboxylic acids with different chain lengths (acetic, propanoic, hexanoic and octanoic). These systems are usually employed as equimolar mixtures to protect ferrous metals against atmospheric corrosion. The key finding of the study was that the vapours released by such equimolar mixtures initially contain almost exclusively free amine. After prolonged vaporisation, a steady-state “azeotrope”-like composition is approached. It contains excess acid and features impaired corrosion-inhibition efficiencies according to the Skinner test. In part, this behaviour can be attributed to the mismatch between the volatilities of the amine and carboxylic acid constituents. / Thesis (PhD)--University of Pretoria, 2013. / gm2013 / Chemical Engineering / unrestricted