RMN de Exchange em estado sólido é uma importante técnica utilizada na caracterização de processos dinâmicos em ciência dos materiais. Entretanto, a utilização desta técnica no estudo de materiais complexos tem sido limitada. Neste trabalho, serão propostas novas metodologias de RMN de Exchange em estado sólido, que permitem analisar eficientemente movimentos moleculares na escala de tempo de milisegundos. A técnica denominada Pure Exchange Solid-State NMR (PUREX), provê a supressão dos segmentos rígidos dos espectros de exchange, tomando possível observar os segmentos com mobilidade na escala de ms seletivamente. A técnica Centerband-Only Detection of Exchange (CODEX), permite a observação e caracterização de reorientações moleculares lentas com a maior sensibilidade e resolução disponíveis em RMN de estado sólido, através de espectros obtidos sob rotação da amostra em tomo do ângulo mágico (MAS). Utilizando essas técnicas as funções e tempos de correlação e a geometria de movimentos moleculares lentos podem ser determinadas diretamente, sem a necessidade da utilização de modelos que relacionem as grandezas medidas e as características do movimento molecular. A utilização dos métodos apresentados, permite a identificação e caracterização da dinâmica lenta em materiais complexos, tais como polímeros amorfos, semicristalinos e proteínas. Com objetivo inicial de demonstrar as técnicas, elas foram aplicadas para confirmar detalhes da dinâmica molecular em amostras modelo. Através destas técnicas foi possível confirmar a escala de tempo e os ângulos de reorientação envolvidos na dinâmica molecular de cristais orgânicos, Dimetil Sulfona (DMS), e também para revisitar processos de relaxação local em alguns polímeros, polimetacritato de metila (PMMA) e isotatico polipropileno (iPP). As metodologias foram também aplicadas no estudo da transição vítrea em polímeros semicristalinos, isotatico poli(1-buteno) (iPB 1) e sindiotático polipropileno, os quais não tinham sido ainda estudados por técnicas de RMN de Exchange, já que neste caso a maioria dos segmentos moleculares (porção cristalina do polímero) é rígida durante a transição vítrea. Utilizando os métodos CODEX e PUREX os movimentos lentos que ocorrem na região amorfa destes polímeros em temperaturas próximas as suas temperaturas de transição vítrea foram caracterizados. Um estudo dos movimentos lentos que ocorrem em tomo das temperaturas de transição vítrea nas cadeias poliméricas de dois tipos de nanocompostos híbridos siloxano/(polietileno glicol) (ormolitas) também é apresentado. Heterogeneidades nos movimentos das cadeias poliméricas associados com a interação PEG/siloxano foram diretamente observadas através de experimentos PUREX 1D de Exchange 2D. Evidenciais da presença de movimentos de grande e pequena amplitude foram observados para os dois tipos de híbridos. Os resultados revelam que a restrição do movimento das cadeias poliméricas pelas estruturas de siloxano depende tanto do comprimento da cadeia como da natureza das interações entre as fases orgânica e inorgânica do nanocomposto. Finalmente os resultados referentes a caracterização da dinâmica molecular rápida e lenta e sua relação com as propriedades estruturais de um hidrogel protéico são apresentados. Utilizando uma versão modificada da técnica CODEX, juntamente com experimentos de polarização direta, polarização cruzada e RMN de correlação 2D, foi possível não somente confirmar a estrutura e o modelo de formação propostos para o gel, mas também determinar a geometria e a escala de tempo dos movimentos lentos que ocorrem na região de hélice do hidrogel protéico em grandes detalhes. A demonstração teórica e experimental das técnicas e suas aplicações no estudo dessas importantes classes de materiais serão apresentadas. / Solid-State Exchange NMR is an important method to characterize details of dynamic process in materials science. However, the application of these techniques to study complex materials has been limited. In this work new solid-state Exchange NMR techniques, which allows efficient analysis of molecular motions in the millisecond time scale, are presented. The Pure Exchange Solid-State NMR (PUREX) method provides the suppression of the rigid segments in standard exchange spectrum, making possible to observe the slow moving moieties selectively. The Centerband-Only Detection of Exchange (CODEX) technique allows observing and characterizing slow segmental reorientations with the highest available NMR sensitivity and site resolution, in a magic angle spinning (MAS) NMR spectrum. Correlation functions, correlation times and information about the motional amplitude and geometry can be direct1y obtained using the techniques, without any model assumption. These methods allowed identifying and characterizing slow dynamics in complex materials such as, semicrystalline and amorphous polymers and proteins. To demonstrated the proposed techniques they have been applied to confirm some kwon aspect of the slow dynamics of model samples. Using the methods it was possible o confirm the time scale and the reorientation angles involved in the molecular dynamics of organic crystals, Dimethyl Sulfone (DMS), and also to revisit some relaxation process in standard polymers, such as the beta relaxation of poly(methyl metacrylate) (PMMA) and the alfa relaxation in isotactic polypropylene (iPP). The time scale and the geometry of the molecular motions responsible by these relaxation process obtained using the PUREX and CODEX techniques are in excellent agreement with the data taken from the literature, confirming the reliability of the proposed methods. Moreover, the techniques were also applied to study the slow molecular motions involved in the glass transition of semicrystalline polymers, such as isotactic poly (l-butene) form I (iPB1) and syndiotactic Polypropylene (sPP). The glass transition of these polymers had not been studied using Exchange NMR methods because most of the molecular segments (crystalline portion of the polymers) are rigid during the glass transition. Using the PUREX and CODEX methods the slow molecular reorientations within the amorphous region of the polymers were characterized for temperatures near its glass transition. A study of the slow motions occurring around the glass transition temperature in the polymer chains of two types of siloxane/(polyethylene glycol) nanocomposites (ormolites) is also presented. Motional heterogeneities associated with PEG/ siloxane interactions were directly observed in the 13C 1D PUREX and 2D exchange data. Evidences of both small and large angle amplitude motions were direct1y observed for both types of hybrids. The results revealed that the hindrance to the slow molecular motions of the polymer chains due to the siloxane structures depends on the chain length and the nature of the interaction between the organic and inorganic phases. Finally the results concerning the characterization of the fast and slow dynamics and its relationship with the structural properties of a protein hidrogel are presented. Using a modified version of the CODEX technique, together with standard direct polarization, cross polarization and 2D NMR correlation experiments, it was possible not only to confirm the proposed structure and the gel formation model, but also to characterize the geometry and the time scale of the slow motions in the helical domains of the protein hidrogel in great detail. The theoretical and experimental demonstration of all proposed methods and also its applications in these important classes of material will be present.

Plutonium Uranium Reduction EXtraction (PUREX) technology is a solvent extraction process used to recover plutonium and uranium from spent nuclear fuel. The solvent system is composed of an aqueous nitric acid phase in contact with an organic phase made up of tributyl phosphate in an organic diluent. During the separation process, the PUREX solvent system is subject to an intense multi-component radiation field (gamma rays, alpha particles, beta particles, neutrons, and fission fragments) rendering it susceptible to radiolytic degradation, which reduces its performance. Despite the PUREX process being used for over sixty years, a complete quantitative mechanistic understanding of the radiolytic degradation processes is not available. Nitrous acid is the most significant radiolytic degradation product of nitric acid, especially as its chemical and physical properties alter the formulation of the PUREX solvent system. Furthermore, nitrous acid exhibits complex redox relationships with a number of actinides, with plutonium being of greatest concern to the performance of the PUREX process. A combination of experimental and computational (stochastic and deterministic) techniques have been used to investigate the radiolysis of the PUREX solvent system's aqueous phase, specifically the radiolytic formation of nitrous acid, and its conjugate base nitrite, as a function of solvent system formulation, absorbed dose (up to 1.7 kGy), and radiation quality (cobalt-60 gamma rays and alpha particles from plutonium and americium alpha decay). The research presented in this thesis focuses on: (i) the experimental radiation chemistry of solutions of nitric acid and sodium nitrate over the range of concentrations 1 × 10-3 to 6 mol dm-3, and (ii) the development of a multi-scale modelling approach for evaluating the radiolysis of aqueous systems in terms of reaction mechanisms. The experimental and modelling studies provide insight into the radiation chemistry of the PUREX solvent system's aqueous phase, mechanistically demonstrating how the radiation chemical yield of nitrous acid and nitrite is dependent upon the interplay between non-homogeneous radiation track chemistry and secondary bulk homogeneous chemistry. This interplay is influenced by low pH, the presence of chemical scavengers and redox active metal ions, and radiation quality. These findings will act as a benchmark for the development of advanced reprocessing schemes, which must seriously consider how modifications in solvent system formulation and fuel composition may affect this dynamic interplay, and ultimately the generation of secondary highly active liquid waste.

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O comportamento das formas de linha dos espectros de RMN estático em função da temperatura assim como os experimentos de PURE Exchange em uma dimensão (PUREX-1D) foram utilizados para elucidar detalhes da dinâmica molecular nos PnMA. Os experimentos PUREX-1D foram realizados na faixa de temperatura de Tg-145 o C a Tg. Nesta faixa de temperatura a dinâmica molecular dos PnMA acontece com tempos de correlação entre 500 micro e 10 milissegundos. Utilizando simulação espectral foi demonstrado que os espectros PUREX-1D dependem tanto do tempo de correlação quanto da geometria das reorientações moleculares. Este fato também foi usado para avaliar as características dos movimentos moleculares responsáveis pela reaxação estrutural beta nos PnMA. Foi observado que os pequenos ângulos de reorientação da cadeia principal associados com a relaxação estrutural beta aumentam com o aumento da temperatura e que os tempos de correlação do movimento podem apresentar uma larga distribuição. Análises das formas de linha obtidas através de experimentos de polarização cruzada (CP) em função da temperatura foram realizadas para se estudar o comportamento da dinâmica molecular responsável pela relaxações estruturais alfa e beta nos PnMA. Os experimentos CP foram realizados em uma faixa de temperaturas entre Tg-50 o C e Tg.+70 o C. Nesta faixa de temperatura as figuras de linha de RMN estática são altamente dependentes da temperatura, do tamanho e do volume do ramo lateral. A dinâmica molecular dos PnMA apresentou um movimento altamente anisotrópico sendo que a isotropização da conformação do espectro induzida pelos movimentos moleculares ocorreu apenas a temperaturas muito acima da Tg, contrariando o comportamento esperado para a maioria dos polímeros amorfos. / The behavior of the static NMR line shapes as a function of the temperature as well as one-dimensional Pure Exchange NMR experiments (PUREX-1D) were used to elucidate details of the molecular dynamics in PnMAs. The 1D-PUREX experiments were carried out in the temperature range of Tg-145 oC to Tg. In this range of temperature the molecular dynamics of PnMAs was found to occur with correlation times between 500m and 10ms. Using spectral simulations it was demonstrated that the 1D-PUREX spectra depend on both, the correlation time and geometry of the molecular reorientations. Hence this feature was used to evaluate the characteristics of the molecular motions responsible by the b structural relaxation of PnMAs. It was found that the small angles reorientation of main chain associated with the b-structural relaxation increases with the temperature and the correlation times present a possible broad distribution. Analysis of the NMR line shapes obtained in Cross Polarization (CP) experiments as a function of temperature was performed to study the behavior of the molecular dynamics responsible for the b and a structural relaxation. The CP experiments were performed in the temperature range of Tg-50 oC to Tg+70 oC. In this temperature range the static NMR line shapes are highly dependent on the temperature, size and bulk of the side-group. The dynamics of the PnMA presents a highly anisotropic motion and the isotropisation of conformation induced by the motion only occurs in temperatures well above Tg, contrary to the behavior of the most fragile amorphous polymers.

O comportamento das formas de linha dos espectros de RMN estático em função da temperatura assim como os experimentos de PURE Exchange em uma dimensão (PUREX-1D) foram utilizados para elucidar detalhes da dinâmica molecular nos PnMA. Os experimentos PUREX-1D foram realizados na faixa de temperatura de Tg-145 o C a Tg. Nesta faixa de temperatura a dinâmica molecular dos PnMA acontece com tempos de correlação entre 500 micro e 10 milissegundos. Utilizando simulação espectral foi demonstrado que os espectros PUREX-1D dependem tanto do tempo de correlação quanto da geometria das reorientações moleculares. Este fato também foi usado para avaliar as características dos movimentos moleculares responsáveis pela reaxação estrutural beta nos PnMA. Foi observado que os pequenos ângulos de reorientação da cadeia principal associados com a relaxação estrutural beta aumentam com o aumento da temperatura e que os tempos de correlação do movimento podem apresentar uma larga distribuição. Análises das formas de linha obtidas através de experimentos de polarização cruzada (CP) em função da temperatura foram realizadas para se estudar o comportamento da dinâmica molecular responsável pela relaxações estruturais alfa e beta nos PnMA. Os experimentos CP foram realizados em uma faixa de temperaturas entre Tg-50 o C e Tg.+70 o C. Nesta faixa de temperatura as figuras de linha de RMN estática são altamente dependentes da temperatura, do tamanho e do volume do ramo lateral. A dinâmica molecular dos PnMA apresentou um movimento altamente anisotrópico sendo que a isotropização da conformação do espectro induzida pelos movimentos moleculares ocorreu apenas a temperaturas muito acima da Tg, contrariando o comportamento esperado para a maioria dos polímeros amorfos. / The behavior of the static NMR line shapes as a function of the temperature as well as one-dimensional Pure Exchange NMR experiments (PUREX-1D) were used to elucidate details of the molecular dynamics in PnMAs. The 1D-PUREX experiments were carried out in the temperature range of Tg-145 oC to Tg. In this range of temperature the molecular dynamics of PnMAs was found to occur with correlation times between 500m and 10ms. Using spectral simulations it was demonstrated that the 1D-PUREX spectra depend on both, the correlation time and geometry of the molecular reorientations. Hence this feature was used to evaluate the characteristics of the molecular motions responsible by the b structural relaxation of PnMAs. It was found that the small angles reorientation of main chain associated with the b-structural relaxation increases with the temperature and the correlation times present a possible broad distribution. Analysis of the NMR line shapes obtained in Cross Polarization (CP) experiments as a function of temperature was performed to study the behavior of the molecular dynamics responsible for the b and a structural relaxation. The CP experiments were performed in the temperature range of Tg-50 oC to Tg+70 oC. In this temperature range the static NMR line shapes are highly dependent on the temperature, size and bulk of the side-group. The dynamics of the PnMA presents a highly anisotropic motion and the isotropisation of conformation induced by the motion only occurs in temperatures well above Tg, contrary to the behavior of the most fragile amorphous polymers.

Third phase formation is an undesirable phenomenon during the PUREX process, which is a continuous liquid-liquid extraction approach for the reprocessing of uranium and plutonium from spent nuclear fuel. When third phase formation occurs, the organic extraction solution splits into two layers. The light upper layer, which is commonly named the light organic phase, contains a lower concentration of metal ions, tri-n-butyl phosphate (TBP) and nitric acids but is rich in the organic diluent. The heavy lower layer, which is commonly named the third phase, contains high concentrations of metal ions, TBP and nitric acids. As the third phase contains high concentrations of the uranium and plutonium complexes it can thus cause processing and safety concerns. Therefore, a comprehensive understanding of the mechanism of third phase formation is needed so as to improve the PUREX flowsheet. To investigate third phase formation through molecular simulations, one should first obtain reliable molecular models. A refined model for TBP, which uses a new set of partial charges generated from our density functional theory calculations, was proposed in this study. To compare its performance with other available TBP models, molecular dynamics simulations were conducted to calculate the thermodynamic properties, transport properties and the microscopic structures of liquid TBP, TBP/water mixtures and TBP/n-alkane mixtures. To our knowledge, it is only TBP model that has been validated to show a good prediction of the microscopic structure of systems that consist of both hydrophobic and hydrophilic species. This thesis also presents evidence that the light-organic/third phase transition in the TBP/n-dodecane/HNO3/H2O systems, which is relevant to the PUREX process, is an unusual transition between two isotropic, bi-continuous micro-emulsion phases. The light-organic /third phase coexistence was first observed using Gibbs Ensemble Monte Carlo (GEMC) simulations and then validated through Gibbs free energy calculations. Snapshots from the simulations as well as the cluster analysis of the light organic and third phases reveal structures akin to bi-continuous micro-emulsion phases, where the polar species reside within a mesh whose surface consists of amphiphilic TBP molecules. The non-polar n-dodecane molecules are outside this mesh. The large-scale structural differences between the two phases lie solely in the dimensions of the mesh. To our knowledge, the observation of the light-organic/third phase coexistence through simulation approaches and a phase transition of this nature have not previously been reported. Finally, this thesis presents evidence that the microscopic structure of the light organic phase of the Zr(IV)/TBP/n-octane/HNO3/H2O system, which is also related to the PUREX process, is different from that of the common hypothesis, where such system is consisted of large ellipsoidal reverse micelles. Snapshots from simulations, hydrogen bonding analysis and cluster analysis showed that the Zr4+, nitrate, TBP and H2O form extended aggregated networks. Thus, as above, we observe a bi-continuous structure but this time with embedded local clusters centred around the Zr4+ ions. The local clusters were found to consist primarily of Zr(NO3)4·3TBP complexes. This finding provides a new view of the structure of the Zr(IV)/TBP/n-octane/HNO3/H2O system.

Lanthanide(III) and actinide complexes with the N-donor extractants which are proposed for se in next generation separation processes, CyMe4-BTPhen and CyMe4-BTBP, have been synthesised and characterised in idealised synthetic and real extraction conditions. Next generation spent nuclear fuel reprocessing is necessary in order to reduce the longevity of activity (from 100,000’s to 100-1,000’s years) through re-use as fuel in GenIV reactor programs. The N donor extractants have been previously shown to preferentially extract the trivalent An ions over the Ln ions in biphasic acidic extraction processes, a necessary task due to the large neutron capture crosssections of the lanthanides, and the reasons behind this selectivity have been investigated here. Proposed processes that use these extractants are called SANEX and GANEX. The SANEX process is undertaken after a PUREX-style process where only the trivalent minor actinides and the lanthanides are present during the separation. Whereas, in the GANEX process the organic phase contains the N-donor molecule and another extractant, such as TBP, with the aqueous phase containing the entire An series in various oxidation states. Speciation of the Ln3+ ions with the N-donor molecules has been shown to be dominated by 1:2 (M:L) complexes in the bulk organic phase post extraction and coordination is completed by a small ligand, either H2O or NO3-. Spectrophotometric titration yielded logβ values for the 1:2 (M:L) complexes of Pr3+, Eu3+ and Tb3+ nitrate salts. In all cases it was shown that the CyMe4-BTPhen molecule has a greater affinity than the CyMe4-BTBP molecule for the Ln3+ ions, as expected given the ‘locked’ design of CyMe4-BTPhen. The uranyl ion was shown to only form 1:1 (M:L) complexes in solution with the N-donor molecules but structural characterisation showed it to also form 2:1 (M:L) complexes with the metal ions bridged by a peroxide anion. The formation of this species was found to require a protic solvent, light and molecular dioxygen. Again, binding was shown, by spectrophotometric titration, to be stronger with CyMe4-BTPhen than CyMe4-BTBP.The speciation of the tetravalent An ions, Pu4+ and Th4+ was studied using 1H NMR and X-ray absorption spectroscopy in GANEX style conditions. When the organic phase contains TBP and the N donor extractants, complexation is completed by TBP in the post extraction organic phase and the extraction of Th4+ is exclusively completed by TBP but by both extractants for Pu4+. In both cases, the major bulk species was identified as Pu/Th(NO3)4.3TBP, although complexes of the N donor extractants and the An4+ have been observed in idealised conditions, in both 1:1 and 1:2 (M:L) stoichiometries, depending on the solution composition. U4+ was shown to form a variety of complexes of a myriad of M:L stoichiometries.