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Benzenesulfonates, para-substituted with amine, chloride and methyl groups were successfully incorporated into layered double hydroxides of two different compositions, 2:1 Mg-Al LDH and 2:1 Zn-Al LDH. These parent materials were also doped with small amounts of nickel and the differences in the two systems were studied. The hexamethylenetetramine route of layered double hydroxide synthesis was investigated to verify if the mechanism is indeed homogeneous. This included attempting preparation of 2:1 Mg-Al LDH, 2:1 Zn-Al LDH and 2:1 Zn-Cr LDH with two different concentrations of hexamethylenetetramine. The analytical data of the products suggest that the homogeneous precipitation may not be the true mechanism of reaction involved in LDH synthesis by this method.

There is a raising need to design a safe and efficient cryogenic fuel tank for the new generation of reusable launch vehicles. The new tank design focuses on composite materials that can achieve the drastic reduction of empty/non-payload and structural weight. In addition to the materials to be compatible with cryogenic temperatures, interior components of the vehicle may be subjected to significantly elevated temperatures due to heat conduction from the vehicle surfaces during and after atmospheric re-entry. Therefore, there is the need to understand the performance of the composites after experiencing extreme thermal environments. Polymer-layered nanocomposites were studied to determine if they can reduce the permeation to the liquid nitrogen used as fuel in the next generation of space vehicles. Due to the non-permeable nature of the silicates and the exfoliated structure they adopt into the polymer matrix the addition of nanoclays into a polymer is expected to reduce the permeation to several gases without sacrificing the mechanical strength of the nanocomposite as well as providing additional improvements such as increase of thermal stability of the nanocomposite. Several types of matrixes modified with different types and content of nanoclays were tested and their permeability coefficient was calculated. The permeability values obtained for the different formulations assisted to understand the transport properties of nanoclay modified composites. In addition to this, thermal characterization was performed with the help of dynamic mechanical analysis, thermogravimetric analyses and differential scanning calorimetry studies. To determine if the nanoclay modified nanocomposites were affected by extreme temperatures the samples were subjected to thermal cycling. Comparison of the transport and thermal properties before and after cycling helped to analyze the effect of the addition of the nanoclays in the nanocomposites. Positron annihilation spectroscopy (PAS) was utilized to comprehend how the distribution of the free volume was affected by the presence of the nanoclays and by the thermal cycling applied. Different permeability models were utilized in an attempt to validate the experimental results of the different nanocomposite structures. This analysis was used to provide additional insight into many aspects of the experimental results obtained in this study.

O presente trabalho trata da preparação e da caracterização textural e espectroscópica de hidróxidos mistos lamelares de composição [Mg3-xCuxAl(OH)8](CO3)0,5.yH2O (x= 0,3; 0,6; 0,9; 1,2; 1,5; 1,8; 2,1; 2,4; 2,7 e 3,0), bem como do estudo da reatividade desses materiais na hidroxilação do fenol, utilizando peróxido de hidrogênio como oxidante. Os sólidos foram preparados através do método da co-precipitação e caracterizados por difratometria de raios X, análises elementares (C, H, N e metais) e termogravimétricas, medidas de área superficial e, também, pelas seguintes técnicas espectroscópicas: vibracional no infravermelho e espalhamento Raman, eletrônica de absorção no visível-infravermelho próximo e ressonância paramagnética eletrônica. Observou-se que quanto maior o conteúdo de cobre(II) nas amostras, maior é a tendência à formação de CuO. Materiais de coloração azul contendo apenas uma fase cristalina foram obtidos por co-precipitação no intervalo de pH 8-10 e efetuando as etapas de envelhecimento e secagem na temperatura ambiente. Quanto maior a quantidade de íons Cu2+ no hidróxido misto lamelar, menor a cristalinidade e a estabilidade térmica do material. Os espectros de EPR são anisotrópicos (parâmetros g// e g? bem definidos), indicando que os íons cobre(II) se encontram em sítio com simetria axial. À medida que a quantidade de Cu2+ nas amostras aumenta, ocorre uma diminuição no sinal do metal de transição, que pode ser interpretada como decorrência de um acoplamento antiferromagnético entre os íons cobre. Dados de espectroscopia vibracional sugerem que nos hidróxidos mistos há dois tipos de íons carbonato. Além disso, foi observado o fenômeno de abaixamento de simetria dos ânions CO32- ao longo do processo de aquecimento, originando, conforme a temperatura e a composição, materiais de coloração variada. O abaixamento de simetria pode estar sendo ocasionado pela coordenação (ou enxertia) dos íons carbonato aos centros metálicos das lamelas. Os sólidos verdes obtidos por aquecimento possuem, além de bandas no espectro eletrônico atribuídas às transições do tipo d-d (700-800 nm), absorção na região abaixo de 400 nm, que pode ser atribuída à transferência de carga O2- -> Cu2+. Apesar dos difratogramas de raios X apresentarem picos de baixas intensidades referentes às fases espinélio, a coloração ocre observada pode ser devida à presença da fase CuAl2O4 (sólido marrom). Nas amostras cinzas e pretas, os difratogramas de raios X mostram picos intensos atribuídos ao CuO. Os testes de reatividade dos hidróxidos mistos sintetizados na hidroxilação do fenol pelo peróxido de hidrogênio em meio aquoso envolveram a variação de parâmetros reacionais como temperatura, tempo, concentração de substrato e influência de luz, mantendo-se constante a relação molar fenol/Cu2+. O substrato orgânico foi oxidado a catecol, hidroquinona e p-benzoquinona. As substâncias no meio reacional foram quantificadas pela deconvolução do espectro eletrônico da mistura na região do ultravioleta. Como esperado, o material sintetizado sem íons cobre(II) não apresenta atividade catalítica para o sistema reacional estudado. / In this work it was investigated the preparation and spectroscopic characterization of layered hydroxides of composition [Mg3-xCuxAl(OH)8](CO3)0.5.yH2O (x = 0.3; 0.6; 0.9; 1.2; 1.5; 1.8; 2.1; 2.4; 2.7 and 3.0), as well the reactivity of these materials towards phenol hydroxylation, using hydrogen peroxide as oxidizing agent. The solids had been prepared through the co-precipitation method and characterized by X ray diffractometry, elemental analysis (C, H, N and metals), thermogravimetric analysis, surface area measurements, and also by the following spectroscopic techniques: infrared vibrational absortion (FTIR), Raman scattering, vis-NIR electronic absorption and electron paramagnetic resonance (EPR). It was observed that the increase of copper(II) content in the samples favours the CuO formation. Materials of blue coloration containing only one crystalline phase were obtained by the co-precipitation method in the pH range 10 – 8, and were submitted to aging and drying processes at room temperature. As the amount of Cu2+ ions increases in the layered hydroxide material, it was observed a decrease in crystallinity and thermal stability. EPR spectra are anisotropic (parameters g// and g? well defined), indicating that copper(II) ions are in sites with axial symmetry. As the amount of Cu2+ in the samples increases, EPR signal decreases, what can be interpreted as result of an antiferromagnetic coupling between copper ions. FTIR data suggests that the layered hydroxides gave two types of cabornate ions. Moreover, the symmetry lowering phenomena of CO32- anions during the heating process was observed, originating, according to the temperature and sample composition, materials of varied coloration. This lowering of symmetry can be due to coordination (or grafting) of carbonate ions to the metal ions in the layers. Vis-NIR electronic spectra of green solids obtained by heating show absorption in the region below 400 nm, besides bands attributed to d-d transitions (700-800 nm), that can be attributed to O2- -> Cu2+ charge transfer transition. Despite the X ray diffraction peaks of low intensities attributed to spinel phases, the ochre coloration observed can be due to the presence of CuAl2O4 (brown solid). For gray and black samples, X ray diffractograms shows intense peaks attributed to CuO. Reactivity tests about phenol hydroxylation involved the variation of experimental parameters as temperature, time, substrate concentration and influence of light, keeping constant the phenol/Cu2+ molar ratio. The organic substrate was oxidized to cathecol, hydroquinone and p-benzoquinone and these products were quantified by deconvolution of the electronic spectra. As expected, the material synthesized without copper(II) ions does not show catalytic activity for the studied reaction.

Due to the combination of their electronic, optical and mechanical properties, graphene and other layered materials (GRMs) have great potential for applications such as flexible optoelectronics and energy storage. Given that GRMs can be dispersed in solvents, solution processing is a particularly interesting approach that allows large volume production with tailored properties according to the targeted applications. \par In this dissertation I investigate liquid phase exfoliation and formulation of GRMs-based inks for flexible (opto) electronics, energy and photocatalysis. First I develop a protocol for the characterization of graphene inks, based on the statistical analysis of their Raman spectra. Such a tool is essential because of the scattering of characteristics in liquid-phase exfoliated material. I then report two novel processing techniques. The first consists on the exfoliation of graphene in organic solvents by the means of $\alpha$-functionalized alkanes as stabilising agents, which allows yield by weight ($Y_W$) of $\sim 100\%$. The second is based on exfoliation of graphite by microfluidization, where the material is stabilised in aqueous solution, with concentrations up to 100g/L. Such inks are successfully deposited by blade coating, leading to films of conductivity $\sim$ 2$\cdot$10$^4$ S/m at 25$\mu$m. I then investigate the use of graphene inks in optoelectronics and energy applications: First, I investigate inkjet printed graphene as hole injection layer (HTL). The cells with graphene HTL show high long-term stability, retaining 85$\%$ of the initial fill factor after 900 hrs in damp heat conditions. I then demonstrate flexible displays with graphene-SWNTs as pixel electrode. A 4x4 inch$^2$ demonstrator is realised integrating the ink into 12,700 pixels. I investigate graphene/MoO$_3$ electrode for supercapacitors with a specific capacitance of 342 F/cm$^3$. The electrode shows high cyclic stability, preserving $\sim$96$\%$ of the initial capacitance after 10,000 cycles. I finally report the production of TiO$_2$/exfoliated graphite as efficient photocatalytic composite able to degrade $\sim$100$\%$ more model pollutant with respect to TiO$_2$.

This paper presents a static analysis of functionally graded single and sandwich beams by using an efficient 7DOFs quasi-3D hybrid type theory. The governing equations are derived by employing the principle of virtual works in a weak form and solved by means of the Finite Element Method (FEM). A C1 cubic Hermite interpolation is used for the vertical deflection variables while C0 linear interpolation is employed for the other kinematics variables. Convergence rates are studied in order to validate the finite element technique. Numerical results of the present formulation are compared with analytical and FEM solutions available in the literature. / Revisión por pares

O presente trabalho trata da preparação e da caracterização textural e espectroscópica de hidróxidos mistos lamelares de composição [Mg3-xCuxAl(OH)8](CO3)0,5.yH2O (x= 0,3; 0,6; 0,9; 1,2; 1,5; 1,8; 2,1; 2,4; 2,7 e 3,0), bem como do estudo da reatividade desses materiais na hidroxilação do fenol, utilizando peróxido de hidrogênio como oxidante. Os sólidos foram preparados através do método da co-precipitação e caracterizados por difratometria de raios X, análises elementares (C, H, N e metais) e termogravimétricas, medidas de área superficial e, também, pelas seguintes técnicas espectroscópicas: vibracional no infravermelho e espalhamento Raman, eletrônica de absorção no visível-infravermelho próximo e ressonância paramagnética eletrônica. Observou-se que quanto maior o conteúdo de cobre(II) nas amostras, maior é a tendência à formação de CuO. Materiais de coloração azul contendo apenas uma fase cristalina foram obtidos por co-precipitação no intervalo de pH 8-10 e efetuando as etapas de envelhecimento e secagem na temperatura ambiente. Quanto maior a quantidade de íons Cu2+ no hidróxido misto lamelar, menor a cristalinidade e a estabilidade térmica do material. Os espectros de EPR são anisotrópicos (parâmetros g// e g? bem definidos), indicando que os íons cobre(II) se encontram em sítio com simetria axial. À medida que a quantidade de Cu2+ nas amostras aumenta, ocorre uma diminuição no sinal do metal de transição, que pode ser interpretada como decorrência de um acoplamento antiferromagnético entre os íons cobre. Dados de espectroscopia vibracional sugerem que nos hidróxidos mistos há dois tipos de íons carbonato. Além disso, foi observado o fenômeno de abaixamento de simetria dos ânions CO32- ao longo do processo de aquecimento, originando, conforme a temperatura e a composição, materiais de coloração variada. O abaixamento de simetria pode estar sendo ocasionado pela coordenação (ou enxertia) dos íons carbonato aos centros metálicos das lamelas. Os sólidos verdes obtidos por aquecimento possuem, além de bandas no espectro eletrônico atribuídas às transições do tipo d-d (700-800 nm), absorção na região abaixo de 400 nm, que pode ser atribuída à transferência de carga O2- -> Cu2+. Apesar dos difratogramas de raios X apresentarem picos de baixas intensidades referentes às fases espinélio, a coloração ocre observada pode ser devida à presença da fase CuAl2O4 (sólido marrom). Nas amostras cinzas e pretas, os difratogramas de raios X mostram picos intensos atribuídos ao CuO. Os testes de reatividade dos hidróxidos mistos sintetizados na hidroxilação do fenol pelo peróxido de hidrogênio em meio aquoso envolveram a variação de parâmetros reacionais como temperatura, tempo, concentração de substrato e influência de luz, mantendo-se constante a relação molar fenol/Cu2+. O substrato orgânico foi oxidado a catecol, hidroquinona e p-benzoquinona. As substâncias no meio reacional foram quantificadas pela deconvolução do espectro eletrônico da mistura na região do ultravioleta. Como esperado, o material sintetizado sem íons cobre(II) não apresenta atividade catalítica para o sistema reacional estudado. / In this work it was investigated the preparation and spectroscopic characterization of layered hydroxides of composition [Mg3-xCuxAl(OH)8](CO3)0.5.yH2O (x = 0.3; 0.6; 0.9; 1.2; 1.5; 1.8; 2.1; 2.4; 2.7 and 3.0), as well the reactivity of these materials towards phenol hydroxylation, using hydrogen peroxide as oxidizing agent. The solids had been prepared through the co-precipitation method and characterized by X ray diffractometry, elemental analysis (C, H, N and metals), thermogravimetric analysis, surface area measurements, and also by the following spectroscopic techniques: infrared vibrational absortion (FTIR), Raman scattering, vis-NIR electronic absorption and electron paramagnetic resonance (EPR). It was observed that the increase of copper(II) content in the samples favours the CuO formation. Materials of blue coloration containing only one crystalline phase were obtained by the co-precipitation method in the pH range 10 – 8, and were submitted to aging and drying processes at room temperature. As the amount of Cu2+ ions increases in the layered hydroxide material, it was observed a decrease in crystallinity and thermal stability. EPR spectra are anisotropic (parameters g// and g? well defined), indicating that copper(II) ions are in sites with axial symmetry. As the amount of Cu2+ in the samples increases, EPR signal decreases, what can be interpreted as result of an antiferromagnetic coupling between copper ions. FTIR data suggests that the layered hydroxides gave two types of cabornate ions. Moreover, the symmetry lowering phenomena of CO32- anions during the heating process was observed, originating, according to the temperature and sample composition, materials of varied coloration. This lowering of symmetry can be due to coordination (or grafting) of carbonate ions to the metal ions in the layers. Vis-NIR electronic spectra of green solids obtained by heating show absorption in the region below 400 nm, besides bands attributed to d-d transitions (700-800 nm), that can be attributed to O2- -> Cu2+ charge transfer transition. Despite the X ray diffraction peaks of low intensities attributed to spinel phases, the ochre coloration observed can be due to the presence of CuAl2O4 (brown solid). For gray and black samples, X ray diffractograms shows intense peaks attributed to CuO. Reactivity tests about phenol hydroxylation involved the variation of experimental parameters as temperature, time, substrate concentration and influence of light, keeping constant the phenol/Cu2+ molar ratio. The organic substrate was oxidized to cathecol, hydroquinone and p-benzoquinone and these products were quantified by deconvolution of the electronic spectra. As expected, the material synthesized without copper(II) ions does not show catalytic activity for the studied reaction.

The resin composite (RC) layering technique attempts to replicate the natural structure of teeth by using an opaque dark layer (replicating dentin) covered with a translucent layer (replicating enamel). Previous studies have confirmed that the shade of dentin and the thickness and translucency of the enamel layer are essential factors in the color of natural teeth. However, these findings have never been validated with the RC layering technique. RC layering technique provides superior esthetic results; however, the chemical composition and optical properties of RC are different than natural dentition. Hence, the color interaction between the enamel and dentin RC layers makes the color of the final restoration unpredictable. The objective of this dissertation was to determine the color interaction between the enamel and dentin layers using a unique and novel sample design: a double-layered RC with variant enamel thicknesses (0.5, 0.7, 1.0 mm) and variant dentin shades (lighter and darker shades). The study methods tested the interaction between certain shades as per manufacturers’ instructions to reproduce certain shades. Two different RC systems that are fundamentally different with regards to their shading system were tested in this study. A potential link between the color of the double layered RC samples to the VITA 3D master shade guide which has been overlooked by clinicians and researchers, have been investigated in this study. Research aims included validating the sample design we have incorporated into our studies. Furthermore, other aims investigated the double-layering techniques in comparison to their corresponding shades from the VITA classical and VITA 3D Master shade guides. The outcomes of this study are clinical recommendations on the optimal combination of dentin shades and enamel layer thicknesses to use in order to best match the color of natural teeth.

This work concerns some synthetic processes and basic properties of layered double hydroxides (LDHs). A series of LDHs, a family of newly developed materials found to have many potential uses in industry, were investigated in relating to the origin of life on early Earth. In this work, I successfully intercalated some inorganic as well as organic species. Ammonium, accompanied with ferrocyanide ion, can enter the layered space. It was found there were two kin go f intercalated ferrocyanide species: one is that exchanged with anions and became a part of layered double hydroxide, while the other is suggested to be related to ammonium ferrocyanide neutral species. Formaldehyde, ethanolamine and formate can also be involved into LDHs. To improve the crystallinity, homogeneous precipitation method, which used Urea and Hexamine, was employed. The results reveal the success in the case by Urea but not in that by Hexamine. Annealing could also be used for this purpose. However, it needs to be preocessed in its mother liquor; no improvement on the crystallinity if the material has been washed before annealing.

In this thesis, the author proposes and develops novel multilayered Surface Acoustic Wave (SAW) devices with unique attributes for gas sensing applications. The design, simulation, fabrication and gas sensing performance of three multilayered SAW structures has been undertaken. The investigated structures are based on two substrates having high electromechanical coupling coefficient: lithium niobate (LiNbO3) and lithium tantalate (LiTaO3), with a piezoelectric zinc oxide (ZnO) intermediate layer. Sensitivity towards target gas analytes is provided by thin film indium oxide (InOx) or tungsten trioxide (WO3). The high performance of the gas sensors is achieved by adjusting the intermediate ZnO layer thickness. Sensitivity calculations, undertaken with perturbation theory illustrate how the intermediate ZnO layer can be employed to modify the velocity-permittivity product of the supported SAW modes, resulting in highly sensitive conductometric SAW gas sensors. The work contained within this thesis addresses a broad spectrum of issues relating to multilayered SAW gas sensors. Topics include finite-element modelling, perturbation theory, micro-fabrication, metal oxide deposition, material characterisation and experiential evaluation of the layered SAW sensors towards nitrogen dioxide (NO2), hydrogen (H2) and ethanol gas phase analytes. The development of two-dimensional (2D) and three dimensional (3D) finite-element models provides a deep insight and understanding of acoustic wave propagation in layered anisotropic media, whilst also illustrating that the entire surface of the device can and should be used as the active sensing area. Additionally, the unique and distinctive surface morphology of the layered structures are examined by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The crystalline structure and orientation of the ZnO and WO3 layers are also examined by X-ray Diffraction Spectroscopy (XRD). The novel multilayered SAW structures a re shown to be highly sensitive, capable of sensing NO2 and ethanol concentration levels in the parts-per-billion and parts-per-million range, respectively, and H2 concentrations below 1.00% in air. The addition of platinum or gold catalyst activator layers on the WO3 sensitive layer is shown to improve sensitivity and dynamic performance, with response magnitudes up to 50 times larger than bare WO3. The gas sensing performance of the investigated structures provide strong evidence that high sensitivity can be achieved utilising multilayered SAW structures for conductometric gas sensing applications.