No presente estudo, sílicas funcionalizadas com grupos octadecilsilano (ODS) foram obtidas pelas rotas de grafting e sol-gel. Na rota grafting foram variadas as temperaturas de pré-tratamento da sílica comercial na faixa de 100-450 °C. Na rota sol-gel, foram variadas as razões molares ODS: TEOS, o instante de adição do ODS e a velocidade de agitação da reação. As sílicas foram caracterizadas em termos do teor de carbono, da natureza das espécies imobilizadas, da textura e morfologia pelas técnicas complementares de Análise Elementar (CHN), Espectroscopia Fotoeletrônica de Raios-X (XPS), Espectroscopia molecular no Infravermelho com Transformada de Fourier (FTIR), Espectroscopia de Ressonância Magnética Nuclear de 29Si e 13C (NMR de 29Si e 13C), Adsorção de nitrogênio, Análise Termogravimétrica (TGA), Espalhamento de Laser (LLS), Espectroscopia de Espalhamento de Raios-X em Baixo Ângulo (SAXS), Microscopia de Força Atômica (AFM) e Microscopia Eletrônica de Varredura com Espectroscopia de Emissão de Raios-X por Dispersão de Energia (SEM-EDX).As sílicas funcionalizadas por grafting apresentaram teores de carbono determinados por CHN na faixa de 1,2-3,5 %, morfologia irregular e conformação de grupos ODS próxima ao estado líquido. Já as sílicas funcionalizadas por sol-gel, apresentaram teores de carbono na faixa de 5,0-53 %, combinação de morfologia esférica com lamelar e conformação de grupos ODS próximas ao estado cristalino. A potencialidade das sílicas funcionalizadas como adsorventes de compostos aromáticos em amostras ambientais de água e ar foi avaliada. / In the present study, octadecylsilane-modified silicas were obtained by the grafting and the sol-gel methods. In the grafting route, silica pretreatment temperature was varied between 100 and 450 °C. In the sol-gel one, the following variables were evaluated: ODS:TEOS molar ratio, ODS addition time and stirring speed. The resulting silicas were characterized in terms of carbon content, nature of the surface species, texture and morphology by a set of complementary techniques, namely: elemental analysis (CHN), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy with Fourier Transform (FTIR), 29Si e 13C nuclear magnetic resonance (29Si e 13C NMR), nitrogen adsorption, thermogravimetric analysis (TGA), laser-light scattering (LLS), small angle X-ray scattering (SAXS), atomic force microscopy (AFM) and electron scanning microscopy combined with energy dispersive X-ray analysis (SEM-EDX). Chemically-modified silica by grafting presented low carbon content in the range of 1.2 – 3.5 wt.%, irregular morphology and ODS conformation groups close to the liquid state. Hybrid silica prepared by the sol-gel method showed carbon contents between 5.0 and 53.0 wt.%, combining spherical and lamellar morphology, and ODS groups conformation close to the crystalline state. The potentiality of the chemically-modified silicas as sorbents for aromatic compounds was evaluated in environmental water and air matrices.

The aim of this project was to prepare a series of silica materials based on sol-gel processing of alkoxysilanes using glucose and glycerol as templates for potential applications in membrane design for pervaporation. The materials were characterized using structural and dynamic techniques to gain information about the effect of the templates on the formation of micro- and mesoporous silicates. The interaction between templates and silica matrices were investigated using FTIR, Raman Spectroscopy, Solid State NMR Spectroscopy, Physisorption and SEM. Close contact between templates and silica networks was observed by NMR cross polarization studies. The chemistry was then extended to prepare hybrid organic-inorganic silica materials by introducing organic ligands, with glycerol as a template to control the porosity of the hybrid materials. By varying the ligand as well as the template, the physical properties of the gel can be controlled. Composites of hydroxypropylcellulose, HPC, and silica were also prepared and characterized. There was no phase separation during sol-gel processing suggesting HPC was dispersed homogenously in the silica matrices. This was also confirmed by solid state NMR. Temperature dependence showed some indications of conformational change in the HPC within the silicate, above 308K. The transport properties of the hybrid materials were observed by monitoring the diffusion behaviour of water and several selected solvents using Pulsed Field Gradient NMR. The self-diffusion of water and the organic solvents in the hybrid silica materials were two to three orders of magnitude smaller than in the liquid bulk suggesting restricted diffusion at the pore surface. The effect of surface polarity also contributed to water and solvents diffusivities. The temperature dependence of diffusion was useful to derive the activation energy whereas the dependence on NMR observation time provided information on both tortuosity and pore connectivity of the hybrid silica materials. The hybrid silica membranes were prepared by spin coating of polymeric silica sol on top of a macroporous alumina support after being occluded by colloidal silica. It was then used for pervaporation of water ethanol mixtures. The results implied that separation factor increased as the temperature increased. However permeate fluxes were less affected.

A new technique for determining the amount of opal in deep-sea sediments of any age is described. Using a normative calculation, a portion of the analytical silica concentration of sediments is subtracted as non-biogenic in proportion to the concentration of aluminum in the sample. The ratio of SiO₂:Al₂O₃ used to characterize the non-biogenic sediment fraction was determined by X-ray diffraction analysis of opal-free sediments. The procedure was tested against the X-ray diffraction method for determining opal in deep-sea sediments The biogenic silica content of Cenozoic sediments from 20 Deep Sea Drilling Project sites in the central equatorial Pacific was determined using the normative calculation technique for opal determination. The equatorial Pacific lies beneath the equatorial current system where upwelling of nutrient-rich waters results in high plankton productivity. Accumulation rates of biogenically produced silica were calculated from the opal contents. Maps of these accumulation rates for time intervals during the Cenozoic show that opal accumulation was highest near the equator or paleoequator during the last 50 m.y. Superimposed on this pattern are fluctuations in the rate of opal accumulation in the entire area with time. Regional maxima in opal accumulation in the entire area with time. Regional maxima in opal accumulation occurred during the middle Eocene (42-45 m.y. ago) and the late Miocene (7-10 m.y. ago). The accumulation rates during these maxima are an order of magnitude higher than those during times of minimum accumulation: the late Oligocene (25 m.y. ago) and the present. The percent of biogenic silica in the sediments varies synchronously with the accumulation rates, but is low to the east due to dilution by non-biogenic sediment from terrigenous and volcanic sources. Surface productivity controls the accumulation of opal in the equatorial Pacific and opaline sediments are not subject to differential solution with depth. The opal productivity indicated by opal accumulation rates is not related to changes in sea surface or bottom water temperatures and is therefore not directly governed by climate. The association of equatorial productivity and upwelling suggests that changes in circulation which cause upwelling were the principal factors controlling productivity and accumulation of biogenic silica in the past. / Graduation date: 1976

Graduation date: 1969

Graduation date: 1995

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Mary J. Wirth, Dept. of Chemistry and Biochemistry. Includes bibliographical references.

Under unsaturated conditions, both moisture flow and the transport of ions strongly depend on the degree of saturation in concrete. In the current literature, most theories and empirical models describe moisture flow and the transport of ions in concrete based on the assumption that concrete is fully submerged in a liquid phase. This simplistic assumption often leads to a systematic underestimation in the amount of ions, such as chlorides, especially in the case of concrete applications subjected to cyclic wetting and drying conditions. In this study, an experimental program was established to determine the key hydraulic parameters needed for modeling the moisture flow and the transport of ions in five types of concrete mixes under unsaturated conditions. The required hydraulic parameters of the five concrete mixes include the saturated hydraulic permeability, the moisture retention function, and the dependency of the relative diffusion coefficient on degree of saturation. A centrifuge technique was used to determine the saturated hydraulic permeability of the five concrete mixes. The moisture retention data of all concrete mixes were determined using a vapour equilibrium technique. The moisture retention data were then used to determine the van Genuchten empirical parameters for an analytical characterization of the capillary pressure-degree of water saturation and the relative permeability-degree of saturation relationships. The dependency of the relative diffusion coefficient on the degree of water saturation was characterized for each type of concrete mix indirectly using an electrical resistivity technique. The experimental results of this study were used in different empirical models that have been originally developed for soils to examine whether they could be applied for concrete The five concrete mixes used in this study were characterized by the usage of a different proportion of dry densified silica fume in each concrete mix. Those mixes were used to determine the effect of silica fume on the experimental and the empirical key hydraulic parameters considered in this study.

Abstract A series of polyimide/silica hybrid composites have been synthesized by simultaneous polycondensation of the organic polyimide (PI) phase and the sol-gel reactions (hydrolysis and condensation) of the inorganic silica phase. Sol-gel parameters such as pH value, solvent, water/Si ratio, were systematically varied so that their effect on the microstructure of silica could be explored. Emphasis has been placed on the interactions between the organic and the inorganic phases by FTIR with the introduction of two coupling agents, i.e., g-glycidyloxypropyl- trimethoxysilane (GOPTMS) and 3-amino-propyltriethoxysilane (ATPES). Thermal and electrical properties of the hybrid composites were examined by TGA, DSC, and AC impedance and the morphology by SEM; these properties were correlated to their synthesis chemistry. FTIR results indicate complete imidization of PI, not affected by the presence of the catalyst, solvent ethanol, and silica particles of the inorganic phase. The hybrid films with lower silica content give higher transparency. TGA results indicate ~ 25 ¢Jincrease of decomposition temperature for the hybrid composites compared to the neat PI; it shows a minimum when pH = 4. The thermal stability of the APTES system is generally better than the GOPTMS system. SEM results indicate that maximum particle size is obtained for the system with pH = 4. AC impedance results indicate that dielectric constant increases with the silica particle size and the silica content. The coupling agents help to reduce the silica particle size (~ 100 nm for GOPTMS, ~ 200 nm for ATPES, and > 400 nm with no coupling agent) and to distribute evenly the silica particles in the PI matrix.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

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