Orientador: Dimas Roberto Vollet / Banca: Dario Antonio Donatti / Banca: Luiz Antonio Barreiro / Resumo: As propriedades estruturais de sonogéis de sílica preparados a partir da sonohidrólise do tetraetilortosilicato (TEOS) foram estudadas em função da porosidade. Sonogéis com diferentes porosidades foram preparados usando diferentes razões molares água/TEOS (R) na etapa de hidrólise do processo. Os valores de R utilizados foram R = 4, 6, 8, 12, e 16. Um dos objetivos foi obter géis com diferentes "porosidades" no estado úmido e estudar o efeito da porosidade nas propriedades estruturais dos sonogéis. Também foi objetivo estudar e comparar técnicas alternativas, como DSC e SAXS, aplicáveis na caracterização estrutural de géis ainda no estado úmido de preparação. Os géis foram estudados em estágios que vão desde o estado saturado (gel úmido) até o estado seco do gel, resultante do processo de secagem supercrítica (aerogel). Os géis úmidos foram estudados por termogravimetria (TG), calorimetria diferencial exploratória (DSC) e espalhamento de raios-X a baixo ângulo (SAXS). Os aerogéis foram estudados por adsorção de nitrogênio e espalhamento de raios-X a baixo ângulo (SAXS). Géis úmidos exibem uma estrutura fractal de massa, num certo domínio do intervalo de distâncias, explorado por valores grandes do módulo q do vetor de espalhamento de raios-X a baixo ângulo. A dimensão fractal de massa D nos géis úmidos é essencialmente igual a 2, aproximadamente independente de R. O tamanho da estrutura fractal de massa dos géis úmidos é limitada a um comprimento característico x, que aumenta de cerca de 3,3 nm para 7,2 nm com o aumento de R de 4 para 16. A "porosidade" dos géis úmidos varia entre cerca de 87% a 91% do volume da amostra, com o aumento de R de 4 para 16. A troca da fase líquida dos géis úmidos por água pura, para os ensaios de DSC, aumenta a dimensão fractal D... (REsumo completo, clicar acesso eletrônico abaixo) / Abstract: The structural property of silica sonogels prepared from the sonohydrolysis of tetraethoxysilane (TEOS), were studied in function of the porosity. Sonogels with porosities were prepared using different molar ratio water/TEOS (R) in the stage of hydrolysis of process. The values of used R were 4,6,8,12,16. One of the objectives was to obtain gels with different "porosities" in the wet state and to study the effect of the porosity in the structural properties of the sonogels. It was also objective to study and to compare alternative techniques, like DSC and SAXS, applicable in the structural characterization of gels still in the wet state of preparation. The gels were studied in stages that are going from the saturated state (wet gel) until the dry state of the gel, resulting from the process of drying supercritical (aerogel). The wet gels were studied by termogravimetria (TG), exploratory differential calorimetry (DSC) and small angle X-Ray scattering (SAXS). The aerogels were studied by adsorption of nitrogen and small angle X-Ray scattering (SAXS). Wet gels exhibit a mass fractal structure, in a certain domain of the interval of distances, explored by big values of the module q of the scattering vector from ray-X to low angle. The dimension mass fractal D in the wet gels is essentially equal to 2, approximately independent of R. The size of the fractal mass structure of the wet gels is limited to a characteristic length, that it increases about 3,3 nm for 7,2 nm with the increase of R of 4 for 16. The "porosity" of the wet gels range about 87% to 91% of the volume of the sample, with the increase of R of 4 for 16. The change of the liquid phase of the wet gels for pure water, for the rehearsals of DSC, increases the dimension fractal D and it reduces the characteristic size ξ. The value of D in the changed gels range... (Complete abstract click electronic access below) / Mestre

Made available in DSpace on 2014-06-11T19:25:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-07-31Bitstream added on 2014-06-13T18:53:36Z : No. of bitstreams: 1 scalari_jp_me_rcla.pdf: 750413 bytes, checksum: 4fc1949588e5805b6e1a9d568b6844da (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / As propriedades estruturais de sonogéis de sílica preparados a partir da sonohidrólise do tetraetilortosilicato (TEOS) foram estudadas em função da porosidade. Sonogéis com diferentes porosidades foram preparados usando diferentes razões molares água/TEOS (R) na etapa de hidrólise do processo. Os valores de R utilizados foram R = 4, 6, 8, 12, e 16. Um dos objetivos foi obter géis com diferentes “porosidades” no estado úmido e estudar o efeito da porosidade nas propriedades estruturais dos sonogéis. Também foi objetivo estudar e comparar técnicas alternativas, como DSC e SAXS, aplicáveis na caracterização estrutural de géis ainda no estado úmido de preparação. Os géis foram estudados em estágios que vão desde o estado saturado (gel úmido) até o estado seco do gel, resultante do processo de secagem supercrítica (aerogel). Os géis úmidos foram estudados por termogravimetria (TG), calorimetria diferencial exploratória (DSC) e espalhamento de raios-X a baixo ângulo (SAXS). Os aerogéis foram estudados por adsorção de nitrogênio e espalhamento de raios-X a baixo ângulo (SAXS). Géis úmidos exibem uma estrutura fractal de massa, num certo domínio do intervalo de distâncias, explorado por valores grandes do módulo q do vetor de espalhamento de raios-X a baixo ângulo. A dimensão fractal de massa D nos géis úmidos é essencialmente igual a 2, aproximadamente independente de R. O tamanho da estrutura fractal de massa dos géis úmidos é limitada a um comprimento característico x, que aumenta de cerca de 3,3 nm para 7,2 nm com o aumento de R de 4 para 16. A “porosidade” dos géis úmidos varia entre cerca de 87% a 91% do volume da amostra, com o aumento de R de 4 para 16. A troca da fase líquida dos géis úmidos por água pura, para os ensaios de DSC, aumenta a dimensão fractal D... / The structural property of silica sonogels prepared from the sonohydrolysis of tetraethoxysilane (TEOS), were studied in function of the porosity. Sonogels with porosities were prepared using different molar ratio water/TEOS (R) in the stage of hydrolysis of process. The values of used R were 4,6,8,12,16. One of the objectives was to obtain gels with different porosities in the wet state and to study the effect of the porosity in the structural properties of the sonogels. It was also objective to study and to compare alternative techniques, like DSC and SAXS, applicable in the structural characterization of gels still in the wet state of preparation. The gels were studied in stages that are going from the saturated state (wet gel) until the dry state of the gel, resulting from the process of drying supercritical (aerogel). The wet gels were studied by termogravimetria (TG), exploratory differential calorimetry (DSC) and small angle X-Ray scattering (SAXS). The aerogels were studied by adsorption of nitrogen and small angle X-Ray scattering (SAXS). Wet gels exhibit a mass fractal structure, in a certain domain of the interval of distances, explored by big values of the module q of the scattering vector from ray-X to low angle. The dimension mass fractal D in the wet gels is essentially equal to 2, approximately independent of R. The size of the fractal mass structure of the wet gels is limited to a characteristic length, that it increases about 3,3 nm for 7,2 nm with the increase of R of 4 for 16. The porosity of the wet gels range about 87% to 91% of the volume of the sample, with the increase of R of 4 for 16. The change of the liquid phase of the wet gels for pure water, for the rehearsals of DSC, increases the dimension fractal D and it reduces the characteristic size ξ. The value of D in the changed gels range... (Complete abstract click electronic access below)

Resumo: As características estruturais de sonogéis obtidos a partir da hidrólise ácida do TEOS estimulada por ultrasom foram estudadas por espalhamento de raios-x a baixo ângulo (SAXS). O estudo inclui: i) o processo de agregação em diferentes temperaturas; ii) o envelhecimento dos géis úmidos na fase líquida de preparação e depois da troca da fase líquida por álcool e acetona; iii) a secagem dos géis; iv) a estrutural evolução de xerogéis e aerogéis com o tratamento térmico até 1100 oC; e v) um estudo comparativo usando SAXS e adsorção de nitrogênio na caracterização de aerogéis e xerogéis... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The structural characteristics of acid-catalyzed and ultrasound stimulated TEOS-derived sonogels were studied by small-angle x-ray scattering (SAXS). The study includes: i) the aggregation process at different temperatures; ii) the ageing of the wet gels in the liquid phase as prepared and after exchanging the liquid phase by alcohol and acetone; iii) the drying of the gels; iv) the structural evolution of xerogels and aerogels under heat treatment up to 1100 oC; and v) a comparative study using SAXS and nitrogen adsorption in the characterization of aerogels and xerogels... (Complete abstract, click electronic access below)

Chapter 1. Supramolecular Gels and their Applications Supramolecular gels are viscoelastic materials composed of a solid like three dimensional fibrillary network that is embedded in a liquid. Supramolecular gels are derived from low molecular weight compounds (typically MW < 3000). In the 1990s, the investigations on gels were mainly focused on designing new gelator molecules. However, during the last decade, research focus shifted towards designing functional gels and their applications. As a result of extensive work in this area, gels have been found to have varied applications in the templated synthesis of inorganic nanomaterials, hybrid materials, light harvesting systems, as responsive system and sensors, and also in drug delivery, tissue engineering etc. This chapter gives an introduction to supramolecular hydrogels/organogels and relevant bile acid chemistry touching upon the gelation properties of the bile acid derivatives. Diverse applications of the supramolecular gels are also illustrated with several examples. Scheme 1. Various applications of functional supramolecular gels Chapter 2. Bile Acid derived novel Hydrogelators Part 1. Hydrogelation of Bile acid protected Amino acids and Hybrid Materials Hydrogels from low molecular weight molecules have significant importance in biomedical applications. In this chapter, we report injectable hydrogel formation from bile acid conjugates of various amino acids. Hydrogel formation was found to be dependent on multiple factors such as bile acid backbone structure, linkage between the bile acid and the amino acid, pH etc. Single crystal structures of lithocholyl phenylalanine, lithocholyl-glycine, lithocholyl-L valine and lithocholyl-L alanine were also determined. Finally, the hydrogel frameworks were utilized to produce hybrid materials with Gold and ZnO nanoparticles. Scheme 2. (a) Crystal structure of LC-LF-OH gelator molecule, (b) photograph of gel, (c) SEM and (d) AFM image of LC-LF-OH xerogel Part 2. Hydrogelation of bile acid-dipeptide conjugates and in situ synthesis of silver and gold nanoparticles in the hydrogel matrix Fabricating supramolecular hydrogels with embedded metal nanostructures are important for the design of novel hybrid nanocomposite materials for diverse applications such as bio sensing and chemo sensing platforms, catalytic and antibacterial functional materials etc. Supramolecular self-assembly of bile acid-dipeptide conjugates have led to the formation of new supramolecular hydrogels. Gelation of these molecules depends strongly on the hydrophobic character of the bile acids. Ag+ and Au3+ salts were incorporated in the hydrogels, and photo reduction and chemical reduction led to the in situ generation of Ag and Au NPs in these supramolecular hydrogels without the addition of any external stabilizing agent. The color, size and shape of silver nanoparticles formed by photo reduction depended on the amino acid residue on the side chain. Furthermore, the hydrogel-Ag nanocomposite was tested for its antimicrobial activity. Scheme 3. Bile acid based dipeptide hydrogelators and soft hybrid materials Chapter 3. Sonogels of bile salts of In(III): use in the formation of self-templated indium sulfide nanostructures In this chapter, facile hydrogel formation by Indium(III) cholate and deoxy cholate are reported. When In(III) solution was added to aqueous solutions of sodium cholate and sodium deoxy cholate and sonicated, the mixtures formed gels. The gels thus obtained were translucent/turbid and thermos irreversible. Rheological measurements showed that all of them could be classified as viscoelastic soft solids. Scanning electron microscopy and atomic force microscopy showed typical entangled three dimensional fibrous networks. The In-Ch hydrogel were further used to prepare nanostructured In2S3 in which the cholate units possibly acted as a surfactant to confine the growth of the Nano flakes. Scheme 4. In-Ch hydrogel (Photograph and SEM image of In-Ch gel) Chapter 4. Palladium-Hydrogel Nanocomposite for C-C Coupling Reactions Supported metallic nanoparticles are important composite materials owing to their enormous potential for applications in various fields. This chapter describes the in situ formation of palladium nanoparticles in a calcium-cholate (Ca-Ch) hydrogel by reduction with sodium cyan borohydride. The hydrogel matrix appeared to assist the controlled growth as well as stabilization of palladium nanoparticles. The palladium nanoparticle/Ca-Ch hydrogel hybrid was characterized by scanning and transmission electron microscopy, atomic force microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Furthermore, PdNP/Ca-Ch hybrid xerogel was shown to act as an active catalyst for Suzuki reaction under aqueous aerobic conditions, up to 4 cycles. This PdNP/Ca-Ch xerogel retained its catalytic activities on storage for several months. Scheme 5. Palladium-hydrogel nanocomposite for C-C coupling reactions in water Chapter 5. Sensitization of Terbium/Europium in self-assembled cholate hydrogel: An approach towards the detection of amine vapours "Luminescent" lanthanides have intrinsic low molar absorptivity, although this problem can be addressed by complexing the lanthanide ion with suitable chelating ligands which improve the luminescence properties drastically. However the design of such systems often involves careful planning and laborious synthetic steps. It is therefore desirable to have a simpler way to sensitize lanthanides with high efficiency. It was observed in our group that trivalent lanthanides formed hydrogels on the addition of sodium cholate. This chapter describes the discovery of the several biphenyl derivatives (such as 4-biphenylcarbaxaldehyde, 4-acetylbiphenyl) for sensitization of Tb(III) and Eu(III) in lanthanide hydrogels. Sensitization of Tb(III) and Eu(III) were observed by doping was characterized by scanning and transmission electron microscopy, atomic force microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Furthermore, PdNP/Ca-Ch hybrid xerogel was shown to act as an active catalyst for Suzuki reaction under aqueous aerobic conditions, up to 4 cycles. This PdNP/Ca-Ch xerogel retained its catalytic activities on storage for several months. Scheme 6. Schematic representation of the sensitization process (the arrangement of themolecules in the gel fiber is arbitrary)(For figures pl refer the abstract pdf file)