Submitted by AMANDA PASQUOTO PERISSINOTTO null (amandap@rc.unesp.br) on 2016-02-17T12:33:22Z No. of bitstreams: 2 DissertaçãoAmandaok.pdf: 4083559 bytes, checksum: 7362f582721fdb5515688043eff181ca (MD5) DissertaçãoAmandaok.pdf: 4083559 bytes, checksum: 7362f582721fdb5515688043eff181ca (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-02-17T13:06:09Z (GMT) No. of bitstreams: 1 perissinotto_ap_me_rcla.pdf: 4083559 bytes, checksum: 7362f582721fdb5515688043eff181ca (MD5) / Made available in DSpace on 2016-02-17T13:06:09Z (GMT). No. of bitstreams: 1 perissinotto_ap_me_rcla.pdf: 4083559 bytes, checksum: 7362f582721fdb5515688043eff181ca (MD5) Previous issue date: 2016-02-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo deste trabalho foi estudar as características estruturais em géis úmidos de sílica preparados a partir da hidrólise ácida de Tetraetilortosilicato (TEOS) com adições do surfactante aniônico Dodecil Sulfato de Sódio (SDS). O surfactante foi removido após a gelificação. Os géis úmidos exibem uma estrutura fractal de massa com dimensão fractal de massa D (típicamente em torno de 2,25) numa escala de comprimentos que se estende desde o tamanho característico ξ (geralmente em torno de 10 nm) do domínio do fractal de massa até um tamanho característico a0 (típicamente entre 0,3 - 0,4 nm) da partícula primária que constituí o domínio fractal. ξ aumenta enquanto que D e a0 diminuem ligeiramente com o aumento da quantidade de SDS. Aerogéis SCD com superfície específica típica de 1000 m2 /g e massa específica aparente de 0,20 g/cm3 foram obtidos por secagem supercrítica (SCD) dos géis úmidos depois da lavagem com etanol. O volume de poros e o tamanho médio de poros aumentaram com o aumento da quantidade de SDS. Os aerogéis SCD preservaram a maior parte das características do fractal de massa dos géis úmidos originais em larga escala de comprimento e exibiram num nível de resolução em torno de 0,7 nm uma mudança („crossover‟) para uma estrutura de fractal de massa e superfície, com dimensão aparente de fractal de massa Dm ~ 2,4 e dimensão de fractal de superfície Ds ~ 2,6, conforme concluído a partir dos dados de espalhamento de raios-X à baixo angulo (SAXS) e adsorção de Nitrogênio. Aerogéis hidrofóbicos secos a pressão ambiente (APD) apresentaram superfície específica típica de 800 m2 /g e massa específica aparente de 0,20 g/cm3 e foram obtidos após sililação dos precursores géis úmidos com uma mistura de Hexametildisiloxano (HMDSO) e Trimetilclorosilano (TMCS). O volume de poros e o tamanho médio de poros dos aerogéis APD aumentaram com o aumento da quantidade de SDS. Os aerogéis APD preservaram a maior parte das características do fractal de massa do precursor gel úmido em larga escala de comprimento. O raio de giração dos clusters dos aerogéis APD (tipicamente 17 nm) aumentou com o aumento da quantidade de SDS, enquanto que o raio da partícula primária de sílica (tipicamente 2,0 nm) aumentou com a primeira adição de SDS (em relação à amostra sem SDS) e depois diminuiu regularmente com o aumento da quantidade de SDS. A partícula primária apresentou ainda alguma heterogeneidade interna e uma interface do contorno difuso com espessura em torno de 0,7 nm, de acordo com o modelo de gradiente linear para o contorno difuso. / This work aims to study the structural characteristics of silica wet gels prepared from hydrolysis of Tetraethoxysilane (TEOS) with additions of the anionic surfactant Sodium Dodecyl-Sulfate (SDS). The surfactant was removed after gelation. Wet gels exhibited massfractal structure with mass-fractal dimension D (typically around 2.25) in a length scale extending from a characteristic size ξ (typically about 10 nm) of the mass-fractal domains to a characteristic size a0 (typically between 0.3 - 0.4 nm) of the primary particles building up the fractal domains. ξ increased while D and a0 diminished slightly as the SDS quantity increased. Aerogels with typical specific surface of 1000 m 2 /g and density of 0.20 g/cm3 were obtained by supercritical drying (SCD) of the wet gels after washing with ethanol and n-hexane. The pore volume and the mean pore size increased with the increase of the SDS quantity. The aerogels presented most of the mass-fractal characteristics of the original wet gels at large length scales and exhibited at a higher resolution level at about 0.7 nm a crossover to a masssurface fractal structure, with apparent mass-fractal dimension Dm ~ 2.4 and surface-fractal dimension Ds ~ 2.6, as inferred from small-angle X-ray scattering (SAXS) and Nitrogen adsorption data. Hydrophobic ambient pressure drying (APD) aerogels with typical specific surface of 800 m2 /g and bulk density of 0.20 g/cm3 were obtained after silylation of the precursor wet gels with a mixture of Hexamethyldisiloxane (HMDSO) and Trimethylchlorosilane (TMCS). The pore volume and the mean pore size of the APD aerogels increased with increasing the SDS quantity. APD aerogels presented most of the mass-fractal characteristics of the precursor wet gels at large length scales. The radius of gyration of the clusters of the APD aerogels (typically 17 nm) increased with increasing the SDS quantity, while the radius of the silica primary particles (typically 2.0 nm) increased at first with the addition of SDS (with respect to the sample without SDS) and decreased regularly afterward with increasing the SDS quantity. The primary particles presented yet some internal inhomogeneity and a diffuse-boundary interface with thickness of about 0.7 nm, according to a linear-gradient model for the diffuse boundary.

A síntese de vidros pelo método sol-gel tornou-se recentemente de grande interesse, tanto do ponto de vista técnico como científico. Descrevemos neste trabalho o processo utilizado para a obtenção de aerogel de sílica (formação do gel &#8594 secagem hipercrítica &#8594 sinterização) e algumas características físicas e químicas, em diversas temperaturas de sinterização (Ts) dos aerogéis produzidos. Aerogeis de sílica foram preparados pela hidrólise e condensação de sóis de sistema TMOS metanol- H2O com razão molar TMOS: H2O = 4: 1 e razão em volume de TMOS na solução TMOS metanol = 0,2; 0,3; 0,4; 0,5 e 0,6. As suas propriedades estruturais tais como; a densidade aparente e da matriz, a área superficial BET, volume total dos poros, distribuição de tamanho dos poros, constante e perda dielétricas foram sistematicamente investigadas em função do tratamento térmico de sinterização. As propriedades de relaxação da água adsorvida na superfície altamente reativa foram estudadas através das técnicas dielétricas e de ressonância magnética nuclear em função do conteúdo de H2O, 0 &#60 &#952H2O &#60 6, e temperatura. Também foi feito um estudo da cinética de adsorção da água em aerogéis com varias temperaturas de sinterização. / The synthesis of glasses using the sol-gel method appeared recently of great interest either from the technological or from the scientific point of view. We describe the process used to obtain pure vitreous silica (gel formation &#8594 hypercritical drying &#8594 densification) as well as some physical and chemical characteristics of the various products fabricated. Silica aerogels have been prepared by hydrolysis and condensation of sols of composition TMOS methanol - H2O with molar ratio TMOS: H2O = 4.1 and volume ratio of TMOS in solution of TMOS-methanol = 0,2; 0,3; 0,4; 0,5 and 0,6. Their structural properties such as true and apparent densities, BET surface area, total pore volume, pore size distribution, dielectric constant and loss have been systematically investigated as a function of the densification heat treatment. The relaxation properties of water adsorbed on the highly reactive surface have been studied by dielectric and nuclear magnetic resonance techniques as a function of the H2O coverage (0 &#60 &#952H2O &#60 6) and temperature. The adsorption kinetics of the water was studied too in the aerogels with several heat temperature of sinterization.

Chapter 1: Supramolecular gels and their applications Gels are viscoelastic materials composed of a solid-like three dimensional fibrillar network that is embedded in a liquid. Supramolecular gels belong to a class of gels which are derived from low molecular weight compounds (typically < 1000). A variety of non-covalent interactions like H-bonding, π-π stacking, donor-acceptor, metal coordination, solvophobic and van der Waals interactions are involved in the formation of the self-assembled fibrous networks (SAFIN’s) in these gels. These non-covalent interactions are weak in nature and as a result, these gels can be reverted back to sol by heating and this process is reversible. These gels are further classified as hydrogels, organogels and aero/xerogels depending on the medium they encompass. Although low molecular weight gelators were known in the early part of the 20th century, it is only in the last two decades that this field has generated widespread interest among scientists. In the 90s, the investigations on these kinds of gels mainly focused on designing new gelator molecules. However, during the last decade, the research interest in this field has shifted more towards designing functional gels. Such gels Scheme 1. Various applications of functional supramolecular gels have been extensively utilized in the templated synthesis of inorganic nanomaterials, in making hybrid materials, as synthetic light harvesting systems, as sensors, in the field of biomaterials such as drug delivery, screening of enzyme inhibitors and tissue engineering and also in the field of organic optoelectronics. In this chapter a few selected examples from each of these fields are highlighted. Chapter 2: Charge transfer induced organogels from 2,3dialkoxyanthracenes and 2,4,7-trinitrofluorenone 2,3-Di-n-alkoxyanthracenes formed charge transfer (CT) interaction promoted organogels in the presence of electron acceptor 2,4,7-trinitrofluorenone (TNF). These dialkoxyanthracences (in the absence of TNF) have been reported previously to form gels in a variety of organic solvents. The gelation property was found to be dependent on the chain length and the derivatives with C6-C16 chains were found to be gelators. On the other hand derivatives with C5-C1 chains were found to be non-gelators. It was found that TNF not only modulated the gelation property of the efficient organogelators, it also transformed the weak and non-gelators into efficient gelators. This charge transfer induced gelation was observed for the derivatives with C10-C4 chains in alcoholic and hydrocarbon solvents whereas the shorter chain derivatives C3-C1 did not form gels. Several other alkoxy and dialkoxy derivatives with substituents in other positions did not show gelation in the presence of TNF. These results suggested that two structural aspects are necessary for these derivatives to form CT gels- the alkoxy chain length and the position of the alkoxy substituents. The thermal stability of all these gels was found to be maximum with a 1:1 stoichiometry of the donor and the acceptor. The common observation, the intensification of color in going from the sol to the gel phase, supported the crucial role of the charge transfer interaction behind the formation of these gels. The rheological characterization of the gels demonstrated that they Figure 1. Chemical structures of 2,3-dialkoxyanthracenes and TNF (middle) and a fluorescence confocal microscopy image (left) and a photograph (right) of DDOA-TNF gel. behaved like viscoelastic soft solids. Chapter 3: A new class of perfluorinated derivatives of bile acids: Synthesis and gelation properties A new class of bile acid based gelators was designed by connecting the side chains of the facially amphiphilic bile acid with perfluoroalkyl chains of different lengths through two different ester linkages-–O-(CO)-and –(CO)-OCH2-. All these three structural aspects i.e. the bile acid moiety, the fluoroalkyl chain length and the spacer were found to influence the gelation properties of the derivatives. Depending on them, there was a variation in terms of the nature of the solvent gelated, the CGCs, the mechanical properties of the gels, etc among the derivatives. The deoxycholic and lithocholic derivatives with the spacer –O-(CO)-formed gels in aromatic hydrocarbons and also in DMSO depending on the fluoroalkyl chain length. The mechanical properties of the gels formed in DMSO were found to be dependent on the bile acid moiety and the fluoroalkyl chain length. In general, the deoxy analogues showed higher elasticity, stiffness and yield stress values for their gels than the litho derivatives. The perfluorinated derivatives having the spacer –(CO)-OCH2-showed gelation properties in organic-aqueous media and in DMSO. Interestingly, organogelation was observed in the deoxy and lithocholic derivatives from both spacer series whereas in the literature most of the bile acid based organogelators are derived from cholic acid. (b) (c) Figure 2. (a) Perfluorinated derivatives of bile acids, (b) photographs of a few DMSO gels and (c) TEM image of a xerogel of a deoxy derivative Chapter 4: Composite aerogels and organogels from 2,3didecyloxyanthracene and bile-perfluoro derivatives Aerogels are unique materials among solids. They have extremely low densities (up to 95% of their volume is air), large pores and high inner surface area. As a result aerogels have very interesting physical properties such as extremely low thermal conductivity, low sound velocity and high optical transparency. There are only a few reports of aerogel formation by low molecular weight gelators. We have investigated the aerogel formation ability of three long 7 chain perfluoroalkyl esters (two deoxycholic and one lithocholic derivative, chart 1) in supercritical CO2. A deoxy derivative, formed aerogel in sc-CO2. When mixed with DDOA (which has been reported previously to form good aerogels in sc-CO2), the perfluoro compound formed aerogels of better quality. The mixed aerogels were characterized by the presence of very large fibers in the micron range (as observed in the aerogel formed by only the fluoro derivative) as well as fibers of smaller size observed in pure DDOA aerogel. We also investigated the behavior of the composite systems in organic solvents. It was found that in DMSO, another deoxy derivative, Figure 3. SEM images of a mixed aerogel of DDOA-DC23C13F27 (left) and a mixed organogel (DMSO) of DDOA-DC23C11F23 (right). DC23C11F23 formed gels with higher thermal stability and improved mechanical properties compared to the native gels of the perfluoro compound or DDOA. Chapter 5: Hydrogels from lanthanide(III) cholates: Tunable, multiple color luminescence from hydrogels and xerogels In this chapter, facile hydrogel formation by several lanthanide cholates is reported. When sodium cholate was added to aqueous solutions of Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III) and Yb(III) and sonicated, the mixtures formed gels within a few seconds. The gels thus obtained were transparent/translucent and thermoirreversible. Rheological measurements showed that all of them could be classified as viscoelastic soft solids. A naphthalene derivative, 2,3-dihyroxynaphthalene was found to sensitize Tb(III) emission very efficiently in its cholate gel when doped in micromolar concentrations. The importance of the gel matrix behind sensitization of Tb(III) was demonstrated by the inefficiency of the same sensitizer DHN in an SDS micellar solution. In mixed gels of Tb(III)-Eu(III) doped with DHN, a energy transfer pathway was found to occur from the sensitized Tb(III) to Eu(III). By a simple tuning of the ratio of these two lanthanide ions, multiple color emissive gels could be made.The emissive properties of the hydrogels were retained in the xerogels and the suspensions of these xerogels in n-hexane were used for making luminescent coatings on glass surface. Figure 4. Tunable, multi-color luminescent hydrogels and xerogels of lanthanide cholates

L'amélioration des propriétés des matériaux pour l'isolation thermique est un défi clé pour la réduction de la consommation énergétique et de l'émission de gaz à effets de serre. Cette thèse a pour objectif l'élaboration de matériaux composites nanostructurés, combinant les bonnes propriétés mécaniques des bio-aérogels avec les excellentes propriétés d'isolation thermique des aérogels de silice. Deux polysaccharides ont été étudiés comme source de bio-aérogels : la cellulose et la pectine. Deux stratégies pour l'élaboration des composites ont été considérées : un procédé « one-pot »; et l'imprégnation d'une matrice polysaccharide poreuse. Les aérogels composites ont été obtenus par séchage au CO2 supercritique. Alors que la méthode « one-pot » génère des particules de silice micrométriques au sein d'un réseau poreux, le procédé d'imprégnation a permis d'obtenir un réseau nanostructuré interpénétré. La surface spécifique atteint 700-800 cm².g-1, les propriétés mécaniques sont améliorées par rapport aux aérogels de silice et la conductivité thermique est réduite comparée à l'Aerocellulose pure. Utiliser une cellulose hydrophobisée chimiquement, la tritylcellulose, comme matrice d'imprégnation, a permis d'obtenir des composites hydrophobes ayant un angle de contact avec l'eau de 133° et des conductivités thermiques de 0.021-0.022 W.m-1.K-1. Les aérogels à base de pectine réticulée et leurs composites avec la silice présentent des densités extrêmement basses (0.05 g.cm3) et des conductivités thermiques de 0.013-0.022 W.m-1.K-1. / Improving the thermal insulation of materials is a key challenge to lower global energy consumption and greenhouse effect gas emissions in the coming decades. This thesis focuses on the preparation and characterization of nanostructured composite materials combining the good mechanical properties of bio-aerogels with the excellent thermal insulation properties of silica aerogels. Two polysaccharides were used to make bio-aerogels: cellulose and pectin. Two strategies aiming to elaborate composite materials were investigated: “one-pot” process and impregnation of a porous “wet” polysaccharide matrix by polyethoxydisiloxane. Drying with supercritical CO2 yields the composite aerogels. While the one-pot method gave micron-sized silica particles embedded in a porous cellulose network, impregnation process allowed obtaining a nanostructured interpenetrated network of cellulose and silica. The specific surface area was 700-800 cm².g-1, the mechanical properties improved as compared to neat silica aerogels and thermal conductivity lower than that of cellulose aerogels. Using a chemically hydrophobized cellulose, tritylcellulose, as the impregnation matrix, hydrophobic composites were obtained showing a contact angle with water of 133° and thermal conductivities of 0.021 W.m-1.K-1. Aerogels from cross-linked pectin and their composites with silica show extremely low densities (around 0.05 g/cm3 for the neat pectin aerogels) and thermal conductivities in the 0.013-0.022 W.m-1.K-1 range.

Cellulose nanofibrils are a biobased and renewable material with potential to be used in many different applications. Such applications include air filtration, absorption of liquids, and thermal insulation.  To be used for these applications the cellulose nanofibrils must form a porous and dry material. However, maintaining some degree of porosity after drying is difficult, since the fibrils are extracted in liquid and tend to collapse into a dense material upon drying. Certain methods have proven effective for making a dry porous material from cellulose nanofibrils, but these are often expensive and not suitable for large scale production. The aim of this project is to test possible methods for making a highly porous cellulose nanofibril-based material. These methods must be environmentally sustainable and suitable for large scale production. An extensive screening has been conducted with the aim of identifying methods resulting in materials with high porosity. The obtained materials have been analysed further to give a more thorough understanding of the porosity as well as other characteristics. The results indicate that cross-links in the material strengthen the structure, and that drying samples from water always results in complete collapse or very dense materials while drying samples from certain solvents other than water results in more porous materials. The analysed materials had very different porosities, some of which were relatively high. The most porous material analysed by Brunauer-Emmett-Teller gas adsorption had a surface area of 9.5 m2/g. This project gives insight into how cross-linking chemistries and treatment with different solvents and pH affect the resulting cellulose nanofibril-based material, as well as knowledge about which methods can be used to successfully produce dry porous cellulose nanofibril-based materials.

Les aérogels sont des matériaux ultra-poreux et nanostructurés aux possibilités d’applications variées. Une nouvelle génération d’aérogels à base de polysaccharides est aujourd’hui en plein essor : les bio-aérogels. Ils sont particulièrement prometteurs pour leur respect de l'environnement et leur biocompatibilité. De nos jours, la production de bio-aérogels sous forme de monolithes est maîtrisée. Pour optimiser leur procédé de fabrication et pour répondre à des besoins spécifiques d'applications (pharmaceutiques, alimentaire, absorption ou adsorption, etc), les aérogels doivent avoir la forme de particules. Ce travail était focalisé sur la préparation et caractérisation de billes d’aérogels à base de cellulose et a été réalisé dans le cadre du projet Européen « Nanohybrids ». Deux objectifs principaux ont été atteints. Le premier était la préparation et la compréhension des propriétés de nouveaux matériaux, tout en diminuant leurs coûts de production. Deux types de matériaux poreux ont été produits et étudiés : • Des xérogels à base de cellulose (en évitant le séchage sous CO2 supercritique), avec des propriétés comparables à celles de leurs homologues aérogels (densité autour de 0,12 g cm-3 et surface spécifique jusqu'à 300 m² g-1). • Des aérogels à base de pâte à papier. L'influence de chaque composant de la pâte (cellulose, hémicellulose, lignine) et de leur teneur sur la structure et les propriétés des aérogels a été évaluée. Le deuxième objectif était le développement de méthodes de mise en forme d'aérogels de cellulose sous forme de billes de différentes tailles. Deux techniques ont été appliquées avec succès : • Le "JetCutting" : des billes d’aérogels à base de cellulose et de pâte à papier, de taille variant de centaines de micromètres à quelques millimètres, dissout dans deux types solvants (NaOH-eau et liquides ioniques) ont été obtenus. • L'émulsification : des particules d’aérogels de cellulose d’une dizaine de micromètres ont été préparé par le développement d'une nouvelle méthode d'émulsification-coagulation. / Aerogels are ultra-porous and nanostructured materials with a wide range of applications. Bio-aerogels is a new generation of polysaccharide-based aerogels. These fast developing materials are particularly promising for their environmental friendliness and biocompatibility. Nowadays, the production of bio-aerogels in the form of monoliths is mastered. To optimize their manufacturing process and to meet specific application needs (pharmaceutical, food, absorption or adsorption, etc.), aerogels must be in the form of particles. This work focused on the preparation and characterization of cellulose aerogel beads and was conducted in the framework of the European project "Nanohybrids". Two main objectives were achieved. The first was the preparation and understanding of the properties of new materials while reducing their production costs. Two types of porous materials were produced and studied: • Cellulose-based xerogels (obviating drying under supercritical CO2), with properties comparable to those of their aerogel counterparts (density around 0.12 g cm-3 and specific surface area up to 300 m² g-1). • Pulp-based aerogels. The influence of each pulp component (cellulose, hemicellulose, lignin) and their content on the structure and properties of aerogels was assessed. The second objective was the development of methods for shaping cellulose aerogels into beads of different sizes. Two techniques were successfully applied: • JetCutting: aerogel beads based on cellulose and pulps, varying in size from hundreds of micrometres to a few millimetres, dissolved in two types of solvents (NaOH-water and ionic liquids) were obtained. • Emulsification: cellulose aerogel particles of about few tens of micrometres were prepared by the development of a new method of emulsification-coagulation.

Essentially, the term aerogel describes a special geometric structure of matter. It is neither limited to any material nor to any synthesis procedure. Hence, the possible variety of materials and therefore the multitude of their applications are almost unbounded. Here we present a comprehensive picture of the most promising developments in the field during the last decades.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18096号 / 理博第3974号 / 新制||理||1573(附属図書館) / 30954 / 京都大学大学院理学研究科化学専攻 / (主査)准教授 中西 和樹, 教授 北川 宏, 教授 竹腰 清乃理 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

No description available.