In this work, three different classes of colour converting layers (CCLs) for the down-conversion of blue and green Organic Light Emitting Devices (OLEDs) have been developed. In Chapter 3, the dispersion of organic dyes into polymer matrices via solution processing and solid state methods is presented. Application of hybrid organic-inorganic fluorescent particles, composed of organic fluorescent molecules absorbed into porous supporting materials, is discussed in Chapter 4. This solution allows for the dispersion of the organic molecule into an otherwise non-miscible polysiloxane matrix and resulted in the discovery of unusual optical properties of one of the organic dye (fluorescein disodium salt). This peculiar emission has been studied in more detail during Chapter 5. In addition, the possible use of fluorescent nanodiamonds, produced by gamma radiation, as luminescent materials, has been investigated in Chapter 6.

Organic – ordered mesoporous silica (OMS) hybrid materials have attracted great interest due to their potential applications for gas separations, and heterogeneous catalysis. Amine-functionalized OMS materials are active in a variety of base-catalyzed reactions. The key to successfully achieving the desired reactivity is the ability to rationally tether the targeted organic functionality onto the OMS surface. Understanding the organic-inorganic interface is crucial for rational design of heterogeneous catalysts, because the local structure and molecule dynamics are paramount in determining the reactivity of the organic groups attached to the OMS surface. This dissertation focuses on three goals that will lead to a description of the organic-OMS interface and designing hybrid catalysts: 1) Determining the dynamics of organic groups attached to the OMS surface, 2) Catalytic testing to understand how the local structure and dynamics of the organic moiety influence the catalytic properties of organic-OMS catalysts, 3) Designing more active hybrid catalysts by introducing higher loadings of organic group using dendrimer structures. Solid-state NMR is uniquely suited for quantifying dynamics in the milli- to nano-second time scale. Deuterium (2H) NMR is a powerful tool to obtain detailed information about the dynamics or organic molecules. In this study, several simple functional groups isotopically labeled with deuterium have been attached to MCM-41 and SBA-15. The spectra display different molecular motions for different organic moieties. The results have indicated that the interactions between the functional groups and silanol groups on the surface influence the mobility of the organic fragments. Also, the porosity of the solid supports effects dynamics via confinement. The catalytic properties of simple amine groups attached to MCM-41, containing primary, secondary, and tertiary amines have been compared in the Nitroaldol (Henry) reaction. The effects of amine identity, structure, loading, presence of surface silanols, and the substrate topology on the catalytic properties have been investigated. The dramatic decrease of the activity of amine-functionalized MCM-41 by capping the residual silanol groups with hexamethyldisilazane was ascribed to the decrease of the interactions of hydrogen bonding between the amine functional groups and surface silanols. The result was consistent with the changes of the molecular motions shown by 2H NMR measurements. Fabricating OMS hybrid materials with high densities of organic functional groups leads to challenges in realizing uniform, catalytically active sites. Our group has immobilized melamine-based dendrimers on the surfaces of amine-functionalized SBA-15 materials by iterative synthesis procedures. The current studies in this dissertation mainly describe the catalytic properties of these dendrimers on SBA-15 and MCM-41 in the Nitroaldol (Henry) reaction, the transesterification reaction of triglycerides and methanol to synthesize methyl esters, and the cross aldol reaction between acetone and 5-hydroxymethylfurfural. The results indicate that the OMS-dendron materials have potential as solid base catalysts for a range of reactions.

Resumo: Nos últimos anos materiais com propriedades híbridas têm sido muito estudados, um exemplo é a compatibilização de cerâmicas em matrizes poliméricas. Neste trabalho, foi estudada uma metodologia para criar funcionalidades em nanomateriais por intermédio da síntese e modificação da superfície de cerâmicas (TiO2 e SiO2) e compósitos (Tio2/Ag e SiO2/Ag). Inicialmente foi estudada a reação entre o 3-aminopropiltrietoxisilano (APS) e nanopartículas comerciais de TiO2 e SiO2, em que os resultaados e espectroscopia na região do infra-vermelho (IV) e análise elementar de carbono (CHN) mostraram que a reação entre o siloxano e as partículas ocorre, formando um híbrido. Em seguida foram realizadas sínteses pelo método sol-gel dos óxidos e dos compósitos de TiO2/Ag e SiO2/Ag e ambos foram funcionalizados com siloxano. O APS foi introduzido na reação posteriormente a formação das partículas gerando um material híbrido. Os resultados de IV ilustram que todos os materiais foram funcionalizados, pois ilustravam as absorções em aproximadamente 1600 e 3000 cm-1, atribuídos ao estiramento da ligação CH2-NH@. A funcionallização foi fundamenetal para que filmes de TiO2/APS pudessem ser aplicados por dip-coating em superfícies de vidros a 150 gráus C, com excelente propriedades self-clean, determinadas pela degradação da Rodamina B. Os nanocompósitos de SiO2/Ag com APS apresentaram propriedades bactericidas segundo a norma JIS Z 2801 quando aplicado na forma de filmes finos em superfície de vidro ou incorporado em matriz polimérica de polipropileno. / Abstract: In recent years, materials with hybrid properties have been studied, and one example is the compatibility of ceramics with polymeric matrix. In this work, we have studied a method to introduce functionalities in nanomaterials through the synthesis and surface modification of ceramics (TiO2 and SiO2) and composites (TiO2/Ag and SiO2/Ag). Initialy it were studied the reaction between the 3-aminopropyltriethoxysilane (APS) and commercial nanoparticles of TiO2 and SiO2, where the results of infra-red spectroscopy (CHN) showed that the reaction between the siloxane and the particles occurs, resulting in hybrid materials. Then, it was carried out syntheses of oxides by the method of sol-gel and composites of TiO2/Ag and SiO2/Ag both functionalized with siloxane. The APS was introduced in the reaction after the formation of particles given rise hybrid materials. The results of IR ilustrated that all materials have been functionalized, as illustrated in the absortion around 1600 and 3000 cm-1, attributed to the stretching of CH2-NH2 bonding. The functionalization was crucial by dip-coating on glass surfaces at 150 degrees C films of TiO2/APS. With excellent self-clean properties, determined by the degradation of rhodamine B. The nanocomposites of APS SiO2/Ag exhibits bactericidal properties according to JIS Z 2801 standard when applied as thin films on glass surface or embedded in polymeric matrix of polypropylene. / Orientador: Elson Longo da Silva / Coorientador: José Arana Varela / Banca: Mario Cilense / Banca: Adhemar Colla Ruvolo Filho / Banca: Renato de Figueiredo Jardim / Banca: Sidnei Antonio Pianaro / Doutor

Made available in DSpace on 2014-06-11T19:35:07Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-08-21Bitstream added on 2014-06-13T21:07:09Z : No. of bitstreams: 1 simoes_lgp_dr_araiq_prot.pdf: 2153738 bytes, checksum: 66c238b6a746cef4ca77e4c10263010b (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Nos últimos anos materiais com propriedades híbridas têm sido muito estudados, um exemplo é a compatibilização de cerâmicas em matrizes poliméricas. Neste trabalho, foi estudada uma metodologia para criar funcionalidades em nanomateriais por intermédio da síntese e modificação da superfície de cerâmicas (TiO2 e SiO2) e compósitos (Tio2/Ag e SiO2/Ag). Inicialmente foi estudada a reação entre o 3-aminopropiltrietoxisilano (APS) e nanopartículas comerciais de TiO2 e SiO2, em que os resultaados e espectroscopia na região do infra-vermelho (IV) e análise elementar de carbono (CHN) mostraram que a reação entre o siloxano e as partículas ocorre, formando um híbrido. Em seguida foram realizadas sínteses pelo método sol-gel dos óxidos e dos compósitos de TiO2/Ag e SiO2/Ag e ambos foram funcionalizados com siloxano. O APS foi introduzido na reação posteriormente a formação das partículas gerando um material híbrido. Os resultados de IV ilustram que todos os materiais foram funcionalizados, pois ilustravam as absorções em aproximadamente 1600 e 3000 cm-1, atribuídos ao estiramento da ligação CH2-NH@. A funcionallização foi fundamenetal para que filmes de TiO2/APS pudessem ser aplicados por dip-coating em superfícies de vidros a 150 gráus C, com excelente propriedades self-clean, determinadas pela degradação da Rodamina B. Os nanocompósitos de SiO2/Ag com APS apresentaram propriedades bactericidas segundo a norma JIS Z 2801 quando aplicado na forma de filmes finos em superfície de vidro ou incorporado em matriz polimérica de polipropileno. / In recent years, materials with hybrid properties have been studied, and one example is the compatibility of ceramics with polymeric matrix. In this work, we have studied a method to introduce functionalities in nanomaterials through the synthesis and surface modification of ceramics (TiO2 and SiO2) and composites (TiO2/Ag and SiO2/Ag). Initialy it were studied the reaction between the 3-aminopropyltriethoxysilane (APS) and commercial nanoparticles of TiO2 and SiO2, where the results of infra-red spectroscopy (CHN) showed that the reaction between the siloxane and the particles occurs, resulting in hybrid materials. Then, it was carried out syntheses of oxides by the method of sol-gel and composites of TiO2/Ag and SiO2/Ag both functionalized with siloxane. The APS was introduced in the reaction after the formation of particles given rise hybrid materials. The results of IR ilustrated that all materials have been functionalized, as illustrated in the absortion around 1600 and 3000 cm-1, attributed to the stretching of CH2-NH2 bonding. The functionalization was crucial by dip-coating on glass surfaces at 150 degrees C films of TiO2/APS. With excellent self-clean properties, determined by the degradation of rhodamine B. The nanocomposites of APS SiO2/Ag exhibits bactericidal properties according to JIS Z 2801 standard when applied as thin films on glass surface or embedded in polymeric matrix of polypropylene.

The present PhD thesis, entitled "Design of novel bio-gated nanomaterials for sensing and therapeutic applications", is focused on the design, preparation, characterization and evaluation of new smart hybrid organic-inorganic materials for their applications on the field of sensing and controlled drug delivery. The first chapter of this thesis introduces the concept of organic-inorganic hybrid materials containing switchable "gate-like" ensembles and their applications in the detection of chemical and biochemical species and as suitable materials for drug delivery applications. The second chapter describes the preparation of an aptamer-capped mesoporous material for the fluorogenic detection of thrombin in human plasma and serum. For the preparation of the material dye-loaded MCM-41 particles were capped with a thrombin aptamer (TBA). In the presence of thrombin, TBA was displaced from the surface due to the formation of TBA-protein complex, triggering the release of the dye. The capped system was tested in simulated human blood plasma and in PBS buffer with 10% of human serum and achieved a low limit of detection (LOD) for thrombin. Moreover, the prepared material displayed great selectivity for thrombin in the presence of other non-exclusive binding proteins. The gated-nanomaterial resulted suitable to perform an accurate thrombin detection in human serum. In the third chapter a new fluorogenic sensing nanoprobe for the detection of As(III) is described. The system consists of the combination of MSNs with an aptamer (Ars-3), which possesses a very high affinity to As(III), as a pore blocking agent. The sensitivity of the nanocarrier for As(III) was further studied. Furthermore, the selectivity of the nanocarrier towards As(III) in the presence of other cations was also successfully verified. In addition, the sensor allowed accurate As(III) determination in real media. The fourth chapter reports a novel proof-of-concept to detect Mycoplasma genomic DNA and cocaine. The new approach combined gated mesoporous silica nanoparticles and surface-enhanced Raman scattering (SERS) spectroscopy. In particular, two gated-hybrid mesoporous materials loaded with a SERS reporter and capped with suitable oligonucleotide sequences to detect Mycoplasma genomic DNA or cocaine, were prepared. Release of the reporter was triggered from the different materials by the presence of the corresponding target, and was detected by SERS upon adsorption on gold nanotriangles. This novel procedure allowed detecting Mycoplasma genomic DNA and cocaine with a high selectivity and sensitivity. The fifth chapter describes the development of a nanodevice able to deliver insulin as a function of the glucose concentration, in simulated human blood plasma. The glucose-driven nanomaterial consisted of ß-cyclodextrin-modified glucose oxidase (CD-GOx)-capped silica nanoparticles loaded with insulin. The reaction of glucose by the capping enzyme (GOx) triggered insulin release in a self-regulated manner. Furthermore, the response to glucose was found to be selective and other saccharides were unable to deliver the entrapped insulin. We hope the results obtained in this thesis may inspire further works to design smart nanodevices with application in analytical chemistry, clinical or environmental assays and self-regulated drug delivery systems. / La presente tesis doctoral, titulada "Diseño de nuevos nanomateriales con puertas moleculares biológicas para aplicaciones de detección y terapéuticas", se centra en el diseño, preparación, caracterización y evaluación de nuevos materiales híbridos orgánicos-inorgánicos inteligentes para su aplicación en el campo de la detección y liberación controlada de fármacos. El primer capítulo de la presente tesis introduce el concepto de los materiales híbridos orgánicos-inorgánicos funcionalizados con puertas moleculares y su aplicación en la detección de especies químicas y bioquímicas de interés y como materiales adecuados para su aplicación en liberación controlada de fármacos. El segundo capítulo describe la preparación de un material mesoporoso con aptámeros como puerta moleculares, para la detección fluorogénica de trombina en plasma y suero humano. En la preparación del material se utilizaron partículas de MCM-41 cargadas con un colorante y cuyos poros se taparon con un aptámero que reconoce la proteína trombina (TBA). En presencia de trombina el TBA se desplazó de la superficie debido a la formación del complejo TBA-proteína permitiendo así la liberación del colorante. El funcionamiento del material se evaluó en plasma humano simulado y en PBS con 10% de suero humano y se alcanzó un bajo límite de detección (LOD) para trombina. Además, el material resultó ser selectivo para trombina en presencia de otras proteínas no específicas. El nanomaterial resultó adecuado para la detección precisa de trombina en suero humano. En el tercer capítulo se describe una nuevo nanomaterial sensor para la detección fluorogénica de As (III). El sistema consiste en la combinación de nanopartículas mesoporosas de sílice (MSNs) con un aptámero (Ars-3), que posee una alta afinidad por el As(III), como agente bloqueante de los poros. Además, se estudió la sensibilidad del nanomaterial para As(III). Por otro lado, se demostró la selectividad del nanomaterial para As(III) en presencia de otros cationes. Adicionalmente, el sensor permitió una determinación precisa de As(III) en un medio real. El cuarto capítulo describe una novedosa prueba de concepto para la detección de ADN genómico de Mycoplasma y cocaína. El nuevo enfoque combinó MSNs con puertas moleculares y espectroscopía Raman amplificada en superficie (SERS). En particular, se prepararon dos materiales híbridos con puertas moleculares y cargados con un reportero SERS. Como puertas moleculares se utilizaron dos secuencias de oligonucleótidos para detectar ADN genómico de Mycoplasma o cocaína. La liberación del reportero SERS desde los materiales se indujo por la presencia del analito correspondiente, y fue detectado por SERS tras su adsorción sobre nanotríangulos de oro. Este nuevo procedimiento permitió detectar ADN genómico de Mycoplasma y cocaína con alta selectividad y sensibilidad. El quinto capítulo describe el desarrollo de un nanodispositivo capaz de liberar insulina en función de la concentración de glucosa en plasma sanguíneo humano simulado. El nanomaterial consiste en nanopartículas de sílice funcionalizadas cuyos poros se taparon con la enzima glucosa-oxidasa modificada con ß-ciclodextrinas (CD-GOx) y cargadas con insulina. La reacción de la glucosa por la enzima bloquenate (GOx) desencadenó la liberación autorregulada de insulina. Asimismo, se encontró que la respuesta a la glucosa era selectiva y otros azúcares no indujeron la liberación de la insulina cargada. Esperamos que los resultados obtenidos en esta tesis puedan inspirar otros trabajos para diseñar nanodispositivos inteligentes con aplicación en la química analítica, ensayos clínicos o medioambientales y en sistemas de liberación autorregulada de fármacos. / La present tesi doctoral, titulada "Disseny de nous nanomaterials amb portes moleculars biològiques per a aplicacions de detecció i terapèutiques", es centra en el disseny, preparació, caracterització i avaluació de nous materials híbrids orgànics-inorgànics intel·ligents per a la seua aplicació en el camp de la detecció i lliberació controlada de fàrmacs. El primer capítol de la present tesi introduïx el concepte dels materials híbrids orgànics-inorgànics funcionalizats amb portes moleculars i la seua aplicació en la detecció d'espècies químiques i bioquímiques d'interés i com a materials adequats per a la lliberació controlada de fàrmacs. El segon capítol descriu la preparació d'un material mesoporós amb aptámeros com a porta molecular, per a la detecció fluorogénica de trombina en plasma i sèrum humà. En la preparació del material es van utilitzar partícules de MCM-41 carregades amb un colorant i els porus del qual es van tapar amb un aptàmer que reconeix la proteïna trombina (TBA). En presència de trombina el TBA es va desplaçar de la superfície a causa de la formació del complex TBA-proteïna permetent així l'alliberament del colorant. El funcionament del material es va avaluar en plasma humà simulat i en PBS amb 10% de sèrum humà i es va aconseguir un baix límit de detecció (LOD) per a trombina. A més, el material va resultar ser selectiu para trombina en presència d'altres proteïnes no específiques. El nanomaterial va resultar adequat per a la detecció precisa de trombina en sèrum humà. En el tercer capítol es descriu un nou nanomaterial sensor per a la detecció fluorogènica d'As(III). El sistema consistix en la combinació de nanopartícules mesoporoses de sílice (MSNs) amb un aptàmer (Ars-3), que posseïx una alta afinitat per l'As(III), com a agent bloquejant dels porus. A més, es va estudiar la sensibilitat del nanomaterial per a As(III). D'altra banda, es va demostrar la selectivitat del nanomaterial per a As(III) en presència d'altres cations. Addicionalment, el sensor va permetre una determinació precisa d'As(III) en un medi real. El Quart capítol descriu una nova prova de concepte per a la detecció de ADN genòmic de Mycoplasma i cocaïna. El nou enfocament va combinar MSNs amb portes moleculars i espectroscòpia Raman amplificada en superfície (SERS). Concretament, es van preparar dos materials híbrids amb portes moleculars i carregats amb un reporter SERS. Com a portes moleculars es van utilitzar dos seqüències d'oligonucleòtids per a detectar ADN genòmic de Mycoplasma o cocaïna. L'alliberament del reporter SERS des dels materials es va induir per la presència de l'anàlit corresponent, i va ser detectada per SERS després de la seua adsorció sobre nanotriangles d'or. Este nou procediment va permetre detectar ADN genòmic de Mycoplasma i cocaïna amb alta selectivitat i sensibilitat. El quint capítol descriu el desenrotllament d'un nanodispositiu capaç d'alliberar insulina en funció de la concentració de glucosa en plasma sanguini humà simulat. El nanomaterial consistix en nanopartícules de sílice funcionalizades els porus del qual es van tapar amb l'enzim glucosa-oxidasa modificada amb ß-ciclodextrinas (CD-GOx) i carregades amb insulina. La reacció de la glucosa per l'enzim bloquejant (GOx) va desencadenar l'alliberament autoregulat d'insulina. Així mateix, es va trobar que la resposta a la glucosa va ser selectiva i altres sucres no van induir la lliberació de la insulina carregada. Esperem que els resultats obtinguts en aquesta tesi puguen inspirar nus treballs per a dissenyar nanodispositius intel·ligents amb aplicació en la química analítica, assajos clínics o mediambientals i en sistemes de lliberació autoregulada de fàrmacs. / Oroval Cucarella, MDM. (2017). Design of novel bio-gated nanomaterials for sensing and therapeutic applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/78836 / TESIS

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Orientador: Carlos Cesar Bof Bufon / Banca: Lucas Fugikawa Santos / Banca: Nilson Cristino da Cruz / Resumo: A técnica de autoenrolamento de nanomembrana foi utilizada neste trabalho para a fabricação de capacitores ultracompactos (UCCap), permitindo a caracterização de filmes finos de materiais orgânicos e híbridos. O método é conhecido como roll-up, e consiste na formação de uma nanomembrana tensionada, elaborada a fim de produzir estruturas autosustentadas, que promovem o enrolamento do sistema ao serem libertadas de um substrato, determinando uma arquitetura em 3D. Neste trabalho, a tecnologia de nanomembranas foi utilizada com o objetivo de determinar as propriedades elétricas e dielétricas, sob diferentes temperaturas, de camadas de moléculas semicondutoras (CoPc, CuPc e F16CuPc) e de camadas de estruturas híbridas metal-orgânicas (HKUST-1). A caracterização desses materiais em nanoescala foi possível por meio de sua incorporação em UCCap. Os dispositivos foram caracterizados por medidas de espectroscopia de impedância e corrente elétrica. Em filmes finos das ftalocianinas (= 5 nm) na temperatura ambiente (≈ 296 K), foram encontrados valores de 2,1 ± 0,5 para a constante dielétrica da CoPc (kCoPc), 3,1 ± 0,6 para a CuPc (kCuPc) e 1,2 ± 0,6 para F16CuPc (kF16CuPc). As propriedades elétricas / dielétricas dos filmes das ftalocianinas foram analisadas sob diferentes temperaturas e filmes de CoPc foram explorados na presença de campos magnéticos aplicados com valores de magnitude entre - 500 e + 500 mT. As camadas de HKUST-1 incorporadas ao UCCap possibilitaram a determinação do v... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The rolled-up nanomembrane-based technique was used in this work to the manufacture of ultracompact capacitors (UCCap), allowing the characterization of thin films of organic and hybrid materials. The method, known as roll-up, consists in the formation of a strained nanomembrane, elaborated in order to produce self-supported structures that promote the winding of the system when released from a substrate, determining a 3D architecture. In this work, the nanomembrane technology was used to determine the electrical and dielectric properties, for different conditions of temperatures, in layers of semiconductor molecules (CoPc, CuPc and F16CuPc) and layers of hybrid metal-organic structures (HKUST-1). The characterization of these materials at nanoscale was possible by their incorporation into UCCap. Current-voltage and impedance spectroscopy measurements were used to characterize the devices. For thin films of the phthalocyanines (= 5 nm) at room temperature (≈ 296 K), values of 2,1 ± 0,5 were found for CoPc dielectric constant (kCoPc), 3,1 ± 0,6 for CuPc (kCoPc) and 1,2 ± 0,6 for F16CuPc (kF16CoPc). The electrical / dielectric properties of the phthalocyanine films were analyzed under different temperatures and CoPc films were screened in the presence of applied magnetic fields with magnitude values between - 500 and + 500 mT. The HKUST-1 layers incorporated into the UCCap allowed the determination of a value of 3,2 ± 1,6 for its dielectric constant (kHKUST-1) at ≈ 296 K. The v... (Complete abstract click electronic access below) / Mestre

<div>The rate effect of fiber-matrix interfacial debonding behavior of SC-15 epoxy and various fiber reinforcements was studied via in-situ visualization of the debonding event. Special focus has been placed on the dynamic transverse debonding of single fiber reinforced polymer composites. In this study, the debonding force history, debonding initiation, debonding crack velocity, and crack geometry were characterized using a quasi-static load frame and a modified tension Kolsky bar at loading velocities of 0.25 mm/s and 2.5 m/s. Cruciform-shaped specimens were used for interfacial transverse debonding between SC-15 epoxy matrix and various fiber reinforcements including S-2 glass, Kevlar® KM2, and tungsten fiber materials. The load history and high-speed images of the debonding event were simultaneously recorded. A major increase was observed for the average peak debonding force and a minor increase was observed for the average crack velocity with increasing loading velocity. The crack geometry of the cruciform specimens under both loading velocities was also tracked. Scanning electron microscopy of the recovered specimens revealed the debonding direction along the fiber-matrix interface through angled patterns on the failure surface.</div><div><br></div><div>The dynamic shear debonding of single fiber reinforced plastic composites were also studied via the real-time visualization with the fiber pull-out method. The interfacial shear debonding was studied between SC-15 epoxy and fiber reinforcements including S-2 glass, tungsten, steel, and carbon composite Z-pin fiber materials at 2.5 m/s and 5.0 m/s. Both S-2 glass fiber and Z-pin experienced catastrophic interfacial debonding whereas tungsten and steel wire experienced both catastrophic debonding and stick-slip behavior. Scanning electron microscope imaging of recovered epoxy beads revealed a snap-back behavior around the meniscus region of the bead for S-2 glass, tungsten, and steel fiber materials at 5.0 m/s whereas those at 2.5 m/s exhibited no snap-back behavior.</div>

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The present work analyses the physicochemical phenomena responsible for the microstructure of Pd/SiO2 xerogel catalysts and of metal-free hybrid SiO2 xerogels synthesized by sol-gel process. The samples are synthesized by co-polymerizing tetraethoxysilane (TEOS) with 3-aminopropyltriethoxysilane or 3-(2-aminoethylamino)propyltrimethoxysilane in ethanol, the latter co-reactant possibly forming a complex with palladium. The analysis is conducted by following in situ the formation of the gels' nanostructure by Small-Angle X-ray Scattering (SAXS), by characterizing the microstructure of the final gels by beam-bending, and by analyzing the microstructure of the xerogels after desiccation, most notably by electron tomography. The in situ SAXS analysis shows that the nanometer structure of the gels forms via a reaction-induced phase separation. The microstructure of the hybrid xerogels is hierarchical, as assessed by electron microscopy, nitrogen adsorption and SAXS. Its structure is that of a microcellular foam at large scale, with pores a few hundred nanometers across, supported by elongated filaments, a few ten nanometers wide, each filament being made up by smaller structures, a few nanometers wide. The characteristics of the various structural levels depend on the nature and concentration of the co-reactant used. In the case of xerogel catalysts, electron tomography shows that Pd nanoparticles are regularly dispersed inside the silica, with distances between them comparable to the thickness of the skeleton. On the basis of the time-resolved SAXS and of the characterization of the xerogels, it is argued that a double phase separation process is responsible for the structuring of the gels, with a primary phase separation leading to the microcellular foam morphology, and a secondary phase separation being responsible for the substructure of the filaments. The large scale structure of the gels themselves, before desiccation, is analyzed by beam bending. This enables one to estimate the mechanical properties of the gels as well as the size of their largest pores. The microstructure of aerogels obtained by supercritical drying of the samples is also investigated. The comparison of the characterization data show that the nature and concentration of the co-reactant controls the amount of shrinkage that the gels undergo during desiccation, at the macroscopic scale as well as at the scale of the filaments.