Dissertations / Theses on the topic 'Porous Nanocomposite'

Due to their large internal surface area, microporous materials have been widely used in applications where high surface activity is desired. Example applications are extracellular scaffolds for tissue engineering, porous substrates for catalytic reaction, and permeable media for membrane filtration, etc. To realize these potential applications, various techniques such as TIPS (thermal induced phase separation), particle leaching, and SFF (solid freeform fabrication) were proposed and investigated. Despite of being able to generate microporous for specific applications, these available fabrication techniques have limitations on controlling the inner porous structure and the outer geometry in a cost-effective manner. To address these technical challenges, a systematic study focusing on the generation of microporous structures using co-continuous polymer blend was conducted. Under this topic, five subtopics were explored: 1) generation of gradient porous structures; 2) geometrical confining effect in compression molding of co-continuous polymer blend; 3) microporous composite with high nanoparticle loading; 4) micropatterning of porous structure; 5) simulation strategy for kinetics of co-continuous polymer blend phase coarsening process.

In the field of tissue engineering, a major area of study is developing bone scaffolds that will provide support for osteoblasts. Despite many advances in recent years there is still a significant need for new bio-based 3-D porous scaffolds that possess sufficient initial mechanical properties to prevent immediate failure upon implantation. Ovalbumin (OVA), a glycoprotein from chicken egg whites, has been use to fabricate biodegradable, porous hydrogel bone scaffolds that promote osteoblast attachment and proliferation. Although ovalbumin scaffolds encourage bioactivity and are naturally resorbed into the body after bone regeneration, they are also very fragile. Extremely stiff cellulose nanocrystals (CNCs), derived from wood pulp, can be utilized to reinforce these scaffolds while improving biocompatibility. When chemically modified to incorporate surface amine groups, cellulose nanocrystals become capable of covalently crosslinking with the OVA matrix for improved mechanical resilience. Three concentrations (2, 5, 10 wt. %) of CNCs were incorporated and crosslinked to form nanocomposite scaffolds then were compared to pure OVA scaffolds. After fabrication, pore size morphology was compared between each CNC loading using SEM. The images revealed that the 10 wt. % CNC concentration doubled the pore compared to pure OVA scaffolds. Under high magnification, the CNCs were incorporated into the pore walls, providing a contoured surface. AFM was applied to analyze the topography of OVA with CNCs present. The surfaces laden with CNCs had a higher mean surface roughness, but was insufficient to impact cell behavior. Compression testing was carried out on both Instron and DMA machines to demonstrate any reinforcing effect provided by the CNCs. While the compressive modulus remained constant, the elastic limit and strain increased with CNC loading, indicating a change in the resilience of the reinforced scaffolds. With a MTT Assay, it was shown that MC3T3-E1 preosteoblasts significantly increase in metabolic activity on 2 wt. % films and scaffolds, an indication of proliferation. All scaffolds had a net increase in metabolic activity suggesting overall biocompatibility for OVA scaffolds and those incorporating CNCs. Overall, the 5 wt. % scaffolds had the highest mechanical strength and had a positive cell response.
Master of Science

The thermal properties of porous silicon and composite «PS-liquid» system have been investigated in this paper. Using the photoacoustic method the values of thermal conductivity of porous silicon and composite systems with liquid have been obtained. It is shown that the value of thermal conductivity «PS-liquid» substantially exceeds the value determined by the model of «parallel structures». The increase of thermal conductivity is due to the improvement of thermal contacts among the crystallites when introducing liquid into the pores. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35111

Current electrochemical energy storage systems are not sufficient to meet ever-rising energy storage requirements of emerging technologies. Hence, development of alternative electrode materials is inevitable. This thesis aims to establish novel electrode materials demonstrating both high energy and power density with prolonged cycle life derived from fundamental understandings on electrochemical reactions of chalcogens, such as sulfur (S) and selenium (Se). First, the effects of the pore size distribution, pore volume and specific surface area of porous carbons on the temperature-dependent electrochemical performance of S-infiltrated carbon cathodes in electrolytes having different salt concentrations are investigated. Additionally, the carbide derived carbon (CDC) synthesis temperature, electrolyte composition, and electrochemical S utilization have been correlated. The effects of thin Li-ion permeable but polysulfide non-permeable Al2O3 layer coating on the surface of S infiltrated carbon cathode are also examined. Similar with S studies, Se infiltrated ordered meso- and microporous CDC composites are prepared and the correlations between pore structure designing and electrolyte molarity are explored. Finally, this thesis demonstrates a simple process to form a protective solid electrolyte layer on the Se cathode surface in-situ. This technique adopts fluoroethylene carbonate to convert into a layer that remains permeable to Li ions, but prevents transport of polyselenides. As a whole, the correlations of multiple cell parameters, such as the cathode structure, the electrolyte composition, and operating temperature on the performances of lithium-chalcogen batteries are discussed.

Thesis (M. S.)--Chemical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Nair, Sankar; Committee Member: Koros, William; Committee Member: Ludovice, Peter; Committee Member: Meredith, Carson; Committee Member: Thio, Yonathan; Committee Member: Zhou, Min.

The electrical properties of hybrid nanosystem based on poly(3,4 ethylenedioxythiophene) with ZnO and porous silicon nanoparticles were studied by the methods of current-voltage characteristics and thermally stimulated conductivity. The dependence of electrical parameters of hybrid films on their composition has been found. The analysis of the temperature dependences of the composites conductivity in the temperature range of 80-330 К indicates the activation character of charge transfer and presence the trapping of unequilibrium carriers at the porous silicon and ZnO nanoparticle – polymer interface.

Nanostructured porous materials generally, and nanoporous noble metals specifically, have received considerable attention due to their superior chemical and physical properties over nanoparticles and bulk counterparts. This dissertation work aims to develop well-established strategies for the preparation of multifunctional nanostructured porous materials based on the combination of inorganic-chemistry, organic-chemistry and electrochemistry. The preparation strategies involved one or more of the following processes: sol-gel synthesis, co-electrodeposition, metal ions reduction, electropolymerization and dealloying or chemical etching. The study did not stop at the preparation limits but extended to investigate the reaction mechanism behind the formation of these multifunctional nanoporous structures in order to determine the different factors controlling the nanoporous structures formation. First, gold-silica nanocomposites were prepared and used as a building blocks for the fabrication of high surface area gold coral electrodes. Well-controlled surface area enhancement, film thickness and morphology were achieved. An enhancement in the electrode’s surface area up to 57 times relative to the geometric area was achieved. A critical sol-gel monomer concentration was also noted at which the deposited silica around the gold coral was able to stabilize the gold corals and below which the deposited coral structures are not stable. Second, free-standing and transferable strata-like 3D porous polypyrrole nanostructures were obtained from chemical etching of the electrodeposited polypyrrole-silica nanocomposite films. A new reaction mechanism was developed and a new structural directing factor has been discovered for the first time. Finally, silver-rich platinum alloys were prepared and dealloyed in acidic medium to produce 3D bicontinuous nanoporous platinum nanorods and films with a nanoporous gold-like structure. The 3D-BC-NP-Pt displayed high surface area, typical electrochemical sensing properties in an aqueous medium, and exceptional electrochemical sensing capability in a complex biofouling environment containing fibrinogen. The 3D-BC-NP-Pt displayed high catalytic activity toward the methanol electro-oxidation that is 30 times higher that of planar platinum and high volumetric capacitance of 400 F/cm3. These findings will pave the way toward the development of high performance and reliable electrodes for catalysis, sensing, high power outputs fuel cells, battery-like supercapacitors and miniaturized device applications.

Polymeric bone scaffolds are a promising tissue engineering approach for the repair of critical-size bone defects. Porous three-dimensional (3D) scaffolds play an essential role as templates to guide new tissue formation. However, there are critical challenges arising from the poor mechanical properties and low bioactivity of bioresorbable polymers, such as poly(epsilon-caprolactone) (PCL) in bone tissue engineering applications. This research investigates the potential use of cellulose nanocrystals (CNCs) as multi-functional additives that enhance the mechanical properties and increase the biomineralization rate of PCL. To this end, an in vitro biomineralization study of both sulfuric acid hydrolyzed-CNCs (SH-CNCs) and surface oxidized-CNCs (SO-CNCs) has been performed in simulated body fluid in order to evaluate the bioactivity of the surface functional groups, sulfate and carboxyl groups, respectively. PCL nanocomposites were prepared with different SO-CNC contents and the chemical/physical properties of the nanocomposites were analyzed. 3D porous scaffolds with fully interconnected pores and well-controlled pore sizes were fabricated from the PCL nanocomposites with a 3D printer. The mechanical stability of the scaffolds were studied using creep test under dry and submersion conditions. Lastly, the biocompatibility of CNCs and 3D printed porous scaffolds were assessed in vitro. The carboxyl groups on the surface of SO-CNCs provided a significantly improved calcium ion binding ability which could play an important role in the biomineralization (bioactivity) by induction of mineral formation for bone tissue engineering applications. In addition, the mechanical properties of porous PCL nanocomposite scaffolds were pronouncedly reinforced by incorporation of SO-CNCs. Both the compressive modulus and creep resistance of the PCL scaffolds were enhanced either in dry or in submersion conditions at 37 degrees Celsius. Lastly, the biocompatibility study demonstrated that both the CNCs and material fabrication processes (e.g., PCL nanocomposites and 3D printing) were not toxic to the preosteoblasts (MC3T3 cells). Also, the SO-CNCs showed a positive effect on biomineralization of PCL scaffolds (i.e., accelerated calcium or mineral deposits on the surface of the scaffolds) during in vitro study. Overall, the SO-CNCs could play a critical role in the development of scaffold materials as a potential candidate for reinforcing nanofillers in bone tissue engineering applications.
Ph. D.

Cette thèse porte sur les simulations numériques de l’interaction laser avec des matériaux poreux. Une possibilité de traitement bien contrôlé est particulièrement importante pour la microstructuration laser du verre poreux et le nano-usinage de matériaux poreux semiconducteurs en présence de nanoparticules métalliques. La modélisation auto-cohérente se concentre donc sur une étude détaillée des processus impliqués. En particulier, pour comprendre les structures des micro-vides périodiques produits à l’intérieur du verre poreux par des impulsions laser femtoseconde, une analyse thermodynamique numérique détaillée a été réalisée. Les résultats des calculs montrent la possibilité de contrôler le micro-usinage laser en volume de SiO2 . De plus, les dimensions des structures densifiées par laser sont examinées pour différentes conditions de focalisation à de faibles énergies d’impulsion. Les dimensions caractéristiques obtenues à partir des structures sont corrélées avec les résultats expérimentaux. Comparés au verre poreux, les films mésoporeux TiO2 chargés d’ions Ag et de nanoparticules supportent des ré- sonances plasmoniques localisées. Les films nanocomposites obtenus sont capables de transférer des électrons libres et d’absorber l’énergie laser de manière résonnante, offrant des possibilités supplémentaires pour contrôler la taille des nanoparticules d’Ag. Pour identifier les paramètres optimaux du laser à onde continue, un modèle multi-physique prenant en compte la croissance des nanoparticules d’Ag, photo-oxydation, réduction a été développé. Les simulations réalisées montrent que la vitesse d’écriture laser contrôle la taille des nanoparticules d’Ag. Les calculs ont également représenté une nouvelle vision selon laquelle les nanoparticules d’Ag se développent devant le centre du faisceau laser du fait de la diffusion de chaleur. Il a été démontré que la croissance rapide activée thermiquement suivie d’une photo-oxydation est la principale raison du changement de taille et de température en fonction de la vitesse d’écriture. Un modèle tridimensionnel a été développé et reproduit les lignes écrites au laser. L’écriture de films mésoporeux TiO2 chargés de nanoparticules d’Ag par un laser pulsé promet également d’offrir des possibilités supplémentaires dans la génération de deux types de nanostructures: les rainures de surface périodiques induites par laser (LIPSS) et les nanogratings Ag à l’intérieur du film TiO2 . Pour mieux comprendre les effets d’un laser pulsé, deux modèles multiimpulsions - un semi-analytique et un autre basé sur une méthode par éléments finis (FEM) - sont développés pour simuler la croissance des nanoparticules d’Ag. Le modèle FEM s’avère précis car il traite mieux la diffusion de la chaleur à l’intérieur des films minces TiO2 . Le modèle pourrait être étendu à l’avenir pour comprendre la formation de nanogratings LIPSS et Ag dans de tels milieux en les couplant avec les migrations de nanoparticules, la fusion de surface et l’hydrodynamique.Les résultats obtenus ont ouvert de nouvelles perspectives sur le microtraitement laser des matériaux poreux et un meilleur contrôle laser sur la nanostructuration dans les films semiconducteurs poreux chargés de nanoparticules métalliques
This thesis is focused on numerical simulations of the laser interaction with porous materials. A possibility of well-controlled processing is particularly important for the laser based micro-structuring of porous glass and nano-machining of semiconducting porous materials in the presence of metallic nanoparticles. The self-consistent modeling is, therefore, focused on a detailed investigation of the involved processes. Particularly, to understand the periodic micro-void structures produced inside porous glass by femtosecond laser pulses, a detailed numerical thermodynamic analysis was performed. The calculation results show the possibility to control laser micro-machining in volume of SiO2 . Furthermore, the dimensions of laser-densified structures are examined for different focusing conditions at low pulse energies. The obtained characteristic dimensions of the structures correlate with the experimental results. Comparing to the porous glass, the mesoporous TiO2 films loaded by Ag ions and nanoparticles support localized plasmon resonances. The resulted nanocomposite films are capable to transfer free electrons and to resonantly absorb laser energy providing additional possibilities in controlling Ag nanoparticle size.To identify the optimum parameters of the continuous-wave laser, a multi-physical model considering Ag nanoparticle growth, photo-oxidation, reduction was developed. The performed simulations show that the laser writing speed controls the Ag nanoparticles size. The calculations also depicted a novel view that Ag nanoparticles grow ahead of the laser beam center due to the heat diffusion. The thermally activated fast growth followed by the photo-oxidation was found to be the main reason for the writing speed dependent sizechange and temperature rises. A three-dimensional model was developed and reproduced the laser written lines.Writing of mesoporous TiO2 films loaded with Ag nanoparticles by a pulsed laser is, furthermore, promising to provide additional possibilities in the generation of two kinds of nanostructures: laser induced periodic surface grooves (LIPSS) and Ag nanogratingsinside the TiO2 film. To better understand the effects of a pulsed laser, two multi-pulses models - one semi-analytic and another one based on a finite element method (FEM) are developed to simulate the Ag nanoparticle growth. The FEM model is shown to be precise because it better treats heat diffusion inside the TiO2 thin films. The model could be extended in future to understand the formation of LIPSS and Ag nanogratings in such media by coupling with nanoparticle migrations, surface melting and hydrodynamics. The obtained results provided new insights into laser micro-processing of porous material and better laser controlling over nanostructuring in porous semiconducting films loaded with metallic nanoparticles

Plusieurs verrous scientifiques et technologiques empêchent aujourd'hui de développer une technique et/ou un matériau qui permette de stocker une quantité importante d'hydrogène à pression et température ambiante dans un volume et un poids acceptable pour des applications embarquées. Une possible solution consiste à synthétiser des matériaux hybrides (matériaux poreux/métaux ou alliages) où les processus d'adsorption et d'absorption pourraient coopérer pour obtenir une capacité de stockage d'hydrogène en adéquation avec les besoins des applications. Notre travail a consisté à identifier et caractériser différents matériaux poreux ayant une organisation de pores bien définie et une taille de l'ordre de quelques nanomètres. Parmi eux, ont été choisis : une réplique de carbone (CT) et un réseau organométallique (MOF-5). De plus, plusieurs métaux nobles (Ni, Pd et Pt) ont été choisis pour leur facilité à dissocier l'hydrogène et à former des alliages (Pd-Ni) avec différentes compositions en milieu aqueux (oxydant). Une méthode d'imprégnation par voie chimique ainsi que le broyage mécanique ont été utilisés pour la synthèse des hybrides. L'étude des propriétés structurales, texturales et thermodynamiques (hydrogénation) des composites CT/Pd a montré qu'un effet coopératif existe entre les pores du CT et les nanoparticules métalliques pendant le processus d'ad/absorption d'hydrogène. Cette interaction entraîne une amélioration de la capacité d'hydrogénation par rapport à chacun des constituants de l'hybride.

Today, bulk silicon is one of the best studied semiconductors. However, in its different nano-modifications, e.g. as porous silicon, totally new properties are exhibited. Despite the fact, that porous silicon is widely known and has been extensively studied since the 1990s, many unique features of this material are still unexplored. In this work, specific functionalities of porous silicon prepared, utilising both solid (via electrochemical or stain etching processes) and gas phase (from silane) syntheses, were investigated. Since this study was in-part industry oriented, the emphasis has been placed upon the investigation of porous silicon nanostructures, made from low cost metallurgical grade polycrystalline silicon powder. It has been previously demonstrated that porous silicon exhibits a very large, hydrogenated internal surface area (up to 500 m2 g−1). It is verified in this work, that morphological properties of this material result in a high reductive potential of its internal surface due to hydrogen passivation. Therefore, in this thesis, we would like to show that porous silicon-based reactive templates are promising for their applications in nanometal-supported catalysis. We used salts of platinum, gold, palladium, silver and their mixtures, which were reduced on the silicon nanocrystalline internal surface, resulting in formation of metal nanoparticles embedded into porous silicon matrix. Various experimental techniques were used to evaluate the morphology, size and composition of metal nanoparticles, as well as their growth rates. Hydrogen effusion experiments proved the crucial difference between porous silicon and other chemically inert supporting templates for the process of metal nanoparticles formation. The catalytic activity of the synthesised materials was evaluated in gas phase conversion of CO to CO2. Furthermore, the new porous silicon-based catalysts were tested in gas/liquid phase reactions as well, using hydrogenation, oxidation, dehalogenation and C-C coupling class reactions. Following the trends of “state of the art” current Si technology, we present the design of the developed flow microreactor, based on patterned Si wafer, which can be implemented in future work to catalyse selected reactions. Results obtained in this work suggest that porous silicon matrices are promising supports for metal nanoparticle based catalysis.

Thesis (Ph. D.)--Ohio State University, 1998.
Advisor: John J. Lannutti, Dept. of Materials Science and Engineering. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The paper describes the fabrication process of templates with high aspect ratio suitable for formation of nanomposites with enhanced anisotropy. The templates are thick ordered porous silicon layers formed with the pulsed galvanostatic mode. Characteristic feature of the developed mode is a short reversed polarity pulse of certain amplitude. In the present paper the achieved thickness of porous silicon templates is 50 m with pore diameter 80 nm. The aspect ratio of those structures 1:600. The maximum thickness of formed silicon layers is not principally limited allowing obtaining nanostructures with even higher aspect ratio. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35088

Despite advances in diagnostic procedures and treatments, the overall survival rate from cancer has not improved substantially over the past 30 years. One promising development is the encapsulation of toxic cancer chemotherapeutic reagents within biocompatible nanocomposite materials. The targeted stimuli triggered drug release restrict the toxic drugs to the tumour site, thereby reducing the effects of “free drug” on healthy tissues. One of the most versatile and safe materials used in medicine are iron oxide nanoparticles. This project describes the development of several formulations based on magnetite nanoparticles for drug delivery applications. Utilising magnetic nanoparticles in drug delivery systems allowed for the synergistic effects of hyperthermia and heat triggered drug released. The drug delivery systems developed in this project include magnetoliposomes, magnetic micelles, mesoporous silica-magnetite core-shell nanoparticles, liposome capped mesoporous silica-magnetite core-shell nanoparticles (protocells) and polymer capped mesoporous silica-magnetite core-shell nanoparticles. The drug loading and release profiles of the developed nanomaterials were assessed using two different anticancer drugs; Mitomycin C (MMC) and Doxorubicin (DOX). The drug loading content and drug loading efficiency for different nanocomposites ranged from 0.48 to 10.30% and 16.16 to 85.85%, respectively. Drug release profiles were studied in vitro at 37°C at pH 5.5 and pH 7.4 and at hyperthermia elevated temperature of 43°C to evaluate the effects of pH and temperature on the release profiles. An AC magnetic field with frequency of 406 kHz and variable field of up to 200 G was used to induce magnetic heating and keep the temperature within hyperthermia treatment range. Compared to uncapped mesoporous silica nanoparticles capping the mesopores of the silica nanoparticles with liposome or polymer reduced the drug release by 52.7% and 41.5%, respectively. The efficacy of doxorubicin-containing nanoparticles were evaluated in vitro against breast cancer and glioblastoma cell lines where different formulations demonstrated comparable or increased cytotoxicity compared to free drug. The cells treated with DOX loaded nanoparticles and hyperthermia demonstrated up to 89% lower viability compared to cells treated with free DOX. Silica coated magnetic nanoparticles were also used as enzymes (Pseudomonas Fluorescens Lipase (PFL) and Candida Rugosa Lipase (CRL)) supports in catalysis reactions. The enzymes were immobilised onto nanoparticles through physical adsorption and chemical bonding. The immobilised lipases were used in hydrolysis of pNPP and hydrolysis of cis-3,5-diacetoxy-1-cyclopentene to investigate the catalytic activity of the immobilized enzymes compared to free enzymes. The results indicated that free lipases provided slightly higher conversion than immobilised lipases in the first cycle however, the immobilised lipases were easily recycled and reused in sequential cycles which provides higher total yield per mg of lipase. The chemically immobilised lipase exhibited good reusability without loss of its activity in sequential cycles, however the physically adsorbed lipase showed reduced activity which could be explained by loss of enzyme during recycling between successive reactions. The CRL lipase activity were further assessed in the presence of an AC field where the results showed that exposure to the AC magnetic field resulted in increased lipase activity. The effect of reaction temperature on immobilised lipase activity were studied by performing the hydrolysis of cis-3,5-diacetoxy-1-cyclopentene at two temperatures of 25°C and 37°C where it was observed that both lipases exhibited higher activity at higher temperature which could be due to the fact that for PFL and CRL the optimum temperature is close to 37°C.

With the aging of populations and prolonged life expectancy, there is an increasing demand for bone grafts or synthetic materials that can potentially replace, repair or regenerate lost, injured or diseased bone. Tissue engineering (TE) is one of the approaches being investigated to tackle this problem. In common TE strategies, a three-dimensional structure, termed “scaffold”, fabricated from a suitable artificial or natural material. In bone tissue engineering, a scaffolding material is used either to induce formation of bone from the surrounding tissue or to act as a carrier or template for implanted bone cells or other agents. To serve as a scaffold, the material must be biocompatible, osteoconductive, and osteointegrative, and have enough mechanical strength to provide structural support during the bone growth and remodeling. Several attempts have been successfully made to construct porous scaffolds with desired porosity and appropriate mechanical performance from inorganic materials such as bioactive ceramics and glasses, from biodegradable polymers and their composites. The focus of biomaterial design for tissue engineering applications has recently been directed towards bioactive components that facilitate biomaterial integration and native tissue regeneration at the implant site. During the last four decades, various materials known as ‘bioactive materials’ such as glasses, sintered hydroxyapatite, glass ceramics, composite materials, etc., have been synthesized and developed for medical applications. A significant characteristic of bioactive materials is their ability to bond with living bone through the formation of a hydroxyapatite (HA) interface layer. A recognized method to estimate the bone-bonding potential ability of material is simulated body fluid method (SBF), which involves immersing materials into SBF for bone-like apatite formation on its surface according to Kokubo et al. In other words, the behavior in vivo could be predicted by using SBF method in vitro. One remarkable success of bioactive ceramics as implant materials is the clinical use of sintered hydroxyapatite (HA) due to its bioactivity and osteoconductivity. However, the low fracture toughness of HA ceramic limits the scope of clinical applications. In recent years, more attentions have been focused on developing novel bioactive ceramics with improved properties. More recently, extensive interests have been shown in developing new bioactive inorganic materials containing CaO–SiO2 component for biomedical applications. Calcium silicate-based ceramics have received great attention as materials for bone tissue regeneration due to their excellent bioactivity. Compared to phosphate-based bioceramics, silicate bioceramics possess a wide range of chemical compositions and crystal structures, which contribute to their adjustable physicochemical properties, such as mechanical strength, bioactivity and degradation, providing them with suitable characteristics to be used as biomaterials. However, a major drawback of the CaSiO3 ceramics is their high dissolution rate, leading to a high pH value in the surrounding environment, which is detrimental to cells, which can be modified by incorporation of different elements such as Zn, Mg, Sr, Ti and Zr. In any case, the proposed approach can be extended to those more complex bioceramic compositions. In particular, due to the difficulties with sintering, silicate ceramics are generally obtained by complex techniques, such as the hydrothermal method, devitrification of glass, sol–gel processing, spark plasma-sintering, solution combustion processes etc. The sol–gel method is well suited for the preparation of complex ternary and quaternary silicate ceramics, as it allows for a precise control of the stoichiometry of the starting materials. However, it is of difficult industrialization, in the case of the fabrication of bulk components, because of the cost of the raw materials, the presence of large amounts of solvents and the associated drying problems. The current project is aiming at developing and fabricating of bioactive silicate-based ceramics from preceramic polymers (commercially available polymethylsiloxanes, silicones), and fillers (commercially available MgO, CaO, ZnO, TiO2, nano- and/or micro-particles), in the form of tablets, foams and 3D printed structures using additive manufacturing technology, to be used as bioactive scaffolds and biomaterials, thereby confirming that the proposed approach can be used to obtain components suitable for bone tissue regeneration. The incorporation of fillers, that generally can be passive or active, into the preceramic system is considered one of the most effective strategies to produce the silicate ceramics with different composition and structures as well as, to decrease the shrinkage and the formation of macro-defects in the produced ceramics. The approach of adding different oxide precursors (such as CaO and/or CaO, MgO and TiO2) as fillers enabled developing of different silicate bioactive ceramics (such as wollastonite (CaSiO3), hardystonite (Ca2ZnSi2O7), diopside (CaMgSi2O6) and sphene (CaTiSiO5)) as a result of the reactions between the preceramic polymers and these reactive fillers, occurring during the ceramization process and leading to the formation of specific crystalline phases with highly phase assemblage, that are known to be difficulty achievable by the conventional synthesis methods. A particular attention will be given to the production of open-celled porous components, to be employed as scaffolds for bone tissue engineering. These components will be prepared by various techniques, including unconventional direct foaming of silicone mixtures and additive manufacturing technology. Once the ceramic materials and scaffolds will be prepared, they will be fully characterized in terms of crystalline phase assemblage, physical and mechanical properties as well as microstructure analysis. The remarkable bioactivity of these scaffolds will be the main object of current investigations.
With the aging of populations and prolonged life expectancy, there is an increasing demand for bone grafts or synthetic materials that can potentially replace, repair or regenerate lost, injured or diseased bone. Tissue engineering (TE) is one of the approaches being investigated to tackle this problem. In common TE strategies, a three-dimensional structure, termed “scaffold”, fabricated from a suitable artificial or natural material. In bone tissue engineering, a scaffolding material is used either to induce formation of bone from the surrounding tissue or to act as a carrier or template for implanted bone cells or other agents. To serve as a scaffold, the material must be biocompatible, osteoconductive, and osteointegrative, and have enough mechanical strength to provide structural support during the bone growth and remodeling. Several attempts have been successfully made to construct porous scaffolds with desired porosity and appropriate mechanical performance from inorganic materials such as bioactive ceramics and glasses, from biodegradable polymers and their composites. The focus of biomaterial design for tissue engineering applications has recently been directed towards bioactive components that facilitate biomaterial integration and native tissue regeneration at the implant site. During the last four decades, various materials known as ‘bioactive materials’ such as glasses, sintered hydroxyapatite, glass ceramics, composite materials, etc., have been synthesized and developed for medical applications. A significant characteristic of bioactive materials is their ability to bond with living bone through the formation of a hydroxyapatite (HA) interface layer. A recognized method to estimate the bone-bonding potential ability of material is simulated body fluid method (SBF), which involves immersing materials into SBF for bone-like apatite formation on its surface according to Kokubo et al. In other words, the behavior in vivo could be predicted by using SBF method in vitro. One remarkable success of bioactive ceramics as implant materials is the clinical use of sintered hydroxyapatite (HA) due to its bioactivity and osteoconductivity. However, the low fracture toughness of HA ceramic limits the scope of clinical applications. In recent years, more attentions have been focused on developing novel bioactive ceramics with improved properties. More recently, extensive interests have been shown in developing new bioactive inorganic materials containing CaO–SiO2 component for biomedical applications. Calcium silicate-based ceramics have received great attention as materials for bone tissue regeneration due to their excellent bioactivity. Compared to phosphate-based bioceramics, silicate bioceramics possess a wide range of chemical compositions and crystal structures, which contribute to their adjustable physicochemical properties, such as mechanical strength, bioactivity and degradation, providing them with suitable characteristics to be used as biomaterials. However, a major drawback of the CaSiO3 ceramics is their high dissolution rate, leading to a high pH value in the surrounding environment, which is detrimental to cells, which can be modified by incorporation of different elements such as Zn, Mg, Sr, Ti and Zr. In any case, the proposed approach can be extended to those more complex bioceramic compositions. In particular, due to the difficulties with sintering, silicate ceramics are generally obtained by complex techniques, such as the hydrothermal method, devitrification of glass, sol–gel processing, spark plasma-sintering, solution combustion processes etc. The sol–gel method is well suited for the preparation of complex ternary and quaternary silicate ceramics, as it allows for a precise control of the stoichiometry of the starting materials. However, it is of difficult industrialization, in the case of the fabrication of bulk components, because of the cost of the raw materials, the presence of large amounts of solvents and the associated drying problems. The current project is aiming at developing and fabricating of bioactive silicate-based ceramics from preceramic polymers (commercially available polymethylsiloxanes, silicones), and fillers (commercially available MgO, CaO, ZnO, TiO2, nano- and/or micro-particles), in the form of tablets, foams and 3D printed structures using additive manufacturing technology, to be used as bioactive scaffolds and biomaterials, thereby confirming that the proposed approach can be used to obtain components suitable for bone tissue regeneration. The incorporation of fillers, that generally can be passive or active, into the preceramic system is considered one of the most effective strategies to produce the silicate ceramics with different composition and structures as well as, to decrease the shrinkage and the formation of macro-defects in the produced ceramics. The approach of adding different oxide precursors (such as CaO and/or CaO, MgO and TiO2) as fillers enabled developing of different silicate bioactive ceramics (such as wollastonite (CaSiO3), hardystonite (Ca2ZnSi2O7), diopside (CaMgSi2O6) and sphene (CaTiSiO5)) as a result of the reactions between the preceramic polymers and these reactive fillers, occurring during the ceramization process and leading to the formation of specific crystalline phases with highly phase assemblage, that are known to be difficulty achievable by the conventional synthesis methods. A particular attention will be given to the production of open-celled porous components, to be employed as scaffolds for bone tissue engineering. These components will be prepared by various techniques, including unconventional direct foaming of silicone mixtures and additive manufacturing technology. Once the ceramic materials and scaffolds will be prepared, they will be fully characterized in terms of crystalline phase assemblage, physical and mechanical properties as well as microstructure analysis. The remarkable bioactivity of these scaffolds will be the main object of current investigations.

Les matériaux nanocomposites poreux organisés présentent de nombreuses propriétés dans le domaine de l’adsorption. Cette étude est portée sur la synthèse de matériaux poreux de grande aire spécifique fonctionnalisés par des nanoparticules métalliques en visant des applications dans le domaine de l’adsorption: en phase liquide et en phase gazeuse.La première application concerne la détection en phase liquide de molécules à de faibles concentrations. Des nanocomposites composés d’une matrice poreuse de silice dans laquelle sont insérées des nanoparticules de métaux nobles (i.e. Ag@SiO2 et Au@SiO2) sont étudiés comme substrats SERS en couplant thermodynamique et spectroscopie Raman. Ce couplage de l’étude de la réponse Raman et de l’étude thermodynamique de l’adsorption a conduit à une meilleure compréhension de l’influence des particules sur le seuil de détection de la molécule. L’influence de plusieurs paramètres sur la réponse Raman de la molécule sonde et sur ses propriétés d’adsorption a aussi été étudiée (la taille des particules, la nature chimique du métal, etc.).La seconde application concerne le stockage d’hydrogène. Des nanocomposites composés de matrices poreuses de silice ou de carbone dans lesquelles sont incorporées des nanoparticules d’un métal de transition (i.e. Ni@SiO2 et Ni@Carbone) sont étudiés comme matériaux de stockage en couplant manométrie et microcalorimétrie d’adsorption. La mise en place d’une méthode de réduction adaptée a constitué une étape importante de ce travail. Ce couplage d’études thermodynamiques de l’adsorption a permis de déterminer les propriétés d’adsorption de l’hydrogène à basse température et basses pressions de ces matériaux
Nanocomposite organized porous materials present many properties in particular in the field of adsorption. This study was based on the synthesis of porous materials of high specific surface area functionalized with metal nanoparticles focusing in particular on two applications in the field of adsorption: one in the liquid phase and the other one in the gas phase.The first application is the detection of molecules in the liquid phase at low concentrations. Nanocomposites composed of a porous silica matrix in which are inserted noble metal nanoparticles (i.e. Ag@SiO2 and Au@SiO2) are studied as SERS (Surface Enhanced Raman Scattering) substrates by coupling thermodynamics and Raman spectroscopy. The coupling of the Raman response study and the thermodynamics of adsorption study leads to a better understanding of the influence of the particles on the molecule detection threshold. The influence of various parameters on the Raman response of the probe molecule and its adsorption properties were also studied (the particle size, the chemical nature of the metal, etc.)The second application relates to the storage of hydrogen since Nanocomposites composed of porous silica or carbon matrices in which are incorporated transition metal nanoparticles (i.e. Ni@SiO2 and Ni@Carbon) were studied as storage materials by coupling the adsorption manometry and microcalorimetry. The establishment of a suitable reduction method was an important step in this work. This coupling of thermodynamic studies of the adsorption was used to determine the adsorption properties of hydrogen at low temperature and low pressures of these materials

The paper concerns the study of formation of nanocomposites by electrochemical deposition of metals and semiconductors into the porous silicon. Ni and ZnO were used as experimental materials for deposition. The influence of deposition process parameters and structure of initial porous silicon substrates on morphology and composition of formed metal or semiconductor nanostructures are studied. Obtained nanocomposites demonstrated high filling factor and uniformity. Porous silicon/Ni nanocomposites showed strong magnetic anisotropy. Porous silicon/ZnO nanocomposites after thermal annealing had intensive photoluminescence in the visible range. Applications of obtained nanocomposites in the magnetic and optoelectronic devices discussed as well.

Three types of poly(norbornane carbonate) or PNC oligomers were synthesized and characterized via spectroscopic methods and elemental analyses to validate their chemical structures. Using the results from proton nuclear magnetic resonance (1H NMR) experiments, the degree of polymerization and size of each PNC chain was estimated via end-group analysis. All three types of PNC structures were both thermally-labile and acidolytically-labile, allowing them to be used as sacrificial materials in both direct-write and thermally-processed template systems. Thermogravimetric analysis (TGA) data was used to determine the kinetic parameters for the thermolytic decomposition reactions and evolved-gas analysis via mass spectrometry (TGA-MS) was used to determine the mechanisms for thermolytic degradation. PNC oligomers were freely-mixed with hydrogen silsesquioxane (HSQ) to form solutions that were spin-coated to form templated films. Transmission electron microscopy (TEM) showed that the free-mixing of PNCs with HSQ resulted in the agglomeration of the porogen molecules during the spincoating step. This phase-segregation produced domain sizes much larger than those of the individual chains, and during decomposition large pores were produced. To combat the phase segregation, hydrosilylation reactions were used to covalently bond vinyl end-capped PNC chains to silane-functionalized siloxane and silsesquioxane molecules. These matrix-like materials served as compatibilizers in order to improve the phase-compatibility of the sacrificial polymers in HSQ films. NMR and GPC analyses showed that the solids recovered from the hydrosilylation reactions were binary mixtures of hybrid nanocomposite molecules and residual ungrafted PNC chains. TEM imaging showed that the domains in these nanocomposite films had bimodal size distributions due to the presence of two components in the mixtures. The hybrid molecules produced pores ranging in size from about 6-13 nm as a result of improvements in the phase-compatibility of the grafted oligomers. However, the residual ungrafted oligomers in the blends produced larger domains measuring 30-40 nm. It is believed that separation difficulties can be avoided if the vinyl termination reaction conditions can be adjusted to ensure 100% conversion of all the terminal hydroxyl groups to vinyl groups. Doing so would allow all PNC chains to be grafted during hydrosilylation reaction; thus, avoiding the recovery of free PNC oligomers.

Ce travail a ete consacre a l'etude du transfert d'excitation dans les nanocomposites a base de silicium poreux. Le but etait d'etudier le couplage des porteurs photogeneres dans les nanocristaux de silicium avec leur environnement, liquide, solide ou gazeux. Nous presentons ici l'investigation par des methodes de luminescence continue et resolue dans le temps, de trois structures composites : * le silicium poreux dans sa solution acide de formation : un processus de photodissolution des couches poreuses sous lumiere est mis en evidence et caracterise ; dans ce cas, les porteurs fuient physiquement les cristallites pour participer a la reaction photochimique permettant le passage des atomes de silicium dans la solution. * le silicium poreux impregne de colorants laser : il est demontre que les couches poreuses peuvent etre utilisees comme matrice d'accueil passive (excitation directe des molecules) ou active (transfert d'excitation de la matrice vers les molecules via un couplage dipolaire). * le silicium poreux couvert de liaisons si-h : une conversion de l'energie optique en energie vibrationnelle via un couplage dipolaire entre les porteurs et les vibrations de surface a lieu. Le role important de la surface specifique est alors mis en evidence malgre l'origine quantique de l'emission. Il ressort de cette etude que le silicium poreux, malgre sa faible efficacite quantique, est une bonne matrice d'accueil, grace a sa porosite ouverte et a sa grande surface specifique, et qu'il possede les proprietes d'un donneur d'excitation.

Ce travail est consacre a la fabrication et a la caracterisation de structures nanocomposites silicium poreux/cds. Une etude approfondie de la chimie des solutions contenant des ions cd + + et l'utilisation d'un precurseur de soufre tres reactif, la thioacetamide, ont permis de mettre au point un procede de depot de cds adapte au silicium poreux (faible ph et temperature ambiante). Ce procede de depot, appele depot sequentiel, utilise deux bains separes : un premier bain pour l'adsorption d'hydroxyde de cadmium et un deuxieme bain pour la transformation de cet hydroxyde de cadmium en cds. L'utilisation de techniques de caracterisation comme la spectrometrie auger, la spectrometrie rutherford, la spectrometrie d'electrons ou la diffraction des rayons x confirme qu'il se forme du cds dans les pores du silicium ce qui conduit par ailleurs a la compression de la structure poreuse. La spectrometrie d'electrons et la spectroscopie infrarouge revelent que le materiau poreux est oxyde par les bains de depot, ce qui est probablement a l'origine de la perte de ses proprietes de luminescence. La methylation prealable du squelette poreux avant depot de cds permet d'eviter cette oxydation. Les couches nanocomposites ainsi obtenues conservent leur propriete de photoluminescence et permettent d'obtenir des structures electroluminescentes pour des polarisations electriques d'environ 2 volts, avec cependant un rendement qui reste faible.

This thesis has focused on the synthesis, characterization and catalytic applications of nanocomposite aerogels, made out of an active nanophase dispersed in a highly porous amorphous silica matrix. These nanocomposites have unique properties which mainly depend on the composition, size and distribution of the nanoparticles and on the morphology and porosity of the matrix. Highly porous MFe2O4-SiO2 (M = Co, Ni, Mn, Zn), NiCo2O4-SiO2, Fe/Mo-SiO2, CuO-SiO2, Cu2O-SiO2 e Cu-SiO2 nanocomposite aerogels, with variable amounts of dispersed phase, were prepared by a sol-gel procedure followed by supercritical drying and thermal treatments. This method is based on the co-hydrolysis and co-gelation of the precursors of the matrix and the dispersed phase through the pre-hydrolysis of the TEOS (tetraethoxysilane) under acid conditions followed by gelation under basic conditions, using urea as gelling agent. The detailed characterization of nanocomposite aerogels was carried out using a multitechnique approach involving conventional techniques, such as X-ray diffraction (XRD), nitrogen physisorption at 77 K and transmission electron microscopy (TEM), associated with more advanced techniques such as X-ray absorption spectroscopy (XAS), Mössbauer spectroscopy and SQUID magnetometry. These nanocomposites, thanks to their high porosity, low density and high area surface, were tested as catalysts in important industrial processes such as the synthesis of Carbon Nanotubes via Catalytic Chemical Vapour Deposition (CCVD) and the Water Gas Shift Reaction (WGSR), which plays an important role in the technology of fuel cells (FC), showing interesting catalytic activities. The tests for multiwall carbon nanotubes (MWCNT) production and for WGSR were performed in collaboration with the Applied and Environmental Chemistry Department of Szeged University (Hungary), the Chemistry Department of Rome University “La Sapienza” and the Chemical and Earth Science Department of Cagliari University.

Abstract My Ph.D. project focused on the tailoring of the surface properties of oxide substrates for the preparation of advanced composite materials and devices. The initial focus of my research activity was the surface modification of halloysite nanotubes (HNT), a natural material with unique structural features. I then extended my investigation to other oxides (titanium dioxide, TiO2, and Superparamagnetic Iron Oxide Nanoparticles, SPION), applying the surface modification approaches developed for HNT substrates. The resulting oxide-based hybrid systems showed promising properties as stimuli-responsive devices for health and environmental applications, and as fillers for polymeric nanocomposites with enhanced durability. The main results obtained for each oxide material will be presented in the following sections. 1. Halloysite nanotubes (HNT) Halloysite is a polymorph of kaolinite which naturally wraps itself to form tubular structures (Figure 1A). It is one of the few nanotubular systems presenting an inner lumen and an outer surface characterized by different surface charge and structural composition: the internal surface exposes aluminium hydroxyl groups, while the outermost layer is silica[1]. Among its many potential applications, its tubular dual structure has sparked interest in the field of nanomedicine and polymer nanocomposites[2]. However, only few reports investigated the possibility of a selective functionalization of the inner and outer HNT surfaces. During my first year of PhD, I investigated the selective functionalization of HNT with phosphonates, hetero-organic compounds bearing a C PO(OH)2 group, as potential site-specific linkers for the grafting of active molecules. I took advantage of the phosphonic acid selectivity towards certain oxides (especially aluminium oxides) to achieve surface-specific functionalization of HNT. An in-depth comprehension of such hybrid systems is no trivial matter, as the inner and outer HNT surfaces possess different accessibility and reactivity but are not separable. For this reason, beside HNT, I used purposely prepared model oxides, mimicking the inner and outer nanotube surfaces, to better study the actual selectivity towards SiO2 and AlOOH exhibited by the phosphonate moiety. Octylphosphonic acid (OPA) was chosen as functionalizing agent, as its alkyl chain allowed me to monitor the surface modification through changes in the water contact angle (θ). I found that the oxide isoelectric point (pHIEP) plays a major role in determining a stable OPA adsorption: while AlOOH showed good reactivity towards OPA, SiO2, which is negatively charged at the impregnation pH (pH 4), did not react with the phosphonate heads. The functionalization reversibility was also assessed: Samples showed OPA release at pH values more alkaline than the oxide isoelectric point, when the surface charge is negative. Overall, these results support an OPA-oxide bond governed both by electrostatic and covalent forces. The selective functionalization of HNT inner lumen was also demonstrated via a combination of characterization techniques, including FTIR spectroscopy, ζ-potential measurement and water dispersibility assay. Another scantly investigated topic regarding HNT nanosystems is their covalent modification. Covalent grafting allows for a superior control over the release kinetics of active principles, as the initial release burst observed in the case of electrostatically bound compounds is greatly reduced. In this respect, I studied the covalent attachment of a biologically active molecule to HNT via an imine bond. This type of covalent bond was chosen to open up the possibility for a controlled release of the bioactive molecule activated by pH changes. To this purpose, HNT was functionalized with (3 aminopropyl)triethoxysilane (APTES), a bifunctional linker which can cover the oxide surface with amino groups. Despite being non-selective for either of the two phases, it was chosen based on the relative ease with which it can be grafted to the substrate. Then, tetrathia[7]helicene aldehyde (7-THA) was bound to HNT via APTES, exploiting imine chemistry. 7-THA belongs to a group of polyaromatic molecules capable, thanks to their peculiar helicoidal shape, of intercalating DNA strands, which is at the basis of anti-sense therapy[3]. Nonetheless, HNT abysmal water solubility highly reduces their bioavailability and makes the use of hydrophilic nanocarriers necessary. I tested the relative release efficiency of 7-THA under slightly different pH conditions, representative of lysosomal, tumoral and healthy extracellular pH values. The resulting HNT-7TH system was studied in detail via XPS and angle-resolved near edge X-ray absorption fine structure spectroscopy (NEXAFS) at the Material Science Beamline of the Elettra synchrotron facility. The latter characterization technique required the synthesis and functionalization of oxide films replicating HNT surfaces, in order to probe the orientation of a population of adsorbed molecules with respect to the surface plane. NEXAFS results suggested a preferential orientation of the aromatic rings of helicene normal to the oxide surface, possibly as a result of π-π stacking interactions (Figure 1B). XPS analyses were performed at each stage of the preparation process of HNT-7TH and after the release test at pH 5 (Figure 1C): the observed change in the elemental composition indicated a release of 70% of the loaded 7-THA as a result of pH change. Given the interest for tumour therapy applications, in vitro tests were carried out to assess the selectivity of this system on cancer cells. The effect of HNT-7TH on the viability of bladder cancer cells was tested by Dr Riccardo Vago at the IRCCS San Raffaele Scientific Institute. Two different cell lines, named 5637 and HT-1376, with an extracellular pH of 7.2 and 6.8 respectively, were subjected to increasing concentrations of HNT 7TH and bare HNT as control. HNT 7TH was found to cause a more marked reduction in cell viability on the HT-1376 cell line, suggesting a faster release of the cytotoxic 7-THA at slightly acidic pH values. Release kinetics also supported this hypothesis: a new model system utilizing benzodithiophene (BDT), a more water-soluble mimic of 7-THA, was prepared analogously to the HNT-7TH powders. The release of BDT was monitored via UV-vis spectroscopy at pH 5.0, 6.8 and 7.4. The amount of released BDT at pH 7.4 was negligible even after 48 h; decreasing the pH value to 6.8 visibly increased release rates, while the release efficiency was highest for the treatment at pH 5.0. The natural origin of HNT causes a marked variability in its physicochemical features, such as its morphology and surface charge, depending on the extraction site[4]. I investigated this aspect, often overlooked in the literature, with respect to the integration of HNT as nanofillers in polymer composites. Halloysite has been investigated as filler owing to its low cost, thermal and mechanical resistance, and high aspect ratio, which is crucial to guarantee strong polymer-filler interactions[5]. In this regard, I investigated also the effect of surface functionalization in promoting HNT compatibility with the chosen polymer matrix, Polyamide 6 (PA6). PA6 has a broad range of applications, from the automotive sector to the textile industry, owing to its good mechanical performances and high thermal resistance. However, when exposed to humid conditions, it suffers from degradation in a matter of few weeks[6], as water can interpenetrate within the hydrogen bonds between –NH and C=O groups and disrupt them, leading to the loss of tensile strength and elasticity[6–9]. The addition of nanotubular fillers represents a viable strategy for overcoming this issue, although the additive/polymer interface at high filler content can become a privileged site for moisture accumulation[10]. For this reason, HNT were added to PA6 in very low amounts (< 5%w). The roles played in the reinforcement of the polymer by the physicochemical properties of HNT from two different sources and their functionalization with APTES were investigated in composites prepared by two different dispersion techniques (in situ polymerization vs. melt blending). The aspect ratio (5 vs. 15) and surface charge (−31 vs. −59 mV) of the two HNT samples proved crucial in determining their distribution within the polymer matrix: both in situ and melt blending dispersion techniques showed that lower surface area, higher aspect ratio and greater surface charge enhance filler incorporation and improve the final composite performance. Finally, filler surface modification with APTES played a major role in the durability of the PA6-HNT nanocomposites: after 1680 h of hydrothermal ageing, functionalized HNT reduced the diffusion of water into the polymer, lowering water uptake after 600 h up to 90%, increasing the materials durability. Positive effects could also be measured regarding the molecular weight distribution and rheological behaviour. These improvements could be related to the presence of amino groups on the HNT surface, which lowered the filler surface energy and prevented the diffusion of water molecules into the nanocomposites[11]. 2. Titanium dioxide TiO2 is arguably the most extensively investigated semiconductor for photocatalytic applications, from solar cells to pollutant abatement. However, applications of TiO2 for the preparation of smart surfaces are comparatively less common. My research interest in TiO2 started with the preparation of surfaces with controlled wetting features. First, the surface of commercial TiO2 powders was functionalized with perfluorinated alkylsilanes. Then, I employed the photocatalytic features of TiO2 films to produce patterned surfaces with superhydrophilic/superhydrophobic contrast by means of photocatalytic lithography. During the course of my second year of PhD, I focused on the deposition of TiO2 films with controlled porosity followed by their surface modification to impart them functional properties. These systems were applied as photo renewable coatings for electrochemical sensors and stimuli-responsive surfaces for the controlled release of active compounds. Control over film porosity was achieved by a hard-template approach using polystyrene (PS) nanospheres of different sizes, both commercial and synthesized in-house following a classical procedure[12]. Different film deposition strategies were investigated. First, I deposited a TiO2 layer on top of a porous SiO2 coating on a FTO electrode. Extensive characterization via cyclic voltammetry showed that the addition of a TiO2 layer increased peak currents due to the promoted diffusion of the analyte in the porous structure, driven by capillary effects[13] (Figure 2A). Furthermore, the TiO2 layer promoted the light-activated regeneration of the electrode surface after having been fouled. Starting from there, I investigated the possibility of pure TiO2 mesoporous films, a task made difficult by the intrinsic incompatibility between an alcohol-based TiO2 sol, extremely prone to hydrolysis, and a water-based PS suspension. This issue was solved by either adopting an aqueous TiO2 sol, slowly evaporated in presence of the particle templates (Figure 2B), or by performing a solvent exchange procedure on the PS suspension. The latter procedure resulted in pure TiO2 films with easily tuneable thickness and homogeneous porosity, opening the door to a fine tuning of the cyclovoltammetric response. The self-cleaning features of the pure TiO2 films were also tested by purposely fouling their surface with long-alkyl chain substituents: a fast and complete regeneration of the surface was achieved upon irradiation with UV light. The prepared pure TiO2 porous films were also used as substrates for the loading of bioactive substances. Cinnamaldehyde, a natural substance known for its antimicrobial properties but unstable in environmental conditions, was anchored to the film surface via APTES linkers through an imine bond, using a protocol similar to the one developed for 7-THA-loaded HNT. The immobilized cinnamaldehyde proved stable to environmental conditions for months and tests of pH triggered release performed at pH 5.5 and 7.4, showed a faster release at lower pH values. Finally, the photoactive nature of the oxide substrate could be used to promote the self-cleaning of the fouled surface after usage: after UV-light regeneration, the TiO2 film could be functionalized anew and reused. 3. Superparamagnetic Iron Oxide Nanoparticles (SPION) During my third year of PhD, I spent six months at the Technische Universiteit Delft, Netherlands, in the Advanced Soft Matter group, under the supervision of Dr Laura Rossi. There my research focused on the synthesis and surface modification of Ultrasmall SPION. SPION have gained increasing attention thanks to their peculiar behaviour: being smaller than a single magnetic crystal domain, they are free to rotate unless a specific orientation is induced by an external field. Due to their magnetic properties, they can be adopted in hyperthermia, drug delivery and as contrast agents (CA) for magnetic resonance imaging (MRI)[14]. Contrast agents are commonly used to speed up either T1 or T2 relaxation, enhancing the local contrast in pathological tissue to produce more detailed images. T1 CA are commonly represented by gadolinium complexes, while SPION are generally adopted as T2 CA. The first are preferred by radiologists, while the latter are less favoured because the darker tones they provide can be mistaken with low resolution and background interference[15,16]. Nonetheless, Gd-based CA present a serious health risk for those patients unable to efficiently remove these heavy metal complexes due to pre-existent kidney or liver pathologies[17]. While most SPION act as T2 CA, several papers report their potential use as T1 CA if their size is sufficiently small, indicatively less than 4 nm[18,19]. These materials are known as Ultrasmall SPION, or USPION. My aim was to develop a synthetic protocol to prepare USPION suitable as T1 contrast agents via co-precipitation, to minimize synthetic requirements. To this purpose, the influence of several parameters such as reaction temperature, base type, purification procedure, stabilizing agent and precursor concentration was investigated. Particles were synthesised at room temperature (RT) and 50°C, using NH4OH, N(CH3)4OH or NaOH as base. Particle purification was performed via magnetic decantation, centrifugation and dialysis against different solutions (water, citric acid and sodium citrate solutions). Sodium oleate, (3-aminopropyl)triethoxysilane (APTES) and citric acid were tested as stabilizing agents and precursor concentration was varied between 1 M and 0.5 M. It was found that the best results were obtained at room temperature and that the peptizing effect of the tetramethylammonium ion is crucial to guarantee an optimal colloidal stability, making N(CH3)4OH the base of choice. The concentration of starting precursor solutions proved to be the determining factor acting on particle size, as halving it led to a narrow particle size distribution centred around 3 nm, a significant shift from the starting 7 nm (Figure 3). Centrifugation was ineffective when adopted to wash the nanoparticles, but it proved a promising size-selection tool that could be combined with dialysis in an efficient work up protocol. Dialysis proved to be the most efficient technique to remove potentially toxic impurities, but it negatively impacted the colloidal stability, which could be mitigated by the use of a proper stabilizing agent. To preserve a high colloidal stability even after the removal of N(CH3)4OH, surface modification with several stabilizing agents was tested. Among the tested molecules, citric acid was the only one to show positive effects on particle size and aggregation, more so when added before the start of particle nucleation. These results represent a promising advance in the development of efficient T1 contrast agents based on USPION in terms of lowering the synthetic requirements: monodisperse magnetic nanoparticles were prepared through a simple co-precipitation procedure, performed at room temperature, without the aid of any polymeric additive. References [1] Y. Lvov, W. Wang, L. Zhang, R. Fakhrullin, Halloysite Clay Nanotubes for Loading and Sustained Release of Functional Compounds, Adv. Mater. 28 (2016) 1227–1250. doi:10.1002/adma.201502341. [2] E. Abdullayev, V. Abbasov, A. Tursunbayeva, V. Portnov, H. Ibrahimov, G. Mukhtarova, Y. Lvov, Self-healing coatings based on halloysite clay polymer composites for protection of copper alloys, ACS Appl. Mater. Interfaces. 5 (2013) 4464–4471. doi:10.1021/am400936m. [3] E. Licandro, S. Cauteruccio, D. Dova, Thiahelicenes, in: 2016: pp. 1–46. doi:10.1016/bs.aihch.2015.12.001. [4] E. Joussein, S. Petit, J. Churchman, B. Theng, D. Righi, B. Delvaux, Halloysite clay minerals – a review, Clay Miner. 40 (2005) 383–426. doi:10.1180/0009855054040180. [5] M.R. Ayatollahi, S. Shadlou, M.M. Shokrieh, M. Chitsazzadeh, Effect of multi-walled carbon nanotube aspect ratio on mechanical and electrical properties of epoxy-based nanocomposites, Polym. Test. 30 (2011) 548–556. doi:10.1016/j.polymertesting.2011.04.008. [6] I. Ksouri, O. De Almeida, N. Haddar, Long term ageing of polyamide 6 and polyamide 6 reinforced with 30% of glass fibers: physicochemical, mechanical and morphological characterization, J. Polym. Res. 24 (2017) 133. doi:10.1007/s10965-017-1292-6. [7] H. Shinzawa, J. Mizukado, Water absorption by polyamide (PA) 6 studied with two-trace two-dimensional (2T2D) near-infrared (NIR) correlation spectroscopy, J. Mol. Struct. 1217 (2020) 128389. doi:10.1016/j.molstruc.2020.128389. [8] K.R. Rajeesh, R. Gnanamoorthy, R. Velmurugan, Effect of humidity on the indentation hardness and flexural fatigue behavior of polyamide 6 nanocomposite, Mater. Sci. Eng. A. 527 (2010) 2826–2830. doi:10.1016/j.msea.2010.01.070. [9] D.P.N. Vlasveld, J. Groenewold, H.E.N. Bersee, S.J. Picken, Moisture absorption in polyamide-6 silicate nanocomposites and its influence on the mechanical properties, Polymer (Guildf). 46 (2005) 12567–12576. doi:10.1016/j.polymer.2005.10.096. [10] K.P. Pramoda, T. Liu, Effect of moisture on the dynamic mechanical relaxation of polyamide-6/clay nanocomposites, J. Polym. Sci. Part B Polym. Phys. 42 (2004) 1823–1830. doi:10.1002/polb.20061. [11] K. Prashantha, M.F. Lacrampe, P. Krawczak, Processing and characterization of halloysite nanotubes filled polypropylene nanocomposites based on a masterbatch route: effect of halloysites treatment on structural and mechanical properties, Express Polym. Lett. 5 (2011) 295–307. doi:10.3144/expresspolymlett.2011.30. [12] J.W. Goodwin, J. Hearn, C.C. Ho, R.H. Ottewill, Studies on the preparation and characterization of monodisperse polystyrene latices, Colloid Polym. Sci. 252 (1974) 464–471. [13] L. Rimoldi, V. Pifferi, D. Meroni, G. Soliveri, S. Ardizzone, L. Falciola, Three-dimensional mesoporous silica networks with improved diffusion and interference-abating properties for electrochemical sensing, Electrochim. Acta. 291 (2018) 73–83. doi:10.1016/j.electacta.2018.08.131. [14] J. Dulińska-Litewka, A. Łazarczyk, P. Hałubiec, O. Szafrański, K. Karnas, A. Karewicz, Superparamagnetic Iron Oxide Nanoparticles—Current and Prospective Medical Applications, Materials (Basel). 12 (2019) 617. doi:10.3390/ma12040617. [15] Y. Okuhata, Delivery of diagnostic agents for magnetic resonance imaging, Adv. Drug Deliv. Rev. 37 (1999) 121–137. doi:10.1016/S0169-409X(98)00103-3. [16] J.-C. Brisset, M. Sigovan, F. Chauveau, A. Riou, E. Devillard, V. Desestret, M. Touret, S. Nataf, J. Honnorat, E. Canet-Soulas, N. Nighoghossian, Y. Berthezene, M. Wiart, Quantification of Iron-Labeled Cells with Positive Contrast in Mouse Brains, Mol. Imaging Biol. 13 (2011) 672–678. doi:10.1007/s11307-010-0402-1. [17] M. Rogosnitzky, S. Branch, Gadolinium-based contrast agent toxicity: a review of known and proposed mechanisms, BioMetals. 29 (2016) 365–376. doi:10.1007/s10534-016-9931-7. [18] H. Wei, O.T. Bruns, M.G. Kaul, E.C. Hansen, M. Barch, A. Wiśniowska, O. Chen, Y. Chen, N. Li, S. Okada, J.M. Cordero, M. Heine, C.T. Farrar, D.M. Montana, G. Adam, H. Ittrich, A. Jasanoff, P. Nielsen, M.G. Bawendi, Exceedingly small iron oxide nanoparticles as positive MRI contrast agents, Proc. Natl. Acad. Sci. 114 (2017) 2325–2330. doi:10.1073/pnas.1620145114. [19] Y. Bao, J.A. Sherwood, Z. Sun, Magnetic iron oxide nanoparticles as T 1 contrast agents for magnetic resonance imaging, J. Mater. Chem. C. 6 (2018) 1280–1290. doi:10.1039/C7TC05854C.

Ce memoire presente l'etude de differents nanocomposites de silicium. Dans une premiere approche nous introduisons par electrochimie des semiconducteurs ii-vi dans des couches de silicium poreux. Les conditions de co-depot de cdte et znse sont prealablement etudiees sur electrode metallique puis sur silicium. Le depot de cdte est tres cristallin mais il degrade fortement la luminescence des couches de silicium poreux. Le depot de znse est amorphe mais preserve en revanche la photoluminescence du silicium poreux. On montre que pour des substrats de silicium de type n, le depot se realise preferentiellement en haut de la couche poreuse. Ce resultat est explique par le fait que le processus electrochimique est limite par la diffusion des especes en solution. Nous avons mis au point une localisation du depot en utilisant un eclairement infrarouge de substrats de type p pour que les electrons necessaires aux reactions electrochimiques soient generes dans la partie inferieure des couches. Le depot se propage depuis l'interface silicium poreux/silicium massif vers le sommet de la couche. Un contact intime du depot de znse avec les cristallites de silicium est mis en evidence. Les proprietes electro-optiques des nanocomposites znse/silicium formes sont nettement ameliorees par rapport aux couches simples de silicium poreux. Dans une seconde approche, des couches de silicium amorphe sont partiellement cristallisees. Pour des couches simples, un pre-traitement avec un plasma d'hydrogene accelere la cristallisation. La photoluminescence dans le domaine visible est attribuee a une diminution de la concentration de defauts dans le gap et non a un effet de confinement quantique. Des multicouches de nanocristaux de silicium dans de la silice ont aussi ete realisees ; l'hysteresis qui est observee dans les caracteristiques c-v de ces dispositifs est attribuee au blocage de coulomb des electrons dans les nanocristaux. La realisation de memoires non-volatile est demontree.

A produção de elementos filtrantes para água a partir de polímeros é bastante difundida no mercado, mas possui uma característica indesejada: nem sempre são eficientes e capazes de reter ou eliminar microorganismos presentes. O presente trabalho propõe-se a produzir filtros com propriedade biocida compostos por nanocompósitos de polietileno de ultra alta massa molar (PEUAMM), modificados com surfactante não iônico e nanopartículas de prata, sendo os polímeros responsáveis pela estrutura porosa uniforme dos filtros e as nanopartículas de prata incorporadas nos elementos filtrantes pela ação biocida. Os polímeros particulados foram classificados por peneiramento e apresentaram duas curvas granulométricas distintas de 150 a 200?m e de 300 a 400?m, sendo posteriormente utilizados para a sinterização dos elementos filtrantes. As nanopartículas de prata foram incorporadas aos elementos filtrantes, obtendo-se corpos de prova que foram caracterizados através do uso das técnicas de difratometria de raios-X, microscopia eletrônica de varredura, microanálise por espectroscopia de raios-X por dispersão de energia. Foram também realizadas avaliações dos elementos filtrantes através de ensaios de ação biocida, vazão e taxa de filtração e presença de extraíveis. Os resultados obtidos indicaram a formação do nanocompósito e diferentes propriedades foram observadas para os elementos filtrantes em função da porosidade alcançada.
The production of polymer based filter elements for water is widespread in the market but has an undesirable characteristic: they are not always efficient and capable of retaining or eliminating microorganisms. This paper proposes the production of filters with biocidal activity, composed by nanocomposites of ultra high molar mass polyethylene (UHMMPE), modified by non-ionic surfactant and silver nanoparticles. The polymers are responsible for the uniform porous structure of the filters and the silver nanoparticles for its biocidal action. The particulate polymers were classified by sieving and presented two distinct grain size ranges, one of 150 to 200?m and the other of 300 to 400?m. Samples were collected from the prepared filter elements and characterized by X-ray diffractometry, scanning electron microscopy and microanalysis. Evaluation of the filter elements were also carried out and their biocidal activity was tested, as well as the flow and filtration rates and the presence of extractables were determined. The results indicate the formation of the nanocomposite and different properties were observed for the filter elements according to its porosity.

La réalisation de nanocomposites à propriétés optiques non linéaires importantes à base de silicium poreux (ou silice poreuse) et de polymères conjugués est très intéressante. En effet, on peut facilement intégrer cette technologie à celle de la microélectronique. Nous présentons tout d'abord, la caractérisation de la matrice en silicium poreux ainsi que celle en silice poreuse. Nous avons déterminé les caractéristiques physico-chimiques de nos matrices ainsi que leurs morphologies. Ensuite, nous avons introduit des matériaux actifs à l'intérieur des pores. Nous avons rempli électrochimiquement le silicium poreux par le poly(3-alkylthiophène) : PT12 et nous avons réalisé un nanocomposite de silice poreuse remplie par le poly(diacétylène para toluène sulfonate) : PDA-TS. Les propriétés optiques non linéaires intéressantes de ces nanocomposites ont été mises en évidence. Nous avons aussi rempli des guides plans par ces deux méthodes, et par la même, obtenu un guide optique actif
Nanocomposites containing porous silicon (or porous silica) and conjugated plymers have been realized. They present significant nonlinear optical properties. Indeed, one can easily integrate this technology into micro-electronics. We first present the characterization of the porous silicon and the porous silica matrices. We have determined the physicochemical characteristics of our matrices and their morphologies. Then, we have introduced optically active materials within the pores. We filled electrochemically the porous silicon by poly(3-alkylthiophène): PT12 and we obtained a nanocomposite with porous silica filled by the poly(diacetylene para toluene sulphonate): PDA-TS. The interesting nonlinear optical properties of these nanocomposites are highlighted. We have also built up planar guides by these two methods. We obtained an active waveguide

Orientador: Oswaldo Luiz Alves
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica
Made available in DSpace on 2018-07-22T05:19:50Z (GMT). No. of bitstreams: 1 Zarbin_AldoJoseGorgatti_D.pdf: 5488325 bytes, checksum: e58549cb8bdbe80c1f5fef703a1fc617 (MD5) Previous issue date: 1997
Doutorado

O objetivo do presente trabalho é o desenvolvimento de nanocompósitos de silício poroso/azul de metileno (PS/MB) utilizando-se substratos de silício macroporoso e mesoporoso para sua aplicação no monitoramento de gases orgânicos. Foram estudados processos de formação de PS/MB usando PS macroporoso e controlando o pH da solução. Os resultados obtidos indicam que a acidez da solução compromete a adsorção eficiente das moléculas de MB, sendo necessário a utilização de uma solução tampão para elevar o nível do pH. A necessidade de controlar o nível de pH da solução deve-se principalmente à característica ácida da superfície de PS recém formada, já que a superfície está constituída principalmente de ligações do tipo Si-Hx que são altamente hidrofóbicas. Os resultados da emissão fotoluminescente (PL) das estruturas de PS/MB em substrato de PS oxidado mostraram que a intensidade de emissão PL das moléculas de MB é mais intensa se comparada com a emissão das moléculas de MB em solução aquosa de baixa concentração. Esse resultado evidencia que a interação entre os elétrons p e a superfície do filme de PS otimiza a recombinação radiativa, minimizando possíveis caminhos não radiativos do estado excitado da molécula de MB. Adicionalmente, o resultado mostrou que as moléculas de MB adsorvidas sobre substratos de PS oxidados preservam suas características moleculares, atuando em forma monomérica. No caso de moléculas MB adsorvidas em substratos de PS não oxidados, os espectros de emissão PL mostraram que as moléculas de MB perderam sua identidade molecular formando, possivelmente, complexos na superfície do PS. Os resultados dos ensaios de adsorção das moléculas de MB em substratos de silício mesoporoso demonstraram ser mais eficientes quando o solvente utilizado foi o etanol, em condição de pH neutro. A monitoração de ambientes de vapores orgânicos foi efetuada através da resposta PL de uma estrutura de silício mesoporoso oxidado com moléculas de MB adsorvidas (Ox- PS/MB). Os resultados da emissão PL da estrutura Ox-PS/MB para os diferentes ambientes orgânicos apresentaram sinais de PL característicos para cada tipo de gás. Esses resultados mostraram o grande potencial de aplicação da estrutura Ox- PS/MB em um sistema de nariz óptico.
The objective of the present work is the porous silicon/methylene-blue (PS/MB) nanocomposite fabrication by using the macro-porous and mesoporous silicon substrate in order to be applied for organic solvent detection. The PS/MB formation process was studied PS/MB by using the macroporous silicon substrate by the pH value controlling of the solution moieties. The results showed that the acid condition of the solution compromises the efficiency of the MB adsorption wherever it was necessary to use the buffer in order to control the pH level of the solution. This additional process was a necessary condition because the fresh PS surface had had acid feature because the surface moieties at fresh PS are formed for the highly hydrophobic Si-Hx bonds. The PL spectra results from the PS/MB formed at oxidized PS substrate showed that the PL emission from the adsorbed MB molecules is more intense than the emission from the MB molecules in low concentrated solution. These results suggest that the PS surface and electrons p (in the MB) interaction minimizes the non-radioactive path for the excited state recombination of the MB molecules. Additionally this result showed that the adsorbed MB molecules preserved their molecular identity aging as a monomer moiety. In the case of the MB adsorbed at non-oxidized PS substrate, the PL spectra showed that the MB molecules lost their identity forming possible complex moieties at PS surface. The experimental results of the MB adsorption at the mesoporous silicon surface showed to be more efficient when the solution was ethanol at neutral pH value. The organic vapor ambient monitoring was made throughout the PL emission response of the Ox-PS/MB structure. These results showed that the PL emission had had the characteristic feature for each type of gas used in the experiment. These results showed the high potential application of the Ox-PS/MB structure in the optical nose system.

La grande surface développée du silicium poreux fait de lui un hôte potentiel pour l'incorporation de molécules organiques. Les nanocomposites hybrides à base de molécules conjuguées luminescentes pourraient se prêter à des applications en optoélectronique.
L'étude comprend deux parties : la première est consacrée à l'étude morphologique et optique des couches minces et des membranes auto-supportées de silicium poreux fabriquées au laboratoire en utilisant la microscopie électronique, l'ellipsométrie spectroscopique et l'absorption. L'analyse microstructurale des couches poreuses par diffusion Raman nous a permis d'estimer la distribution de tailles des nanocristallites via le modèle de confinement des phonons et de confirmer l'absence de porteurs de charges libres. Une étude de Raman polarisé sur des membranes poreuses libres permet de sonder les inhomogénéités de propagation de la lumière dans ce milieu.
La seconde partie présente les études concernant l'imprégnation de molécules fluorescentes dans les pores. La photoluminescence donne un moyen de vérifier l'efficacité de l'incorporation de molécule de Rodhamine R6G et son homogénéité. L'excitation sélective permet une approche des transferts d'énergie entre les deux matériaux. La photoluminescence résolue en temps montre que la présence de la R6G crée de nouveaux canaux de désexcitation non radiative.
Le THD est incorporé dans des membranes libres rendues organophiles, puis polymérise spontanément in situ en son poly-Diacétylène. La variation angulaire de la photoluminescence et du Raman témoignent de la présence de chaînes de polymères dont le degré d'orientation est compatible avec une croissance le long des pores.

Orientador: Oswaldo Luiz Alves
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
Made available in DSpace on 2018-07-27T12:31:41Z (GMT). No. of bitstreams: 1 Oliveira_MarcelaMohallem_M.pdf: 7740897 bytes, checksum: 61f78edf222c0d4e9f7e7c50d0e31031 (MD5) Previous issue date: 2000
Mestrado

This PhD project aims to address the low energy storage issues of electrode materials for supercapacitors through morphological and defect engineering. The key scientific contribution in this thesis includes: revealing the superior intrinsic electrochemical properties of NiCo-sulfide to hydroxide/oxides, demonstrating a facial defect engineering to enhance electrochemical properties of CoxNi1-xS2 by low temperature plasma, developing a new method for synthesis of high-performance carbon material derived by biomass.

Les couches minces monocomposites carbone/métal, constituées de nanoparticules métalliques dans une matrice de carbone amorphe, présentent des propriétés physico-chimiques spécifiques et modulables selon leur microstructure et composition. La morphologie et la microstructure de ces matériaux sont explorées sur une grande plage de composition chimique en utilisant des techniques de microscopie électronique, EDX, XPS, DRX et spectroscopie Raman. L'influence de la nature du métal sur la microstructure et les propriétés électriques des couches minces nanocomposites métal/carbone a été étudiée pour deux métaux : le nickel et le cuivre. Les couches ont été déposées par deux procédés plasmas différents : l'un combinant la pulvérisation cathodique magnétron de la cible métallique (nickel ou cuivre) et le dépôt chimique en phase vapeur assisté par plasma de méthane et d'argon, et l'autre consistant en la pulvérisation simultanée de la cible métallique et d'une cible de graphite. L'étude des propriétés électriques de ces matériaux met en évidence un phénomène de percolation électrique des grains métalliques. Les propriétés du catalyseur pour la croissance des nanotubes de carbone et de piézorésistivité des couches à base de nickel ont été étudiées. Une nouvelle méthode de synthèse de couches de carbone nanoporeuses, par gravure sélective du cuivre contenu dans les couches nc-Cu/C, a aussi été élaborée
Nanocomposite metal/carbon thin films, consisting of metal rich nanoparticles embedded in an amorphous carbon matrix, present specific and tunable physicochemical properties, depending on the chemical composition of thin films. The morphology and the microstructure of these materials have been explored on a wide range of chemical composition using electronic microscopy, EDX, XPS, XRD, and Raman spectroscopy. The influence of the metal nature on the nanocomposite metal/carbon thin film microstructure and electrical properties was studied for two metals : nickel and copper. The thin films were deposited using two different plasma processes : a first one combining the magnetron sputtering of the metal target (nickel or copper) and the plasma enhanced chemical vapour deposition in an argon/methane gas mixture, and the other one consisting in the cosputtering of metal and graphite targets. The study of the electrical properties highlighted an electrical percolation phenomenon. The catalytic properties for the carbon nanotubes growth and the piezoresistive behavior of nickel based thin films were studies. In addition, an original method based on the selective etching of copper nanoparticles contained in nc-Cu/C thin films was developed, leading to the synthesis of nanoporous carbon electrodes

Ce travail de thèse est réalisé en cotutelle entre l‟IMN de Nantes (France) et UTCM de Sofia (Bulgarie) dans le cadre d‟une bourse du Gouvernement Français. Il consiste en l‟élaboration et caractérisation de nouveaux nanocomposites à base d‟une matrice de silicium poreux remplie avec des polymères qui présentent des propriétés optique non linéaires pour des applications de télécommunication, pour le traitement du signal optique en mode tout optique ultrarapide. Après une brève bibliographie, nous présentons une première partie de nos études qui consiste en l‟élaboration de la matrice en silicium poreux soit de type dopé p, soit dopé n, qui doit répondre aux besoins optiques : avoir une porosité élevée, des pores dans l‟échelle « mésoporeux » (20-50nm) et une épaisseur de la couche poreuse la plus importante possible. La morphologie et les caractéristiques physico-chimiques sont déterminées par différentes techniques de caractérisation. Une seconde partie traite des possibilités de modifier la nature chimique de la surface poreuse par oxydation et greffage d‟organosilanes fluoré ou aminé, pour optimiser le remplissage de la couche poreuse. Enfin la dernière partie présente la réalisation des nanocomposites à matrice de silicium poreux avec le poly (terthiophène-acide acétique) et ses complexes. Nous avons mis en évidence le remplissage par une nouvelle méthode - à la fusion. Une approche des mesures optiques a été menée pour montrer les propriétés optique non linéaires de ce matériau
This work is realized in partnership between IMN in Nantes (France) and UCTM in Sofia (Bulgaria) financed by a French Government Scholarship. It consists in the elaboration and characterization of new nanocomposites based on a porous silicon matrix filled with polymers showing non linear optical properties used in the field of telecommunication. The tendency of communications networks is to use devices for ultrafast optical signal processing. Following à short bibliography, we present the first section of our work, which is the elaboration of porous silicon matrix from p and n doped silicon. This matrix must have a high porous volume, mesoporous diameter (20-50 nm) of the pores and the highest thickness. The morphology and the physicochemical characterization of our matrix are determined by different methods. In the second section we have optimized the chemical properties of the porous silicon surface by oxidation and surface modification with fluorinated and amino organosilanes to enhance the filling of the porous layer. Finally we have obtained a nanocomposite with a porous silicon matrix and poly (terthiophene-acetic-acid) and its complexes. The filling of the porous layer is realized by a new melting-based method. Primary measurements have been carried out to demonstrate the nonlinear optical properties of these nanocomposites

As the miniaturization of functional devices in integrated circuit (IC) continues to scale down to sub-nanometer size, the process complexity increases and makes materials characterization difficult. One of our research effort demonstrates the development and application of novel Multiple Internal Reflection Infrared Spectroscopy (MIR-IR) as a sensitive (sub-5 nm) metrology tool to provide precise chemical bonding information that can effectively guide through the development of more efficient process control. In this work, we investigated the chemical bonding structure of thin fluorocarbon polymer films deposited on low-k dielectric nanostructures, using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Complemented by functional group specific chemical derivatization reactions, fluorocarbon film was established to contain fluorinated alkenes and carbonyl moieties embedded in a highly cross-linked, branched fluorocarbon structure and a model bonding structure was proposed for the first time. In addition, plasma induced damage to high aspect ratio trench low-k structures especially on the trench sidewalls was evaluated both qualitatively and quantitatively. Damage from different plasma processing was correlated with Si-OH formation and breakage of Si-CH3 bonds with increase in C=O functionality. In another endeavor, TiN hard mask defect formation after fluorocarbon plasma etch was characterized and investigated. Finding suggest the presence of water soluble amines that could possibly trigger the formation of TiN surface defect. An effective post etch treatment (PET) methods were applied for etch residue defect removal/suppression.

Le procédé sol-gel non-hydrolytique (SGNH) offre une alternative intéressante au procédés sol-gel classiques. Notamment, la « voie éther », impliquant la réaction de précurseurs chlorures ou oxychlorures avec avec un éther comme donneur d’oxygène, est une méthode simple et efficace pour la préparation d’oxydes et d’oxydes mixtes mésoporeux. Les batteries Li-ion sont omniprésentes aussi bien dans des applications portables que pour des véhicules électriques ou hybrides. Cependant, les performances des électrodes commerciales sont insuffisantes pour des applications haute puissance. TiO2 est un candidat prometteur pour remplacer les anodes de graphitie dans les batteries Li-ion, mais sa conductivité électronique doit être améliorée. L’objectif de ce travail de thèse est d’utiliser les avantages du procédé SGNH pour préparer des matériaux d’électrodes à base de TiO2. Deux approches ont été explorées, mettant en jeu la voie éther en l’absence de tout solvant ou additif. Premièrement, des oxydes mésoporeux à structure hiérarchique, TiO2 et TiO2-V2O5, ont été synthétisés par calcination des xérogels. Deuxièmement, des nanocomposites mésoporeux constitués de nanoparticules de TiO2 recouvertes d’un film de carbone ont été obtenus par pyrolyse sous atmosphère d’argon, l’éther jouant le rôle de donneur d’oxygène et aussi, pour la première fois, de source de carbone. Les matériaux ont été caractérisés par physisorption d’azote, microscopie électronique, DRX, spectroscopie Raman, ATG ainsi que par RMN 13C CPMAS pour les nanocomposites. Les performances en insertion-désinsertion du lithium ont été étudiées par cyclage galvanostatique à différentes densités de courant
Non-hydrolytic sol-gel (NHSG) provides useful alternatives to conventional sol-gel routes. In particular, the ether route based on the reaction of chloride or oxychloride precursors with ether oxygen donors is a well-established method for the preparation of mesoporous oxides and mixed-oxides. Li-ion batteries are ubiquitous in the field of electrochemical energy storage, from mobile devices to electric and hybrid vehicles. However, commercial electrode materials do not fulfill all the requirements needed for high-power applications. TiO2 is as a promising material to replace graphite anodes in high-power Li-ion batteries, despite its poor electronic conductivity, which must be improved. In this context, the objective of this PhD thesis is the conception of different TiO2-based electrode materials benefitting from NHSG advantages. Two different approaches were developed, using the ether route in the absence of any solvent or additive. First, hierarchical mesoporous oxides, TiO2 and TiO2-V2O5, were synthesized by calcination of xerogels in air. Secondly, mesoporous nanocomposites built of carbon-coated TiO2 nanoparticles were obtained by pyrolysis under argon of the xerogels; in this case, the ether is used for the first time as both as an oxygen donor and a carbon source. The texture and the structure of the resulting materials were characterized by N2 physisorption, electron microscopy, XRD, and Raman spectroscopy. TiO2/C samples were further analyzed by TGA and 13C CPMAS-NMR. Galvanostatic cycling at different current rates was performed to determine the electrochemical performances in lithium insertion-deinsertion

Ce travail porte sur la réalisation et la caractérisation d'électrodes pour piles à combustible (PAC). L'approche bottom-up adoptée associe par voie liquide des nanoparticules de platine enrobées par des molécules (NP) et des nanotubes de carbone (NT) préformés afin d'obtenir une dispersion liquide de nanocomposite. Ce procédé permet de contrôler dans une large gamme la couverture des nanotubes de carbone par les nanoparticules de platine. Puis, par filtration sur feutre de carbone nous obtenons des électrodes de PAC avec des couches actives de compositions très diverses (1 à 300 g Pt/cm², épaisseurs de 10 à 80 µm). Nous avons ensuite qualifié ex situ ces électrodes à l'aide de paramètres pertinents dont l'un est directement associé à la réduction de l'oxygène. Nous avons utilisé la voltampérométrie cyclique dans les conditions où les électrodes sont imprégnées d'électrolyte et calculé ces paramètres pour chaque électrode. Des différences observées dans ces paramètres entre deux méthodes d'imprégnation des électrodes ont révélé l'importance des modulations de mouillabilité des couches actives avec le rapport massique NP/NT et la nature de l'enrobage des nanoparticules. Cela débouche sur la possibilité de réaliser des électrodes modèles permettant à terme d'optimiser la gestion des points triples et donc l'utilisation du catalyseur dans les électrodes de PAC. Des tests en pile avec nos électrodes illustrent ainsi la possibilité de diminuer à l'avenir de manière très significative les densités de platine dans les PAC.

Dans cette étude, nous avons cherché à développer de nouvelles formulations pour améliorer la stabilité thermique et le comportement au feu de trois matrices polymères de grande diffusion: le polyéthylène (PE), le polystyrène (PS) et le polyamide 66 (PA66). Le système intumescent employé consiste à combiner des retardateurs de flammes classiques (polyphosphate d’ammonium (APP) et pentaérythritol (PER)) avec une faible quantité de nanooxydes métalliques dont les propriétés auraient été ajustées sur mesure de façon à améliorer la compatibilité du mélange à l’état fondu, ou encore pour changer le mécanisme de dégradation d’un point de vue chimique (effets catalytiques) ou physiques (effet barrière, viscosité etc…). Une partie importante de cette étude a donc été d’abord consacrée à la synthèse d’oxydes à morphologie, porosité, structure ou fonctionnalités particulières. A cet égard, les silices mésoporeuses possèdent l’avantage de présenter des surfaces spécifiques élevées (700-1400 m²/g) et une taille de pores compatible avec les chaines polymères. En adaptant les conditions de synthèse, nous avons cherché à établir des relations entre certains paramètres relatifs aux silices préparées (tels que la (1) surface spécifique (2) la taille des particules (3) la taille des pores (4) la morphologie et (5) le type de structure (en général SBA-15)) sur la stabilité thermique et le comportement au feu du polyéthylène. Préalablement, les propriétés texturales, structurales et chimiques de ces silices ont été caractérisées par porosimétrie à l’azote à 77K, DRX et FTIR. Globalement, les améliorations apportées par les silices mésostructurées restent modestes par rapport à celles induites par les RF classiques seuls et ceci particulièrement pour les polymères non charbonnants (PE et PS). Ceci est dû probablement à la très grande disparité des teneurs respectives en silice et RF dans les composites testés (1 et 24% en masse, respectivement). L’effet du taux de silice SBA-15 (0,5-10wt%) à taux de charge constant et égal à 25% massique a été également étudié pour les trois matrices polymères. Les valeurs maximales d’IOL (indice limite d’oxygène) sont toujours obtenues pour 1-2% de SBA-15. Les modifications de surface des silices SBA-15 par greffage des différentes fonctions organiques (CTAB, amine, thiol, phénol, phosphonate, acide benzoïque et diphénylphosphate), inorganiques (aluminium, acide phosphorique et acide tungstophosphorique) ou métalliques (cuivre, nickel) ont fait l’objet de caractérisations poussées afin d’évaluer la quantité et la stabilité thermique des espèces greffées ainsi que la nature des liaisons de surface. D’autres types de nanooxydes synthétiques (aluminophosphates, phosphate de zirconium et nanotubes de type titanates) ou commerciaux (CeO2, ZrO2, CeZr et CePr) ont également été étudiés. La plupart de ces échantillons a montré un effet légèrement positif sur la stabilité thermique et le comportement au feu des polymères. De point de vue mécanistique, les analyses réalisées en Py-GC-MS montrent que les oxydes greffés par des acides catalysent la transformation des alcènes et des diènes issus de la décomposition du PE en aromatiques. En présence de SBA-15, l’analyse des résidus carbonés (par DRX, FTIR) montrent la formation de nouvelles phases cristallines phosphosiliciques qui renforcent la couche protectrice. Les phases condensées et gazeuses de quelques formulations performantes en IOL ont été analysée par cône calorimètre et microcalorimètre (PCFC). La substitution d'une fraction d'APP/PER par de la silice SBA-15 a un effet plus marqué sur la stabilité thermique et le comportement au feu de la matrice PA66 (IOL= 48,5 (+10 par rapport au PA66/APP/PER), comparé aux matrices PE (IOL=25 (+0,5 par rapport au PE/APP/PER) et PS (IOL= 24,1 (+0,8 par rapport au PS/APP/PER). De plus, la fonctionnalisation [...]
In this study, we have tried to develop new formulations to improve the thermal stability and fire behavior of three polymer matrices widely used: the polyethylene (PE), the polystyrene (PS) and the polyamide 66 (PA 66). The intumescent system used consists to combine a classical flame retardants (ammonium polyphosphate (APP) and pentaeryhthritol (PER)) with a small amount of nanooxides whose properties can be adjusted in order to improve the compatibility of the melting mixture, or to change the degradation mechanism by a chemical (catalytic effect) or physical (insulating layer, viscosity, etc …) process. The total amount of additives has been set at 25wt%. An important part of this study was consecrated to the synthesis of oxides with different morphologies, porosities, structures and functionalities. In this regard, the mesoporous silica has an advantage of having a high surface area (700-1400 m²/g) and a pore size compatible with the polymer chains. By adapting the synthesis conditions, we have aimed to correlate between some parameters related to the prepared silicas (such as (1) the specific surface area (2) particle size (3) pore size (4) morphology and (5) the type of structure (usually SBA-15)) on the thermal stability and fire behavior of different polymer matrices. A comprehensive study has been conducted globally, regardless of the matrix, that the improvements provided by the mesostructured silicas are modest compared to those elicited by classical FR. However, the fire behavior has been improved (particularly LOI) by combining APP/PER system with 1-2wt% of SBA-15. The surface modification of SBA-15 by grafting a different organic functions (CTAB, amine, thiol, phenol, phosphonate, benzoic acid and diphenylphosphate), inorganic species (aluminum, phosphoric acid and tungstophosphoric acid) or metals (copper, nickel) have been the subject of an advanced characterizations in order to assess the amount and the thermal stability of the grafted species, well as the nature of the surface bonds. Other types of synthetic nanooxides (aluminophosphates, zirconium phosphate and titanate nanotubes) or commercial (CeO2, ZrO2, CeZr and CePr) have been also studied. Most of these particles in combination with APP/PER system have shown a slightly positive effect on the thermal stability and fire behavior of polymers. In mechanistic terms, the nanooxides have mainly an effect on enhancing the barrier effect. The analyses carried out by Py/GC/MS showed that the grafted oxides by acidic species catalyze the conversion of alkenes and dienes (resulting from the decomposition of PE) to aromatics. In the presence of SBA-15, the analysis of char (by XRD and FTIR) shows the formation of new crystalline phases which enhance the protective layer

碩士
中原大學
化學研究所
94
Epoxy resin is widely used as matrix materials for fabrication of the advanced composites in the electrical/electronic industry, owning to their high tensile strength and modulus, good adhesive properties, good chemical and corrosion resistance, low shrinkage in cure, and excellent thermal and dimensional stability. As we known, it is one of the most-used synthetic resins today. In this research, we will focus on preparation and property of epoxy resin (Triphenylolmethane triglycidyl ether, TGTPM) nanocomposite materials and epoxy resin porous materials. This essay is divided into two parts. In the first part, epoxy resin nanocomposite materials studies on two types of intercalated or/and exfoliated silicate platelets were allowed to disperse in tri-functional epoxy matrix cured tri-functional amine hardener (T-403) followed by a typical ring opening polymerization. The different dispersing forms of these silicate platelets by in situ along with the PCN materials may alter their gas barrier, thermal stability, mechanical strength, and fire retardant properties. The Φ3P+-C12-modified clay PCN materials showed superior corrosion protection compared to Me3N+-C16-modified when tested for performance in series of electrochemical measurements of corrosion protection, polarization resistance, corrosion current and impedance spectroscopy. At the same time, molecular (e.g. O2 and H2O) permeability results also support the products of electrochemical measurements. Heat-distortion, and dynamic mechanical properties were also investigated the difference between both PCN materials (TECP system and TECN system). The results of TECP system owns high glass transition temperature and mechanical behavior were found by DSC, DMA. Moreover, thermal stability and flame retardant properties were evaluated, and TECP system exhibits high results. The TGA, and LOI shall identity, respectively. The second part, epoxy resin porous materials will be researched. High performance epoxy resin plays an important role as insulating materials in manufacturing components. In order to increase the application of epoxy resin, some drawbacks associated with epoxy networks like high dielectric constant values (3.8-4.5) must overcome. And a porous structure can make it. In this case, the epoxy resin of micro- / macro- voids were formed in poly(ethyl glycol), PEG, which was according to “solvent-casting particulate leaching” and “molecularly imprinting polymer”. The cavitation is later established, when PEG is extracting, leaving behind empty pores. As a result, a reduction in dielectric constant from 4.11 to 2.89 is realized simply by replacing the polymer with air which has a dielectric constant of 1. At the same time, the value of dielectric loss decreased to 0.03. The phenomenon shows that epoxy resin porous material has an ability of “electrical/electronic damping” indistinctly. Furthermore, permeability is a property which defines the resistance to the penetration of aggressive substance, such as light, electron, heat…etc. The first difference on appearance transfers from clear to opaque. The epoxy resin with its pores structure, showed a high R% and low permeability values which are measured by UV-vis of R%. This result means the porous material can stop the sunlight, and might be a well divided material. On the other hand, a lowering of thermal transport properties (e.g. thermal conductivity and thermal diffusivity) which investigates by transient plane source (TPS) technique. The report also shows obviously a reduction in thermal transport properties of porous epoxy resin, that attributed to the incorporation of air exists into matrix. Effects of those abilities on porous epoxy resin were done an excellent adiabatic material.

博士
國立雲林科技大學
工程科技研究所
106
In typical dye-sensitized solar cells (DSSCs), a porous nanocrystalline TiO2 photoanode plays the important role for mass dye-loading and electrons transport. However, the power conversion efficiency of DSSCs is limited by that the charge recombination during the electron transport in the porous nanocrystalline TiO2 photoanode and partial light harvesting from incident light. Therefore, we propose the ZnO nanorods arrays/TiO2 nanoparticles (ZnO NRs/TiO2 NPs) and deformed TiO2 aggregates/Au nanoparticles (DTA/AuNPs) composite films as the photoanode, according to the good electron affinity of ZnO NRs, the high specific surface area, light scattering of DTA and the Schottky barrier effect of plasmonic AuNPs. In this study, the features of ZnO NRs/TiO2 NPs and DTA/AuNPs composite films have been demonstrated by using scanning electron microscope (SEM), transmission electron microscope (TEM), x-ray diffractometer (XRD), UV-Visible spectrophotometer, and specific surface area/pore size distribution analyzer. The photovoltaic performances and electrochemical impedances of DSSCs with ZnO NRs/TiO2 NPs and DTA/AuNPs photoanodes are also investigated by using the solar cell measurement system with a solar simulator and the electrochemical impedances spectroscopy. The photovoltaic performances of DSSCs with ZnO NRs/TiO2 NPs photoanode annealed at 550˚C has the best fill-factor of 44 and power conversion efficiency of 0.19%. The DSSCs with DTA/AuNPs based photoanode exhibit a high Jsc of 7.58 mA/cm2, a Voc of 0.78V, a fill-factor of 59.31 and a power conversion efficiency of 3.06%, which suggests that the enhancement of short-circuit current density and power conversion efficiency would be contributed by sufficient specific surface area for dye loading and the long electron lifetime in the photoanode film.

Anodisation is a surface treatment process, commonly used to form a protective oxide coating on the surface of metals like aluminium. Anodised coatings, being grown out of the base metal have excellent interface strength but are porous and brittle. Porosity of the coating reduces the hardness and the brittle nature of the oxide induces cracking. In practice, the pores are typically filled with organic dye and sealed. Under certain controlled electrochemical conditions, anodisation results in a highly ordered hexagonal porous structure in pure aluminium. In this work, we explore the possibility of using this ordered porous alumina to form a novel metal nanocomposite as a tribological coating. By optimizing the nonporous structure and tuning the electrodeposition process, we uniformly filled the ordered pores with copper. We have measured the hardness of the resulting ordered and aligned nanocomposite. We explore the possibility of using this composite coating for tribological applications by carrying out some preliminary reciprocating wear test. Ordered porous alumina layer is formed by a two-step anodisation process. By optimizing the anodisation conditions, we control the thickness of the coating and the pore size. The interface of the porous structure and aluminium substrate is defined by a non-conducting dense barrier oxide layer. However, to deposit metal into the pores, a conducting path should be established through the barrier layer. One possibility is to etch out the bottom of the pores at the cost of the interface strength and losing out on the main advantage of anodised coatings. To be able to fill metal without this sacrifice, we utilised the dendritic structure in the barrier layer formed by a step-wise reduction of voltage towards the end of anodisation process. Optimisation of this dendritic structure led to uniform deposition of metal into pores, achieved by pulsed electrodeposition. In pulse lectrodeposition, a positive pulse is applied to remove accumulated charge near to the bottom of pores, followed by a negative pulse to deposit metal and a delay to allow diffusion of ions. By optimising the pulse shape and duration, we have achieved uniform growth of metal into pores. Further, monitoring the deposition current helped us to identify and control different phases of growth of the nanowire. The properties of the porous alumina and the nanocomposite were measured by nanoindentation. The deformation characteristics were obtained by observing the indents in a FE-SEM. We find that dendritic modification of interface has very little effect on the hardness of the porous alumina layer. We also found that the porous alumina deformed either by compaction or by forming circumferential and radial cracks. When copper is filled in the nano pores, the hardness increased by 50% and no circumferential cracks were found up to the load of 10 mN for a film thickness of about 1 µm. Coefficient of friction of the coating reciprocated against steel in dry condition is found to be around 0.4. Minimal wear was observed from the SEM images of wear track. In summary, a novel nanocomposite coating with ordered porous alumina as matrix embedded with aligned metal nano rods has been developed. This was achieved by optimally modifying the barrier layer without sacrificing the interfacial strength. Uniform coating has been achieved over an area of 10 mm x 10 mm. The coating is found to have high hardness and high wear resistance.

Anodisation is a surface treatment process, commonly used to form a protective oxide coating on the surface of metals like aluminium. Anodised coatings, being grown out of the base metal have excellent interface strength but are porous and brittle. Porosity of the coating reduces the hardness and the brittle nature of the oxide induces cracking. In practice, the pores are typically filled with organic dye and sealed. Under certain controlled electrochemical conditions, anodisation results in a highly ordered hexagonal porous structure in pure aluminium. In this work, we explore the possibility of using this ordered porous alumina to form a novel metal nanocomposite as a tribological coating. By optimizing the nonporous structure and tuning the electrodeposition process, we uniformly filled the ordered pores with copper. We have measured the hardness of the resulting ordered and aligned nanocomposite. We explore the possibility of using this composite coating for tribological applications by carrying out some preliminary reciprocating wear test. Ordered porous alumina layer is formed by a two-step anodisation process. By optimizing the anodisation conditions, we control the thickness of the coating and the pore size. The interface of the porous structure and aluminium substrate is defined by a non-conducting dense barrier oxide layer. However, to deposit metal into the pores, a conducting path should be established through the barrier layer. One possibility is to etch out the bottom of the pores at the cost of the interface strength and losing out on the main advantage of anodised coatings. To be able to fill metal without this sacrifice, we utilised the dendritic structure in the barrier layer formed by a step-wise reduction of voltage towards the end of anodisation process. Optimisation of this dendritic structure led to uniform deposition of metal into pores, achieved by pulsed electrodeposition. In pulse lectrodeposition, a positive pulse is applied to remove accumulated charge near to the bottom of pores, followed by a negative pulse to deposit metal and a delay to allow diffusion of ions. By optimising the pulse shape and duration, we have achieved uniform growth of metal into pores. Further, monitoring the deposition current helped us to identify and control different phases of growth of the nanowire. The properties of the porous alumina and the nanocomposite were measured by nanoindentation. The deformation characteristics were obtained by observing the indents in a FE-SEM. We find that dendritic modification of interface has very little effect on the hardness of the porous alumina layer. We also found that the porous alumina deformed either by compaction or by forming circumferential and radial cracks. When copper is filled in the nano pores, the hardness increased by 50% and no circumferential cracks were found up to the load of 10 mN for a film thickness of about 1 µm. Coefficient of friction of the coating reciprocated against steel in dry condition is found to be around 0.4. Minimal wear was observed from the SEM images of wear track. In summary, a novel nanocomposite coating with ordered porous alumina as matrix embedded with aligned metal nano rods has been developed. This was achieved by optimally modifying the barrier layer without sacrificing the interfacial strength. Uniform coating has been achieved over an area of 10 mm x 10 mm. The coating is found to have high hardness and high wear resistance.

碩士
明志科技大學
材料工程系碩士班
105
In this study, Ta-Cu and TaN-Cu films were first prepared using reactive co-sputtering processes. After deposition, the films were annealed in order to cause the emergence of Cu phase. After characterization on these films, Cu phase was further etched away to form specially aligned nano-porous Ta and TaN (p-Ta and p-TaN) structures. These films with and without etching were characterized using four-point probe, nano-indentation, XRD, and FE-SEM. The results showed that the porosity of these films could be varied depending on Cu contents. P-Ta films have elastic modulus in the range of 0.4–1.3 GPa, which is closer to that of natural cortical bone (12–18 GPa) and cancellous bone (0.1–0.5 GPa). For the most commonly used implant materials, it is noticed that the modulus is much higher, ex: titanium alloy (106–115 GPa). The p-Ta samples were then treated using rapid thermal annealing (RTA) process to form oxide and oxy-nitride in various atmospheres. At final, these nano-porous samples are tested for their biocompatibility and viability using MG-63 cells. According to the experimental results, some important conclusions can be drawn. Firstly, the formed p-Ta had a horizontally aligned porous structure. Secondly, p-Ta thin films can be transformed into porous Ta2O5 and porous TaOxNy. Thirdly, the porous tantalum-based films have similar structure and surface roughness. With these characteristics, it can be demonstrated that the biocompatibility of the films is affected by the chemical composition, rather than surface roughness. Lastly, compared with Ta films, the porous Ta, TaOxNy and Ta2O5 are more elastic in its mechanical behaviors.

Tese de doutoramento em Ciências (área de especialização em Física)
Electroactive polymer composites are interesting materials for advance technological applications due to the possibility to combine the electroactive properties of the polymer matrix with a large variety of fillers that allow tailored responses for specific applications. The best all-around electroactive polymers are poly(vinylidene fluoride) (PVDF) and its copolymers which allied with the properties of porous zeolite materials, with tailored shape, size and Si/Al ratio, among others, leads to the possibility of development of promising PVDF/zeolite composites. In this way, a study of the structural, thermal and electrical properties of PVDF composites prepared with different framework zeolite types (LTL, LTA, FAU and MFI), different polymer solvents (DMF, DMSO, TEP) and different zeolite (NaY) concentrations (4, 16, 24 and 32 wt %) was performed. Further, the dielectric response, electrical conductivity and electric modulus of the composites were investigated as a function of NaYzeolite content. The zeolite influence on the electroactive γ-phase crystallization of PVDF was explored, as well as the effect of clay layered structure (Montmorillonite, Kaolinite and Laponite) on the electroactive γ-phase nucleation and on the optical transparency of the composite. It was found that the obtained composites showed an electrical response dependence on the pore structure and chemical content of the inorganic host. The dielectric response of the composites is directly related to the Si/Al ratio, leading zeolites with lower Si/Al ratios to larger dielectric responses and encapsulation efficiencies in the composites. It was also found that the zeolite content strongly influences the macroscopic response of dielectric response, which increases for increasing filler content. The dielectric constant at room temperature reaches values larger than 1000 for the 32 wt.% composite at 1 kHz what is mainly attributed to restricted ion mobility and interfacial polarization effects due to the zeolite inclusion, leading also to high dielectric losses. For the higher zeolite concentrations the composite d.c. electrical conductivity is characterized by two conducting regimes separated by a concentration independent breaking voltage of 4 V, which is associated to an intrazeolite charge transport. Dielectric relaxation studies show that the main relaxation process (β-relaxation) of the amorphous phase of the polymer matrix is not affected by the presence of the zeolite and, in a similar way, the zeolite low temperature relaxation is not significantly affected by the polymer phase. On the other hand, the electric modulus formalism reveals significant contributions of the fillers to the electrical permittivity and conductivity of the composites. The presence of the zeolite particles increases a.c. conductivity and the Maxwell-Wagner-Sillars contribution that is predominant at low frequencies with respect to the ohmic contribution to permittivity. The ability of zeolites to induce the eletroactive γ-phase nucleation of PVDF is directly dependent on the Si/Al ratio and zeolite content; however it only occurs when the composite is melted at temperatures below 200 ºC. The complete γ-phase crystallization of the polymer crystalline phase occurs for a filler content of 16 wt% of LTA or FAU zeolite structure. The even higher surface interaction of clays when exfoliated leads to the same phenomenon with an amount of 0.50 % of Montmorillonite clay content. The electroactivity of the material has been proven by measuring the piezoelectric d33 response of the material, which presents a value of −7 pC/N, lower than for β-PVDF obtained by mechanical stretching but still among the largest coefficients obtained for polymers. Further, the optical transmittance in the visible range is strongly enhanced with respect to the transmittance of the pure polymer. The development, characterization and physical-chemical understanding of these PVDF/zeolite and PVDF/clay composites resulted in suitable materials for applications in diverse areas including battery separator membranes and biomedical applications.
Os compósitos poliméricos electroativos são materiais muito interessantes para aplicações tecnológicas devido à possibilidade de combinar as propriedades electroativas da matriz polimérica com uma larga variedade de materiais que deste modo permitem a manipulação das suas respostas para as fazer adequadas a aplicações específicas. De entre os poucos polímeros electroativos, as melhores respostas são obtidas no poli(fluoreto de vinilideno) (PVDF) e nos seus copolímeros que, aliados às propriedades dos materiais porosos de zeólitos, com forma, tamanho e razão Si/Al modificáveis, entre outras características, leva à possibilidade de desenvolver compósitos promissores de PVDF/zeólitos. Deste modo, foi efetuado um estudo das propriedades estruturais, térmicas e elétricas dos compósitos de PVDF preparados com diferentes tipos de zeólitos (LTL, LTA, FAU e MFI), diferentes solventes do polímero (DMF, DMSO, TEP) e diferentes concentrações de zeólito (NaY) (4, 16, 24 e 32 % em peso). Foi ainda investigada a resposta dielétrica, condutividade eléctrica e modulo elétrico dos compósitos em função da concentração do zeólito NaY. A influência do zeólito na cristalização da fase electroativa γ do PVDF foi explorada, bem como o efeito da estrutura lamelar das argilas (Montmorillonite, Kaolinite e Laponite) na nucleação da fase-γ e na transparência ótica do compósito. Descobriu-se que os compósitos obtidos exibiam uma resposta elétrica dependente da estrutura porosa e da composição química dos compostos inorgânicos encapsulados. A resposta dielétrica dos compósitos está diretamente relacionada com a razão Si/Al, levando a que os zeólitos com uma baixa razão Si/Al apresentem elevadas respostas dielétricas e maior eficiência de encapsulamento no compósito. Foi também descoberto que o teor de zeólito influencia fortemente a resposta dielétrica macroscópica, aumentando com a concentração de zeólitos no compósito. A constante dielétrica à temperatura ambiente atinge valores superiores a 1000 para o compósito com 32 % em peso de NaY a 1kHz, o que é atribuído principalmente à mobilidade iónica restrita e a efeitos de polarização interfacial devido à inclusão de zeólito, levando também a grandes perdas dielétricas. Para concentrações de zeólito elevada, a condutividade elétrica d.c. do compósito é caracterizada por dois regimes de condutividade separados por um potencial de disrupção de 4 V, independente da concentração, que está associado ao transporte de carga intrazeólito. Estudos de relaxação dielétrica mostram que o processo de relaxação β da fase amorfa da matriz polimérica não é afetada pela presença do zeólito e, de um modo semelhante, a relaxação de baixa temperatura do zeólito não é afetada significativamente pela presença da fase polimérica. Por outro lado, o formalismo do modulo elétrico revela contributos relevantes das inclusões para a permitividade elétrica e condutividade dos compósitos. A presença das partículas de zeólito aumenta a condutividade a.c. e a contribuição Maxwell-Wagner-Sillars que predomina a baixas frequências relativamente à contribuição ohmica para a permitividade. A capacidade dos zeólitos induzirem a nucleação da fase eletroativa γ do PVDF depende diretamente da razão Si/Al e da quantidade de zeólito; contudo, apenas se verifica quando o compósito é fundido a temperaturas inferiores a 200 ºC. A cristalização completa em fase γ pode ocorrer para uma concentração de 16% das estruturas de zeólito LTA ou FAU. A ainda maior superfície de interacção das argilas, quando exfoliadas, resulta no mesmo fenómeno com uma concentração de 0.5% de argila Montmorillonite. A eletroatividade do material foi comprovada através da medição da resposta piezoelétrica d33 do material, que apresenta um valor de –7 pC/N, mais baixo do que o de β-PVDF obtido por estiramento mecânico mas ainda entre os maiores coeficientes piezoelétricos obtidos para polímeros. Mais ainda, a transmitância ótica na gama visível é fortemente melhorada relativamente à transmitância do polímero puro. O desenvolvimento, caracterização e compreensão físico-química destes compósitos PVDF/zeólito e PVDF/argila resultou em materiais adequados para aplicações em áreas diversas que incluem membranas para baterias e aplicações biomédicas.

Nanoemulsions are templates that have the potential to fill the gap between micellar systems and latex particles in the preparation of porous materials. A nanoemulsion can also be used as a carrier for uploading the desired materials inside the pore formed after the removal of the template. In this research, oil-in-water (O/W) nanoemulsions were prepared by means of a low-energy method based on a phase inversion composition (PIC) technique, using two nonionic surfactants (Tween 80 and Span 80), which can be mixed in order to adjust the hydrophilic-lipophilic balance (HLB). The influence of a number of parameters on the tunability and stability of such nanoemulsions was also studied. The effect of the simultaneous intercrossing of multifactors on droplet size was explored using a process- mixture design, and the size of the nanoemulsion oil droplets was measured by means of dynamic light scattering (DLS). The nanoemulsions were combined with sol-gel method in order to prepare porous silica with a macroporosity in the 50 nm to 400 nm range. The results demonstrate that a precise synergy between the silica source and the nanoemulsions is essential for effective interactions and homogeneous structures. Depending on the nature of such interactions, a variety of materials were observed, from hollow particles to continuous gels. Changing the size of the oil droplet and the volume of the nanoemulsions produced silica with differing pore sizes and varying total pore volumes. The obtained hierarchical porous silica (HPS) were characterized using mercury porosimetry, small angle X-ray scattering (SAXS), nitrogen isotherms, Fourier transform infrared (FTIR) analysis, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The parallel use of the oil vesicles as containers for the further synthesis of metal oxide is a novel method of internally functionalizing the silica. When hydrophobic metal precursors are dissolved into the oil phase before the preparation of the nanoemulsion, they are confined within the globular cavities of the silica. The thermal treatment applied to the material to burn the organics then leads to the final formation of metal oxide nanoparticles, which are larger than the porosity of the silica matrix but entrapped within the large cavities, producing a "rattle-like" structure. This method was demonstrated through the synthesis of Fe2O3, Fe3O4, and Co3O4 nanoparticles, and the results showed that a rather large amount of metal oxide (up to a 60 wt.% of metal oxide in nanocomposites) be generated while still maintaining the nanometric size observed at lower concentrations. This method allows control of the type of metal oxide, the concentration of the metal oxide, and the pore size, which enables the creation of different types of nanocomposites. Metal oxide hierarchical porous silica (MHPS) nanocomposites were characterized based on nitrogen isotherms, TEM and SEM observations, FTIR analysis, X-ray diffraction (XRD), and Mossbauer spectroscopy. Magnetic measurements were also taken. This new method, using the new templating objects, is a perfect illustration of the concept of "integrative synthesis,??? whereby the combination of building units and reactional mechanisms leads to complex structures as a result of true synergy among the elements during the reaction. In this case, the size of the nanoemulsion and the total water volume both contribute to the generation of distinctive architectures. In addition, the reaction of the metal oxide precursors within the cavities limits the extension of the final crystal size, but the surrounding solid matrix plays a role as well by keeping the particles apart. The final factor is that the reactive materials cannot leak from the silica because of the rattle-like structure, but the reagents can reach those particles through the porosity of the silica framework.