Philosophiae Doctor - PhD / This work investigated the synthesis of Al2O3-coated TiO2 nanotubes via the anodisation technique for application in DSCs. TiO2 nanotube arrays with an average length of 15 μm, diameter of 50 nm and wall thickness of 15 nm were synthesised via anodisation using an organic neutral electrolyte consisting of 2 M H2O + 0.15 M NH4F + ethylene glycol (EG) at an applied voltage of 60 V for 6 hours. In addition, scanning electron microscope (SEM) micrographs showed that anodisation at these conditions yields nanotubes with smooth walls and hexagonally shaped, closed bottoms. X-ray diffraction (XRD) patterns revealed that the as-anodised nanotubes were amorphous and as such were annealed at 450 °C for 2 hours in air at atmospheric pressure, which yielded crystalline anatase TiO2 nanotubes. Highresolution transmission electron microscope (TEM) images revealed that the nanotube walls comprised of individual nano-sized TiO2 crystallites. Photoluminescence (PL) spectroscopy showed that the optical properties, especially the bandgap of the TiO2 nanotubes are dependent on the crystallinity, which in turn was dependent on the structural characteristics, such as the wall thickness, diameter and length. The PL measurements were supplemented by Raman spectra, which revealed an increased in the quantum confinement of the optical phonon modes of the nanotubes synthesised at low anodisation voltages, consequently yielding a larger bandgap The annealed nanotubes were then coated with a thin layer of alumina (Al2O3) using a simple sol-gel dip coating method, effectively used to coat films of nanoparticles. Atomic force microscopy (AFM) showed that the average nanotube diameter increased post sol-gel deposition, which suggests that the nanotubes are coated with a layer of Al2O3. This was confirmed with HR-TEM, in conjunction with selected area electron diffraction (SAED) and XRD analyses, which showed the coating of the nanotube walls with a thin layer of amorphous Al2O3 with a thickness between 4 and 7 nm. Ultraviolet-visible (UVvis) absorbance spectra showed that the dye-adsorption ability of the nanotubes are enhanced by the Al2O3 coating and hence is a viable material for solar cell application. Upon application in the DSC, it was found by means of photo-current density – voltage (I – V) measurements that a DSC fabricated with a 15 μm thick layer of bare TiO2 nanotubes has a photon-to-light conversion efficiency of 4.56%, which increased to 4.88% after coating the nanotubes with a layer of alumina. However, these devices had poorer conversion efficiencies than bare and Al2O3-coated TiO2 nanoparticle based DSCs, which boasted with efficiencies of 6.54 and 7.26%, respectively. The low efficiencies of the TiO2 nanotube based DSCs are ascribed to the low surface area of the layer of nanotubes, which yielded low photocurrent densities. Electrochemical impedance spectroscopy (EIS) showed that the electron lifetime in the alumina coated nanotubes are almost 20 times greater than in a bare layer of nanoparticles. In addition, it was also found that the charge transfer resistance at the interface of the TiO2/dye/electrolyte is the lowest for an Al2O3-coated TiO2 layer.

This thesis presents the results of computer simulation studies of the structure, dynamics, and deformation of cross-linked polymer gels. Obtaining a fundamental understanding of the interrelation between the detailed structure and the properties of polymer gels is a challenge and a key issue towards designing materials for specific purposes. A new off-lattice method for constructing a closed network is presented that is free from defects, such as looping chains and dangling ends. Using these model networks in Brownian dynamics simulations, I show results for the structure and dynamics of bulk gels and describe a novel approach using spherical boundary conditions as an alternative to the periodic boundary conditions commonly used in simulations. This algorithm was also applied for simulating the diffusion of tracer particles within a static and dynamic network, to illustrate the quantitative difference and importance of including network mobility for large particles, as dynamic chains facilitate the escape of particles that become entrapped. I further investigate two technologically relevant properties of polymer gels: their stimuli-responsive behaviour and their mechanical properties. The collapse of core-shell nanogels was studied for a range of parameters, including the cross-linking degree and shell thickness. Two distinct regimes of gel collapse could be observed, with a rapid formation of small clusters followed by a coarsening stage. It is shown that in some cases, a collapsing shell may lead to an inversion of the core-shell particle which exposes the core polymer chains to the environment. This thesis also explores the deformation of bimodal gels consisting of both short and long chains, subject to uniaxial elongation, with the aim to understand the role of both network composition as well as structural heterogeneity on the mechanical response and the reinforcement mechanism of these materials. It is shown that a bimodal molecular weight distribution alone is sufficient to strongly alter the mechanical properties of networks compared to the corresponding unimodal networks with the same number-average chain length. Furthermore, it is shown that heterogeneities in the form of high-density short-chain clusters affect the mechanical properties relative to a homogeneous network, primarily by providing extensibility.

Grâce aux plasmons de surface des nanoparticules métalliques et aux propriétés optiques et électroniques des quantum dots (QDs), les nanostructures QD/métal suscitent beaucoup d'intérêt. Cependant, bien que prometteurs, les hybrides QD/or colloïdaux n'ont été que rarement obtenus.Nous avons mis au point la première méthode de synthèse généralisée conduisant à des structures hybrides cœur/coque/coque QD/SiO2/Au (appelées QDs dorés). Tout d'abord, les QDs hydrophobes sont encapsulés individuellement dans des billes de silice par émulsion inverse. Les nanoparticules obtenues sont ensuite recouvertes d'une coque d'or continue via un processus de dépôt en solution. Les épaisseurs de silice et d'or peuvent être ajustées indépendamment aux dimensions voulues. Nous avons montré que les QDs dorés individuels à base de QDs CdSe/CdS à coque épaisse possèdent une émission stable et poissonienne à température ambiante et sont très photostables. Cette nouvelle structure se comporte comme un résonateur plasmonique avec un facteur de Purcell élevé (~6), en très bon accord avec les simulations.Nous présentons également des auto-assemblages de QDs hydrophobes en superparticules (SPs). Un choix judicieux de QDs donne aux SPs des propriétés exceptionnelles telles qu'une émission de fluorescence intense, non-clignotante et multicolore. Des SPs multifonctionnelles peuvent aussi être obtenues en associant des nanocristaux magnétiques et fluorescents. La croissance d'une coque de silice sur les SPs a permis d'augmenter leur stabilité et nous avons démontré que cette couche de silice pouvait être recouverte d'une coque d'or pour améliorer la photostabilité et la biocompatibilité de ces SPs. / Due to the surface plasmons in metallic nanostructures and the exceptional optical and electrical properties of colloidal semiconductor quantum dots (QDs), QD/metal hybrid nanostructures attract much attention. However, although these structures are very promising, colloidal single QD/gold hybrids have rarely been synthesized.We managed to develop for the first time a generalized synthetic route to synthesize a QD/SiO2/Au core/shell/shell hybrid structure (golden QDs). First, hydrophobic QDs are individually encapsulated in silica beads via reverse microemulsion. The obtained QD/SiO2 nanoparticles are then coated with a continuous gold nanoshell using a solution deposition process. The thicknesses of the silica and the gold layers can be tailored independently to various dimensions. We showed that single golden thick-shell CdSe/CdS QDs provide a system with a stable and poissonian emission at room temperature and a high photostability. This novel hybrid golden QD structure behaves as a plasmonic resonator with a strong (~ 6) Purcell factor, in very good agreement with simulations. We also present the self-assembly of hydrophobic QDs into colloidal superparticles (SPs). With a fine choice of QDs, SPs could indeed possess outstanding properties including non-blinking fluorescence, high fluorescence intensity and multi-color emission. Multi-functional SPs could also be obtained by mixing fluorescent or magnetic nanocrystals. The subsequent growth of a silica shell on the SPs allowed an enhancement of their stability and we demonstrated this silica shell could itself be covered by a gold nanoshell to further improve the SPs photostability and biocompatibility.

<p>U ovom radu sintetisani su kompozitni nanoprahovi i nanoprahovi tipa jezgro&ndash; omotač sa dielektričnom i magnetnom fazom, kao pogodan polazni materijal za procesiranje kompozitne keramike za primenu u mikroelektronici. Osnovni cilj ove doktorske disertacije je bio utvrđivanje veza između uslova sinteze, morfologije čestica, uslova procesiranja i mikrostrukture kompozitne keramike. Nanoprahovi su sintetisani hemijskim metodama sinteze u tečnoj fazi (sol-gel i koprecipitacija) i gasnoj fazi (CVS), pri čemu je vr&scaron;ena optimizacija procesnih uslova u cilju sinteze čestica željene strukture i hemijskog sastava. Istraživanja su vr&scaron;ena na nekoliko modelnih sistema sa feritima kao magnetnom fazom i titanatima ili silikom kao dielektričnom fazom: NiFe2O4SiO2, Fe3O4SiO2, SrTiO3NiFe2O4, BaTiO3NiFe2O4 i BaTiO3Fe3O4. Hemijska sinteza u tečnoj fazi se pokazala pogodnom zato &scaron;to pruža mogućnost kontrolisanja morfologije kompozitnih čestica ne samo pode&scaron;avanjem procesnih parametara sinteze već i funkcionalizacijom faza kojom se uzrokuje njihovo elektrostatičko privlačenje i formiranje strukture jezgro&ndash;omotač. Ipak, zbog velikog stepena aglomeracije prisutnog tokom sinteze u tečnoj fazi, dobijanje omotača uniformne debljine i izbegavanje homogene nukleacije faza se pokazalo te&scaron;ko. Hemijskom sintezom u gasnoj fazi (CVS) je po prvi put sintetisan kompozitni nanoprah na bazi kompleksnih oksida titanata i ferita.<br />Utvrđeno je da i pored velikog potencijala CVS metode u smislu sinteze ultrafinih prahova na bazi titanata i ferita u jednom koraku, ova metoda nudi relativno slabu kontrolu morfologije kompozitnih čestica pri visokim procesnim temperaturama koje su neophodne za kristalizaciju dve faze. Sintetisani nanoprahovi na bazi titanata i ferita (SrTiO3NiFe2O4 i BaTiO3NiFe2O4) procesirani su u gustu kompozitnu keramiku visokotemperaturnim sinterovanjem, u cilju ispitivanja veze morfologije čestica i mikrostrukture kompozita, optimizacije režima sinterovanja i funkcionalne karakterizacije dobijene keramike sa različitim masenim odnosom faza. Prahovi su sinterovani putem konvencionalnog sinterovanja u atmosferi vazduha, spark plazma sinterovanja (SPS) ili kombinacijom ove dve metode. Utvrđeno je da prahovi strukture jezgro&ndash;omotač densifikuju u značajno gu&scaron;ću i homogeniju keramiku u odnosu na kompozitne prahove istog sastava na istim procesnim temperaturama. Pored toga, pH vrednost sinteze čestica i atmosfera visokotemperaturnog sinterovanja su se pokazali veoma značajnim u smislu održavanja željenog faznog sastava dobijenih kompozita. U pogledu režima sinterovanja dobijenih prahova, kombinacija niskotemperaturnog konvencionalnog i SPS sinterovanja (1000 &deg;C) je dala najbolje rezultate u smislu postizanja zadovoljavajuće gustine kompozita (&gt;95% teorijske gustine), održavanja željenog faznog sastava i homogene distribucije faza. Funkcionalna karakterizacija sinterovane keramike sa različitim masenim odnosom faza (BaTiO3 : NiFe2O4 = 1,2,8) potvrdila je očekivano dielektrično, feroelektrično i ferimagnetno pona&scaron;anje dobijenih kompozita.</p> / <p>Composite and core&ndash;shell nanopowders with dielectric and magnetic phase have been synthesized in this work, as a suitable starting material for processing of composite ceramics for microelectronic application. The main goal of this doctoral dissertation was the determination of the link between synthesis conditions, particle morphology, processing conditions and microstructure of composite ceramics. Nanopowders have been synthesized by chemical synthesis methods in wet phase (sol&ndash;gel and coprecipitation) and gas phase (CVS), whereas the optimization of processing parameters was conducted with the goal to synthesize particles of desired structure and chemical composition. Studies were conducted on the few model systems with ferrites as a magnetic and titanates as a dielectric phase: NiFe2O4SiO2, Fe3O4SiO2, SrTiO3NiFe2O4, BaTiO3NiFe2O4 and BaTiO3Fe3O4. Chemical wet synthesis has proven suitable because it offers composite particle morphology control not only by adjustment of synthesis parameters but also by phase functionalization causing their mutual electrostatic attraction and thus core&ndash;shell structure formation. However, due to the high degree of agglomeration present during the wet phase synthesis, formation of the shell with uniform thickness and avoidance of homogeneous nucleation has proven difficult. For the first time, composite ferrite and titanate-based nanopowder has been synthesized by means of Chemical Vapor Synthesis (CVS). It has been found that beside high potential of CVS method for one-step synthesis of ultrafine titanate and ferrite-based nanopowders, this method offers relatively low control of composite particle morphology at high processing temperatures which are necessary for crystallization of both phases. Synthesized titanate and ferrite-based nanopowders (SrTiO3NiFe2O4 and BaTiO3NiFe2O4) were processed into dense ceramics by high-temperature sintering, in order to find the link between particle morphology and composite microstructure, optimize the sintering regime and conduct the functional characterization of obtained ceramics with different phase mass ratio.<br />The powders were sintered by conventional sintering in air, spark plasma sintering<br />(SPS) or combination of these two methods. It was found that core&ndash;shell powders densify in ceramics with considerably higher density and homogeneity at the same processing temperature, than the composite powders with the same composition. Moreover, synthesis pH value and sintering temperature was found to be very important in terms of phase composition preservation of obtained composites. Regarding the sintering regime of obtained powders, combination of low-temperature conventional and SPS sintering (1000 &deg;C) has given the best results in terms of achieving adequate composite density (&gt;95% theoretical density), phase preservation and homogeneous phase distribution. Functional characterization of sintered ceramics with different phase mass ratio (BaTiO3 : NiFe2O4 = 1,2,8) confirmed the expected dielectric, ferroelectric and ferromagnetic behaviour of obtained composites.</p>

This thesis deals with biosensors based on modified semiconductor core/shell quantum dots (QDs) for diagnosis. The work is divided into four main parts. The first one discusses the theory required for the use of QDs in bioaplications, there are described methods of synthesis, modification, application and bioconjugation of QDs. In the experimental part, CdTe/ZnS QDs with core/shell structure were prepared, in which the core was modified by MPA, GSH and TGA. In the next step, these QDs were further modified using CDI, EDC and NHS as mediators in order to increase affinity to BSA (bovine serum albumine) and IgG (imunoglobuline G). Prepared conjugates were characterized by fluorescence spectroscopy (Infinite M200Pro, Tecan) and capillary electrophoresis (Agilent 7100).

The aim of this master thesis is synthesis of SiO2/Au core/shell nanoparticles. These nanoparticles should improve the signal of optical coherence tomography (OCT). The procedure of nanoparticle synthesis is described in the work. Synthetized nanoparticles were analyzed by scanning electron microscopy (SEM), Ultraviolet-Visible spectroscopy (UV-Vis), Near-infrared spectroscopy (NIRS), Fourier transform-infrared spectroscopy (FT-IR) and Dynamic light scattering (DLS). Then, the synthetized nanoparticles were tested for enhancement of OCT signal. For this testing were also used commercial nanoparticles with the same structure and similar size.

L’administration d’aliments fonctionnels contenant des cellules probiotiques est une des voies de rétablissement de l'équilibre du microbiota. Pour assurer la protection des probiotiques pendant la transformation des aliments et le passage gastro-intestinal, l'encapsulation est essentielle. Nous proposons ici des supports hybrides à base de silice en tant que nouveaux systèmes d’encapsulation de probiotiques. Lactobacillus rhamnosus GG (LGG) a été choisi comme modèle de bactéries probiotiques et l'alginate comme polymère prébiotique. Deux types de supports ont été préparés, soit par émulsification, soit par électrospraying: (i) des billes hybrides de 10-30 μm dans lesquelles les bactéries étaient en contact direct avec un mélange d'alginate et de silice et (ii) des particules cœur-couronne de 200-600 μm dans lesquelles les bactéries sont d'abord encapsulées dans un gel d'alginate, puis recouvertes d'une couche de silice. La viabilité des LGG a été efficacement maintenue seulement dans les particules cœur-couronne, dans lesquelles LGG n’ont pas était directement exposées à la silice. Ces prototypes cargo ont permis la protection de LGG pendant le stockage dans la bière ou le jus de pomme, ainsi que pendant le passage à travers le tractus gastro-intestinal. En outre, les LGG libérées dans un écosystème fécal se sont multipliées au détriment des autres membres de la communauté de Lactobacilli. Cette étude offre donc une preuve de concept quant à la potentialité des systèmes hybrides silice/biopolymère pour l'administration orale de bactéries probiotiques / One way to reestablish the microbiota equilibrium is to administrate a functional food containing probiotic cells. To insure protection of the living matter during the food processing and the gastrointestinal passage, encapsulation is essential. Herein we propose silica-based hybrid carriers as new probiotic delivery systems. Lactobacillus rhamnosus GG (LGG) was chosen as a model probiotic bacteria and alginate as prebiotic polymer. Two types of carriers were prepared either by emulsification or by electrospraying: (i) hybrid beads of 10-30 m in which the bacteria was in direct contact with a mixture of alginate and silica and (ii) core-shell beads of 200-600 m in which the bacteria are first embedded in an aqueous core of alginate, then coated with a silica shell. The viability of LGG was efficiently maintained only in core-shell particles, in which LGG was not directly exposed to silica. Those core-shell prototype carriers allowed the protection of LGG during storage in beer or apple juice, and during the passage through the gastrointestinal tract. Additionally the LGG released in the colon outcompete other members of the Lactobacilli community and it was able to thrive within a fecal ecosystem. This study offers thus a proof of concept for the potential use of hybrid silica/biopolymer systems in oral delivery of probiotic bacteria

Nanoparticles (NPs) have considerable potential in targeted medicine. NPs can merge various functions and serve as labels for imaging or as nanocarriers in therapy. Modification of NPs with targeting ligands can lead to highly specific interactions with targeted cancer cells. However, the efficacy of targeting depends on the ratio between specific and non-specific interactions of a NP with the cell. Non-specific interactions of NPs are unrelated to targeted receptors and need to be eliminated in order to decrease background noise during imaging and adverse effect of drugs on healthy tissues. In this thesis, surface modifications of NPs were explored mainly on biocompatible carbon NPs called nanodiamonds (NDs), which have exceptional fluorescent properties such as long fluorescence lifetime, no photobleaching and photoblinking and sensitivity of their fluorescence to electric and magnetic field. Main issues addressed in this thesis are low colloidal stability of NDs in buffers and media, their non-specific interactions with proteins and cells and limited approaches for ND surface modifications. These issues were solved by coating NDs with a layer of biocompatible, hydrophilic, and electroneutral poly(ethylene glycol) or poly[N-(2- hydroxypropyl) methacrylamide] polymers. Optimized polymer coating...

Im Rahmen dieser Arbeit wurden schalenartig aufgebaute Nanoheterostrukturen aus CdTe, CdS und CdSe hergestellt und insbesondere im Hinblick auf ihre optischen Eigenschaften untersucht. Eine neue Variante der CdTe Nanokristallsynthese in ODE als hochsiedendem, nicht koordinierendem Lösungsmittel wurde entwickelt. Diese weist deutliche Vorteile im Bezug auf Reproduzierbarkeit und Wachstumskinetik gegenüber der älteren Synthese in TOP/TOPO auf, da durch ein deutlich verlangsamtes Wachstum die gezielte Synthese von Nanokristallen definierter Größe deutlich erleichtert wird. Diese CdTe Nanokristalle wurden sowohl mit CdS als auch mit CdSe beschichtet. Dabei wurden für beide Arten der Beschichtung verschiedene Methoden getestet und es konnte jeweils eine Synthesemethode gefunden werden, welche Kern-Schale Nanokristalle mit geringer Polydispersität und guten optischen Eigenschaften (schmale Emissionssignale und hohe Quantenausbeuten) liefert. Weiterhin wurden Kern-Schale-Schale Nanokristalle aus CdTe/CdS/CdSe synthetisiert. Dieses System besitzt besonders interessante Eigenschaften, die sich vor allem in Form einer über die eingebettete CdS Schicht einstellbare Ladungsträgertrennung im angeregten Zustand der Nanokristalle und der damit einhergehenden verlängerten Emissionslebensdauer zeigen. Die optischen Eigenschaften (erster elektronischer Übergang) der hergestellten Kern-Schale und Kern-Schale-Schale Teilchen wurden mit theoretischen Berechnungen im Rahmen der „Effektive-Masse-Näherung“ verglichen. Dieser Vergleich ergab für die mit CdSe beschichteten Teilchen eine gute, für die mit CdS beschichteten Teilchen allerdings nur eine mäßige Übereinstimmung. Auch die transmissionselektronenmikroskopischen Aufnahmen legen nahe, dass insbesondere die Beschichtung mit CdS nicht quantitativ im Bezug auf die eingesetzte Precursormenge abläuft. Die Emissionslebensdauern der verschiedenen Systeme zeigen nichts desto trotz, dass die theoretisch zu erwartende Ladungsträgertrennung im angeregten Zustand der CdTe/CdS/CdSe Kern-Schale-Schale Nanokristalle tatsächlich eintritt. Durch Einführen der CdS Schicht konnte eine Verlängerung der Emissionslebensdauer der Nanokristalle erreicht werden. Insbesondere wurde gezeigt, dass es möglich ist, verschiedene Nanoheterostrukturen herzustellen, deren Emissionslebensdauern unterschiedlich sind, obwohl sie bei derselben Wellenlänge Licht emittieren. Diese Eigenschaft kann mit Nanokristallen aus nur einem Material nicht erreicht werden. Durch die richtige Kombination von Halbleitermaterialien ist es also möglich, neben der bereits lange bekannten Möglichkeit der Einstellbarkeit der Emissionswellenlänge von Nanokristallen nun auch die Emissionslebensdauer der Nanokristalle zu beeinflussen.

The main goal of this work is design and synthesis of novel composite hydrogel-based core-shell microparticles and their application for fabrication of coatings, which provide the “inverse-switching” behaviour to the surface, namely, to become more hydrophobic in water environment. Since contact angle of heterogeneous surfaces is dependent on the nature and ratio of surface components, an increase of amount of more hydrophobic component on the surface will cause the reducing of surface wettability. It was suggested that core-shell particles having water-swellable hydrogel core and hydrophobic, but permeable for water shell when deposited on the hydrophilic substrate should increase the total amount of hydrophobic component on the surface when the cores of particles will swell in water. During the work different approaches to obtain freely dispersed and surface-immobilized core-shell particles with required structure were developed. Obtained particles were applied for preparation of coatings with ability to display “inverse-switching” behaviour. It was demonstrated that properly designed and properly prepared core-shell particles could be successfully used for creation of smart adaptive coatings having the ability to alter the surface properties upon changing of the environment.