Rozprawy doktorskie na temat „Nanocomposite colloid”

Les colloïdes nanocomposites organiques/inorganiques suscitent une attention considérable en raison de leur large gamme d'applications potentielles. L'auto-assemblage induit par la polymérisation (PISA) de copolymères à blocs en surface de nanoparticules inorganiques est reconnu comme une stratégie particulièrement efficace pour la synthèse de ces matériaux. Cette étude vise à synthétiser des brosses de polymères hydrophiles à la surface de particules de silice en utilisant la polymérisation radicalaire contrôlée par la voie nitroxyde (NMP) et à les utiliser par la suite comme macroamorceurs pour la croissance d'un second bloc hydrophobe. Des colloïdes hybrides avec des morphologies bien définies sont ainsi obtenus grâce à l'auto-assemblage des copolymères à blocs greffés et de leurs analogues non greffés. La première partie de ce travail est dédiée au greffage de brosses de polyélectrolytes faibles, le poly(acide méthacrylique-co-styrène) (P(AMA-co-S)), à partir de la surface de particules de silice. Des alcoxyamines ont été liées de manière covalente à des particules de silice de tailles variées en deux étapes, et avec une large gamme de densités de greffage. Ces particules de silice modifiées ont ensuite été utilisées comme amorceurs « supportés » pour la NMP de l’acide méthacrylique (AMA) en présence d’une faible quantité de styrène. En faisant varier systématiquement les conditions expérimentales, des particules de silice fonctionnalisées par des brosses de P(AMA-co-S) présentant différentes densités de greffage et différentes masses molaires, ont été obtenues. Leur comportement en solution aqueuse en fonction du pH et de la présence de sel ajouté a ensuite été étudié. Les particules de silice fonctionnalisées par les chaînes de P(AMA-co-S) ont été ensuite utilisées pour amorcer la copolymérisation en émulsion du méthacrylate de méthyle (MMA) et du styrène en présence de macroamorceur non greffé. Les expériences de contrôle effectuées en l’absence de silice ont conduit à la formation de particules de latex sphériques auto-stabilisées par le procédé PISA. L’influence de la concentration en macroamorceur, de sa masse molaire, du taux de solide et de la température sur la cinétique de polymérisation et la taille des particules de latex a été étudié en détails. Lorsque les particules de silice greffées ont été utilisées, l'auto-assemblage des copolymères à blocs amphiphiles à leur surface a conduit à la formation de particules hybrides de type framboise, cœur-coquille ou multicœur, en fonction de la taille des particules de silice, de la concentration en sel, ainsi que de la densité de greffage ou de la masse molaire du macroamorceur utilisé. La troisième partie de ce travail est consacrée à la synthèse par NMP de nano-objets à base de copolymères à blocs de type P(AMA-co-S)-b-P(MABz-co-S) stabilisés stériquement, par polymérisation en dispersion du méthacrylate de benzyle (MABz) en milieu alcoolique. La polymérisation réalisée à 85°C dans l'éthanol absolu est bien contrôlée, et conduit à la formation de particules sphériques, ainsi qu’à des morphologies supérieures telles que des batônnets, des fibres ou des vésicules selon la masse molaire du macroamorceur, de sa concentration et de la teneur en monomère. En présence des particules de silice fonctionnalisées, des morphologies hybrides originales composées de fibres courtes ou de vésicules liées à la surface de la silice ont été obtenues à nouveau par co-assemblage entre les chaînes de copolymères à bloc greffées et les chaînes non greffées. Ainsi, en faisant varier les conditions expérimentales et la nature chimique du monomère hydrophobe, une large gamme de morphologies hybrides a été obtenue à partir des mêmes particules de silice modifiées par des brosses de PAMA
Organic/inorganic nanocomposite colloids are attracting considerable attention due to their diverse range of potential applications. Polymerization-induced self-assembly of block copolymers on the surface of inorganic nanoparticles is recognized as a particularly effective strategy for the synthesis of these materials. This study aims to synthesize hydrophilic polymer brushes on silica particles using nitroxide-mediated radical polymerization (NMP) and subsequently employ them as macroinitiators for the growth of a second hydrophobic block. Hybrid colloids with well-defined morphologies are thus obtained through the co-assembly of surface-grafted and “free” ungrafted block copolymers. The first part of this work explores the grafting of weak polyelectrolyte brushes, namely poly(methacrylic acid-co-styrene) (P(MAA-co-S)), from the surface of silica particles. Alkoxyamine initiators were covalently attached to silica particles of varying sizes in two-steps, resulting in a large range of alkoxyamine grafting densities. These modified silica particles were subsequently employed as initiators for the NMP of MAA in the presence of a small amount of styrene as a controlling comonomer. By systematically varying the experimental conditions, silica particles functionalized with P(MAA-co-S) brushes, with tunable grafting densities and molar masses, were synthesized, and their pH- and salt-responsive behaviors were investigated. The resulting P(MAA-co-S)-functionalized silica particles were then employed in the aqueous emulsion copolymerization of methyl methacrylate (MMA) and styrene in the presence of free macroinitiator. Control experiments conducted without silica produced electrosterically stabilized spherical latex particles via polymerization-induced self-assembly. The effects of macroinitiator concentration, molar mass, solids content, and temperature on the polymerization kinetics and latex particles size were systematically studied. When PMAA-grafted silica particles were used, the co-assembly of the amphiphilic block copolymers on the silica surface and in solution, resulted in hybrid particles with raspberry, core-shell, or multicore morphologies depending on silica particle size, salt concentration, and the grafting density and molecular weight of the macroinitiator. The third part of this work reports the synthesis of sterically stabilized P(MAA-co-S)-b-P(BzMA-co-S) block copolymers nano-objects through alcoholic NMP dispersion polymerization of benzyl methacrylate (BzMA). The polymerization was well-controlled at 85°C in pure ethanol, producing copolymers that not only formed spherical particles but also self-assembled into more complex structures, such as worms and vesicles depending on the molar mass or concentration of the macroinitiator, and monomer content. Upon introducing P(MAA-co-S)-functionalized silica particles into the dispersion polymerization system, co-assembly of grafted and free block copolymers resulted in original hybrid morphologies composed of surface-tethered short worms or vesicles. By modifying the reaction conditions and monomer types, a wide range of nanocomposite colloidal morphologies were achieved using the same polymer brush-modified silica particles

The work presented in this thesis provides a new route to a colloidal form of polyaniline, which uses colloidal silica as a dispersant. We obtained stable colloidal dispersions of polyaniline-silica composite particles with a 'raspberry' morphology. Compressed pellets of these particles exhibit solid-state conductivities of 1O-!_10-2 S crrr l, which is approximately 1-2 orders of magnitude lower than that of polyaniline bulk powder. This novel colloidal form of polyaniline has significantly improved processability compared to conventionally synthesised polyaniline. The synthesis and chemical characterisations are presented for various polyaniline-silica colloidal nanocomposites. The quantity of polyaniline incorporated into the nanocomposite particles can be controlled by varying the diameter of the silica dispersant, approximately 20% and 60 % polyaniline content being obtained using 120 nm and 10 nm diameter silica respectively. The average particle size ranges of nanocomposites was found to be 150 to 700 nm and 330 to 560 nm, as determined by transmission electron microscopy (TEM) and disc centrifuge photosedimentometry (DCP) respectively. The nanomorphology and surface composition of the polyanilinesilica particles were determined by small angle X-ray scattering (SAXS) and X-ray photoelectron spectroscopy (XPS) respectively. The average inter-particle separation distance of the silica particles within the polyaniline-silica raspberries was determined by SAXS to be 4 nm, a dimension equivalent to molecular polyaniline. The XPS data suggests that the surface of the particles is silica rich, this is consistant with their long term colloidal stability in 1.2 mole dm-3 HCl. The kinetics of polymerisation was studied using 1H NMR spectroscopy to monitor the disappearance of aniline monomer. Polymerisation rates during the synthesis of polyaniline-silica nanocomposites were appreciably faster than the corresponding precipitation polymerisations carried out in the absence of silica dispersants, due primarily to an increase in the second auto-catalytic step of the reaction. Rate constants were determined for both these types of synthesis; the values obtained for the precipitation polymerisations were in reasonably good agreement with literature values.

Underfill material is a special colloidal dispersion system with silicon dioxide particles in the organic liquid. It is used to improve the reliability of integrated circuits (IC) packaging in the microelectronics. In order to successfully synthesize the nanocomposite underfill meeting the requirements of the chip package, it is necessary to have a fundamental understanding about the particle stability in the non-aqueous liquid and the relationship between materials properties and interphase structure in the composite. The results of this thesis contribute to the knowledge of colloidal dispersion of nanoparticles in organic liquid by systematically investigating the effects of particle size, particle surface chemistry and surface tension, and liquid medium polarity upon the rheological and thermal mechanical properties of underfill materials. The relaxation and dielectric properties studies indicate that the polymer molecular chain motion and polarization in the interphase region can strongly influence the material properties of nanocomposite, and so a good interaction between particle and polymer matrix is key. With this study, a potential nanocomposite underfill can be synthesized with low viscosity, low thermal expansion, and high glass transition temperature. The excellent transmittance of nanoparticles leads to further investigation of their ability as reinforcing filler in the photo-curable polymer.

The objective of this research was the development of an efficient method for the preparation of silver-polymer nanocomposites containing finely dispersed silver nanoparticles. The surface of nanosilver was functionalized by thiolation with 2-aminoethanethiol. Amino-modified nanosilver was covalently bonded to polyacrylic acid, biodegradable polymers like acid terminated polylactic acid, ester terminated poly(DL-lactide-co-glycolide) and acid terminated poly(DL lactide-co-glycolide) in the presence of diisopropylcarbodiimide by carbodiimide method. Esterification of the carboxyl groups of Ag-polyacrylic acid by hydrochloric acid in methanol resulted in the formation of a stable colloidal dispersion of Ag nanoparticles in the polymer matrix. It was observed that not just acid terminated polymers but also ester terminated polymers could react with functionalized nanosilver. This unusual reaction was due to the aminolysis of the ester bond in the polymer chain by the surface amino groups. Silver-polymer nanocomposites obtained with acid terminated polylactic acid and poly(DL-lactide-co-glycolide) contained highly dispersed nanosilver in the polymer matrix in comparison with the ester terminated poly(DL-lactide-co-glycolide). Chemical and structural characteristics of the obtained materials were studied by instrumental methods. Attained biodegradable materials confirmed X-ray contrast and bactericidal properties, which could be eventually used for biomedical applications.

In this work we present the proof of the concept of the novel strategy to improve the thermoelectric properties of Bi2S3based nanostructured bulk materials by blending the metallic nanoinclustions with the semiconductor nanoparticles forming the nanocomposites (NCts). The obtained NCts were composed of Bi2S3nanorods (length - 100 nm and width – 10 nm) and Ag nanoparticles (diameter - 2- 3 nm) synthesized by colloidal method. The morpohology, phase and chemical composition, electrical conductivity and Seebeck coefficient of NCts were investigated by using transmission electron microscopy (TEM), X-ray diffraction, energy dispersive X-ray analysis (EDAX), 4-point probes method and static dc-method. This strategy is the perspective way to improve the conversion efficiency of others thermoelectric materials.

This work developed various two-phase colloidal nanomaterials from aqueous dispersions and applied them as pressure-sensitive adhesives. A fundamental understanding of the nano-scale interfacial friction and the macro-scale viscoelasticity and adhesive properties of these nanomaterials was developed via various existing models.

Le nanoparticelle (NP) di SiO2 sono note per migliorare le proprietà meccaniche e funzionali dei materiali nanocompositi (NC) e sono ampiamente utilizzate come filler di rinforzo negli pneumatici. Le proprietà dei NC dipendono dalla distribuzione delle NP di filler, che a sua volta dipende dalla morfologia e dalla chimica superficiale delle NP. La dispersione di SiO2 NPs idrofiliche in matrici polimeriche è tipicamente ottenuta tramite funzionalizzazione con silani a catena corta. Mentre le NP anisotropiche sono note per auto-organizzarsi in strutture ordinate, producendo migliori proprietà meccaniche nei NC elastomerici, è stato dimostrato che anche le NP sferiche di SiO2 ricoperte con catene di oligomeri, ovvero le SiO2 Hairy NP (SiO2 HNP), possono migliorare la compatibilizzazione filler/matrice mentre si auto-organizzano in superstrutture anisotropiche. Tuttavia, la sintesi di SiO2 HNP con gusci elastomerici è ancora largamente inesplorata, e la relazione tra l'auto-organizzazione delle HNP e le proprietà meccaniche dei NC deve ancora essere del tutto compresa. In questo contesto, lo scopo di questa tesi è stato quello di i) sviluppare una sintesi efficiente di SiO2 HNPs con dimensioni, morfologia e chimica di superficie controllate; ii) preparare NC elastomerici basati su SiO2 HNP con rinforzo migliorato e isteresi ridotta; iii) valutare gli effetti dell'auto-organizzazione sulle prestazioni meccaniche dei materiali e iv) studiare le interazioni tra SiO2 HNPs per determinare quali parametri controllano i processi di auto-organizzazione. Durante il primo anno di attività di dottorato è stata ottimizzata la sintesi di SiO2 HNP funzionalizzate con polibutadiene (PB) con un approccio colloidale. La sintesi ha garantito un eccellente controllo della morfologia e della chimica di superficie delle HNPs. Le particelle non funzionalizzate e funzionalizzate sono state completamente caratterizzate con una pletora di metodi morfologici e fisico-chimici mostrando evidenza di auto-organizzazione. Durante il secondo anno, le SiO2 HNP sono state utilizzate per preparare NC elastomerici in una formulazione industriale. Le proprietà meccaniche dei NC vulcanizzati e non vulcanizzati sono state caratterizzate da analisi dinamico-meccaniche e prove di trazione, mostrando che le HNP migliorano fortemente il rinforzo riducendo la dissipazione di energia, evidenziando migliori interazioni filler/matrice rispetto alle NP SiO2 non funzionalizzate e funzionalizzate con silano. La caratterizzazione morfologica delle NC ha confermato il miglioramento della dispersione e della distribuzione del filler con l'aumento della funzionalizzazione con PB e ha mostrato l'auto-organizzazione delle HNP in sovrastrutture anisotropiche simili a stringhe. Durante il terzo anno, il modello delle HNP è stato adattato a una formulazione riproducibile su scala industriale usando un silano macromolecolare a base di PB (MacroSil) e silice commerciale. Le proprietà meccaniche degli NC elastomerici sono state caratterizzate in modo approfondito con analisi meccaniche dinamiche, prove di trazione e analisi Large Amplitude Oscillatory Shear (LAOS), dimostrando che l'aggiunta di MacroSil migliora significativamente le prestazioni meccaniche degli NC rispetto a un silano a catena corta. Infine, esperimenti di Small-Angle X-Ray Scattering (SAXS) sulle dispersioni di SiO2 HNPs in collaborazione con il Prof. Simone Mascotto dell'Università di Amburgo hanno fornito parametri strutturali fondamentali che sono stati utilizzati per formulare un modello teorico delle interazioni tra HNP, in collaborazione con il Prof. Arturo Moncho dell'Università di Granada e il Prof. Gerardo Odriozola della UAM-Azcapotzalco. Il modello teorico ha predetto la formazione delle sovrastrutture anisotropiche di SiO2 HNP osservate sia nelle particelle prive di matrice sia nei NC elastomerici.
SiO2 nanoparticles (NPs) are known to improve the mechanical and functional properties of nanocomposite (NC) materials and are widely used as reinforcing fillers in tyres. The properties of NCs depend on the distribution of filler NPs, which in turn depends on the morphology and surface chemistry of filler NPs. The dispersion of hydrophilic SiO2 NPs in polymer matrices is typically achieved by functionalization with short-chain silanes. While anisotropic NPs are known to self-organize in ordered structures, producing improved mechanical properties in rubber NCs, evidence has shown that also spherical SiO2 NPs grafted with oligomer chains, i.e. SiO2 Hairy NPs (SiO2 HNPs), can improve filler/matrix compatibilization while self-organizing in anisotropic superstructures. However, the synthesis of SiO2 HNPs with rubbery shells is still largely unexplored, and the relationship between HNPs self-assembly and the mechanical properties of NCs is yet to be understood. In this context, the aim of this thesis was i) to develp an efficient synthesis of SiO2 HNPs with tunable size, controlled morphology and tailored surface chemistry; ii) to prepare rubber NCs based on SiO2 HNPs with improved reinforcement and reduced hysteresis; iii) to assess the self-assembly effects on the mechanical performance of the materials and iv) to study the interactions between SiO2 HNPs in order to determine which parameters control the self-assembly processes. During the first year of PhD activity the synthesis of polybutadiene (PB)-grafted SiO2 HNPs by a colloidal approach was optimized. The synthesis granted excellent control of HNPs morphology and surface chemistry. The bare and functionalized particles were fully characterized by a plethora of morphological and physico-chemical methods showing evidence of self-assembly. During the second year, SiO2 HNPs were used to prepare rubber NCs in an industrial formulation. The mechanical properties of the cured and uncured NCs were characterized by dynamic-mechanical analysis and tensile tests, showing that HNPs strongly improve reinforcement while reducing energy dissipation, highlighting improved filler/matrix interactions compared to both bare and silane-functionalized SiO2 NPs. Morphological characterization of the NCs confirmed the improvement of filler dispersion and distribution with increased PB functionalization and showed the self-organization of HNPs in anisotropic string-like superstructures. During the third year, the HNPs model was adapted to a scalable industrial rubber formulation using a PB macromolecular silane (MacroSil) and commercial precipitated silica. The mechanical properties of the rubber NCs were thoroughly characterized with dynamic mechanical analysis, tensile tests and Large Amplitude Oscillatory Shear (LAOS) analysis, showing that the addition of MacroSil significantly improves the mechanical performance of NCs compared to a short-chain silane. Finally, Small-Angle X-Ray Scattering of SiO2 HNPs dispersions in collaboration with Prof. Simone Mascotto at Hamburg University provided crucial structural parameters which were used to formulate a theoretical model of HNPs interactions, in collaboration with Prof. Arturo Moncho of the University of Granada and Prof. Gerardo Odriozola of UAM-Azcapotzalco. The theoretical model predicted the formation of the SiO2 HNPs anisotropic superstructures observed both in matrix free conditions and rubber NCs.

The search for cellulosic based products as a viable alternative for petroleum-based products was the impetus for covalently crosslinking lignocellulosic fibers and nanocellulose whiskers with poly(methyl vinyl ether) co maleic acid (PMVEMA) - polyethylene glycol (PEG). The lignocellulosics used were ECF bleached softwood (pine) and ECF bleached birch kraft pulp. This thesis also tests the hypothesis that water absorption and retention can be improved by grafting PMVEMA-PEG to the surface of ECF bleached kraft pulp hardwood and softwood fibers via microwave initiated crosslinking. The crosslinking of the PMVEMA to hardwood and softwood kraft ECF bleached pulp fibers resulted in enhanced water absorbing pulp fibers where the PMVEMA is grafted onto the surface of the fibers. The crosslinking was initiated both thermally and via microwave irradiation and the water absorption and water retention was measured as the percent of grafted PMVEMA. This was the first application of microwave crosslinking of pulp fibers with the goal of creating water absorbing pulp fibers. Ultimately, the water absorption values ranged from 28.70 g water per g dry crosslinked pulp fiber (g/g) to 230.10 g/g and the water retention values ranged from 26% to 71% of the water retained that was absorbed by the crosslinked pulp fibers. The microwave initiated crosslinked fibers had comparable results to the thermally crosslinked fibers with a decreased reaction time, from 6.50 min (thermal) to 1 min 45 sec (microwave). Cellulose nanowhiskers, crystalline rods of cellulose, have been investigated due to their unique properties, such as nanoscale dimensions, low density, high surface area, mechanical strength, and surface morphology and available surface chemistry. Prior to this study, the crosslinking of cellulose whiskers with the matrix via solution casting of liquid suspensions of whiskers and matrix had not been explored. The hypothesis to be investigated was that incorporating cellulosic whiskers with the PMVEMA-PEG matrix and crosslinking the whiskers with the matrix would yield films that demonstrate unique properties when compared to prior work of crosslinking of PMVEMA-PEG to macroscopic ECF bleached kraft pulp fibers. Solution cast composites of cellulose nanowhiskers-PMVEMA-PEG were crosslinked at 135 °C for 6.5 min and analyzed for crosslinking, thermal stability, strength and mechanical properties, whisker dispersion, and water absorption and uptake rates. The whisker-composites demonstrated unique properties upon crosslinking the whiskers with PMVEMA-PEG, especially the elongation at break and tensile strength upon conditioning of the final materials at various relative humidities. In addition, the whiskers improved the thermal stability of the PMVEMA-PEG matrix. This is significant as methods of improving processing thermal stability are key to developing new materials that utilize cellulose whiskers, PMVEMA, and PEG. This thesis addresses the hypothesis that cellulose nanowhiskers that are crosslinked with a matrix can create new whisker-matrix composites that behave differently after crosslinking.

L’industria degli pneumatici si prefigge di indagare possibili strategie sintetiche per ridurre l’impatto ambientale durante tutto il ciclo di vita dello pneumatico, attraverso l’uso di materiali sostenibili e lo sviluppo di tecniche innovative che riducano il consumo di energia e le emissioni di CO2. In questo contesto, questa progetto di dottorato è focalizzato sulla preparazione di nanocompositi eco-sostenibili attraverso l’uso di un approccio colloidale per aumentare la dispersione di filler idrofilici, in linea con i nuovi requisiti di sostenibilità delle politiche europee. L’approccio colloidale punta a produrre nanocompositi con filler idrofilici, la cui efficiente dispersione attraverso tecniche di miscelazione tradizionali rimane difficoltosa a causa della scarsa compatibilità con la matrice organica. Questa tecnica si focalizza sull’incremento della dispersione di filler senza alcuna modifica superficiale, con l’eliminazione delle poveri prodotte durante il mescolamento con significativi benefici per l’ambiente e i lavoratori. Due diversi approcci colloidali sono stati utilizzati: i) una tecnica di miscelazione in lattice e ii) una in situ polimerizzazione in emulsione per la produzione di nanocompositi altamente caricati contenenti filler come silice e sepiolite (Sep), questi ultimi sono considerati filler promettenti nell’ambito del rinforzo dei polimeri grazie alla loro struttura fibrosa e all’elevato rapporto di forma. La concentrazione, la carica, la forma dei nanofiller a base silicea sono stati studiati come parametri rilevanti per la stabilizzazione e destabilizzazione di lattici a base di poliisoprene naturale e sintetico. Una efficiente procedura di miscelazione in lattice è stata messa a punto per produrre compositi eco-sostenibili, chiamati masterbatches (MBs), attraverso l’incorporazione di silice o Sep nel lattice di gomma naturale (emulsione in acqua di cis-1,4-poliisoprene), attraverso la flocculazione (aggregazione risultante dalla coesione di particelle di polimero) di una miscela acquosa di nanofiller a base silicea e gomma. La tecnica di miscelazione in lattice ha dimostrato di favorire una omogenea dispersione di fibre di sepiolite idrofilica in matrice di gomma. La principali caratteristiche fisico-chimiche che controllano i processi di aggregazione in acqua come il pH, il potenziale Z, la concentrazione, assieme alle caratteristiche morfologiche del MB Sep-gomma naturale, sono state prese in considerazione allo scopo di investigare le interazioni Sep-gomma naturale. E’ stato proposto un meccanismo di flocculazione basato su attrazioni elettrostatiche e depletive, connesso all’elevato contenuto di filler (50% in peso) e alla peculiare anisotropia delle particelle di Sep. Inoltre, i MBs sono stati utilizzati per preparare compositi sostenibili attraverso la combinazione di miscelazione in lattice e mescolazione meccanica. Questo approccio combinato sfrutta la buona distribuzione del filler e previene il rilascio di polveri durante il processo. Una polimerizzazione Pickering in situ è stata considerata come alternativa per la produzione di nanocompositi eco-sostenibili. Particelle poliisoprene/filler a base silicea sono state sintetizzate sfruttando dell’effetto stabilizzante di filler inorganici che agiscono come tensioattivi riducendo la tensione superficiale e stabilizzando l’emulsione. Sulla base dei nostri risultati, viene suggerito un possibile meccanismo di polimerizzazione in emulsione stabilizzata da particelle solide. In conclusione, l’approccio colloidale, basato su miscelazione in lattice e polimerizzazione Pickering in situ, può essere considerato un metodo sostenibile, semplice ed efficace adatto per applicazioni tecnologiche altamente performanti. I risultati indicano che le strategie utilizzate sono adatte per produrre nanocompositi altamente caricati di filler a base silicea.
Sustainability has become a field of great interest in the world industry. For the scientific community the challenge lies in the identification of green synthetic approaches and new alternatives to petroleum-based materials. In the case of the tyre industry, the challenge is to identify possible design strategies and alternatives to reduce the environmental impact throughout the life cycle of tyres, by means of both the use of environmentally friendly materials and the development of innovative products, having reduced energy consumption and CO2 emissions. In this context, this PhD thesis is focused on the preparation of eco-friendly silica-based nanocomposites by using a colloidal approach to increase the dispersion of hydrophilic fillers in line with the new requirements of sustainability from the EU policies. The colloidal approach aims at compounding nanocomposites with hydrophilic fillers, whose efficient dispersion through traditional mixing still remains a challenging issue, due to their poor compatibility with the organic matrix. This technique aims at increasing the filler dispersion without any expensive surface modification, with the elimination of the volatile component released during mixing, producing significant benefits for environment and workers. Two different colloidal approaches were applied: i) latex compounding technique (LCT) and ii) in situ emulsion polymerization to prepare highly-loaded nanocomposite rubber materials containing silica-based fillers, silica and sepiolite (Sep) clay, considered a promising filler candidate for the polymer strengthening due to its fibrous structure and high particle aspect ratio (AR). The concentration, the charge and the shape of silica-based nanofillers were studied as relevant parameters on stabilization and destabilization of natural and synthetic polyisoprene latexes. An effective LCT procedure was established to produce eco-friendly composites, namely masterbaches (MBs), by incorporating silica or Sep into natural rubber latex (i.e. emulsion in water of cis-1,4-polyisoprene), through the flocculation (i.e. aggregation resulting from the bridging of polymer particles) of the silica-based nanofillers/rubber mixed aqueous system. LCT showed to favour a homogeneous dispersion of hydrophilic Sep fibers in the rubber matrix. The main physicochemical parameters which control aggregation processes in the aqueous medium, i.e. pH, -potential, concentration, as well as the morphological features of the final Sep-natural rubber MBs, were comprehensively investigated helping to figure out the Sep-NR interactions and to propose a flocculation mechanism, based on electrostatic and depletion attraction forces, remarkably connected both to the high content (50 wt.%) and to the peculiar anisotropy of Sep fibers. Furthermore, the MBs with high filler loadings were used to produce environmentally friendly composites, by combining LTC and melt mixing. This combined approach could take advantage of the good filler distribution and prevents dust from floating in the air during processing. In situ Pickering polymerization was considered as an alternative colloidal approach to produce eco-friendly nanocomposites. Polyisoprene/silica-based structured particles were synthesized on the base of the stabilizing effects of inorganic fillers which act like surfactants lowering the interfacial tension and stabilizing the emulsion. On the basis of our results, we suggested a possible mechanism for emulsion polymerizations stabilized by solid particles. In conclusion, the colloidal approach, based on both LTC and in situ Pickering emulsion polymerization, can be considered as green, simple and effective method suitable for high-performance technological applications. The outcomes indicate the suitability of the adopted strategies as a sustainable procedure for the production of high-loaded silica based-rubber nanocomposites.

Phosphorus-containing high performance polymers have been extensively studied during the last 10 years. These materials are of interest for a variety of optical and fire resistant properties, as well as for their ability to complex with the inorganic salts. This dissertation has focused on the nature of the phosphonyl group interactions with hydroxyl containing polymers, such as the poly(hydroxy ether)s. These may be considered linear models of epoxy resins and are also closely related to dimethacrylate (vinyl ester) matrix resins that are important for composite systems. It has been shown that bisphenol A poly(arylene ether phosphine oxide/sulfone) homo- or statistical copolymers are miscible with a bisphenol A-epichlorohydrin based poly(hydroxy ethers) (PHE), as shown by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC), infrared spectroscopy and , solid state cross polarization-magic angle spinning nuclear magnetic resonance (CP-MAS). These measurements illustrate the strong hydrogen bonding between the phosphonyl groups of the copolymers and the pendent hydroxyl groups of the PHE as the miscibility inducing mechanism. Complete miscibility at all blend compositions was achieved with as little as 20 mole% of phosphine oxide units in the poly(arylene ether) copolymer. Replacement of the bisphenol A moiety by other diphenols, such as hydroquinone, hexafluorobisphenol A and biphenol did not significantly affect blend miscibilities. Miscible polymer blends with PHE were also made by blending poly(arylene thioether phosphine oxide), and fully cyclized phosphine oxide containing polyimides based on (prepared from 2,2'-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) and bis(m-aminophenyl) methyl phosphine oxide (DAMPO)) or bis(m-aminophenyl) phenyl phosphine oxide). Additional research has focused on the influence of these materials on the property characteristics of vinyl ester matrix resins and has shown that the concentration of phosphonyl groups controls the homogeneity of both oligomers and the resulting networks. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and fracture toughness measurements further confirmed the qualitative observations. Metal salts, such as CoCl2 and CuCl2 had earlier been demonstrated to form complexes/nanocomposites with phosphorus-containing poly(arylene ethers). It has been possible to prepare transparent films with 100 mol% of metal chlorides, based upon the phosphonyl groups. The films are transparent, unlike the opaque polysulfone control systems. FTIR results suggested the formation of inorganic salt and polymer complexes at low concentrations. TEM showed homogeneous morphology at low concentrations and excellent dispersion even at high mole % of salts. Cobalt materials reinforce the basic poly(arylene ether)s to provide higher modulus values and influence positively the char yield generated after TGA experiments in air. The cobalt salt/BPADA-DAMPO polyimide composites also yield transparent films, implying very small dimensions. Silica-polymer nanocomposites were also produced by mixing commercial silica colloid/N,N-dimethylacetamide (DMAc) fine dispersions (~ 12 nm) with bisphenol A poly(arylene ether phenyl phosphine oxide). The dry films produced by solution casting are transparent and silica colloids are evenly dispersed (~ 12 nm) into the polymer matrix as shown by TEM. These nanocomposites increased char yield compared with the polymer control, suggesting their fire retardant character. In comparison, the silica/polysulfone hybrid films prepared by the same methods were opaque and the char yield was not improved. This different phase behavior has been explained to be due to the hydrogen bonding between phosphonyl groups and silanol hydroxyl groups on the surface of the nanosilica.
Ph. D.

El YBa2Cu3O7-δ es el superconductor de alta temperatura con mayor potencial tecnológico para aplicaciones de potencia e imanes que trabajan bajo campos magnéticos elevados. Sin embargo, todavía es un reto mejorar sus prestaciones en forma de película delgada epitaxial con un coste bajo de fabricación. La deposición de soluciones químicas ha surgido como una técnica muy competitiva para obtener láminas delgadas epitaxiales y multicapas de alta calidad con nanoestructuras controladas. Hemos desarrollado un proceso novedoso de crecimiento mediante Calentamiento Flash que muestra un excelente potencial para la producción industrial en continuo de conductores epitaxiales de YBa2Cu3O7-δ. En esta tesis hemos establecido, por primera vez, una imagen completa que describe las fases intermedias y la evolución de la microestructura durante el calentamiento. Hemos extendido la ventana de la temperatura de crecimiento sin ninguna degradación de las propiedades superconductoras, por lo que la deposición de conductores epitaxiales de YBa2Cu3O7-δ es compatible con el uso de sustratos de cinta metálica con capas tampón de CeO2. Además, también hemos encontrado que este proceso de crecimiento promueve la formación de una alta concentración de defectos de apilamiento y, por lo tanto, de tensiones a escala nanométrica. Las láminas ultrafinas de YBa2Cu3O7-δ y nanocompuestos, en el rango de 5-50 nm, se prepararon después de una optimización de los parámetros de crecimiento. La reducción de la energía interfacial induce una alta densidad de defectos de apilamiento, lo que conduce a una matriz de YBa2Cu3O7-δ altamente distorsionada. Esta modificación microestructural se vuelve extremadamente grave cuando el grosor de la lámina delgada disminuye por debajo de 25 nm, degradando significativamente las propiedades superconductoras. También hemos estudiado la evolución de las características de las nanopartículas segregadas espontáneamente con el espesor de las láminas delgadas y su influencia en la eficiencia del anclaje de vórtices. La preparación de nanocompuestos de YBa2Cu3O7-δ a partir de nanopartículas de óxido preformadas y no reactivas que forman soluciones coloidales ha demostrado ser una estrategia muy exitosa para lograr un estricto control de las características de las nanopartículas y la optimización de la nanoestructura de las láminas delgadas superconductoras. Las perovskitas BaMO3 (M = Zr, Hf) son las composiciones más prometedoras de nanopartículas preformadas que hasta ahora han conducido a láminas delgadas de nanocompuestos de alta calidad con altas concentraciones de nanopartículas (20-25% molar). La composición y el tamaño de las nanopartículas han demostrado ser factores cruciales para adaptar el rendimiento del anclaje de vórtices bajo campos magnéticos aplicados. La aplicación del proceso de crecimiento de calentamiento flash al crecimiento de láminas delgadas nanocompuestas permite la preservación del tamaño de las nanopartículas y la generación de una alta densidad de defectos de apilamiento de pequeña longitud, que desempeñan un efecto sinérgico para aumentar la eficiencia de los centros de anclaje de vórtices artificiales y mejorar así las propiedades de los conductores. La técnica de multideposición es efectiva para aumentar aún más el espesor de la lámina delgada, mientras que la eficacia del anclaje de vórtices se conserva y la capacidad de transporte de corriente eléctrica de las láminas delgadas nanocompuestas aumenta.
YBa2Cu3O7-δ (YBCO) is the best material choice to address the performances required in power applications and magnets working under high magnetic fields. However, it is still challenging to achieve low manufacturing costs and high superconducting performances of coated conductors (CCs) for large scale power applications. Chemical Solution Deposition has emerged as a very competitive technique to obtain epitaxial films and multi-layers of high quality with controlled nanostructures. We have developed a novel Flash Heating growth process that shows high potential to be compatible with the industrial reel-to-reel production of YBCO CCs. Here we have set up, for the first time, a full image describing the intermediate phase and microstructure evolution during this heating process. We extend the growth temperature window down to 750 ºC without any degradation of superconducting properties, making it being compatible with the deposition of YBCO CCs on CeO2-caped metallic tape substrates. In addition, we have also found that this growth process promotes the formation of a high concentration of stacking faults and so of nanostrain. YBCO and nanocomposite ultrathin films, in the range of 5-50 nm, have been prepared after a series optimization of growth parameters. The relief of the interfacial energy induces a high density of stacking faults, leading to a highly distorted YBCO matrix. Such microstructural disorder becomes extremely serious when the film thicknesses decrease below 25 nm, significantly degrading the superconductivity. We have also studied the evolution of the characteristics of spontaneous segregated nanoparticles with nanocomposite film thicknesses and their influence on the vortex pinning efficiency. The preparation of YBCO nanocomposites from non-reactive preformed oxide nanoparticles forming colloidal solutions has demonstrated to be a very successful strategy to achieve a tight control of the nanoparticle characteristics and the optimized nanostructural landscape on the superconducting films. BaMO3 (M=Zr, Hf) perovskites are shown to be the most promising compositions of preformed nanoparticles up to now that led to high quality nanocomposite films at high nanoparticle concentrations (20-25 mol%). The composition and size of nanoparticles have demonstrated to be crucial factors for tailoring vortex pinning performance in applied magnetic field. The application of the Flash Heating growth process in the growth of nanocomposite films allows both the preservation of nanoparticle size and the generation of a high density of short stacking faults, which play a synergistic effect to increase the artificial pinning centers and enhance the strong pinning contribution. Multi-deposition technique is proved effective to further enhance the film thickness while vortex pinning efficiency is preserved and current-carrying capacity of the nanocomposite films is increased.

In the last decades, the research field known as nanotechnology has been deeply investigated since it helps to understand the properties of the materials, and provides a useful tool to design materials with tailored properties, that can be exploited for many applications across the whole field of science. Nanomaterials exhibit distinctive size-dependent properties, and a high surface to volume ratio, extremely useful in applications like sensing and catalysis. In this doctoral project, different combinations of noble metals and transition metal oxides have been used to prepare inorganic thin films to be used as reducing gases sensors through an optical interface: while the semiconductive metal oxide is usually responsible for the detection mechanism, metal nanoparticles play the role of optical probes, enhancing the optical response, and/or catalysts, improving the sensor performances. The main work presented here was focused on the synthesis of these nanocomposite materials through different strategies, according to the desired quality of the final material, the easiness of the procedure, the control on key aspects like size and shape of the particles, their size distribution, the crystallinity of the different components, the porosity. In the first part, noble metal (Au, Ag, Pt) ions have been embedded inside oxide matrixes by means of sol-gel or impregnation processes, and reduced to metal nanoparticles through high temperature annealing, which is necessary also to promote the oxides crystallization: remarkable gas sensing properties have been observed for NiTiO3-TiO2-Au films for hydrogen sulfide detection, with extremely good sensitivity and selectivity towards interfering gases like CO and H2. The experimental results suggest a catalytic oxidation of H2S to sulfur oxides promoted by NiTiO3 crystals, while Au nanoparticles are not involved directly in the reaction mechanism, but act as probes providing an easily detectable optical signal. Quite good sensing properties for CO and hydrogen detection have been presented for other nanocrystalline thin films like SiO2-NiO-Ag prepared combining sol-gel and impregnation processes, sol-gel ZnO-NiO-Au nanocomposites, and microstructured WO3-Au-Pt films synthesized with the sputtering technique and a subsequent impregnation process. The second part is based on the colloidal synthesis of metal (Au, Pt, Au@Pt core@shell) and oxide (TiO2, ZnO pure and doped with transition metal ions) nanoparticles with desired size and distribution: purification and concentration protocols have been developed and the final colloidal solutions have been directly used for films deposition, obtaining nanocrystalline coatings at low temperatures. TiO2-based films show good sensitivity for CO and H2, with a detection threshold of about 2 ppm, quite remarkable considering that films are only 40-60 nm thick. These materials were also able to detect ethanol vapors at room temperature. Moreover samples containing both Au and Pt NPs are able to reversibly detect hydrogen at room temperature, thanks to the synergetic effect occurring between the optical properties of Au and the catalytic properties of Pt. ZnO-based samples have been tested as CO sensors with a detection limit down to 1-2 ppm, and a relationship between type of dopant (Ni, Co, Mn) and response intensity has been presented. The third part is focused on the deposition of Au nanoparticles layers on properly functionalized substrates, and their subsequent coating with sol-gel films: when Au nanoparticles are in close contact with each other, a coupling of the plasmon frequencies is found to occur, and this effect can be used to enhance sensing, SERS and catalytic performances. Au nanoparticles layers covered with NiO or TiO2 films showed promising gas sensing properties for CO and hydrogen detection at high temperatures, and for ethanol sensing at low temperatures. More complex structures composed of an Au nanoparticles layer sandwiched between two different oxide layers (NiO, TiO2, ZnO) are also prepared, trying to enhance the selectivity towards interfering gases by providing two different noble metal / metal oxide interfaces.
Negli ultimi decenni, il campo delle nanotecnologie è stato largamente studiato, poiché tramite esso si è in grado di comprendere le proprietà dei materiali, ed esso stesso fornisce un mezzo per progettare materiali aventi le proprietà desiderate, che possono essere utilizzati in diverse applicazioni nell’intero campo della scienza. I nanomateriali presentano interessanti proprietà dipendenti dalla dimensione delle particelle, e inoltre il rapporto superficie-volume in questi materiali è estremamente alto, il che li rende utili per applicazioni in sensoristica e catalisi. In questo progetto di dottorato, diverse combinazioni di metalli nobili e ossidi di metalli di transizione sono state sfruttate per preparare film sottili inorganici, utilizzati come sensori ottici di gas riducenti: solitamente l’ossido semiconduttivo è responsabile per il meccanismo di rilevazione, mentre le nanoparticelle metalliche agiscono da sonde ottiche, aumentando la sensibilità, e/o da catalizzatori, migliorando le prestazioni del sensore. Il principale lavoro presentato in questa tesi è stato focalizzato sulla sintesi di questi materiali attraverso diverse strategie, a seconda della qualità desiderata per il materiale finale, della semplicità operativa, del controllo su parametri chiave come forma e dimensione delle particelle, la loro distribuzione dimensionale, la cristallinità dei diversi costituenti, la porosità. Nella prima parte, ioni di metalli nobili (Ag, Au, Pt) sono stati inseriti all’interno di matrici di ossidi attraverso sintesi sol-gel o processi di impregnazione, e successivamente ridotti a particelle metalliche attraverso trattamenti termici ad alta temperatura, che sono necessari anche per la cristallizzazione degli ossidi: i sistemi NiTiO3-TiO2-Au hanno dimostrato notevoli proprietà sensoristiche nella rilevazione di acido solfidrico, con elevata sensibilità e selettività nei confronti di gas interferenti quali H2 e CO. I risultati sperimentali suggeriscono un effetto dei cristalli di NiTiO3 nel promuovere l’ossidazione catalitica dell’H2S a ossidi di zolfo, mentre le nanoparticelle di oro non sono coinvolte direttamente nella reazione, ma agiscono come sonde ottiche, producendo un segnale ottico facilmente rilevabile. Discreti risultati per la rilevazione di CO e idrogeno sono stati presentati per altri film sottili nanocristallini, come SiO2-NiO-Ag, preparati combinando la tecnica sol-gel e il processo di impregnazione, film sol-gel a base di una matrice di ZnO e NiO contenenti nanoparticelle di Au, e film microstrutturati di WO3 contenenti nanoparticelle di Au e Pt sintetizzati combinando sputtering e impregnazione. La seconda parte di questa tesi è basata sulla sintesi colloidale di nanoparticelle di metalli (Au, Pt, Au@Pt core@shell) e di ossidi (TiO2, ZnO puro e drogato con ioni di metalli di transizione), aventi la desiderata dimensione e distribuzione dimensionale: protocolli di purificazione e concentrazione sono stati sviluppati, e le soluzioni ottenute sono state direttamente utilizzate per la deposizione di film sottili, ottenendo così rivestimenti nanocristallini a bassa temperatura. I film a base di TiO2 hanno mostrato buona sensibilità per idrogeno e CO, con un limite di rilevazione di circa 2 ppm, notevole se considerato che i film sono spessi solo 40-60 nm. Inoltre questi materiali si sono dimostrati capaci di rilevare vapori di etanolo a temperatura ambiente. Infine, campioni contenenti nanoparticelle di oro e platino sono in grado di rilevare idrogeno a temperatura ambiente, grazie all’effetto sinergico che avviene tra le proprietà ottiche dell’oro e quelle catalitiche del platino. I film a base di ZnO sono stati testati come sensori di CO, dimostrando una soglia di rilevazione di circa 1-2 ppm, e una relazione fra il tipo di dopante utilizzato (Ni, Co, Mn) e l’intensità della risposta è stata presentata. La terza parte è focalizzata sulla deposizione di strati di nanoparticelle di oro su substrati opportunamente funzionalizzati, e il loro successivo ricoprimento con film sol-gel: quando le particelle di oro sono molto vicine le une alle altre, le risonanze plasmoniche si accoppiano, e questo effetto può essere sfruttato per migliorare le prestazioni in ambiti quali sensoristica, SERS e catalisi. Strati di particelle di Au ricoperti da film di NiO o TiO2 hanno mostrato promettenti proprietà per la rilevazione di CO e idrogeno ad alte temperature, e di vapori di etanolo a basse temperature. Inoltre, strutture più complesse a base di uno strato di particelle di oro immobilizzato fra due film di ossidi diversi (NiO, TiO2, ZnO) sono state preparate, con lo scopo di migliorare la selettività verso gas interferenti, fornendo due diverse interfacce metallo/ossido.

Colloidal particles dispersed in complex fluids such as hydrogels and polymer melts are important because nano-scale inclusions often impart unexpected and commercially attractive changes in the dispersed phase. Future development of these colloidal composites, and diagnostics to characterize their microstructure, demand a sound understanding of micro-scale dynamics. Accordingly, this thesis addresses (i) the steady and dynamic electric-field-induced displacements of spherical colloidal particles embedded in hydrogels, and (ii) the anomalous viscosity reduction of polymer-nanocomposite melts. The first problem is undertaken by solving a multi-phase electrokinetic model that quantifies how the viscoelasticity, compressibility, and hydrodynamic permeability of the hydrogel skeleton, and physicochemical properties of the inclusions, modulate the particle dynamics and electroacoustic responses. For the second problem, a hydrodynamic model is developed, and its analytical solution and numerical extension are adopted to interpret recent experiments in the literature where the bulk viscosity decreases anomalously with increasing particle volume fraction.
Les particules colloïdales dispersées dans les fluides complexes comme les hydrogels et des fontes de polymères sont importantes parce que les inclusions à nano-échelle répandent souvent des changements inattendus et commercialement intéressants dans la phase dispersée. Les développements futurs de ces composites colloïdales et des diagnostiques pour caractériser leur microstructure, demande une bonne compréhension de la dynamique à micro-échelle. En conséquence, cette thèse porte sure (i) la progression régulière et dynamique des déplacements de particules colloïdales sphériques embarqués dans des hydrogels induits par le champ électrique, et (ii) la réduction anormale de la viscosité des fontes en polymères nanocomposites. Le premier problème est entrepris par la résolution d'un modèle électrocinétique à multiple phases qui quantifie de façon où la viscoélasticité, de compression, la perméabilité hydrodynamiques de squelette d'hydrogel et des propriétés physico-chimiques des inclusions, et de moduler la dynamique des particules et réponses électroacoustiques. Pour le deuxième problème, un modèle hydrodynamique est développé, sa solution analytique et son extension numérique sont adoptées pour interpréter les expériences récentes en littérature où la plus grande viscosité diminue anormalement avec l'augmentation du volume fraction des particules.

The thesis presents work regarding amphiphilic molecules associated in aqueous solution or at the liquid/solid interface. Two main topics are included: the temperature-dependent behavior of micelles and the adsorption of dispersants on carbon nanotube (CNT) surfaces. Various NMR methods were used to analyze those systems, such as chemical shift detection, spectral intensity measurements, spin relaxation and, in particular, self-diffusion experiments. Besides this, small angle X-ray scattering (SAXS) was also applied for structural characterization.   A particular form of phase transition, core freezing, was detected as a function of temperature in micelles composed by a single sort of Brij-type surfactants. In mixed micelles, that phase transition still occurs accompanied by a reversible segregation of different surfactants into distinct aggregates. Adding a hydrophobic solubilizate shifts the core freezing point to a lower temperature. Upon lowering the temperature to the core freezing point, the solubilizate is released. The temperature course of the release curves with different initial solubilizate loadings is rationalized in terms of a temperature-dependent loading capacity.   The behavior of amphiphilic dispersant molecules in aqueous dispersions of carbon nanotubes (CNTs) has been investigated with a Pluronic-type block copolymer as frequent model dispersant. Detailed dispersion curves were recorded and the distribution of the dispersant among different available environments was analyzed. The amount of dispersed CNT was shown to be defined by a complex interplay of several factors during the dispersion process such as dispersant concentration, sonication time, centrifugation and CNT loading. In the dispersion process, high amphiphilic concentration is required because the pristine CNT surfaces made available by sonication must be rapidly covered by dispersants to avoid their re-attachment. In the prepared dispersions, the competitive adsorption of possible dispersants was investigated that provided information about the relative strength of the interaction of those with the nanotube surfaces. Anionic surfactants were found to have a strong tendency to replace Pluronics, which indicates a strong binding of those surfactants.   CNTs were dispersed in an epoxy resin to prepare nanotube-polymer composites. The molecular mobility of epoxy was investigated and the results demonstrated the presence of loosely associated CNT aggregates within which the molecular transport of epoxy is slow because of strong attractive intermolecular interactions between epoxy and the CNT surface. The rheological behavior is dominated by aggregate-aggregate jamming.

QC 20180103

Liquid crystals (LCs) are an interesting class of materials that are attracting significant attention due to their ever-growing applications in a wide variety of fields such as liquid crystal display (LCD) technology, materials science and bioscience. In recent years, along with the developments of materials at the nanoscale, doping LCs with nanoparticles (NPs) has emerged as a very promising approach for improving LC properties. Nanoparticle additives can introduce novel effects on optical and electro-optical properties of nematic liquid crystals (N-LCs), such as altered molecular alignment, faster response time and increased efficiency. This thesis studies the impacts that the inclusion of metallic NPs made of gold or semiconductor CdSe quantum dots (QDs), have on optical and electro-optical properties of N-LCs. Using polarized optical microscopy and detailed capacitance and transmittance measurements of nematic mixtures in electro-optic test cells, characteristics such as optical texture, phase transition temperatures, switching voltages and dielectric anisotropy are investigated in pure as well as doped samples. Surface ligands in NPs and their chemical functionalization play an important role in the LC-NP interactions, largely by determining the dispersibility of NPs and stability of the nanocomposites. One important objective of this thesis is to investigate and prepare a series of gold nanoparticles (Au NPs) with specially formulated robust coatings that maximizes solubility and stability in LC medium. Silanization of NPs is developed as a method to overcome the stability challenge. The functionalization of silanized NPs with aliphatic ligands or liquid crystalline molecules, provides chemically and thermally stable NPs with hydrophobic and structurally compatible surfaces required for dispersion in N-LCs. After complete characterization the synthesized particles are used to make the new nematic nanocomposites. By analysis of the structure-property relationships governing LC-nanomaterial composites and by comparison of new results and data from previous studies on other types of NPs, this thesis will further reveal the mechanism of the interrelations between host LC molecules and NP, considering the role of variables such as core composition, size and surface chemistry of NPs (e.g. siloxane shell, aliphatic ligand vs. liquid crystalline ligand) in achieving stable LC composites with desired optical and electro-optical properties.

Ce travail de thèse porte sur le développement de nouvelles couches minces nanocomposites par plasma froid à la pression atmosphérique. L'objectif principal est d'améliorer la compréhension des mécanismes physico-chimiques régissant ce procédé de synthèse. La stratégie adoptée est basée sur l'injection via un aérosol d'une suspension colloïdale de nanoparticules d'oxyde métallique dans une décharge à barrière diélectrique opérant en atmosphère d'azote (décharge de Townsend). Dans un premier temps, la synthèse est réalisée de manière séquentielle, la fabrication d'une matrice inorganique de silice (SiO2) étant séparée du dépôt des nanoparticules (TiO2). Ensuite, les couches nanocomposites sont obtenues par un procédé en une seule étape à travers l'injection simultanée dans la décharge des nanoparticules et d'un précurseur polymérisable organosiliciée (HMDSO). Les travaux présentés dans ce manuscrit se divisent en quatre grandes parties : tout d'abord le procédé de fabrication des nanoparticules est présenté, et une étude de leur dispersion dans divers solvants chimiques est réalisée. Puis la deuxième partie s'intéresse à l'étape de nébulisation de la suspension colloïdale, à l'analyse des distributions de taille des objets injectés et à l'étude de leur transport sans plasma. En particulier, une étude de l'influence des principales forces agissant sur leur transport est réalisée. Ces résultats permettent ensuite d'évaluer l'impact de la décharge sur le transport, et sur la réalisation des couches minces nanocomposites. Finalement, l'analyse des propriétés obtenues pour ces couches minces sur des substrats de bois est présentée dans une dernière partie
This PhD work is focused on the development of a new generation of nanocomposite thin films using cold plasma at atmospheric pressure. The main objective is to improve the understanding of the mechanisms involved in this process.The strategy is based on the injection of a metal oxide nanoparticles suspension in a dielectric barrier discharge operating in nitrogen (Townsend discharge). At first, the nanocomposite thin film is deposited sequentially: the fabrication of the inorganic matrix of silica (SiO2) is separated from the collection of the nanoparticles (TiO2). Then, the nanocomposite layers are obtained by a one-step process using a direct injection inside the discharge of nanoparticles dispersed in a polymerizable organosilicon precursor (HMDSO). This manuscript is divided into four major parts: first, the synthesis of the nanoparticles and the study of their dispersion in different solvents are presented. Then, in the second part we focus on the atomization of the colloidal suspension, on the analysis of the size distributions of the injected objects and on the study of their transport towards the discharge area. These results are then used to assess the influence of the discharge on the transport and the quality of deposited nanocomposite thin films. Finally, the thin films properties are investigated when depositing on wood substrates

Les assemblages colloïdaux représentent une nouvelle piste très prometteuse dans le domaine de l'ingénierie tissulaire. Idéalement, ce type d'assemblage permet l'obtention de matériaux injectables et gélifiants sur le site lésionnel, favorisant par la suite le développement de néo-tissus viables. Ce travail porte sur la formation de tels assemblages à base de chitosane et de poly(acide lactique) (PLA). Deux types d'assemblages ont été conçus et étudiés dans ce travail. Dans une première approche, le mélange de particules anioniques de poly (acide lactique) (PLA) avec du chitosane en solution faiblement acide conduit à la formation de « gels composites », résultant des interactions colloïde-polymère. Des analyses rhéologiques et de diffusion des rayons X aux petits angles ont permit de mettre en évidence le mode de formation et l'influence de plusieurs paramètres sur les propriétés finales de ces gels. Notamment, ils présentent des propriétés rhéofluidifiantes et un caractère réversible, c'est-à-dire que le gel peut se reformer après déstructuration mécanique. Le second type d'assemblage résulte du mélange de particules anioniques de PLA et de nanogels cationiques de chitosane, conduisant à la formation de « gels colloïdaux », par interactions colloïde-colloïde. L'influence de plusieurs facteurs sur la formation et les propriétés de ces gels a également été étudiée par mesures rhéologiques. Notre étude s'est notamment orientée sur la caractérisation et la stabilité des hydrogels physiques de chitosane sous forme colloïdale, ainsi que sur l'optimisation de leur cohésion
Colloidal assemblies may be a promising pathway to obtain injectable scaffolds favoring the development of neo-tissue in regenerative medicine. This work investigates the formation of such assemblies composed of chitosan, soluble or in suspension (nano-hydrogel), and poly(lactic acid) (PLA) nanoparticles. Two types of assemblies are studied. As a first approach, mixing negatively charged PLA particles and chitosan solution leads to the formation of “composite gels”, based on colloidpolymer interactions. Rheological and Small Angle X-Ray Scattering measurements highlighted the formation process and the influence of various parameters on final properties of these gels, which features shear-thinning and reversibility behavior, that is, the capacity to gel again after yielding. PLA nanoparticles could also be mixed with cationic chitosan nanoparticles, which are crosslinker free nano-hydrogels, leading to the formation of “colloidal gels”, based on colloid-colloid interactions. Influence of various parameters on gel synthesis and properties are investigated through rheological measurements. The study also focuses on the characterization and control of the morphological and cohesion properties of chitosan nanogel

For more than a decade nanomaterials have attained huge attraction owing to the exceptionally different and excellent characteristics as compared to their bulk form. In the present research, we focus on understanding the properties and performance of nanocomposites in solid and liquid states. There are three major areas involved in this thesis research. Firstly, we will identify effective methods or techniques to evaluate nanomaterials. Conventional and non-conventional techniques will be implied. The second part is to study the interfacial reactions between nanoparticles (NPs) and fluid molecules. This is to obtain basic understanding of nanoparticles and their interactions with matrix materials. Thirdly, we will investigate the mechanical properties of nanocomposites. Experimental results showed that the mechanical properties of nanocomposites measured at macroscale exhibited differences when the shape and size of gold NPs were changed. The morphological characteristics of the material were shown effectively at the nanoscale based on the NPs' shape and size. The properties of NPs influenced the properties of gold colloid. Such changes were the result of the interfacial interaction of gold NPs and the host material.

博士
國防大學中正理工學院
國防科學研究所
96
Dispersion degree strongly influences the rheological properties of nanoparticles containing suspension and, as a consequence, the quality of the deposited film. Furthermore, their applications will be rigorously restricted if the bad dispersion can not be solved effectively. Therefore, knowing the dispersion degree of pastes before its application is inevitable. In this study, the dispersion of nanoparticles utilizing the physical and/or the chemical method within several suspension systems were investigated. The great emphasis is put on the effect of dispersion on the rheological properties of suspension. Both particle size measurement and morphology were usually carried out to analyze the effect of dispersion. However, these kinds of analysis are time-consuming, and their results might only display parts of the whole picture. The dispersed quality is very difficult to judge with only one single instrument. The studies on the rheological characteristics which offer the real on-time and intact processing data provide us a reliable way to analyze the dispersion degree of particles. The results show After SiO2 powders are treated with a silane coupling agent, leading to an improvement of the compatibility between particles and medium on one hand; That mixing with a three roll mill is an effective tool to break the agglomerates of silver nanoparticles in solvent, resulting in a better dispersion. In addition, the film deposited from suspension with Ag nanoparticles mixed by three roller mill has the lowest resistivity of approximately 3.64×102 μΩcm; The dispersion of Catalyst show that the catalyst can be dispersed more effectively by mixing with planet mixer than that by homogenizer based on our dispersal conditions. As an anionic surfactant SA is used as a dispersant, the adsorbed SA layer on the catalyst surfaces provides an electrostatic stabilization effect, resulting in a better dispersion degree. In addition, the effect of Disper Anion H14N(SA) on the activity of catalyst is insignificant. It is worth to be mentioned that some works are dedicated to investigate the rheological behaviors of the shear thickening fluid (STF). The shear thickening fluid has been reported that it can be applied in the defensive and the protective equipments. Utilization of this shear thickening characteristic, the ballistic protection capability afforded by fabricated, flexible body liquid armor can be enhanced tremendously. Not merely have military value, it can be further used to make the anti-impact materials to protect the human body, and, thus, increase the social welfare.

碩士
國立高雄師範大學
化學系
96
A novel organic/inorganic nanocomposite with highly transparent, heat resistance and mechanical properties was prepared by sol-gel process. In this experiment, the organic matrix was synthesized by the condensation reaction of waterborne polyurethane (WPU), acrylate monomer (SR-444) and coupling agent (SAPSH). Then this complex was hydrolysis in acid solution at 70~75 ℃ to form a silanol derivative which could successfully bond with inorganic anti-static reagent (colloid Al2O3). Finally, the WPU/SR-444/SAPSH/Al2O3 organic/inorganic nanocomposite was crosslinked and synthesized by chain polymerization. TAIC , which contains three active vinyl groups, was used as a crosslinking agent to improve the thermal and mechanical characters of these nanocomposites. The new composites would be excellent optical materials used in photoelectric industry. The result showed that the surface resistance of WPU/SR-444 /SAPSH/colloid Al2O3 organic/inorganic nanocomposites had decreased. Besides, when 0~15wt% of colloid Al2O3 was used , the surface resistance of hybrid films reduced from 2.65×1011 to 2.05×109Ω/cm2 and it also achieved the anti-static character. Moreover, according to the best synthesis component of this nanocomposite, the Td value was 427.55 ℃ which was higher 14.66 ℃and34.24 ℃ than that of pure acrylate (polymerized from SR-444) and pure WPU resins respectively. When we added TAIC crosslinking reagent to strengthen the network bonding of WPU/SR-444/SAPSH/Al2O3 nanocomposite, the Td value was even up to 446.67 ℃,which was higher 19.12 ℃ than that of nanocomposite with non-crosslinking reagent. The hardness of transparent hybrid films could be attained to 8H~9H. In addition, the glass transition temperature was not detected below 200 ℃ by DSC. The excellent optical transparency was achieved in the visible region and its optical transparent degree could reach over 85 %. Finally, the morphology of the optic thin films, which were estimated by TEM, was evenly distributed with inorganic colloidal particles and the average particle size of these composites was 20~30 nm.

This dissertation work addresses two important aspects of nanotechnology - stable dispersion and self-assembly of colloidal nanostructures. Three distinctly different types of nano-scaled materials have been studied: 0-dimensional ZnO quantum dots (QDs), 1-dimensional carbon nanotubes (CNTs), and 2-dimensional alpha-zirconium phosphate (ZrP) nanoplatelets. Specifically, highly crystalline ZrP layered compounds with differences in diameters have been synthesized and fully exfoliated into monolayer platelets with uniform thickness, followed by their self-assembly into liquid crystalline structures, i.e., nematic and smectic. A novel colloidal approach to debundle and disperse CNTs has been developed by utilizing nanoplatelets to gather and concentrate sonication energy onto nanotube bundles. In such a fashion, CNTs are fully exfoliated into individual tubes through physical means to preserve their exceptional physical properties. Moreover, monodisperse ZnO QDs with high purity have been synthesized through a simple colloidal approach. Exfoliated ZrP nanoplatelets are used to tune the dispersion of ligand-free ZnO QDs from micron-sized aggregates to an individual QD level depending on the ratio between nanoplatelets and QDs. Dynamic analysis suggests that the dispersion mechanism mainly involves the change of QD dispersion free energy due to the presence of nanoplatelets, so that QDs can interact favorably with the surrounding media. In addition, the nanoplatelet-assisted dispersion approach has been utilized to disperse QDs and CNTs into polymeric matrices. Dispersion - property relationship in polymer nanocomposites has been systematically investigated with emphasis on optical properties for QDs and mechanical properties for CNTs.

碩士
中原大學
化學研究所
94
Here we report the homogeneous dispersion of nanoscale mesoporous silica (NMS) and colloidal alumina into PVA matrix to form novel PVA/NMS nanocomposites and PVA/ colloidal alumina nanocomposites via hydrogen bonding. The properties of the hybrids were studied in the film form as a function of the NMS and colloidal alumina concentration in the matrix polymer. The NMS and colloidal alumina concentration of the composites was varied from 0 to 10 wt %. The nanoscale mesoporous silica materials and colloidal alumina are characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Effects of the material composition on the thermal stability, mechanical strength, optical clarity, barrier properties of PVA along with a series of PVA/NMS nanocomposites and PVA/ colloidal alumina nanocomposites materials, in the form of fine powder and free-standing film, are also studied by TGA, DSC, DMA, UV–visible transmission spectra, GPA and VPA respectively. In addition, thermal, mechanical and barrier properties of the PVA were investigated after incorporation of the NMS and colloidal alumina.

Nanoparticles (such as, carbon nanotubes, carbon black, clay etc.) have one or more dimensions of the order of 100 nm or less. Owing to very high van der Waals force of attraction, these nanoparticles exist in a highly aggregated state. It is often required to break these aggregates to truly experience the “nanosize” effect for any required end use. There are several strategies proposed for dispersing/exfoliating nanoparticles but limited progress has been made towards controlling their dispersion state. The ability to tailor nanoparticle dispersion state in liquid and solid media can ultimately provide a powerful method for tailoring the properties of solution processed nanoparticle-filled polymer composites. This dissertation reports the use of a variety of stimuli-responsive polymers to control the dispersion state of single-walled carbon nanotubes. Stimuli-responsive polymers exhibit conformational transitions as a function of applied stimulus (like pH, temp, chemical etc.). These variations in conformations of the polymer can be used tailor nanotube dispersion state in water and solid composites.The use of pH and temperature responsive polymers to stabilize/disperse single walled carbon nanotubes (SWNTs) in water is presented. Non-covalent functionalization of SWNTs using pH and temperature responsive polymer show tailored dispersion state as a function of pH and temperature, respectively. Carbon nanotube microstructure in these aqueous suspensions was characterized using several techniques (cryo-TEM, viscosity measurements, uv-vis spectroscopy, zeta potential measurements and settling behavior). Furthermore, nanotube dispersion state in aqueous suspensions is preserved to a large extent in the composites formed by drying these suspensions as evidenced by SEM images and electrical conductivity measurements. Based on the results obtained a mechanism is proposed to explain the tailored dispersion of SWNTs as a functions of applied external stimulus (i.e., pH, temperature). Such stimuli-controlled dispersion of carbon nanotubes could have a variety of applications in nanoelectronics, sensing, and drug and gene delivery systems. Furthermore, this dissertation also contains a published study focused on controlling the dispersion state of carbon black (CB) in epoxy composites using clay.

abstract: Satisfying the ever-increasing demand for electricity while maintaining sustainability and eco-friendliness has become a key challenge for humanity. Around 70% of energy is rejected as heat from different sectors. Thermoelectric energy harvesting has immense potential to convert this heat into electricity in an environmentally friendly manner. However, low efficiency and high manufacturing costs inhibit the widespread application of thermoelectric devices. In this work, an inexpensive solution processing technique and a nanostructuring approach are utilized to create thermoelectric materials. Specifically, the solution-state and solid-state structure of a lead selenide (PbSe) precursor is characterized by different spectroscopic techniques. This precursor has shown promise for preparing thermoelectric lead selenide telluride (PbSexTe1-x) thin films. The precursor was prepared by reacting lead and diphenyl diselenide in different solvents. The characterization reveals the formation of a solvated lead(II) phenylselenolate complex which deepens the understanding of the formation of these precursors. Further, using slightly different chemistry, a low-temperature tin(II) selenide (SnSe) precursor was synthesized and identified as tin(IV) methylselenolate. The low transformation temperature makes it compatible with colloidal PbSe nanocrystals. The colloidal PbSe nanocrystals were chemically treated with a SnSe precursor and subjected to mild annealing to form conductive nanocomposites. Finally, the room temperature thermoelectric characterization of solution-processed PbSexTe1-x thin films is presented. This is followed by a setup development for temperature-dependent measurements and preliminary temperature-dependent measurements on PbSexTe1-x thin films.
Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2020

Ce travail de thèse porte sur le développement de nouvelles couches minces nanocomposites par plasma froid à la pression atmosphérique. L’objectif principal est d’améliorer la compréhension des mécanismes physico-chimiques régissant ce procédé de synthèse. La stratégie adoptée est basée sur l’injection via un aérosol d’une suspension colloïdale de nanoparticules d’oxyde métallique dans une décharge à barrière diélectrique opérant en atmosphère d’azote (décharge de Townsend). Dans un premier temps, la synthèse est réalisée de manière séquentielle, la fabrication d’une matrice inorganique de silice (SiO2) étant séparée du dépôt des nanoparticules (TiO2). Ensuite, les couches nanocomposites sont obtenues par un procédé en une seule étape à travers l’injection simultanée dans la décharge des nanoparticules et d’un précurseur polymérisable organosiliciée (HMDSO). Les travaux présentés dans ce manuscrit se divisent en quatre grandes parties : tout d’abord le procédé de fabrication des nanoparticules est présenté, et une étude de leur dispersion dans divers solvants chimiques est réalisée. Puis la deuxième partie s’intéresse à l’étape de nébulisation de la suspension colloïdale, à l’analyse des distributions de taille des objets injectés et à l’étude de leur transport sans plasma. En particulier, une étude de l'influence des principales forces agissant sur leur transport est réalisée. Ces résultats permettent ensuite d’évaluer l’impact de la décharge sur le transport, et sur la réalisation des couches minces nanocomposites. Finalement, l’analyse des propriétés obtenues pour ces couches minces sur des substrats de bois est présentée dans une dernière partie.
This PhD work is focused on the development of a new generation of nanocomposite thin films using cold plasma at atmospheric pressure. The main objective is to improve the understanding of the mechanisms involved in this process. The strategy is based on the injection of a metal oxide nanoparticles suspension in a dielectric barrier discharge operating in nitrogen (Townsend discharge). At first, the nanocomposite thin film is deposited sequentially: the fabrication of the inorganic matrix of silica (SiO2) is separated from the collection of the nanoparticles (TiO2). Then, the nanocomposite layers are obtained by a one-step process using a direct injection inside the discharge of nanoparticles dispersed in a polymerizable organosilicon precursor (HMDSO). This manuscript is divided into four major parts: first, the synthesis of the nanoparticles and the study of their dispersion in different solvents are presented. Then, in the second part we focus on the atomization of the colloidal suspension, on the analysis of the size distributions of the injected objects and on the study of their transport towards the discharge area. These results are then used to assess the influence of the discharge on the transport and the quality of deposited nanocomposite thin films. Finally, the thin films properties are investigated when depositing on wood substrates.

This dissertation develops a novel application of the resonant-infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) technique toward the end goal of conjugated-polymer-based optoelectronic device fabrication. Conjugated polymers are attractive materials that are being investigated in the development of efficient optoelectronic devices due to their inexpensive material costs. Moreover, they can easily be combined with inorganic nanomaterials, such as colloidal quantum dots (CQDs), so as to realize hybrid nanocomposite-based optoelectronic devices with tunable optoelectronic characteristics and enhanced desirable features. One of the most significant challenges to the realization of optimal conjugated polymer-CQD hybrid nanocomposite-based optoelectronics has been the processes by which these materials are deposited as thin films, that is, conjugated polymer thin film processing techniques lack sufficient control so as to maintain preferred optoelectronic device behavior. More specifically, conjugated-polymer-based optoelectronics device operation and efficiency are a function of several attributes, including surface film morphology, internal polymer chain morphology, and the distribution and type of nanomaterials in the film bulk. Typical conjugated-polymer thin-film fabrication methodologies involve solution-based deposition, and the presence of the solvent has a deleterious impact, resulting in films with poor charge transport properties and subsequently poor device efficiencies. In addition, many next-generation conjugated polymer-based optoelectronics will require multi-layer device architectures, which can be difficult to achieve using traditional solution processing techniques. These issues direct the need for the development of a new polymer thin film processing technique that is less susceptible to solvent-related polymer chain morphology problems and is more capable of achieving better controlled nanocomposite thin films and multi-layer heterostructures comprising a wide range of materials. Therefore, this dissertation describes the development of a new variety of RIR-MAPLE that uses a unique target emulsion technique to address the aforementioned challenges.

The emulsion-based RIR-MAPLE technique was first developed for the controlled deposition of the conjugated polymers poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and poly[2-methoxy-5-(2'ethylhexyloxy)-1,4-(1-cyanovinylene) phenylene] (MEH-CN-PPV) into homogenous thin films. Therein, it was identified that target composition had the most significant influence on film surface morphology, and by tuning the concentration of hydroxyl bonds in the target bulk, the laser-target absorption depth could be tuned so as to yield more or less evaporative deposition, resulting in films with tunable surface morphologies and optical behaviors.

Next, the internal morphologies of emulsion-based RIR-MAPLE-deposited MEH-PPV thin films were investigated by measuring their hole drift mobilities using the time-of-flight (TOF) photoconductivity method in the context of amorphous materials disorder models (Bässler's Gaussian Disorder model and the Correlated Disorder model) in order to provide a quantitative measure of polymer chain packing. The polymer chain packing of the RIR-MAPLE-deposited films was demonstrated to be superior and more conducive to charge transport in comparison to spin-cast and drop-cast MEH-PPV films, yielding enhanced hole mobilities.

The emulsion-based RIR-MAPLE technique was also developed for the deposition of different classes of inorganic nanoparticles, namely un-encapsulated nanoparticles and ligand-encapsulated nanoparticles. These different classes of nanoparticles were identified to have different film growth regimes, such that either rough or smooth films were obtained, respectively. The ligand-encapsulated nanoparticles were then co-deposited with MEH-PPV as conjugated polymer-CQD hybrid nanocomposites, wherein the distributions of the constituent materials in the film bulk were identified to be tunable, from homogeneous to highly clustered. The RIR-MAPLE deposition regime determined the said distributions, that is, if the polymer and CQDs were sequentially deposited from a sectioned target or simultaneously deposited from a single target, respectively. The homogeneous conjugated polymer-CQD nanocomposites were also investigated in terms of their charge transport properties using the TOF photoconductivity technique, where it was identified that despite the enhanced dispersion of CQDs in the film bulk, the presence of a high concentration of CQDs degraded hole drift mobility, which indicates that special considerations must be taken when incorporating CQDs into conjugated-polymer-based nanocomposite optoelectronics.

Finally, the unique capability of RIR-MAPLE to enable novel conjugated polymer-based optical heterostructures and optoelectronic devices was evaluated by the successful demonstration of a conjugated polymer-based distributed Bragg reflector (DBR), a plasmonic absorption enhancement layer, and a conjugated polymer-based photovoltaic solar cell featuring a novel electron-transporting layer. These optical heterostructures and optoelectronic devices demonstrate that all of the constituent polymer and nanocomposite layers have controllable thicknesses and abrupt interfaces, thereby confirming the capability of RIR-MAPLE to achieve multi-layer, conjugated polymer-based heterostructures and device architectures that are appropriate for enhancing specific desired optical behaviors and optoelectronic device efficiencies.

Dissertation

The thesis describes the study of slow dynamics of confined polymers and soft colloids. We study the finite size effect on the dynamics of glassy polymers using newly developed interfacial microrheology technique. Systematic measurement have been performed to address the issue of reduction of glass transition under confinements. Slow and heterogeneous dynamics are the underlined observed behavior for dynamics in confined glassy polymers. The slow relaxation dynamics and dynamical heterogeneity in polymer grafted nanoparticles (PGNPs) systems were studied using advanced X - ray photon correlation spectroscopy (XPCS) techniques. Our studies presented in this thesis on dynamics of polymer grafted nanoparticle systems in melts and solution are the first attempt to study them experimentally. Thus our work shed the light about new technique to study confined system more accurately and explore new soft colloidal system to study fascinating dynamics and interesting phase behavior. In Chapter 1, we provide the theoretical background along with brief review of the literature for understanding the results presented in this thesis. The details of the experimental set up and their operating principle along with the details of the experimental conditions are provided in Chapter 2. In Chapter 3 we present our newly developed technique (interfacial microrhelogy) and its consequences to study the complex fluids at interface. Chapter 4 discusses the concentration and temperature dependent glassy dynamics in confined glassy polymers. In Chapter 5 we provide the structural and dynamical study of polymer grafted nanoparticles in melts and solutions. We provide the summary of our result and the future prospective of the work in Chapter 6. Chapter-1 provides the ground work and theoretical aspects for understanding the results presented in this thesis. It starts with the discussion about the slow dynamics of complex fluids and transit to dynamic behavior of polymer in confinement, glassy dynamics in confinements . This also discusses the basic aspects of studying viscoelastic properties using rheology, interface rheology, microrheology, interface microrheology techinques. In continuation it discusses structure and dynamics of different soft colloids investigated for last decade and then theoretical aspects of XPCS is discussed. Towards the end of this Chapter, we discuss the procedure to explain and understand systems dynamical heterogeneity near glass like phase transition. Chapter-2 contains the details of the experimental techniques which has been used for the study of confined polymers and soft colloids. Brief introduction to basic principles of the measurements followed by details of the material and methods have been provided. Chapter-3 we discuss the interafacial microrheology of different complex fluids and advantages of the techniques is discussed in Chapter 3. This includes discussion about the technique sensitivity at the surface using quantum dots (QDs) as a probe and about the configuration of the QDs at/on monolayer. Later on establishment of the technique has been demonstrated through easurements on arachidic acid, poly(methylmethacrylate) (PMMA), poly(vinylacetate) (PVAc), poly(methylacrylate) (PMA) monolayers. The extracted subdiffusive nature of QDs in on monolayers through mean square displacement has been explained using fractional Brownian motion model. Towards the end of the chapter we discuss about the extraction of real and imaginary elastic modulus from mean square displacement data using generalized Stokes-Einstein relation for the quasi two dimensional systems and explains about the possible viscoelastic transition in the different monolayers. The concentration and temperature dependent glassy dynamics of confined polymers (PMMA) are discussed in Chapter-4. We demonstrate the microscopic nature of spatio-temporal variation of dynamics of glassy polymers confined to a monolayer of 2 􀀀 3 nm thickness as a function of surface density and temperature. It illustrates the systems dynamical heterogeneity and explain the observed large reduction of glass transition temperature in confined system through finite size effect. In Chapter 5 we discuss the result based on systematic studies of dynamics of PGNPs in melts and solutions. In addition it also illustrates the structural anisotropy and anomalous dynamical transitions in binary mixture of PGNPs and homopolymers in good solvent condition. It provides temperature and wave vector dependent XPCS measurements on polymer grafted nanoparticles with the variation of functionality. The functionality ( f ) dependent nonmonotonic relaxation in melts of PGNPs and solvent quality dependent non monotonic relaxation of PGNPs system have been elaborated in the continuation. We present possible phase behavior of PGNPs system in good solvent with addition of homopolymer of two different molecular weight. Chapter 6 contains the summary and the future perspective of the work presented.

The thesis describes the study of slow dynamics of confined polymers and soft colloids. We study the finite size effect on the dynamics of glassy polymers using newly developed interfacial microrheology technique. Systematic measurement have been performed to address the issue of reduction of glass transition under confinements. Slow and heterogeneous dynamics are the underlined observed behavior for dynamics in confined glassy polymers. The slow relaxation dynamics and dynamical heterogeneity in polymer grafted nanoparticles (PGNPs) systems were studied using advanced X - ray photon correlation spectroscopy (XPCS) techniques. Our studies presented in this thesis on dynamics of polymer grafted nanoparticle systems in melts and solution are the first attempt to study them experimentally. Thus our work shed the light about new technique to study confined system more accurately and explore new soft colloidal system to study fascinating dynamics and interesting phase behavior. In Chapter 1, we provide the theoretical background along with brief review of the literature for understanding the results presented in this thesis. The details of the experimental set up and their operating principle along with the details of the experimental conditions are provided in Chapter 2. In Chapter 3 we present our newly developed technique (interfacial microrhelogy) and its consequences to study the complex fluids at interface. Chapter 4 discusses the concentration and temperature dependent glassy dynamics in confined glassy polymers. In Chapter 5 we provide the structural and dynamical study of polymer grafted nanoparticles in melts and solutions. We provide the summary of our result and the future prospective of the work in Chapter 6. Chapter-1 provides the ground work and theoretical aspects for understanding the results presented in this thesis. It starts with the discussion about the slow dynamics of complex fluids and transit to dynamic behavior of polymer in confinement, glassy dynamics in confinements . This also discusses the basic aspects of studying viscoelastic properties using rheology, interface rheology, microrheology, interface microrheology techinques. In continuation it discusses structure and dynamics of different soft colloids investigated for last decade and then theoretical aspects of XPCS is discussed. Towards the end of this Chapter, we discuss the procedure to explain and understand systems dynamical heterogeneity near glass like phase transition. Chapter-2 contains the details of the experimental techniques which has been used for the study of confined polymers and soft colloids. Brief introduction to basic principles of the measurements followed by details of the material and methods have been provided. Chapter-3 we discuss the interafacial microrheology of different complex fluids and advantages of the techniques is discussed in Chapter 3. This includes discussion about the technique sensitivity at the surface using quantum dots (QDs) as a probe and about the configuration of the QDs at/on monolayer. Later on establishment of the technique has been demonstrated through easurements on arachidic acid, poly(methylmethacrylate) (PMMA), poly(vinylacetate) (PVAc), poly(methylacrylate) (PMA) monolayers. The extracted subdiffusive nature of QDs in on monolayers through mean square displacement has been explained using fractional Brownian motion model. Towards the end of the chapter we discuss about the extraction of real and imaginary elastic modulus from mean square displacement data using generalized Stokes-Einstein relation for the quasi two dimensional systems and explains about the possible viscoelastic transition in the different monolayers. The concentration and temperature dependent glassy dynamics of confined polymers (PMMA) are discussed in Chapter-4. We demonstrate the microscopic nature of spatio-temporal variation of dynamics of glassy polymers confined to a monolayer of 2 3 nm thickness as a function of surface density and temperature. It illustrates the systems dynamical heterogeneity and explain the observed large reduction of glass transition temperature in confined system through finite size effect. In Chapter 5 we discuss the result based on systematic studies of dynamics of PGNPs in melts and solutions. In addition it also illustrates the structural anisotropy and anomalous dynamical transitions in binary mixture of PGNPs and homopolymers in good solvent condition. It provides temperature and wave vector dependent XPCS measurements on polymer grafted nanoparticles with the variation of functionality. The functionality ( f ) dependent nonmonotonic relaxation in melts of PGNPs and solvent quality dependent non monotonic relaxation of PGNPs system have been elaborated in the continuation. We present possible phase behavior of PGNPs system in good solvent with addition of homopolymer of two different molecular weight. Chapter 6 contains the summary and the future perspective of the work presented.

Recent advancements in nanotechnology and emerging applications of nanomaterials in various fields have stimulated interest in fundamental scientific research dealing with the size and structure controlled synthesis of nanoparticles. The unique properties of nanoparticles are largely size dependent which could be tuned further by varying shape, structure, and surface properties, etc. The preparation of monodisperse nanoparticles is desirable for many applications due to better control over properties and higher performance compared to polydispersity nanoparticles. There are several methods for the synthesis of nanoparticles based on top-down and bottom-up approaches. The main disadvantage of top-down approach is the difficulty in achieving size control. Whereas, uniform nanoparticles with controllable size could be obtained by chemical methods but most of them are difficult to scale up. Moreover, a separate step of size separation is necessary in order to achieve monodispersed which may lead to material loss. In this context, a post-synthetic size modification process known as digestive ripening is highly significant. In this process, addition of a capping agent to poly disperse colloid renders it highly monodisperse either under ambient or thermal conditions. In addition to size control, digestive ripening is also effective in controlling the structure of nanoparticles in colloidal solution comprising two different elements. Use of co-digestive ripening strategy in conjunction with solvated metal atom dispersion (SMAD) method of synthesis resulted in hetero structures such as core–shell, alloy, and composite nanoparticles. Despite the versatility of digestive ripening process, the underlying mechanism in controlling size and structure of nanoparticles are not understood to date. The aim of this thesis is to gain mechanistic insight into size control of digestive ripening as well as to investigate structure control in various binary systems. Objectives  Study digestive ripening of Au nanoparticles using various alkyl amines to probe the mechanism  Study co-digestive ripening of binary colloids consisting of two metals, Pd and Cu prepared separately by SMAD method  Study co-digestive ripening of binary colloids consisting of a metal (Au) and a semiconductor (CdS) prepared separately by SMAD method  Study vaporization of bulk brass in SMAD reactor and analyse phase, structure, and morphology of various Cu/Zn bimetallic nanoparticles obtained from bulk brass under various experimental conditions Significant results In chapter 1, fundamental processes of nanoparticle formation and common synthetic techniques for the preparation of monodisperse nanoparticles are briefly discussed. Chapter 2 presents a mechanistic study of digestive ripening process with regard to size control using Au nanoparticles as a model system. Three long chain alkyl amine molecules having different chain length were used as digestive ripening agents. The course of digestive ripening process was analysed by UV-visible spectroscopy and transmission electron microscopy. The experimental conditions such as concentration of digestive ripening agent, time, and temperature were found to influence the size distribution of nanoparticles. The average particle size was found to be characteristic of metal-digestive ripening agent combination which is considered as the optimum size preferred during digestive ripening under a given set of experimental conditions. This study discusses stabilization of optimum sized particles, surface etching, and reversibility in digestive ripening. Chapter 3 describes the synthesis and characterization of PdCu alloy nanoparticles by co-digestive ripening method. Syntheses of individual Pd and Cu colloids were carried out by SMAD method. Pd nanoparticles obtained using THF as solvent and in the absence of any capping agent resulted in an extended small Pd nanowire network assembly. Morphological evolution of spherical Pd nanoparticles from Pd nanowire network structure was observed with the use of capping agent, hexadecyl amine (HDA) in SMAD method. Co-digestive ripening of Pd and Cu colloids was studied at various temperatures. This study revealed temperature dependent diffusion of Cu atoms into Pd lattice forming PdCu alloy nanoparticles. Next, co-digestive ripening of a colloidal system comprising a metal and a semiconductor was explored. Au-CdS combination was chosen for this study owing to its interesting photocatalytic properties. Chapter 4 deals with the synthesis of Au and CdS nanoparticles by SMAD method and Au/CdS nanocomposite by co-digestive ripening. CdS nanoparticles of size 4.0 + 1.2 nm and Au nanoparticles of size 5.6 + 1.1 nm were obtained as a result of digestive ripening process. Au/CdS nanocomposite obtained by co-digestive ripening was characterized by a matrix-like structure made up of CdS nanoparticles in which Au nanoparticles were embedded. CdS nanoparticles were found to establish an intimate surface contact with Au nanoparticles and the matrix of CdS surrounding Au was developed via aggregation during digestive ripening. Chapter 5 describes a comprehensive study on various Cu/Zn bimetallic nanoparticles obtained from bulk brass. Vaporization of bulk brass in SMAD reactor led to a deploying process and further growth of nanoparticles from phase separated Cu and Zn atoms formed a composite structure. The characterization of Cu/Zn nanocomposite revealed covering of composite surface with Cu resulting in a core-shell structure, Cu/Zn@Cu. Post-synthetic digestive ripening of these core-shell composite particles showed diffusion of Zn atoms to the composite surface in addition to size and shape modification. Annealing of Cu/Zn nanocomposites prepared in THF resulted in α-CuZn alloy nanoparticles via sequential transformation through η-CuZn5, γ-Cu5Zn8, and β-CuZn (observed as marten site) phases.

Recent advancements in nanotechnology and emerging applications of nanomaterials in various fields have stimulated interest in fundamental scientific research dealing with the size and structure controlled synthesis of nanoparticles. The unique properties of nanoparticles are largely size dependent which could be tuned further by varying shape, structure, and surface properties, etc. The preparation of monodisperse nanoparticles is desirable for many applications due to better control over properties and higher performance compared to polydispersity nanoparticles. There are several methods for the synthesis of nanoparticles based on top-down and bottom-up approaches. The main disadvantage of top-down approach is the difficulty in achieving size control. Whereas, uniform nanoparticles with controllable size could be obtained by chemical methods but most of them are difficult to scale up. Moreover, a separate step of size separation is necessary in order to achieve monodispersed which may lead to material loss. In this context, a post-synthetic size modification process known as digestive ripening is highly significant. In this process, addition of a capping agent to poly disperse colloid renders it highly monodisperse either under ambient or thermal conditions. In addition to size control, digestive ripening is also effective in controlling the structure of nanoparticles in colloidal solution comprising two different elements. Use of co-digestive ripening strategy in conjunction with solvated metal atom dispersion (SMAD) method of synthesis resulted in hetero structures such as core–shell, alloy, and composite nanoparticles. Despite the versatility of digestive ripening process, the underlying mechanism in controlling size and structure of nanoparticles are not understood to date. The aim of this thesis is to gain mechanistic insight into size control of digestive ripening as well as to investigate structure control in various binary systems. Objectives  Study digestive ripening of Au nanoparticles using various alkyl amines to probe the mechanism  Study co-digestive ripening of binary colloids consisting of two metals, Pd and Cu prepared separately by SMAD method  Study co-digestive ripening of binary colloids consisting of a metal (Au) and a semiconductor (CdS) prepared separately by SMAD method  Study vaporization of bulk brass in SMAD reactor and analyse phase, structure, and morphology of various Cu/Zn bimetallic nanoparticles obtained from bulk brass under various experimental conditions Significant results In chapter 1, fundamental processes of nanoparticle formation and common synthetic techniques for the preparation of monodisperse nanoparticles are briefly discussed. Chapter 2 presents a mechanistic study of digestive ripening process with regard to size control using Au nanoparticles as a model system. Three long chain alkyl amine molecules having different chain length were used as digestive ripening agents. The course of digestive ripening process was analysed by UV-visible spectroscopy and transmission electron microscopy. The experimental conditions such as concentration of digestive ripening agent, time, and temperature were found to influence the size distribution of nanoparticles. The average particle size was found to be characteristic of metal-digestive ripening agent combination which is considered as the optimum size preferred during digestive ripening under a given set of experimental conditions. This study discusses stabilization of optimum sized particles, surface etching, and reversibility in digestive ripening. Chapter 3 describes the synthesis and characterization of PdCu alloy nanoparticles by co-digestive ripening method. Syntheses of individual Pd and Cu colloids were carried out by SMAD method. Pd nanoparticles obtained using THF as solvent and in the absence of any capping agent resulted in an extended small Pd nanowire network assembly. Morphological evolution of spherical Pd nanoparticles from Pd nanowire network structure was observed with the use of capping agent, hexadecyl amine (HDA) in SMAD method. Co-digestive ripening of Pd and Cu colloids was studied at various temperatures. This study revealed temperature dependent diffusion of Cu atoms into Pd lattice forming PdCu alloy nanoparticles. Next, co-digestive ripening of a colloidal system comprising a metal and a semiconductor was explored. Au-CdS combination was chosen for this study owing to its interesting photocatalytic properties. Chapter 4 deals with the synthesis of Au and CdS nanoparticles by SMAD method and Au/CdS nanocomposite by co-digestive ripening. CdS nanoparticles of size 4.0 + 1.2 nm and Au nanoparticles of size 5.6 + 1.1 nm were obtained as a result of digestive ripening process. Au/CdS nanocomposite obtained by co-digestive ripening was characterized by a matrix-like structure made up of CdS nanoparticles in which Au nanoparticles were embedded. CdS nanoparticles were found to establish an intimate surface contact with Au nanoparticles and the matrix of CdS surrounding Au was developed via aggregation during digestive ripening. Chapter 5 describes a comprehensive study on various Cu/Zn bimetallic nanoparticles obtained from bulk brass. Vaporization of bulk brass in SMAD reactor led to a deploying process and further growth of nanoparticles from phase separated Cu and Zn atoms formed a composite structure. The characterization of Cu/Zn nanocomposite revealed covering of composite surface with Cu resulting in a core-shell structure, Cu/Zn@Cu. Post-synthetic digestive ripening of these core-shell composite particles showed diffusion of Zn atoms to the composite surface in addition to size and shape modification. Annealing of Cu/Zn nanocomposites prepared in THF resulted in α-CuZn alloy nanoparticles via sequential transformation through η-CuZn5, γ-Cu5Zn8, and β-CuZn (observed as marten site) phases.