This disseration covers the processing and characterization of nanocellulose polymer composites. In this disseration, two fiber spinning methods were developed to create high stiffness nanocomposite fibers from renewably-sourced materials and the properties of these nanocomposites were evaluated. Additionally, bulk nanocomposites were created and some of the properties of these materials, for different types of nanoparticles, are also discussed. Evaluation of nanocellulose as a nucleation agent in poly(lactic acid) is also presented for very small concentrations of nanocelluloses in a plasticized polymer.

<p>Functional oxide-based thin films have attracted much attention owing to their broad applications in modern society. The multifunction tuning in oxide thin films is critical for obtaining enhanced properties. In this dissertation, four new nanocomposite thin film systems with highly textured growth have been fabricated by pulsed laser deposition technique. The functionalities including ferromagnetism, ferroelectricity, multiferroism, magnetoelectric coupling, low-field magnetoresistance, transmittance, optical bandgap and dielectric constants have been demonstrated. Besides, the tunability of the functionalities have been studied via different approaches.</p> <p>First, varies deposition frequencies have been used in vertically aligned nanocomposite BaTiO₃:YMnO₃ (BTO:YMO) and BaTiO₃:La_0.7Sr_0.3Mn₃(BTO:LSMO) thin films. In both systems, the strain coupling effect between the phases are affected by the density of grain boundaries. Increasing deposition frequency generates thinner columns in BTO:YMO thin films, which enhances the anisotropic ferromagnetic response in the thin films. In contrast, the columns in BTO:LSMO thin films become discontinuous as the deposition frequency increases, leading to the diminished anisotropic ferromagnetic response. Coupling with the ferroelectricity in BTO, the room temperature multiferroic properties have been obtained in these two systems.</p> <p> Second, the impact of the film composition has been demonstrated in La_0.7Ca_0.3MnO₃ (LCMO):CeO₂thin film system, which has an insulating CeO₂in ferromagnetic conducting LCMO matrix structure. As the atomic percentage of the CeO₂increases, enhanced low-field magnetoresistance and increased metal-to-insulator transition temperature are observed. The thin films also show enhanced anisotropic ferromagnetic response comparing with the pure LCMO film.</p> <p> Third, the transition metal element in Bi₃MoM_TO₉(M_T, transition metals of Mn, Fe, Co and Ni) thin films have been varied. The thin films have a multilayered structure with M_T-rich pillar-like domains embedded in Mo-rich matrix structure. The anisotropic magnetic easy axis and optical properties have been demonstrated. By the element variation, the optical bandgaps, dielectric constants as well as anisotropic ferromagnetic properties have been achieved. </p> <p> The studies in this dissertation demonstrate several examples of tuning the multifunctionalities in oxide-based nanocomposite thin films. These enhanced properties can broaden the applications of functional oxides for advanced nanoscale devices.</p><br>

Les matériaux (nano)composites font partie intégrante de l’industrie de l’aéronautique et de l’espace depuis plus de 50 ans. De nos jours, le concept de matériaux multifonctionnels combinant diverses propriétés pour réaliser des objectifs de performance multiples en un seul et unique système est devenu une exigence pour le développement de surfaces innovantes, et ce, pour une vaste gamme d’applications technologiques. Cependant, pour plusieurs applications, un des principaux verrous est l’obtention de revêtements formés de nanoparticules isolées (non-agrégées) et de petite taille (<10 nm) dispersées de manière contrôlée dans une matrice. Dans ce contexte, une nouvelle méthode de synthèse souple, verte, sécuritaire et industrialisable a récemment été proposée. Celle-ci repose sur un réacteur-injecteur de nanoparticules et permet de synthétiser des nanoparticules à partir de précurseurs organométalliques liquides juste avant de les injecter dans un réacteur de dépôt par plasma en limitant les phénomènes d’agglomération associés à la vaporisation de gouttelettes et en évitant les problèmes de toxicité éventuelle en lien avec la manipulation de nanoparticules avant le dépôt. Cependant, contrairement aux procédés de dépôt par plasma habituels qui s’effectuent la plupart du temps à pression constante, la conception du réacteur-injecteur de nanoparticules implique inévitablement une dynamique temporelle complexe associée à des variations assez brutales de la pression dans le réacteur à plasma. À l’évidence, ces variations temporelles de pressions vont se répercuter sur l’évolution temporelle des propriétés fondamentales du plasma telles que la densité et la température des électrons. Dans ce travail de maîtrise, nous avons eu recours à la spectroscopie optique d’émission couplée aux prédictions de modèles collisionnels-radiatifs pour déterminer des conditions opératoires du réacteur-injecteur dans un plasma rf d’argon minimisant ces variations d’une part, et permettant de mieux comprendre leurs implications sur la température des électrons, d’autre part. Ces travaux serviront ainsi d’effet levier à des études plus complexes en présence de précurseurs et de nanoparticules. / (Nano) Composite materials have been an integral part of the aeronautics and space industry for more than 50 years. Nowadays, the concept of multifunctional materials combining various properties to achieve multiple performance objectives in a single system has become a prerogative in the development of innovative surfaces for a wide range of technological applications. However, for several applications, one of the main challenges is the production of coatings formed of isolated (non-aggregated) and small (<10 nm) nanoparticles dispersed in a controlled manner in a matrix. In this context, a new flexible, green, safe and scalable method of synthesis has recently been proposed. It is based on a reactor-injector of nanoparticles and can synthesize nanoparticles from liquid organometallic precursors just before injecting them into a plasma deposition reactor by limiting the agglomeration phenomena associated with the vaporization of droplets and by avoiding problems of possible toxicity related to the manipulation of nanoparticles before the deposit. However, unlike conventional plasma deposition processes, which are usually carried out at constant pressure, the design of the reactor-injector of nanoparticles inevitably involves a complex temporal dynamic associated with rather sudden changes in the pressure in the plasma reactor. Obviously, these temporal variations of pressures will affect the temporal evolution of the fundamental properties of the plasma such as the density and the temperature of the electrons. In this master work, we used optical emission spectroscopy coupled with the predictions of collisional-radiative models to determine operating conditions of the reactor-injector in an argon rf plasma minimizing these variations on the one hand, and to better understand their implications on the electron temperature, on the other hand. This work can thus be expected to serve as building blocks for more complex studies in the presence of precursors and nanoparticles.

The new nickel/layered silicate nanocomposites were electrodeposited from different pHs to study the influence on the metal ions/layered silicate plating solution and on the properties of the deposited films. Nickel/layered silicate nanocomposites were fabricated from citrate bath atacidic pHs (1.6−3.0), from Watts’ type solution (pH ~4-5), and from citrate bath at basic pH (~9). Additionally, the new nickel/molybdenum/layered silicate nanocomposites were electrodeposited from citrate bath at pH 9.5. The silicate, montmorillonite (MMT), was exfoliated by stirring in aqueous solution over 24 hours. The plating solutions were analyzed for zeta potential, particle size, viscosity, and conductivity to investigate the effects of the composition at various pHs. The preferred crystalline orientation and the crystalline size of nickel, nickel/layered silicate, nickel/molybdenum, and nickel/molybdenum/layered silicate films were examined by X-ray diffraction. The microstructure of the coatings and the surface roughness was investigated by scanning electron microscopy and atomic force microscopy. Nickel/molybdenum/layered silicate nanocomposites containing low content of layered silicate (1.0 g/L) had increase 32 % hardness and 22 % Young’s modulus values over the pure nickel/molybdenum alloy films. The potentiodynamic polarization and electrochemical impedance measurements showed that the nickel/molybdenum/layered silicate nanocomposite layers have higher corrosion resistance in 3.5% NaCl compared to the pure alloy films. The corrosion current density of the nickel/molybdenum/layered silicate nanocomposite composed of 0.5 g/L MMT is 0.63 µA·cm-2 as compare to a nickel/molybdenum alloy which is 2.00 µA·cm-2.

<p>Devices that can process more information in reduced dimensions are essential for an increasingly information- and efficiency-driven future. To this end, nanocomposites are promising due to their inherent multifunctional properties and special behavior at the nanoscale. Vertically aligned nanocomposites (VANs) are particularly interesting because of their ability to self-assemble into anisotropic nanostructures and high density of heterointerfaces – characteristics which introduce unique functionalities and offer exciting new avenues for device applications. However, a vast majority of VAN systems are currently fabricated on single-crystal oxide substrates, which may be cost-prohibitive at large scales and are generally incompatible with the prevalent device fabrication techniques. Thus, integration of VAN thin films on silicon becomes a critical step toward implementing VANs in a well-established semiconductor manufacturing industry. </p> <p>In this dissertation, the viability of oxide-metal and nitride-metal VAN thin films integrated on silicon substrates has been demonstrated through a set of unique buffer layer designs. For the first three systems presented in this dissertation, namely, LaSrFeO₄-Fe, BaTiO₃-Au, and BaTiO₃-Fe, microstructural and physical property (i.e. electrical, magnetic, and optical) analyses confirm their successful epitaxial growth on silicon, with only minor differences compared to their counterparts grown on single-crystal oxide substrates. For the fourth system, a new and robust TiN-Fe VAN has been proposed and demonstrated. The new TiN-Fe VAN system on Si exhibits superior magnetic properties and unusual optical properties. With further growth optimization and/or patterning techniques, VAN thin film integration on silicon presents itself as a feasible and cost-effective approach to designing electronic, spintronic, photonic, and sensing devices.</p>

Magister Philosophiae - MPhil / The fascinating optical properties of metallic nanostructures, dominated by collective oscillations of free electrons known as plasmons, open new opportunities for the development of devices fabrication based on noble metal nanoparticle composite materials. This thesis demonstrates a low-cost and versatile technique to produce stimuli-responsive ultrafast plasmonic nanostructures with reversible tunable optical properties. Albeit challenging, further control using thermal external stimuli to tune the local environment of gold nanoparticles embedded in V02 host matrix would be ideal for the design of responsive functional nanocomposites. We prepared Au-V02 nanocomposite thin films by the inverted cylindrical reactive magnetron sputtering (ICMS) known as hollow cathode magnetron sputtering for the first time and report the reversible tuning of surface plasmon resonance of Au nanoparticles by only adjusting the external temperature stimuli. The structural, morphological, interfacial analysis and optical properties of the optimized nanostructures have been studied. ICMS has been attracting much attention for its enclosed geometry and its ability to deposit on large area, uniform coating of smart nanocomposites at high deposition rate. Before achieving the aforementioned goals, a systematic study and optimization process of V02 host matrix has been done by studying the influence of deposition parameters on the structural, morphological and optical switching properties of V02 thin films. A reversible thermal tunability of the optical/dielectric constants of V02 thin films by spectroscopic ellipsometry has been intensively also studied in order to bring more insights about the shift of the plasmon of gold nanoparticles imbedded in V02 host matrix.

<p>Istraživanja u okviru teze imaju za cilj dobijanje polimernih mreža kod kojih se regulacijom sirovinskog sastava i uslova sinteze mogu menjati svojstva siloksanskih materijala u skladu sa krajnjom primenom. Osnovni cilj istraživanja ove teze je razvoj novih postupaka sinteze hibridnih siloksanskih nanokompozita na osnovu različitih prekursora mreža. Takođe, ispitan je i uticaj različitih tipova funkcionalizacije povr&scaron;ina nanopunila silicijum(IV) oksida (sa hidrofobnom i hidrofilnom povr&scaron;inom) na svojstva kompozitnih materijala za specifične namene. Nanokompoziti na osnovu polimernih mreža se uglavnom koriste u onim primenama gde tradicionalne polimerne mreže ne mogu da zadovolje potrebe koje se pred njih stavljaju. Zato je potrebno razviti postupak koji bi omogućio dobijanje materijala na osnovu polimernih mreža sa pobolj&scaron;anim mehaničkim, elastičnim i toplotnim svojstvima. Motivacija je vođena potrebom razvoja novih kompozitnih materijala koji imaju jedinstvena mehanička, toplotna, termomehanička svojstva sa mogućno&scaron;ću da pomognu u re&scaron;avanju problema okoline, kao &scaron;to su problem sa prostorom, sa automobilima, u elektronici i infrastrukturi, i naravno, oni će biti veliki izazov u nauci materijala i industriji.<br />Siloksanske mreže su dobijene od &alpha;, &omega;-divinil poli(dimetilsiloksana) i poli(metil-hidrogen<br />siloksana) u odnosu 60/40; 50/50 i 40/60. Nanokompoziti su sintetisani dodavanjem različitih sadržaja nanopunila silicijum(IV) oksida (1, 2, 5, 10 i 20 mas.%). Za potvrdu pretpostavljenog mehanizma reakcije umrežavanja siloksana kori&scaron;ćena je FTIR spektroskopija. TEM analiza je kori&scaron;ćena za procenu topologije i potvrdila je dobru disperziju punila u polimernom matriksu. Dodavanje nanopunila pobolj&scaron;ava mehanička svojstva dobijenih materijala i povećanje vrednosti prekidne jačine za kompozite sa hidrofobnim silicijum(IV)oksidom je veće u poređenju sa kompozitima sa hidrofilnim punilima, &scaron;to je očekivano zbog bolje kompatibilnosti hidrofobne matrice i hidrofobnih punila. Termogravimetrijska analiza kori&scaron;ćena je za analizu uticaja vrste funkcionalizacije silicijum(IV) oksida na termičku stabilnost siloksanskih elastomernih<br />materijala. Kao &scaron;to se i očekivalo, porast sadržaja nanopunila povećava termičku stabilnost dobijenih hibridnih materijala. Uticaj punila na temperature faznog prelaza siloksanskih materijala analiziran je diferencijalnom skenirajućom kalorimetrijom. Zbog slabije kompatibilnosti hidrofilnog punila i hidrofobne matrice primećeno je smanjenje vrednosti Tm, a najmanja vrednost temperature topljenja primećena je za uzorak sa najvećim udelom hidrofilnog punila.<br />Uticaj nanopunila na mehaničke i termičke karakteristike dobijenih materijala biće detaljno analiziran, pri čemu je potvrđeno pobolj&scaron;anje mehaničkih svojstava siloksanskih elastomera dodatkom nanopunila. U cilju razvoja novih biokompatibilnih materijala i pobolj&scaron;anja svojstava biorazgradivosti siloksanskih materijala biće sintetisani ABA blok kopolimeri koji se sastoje od segmenata poli(dimetilsiloksana) i poli(laktida). Kao makroinicijator za sintezu blok kopolimera kori&scaron;ćen je polidimetilisiloksan, pa je polimerizacija laktida inicirana hidroksilnim grupama siloksana. Poli(laktid) se odlikuje veoma dobrim mehaničkim svojstvima i biorazgradivo&scaron;ću, dok se kopolimerizacijom sa siloksanima utiče na mehanička svojstva kao i na svojstva povr&scaron;ine sintetisanog kopolimera.</p> / <p>Research in the thesis aims to obtain polymeric networks in which the regulation of the raw<br />material composition and the conditions of the synthesis can alter the properties of the silicone<br />materials in accordance with the final application. The main goal of the research of this thesis is<br />the development of new procedures for the synthesis of hybrid silicone nanocomposites based on<br />different precursors. The influence of different types of surface functionalisation of nanofillers<br />(with hydrophobic and hydrophilic functionalised surface) on the properties of composite<br />materials for specific purposes was investigated. Nanocomposites based on polymer networks are<br />mainly used in those applications where traditional polymer networks cannot meet the needs that<br />are expected. It is therefore necessary to develop a process that would enable the production of<br />materials based on polymeric networks with improved mechanical, elastic and thermal properties.<br />Motivation is driven by the need to develop new composite materials that have unique<br />mechanical, thermal, thermo-mechanical properties with the ability to help solve environmental problems, such as space problems, cars, electronics and infrastructure, and of course they will be<br />a challenge in the material science and industry. Siloxane networks were prepared from &alpha;,&omega;-<br />divinyl poly(dimethylsiloxane) and poli(methyl-hydrogen siloxane) with a ratio 60/40; 50/50 and<br />40/60. Nanocomposites were synthesised with the addition of different contents of silica<br />nanofiller (1, 2 5, 10 and 20 wt%). For the confirmation of the presumed mechanism of siloxane<br />crosslinking reaction FTIR spectroscopy was used. TEM analysis was used for topology<br />evaluation and confirmed good dispersion of the fillers into the polymer matrix. Addition of<br />nanofillers increased the mechanical properties of obtained materials and greater increase of the<br />tensile strength for the composites based on hydrophobic silicon(IV)-oxide was assessed,<br />compared with the hydrophilic ones. It was expected due to better compatibility of hydrophobic<br />silicone matrix and hydrophobic filler particles. Thermogravimetric analysis was used for the<br />evaluation of the influence of the types of silicon(IV)oxide functionalisation, on the thermal<br />degradation of elastomeric materials. As it was expected the increases of nanofillers content<br />increased the thermal stability of obtained hybrid materials. The influence of fillers on the phase<br />transition temperatures of siloxanematerials was analysed with the differential scanning<br />calorimetry. Due to the lower compatibility of hydrophilic filler and hydrophobic matrix<br />decreasing of Tm values was observed, and the lowest value of melting temperature was noticed<br />for the sample with the highest loading of hydrophilic filler.<br />In order to develop new biocompatible materials and improve the biodegradability properties of<br />silicone materials, ABA types of block copolymers consisting of segments of<br />poly(dimethylsiloxane) and poly(lactide) was synthesized. As a macroinitiator for the synthesis of<br />the block copolymer, poly(dimethylisiloxane) was used, so the lactide polymerization starts from<br />the hydroxyl groups of siloxanes. Poly(lactide) is characterized by poor mechanical properties<br />and biodegradability, while copolymerization with silicones will affect the mechanical and<br />surface properties of the synthesized copolymer.</p>

Les électrocatalyseurs nanostructurés à base de fer, de carbone et d’azote (Fe/C/N) sont de bonnes alternatives au platine dans les piles à combustible acide. Les Fe/C/N sont synthétisés par pyrolyse laser et sont obtenus à partir de deux précurseurs de fer (FeOOH ou Fe(acac)3), de la pyridine, (avec ou sans méthilimidazole) en présence de NH3. La variation de la fraction volumique de NH3 (RNH3) est étudiée sur une large gamme. Les caractéristiques physico-chimiques des matériaux évoluent de façon monotone avec la variation de RNH3. Les analyses par XPS permettent d’identifier une phase assimilable à du nitrure de fer pour les fortes valeurs de RNH3. Les matériaux les plus actifs en éléctrochimie sont ceux contenant une phase de nitrure de fer. Ceci suggère que la présence de nitrure de fer, permet la formation de sites actifs pour la réduction de O2..L’utilisation de toluène (mélangé à de la pyridine ou à du méthylimidazole) en présence ou non de Fe(acac)3 permet d’obtenir de nouveaux matériaux Fe/C/N ou C/N. Les matériaux C/N moins actifs que ceux contenant du fer, indiquent la présence de sites actifs à base de fer. Des recuits sous Ar ou sous NH3 à 1100°C améliorent l’activité des matériaux. Elle est due à l’élimination de sites azotés inactifs et à la transformation de sites pyridiniques en sites graphitiques. Le recuit sous NH3, plus efficace que celui sous Ar, induit une augmentation de la surface spécifique (Sspé max > 1100 m²/g). Pour un même matériau recuit sous Ar ou sous NH3 la sélectivité de la réduction de O2 (n) atteint 3,70 e- contre 3,93 e- respectivement. Le plus actif d’entre eux atteint un Edép > 950mV/ENH. / Nanostructured Iron-nitrogen-carbon (Fe/N/C) electrocatalysts is a good substitute for platinum in acidic fuel cells. Laser pyrolysis synthesis allows to obtain iron nanocomposites (Fe/N/C). The reaction involves two iron precursors, FeOOH and Fe(acac)3, combined with pyridine (and possibly methylimidazole) in the presence of NH3. The effect of large range variations of NH3’s volume fraction (RNH3) in the reactions is studied. Physicochemical properties of the materials increase monotonically with RNH3. XPS analysis shows that an iron nitride phase appears when RNH3 increase, and electrochemical analysis shows that materials with this iron nitride phase are the most active ones. These results suggest that iron nitride presence triggers the formation of active sites for the oxygen reduction reaction (ORR).Finally, we synthetize new Fe/N/C, or N/C materials using toluene (mixed with pyridine or methylimidazole) in the presence or absence of Fe(acac)3. The obtained Fe/N/C materials are more active than the N/C materials which indicates that iron plays a role in the presence of active sites for the ORR. Annealing under Ar or NH3 at a temperature of 1100°C increases the activity of all the materials. This improvement is due to the suppression of inactive nitrogen sites, and the transformation of some pyridinic sites to graphitic sites. Annealing under NH3 is more effective under Ar beacuse of the increase of the specific surface area (Sspe max > 1100 m2/g). For the same material annealed under Ar versus NH3, the selectivity (n) of the ORR goes from 3.70 up to 3.93 e- respectively. The most active one reaches Edep > 950 mV/ENH.

Indiana University-Purdue University Indianapolis (IUPUI) / Nanocomposite ceramics have been widely studied in order to tailor desired properties at high temperatures. Methodologies for development of material design are still under effect. While finite element modeling (FEM) provides significant insight on material behavior, few design researchers have addressed the design paradox that accompanies this rapid design space expansion. A surrogate optimization model management framework has been proposed to make this design process tractable. In the surrogate optimization material design tool, the analysis cost is reduced by performing simulations on the surrogate model instead of high fidelity finite element model. The methodology is incorporated to and the optimal number of silicon carbide (SiC) particles, in a silicon-nitride(Si3N4) composite with maximum fracture energy [2]. Along with a deterministic optimization algorithm, model uncertainties have also been considered with the use of robust design optimization (RDO) method ensuring a design of minimum sensitivity to changes in the parameters. These methodologies applied to nanocomposites design have a significant impact on cost and design cycle time reduced.

Tato dizertační práce je zaměřená na základní výzkum procesů samouspořádávání nanočástic v polymerních kapalinách a na vlastnosti připravených polymerních nanokompozitů s řízenou disperzí nanočástic. Navzdory současnému pokroku v porozumění polymerních nanokompozitech, stále chybí mnohé fundamentální znalosti relaxačních a mechanických vlastností polymerních nanostruktur, které by mohly poskytnout klíčové informace pro návrh hierarchických funkčních kompozitů zpracovatelných aditivními výrobními technikami. Hlavní důraz byl kladen na výzkum vlivu postupu přípravy nanokompozitu na finální stav disperze nanočástic, přípravu řízených nanostruktur – individuálně dispergované nanočástice, řetězci vázáné klastry a kontaktní agregáty - a určení jejich relaxačních a mechanických vlastností. Navíc byly nanočástice využity jako „sondy“ v polymerní matrici, které ovlivňují segmentální uspořádání a relaxační dynamiku polymerních řetězců a mohou poskytnout o těchto dějích zásadní informace. Tento přístup může pomoci nalezení vztahů mezi segmentální dynamikou na nano škále a mechanickými vlastnostmi polymerních skel na makro škále, což je náročný fundamentální problém s extrémní technologickou důležitostí. Neroubované keramické nanočástice a polymerní skla byly použity, aby se minimalizoval vliv silných interakcí mezi nanočásticemi a řetězci. Podrobný výzkum byl vykonán na modelovém systému PMMA/SiO2 a následně rozšířen na systémy s jinými matricemi (PC a PS) a jinými nanočásticemi (ZnO2 and Fe2O3) za účelem zobecnění obdržených výsledků. Byla určena závislost relaxačních a mechanických vlastností (teplota skelného přechodu, reptační čas, modul kaučukovitého plata, počet zapletenin, napětí na mezi kluzu, pokles napětí po mezi kluzu, elastický modul, modul deformačního zpevnění a odezvy při toku za studeny) na nanostruktuře, objemovém zlomku a složení. Získané výsledky byly interpretovány za použití současných modelů. Stanovené relaxační a mechanické vlastnosti byly propojeny, aby poskytli informace o molekulárních deformačních procesech řídících mechanickou odezvu makroskopických kompozitních těles.