Polymeric materials are widely used in diverse applications. However, a major weakness in the majority of the thermoplastic polymers is their lack of ability to resist fire. Most of the chemicals and additives currently used to improve fire retardancy have deleterious effects on the environment. This research focuses on developing an environmentally safe and effective fire-retardant system for high density polyethylene (HDPE), using cellulose nanocrystals (CNCs) and zinc oxide (ZnO). The effect of CNCs coated with nano ZnO has been investigated for improving the fire resistance properties of the HDPE. Improved dispersion of CNCs into HDPE matrix was achieved by employing maleic anhydride as a coupling agent. It was found that addition of CNCs-ZnO can introduce a reasonable level of flame retardancy in HDPE matrix in addition to improving the maximum tensile strength and elongation at break.

<div>Nature has evolved efficient strategies to make materials with hierarchical internal structure that often exhibit exceptional mechanical properties. One such example is found in cellulose, which has achieved a high order of functionality and mechanical properties through a hierarchical structure with an exceptional control from the atomic level all the way to the macroscopic level. Cellulose is present in a wide variety of living species (trees, plants, algae, bacteria, tunicates), and provides the base reinforcement structure used by organisms for high mechanical strength, high strength-to-weight ratio, and high toughness. Additionally, being the most abundant organic substance on earth, cellulose has been used by our society as an engineering material for thousands of years, and are prolific within our society, as demonstrated by the enormity of the world-wide industries in cellulose derivatives, paper/packaging, textiles, and forest products.</div><div><br></div><div><div>More recently, a new class of cellulose base particles are being extracted from plants/trees, cellulose nanocrystals (CNCs), which are spindle-shaped nano-sized particles (3 ̶ 20 nm in width and 50 ̶ 500 nm in length) that are distinct from the more traditional cellulose materials currently used (e.g. molecular cellulose and wood pulp). They offer a new combination of particle morphology, properties and chemical functionalities that enable CNCs for use in applications that were once thought impossible for cellulosic materials.</div></div><div><br></div><div><div>CNCs have shown utility in many engineering applications, for example, biomedical, nanocomposites, barrier/separation membranes and cementitious materials. To gain greater insight as to how best use CNCs in various engineering application areas, a comprehensive understanding of the mechanics of CNCs is needed. The characterization of the mechanical properties of nanomaterials via experimental testing has always been challenging due to their small size, resulting in large uncertainties related to testing near sensitivity limits of a given technique, the same is true when characterizing CNCs. For CNCs, to help offset limitations in experimental testing, numerical modeling has been useful in predicting the mechanical properties of CNCs. We present a continuum-based structural model to study the mechanical behavior of cellulose nanocrystals (CNCs), and analyze the effect of bonded and non-bonded interactions on the mechanical properties under various loading conditions. In particular, this model assumes the uncoupling between the bonded and nonbonded interactions and their behavior is obtained from atomistic simulations.</div></div><div><br></div><div><div>For large deformations and when there is interaction and dynamics of many particles involved, continuum models could become as expensive as MD simulations. In addition, it has been shown that traditional material models in the continuum mechanics context, cannot model all the mechanical properties of CNC, especially for large deformation. To overcome these setbacks and to be able to model real size of CNC, 50-1000 nm, and/or to increase the number of particles involved in the simulation, a so called ‘‘coarse-grained’’ (CG) model for mechanical and interfacial properties of CNC is proposed. The proposed CG model is based on both mechanical properties and crystal-crystal interactions. Parametrization of the model is carried out in comparison with all-atom (AA) molecular dynamics and experimental results of some specific mechanical and interfacial tests.</div></div><div><br></div><div><div>Subsequently, verification is done with other tests. Finally, we analyze the effect of interface properties on the mechanical performance of CNC-based materials including, bending of a CNC bundle, tensile load and fracture in bioinspired structure of CNCs such as staggered brick-and-mortar and Bouligand structures of interest.</div></div>

Les objectifs principaux de ce travail étaient d'étudier la nature des composés de cuivre formés dans les nano-zéolithes en utilisant deux approches: (i) incorporation directe du Cu via une synthèse mono pot et (ii) incorporation post-synthèse du Cu suivi par une réduction chimique. Une étude détaillée de l'évolution des espèces de cuivre dans la suspension de nano-zéolithe LTL réduite avec de l'hydrazine a révélé la formation de nanoparticules de cuivre avec des dimensions limitées par la taille de canaux et des cages de la zéolithe. Cependant, avec un temps de réduction prolongé, les NPs de Cu ont tendance à migrer vers la surface de la zéolithe en raison de leur forte mobilité dans les milieux aqueux, et donne lieu à de grosses particules de cuivre, tout en conservant la structure de la zéolithe. La réduction du cuivre donne lieu à un système complexe contenant différentes espèces de cuivre: des résidus de Cu2+, Cu+ et des NPs de Cu. Les études par spectroscopie IRTF montrent l'hétérogénéité des cations Cu 2+ et Cu + dans la zéolithe Cu-LTL préparée par échange ionique. Il a été prouvé, que l'état et le comportement du cuivre dans la zéolithe LTL dépendent fortement de la méthode utilisée pour l'incorporation du Cu, soit par échange ionique, soit par incorporation directe du Cu. Il est devenu évident que le cuivre ajouté au mélange de synthèse possède un environnement distinct et occupe une position différente quand il est comparé à celui de l’échange ionique. Il est vraisemblablement partiellement localisé dans la charpente zéolithique ou /caché dans la structureet est inaccessible pour les molécules adsorbées. De plus, les modifications post-synthèse du matériau obtenu par synthèse directe entrainent un déplacement vers des positions hors structure d’un nombre important de Cu.De plus, les films minces de zéolithes contenant du métal avec des épaisseurs différentes ont été obtenue par un procédé de revêtement par centrifugation de supports de silicium et/ou des supports optiques CaF 2. Ce dernier a été utilisé pour la détection de CO en faible concentration à température ambiante et l’étude de la réponse optique ultrarapide du matériau photo-excité en résonance avec la bande du plasmon des NPs métalliques. En résume, ce travail couvre entièrement toutes les étapes de la synthèse, la modification, la caractérisation complète et l’utilisation de nano-cristaux de zéolithe contenant du métal. La combinaison des propriétés uniques des nanoparticules de cuivre et de la polyvalence des nano-zéolites donne lieu à des matériaux avancées intéressants pour de nombreuses d'applications dans des dispositifs de taille nanométrique, la détection sélective de produit chimique, la catalyse, etc. / The main objectives of this work were to study the nature of copper species formed in the nanosized zeolites using two approaches: (i) direct incorporation of Cu via one pot synthesis, and (ii) post synthesis incorporation of Cu followed by chemical reduction. A detailed study of the evolution of copper species in the LTL nanosized zeolite suspension reduced with hydrazine revealed the formation of copper nanoparticles with the dimensions limited by the size of zeolite channels and cages. However, with prolonged reduction time, the Cu NPs tend to migrate to the zeolite surface due to their high mobility in aqueous media, resulting in large copper particles, while the zeolite structure is preserved. The reduction of copper resulted in a complex system, containing different copper species: residuals of Cu2+, Cu+, CuNPs. The results of FTIR spectroscopy show the heterogeneity of Cu2+ and Cu+ cations in the Cu-LTL zeolite prepared by ion-exchange procedure. It has been proven, that the state and behavior of copper in LTL zeolite strongly depend on the method used for Cu inclusion: ion exchange or direct Cu incorporation. It became evident, that copper added to the synthesis mixture shows distinct environment and occupies different position when compared to ion exchange. It is presumably partially located in the zeolite framework or occluded in its walls and is inaccessible by adsorbed molecules. In addition, the post-synthesis modifications of the material obtained by direct synthesis cause the displacement of a significant amount of Cu to the extra-framework positions.Further, the metal containing zeolite thin films with different thickness were obtained by spin-coating approach on silicon wafers and CaF2 optical plates. The latter were after employed for detection of low concentration of CO at ambient temperature and investigation of the ultrafast optical response of the materials photo-excited in resonance with the plasmon band of the Me NPs. In summary, the present PhD thesis fully covers the all steps from the synthesis, modification, thorough characterization, and application of metal-containing nanosized zeolite crystals. The combination of unique properties of copper nanoparticles with versatility of nanozeolites give rise to the development of advanced materials which are interesting for many applications in nanoscale devices, selective chemical sensing, catalysis etc.

Název práce: Nelineární optické vlastnosti křemíkových nanostruktur Autor: Karel Žídek Katedra (ústav): Katedra chemické fyziky a optiky Vedoucí disertační práce: Doc. RNDr. František Trojánek, Ph.D. E-mail vedoucího: trojanek@karlov.mff.cuni.cz Abstrakt: Disertační práce se zabývá nelineárními optickými jevy a ultrarychlým vývojem luminis- cence křemíkových nanokrystalů. Pomocí metody optického hradlování signálu (časové rozlišení až 250 fs) porovnáváme ultrarychlý vývoj luminiscence křemíkových nanokrystalů s různými ve- likostmi (v řádu jednotek nanometrů) a také s rozdílnými formami pasivace. Pro nanokrystaly, kde po excitaci dominuje vliv zachytávání nosičů do povrchových stavů nanokrystalu, navrhujeme teoretický popis závislosti rychlosti těchto procesů na vlastnostech nanokrystalů. Dále v práci podrobně zkoumáme působení Augerovy rekombinace, která se projevuje jak v časově rozlišené, tak i v časově integrované emisi vzorků. Experimentální data velmi dobře popisuje námi navržený model na bázi kinetických rovnic. Závěr práce se zaměřuje na zkoumání ultrarychle dohasínající stimulované emise. U stávajících metod měření optického zisku (VSL a SES) navrhujeme jejich rozšíření pro...

Nanodiamonds (NDs) are an interesting platform in biological applications and disease treatment. Because of their photoluminescence properties and modifiable surface, they have been investigated as potential carriers for drugs and nucleic acids as well as fluorescent probes. In order to design NDs meeting specifically desired parameters, which would succeed in clinical trials and in medicinal therapy, understanding the mechanism of uptake and intracellular fate of NDs is crucial. The diploma thesis is focused on mechanistic investigation of ND-based nanoparticles delivering nucleic acids to human cells. First, NDs coated with a novel cationic co-polymer were prepared. NDs were then complexed with siRNA in order to transfect siRNA inside U-2 OS cells. NDs proved to be biocompatible and effective transfection particles as observed by qPCR and colorimetric cytotoxicity and cell viability tests. To examine ND uptake by cells, we inhibited endocytosis by specific inhibitors. Obtained results implicated that ND uptake was clathrin- and caveolin dependent. Nonetheless, more than half of NDs was internalized by cells in a different fashion. Some NDs colocalized with early endosomes, lysosomes and caveolin-derived endosomes after internalization. Other NDs resided either in unknown cell structures or escaped from...

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Plasmonic nanocrystals have a unique ability to support localized surface plasmon resonances and exhibit rich and intriguing optical properties. Engineering plasmonic nanocrystals can maximize their potentials for specific applications. In this dissertation, we developed three unprecedented Au nanorod-based plasmonic nanocrystals through rational design of the crystal shape and/or composition, and successfully demonstrated their applications in light condensation, photothermal conversion, and surface-enhanced Raman spectroscopy (SERS). The “Au nanorod-Au nanosphere dimer” nanocrystal was synthesized via the ligand-induced asymmetric growth of a Au nanosphere on a Au nanorod. This dimeric nanostructure features an extraordinary broadband optical absorption in the range of 400‒1400nm, and it proved to be an ideal black-body material for light condensation and an efficient solar-light harvester for photothermal conversion. The “Au nanorod (core) @ AuAg alloy (shell)” nanocrystal was built through the epitaxial growth of homogeneously alloyed AuAg shells on Au nanorods by precisely controlled synthesis. The resulting core-shell structured, bimetallic nanorods integrate the merits of the AuAg alloy with the advantages of anisotropic nanorods, exhibiting strong, stable and tunable surface plasmon resonances that are essential for SERS applications in a corrosive environment. The “high-index faceted Au nanorod (core) @ AuPd alloy (shell)” nanocrystal was produced via site-specific epitaxial growth of AuPd alloyed horns at the ends of Au nanorods. The AuPd alloyed horns are bound with high-index side facets, while the Au nanorod concentrates an intensive electric field at each end. This unique configuration unites highly active catalytic sites with strong SERS sites into a single entity and was demonstrated to be ideal for in situ monitoring of Pd-catalyzed reactions by SERS. The synthetic strategies developed here are promising towards the fabrication of novel plasmonic nanocrystals with fascinating properties for nanoplasmonics and nanophotonics.

Cellulose nanocrystals (CNC) are great candidates for composite materials. The reasons why CNCs are such attractive materials for them are due to their great mechanical properties, high aspect ratio and low density. On the other hand, hydroxyapatite (HAp) is a kind of calcium phosphate and a main component of bones and teeth. The purpose of the present study is to make oriented nano-sized composites with CNC and HAp. Although some researchers carried out to make CNC composites with HAp for biomedical materials, nano-sized and oriented ones haven’t been achieved yet. Also, films made of CNC and other compounds are known to be transparent and have good oxygen permeability. Especially when CNCs’ direction is in parallel, they show high strength. However most previous researches dealt with particles or plate-like minerals in inorganic/CNC films, so there is no case that coated CNCs themselves were aligned in the films. Therefore fabrication of composite-oriented thin films is quite unique and it will be a potential step for bone-like hierarchical structure. In experiment, certain amount of CNC suspension with functional groups were put into revised simulated body fluid (r-SBF) solutions which were adjusted between pH 6.9-7.9 to make the molar ratio of calcium ion per functional groups on CNC surfaces between 30-230. The suspensions were put into the ultrasonic bath for 15 minutes and stirred in the thermostatic oven at 37 ⁰C for 1 hour. The process of ultrasound and stirring in oven was repeated 1-3 times depending on conditions. Precipitated products were collected with the centrifuge instrument and dried with the freeze dryer. Functional groups induced HAp’s nucleation and the HAp/CNC composites could be obtained under control of molar ratio of calcium ions per functional groups on CNC and pH. Morphology of the composites could be determined by pH and HAp content could be controlled between 25-75 wt% by initial molar ratio. The suspension having the composites synthesized in pH 7.9 with low initial molar ratio was dropped on superhydrophilic glass substrates. At the moment, the substrates were set with leans of 20 degrees. Then they were dried at 60 oC for 3 hours and transparent films containing 25-40 wt% of HAp were obtained. The transmittances of the films were more than 90 % and their thicknesses were 2.2-4.2 μm. The films were suggested to have oriented structure by polarization microscope when the shape of the composites were needle-like homogeneously and independent each other. From the results from SEM, they were aligned longitudinally at both ends of the film and laterally at the upper middle part of the films. It is considered that controlling drying direction influenced on the orientation. The current study should become a promising step to build up a bone-like hierarchical structure artificially.

As an efficient means of energy storage, rechargeable batteries, especially the lithium-ion batteries (LIBs) have been a vital component in solving the upcoming energy crisis and environmental problems. Recently, the development of electric vehicle market puts new requirement on the next generation LIBs, including superior energy density, safety and cycling stability, etc. Compared with experimental investigation, Physics-based models provide a surrogate method to not only tackle the underlying physics of the complex battery system, but also optimize the design of battery systems. In this thesis, I will show how I use the physics-based continuum model and cooperate with some experimental methods to understand the lithium transport phenomena inside the multiscale battery electrode systems, based on which the models are then applied to guide the experimental optimization of battery electrode design and to quantitively understand the degradation of high-performance electrodes. The thesis is divided into three parts. First part (Chapter 2) presents a systematical model selection study on the multiscale LiNi₀.₃₃Mn₀.₃₃Co₀.₃₃O₂ (NMC₁₁₁) electrode. Discharge and voltage relaxation curves, interrogated with theory, are used to distinguish between lithium transport impedance that arise on the scale of the active crystal and on the scale of agglomerates (secondary particles) comprised of nanoscale crystals. Model-selection algorithms are applied to determine that the agglomerate scale transport is dominant in the NMC₁₁₁ electrode studied here. This study not only discovers the dominant length scale for lithium transport, but also provide a validated model (the agglomerate model) for later study. The second part (Chapter 3 & 4) talks about understanding & optimization of ion transport in porous electrodes. In Chapter 3, multi-scale physics-based models for different active material systems, which have been parameterized and validated with discharge experiments, are optimized by varying porosity and mass loading to achieve maximum volumetric energy density. The optimization results show that with a re-scaling of the current rate, the optimal results follow a general design rule that is captured in a convenient correlation. Chapter 4 extends the model to simulate the performance of advanced electrode architectures utilizing aligned channels, by quantifying the impact of aligned channel electrode structures on cell rate capability. Then the optimization algorithm in Chapter 3 is applied to these aligned-channel electrodes. The final part (Chapter 5) shows how I use the physics-based model to quantitatively analyze the battery degradation. The validated model is applied to cycling data to obtain parameter estimates indicative of degradation modes. It’s found that growth rates of interfacial impedance and active material loss are greater at 4.5 V, as might be expected. However, when charged to 4.5V, degradation rates are lower at a cycling C-rate of 1.0 h⁻¹ than at 0.5 h⁻¹. Once performance changes are quantified, we use further simulation to evaluate the contribution of individual degradation modes to fade of cell performance metric such as capacity, power density, and energy density.

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology / The understanding of the fundamental properties and potential use of semiconductor materials in nanotechnology has stimulated the interest of many researchers. Coordination compounds containing ligands with chalcogenide atoms as donors have received considerable attention. Among these chalcogenide ligands, thiourea and urea have been extensively used previously to form single source precursors for the synthesis of group II–VI semiconductor nanoparticles. The synthesis and study of semiconductor nanocrystals has become a subject area of considerable research interest because they have potentially useful applications such as biomedical imaging, sensing, light-emitting diodes (LEDs), photovoltaics and displays. In this work, special attention has been given to the synthesis and characterization of cadmium and nickel chalcogenides nanoparticles because of their interesting and unique optical properties, using a single source precursor method. The mixed chalcogenide sources are also explored for their complexes or simple reactions to produce semiconductor nanoparticles. The advantages of single molecular precursors over other existing methods for the synthesis of metal chalcogenide nanoparticles has proven to be a more efficient route for the synthesis of high-quality nanocrystals. Cadmium and nickel complexes of urea and thiourea were successfully synthesized by refluxing metal salts of cadmium and nickel with thiourea and urea at 30-40 °C for an hour and the complex mixture was cooled at room temperature. The synthesized complexes were washed with methanol and acetone to remove impurities and dried in air. All other complexes were synthesized using the same refluxing synthesis method mentioned above. The characterization of all complexes was done using Fourier-Transform infrared spectroscopy, thermogravimetric analysis and CARLO ERBA elemental analysis. Nickel thiourea and cadmium thiourea complexes were found to be coordinating with the center metal through a sulfur atom, and the urea complexes through an oxygen atom. This observation of the coordination of metals with ligands makes these complexes suitable for use as the single source precursor for the synthesis of metal chalcogenides nanoparticles. The six resulted complexes from above synthesis are of cadmium sulphide, cadmium oxide, and nickel sulphide, nickel oxide. The TGA showed that all the complexes were stable at room temperature, as they decomposed around 200 °C, which makes these complexes suitable to be used for the synthesis of nanoparticles. The synthesized complexes reported in this study were used as a single source molecular precursor in the preparation of cadmium oxide, cadmium sulfide, nickel oxide, and nickel sulfide nanoparticles. The precursors were thermalized under nitrogen gas while refluxing at 160 °C for 1 hour, using HDA as the capping agent and TOP was used as the solvent. Crystalline semiconducting nanoparticles were obtained as the end product for all complexes, the resulting nanoparticles were washed with acetone to remove any impurities. The UV-Vis spectra of all the nanoparticles were blue-shifted, with their PL spectra red-shifted from the maximum absorption peak due to change in size of particles from bulk to nano-size. XRD pattern of CdS nanoparticles from Cd-thiourea suggested that a hexagonal phase of CdS was formed, and TEM analysis showed large particle sizes that were polydispersed with the dominance of cubic and rod shaped particles. The XRD patterns of CdS nanoparticles from cadmium thiourea and urea mixture showed the mixture of hexagonal and cubic phase nanoparticles with the predominance of cubic phase and its TEM images shows small particles size ranging from less than 50 nm, and the particles were polydispersed with the predominance of spherical nanoparticles. The XRD pattern of CdO nanoparticles showed the cubic phase nanoparticles with the existence of broad peaks indicating small particle size distribution. The TEM images of CdO nanoparticles confirmed the XRD data showing small particle size distribution with a size average of 6.8 nm. The NiS nanoparticles synthesized from Ni-thiourea complex showed narrow peaks with hkl indices indicating hexagonal phase. Particles has no clear morphology due to the agglomeration of the nanoparticles that can be caused by the instability of the nanoparticles because of their high surface area. A cluster of particles can be observed from the TEM images, making it difficult to determine the particle size and shape of NiS particles from Ni-thiourea complex. NiS particles from nickel thiourea and urea mixture also showed XRD patterns of the hexagonal plane and TEM showed small size conjugated nanocrystals. The TEM of NiO indicated a spherical morphology, existence of other morphology rather than spherical can also be observed from the image. The average particle size was 8 nm, and XRD pattern showed the cubic phase of NiO nanocrystals.