Electronic applications have expanded to encompass a variety of materials. In particular, allotropes of carbon interest researchers for their electronic applications. Knowledge of carbon allotropes and their applications has expanded significantly since the discovery of C60 Buckminsterfullerene in 1985, the discovery of multi- and single-walled carbon nanotubes in the early 1990s, and the isolation of graphene in 2004. Single-walled carbon nanotubes (SWNTs) have the potential to bring next-generation electronic devices to fruition. Such devices could be flexible, conformable, and inexpensive. SWNT-based electronics are promising for chemical and biological sensing applications, for example, where high carrier mobilities are unnecessary, and material conformity and inexpensive processing are significant advantages. Considerable progress has been made in separating semiconducting SWNTs from metallic SWNTs, enabling SWNT incorporation into semiconducting electronic technologies. Selective sorting of semiconducting SWNTs using π-conjugated polymers is an effective and efficient technique to enrich large quantities of ultra-pure semiconducting SWNTs. Following semiconducting enrichment, SWNTs can be incorporated into electronic devices. This thesis focuses on the enrichment of semiconducting SWNTs via conjugated polymer extraction and incorporating the resulting polymer-SWNT dispersions into thin-film transistors (TFTs). Novel copolymers were investigated for their capacity to selectively sort and disperse large-diameter sc-SWNTs synthesized using the plasma torch technique. Absorption and Raman spectroscopy were employed to monitor the efficacy of the conjugated polymer extraction procedure. Following enrichment, the polymer-SWNT dispersions were incorporated into TFTs. The interaction between the conjugated polymer and the SWNT and the conjugated polymer and dielectric was an essential component of TFT optimization. Furthermore, the procedure of sorting and dispersing sc-SWNTs is investigated for its effect on TFT performance and was another component of TFT optimization. TFTs were electrically characterized in terms of carrier mobility, threshold voltage, hysteresis, and current on/off ratio. The film morphology of the SWNT TFTs was also investigated. Atomic force microscopy and Raman mapping were used to provide insight into the nanometre and micrometre scale film morphology, respectively.

Yes / The bond between FRP bars and concrete, the foremost performance for implementation of such reinforcements to corrosion-free concrete structures, is still unsatisfied due to the weak nature of duplex film in the interface. The existing approaches show low efficiency in improving the microstructures and bond between FRP bars and concrete. To address these issues, this paper provided a new approach for improving the bond between FRP bars and concrete by incorporating nanomaterials, as well as explored the modifying mechanisms and established the bond-slip models. For these purposes, the pull-out test, scanning electron microscope observation, as well as energy dispersive spectrometry analysis were performed. The experimental results demonstrated that the presence of nanomaterials increased the ultimate bond strengths between glass/carbon FRP bars and concrete by up to 16.2% and 37.8%, while the corresponding slips decreased by 28.7% and 35.4%, respectively. Such modification effects can be attributed to the optimized intrinsic composition and the reduced pore content of hydration products in the interface, especially in the duplex film, through the nanomaterial enrichment and nano-core effects. The bond-slip relationship between FRP bars and concrete with nanomaterials can be accurately predicted by the mBPE model. / The authors would like to thank the funding offered by the National Science Foundation of China (51978127 and 51908103), and the Fundamental Research Funds for the Central Universities (DUT21RC(3) 039).

This dissertation attempts to address the problem of how to prepare protein-based materials with the same level of order and precision at the molecular level similar to the structures we find in nature. It is divided into two parts focusing on feedstock and processing. Part one is devoted to discussing the use of agricultural proteins as a feedstock for material production. Particularly, it focuses on the effect of hydrogen bonding, or lack thereof, between proteins as mediated by hydration or plasticization. The effect of varying plasticizer (glycerol) levels on mechanical properties of a series of proteins is discussed in the context of primary and secondary structure of these proteins. We have found that the extent to which a protein can be plasticized is dependent on its molecular and higher order structure and not simply molecular weight, as it was often assumed in previous studies. The second part of the dissertation focuses on the study of self-assembly as a way to make useful peptide-based materials. There are major efforts underway to study protein self-assembly for various medical and industrial reasons. Despite huge progress, most studies have focused on nanoscale self-assembly but the crossover to the macroscopic scale remains a challenge. We show that peptide self-assembly into macroscopic fibers is possible in vitro under physiological conditions. We characterize the fibers and propose a mechanism by which they form. The macroscopic fibers self-assemble from a combination of β- and α-peptides and are similar to other naturally-occurring systems in which templated self-assembly is used to create functional peptide materials. Finally, the ability to control macroscopic properties of the fiber by varying the ratio of constituent peptides is demonstrated. Owing to the richness of the amino acid building blocks, peptides are highly versatile structural and functional building blocks. The ability to extend and control peptide self-assembly over multiple length scales is a significant leap toward incorporating peptide materials into dynamic systems of higher complexity and functionality. / Ph. D.

Despite the rapid growth in nanotechnology, very little is known about the unintended health or environmental effects of manufactured nanomaterials. The development of nanotechnology risk assessments and regulations requires quantitative information on the potential for exposure to nanomaterials. In addition, to facilitate life-cycle assessments and inhalation toxicology studies, robust methods are needed to generate aerosolized engineered nanoparticles. We conducted a set of field studies to measure the fine particle mass concentrations (PM2.5) as well as nanoparticle number concentrations and size distributions in two nanomaterial manufacturing facilities. Measurements were performed near the reactor, in the breathing zone, and at a background site. Increases in PM2.5 and particle number concentrations were associated with physical handling of nanomaterials. The highest PM2.5 concentration observed was 2700 ug m-3 during sweeping of the reactor in the commercial plant. In most cases, an increase in the number of sub-100 nm particles accounted for the increase in total number concentrations. The results of this research can be used to develop guidelines for workplace regulations to minimize workers' exposure to nanoparticles. Furthermore, we used an atomizer to aerosolize C60 aggregates from a fullerene-water suspension. Measurement of particle size distributions and number concentrations showed that increasing the initial fullerene concentration resulted in increased number of aerosolized particles, while the average size of particles remained relatively constant. To return the aerosolized fullerenes into water, we passed the aerosol sample through an impinger. Reducing the flow rate through the impinger resulted in an increase in the collection efficiency of airborne nanoparticles. / Master of Science

Yes

<p>Polymer nanocomposites are a constantly evolving material category due to the ability to engineer the mechanical, thermal, and optical properties to enhance the efficiency of a variety of systems. While a vast amount of research has focused on the physical phenomena of nanoparticles and their contribution to the improvement of such properties, the ability to implement these materials into existing commercial or newly emerging processing methods has been studied much less extensively. The primary characteristic that determines which processing technique is the most viable is the rheology or viscosity of the material. In this work, we investigate the processing methods and properties of nanocomposites for thermal interface and radiative cooling applications. The first polymer nanocomposite examined here is a two-component PDMS with graphene filler for 3D printing via a direct ink writing approach. The composite acts as a thermal interface material which can enhance cooling between a microprocessor and a heat sink by increasing the thermal conductivity of the gap. Direct ink writing requires a shear thinning ink with specific viscoelastic properties that allow for the material to yield through a nozzle as well as retain its shape without a mold following deposition. No predictive models of viscosity for nanocomposites exist; therefore, several prominent models from literature are fit with experimental data to describe the change in viscosity with the addition of filler for several different PDMS ratios. The result is an understanding of the relationship between the PDMS component ratio and graphene filler concentration with respect to viscosity, with the goal of remaining within the acceptable limits for printing via direct ink writing. The second nanocomposite system whose processability is determined is paint consisting of acrylic filled with reflective nanoparticles for radiative cooling paint applications. The paint is tested with both inkjet and screen-printing procedures with the goal of producing a thermally invisible ink. Radiative cooling paint is successfully printed for the first time with solvent modification. This work evaluates the processability of polymer nanocomposites through rheological tailoring. </p><br>

La Microscopie Electronique à Balayage Environnementale permet l'observation de liquides dans certaines conditions de pression et température. En travaillant en transmission, i.e. en mode STEM (Scanning Transmission Electron Microscopy), des nano-objets présents au sein du liquide peuvent même être analysés (mode « Wet-STEM»). Dans les solutions concentrées, l'arrangement du soluté peut changer être un paramètre microstructural important, qu’il est alors nécessaire de caractériser. Dans ce contexte, le but de ce travail est de développer la tomographie électronique sur des suspensions liquides en utilisant le mode STEM en ESEM, de manière à obtenir la structure 3D de nano-objets dispersés dans un liquide. Dans une première partie, le contraste entre des nanoparticules et le film d’eau est étudié en combinant des images expérimentales Wet-STEM (en 2D) et des simulations Monte Carlo. Deux types de nano-matériaux sont choisis : des nanoparticules d’or sphériques, de diamètre environ 40 nm, dispersées dans l’eau, ainsi qu’une suspension aqueuse de latex SBA-PMMA, contenant 3% de PMMA utilisé comme tensioactif stérique. La comparaison entre les résultats simulés et expérimentaux permet d’estimer comment le contraste entre l’eau et les nanomatériaux est affecté par l’épaisseur du film d’eau. Dans une deuxième partie, des expériences de tomographie sont réalisées à sec sur des films de polyuréthane contenant des nanotubes de carbone multiparois greffés ou non, en utilisant une platine développée précédemment au laboratoire. Le volume a pu être reconstruit correctement. Cependant, en effectuant une acquisition 3D sur des suspensions de latex SBA-PMMA, le contrôle de la température de l’échantillon s’est révélé insuffisant. Nous proposons une amélioration à la fois de la platine et des conditions d’observations permettant de mieux contrôler l’évaporation et la condensation de l’eau sur des échantillons liquides. La troisième partie est dévolue à une analyse approfondie d’une suspension de latex SBA-PMMA, de différentes concentrations (d’un état dilué à très concentré), les acquisitions étant effectuées avec les conditions optimisées. L’arrangement des particules de latex est comparé à des modèles issus de la littérature, et avec des résultats expérimentaux obtenus par cryo-SEM sur suspensions congelées. Nous présentons ensuite une étude du même latex en présence de tensioactif. La couche de tensioactif peut être mise en évidence dans les volumes reconstruits et segmentés. En conclusion, nous résumons les potentialités de la tomographie wet-STEM pour la caractérisation de nanomatériaux solides et liquides. Des perspectives sont proposées pour continuer dans l’exploration de ces potentialités et des limites de la technique. / ESEM (Environmental Scanning Electron Microscopy) allows the observation of liquids under specific conditions of pressure and temperature. When working in the transmission mode, i.e. in STEM (Scanning Transmission Electron Microscopy), nano-objects can even be analyzed inside the liquid (“wet-STEM” mode). Moreover, in situ evaporation of water can be performed to study the materials evolution from the wet to the dry state. This work aims at developing electron tomography on liquid suspensions using STEM-in-ESEM, to obtain the 3D structure of nano-objects dispersed in a liquid. In a first part, Monte Carlo simulations and 2D wet-STEM experimental images are combined to study the contrast. Two kinds of liquid nano-materials are chosen as the sample: spherical gold particles (diameter around 40 nm) in suspension in water; latex SBA-PMMA suspension, a copolymer derived from styrene and metacrylic acid esters in aqueous solution, 3% PMMA shell included as steric surfactant. The comparison between simulated and experimental results helps to determine how water can affect the contrast of hydrated nano-materials. Tomography experiments are then performed on dry PU-carbon nanotubes nanocomposites using a previously developed home-made tomography device, and the volume is well reconstructed. When performing tomography on latex suspension, limitations are found on the temperature control of samples. We propose an optimization of the device with new observations conditions to better control water evaporation and condensation of liquid samples. Afterwards, a full 3D analysis on SBA-PMMA latex from dilute suspension to very concentrated one is performed, and a further study is presented in presence of a surfactant. The encouraging reconstruction results are used to model the particles arrangement. This shows the potentialities of wet-STEM tomography for the characterization of both solid and liquid nano-materials.

The exceptional properties of carbon nanomaterials make them ideal reinforcements for polymers. However, the main challenges in utilizing their unique properties are their tendency to form agglomerates, their non-controlled orientation, non-homogeneous distribution and finally the change in their shape/size due to processing. All the above are the result of the nanomaterial/polymer interfacial interactions which dictate the overall performance of the composites including the mechanical properties. The aforementioned uncertainties are the reason for the deviation observed between the experimentally determined properties and the theoretically expected ones. The focus of this study is to understand the reinforcing efficiency of carbon nanomaterials in polymers through finite element modeling that captures the effect of the interfacial interactions on the tensile modulus of polymer nanocomposites (PNCs). The novelty of this work is that the probability distribution functions of nanomaterials dispersion, distribution, orientation and waviness, determined through image analysis by extracting 3-D information from 2-D scanning electron micrographs, are incorporated into the finite element model allowing thus for fundamental understanding of how the nanostructure parameters affect the tensile modulus of the PNCs. The nanocomposites are made using melt mixing followed by either injections molding or melt spinning of fibers. Polypropylene (PP) is used as the polymer and carbon nanotubes (CNT) or exfoliated graphite nanoplatelets (xGnP) are used as nanoreinforcements. The presence of interphase, confirmed and characterized in terms of stiffness and width using atomic force microscopy, is also accounted for in the model. The dispersion and distribution of CNT within the polymer is experimentally altered by using a surfactant and by forcing the molten material to flow through a narrow orifice (melt spinning) that promotes alignment of CNT and even of the polymer chains along the flow/drawing direction. The effect of nanomaterials' geometry on the mechanical behavior of PNCs is also studied by comparing the properties of CNT/PP to those of xGnP/PP composites. Finally the reinforcing efficiency of CNT is determined independently of the viscoelastic behavior of the polymer by conducting tensile testing at temperatures below the glass transition temperature of PP. The finite element model with the incorporated image analysis subroutine has sufficient resolution to distinguish among the different cases (dispersion, distribution, geometry and alignment of nanomaterials) and the predicted tensile modulus is in agreement with the experimentally determined one. In conclusion, this study provides a tool, that integrates finite element modeling and thorough experiments that enables design of polymer nanocomposites with engineered mechanical properties.

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>Magister Scientiae - MSc / Currently, non-renewable sources are mostly used to meet the ever-growing demand for energy. However, these sources are not sustainable. In addition to these energy sources being not sustainable, they are bad for the environment although the energy supply sectors highly depend on them. To address such issues the use of renewable energy sources has been proven to be beneficial for the supply of energy for the global population and its energy needs. Advantageous over non-renewable sources, renewable energy plays a crucial role in minimizing the use of fossil fuel and reduces greenhouse gases. Minimizing use of fossil fuels and greenhouse gases is important, because it helps in the fight against climate change. The use of renewable energy sources can also lead to less air pollution and improved air quality. Although solar energy is the most abundant source of renewable energy that can be converted into electrical energy using various techniques, there are some limitations. Among these techniques are photovoltaic cells which are challenged by low efficiencies and high costs of material fabrication. Hence, current research and innovations are sought towards the reduction of costs and increasing the efficiency of the renewable energy conversion devices.