An environmentally benign process, which uses supercritical carbon dioxide (sc-CO₂) as a processing aid, was developed in this work to help exfoliate and disperse nanoclay into the polymer matrices at high clay content. The process involves the use of a pressurized CO₂ chamber to assist in the exfoliation and delivery of the clay into a stream of polypropylene (PP) melt within the extruder. This CO₂ method was evaluated and compared to other conventional processing techniques. It was observed that the conventional direct-melt compounding methods, with and without the direct injection of CO₂, did not show much improvement in the mechanical properties due to their inability to adequately exfoliate the nanoparticles into the polymer matrix. The commercial RTP sample prepared using a TSE and a MA compatibilizer showed moderate improvements in the clay dispersion and properties due to high shear forces and mixing capabilities of TSE. The most improvements were seen from the technique of using the pressurized CO₂ chamber, which directly injected pre-mixed sc-CO₂ and nanoclay into the polypropylene melt during extrusion. It was observed that the mechanical properties of the PP nanocomposites prepared using the CO₂ chamber technique, especially when combined with maleic anhydride (MA) compatibilizer, outperformed those of the commercial RTP samples and those of samples prepared using conventional melt compounding techniques. WAXD and TEM data showed a good degree of exfoliation for clay concentrations as high as 6.8 wt% when the clay was expanded and mixed with CO₂. At this concentration, mechanical properties such as yield strength and modulus increased by as much as 13% and 69%, respectively, relative to the pure PP, and approximately 15% higher than those of samples prepared by direct melt compounding (without the use of CO₂). Furthermore, yield-like behavior in the viscosity and a plateau in the low-frequency behavior of storage modulus, Gâ , was also attributed to polymer-clay interaction due to strong hydrogen bonding between MA groups and the hydroxyl groups on the clay surface, not just solely to the formation of percolation network due to exfoliation between clay platelets that is commonly reported in literature for clay-filled functionalized polypropylene. / Ph. D.

This work is concerned with mechanical property improvements to poly(ethylene terephthalate), PET, fibers by the addition of layered silicate nanoparticles and by drawing the un-oriented nanocomposite filaments in a second step. No previous studies on PET fibers filled with montmorillonite (MMT) nanoclay examined fiber drawability at temperatures above the glass transition. Therefore, the primary objective of this research was to determine 1) if PET nanocomposite fibers could be drawn to finer diameters and 2) whether drawing imparted improved Young's modulus and tenacity (i.e. strength) relative to un-filled PET fibers. Of equal importance to this work, the subsequent objective was to discern and understand the role of nanoclay in 1) the production of improved or reduced mechanical properties and 2) the ability to draw PET to lower or higher than normal draw ratios. In the first part of this thesis, the improvements in Young's modulus and tenacity of PET fibers filled with various types of organically modified montmorillonite is shown and the method to produce them is discussed. Greater improvements in mechanical properties occurred when the MMT stacks were intercalated with PET. A nominal 1 wt% loading of dimethyl-dehydrogenated tallow quaternary ammonium surface modified MMT in drawn PET fiber showed a 28% and 63% increase in Young's modulus and strength, respectively. Relative to an un-filled PET fiber, these results exceeded the upper-bound of the rule of mixtures estimate. Therefore, both the type of surface modification and concentration of MMT were shown to affect the degree of PET orientation and crystallinity. Furthermore, drawability above Tg and elongation-at-break increased upon the addition of organically modified MMT to un-oriented PET fibers, which was a key distinction of this work from others examining similar systems. Interestingly, the mechanical properties of modulus and tenacity showed a maximum with concentration of alkyl modified clay, but drawability did not show significant variation with increasing nanoclay content. Thermal analysis and Raman spectroscopy was used to examine the role of nanoclay in creating this maximum in mechanical properties. At low loadings, nanoclay was shown to intercalate with PET and enhance amorphous orientation. At higher concentrations of nanoclay the presence of large agglomerates prevented efficient orientation to the fiber axis and acted as stress concentrators to aid in cavitation and failure during testing. Raman spectroscopy showed that the as-spun unfilled PET fibers possessed significantly more trans conformer content of the ethylene glycol moiety than the nanocomposite fibers. The greater gauche content of the nanocomposite fibers delayed crystalline development during non-isothermal DSC scans to higher temperatures was associated with the increased drawability. / Ph. D.

This work explores the computational modeling of electromechanical problems using peridynamics and in particular, its application in studying the potential of carbon nanotube (CNT) reinforced nanocomposites for the purpose of sensing deformation and damage in materials. Peridynamics, a non-local continuum theory which was originally formulated for modeling problems in solid mechanics, has been extended in this research to electromechanical fields and applied to study the electromechanical properties of CNT nanocomposites at multiple length scales. Piezoresistivity is the coupling between the electrical properties of a material and applied mechanical loads, more specifically the change in resistance in response to deformation. This can include both, a geometric effect due to change in dimensions as well as the change in resistivity of the material itself. Nanocomposites referred to in this work are materials which consist of CNTs dispersed in a binding polymer matrix. The origins of the extraordinary piezoresistive properties of nanocomposites lie at the nanoscale where the non-local phenomenon of electron hopping plays a significant role in establishing the properties of the nanocomposite along with CNT network formation and inherent piezoresistivity of CNTs themselves. Electron hopping or tunneling allows for a current to flow between neighboring CNTs even when they are not in contact, provided the energy barrier for electrons to hop is small enough. This phenomenon is highly nonlinear with respect to the intertube distance and is also dependent on other factors such as the potential barrier of the polymer matrix. To investigate this in more detail, peridynamic simulations are first employed to study the piezoresistivity at the CNT bundle scale by considering a nanoscale representative volume element (RVE) of CNTs within polymer matrix, and by explicitly modeling electron hopping effects. This is done by introducing electron hopping bonds and it is shown that the conductivity and the non-local length scale parameter in peridynamics (the horizon) can be derived from a purely physics based model rather than assuming an ad-hoc value. Piezoresistivity can be characterized as a function of the deformation and damage within the material and thereby used as an in-situ indicator of the structural health of the material. As such, a material system for which real time in-situ monitoring may be useful is polymer bonded explosives. While these materials are designed for detonation under conditions of a strong shock, they can be damaged or even ignited under certain low magnitude impact scenarios such as during accidental drop or transportation. Since these materials are a heterogeneous system consisting of explosive grains within a polymer matrix binder, it is proposed that CNTs can be dispersed within the binder medium leading to an inherently piezoresistive hybrid nanocomposite bonded explosive material (NCBX) material which can then be monitored for a continuous assessment of deformation and damage within the material. To explore the potential use of CNT nanocomposites for this novel application, peridynamic simulations are carried out at the microscale level, first under quasistatic conditions and subsequently under dynamic conditions to allow the propagation of elastic waves. Peridynamics equations, which can be discretized to obtain a meshless method are particularly suited to this problem as the explicit modeling of crack initiation and propagation at the microscale is essential to understanding the properties of this material. Moreover, many other parameters such as electrical conductivity of the grain and the properties of the grain-binder interface are studied to understand their effect on the piezoresistive response of the material. For example, it is found that conductivity of the grain plays a major role in the piezoresistive response since it affects the preferential pathways of current density depending on the relative ease of flow through grain vs. binder. The results of this work are promising and are two fold. Peridynamics is found to be an effective method to model such materials, both at the nanoscale and the microscale. It alleviates some of difficulties faced by traditional finite element methods in the modeling of damage in materials and can be extended to coupled fields with relative ease. Secondly, simulations presented in this work show that there is much promise in this novel application of nanocomposites in the field of structural health monitoring of polymer bonded explosives. / Ph. D. / CNT reinforced nanocomposites are known to possess extraordinary mechanical, thermal and especially piezoresistive properties. Piezoresistivity is the change in resistivity of a material in response to mechanical deformation, which can possibly be used as a tool to monitor the structural health of a material. One such set of materials are polymer bonded explosives (PBXs), a heterogeneous composite system consisting of explosive grains dispersed within a binding matrix. These materials are susceptible to mechanical insults during transportation and handling, which can damage the material at the microstructural level, decreasing the reliability and usability and may even lead to accidental detonation. It is proposed that doping the binder phase with CNTs will form inherently piezoresistive NCBX materials, whose resistivity can be monitored for microstructural changes. This may help detect and discern these damage processes that can occur on at sub-macroscale length scales, which may pass unnoticed to the naked eye or even to other non-destructive methods which may not be able to detect internal changes in the material. The current work explores the structural health monitoring (SHM) capability of NCBX materials through a recently developed computational method, peridynamics. These materials are virtually tested under various loading conditions through peridynamics simulations and compared to experimental data. The results of this work are two fold; peridynamics is found to be an effective tool to study coupled phenomena such as piezoresistivity and nancomposite piezoresistivity is well suited to monitor microstructural changes in NCBX materials. This is a first step in establishing computational models for SHM in PBX materials and can be used in various other applications ubiquitous in the engineering world such as aircrafts, spacecrafts, bridges, dams among many others.

Carbon nanotubes (CNTs) and graphite nanoplatelets (GNPs) are carrying great promise as two important constituents of future multifunctional materials. Originating from their minimal defect confined nanostructure, exceptional thermal and electrical properties have been reported for these two allotropic forms of carbon. However, a brief survey of the literature reveals the fact that the incorporation of these species into a polymer matrix enhances its effective properties usually not to the degree predicted by the composite\\textquoteright s upper bound rule. To exploit their full potential, a proper understanding of the physical laws characterizing their behavior is an essential step. With emphasis on the electrical and thermal properties, the following study is an attempt to provide more realistic physical and computational models for studying the transport properties of these nanomaterials. Originated from quantum confinement effects, electron tunneling is believed to be an important phenomenon in determining the electrical properties of nanocomposites comprising CNTs and GNPs. To assess its importance, in this dissertation this phenomenon is incorporated into simulations by utilizing tools from statistical physics. A qualitative parametric study was carried out to demonstrate its dominating importance. Furthermore, a model is adopted from the literature and extended to quantify the electrical conductivity of these nanocomposite. To establish its validity, the model predictions were compared with relevant published findings in the literature. The applicability of the proposed model is confirmed for both CNTs and GNPs. To predict the thermal properties, a statistical continuum based model, originally developed for two-phase composites, is adopted and extended to describe multiphase nanocomposites with high contrast between the transport properties of the constituents. The adopted model is a third order strong-contrast expansion which directly links the thermal properties of the composite to the thermal properties of its constituents by considering the microstructural effects. In this approach, a specimen of the composite is assumed to be confined into a reference medium with known properties subjected to a temperature field in the infinity to predict its effective thermal properties. It was noticed that such approach is highly sensitive to the properties of the reference medium. To overcome this shortcoming, a technique to properly select the reference medium properties was developed. For verification purpose the proposed model predictions were compared with the corresponding finite element calculations for nanocomposites comprising cylindrical and disk-shaped nanoparticles. To shed more light on some conflicting reports about the performance of the hybrid CNT/GNP/polymer nanocomposites, an experimental study was conducted to study a hybrid ternary system. CNT/polymer, GNP/polymer and CNT/GNP/polymer nanocomposite specimens were processed and tested to evaluate their thermal and electrical conductivities. It was observed that the hybrid CNT/GNP/polymer composites outperform polymer composites loaded solely with CNTs or GNPs. Finally, the experimental findings were utilized to serve as basis to validate the models developed in this dissertation. The experimental study was utilized to reduce the modeling uncertainties and the computational predictions of the proposed models were compared with the experimental measurements. Acceptable agreements between the model predictions and experimental data were observed and explained in light of the experimental observations. The work proposed herein will enable significant advancement in understanding the physical phenomena behind the enhanced electrical and thermal conductivities of polymer nanocomposites specifically CNT/GNP/polymer nanocomposites. The dissertation results offer means to tune-up the electrical and thermal properties of the polymer nanocomposite materials to further enhance their performance. / Ph. D.

Yes / Polypropylene (PP) reinforced with 2 and 4 wt% of multi-walled carbon nanotubes (MWNT) were melt-blended in twin screw extruder and then molded by compression or micromolding process. The impact of injection speed on the surface morphology, rheological and tensile characteristics was investigated by using a scanning electron microscope, parallel plate rheometry, and tensiometry. Results showed that the tensile properties of micro-molded specimens were remarkably higher than those of the compression molded sheets. Compared to compression molded sheets, micromolded specimens demonstrated up to 40 and 244% higher tensile stiffness and yield strength, respectively, most likely due to the alignment of polymer chain segments in the flow direction induced during the micromolding process. It was observed that the fast filling speed caused a drop in the tensile properties of the nanocomposites and polymer. Rheological examination revealed that the presence of a rheological percolation network in the nanocomposites produced by micromolding and the fast injection speed was beneficial for establishing the percolated network. Morphological examination revealed that the size of nanotube agglomerations that appeared in micromolded specimens was up to five times smaller than in compression molded sheets and the agglomeration size decreased with the increase of the injection speed.

Titre de l'écran-titre (visionné le 9 mai 2023) / La thèse suivante examine la conversion du CO₂ à partir d'énergie solaire en utilisant des photocatalyseurs, qui est considérée comme l'un des techniques les plus intéressantes pour résoudre les problématiques du réchauffement climatique et de la crise énergétique. Il convient de souligner que cette thèse propose trois nouveaux composites hybrides nanostructurés pour la réduction photocatalytique du CO₂. La récolte de la lumière, la séparation des charges et les réactions de surface sont des aspects critiques qui ont un impact énorme sur la photoréduction du CO₂. Les cadres organiques covalents (COF) sont des candidats appropriés pour ces processus car ils offrent des caractéristiques et des propriétés structurelles exceptionnelles. De nombreux photocatalyseurs nanostructurés sont activement développés pour la photoréduction du CO₂. Les nanostructures multidimensionnelles et les hétérostructures sont largement étudiées en raison de leurs excellents attributs tels que la séparation efficace et la longue durée de vie des porteurs de charges. De manière prometteuse, les nanostructures et les nanocomposites des cadres organiques covalentes avec le graphène et ses dérivés, les dichalcogénures métalliques et les matériaux plasmoniques présentent d'excellentes performances photocatalytiques, selon des études de la littérature. D'abord, un cadre organique covalente, à base de céto-énamine TpPa-1 et de nanofeuillets d'oxyde de graphène réduit (rGO en anglais), a été développé par la technique d'assemblage in situ pour la photoréduction du CO₂ sous la lumière du soleil. Les interactions covalentes entre TpPa-1 et le rGO ont facilité la formation des bandes avec le potentiel requis, ainsi qu'une séparation de charge améliorée et une migration rapide des porteurs de charges vers la surface pour la réduction sélective du CO₂. Le médiateur électronique [Co(bpy)₃]²⁺ a servi pour apporter sites actifs pour la coordination, l'activation et la réduction des molécules de CO₂ en CO. De plus, un cadre organique covalente (COF) nanosphérique creux à base de TpPa-1, intégrée à un atome unique de Co-1T-MOS₂ (TpPa-1/Co-1T-MOS₂), a été conçu et développé via une stratégie à double ligand pour ajuster le potentiel des bandes et améliorer la séparation des charges afin d'optimiser l'efficacité de la photoréduction du CO₂. Les interactions entre TpPa-1 et Co-1T-MoS₂ ont facilité et amélioré la séparation des charges ainsi que la migration des porteurs de charge vers la surface, ce qui a entraîné une conversion sélective du CO₂ en CO. Finalement, les nanoparticules plasmoniques Au adhérés à une structure organique covalente tridimensionnelle, à base de porphyrine creuse (COF-366-Co) et avec un atome unique de Co (COF-366-Co[indice (H)]/Au), augmentent considérablement l'efficacité de la photoréduction du CO₂. Le nanocomposite conçu utilise le transfert d'électrons énergétiques induit par le plasmon, une meilleure collecte de lumière et des réactions de surface facilitées pour conduire les réactions redox photocatalytiques. Le nanocomposite développé (COF-366-Co[indice (H)]/Au) a montré une activité prometteuse vis-à-vis de la réduction photocatalytique du CO₂ sous irradiation à la lumière visible, qui a produit CO à un taux allant jusqu'à ~1200 µmolg⁻¹h⁻¹ et avec une sélectivité de 98 % sur H₂. / The ensuing thesis examines the conversion of carbon dioxide (CO₂) to value-added chemical and fuels under solar light irradiation by employing some of the emerging photocatalytic materials known as covalent organic frameworks (COFs). This approach of photocatalytic process is considered to be one of the most viable remedies to global warming and energy crisis dilemmas. Importantly, this thesis delivers three novel nanostructured hybrid composites based on COFs for photocatalytic CO₂ reduction to value-added chemicals and fuels. Light-harvesting, charge separation, and surface reactions are critical aspects that have an enormous impact on CO₂ photoreduction. Covalent organic frameworks can be suitable candidates for these processes as they offer outstanding structural features and properties. Diverse nanostructured photocatalysts are actively being developed for CO₂ photoreduction. Multidimensional nanostructures and nanocomposite heterostructures are widely studied because of their excellent attributes such as efficient separation and long lifetime of the excited charge carriers. Promisingly, nanostructures and nanocomposites of the covalent organic frameworks with graphene and its derivatives, metal dichalcogenides and plasmonic materials exhibit excellent photocatalytic performance, according to the literature reports. In this investigation, a keto-enamine TpPa-1 covalent organic framework and reduced graphene oxide nanosheet nanocomposite are developed by an in-situ assembling technique. The covalent interactions between TpPa-1 and rGO facilitated the formation of band edges with required potential and thereby to achieve an improved charge separation along with rapid migration of charge carriers to the surface toward the selective reduction of CO₂. By the support of the electron mediator [Co(bpy)₃]²⁺ in the hybrid served as the active sites for the coordination, activation, and reduction of CO₂ molecules to CO. A hollow nano spherical TpPa-1 covalent organic framework (COF) integrated with single atom Co-1T-MoS₂ (TpPa-1/Co-1T-MoS₂) is further designed and developed through a dual-ligand strategy to tune the band edge potential and enhance the charge separation to improve CO₂ photoreduction efficiency of the system. The interactions between TpPa-1 and Co-1T-MoS₂ aided and enhanced the charge separation as well as charge carrier migration to the surface resulted in selective conversion CO₂ to CO. Au plasmonic nanoparticles adorned three-dimensional hollow porphyrin-based covalent organic framework with Co single atom (COF-366-Co[subscript (H)]/Au) is developed via dual-ligand strategy and post-synthetic metallization method and found that this system significantly boosted up the CO₂ photoreduction efficiency. It utilizes the plasmon-induced energetic electron transfer, enhanced light harvesting, and surface reactions to drive the photocatalytic redox reactions. The developed COF-366-Co[subscript (H)]/Au exhibited fine activity toward photocatalytic CO₂ reduction under visible light irradiation, which yielded the CO at a rate up to ~1200 µmolg⁻¹h⁻¹ with a selectivity of 98% over H₂.

L'exploitation de l'énergie solaire présente une solution alternative efficace pour limiter la consommation de l'énergie fossile et résoudre ainsi les problèmes qui en découlent notamment la pollution et le changement climatique. La dissociation de l'eau par le procédé de la photocatalyse est considérée actuellement comme une méthode innovante pour la photogénération de l'hydrogène (H₂) à partir d'une ressource non carbonée. Les photocatalyseurs classiques mis en jeu ne sont malheureusement activables que sous l'irradiation de l'ultraviolet, ce qui limite leur activité catalytique sous la lumière solaire principalement formée par le visible. Grâce à ses propriétés optiques et électroniques, le phosphore noir (BP) est caractérisé par une bonne absorption lumineuse étendue sur le visible, et même l'infrarouge proche. Ainsi, il présente un candidat potentiel pour les procédés photocatalytiques. Ce travail présente une méthode alternative pour la synthèse d'un nanocomposite à base du BP assisté par le phosphure de nickel (Ni₂P). Cette méthode est basée sur la transition de phase induite par l'éthylènediamine en présence des ions nickel (Ni²⁺) pour la formation in-situ du Ni₂P en tant que co-catalyseur à la surface du BP formé. Les résultats obtenus montrent que l'activité photocatalytique du nanocomposite avec un ratio molaire Ni/P de 3 % atteint 406,08 μmol.g⁻¹.h⁻¹, qui est 185 fois plus élevé que le matériau sans co-catalyseur. Le plus important, le photocatalyseur a montré une efficacité quantique élevée allant jusqu'à 48,45 % à 360 nm et 7,90 % à 400 nm. La caractérisation du matériau synthétisé a prouvé que cette performance photocatalytique pourrait être expliquée par l'absorption lumineuse étalée sur le visible ainsi que l'efficacité de la séparation des porteurs de charges assurée par un contact intime entre le co-catalyseur et le matériau principal. Ce contact établi par une liaison covalente permet également d'avoir une stabilité notable. La stabilité du nanocomposite développé s'est manifestée par une capacité importante de réutilisabilité, ce qui lui permettrait d'être un photocatalyseur performant pour une application pratique. / The exploitation of solar energy presents an effective and an alternative solution to limit the consumption of fossil energy and to solve the correspondent problems, particularly the pollution and the climate change. The water splitting using the photocatalysis process is considered currently as an innovative method for the photogeneration of hydrogen (H₂) from a non-carbon resource. The involved conventional photocatalysts are unfortunately activable only under ultraviolet irradiation, which limits their catalytic activity under sunlight, mainly composed of the visible spectrum. Thanks to its optical and electronic properties, black phosphorus (BP) is characterized by a good light absorption including the visible and even the near-infrared spectrum. Thus, it presents a potential candidate for photocatalytic processes. This work presents an alternative method for the synthesis of a BP-based nanocomposite assisted by nickel phosphide (Ni₂P). This method is based on the ethylenediamine-induced phase transition in the presence of nickel ions (Ni²⁺) for the in-situ growth of Ni₂P as a co-catalyst on the surface of the as-synthesized BP. The obtained results show that the photocatalytic activity of the nanocomposite with Ni/P molar ratio of 3% reached 406.08 μmol.g⁻¹.h⁻¹, which is 185 times higher than the bare material. Most importantly, the photocatalyst showed a high quantum efficiency of up to 48.45% at 360 nm and 7.90% at 400 nm. The characterization of the synthesized material proved that this photocatalytic performance could be explained by the light harvesting efficiency including the visible light as well as the charge carrier separation efficiency ensured by the intimate contact between the co-catalyst and the main material. Also, this contact established by a chemical covalent bond provides a notable stability. The stability of the developed nanocomposite is manifested by a significant capacity for reusability, which would allow it to be a powerful photocatalyst in a practical application.

L'une des meilleures alternatives actuelles pour prévenir et/ou réduire les déchets d'emballages est le recours aux polymères renouvelables et biodégradables. Ainsi, il existe un intérêt croissant d'améliorer les emballages existants tels que les emballages multicouches plastiques. Ces derniers contiennent différentes couches de polymères, chacune répondant à un besoin différent comme barrière aux gaz, propriétés mécaniques, qualité du scellage, etc. Pour assurer une barrière à l'oxygène, les polymères utilisés sont généralement des polymères très peu perméables tel que l'alcool éthylène vinylique (EVOH) et le nylon. Cela présente toutefois des inconvénients tels que le coût et la non recyclabilité de l'emballage. Rapportés comme étant les matériaux du 21ème siècle, les polymères nanocomposites (PNCs) sont des alternatifs prometteurs à ces matériaux d'emballages plastiques en raison de leurs caractéristiques écologiques favorables. C'est dans cette optique qu'on a développé dans ce travail des films d'emballages bicouches et quadricouches dégradables à haute barrière à l'oxygène à base de l'alcool polyvinylique (PVA), le chitosane (CS) et d'argile (montmorillonite, MMT). Ce dernier a été choisi comme charge en raison de sa disponibilité et de son prix abordable. En utilisant la technique de dépôt 'Layer-by Layer (LbL)', deux types de films avec du PVA comme couche principale sont développés; l'un avec la MMT et l'autre avec le CS. Les films bicouches et quadricouches étudiés diffèrent non seulement par le nombre de couches de l'unité répétitive (deux et quatre respectivement) mais aussi de la teneur en MMT et en CS dans chaque films. Les films obtenus sont caractérisés par diffraction des rayons X (DRX), spectroscopie infrarouge à transformée de Fourier (FTIR), la diffraction des rayons X à grand angle (WAXD), etc. Cette dernière a révélé que les films obtenus par la méthode 'Spin coating-LbL' présentent une bonne orientation de la macromolécule et des nanoplaquettes de MMT avec des interactions électrostatiques intéressantes. Les études de l'angle de contact (CA) et de la perméabilité à l'oxygène (PO) ont montré que les films quadricouches sont plus hydrophobiques avec des valeurs de PO considérablement réduites. Par conséquent, ils sont des candidats prometteurs pour une application dans l'emballage alimentaire. / One of the best alternatives to reduce current packaging waste is the use of biodegradable polymers. Thus, with the urgent need for green materials, there is a growing interest for the improvement of the existing packaging, such as the multilayer packaging. This packaging has different layers of polymers, each one fulfilling a different need like gas barrier, mechanical properties, and saleability. To ensure the oxygen barrier, a higher barrier polymer, like ethylene vinyl alcohol (EVOH) and Nylon, is generally used. This, however, has some drawbacks, such as the cost and the non recyclability of the packaging. Reported as the materials of the 21st century, polymer nanocomposites (PNCs) are promising alternatives to these plastic packaging materials due to their favorable ecological characteristics. To this aim, we have focused in this work on the development of multilayer films using spin coating assisted layer-by layer assembly technique (LbL). To provide a deeper understanding of the effect of macromolecule and nanoclay platelets orientation on barrier properties, two polymers were chosen to study hydrogen bonding based films: polyvinyl alcohol (PVA) and chitosan (CS). MMT was chosen as a filler because of its availability and affordable price. Using the LbL deposition technique, two different structures, bilayers and quadlayers films were investigated, which differ in the layers number of the repetitive unit (two and four, respectively). Two types of films were developed: PVA/MMT and PVA/CS. For the bilayer structures, two layers were deposited, one composed of PVA and one of MMT for PVA-MMT films and one of PVA and one of CS for PVA-CS films. For the quadlayer structure, four alternated layers are prepared; two composed of PVA and two of MMT for PVA-MMT-PVA-MMT films, and two composed of PVA and two of CS for PVA-CS-PVA-CS films. All films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), etc. The WAXD characterization showed a parallel orientation of the macromolecule and of MMT clay nanoplatelets. The contact angle (CA) and oxygen permeability (PO) characterizations showed that all quadlayers films are hydrophobic and their permeabilities are reduced compared to neat PVA. Therefore, as results, quadlayers films appear to be good candidates for food packaging applications.

De nos jours, le développement de nouveaux matériaux capables de récolter la lumière solaire de manière efficace pour des applications photocatalytiques est un véritable défi pour la science. Par conséquent, les matériaux réticulaires qui agissent comme des blocs de construction, constitués de joints entre des lieurs organiques et des métaux, avec des propriétés plus adaptées à la photocatalyse, sont devenus encore plus attractifs. Cependant, conférer une fonctionnalité à ces matériaux avec un minimum de défauts cristallins, qui conduisent à une recombinaison de charge électron-trou, et une absorption maximale de la lumière reste un problème. Pour cette raison, différentes stratégies, comme le dopage, l'utilisation de cocatalyseur entre autres, ont été rapportées comme alternatives pour minimiser les problèmes mentionnés ci-dessus et par conséquent les désintégrations photocatalytiques. Néanmoins, les nanostructures de métaux nobles ont récemment montré des propriétés exceptionnelles d'absorption de la lumière, dans lesquelles des pairs électron-trous peuvent être générés et utilisés comme « porteurs de charges », qui améliorent l'activité photocatalytique sur les matériaux pour différentes applications. Les propriétés caractéristiques de ces nanostructures sont associées à l'effet des phénomènes de résonance plasmonique de surface localisée (LSPR en anglais). Les stratégies de préparation de matériaux plasmoniques pour les systèmes photocatalytiques sont très importantes pour améliorer les performances des réactions et les processus photocatalytiques souhaités. Des aspects critiques tels que la morphologie, la taille, les précurseurs chimiques entre autres doivent être pris en compte. Par exemple, l'utilisation du même métal avec une forme différente pourrait affecter ses performances photocatalytiques et déterminer son application. Ce document offre des preuves scientifiques intéressantes, dans le domaine de la photocatalyse, que les techniques d'ingénierie mentionnées ci-dessus sont cruciales pour le développement de matériaux à base de plasmons adaptés à la conversion du CO₂. Parmi ces preuves, des nanosphères d'or décorées à la surface d'un cadre d'imidazolate zéolitique (ZIF-67) ont montré un taux de génération de méthanol maximal de 1.6 mmol gcₐₜ⁻¹ h⁻¹ avec un rendement quantique apparent (AQY en anglais) de 6.4 %. Alors que les nanoparticules d'or en forme de nanotige ont doublé ce taux avec un AQY de 7.4 %. De plus, les nanoparticules d'or liées chimiquement avec des agents tensioactifs fonctionnels ont montré une amélioration significative des performances avec des taux de génération de 2.5 mmol gcₐₜ⁻¹ h⁻¹ en utilisant des charges métalliques inférieures et un AQY de 3.7 %. Alors qu'il existe un nombre croissant de rapports sûr de nouveaux matériaux réticulaires nanocomposites pour les processus photochimiques; les rapports de matériaux plasmoniques sur la chimie réticulaire sont encore rares. Par conséquent, ce rapport fournit un aperçu approfondi des différents concepts liés aux matériaux plasmoniques et à leurs applications sur les matériaux réticulaires afin d'identifier leurs opportunités et leurs défis sur la photocatalyse pour de futures considérations industrielles. / Nowadays the development of novel materials that can harvest solar light in an efficient way for photocatalytic applications is a real challenge for science. Therefore, reticular materials that act as building blocks, consisting of joints between organic linkers and metals, with properties more suitable for photocatalysis, have become even more attractive. However, imparting functionality to these materials with minimum crystalline defects, that lead to electron-hole charge recombination, and maximum light absorption is still an issue. For that reason, different strategies like doping, and usage of co-catalyst among others have been reported as alternatives to minimize the above-mentioned problems and consequently photocatalytic decays. Nevertheless, noble metal nanostructures have recently shown exceptional light absorption properties, in which electron-hole pairs can be generated and used as "charge-carriers", that enhance photocatalytic activity on materials for different applications. The characteristic properties of these nanostructures are associated with the effect of localized surface plasmonic resonance phenomena (LSPR). The strategies for the preparation of plasmonic materials for photocatalytic systems are highly crucial to achieve improvement in the performance of desired photocatalytic reactions and processes. Critical aspects such as morphology, size, and chemical precursors among others must be considered. For example, the use of the same metal with a different shape could affect its photocatalytic performance and determine its application. This document offers interesting scientific evidence, on the field of photocatalysis, that above-mentioned engineering techniques are crucial for the development of plasmon-based materials suitable for CO₂ conversion. Among this evidence, gold nanospheres decorated on the surface of zeolitic imidazolate framework (ZIF-67) showed a maximum methanol generation rate of 1.6 mmol gcₐₜ⁻¹ h⁻¹ with an apparent quantum yield (AQY) of 6.4%. While nanorod shape gold nanoparticles doubled this rate with an AQY of 7.4%. Furthermore, chemically bonded gold nanoparticles with functional surfactant agents showed a significant improve on the performance with generation rates of 2.5 mmol gcₐₜ⁻¹ h⁻¹ using lower metal loadings and AQY of 3.7%. While there is a growing number of reports of novel nanocomposite reticular materials for photochemical processes; reports of plasmonic materials on reticular chemistry are still scarce. Therefore, this report provides a brief overview and profound insight into different concepts related to plasmonic materials and their applications on reticular materials to identify their opportunities and challenges in photocatalysis for future industrial considerations.

Note sur les annexes : 7 documents en format mp4, « the nanoparticle tracking analysis (NTA) technique uses the properties of both light scattering and Brownian motion to extract information about the size and concentration of particles in suspension by employing microscopy techniques. Through the use of an objective lens and a camera, NTA is able to record videos of the scattered light produced by individual particles as they traverse a microchannel. » / Les matériaux souples stimulants dotés de propriétés hybrides présentent un grand intérêt dans les domaines de la biomédecine et de la santé, car ils permettent de développer de nouveaux actionneurs intelligents pour des applications telles que l'administration de médicaments, la cicatrisation des plaies et les plateformes de culture cellulaire in vitro. Les hydrogels thermosensibles, tels que l'hydrogel de poly(N-isopropylacrylamide) (pNIPAM), sont couramment utilisés comme matériaux souples en raison de leur biocompatibilité et de leur capacité à subir des modifications de leurs propriétés physiques et/ou chimiques en fonction de la température, par exemple un rétrécissement ou un gonflement volumétrique. L'incorporation de nanoparticules d'or plasmoniques dans le réseau d'hydrogel représente une excellente alternative pour déclencher localement et à distance le retrait volumétrique de l'hydrogel sous l'effet de la lumière. Les nanoparticules d'or supportant des résonances plasmoniques de surface localisées (LSPR) présentent des propriétés photothermiques exceptionnelles en raison de leur grande section d'extinction optique aux longueurs d'onde visibles et proches de l'infrarouge. Il est donc impératif de bien comprendre les paramètres qui influencent leur synthèse pour garantir la réussite de la mise en œuvre de ces nanomatériaux hybrides intelligents dans le domaine biomédical. Cette compréhension est essentielle pour développer des protocoles bien contrôlés et échelonnables avec des propriétés adaptées et des méthodes de fabrication simples, rentables et à grande échelle. L'objectif principal du travail présenté dans cette thèse était de développer un nanomatériau hybride à base plasmonique avec un comportement réversible et une réactivité élevée pour être utilisé comme actionneurs souples intelligents pilotés par la lumière dans des applications biomédicales. À cette fin, des microgels cœur-coquille Au-pNIPAM ont été choisis comme éléments constitutifs des matériaux hybrides sensibles à la lumière et synthétisés par polymérisation par précipitation avec ensemencement. Dans un premier temps, le rôle crucial des points de nucléation dans le processus de polymérisation a été étudié, montrant leur influence, indépendamment de la taille du noyau d'or, sur la modulation de paramètres importants pour la synthèse de microgels Au-pNIPAM, y compris le rendement d'encapsulation des noyaux d'or, la taille et la capacité de rétrécissement du nanomatériau. Deuxièmement, en exploitant le protocole de synthèse bien contrôlé et la stabilité colloïdale des microgels cœur-coquille Au-pNIPAM, une méthode simple basée sur la compression et les colloïdes a été développée pour fabriquer des films minces Au-pNIPAM photopolymérisables. Cette méthode a permis la fabrication de films homogènes, en termes de densité de noyaux d'or, de l'ordre du micron sur des substrats rigides et malléables. Grâce à l'utilisation de la lumière et de photomasques, le patronage des films Au-pNIPAM a permis la fabrication de microgels Au-pNIPAM anisotropes avec des rapports d'aspect largeur-hauteur élevés sur des substrats et des suspensions, ajoutant une nouvelle dimension à la méthode de fabrication mise au point. Enfin, pour démontrer les propriétés d'actionnement de la lumière du matériau hybride développé et en tirant parti des propriétés thermoplasmoniques collectives des nanoparticules d'or, des robots nageurs guidés par la lumière ont été fabriqués. Sous exposition à la lumière, la trajectoire et la rotation des robots nageurs à l'interface air/eau ont été contrôlées avec précision grâce à l'effet Marangoni induit par la lumière. / Stimuli-responsive soft materials possessing hybrid properties are of great interest in the biomedical and healthcare fields to develop novel smart actuators for applications in, for instance, drug delivery, wound healing, and in-vitro cell culture platforms. Thermo-responsive hydrogels, such as the poly(N-isopropylacrylamide) (pNIPAM) hydrogel, are commonly used as soft materials owing to their biocompatibility and capacity to experience changes in their physical and/or chemical properties as a function of temperature, e.g., volumetric shrinkage. Incorporating plasmonic gold nanoparticles within the hydrogel network represents an excellent alternative to locally and remotely trigger the volumetric shrinkage of the hydrogel upon light illumination. Gold nanoparticles supporting localized surface plasmon resonances (LSPR) exhibit exceptional photothermal properties due to their large optical extinction cross-section at visible and near-infrared wavelengths. A comprehensive understanding of the parameters that influence their syntheses is imperative to ensure the successful implementation of these smart hybrid nanomaterials in the biomedical field. This understanding is pivotal in developing well-controlled and scalable protocols with tailored properties and simple, cost-effective, and large-scale fabrication methods. The main objective of the work presented in this thesis was to develop a plasmonic-based hybrid nanomaterial with reversible behavior and high responsivity to be used as light-driven smart soft actuators in biomedical applications. To this, Au-pNIPAM core-shell microgels were chosen as building blocks of light-responsive hybrid materials and synthesized through seeded precipitation polymerization. At first, the crucial role of nucleation points in the polymerization process was studied, showing their influence - regardless of gold core size - on the modulation of significant parameters for the synthesis of Au-pNIPAM core-shell microgels, including encapsulation yield of gold cores, size, and shrinking capacity of the nanomaterial. Secondly, by exploiting the well-controlled synthesis protocol and colloidal stability of Au-pNIPAM core-shell microgels, a simple compression- and colloid-based method was developed to fabricate photopolymerizable thin Au-pNIPAM films. This method allowed the fabrication of homogeneous films - in terms of gold core number density - in the micron-size range onto both rigid and malleable substrates. Through the use of light and photomasks, the patterning of Au-pNIPAM films permitted the fabrication of anisotropic Au-pNIPAM microgels with high width-to-height aspect rations on substrates and suspension, adding a new dimension to the developed fabrication method. Finally, to demonstrate the light-actuation properties of the developed hybrid material and by leveraging the collective thermoplasmonic properties of gold nanoparticles, light-guided swimming robots of millimeter-scale were fabricated. Under light exposure, the trajectory and rotation of swimming robots at the air/water interface were precisely controlled due to the light-induced Marangoni effect.