Les nanocomposites, et plus particulièrement les nanocomposites à renforts plaquettaires, offrent de remarquables propriétés mécaniques. La maîtrise de leur comportement mécanique repose sur une bonne compréhension des mécanismes de déformation en jeu, ainsi que des relations liant leur microstructure à leur réponse à l’échelle macroscopique. L’importance de cette nouvelle classe de matériaux, ainsi que le faible nombre de travaux actuellement disponibles sur leur comportement mécanique ont motivé les travaux présentés dans ce mémoire. Ceux-ci concernent aussi bien la caractérisation expérimentale que la modélisation micromécanique, tant en régime élastique linéaire que pour les réponses non linéaires. On présente d’abord les différentes classes de nanocomposites, et tout particulièrement les nanocomposites à renforts plaquettaires. Puis on décrit les résultats des tests mécaniques réalisées sur un nanocomposite à matrice polypropylène et renforts de nano plaquettes d’argile de Montmorillonite. Afin de fournir une évaluation de la pertinence des méthodes d’homogénéisation linéaires usuellement mises en œuvre, les résultats fournis par le modèle de Mori-Tanaka et par la borne de Ponte Castañeda et Willis sont confrontés à des données expérimentales bibliographiques ou obtenues au cours de cette thèse. Ces confrontations ont permis de démontrer à la fois l’intérêt et les limites des modèles mis en œuvre ; elles ont été aussi à l’origine des investigations permettant de rendre compte des effets de taille de nano renforts, au travers d’une élasticité surfacique du type Gurtin-Murdoch. / Nanocomposites and especially nanocomposites with platelet reinforcements have remarkable mechanical properties. The development of this class of materials requires an understanding of the deformation mechanisms involved in the mechanical behavior and of the link between materials microstrusture and their macroscopic properties. Experimental data and modeling tools of their mechanical behavior are still rare. This has motivated the present study which includes both an experimental characterization and micromechanical modeling in linear regime as well as for non linear response. We first present the different class of nanocomposites and their properties, and especially for the nanocomposites reinforced by nano platelets. Then we show the results of mechanical tests conducted on nanocomposites made up of polypropylene reinforced by montmorillonite clay nano platelets. In order to provide a rigorous evaluation of homogenization techniques classically used for composites, the predictions of Mori-tanaka estimate and Ponte Castañeda and Willis bound are compared to experimental data from bibliography or from tests performed during this thesis. These comparisons allowed to demonstrate the interest of the implemented methods and to show their limits for the description of the nanocomposite behavior. They have motivated the implementation and the evaluation of models which account for size effect of the nano reinforcements by means of a Gurtin-Murdoch type surface elasticity.

No description available.

The Effective Continuum Micromechanics Analysis Code (EC-MAC) was developed for predicting effective properties of composites containing multiple distinct nanoheterogeneities (fibers, spheres, platelets, voids, etc.) each with an arbitrary number of coating layers based upon either the modified Mori-Tanaka method (MTM) and self consistent method (SCM). This code was used to investigate the effect of carbon nanofiber morphology (i.e., hollow versus solid cross-section), nanofiber waviness, and both nanofiber-resin interphase properties and dimensions on bulk nanocomposite elastic moduli. For a given nanofiber axial force-displacement relationship, the elastic modulus for hollow nanofibers can significantly exceed that for solid nanofibers resulting in notable differences in bulk nanocomposite properties. The development of a nanofiber-resin interphase had a notable effect on the bulk elastic moduli. Consistent with results from the literature, small degrees of nanofiber waviness resulted in a significant decrease in effective composite properties. Key aspects of nanofiber morphology were characterized using transmission electron microscopy (TEM) images for VGCNF/vinyl ester (VE) nanocomposites. Three-parameter Weibull probability density functions were generated to describe the statistical variation in nanofiber outer diameters, wall thicknesses, relative wall thicknesses, visible aspect ratios, and visible waviness ratios. Such information could be used to establish more realistic nanofiber moduli and strengths obtained from nanofiber tensile tests, as well as to develop physically motivated computational models for predicting nanocomposite behavior. This study represents one of the first attempts to characterize the distribution of VGCNF features in real thermoset nanocomposites. In addition, the influence of realistic nanoreinforcement geometries, distinct elastic properties, and orientations on the effective elastic moduli was addressed. The effect of multiple distinct heterogeneities, including voids, on the effective elastic moduli was investigated. For the composites containing randomly oriented wavy vapor grown carbon nanofibers (VGCNFs) and voids, the predicted moduli captured the essential character of the experimental data, where the volume fraction of voids was approximated as a nonlinear function of the volume fraction of reinforcements. This study should facilitate the development of multiscale materials design by providing insight into the relationships between nanomaterial morphology and properties across multiple spatial scales that lead to improved macroscale performance.

No description available.

Composite structures for aerospace and wind turbine applications are subjected to high acoustic and vibrational loading and exhibit very high amplitude displacements and thus premature failure. Materials with high damping or absorbing properties are crucially important to extend the life of structures. Traditional damping treatments are based on the combinations of viscoelastic, elastomeric, magnetic, and piezoelectric materials. In this work, the use of carbon nanofibers (CNFs) in the form of interconnected self-supportive paper as reinforcement can significantly improve damping performance. The interfacial friction is the primary source of energy dissipation in CNF paper based nanocomposites. The approach entailed making CNF paper by filtration of well-dispersed nanofibers under controlled processing conditions. The CNF paper was integrated into composite laminates using modified liquid composite molding processes including Resin Transfer Molding (RTM) and Vacuum Assisted Resin Transfer Molding (VARTM). The rheological and curing behaviors of the CNF-modified polymer resin were characterized with Viscometry and Differential Scanning Calorimetry (DSC). The process analysis in mold filling and pressure distribution was conducted using Control Volume Finite Element Method (CVFEM) in an attempt to optimize the quality of multifunctional nanocomposites. The mold filling simulation was validated with flow visualization in a transparent mold. Several tests were performed to study the damping properties of the fabricated composites including Dynamic Mechanical Analysis (DMA) and piezoceramic patch based vibration tests. It was found that the damping performance was significantly enhanced with the incorporation of carbon nanofibers into the composite structures.

Novel electrocchemical and chemical strategies have been developed for the fabrication of functional nanocomposites. New scientific and engineering contribution of this work to colloidal nanotechnology included the development of advanced chelating dispersing agents, such as various small organic molecules and chelating polymers. The unique feature of such dispersion agents is their strong adsorption on the surface of different materials, which allows superior dispersion. The chelating monomers of chelating polymers, such as PAZO and PMSS provided multiple adsorption sites for bonding to metal atoms on the particles surface. We analyzed and developed new fundamental adsorption and dispersion mechanisms. An important finding was the possibility of co-dispersion and co-deposition of advanced materials such as oxides, nitrides, complex oxides and minerals using universal dispersing agents and formation of composites by EPD method. It was found that Caffeic acid (CA) can be used as an efficient dispersing agent for the synthesis of ZnO nanorods of reduced size and a dispersing agent for the EPD of ZnO films. Another important achievement of this work was the application of tannic acid as an efficient capping and dispersing agent for synthesis and EPD of inorganic materials and composites. An important discovery was the use of lauryl gallate dispersant as a reducing agent for the synthesis of AgNp and a vehicle for particle dispersion and extraction in the liquid-liquid extraction method. Further advancements in our new technologies allowed us to develop composite films using anodic EPD using weak polyelectrolytes, such as alginate. The composite coatings exhibited protective and flame retardant properties. We analyzed the deposition mechanisms and kinetics as well as microstructure of the coatings. In another strategy, we developed electrochemical strategies for the deposition of composites, based on strong polyelectrolytes. The approach is based on the EPD of the polyelectrolyte molecules and electrosynthesis of EPD of ceramic particles. The electrostatic heterocoagulation mechanism was proposed for the deposit formation. We investigated the deposition kinetics, composition and microstructure of the composites prepared by the new strategies. The new electrochemical strategies can be used for the deposition of other composites, based on functional polymers with pH independent charge. New methods have been developed for the chemical synthesis of PPy based composites, using PMSS, PMSS–SR11 and PMSS–SR31 as anionic dopants for chemical polymerization and dispersants for MWCNT. The composites showed promising performance for application in electrodes of electrochemical supercapacitors. Good electrochemical performance was achieved at high active mass loadings. The electrodes showed high capacitance, large voltage window and low impedance. The analysis of electrochemical testing results and chemical structure of PMSS, PMSS–SR11 and PMSS–SR31 provided an insight into the influence of the anionic functional groups on the capacitance and capacitance retention a high charge-discharge rates. / Thesis / Master of Applied Science (MASc)

No description available.

Acid oxidation of multi-walled carbon nanotubes (MWCNTs) introduced carboxylic acid sites onto the MWCNT surface, which permitted further functionalization. Derivatization of carboxylic acid sites yielded amide-amine and amide-urea functionalized MWCNTs from oxidized precursors. Conventional MWCNT characterization techniques including X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Raman spectroscopy supported successful MWCNT functionalization. Incorporation of MWCNTs functionalized with hydrogen bonding groups into a segmented polyurethane matrix led to an increase in mechanical properties at optimized MWCNT loadings, in contrast with non-functionalized MWCNTs that resulted in mechanical property decreases across all loadings. Dynamic mechanical analysis (DMA) demonstrated an increase in the polyurethane-MWCNT composite flow temperature with increasing hydrogen bonding MWCNT incorporation, as opposed to non-functionalized MWCNT composites which displayed no significant change in flow temperature. Variable temperature Fourier transform infrared spectroscopy (VT FT-IR) probed temperature-dependent hydrogen bonding in the polyurethane-MWCNT composites and revealed a significant impact on composite hydrogen bonding interactions upon MWCNT incorporation, which was amplified in composites formed using hydrogen bonding functionalized MWCNTs. Acid oxidation of carbon nanohorns (CNHs) yielded carboxylic acid functionalized CNHs, providing sites for further reaction with histamine to afford histamine-functionalized CNHs (His-CNHs). Raman spectroscopy, XPS and TGA confirmed successful functionalization. Transmission electron microscopy (TEM) demonstrated that His-CNHs efficiently complex quantum dots (QDs) through imidazole-Zn interactions. Combination of His-CNHs, QDs, and a poly(oligo-(ethylene glycol9) methyl ether methacrylate)-block-poly(4-vinyl imidazole) copolymer using an interfacial complexation technique afforded stable ternary nanocomplexes with average hydrodynamic diameters under 100 nm. These ternary nanocomplexes represent promising materials for photothermal cancer theranostics due to their size and stability. The efficient reaction of 2-isocyanatoethyl methacrylate with amines afforded urea-containing methacrylic monomers, where the amine-derived pendant groups determined the polymer Tg. Reversible addition-fragmentation chain-transfer (RAFT) polymerization enabled the synthesis of ABA triblock copolymers with urea-containing methacrylic outer blocks and poly(2-ethylhexyl methacrylate) inner blocks. These ABA triblocks copolymers displayed composition dependent phase-separated morphologies and desirable mechanical properties. The urea-containing polymers efficiently complexed gold nanoparticles through urea-gold interactions. Furthermore, urea-containing methacrylic polymers served as a useful matrix for incorporation of silica-coated upconverting nanoparticles, affording upconverting nanoparticle composite films.The novel ionene monomer N1,N2-bis(3-(dimethylamino)propyl)oxalamide permitted synthesis of novel oxalamide-containing ammonium ionenes. The hydrogen bonding, charge density, and counter anion tuned the ionene mechanical properties. The ionene structure also influenced water uptake and conductivity. The differences in physical properties correlated well with the morphology observed in small-angle X-ray scattering. The oxalamide-containing ionenes greatly enhance mechanical properties compared to typical ammonium ionenes, and further expand the library of ionene polymers. / Ph. D.

Cette thèse porte principalement sur la compréhension des relations entre la microstructure et les propriétés rhéologiques des nano-composites à base d’un copolymère d’éthylène-acétate de vinyle (EVA). La première partie de l'étude concerne les nano-composites d’EVA avec de la cellulose nanocrystalline (NCC). Cette partie cherche à inférer la structure d’échantillons inconnus à l’aide de mesures rhéologiques. En analysant les propriétés obtenues par des mesures rhéologiques en cisaillement et en élongation, les principaux mécanismes étant à l’origine du renforcement de ces nano-composites sont étudiés en détail. Dans la deuxième partie du travail, on s’intéresse aux nano-composites contenant des particules isométriques (CaCO3) et anisométrique (argile). L'objectif est de déterminer l'effet de variables structurelles comme les interactions polymère-particule et particule-particule, l'état de dispersion, et en particulier la forme des particules sur les propriétés finales. Les mécanismes par lesquels ces paramètres influencent les propriétés rhélogiques ont été abordés en lien avec les prédictions par un modèle de fonction moléculaire de contrainte (MSF). Il a été constaté que plus les particules sont non-isométriques, plus les interactions polymère-particule et les interactions entre les particules sont élevées. Ainsi, l'effet de l’argile est beaucoup plus important que celui du CaCO3, et ce pour presque tous les comportements rhéologiques étudiés. La plupart des paramètres rhéologiques ont montré une divergence autour du seuil de percolation. Par conséquent, les modèles basés sur la dynamique des chaînes (modèle MSF) ne peuvent prédire le comportement après la percolation. Pour les systèmes percolés, les modèles basés sur le réseau fractal, qui considèrent les interactions entre les particules, ont été utilisés. / The main objective of this thesis is to understand the relations between microstructure and rheological properties of polymer nano-composites based on ethylene vinyl acetate (EVA) copolymer. The first part of the study is related to EVA-nano crystalline cellulose (NCC) composites. As a first step, determination of the unknown structure of the samples using rheological methods was investigated. By analyzing the properties obtained under shear and extensional deformations, the mechanisms leading to polymer reinforcement were investigated in details. In the second part, nano-composites containing isometric (CaCO3) and anisometric (clay) particles were used. The focus here was to determine the effect of structural variables such as polymer-particle and particle-particle interactions, state of dispersion, and in particular particle shape on the final properties of these nano-composites. The mechanisms involving these parameters were investigated through rheological properties and discussed with respect to experimental data. Predictions via the molecular stress function (MSF) model are also presented. It was found that higher particle anisomety led to greater polymer-particle and particle-particle interactions. Therefore, the effect of clay was much higher than CaCO3 on almost all the rheological parameters studied. But, lower predictability was found around the percolation concentration. Consequently, while a model based on chain dynamics could predict the behavior below percolation, such model failed to predict the response at higher concentrations. For percolated systems, models based on fractal networks, which include particle-particle interactions, were used.

Cette thèse présente une étude théorique du transport de chaleur dans les matériaux composites nano poreux et nano fils ainsi qu'une étude théorique des propriétés thermoélectriques de l'alliage Si0:8Ge0:2 confrontée à des mesures expérimentales réalisées pour une partie, dans le cadre de l'étude.La première étude démontre que les alliages poreux affichent des réductions de conductivité thermique à des dimensions de pores beaucoup plus grandes que les matériaux poreux non alliés de même porosité nominale. Si on considère une taille de pores de 1000nm, la conductivité thermique de l'alliage Si0:5Ge0:5 avec 0:1 de porosité est deux fois plus faible que la conductivité thermique d'un matériau non poreux, alors que les pores plus petits que 100 nm sont nécessaires pour obtenir la même réduction relative dans le Si ou Ge pur. Nos résultats indiquent que les alliages nano poreux devraient être avantageux devant les matériaux nano poreux non alliés, et ceux pour les applications nécessitant une faible conductivité thermique, tels que les nouveaux matériaux thermoélectriques.La deuxième étude théorique sur la conductance thermique de nano fils révèle l'effet de la structure sur le transport des phonons. Avec un modèle théorique qui considère la dépendance en fréquence du transport des phonons, nous sommes en mesure quantitativement de rendre compte des résultats expérimentaux sur des nano fils droits et coudés dans la gamme de température qui montre qu'un double coude sur un fil réduit sa conductance thermique de 40% à la température de 5K. Enfin, nous avons procédé à une approche théorique des propriétés thermoélectriques des alliages SiGe frittés, en les comparant aux mesures expérimentales nouvelles et antérieures, tout en évaluant leur potentiel d'amélioration. L'approche théorique a été validée par comparaison de la mobilité prévue et la conductivité thermique prévues, en faisant varier la quantité de Ge et les concentrations de dopage, dans une gamme de température comprise entre 300 et 1000K. Nos calculs suggèrent qu'une optimisation par rapport à l'état de l'art actuel est possible pour le matériau de type n et type p, conduisant potentiellement à une augmentation de 6% (5%) du ZT _a 1000K et 25% (4%) _a température ambiante. Même des améliorations plus grandes devraient être possibles si la probabilité de diffusion des phonons aux joints de grains pouvait être augmentée au-delà de sa valeur actuelle de 10%.