L'ajout de charges (agrégat de taille submicronique) dans une matrice élastomère apporte des propriétés physiques qualitativement différentes de celles de la matrice pure : module complexe dépendant de la température, forts effets non linéaires, forte dissipation... Ces propriétés sont liées à la nature de la matrice et des charges, à leur fraction volumique, et enfin à la force des interactions charge / matrice. Nous présentons d'abord les différents systèmes et la caractérisation de leurs propriétés mécaniques, de façon à clarifier le rôle des différents paramètres.La cristallisation sous traction du caoutchouc naturel a un effet important sur ses propriétés mécaniques. Nous l'avons donc mesurée quantitativement dans chacune des formulations. Nous montrons que le taux de cristallisation à la rupture est toujours de l'ordre de 13%. La nature de l'interface silice / matrice a un effet sur les propriétés mécaniques mais pas sur la cristallisation. Nous avons ensuite étudié le comportement en traction simple d'échantillons pré-entaillés. Nous montrons que la plus grande résistance à la propagation d'entaille du caoutchouc naturel renforcé est corrélée à la présence d'instabilités de propagation (rotation d'entaille). Les mécanismes physiques à l'origine de la rotation d'entaille ne sont pas compris. Nous décrivons la dynamique de propagation des rotations à différentes échelles, et les caractéristiques des rotations.La combinaison de la cristallisation induite et de la présence des charges induit dans le matériau une très grande anisotropie qui pourrait être à l'origine des rotations. / The subject of this PhD thesis is the resistance to tear of reinforced elastomers. The general context of this work is related to the performances of reinforced elastomers, specifically silica reinforced natural rubber, as regards various usage properties : wear of tyre tread, fatigue and tear resistance of tyre flanks, etc. Wear and fatigue mechanisms are very complex. This PhD thesis is a first step towards understanding these mechanisms. We focussed on the parameters which control ultimate properties (resistance to failure, resistance to tear propagation) of uniaxially stretched samples. Reinforced elastomers are nanocomposite materials made of an elastomer matrix in which submicrometric filler particles or aggregates are dispersed. Adding fillers considerably enhances usage properties, specifically ultimate properties. Mechanical and physical properties qualitatively different from those of the pure elastomer matrix are induced: a strongly temperature dependent complex modulus, strong non linear effects (Payne effect), large dissipation, hysteresis, plasticity and long time recovery (Mullins effect). The material parameters which have an influence on the properties are: the nature of the elastomer matrix (natural or synthetic rubber) and of the reinforcing fillers (carbon black or silica), the volume fraction and dispersion state of the fillers, the nature and strength of interactions at filler-matrix interfaces.This work is an experimental study of the resistance to failure and to tearing of uniaxially stretched samples. The various systems which have been studied are presented first. Their mechanical properties have been characterized in the various regimes of strain amplitude. The various samples have been compared systematically in order to clarify the effect of the various material parameters.Natural rubber crystallizes under strain. This phenomenon is very sensitive to the formulation of the various materials and has a tremendous effect on mechanical and ultimate properties. Thus, we have measured quantitatively the amount of crystallinity induced as a function of the applied strain during elongation cycles and up to sample failure. The influence of the nature and volume fraction of the fillers and of the matrix-filler interfaces has been studied. The crystallinity is close to 13% in all studied materials. In samples filled with silica, the nature of the filler-matrix interactions (covalent coupling vs no coupling) has very little influence on crystallization, whereas it modifies strongly the mechanical properties.Then we have studied the resistance to failure of uniaxially stretched pre-notched test samples. Within a macroscopic approach, we have related the ultimate property (energy density at break) to the various tear propagation modes which are observed. We have studied the effect of temperature and drawing speed. It has been shown that the higher resistance to failure of reinforced natural rubber is related to the appearance of spectacular instabilities of the propagation direction (the so-called ‘tear rotation’). The appearance of tear rotation is specific to pre-notched reinforced natural rubber samples. The physical mechanisms responsible for tear rotation are not yet fully understood. The combination of reinforcement due to fillers and of strain-induced crystallization may lead to a strong anisotropy of the elastic material constant of the material in front of the tear tip, and this might be the driving force for tear rotation. The rotation length has been identified as an important parameter which correlates well to the ultimate properties. The tear propagation is described at various scales. The typical length scales associated to tear rotation which are observed have been related to the material properties.

Este trabalho descreve a síntese de látices poliméricos híbridos contendo a argila natural Montmorilonita (MMT) por meio da polimerização radicalar controlada via mecanismo de transferência reversível de cadeia por adição-fragmentação (RAFT) em emulsão sem adição de surfatante. Primeiramente, copolímeros anfifílicos com diferentes estruturas e composições, foram preparados por meio da polimerização via RAFT em solução e caracterizados por ressonância magnética nuclear de hidrogênio (RMN 1H) e cromatografia por exclusão de tamanho (SEC). A interação entre os copolímeros sintetizados, chamados de macroagentes RAFT, e a superfície da MMT foi estudada por meio de isotermas de adsorção experimentais, as quais foram ajustadas por modelos teóricos. Os macroagentes RAFT à base de ácido acrílico (AA), acrilato de metil éter poli(etileno glicol) (PEGA) e acrilato de n-butila (BA) apresentaram afinidade pela argila como mostraram as isotermas do \"tipo L\" (Langmuir) obtidas. Os látices híbridos preparados utilizando esses macroagentes RAFT foram analisados por microscopia eletrônica de transmissão em temperatura criogênica (cryo-TEM), que revelou lamelas de MMT decoradas com nanopartículas poliméricas. As isotermas de adsorção dos macroagentes RAFT catiônicos à base de metacrilato de 2-(dimetilamino)etila (DMAEMA), PEGA e BA foram do \"tipo H\" (alta afinidade). Esses macroagentes RAFT possibilitaram a preparação de dispersões estáveis de complexos de MMT/macroagente RAFT, o que foi verificado por espalhamento dinâmico de luz (DLS), e sua utilização na síntese de látices híbridos levou à formação de uma camada polimérica em torno das lamelas de MMT. Os filmes poliméricos nanocompósitos obtidos a partir de látices catiônicos estáveis de poli(metacrilato de metila-co-acrilato de n-butila)/MMT apresentaram melhor estabilidade térmica e melhores propriedades mecânicas do que os filmes poliméricos preparados sem adição de argila como mostraram, respectivamente, os resultados de análise termogravimétrica (TG) e de análise termodinâmico-mecânica (DMA) dos materiais. / This work describes the synthesis of hybrid polymer latexes containing natural Montmorillonite clay (MMT) by reversible addition-fragmentation chain transfer (RAFT)-mediated surfactant-free emulsion polymerization. Firstly, amphiphilic copolymers with different structures and compositions were prepared by RAFT polymerization in solution and characterized by hydrogen nuclear magnetic resonance (1H NMR) and size exclusion chromatography (SEC). The interaction between these copolymers (referred to as macroRAFT agents) and the MMT surface was studied by experimental adsorption isotherms, which were adjusted by theoretical adsorption models. MacroRAFT agents based on acrylic acid (AA), poly(ethylene glycol) methyl ether acrylate (PEGA) and n-butyl acrylate (BA) displayed affinity for MMT as shown by the \"L-type\" (Langmuir) isotherms obtained. The hybrid latexes prepared using these macroRAFT agents were analyzed by transmission electron microscopy at cryogenic temperatures (cryo-TEM), which revealed polymer-decorated MMT platelets. The adsorption isotherms of cationic macroRAFT agents based on 2-(dimethylamino)ethyl methacrylate (DMAEMA), PEGA and BA were of the \"H-type\" (high affinity). These RAFT macroRAFT agents allowed the preparation of stable dispersions of MMT/macroRAFT agents complexes, which was verified by dynamic light scattering analysis (DLS), and their use in the synthesis of hybrid latexes led to the formation of a polymer layer surrounding the MMT platelets. Nanocomposite films obtained from stable cationic latexes of poly(methyl methacrylate-co-n-butyl acrylate)/MMT showed better thermal stability and better mechanical properties than polymer films prepared without addition of clay as shown, respectively, by the results of thermogravimetric analysis (TG) and dynamic mechanical analysis (DMA) of the final materials.

This thesis focuses on improved processing methods for enhanced mechanical properties in polymer nanocomposites, and controlled drug release in polymer based delivery systems. Supercritical carbon dioxide assisted mixing was successfully used in preparation of polypropylene/sepiolite and polypropylene/multiwall carbon nanotube nanocomposites. Relatively homogeneous dispersed and well separated nanofillers were obtained throughout the PP matrix. A better preservation of nanofiller lengths was observed in the scCO 2 assisted mixing. Mechanical property studies showed a marked increase in Young's modulus and tensile strength with the addition of nanofillers. More interestingly, techniques usually designed to achieve high quality PP nanocomposites, such as the use of masterbatches, maleic anhydride grafted polypropylene compatibilizers or polymer coated MWNTs are not needed to achieve equivalent mechanical properties with scCO2 assisted mixing. ScCO2 was also used as a foaming technique to modify the traditional cured poly(ethyl methacrylate/tetrahydrofurfuryl methacrylate) system for a controlled release of chlorhexidine. Highly porous structures were produced and chlorhexidine released from scCO2 foamed samples was more than 3 times higher than traditionally cured samples. By altering the processing conditions, such as CO2 saturation time and depressurization time the CX release rate was altered. Finally, the electrospinning method was combined with the layering encapsulation technique in order to enable the incorporation of water-soluble drugs in poly(lactic-co-glycolic acid) fibres for biomedical applications. Water-soluble drug, Rhodamine 6G or protein bovine serum albumin, loaded calcium carbonate microparticles were successfully incorporated in PLGA fibres and a bead and string structured composite fibres.

Monolithic materials are not meeting the increasing demand for flexible, lightweight and compact high energy density dielectrics. This limitation in performance is due to the trade-off between dielectric constant and dielectric breakdown. Insulating polymers are of interest owing to their high inherent electrical resistance, low dielectric loss, flexibility, light weight, and low cost; however, capacitors produced with dielectric polymers are limited to an energy density of ~1-2 J/cc. Polymer nanocomposites, i.e., high dielectric particles embedded into a high dielectric breakdown polymer, are promising candidates to overcome the limitations of monolithic materials for energy storage applications. The main objective of this dissertation is to simultaneously increase the dielectric permittivity and dielectric breakdown without increasing the loss, resulting in a significant enhancement in the energy density over the unmodified polymer. The key is maintaining a low volume content to ensure a high inter-particle distance, effectively minimizing the effect of local field on the composite's dielectric breakdown. The first step is studying the particle size and aspect ratio effects on the dielectric properties to ensure a judicious choice in order to obtain the highest enhancement. The best results, as a combination of dielectric constant, loss and dielectric breakdown, were with the particles with the highest aspect ratio. Further improvement in the dielectric behavior is observed when the nanoparticles surface is chemically tailored to tune transport properties. The particles treatment leads to better dispersion, planar distribution and stronger interaction with the polymer matrix. The planar distribution of the high aspect ratio particles is essential to limit the enhancement of local fields, where minimum local fields result in higher dielectric breakdown in the composite. The most significant improvement in the dielectric properties is achieved with chemically-treated nano TiO2 with an aspect ratio of 14 at a low 4.6 vol% loading, where the energy density increased by 500% compared to pure PVDF. At this loading, simultaneous enhancement in the dielectric constant and dielectric breakdown occurs while the dielectric loss remains in the same range as that of the pristine polymer.

This study focuses on the processing, structure and properties of polyacrylonitrile (PAN)/ carbon nanotube (CNT) composite carbon fibers. Small diameter PAN/CNT based carbon fibers have been processed using sheath-core and islands-in-a-sea (INS) fiber spinning technology. These methods resulted in carbon fibers with diameters of ~3.5 μm and ~1 μm (for sheath-core and INS respectively). Poly (methyl methacrylate) has been used as the sheath or the sea component, which has been removed prior to carbonization. These fibers have been stabilized and carbonized using a batch process. The effect of stabilization has been characterized by Fourier Transform Infrared Spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). A non-isothermal extent of cyclization (Mcyc) from the DSC kinetics study was developed in order to obtain an unbiased method for determining the optimal stabilization condition. The results of Mcyc were found to be in good agreement with the experimental FTIR and WAXD observations. The carbon fiber fracture surfaces have been examined using SEM. Various test parameters that affect the tensile properties of the precursor fiber (both PAN and PAN/CNT), as well as carbon fiber have been studied. In an attempt to validate single filament tests, fiber tow testing has also been done using standard test methods. Batch processed carbon fibers obtained via sheath-core geometry exhibited tensile strengths as high as 6.5 GPa, while fibers processed by islands-in-a-sea geometry exhibited strength values as high as 7.7 GPa.

Since the carbon nanotubes were first discovered by Iijima in 1991, CNTs have been the focus of intense research by many groups. Nearly 7000 papers and 700 theses on carbon nanotubes can be found from the eminent journals such as Nature and Science in the last decade. Since carbon nanotubes show impressive mechanical, physical and electronic properties such as high stiffness, high strength, low density, and excellent thermal conductivity, suggesting its role in light-weight high strength material application. A great quantity of important research has evidently been done in this field. The purpose of this thesis research is to investigate the feasibility of MWCNTs for the application of polymer organic photovoltaics, and to study the formed MWCNTs-P3HT polymer nanocomposites properties, which are optical absorption, fluorescence emission, and morphology, as well as the formed photovoltaic device performance. This fundamental research would significantly contribute to the advanced technology development for how to improve the efficiency of the polymer organic photovoltaics.

Polymer clay nanocomposites have been a popular area of materials research since they were first introduced in the 1990s. The inclusion of clays into many different host polymers has been shown to improve the properties of matrix polymers in a number of ways including increased mechanical strength, thermal stability and improved barrier properties while keeping the composite light weight and transparent. Although there is a great deal of published work on the preparation and property measurements of polymer clay nanocomposites, there is no model to design a nanocomposite with a given set of properties for a specific end-use. While it is important to know the structure property relationships of materials, the understanding of how nanocomposites reach their final forms and properties is equally important. A thorough understanding of processing effects on the final structure of polymer clay nanocomposites is still missing. With this perspective, this thesis addresses building structure-processing relationships of polymer clay nanocomposites by analyzing multiaxial deformation behavior using in-situ x-ray scattering techniques. This thesis can be divided into two distinct parts. The first part concerns the design of the in-situ multiaxial deformation device (IMDD) used to create the deformation conditions that polymers go through during processing such as blow molding and thermoforming. The device was designed to overcome several concerns with in situ measurement by maintaining constant sample to detector distance, minimizing the material between the incident beam and the detectors, as well as exposing the same point on the sample throughout deformation. A new design to create biaxial deformation, termed in-situ biaxial deformation device (IBDD), is also introduced in this part of the thesis.. In addition, a new heating unit, attached to IBDD, is designed for higher temperature studies, up to 150°C, to imitate industrial processing conditions more closely. The second part of the thesis addresses the effect of strain, strain rate, and temperature as well as the amount of clay on the polymer morphology evolution during multiaxial deformation.. Two different polymer/clay systems were studied: poly(ethylene)/clay and poly(propylene)/clay. It was observed that the morphological evolution of polyethylene and polypropylene is affected by the existence of clay platelets as well as the deformation temperature and the strain rate. Martensitic transformation of orthorhombic polyethylene crystals into monoclinic crystal form was observed under strain but is hindered in the presence of clay nanoplatelets. The morphology evolution of poly(propylene) crystal structure during multiaxial deformation was more subtle where the most stable α-crystalline form went through strain induced melting. This was more noticeable in the nanocomposites with clays up to 5 wt%. It was also noted that the thickness of the interlamellar amorphous region increased with increasing strain at room temperature due to the elongation of the amorphous chains. The increase in the amorphous layer thickness is slightly higher for the poly(ethylene)/clay nanocomposites compared to neat poly(ethylene) while the increase in the lamellar long spacing is slightly higher for the neat poly(propylene) compared to poly(propylene)/clay nanocomposites. The rate of change in the characteristic repeat distance in both poly(ethylene) and poly(propylene) systems is higher at faster strain rates, at room temperature, where it remained constant during higher temperature deformations. Time dependent recovery after deformation studies have shown that poly(ethylene)/clay system reverts back to its initial configuration. The recovery in the amorphous chains was however observed to take longer in the clay added poly(ethylene)s. Crystalline relaxation was observed to happen almost instantly in the poly(ethylene)/clay system. On the other hand, amorphous chains in the poly(propylene)/clay system did not revert back to the initial configuration in the period of time that the recovery observations were performed while the crystalline configuration recovered back almost fully in the given time.

The viscoelastic relaxation dynamics of a series of poly(methyl methacrylate) [PMMA] based nanocomposites filled with carbon nanotubes have been studied using dynamic mechanical analysis and broadband dielectric spectroscopy. The networks were prepared using four methods: (i) melt mixing, (ii) solution processing, (iii) in-situ polymerization, and (iv) polymer grafting. Nanotube modifications included surface oxidation via acid exposure and surface functionalization for polymer grafting. The effect of variations in processing method and nanotube modification on glass transition temperature (Tg) and relaxation dynamics was investigated. The relaxation behavior of the nanocomposites was sensitive to processing method and nanotube functionalization. Nanotube loading (to 5 wt%) led to a progressive increase in rubbery modulus, with the increase more pronounced in the solution-processed samples owing to enhanced nanotube dispersion. In the case of the oxidized nanotubes, loading led to an increase in modulus, but also a systematic decrease in Tg of ~ 15°C with 3 wt% nanotubes. For in-situ polymerized (PMMA/MWNT-ox) nanocomposites, there was no readily discernable trend in Tg. Composites prepared via in-situ polymerization in the presence of methyl methacrylate functionalized tubes (i.e., polymer grafting) displayed a positive shift in Tg of nearly 20°C at 1 wt% loading. Investigation of the dielectric relaxation of the PMMA/MWNT composites indicated a percolation threshold between 0.3 and 0.4 wt% MWNT.

Polymer nanocomposites (PNCs) are hybrid materials incorporating organic or inorganic nanoparticles (NPs) with at least one dimension in the submicron scale. Over the last two decades, these materials have drawn a remarkable attention due to their central role in industrial formulations and technological applications, extending from food packaging to smart coatings. Incorporating nanoparticles (NPs) to a polymer matrix can significantly alter the conformation and the mobility of the polymer chains in their proximity. Moreover, understanding the delicate balance between the enthalpic and entropic interactions is crucial to control and predict the ability of NPs to diffuse and disperse in the polymer matrix. The impact of these interactions on the structure and the dynamics of polymer chains and NPs is fully revealed in how a number of macroscopic properties changes, justifying the high interest on these materials for industrial applications. In this thesis, the impact on the structure, dynamics, viscosity and thermal conductivity of a number of microscopic properties is investigated by performing Molecular Dynamics (MD) simulations. Specifically, the PNC is represented by a coarse-grained model of a melt of linear homopolymer chains containing spherical NPs. Throughout this work, a number of parameters are modified in order to unveil possible patterns in the PNC’s performance. To this end, this work focuses on the consequences of modifying the NP size dispersity, NP-polymer chain relative size, and chains’ degree of stiffness. Four theoretical models describing the diffusivity of NPs, three of which include nano-scale corrections, have been averaged to study the dependence of dilute NPs’ diffusivity on the NP polydispersity index. By comparing these models to the simulation results at different degrees of polydispersity, it is possible to obtain a more complete picture of their validity as compared to the monodisperse case. Regarding the diffusion of polymer chains, simulation results were in good agreement with the experimental results previously obtained by Composto and coworkers (Soft Matter 2012, 8, 6512), which relate the chains’ diffusivity to the average interparticle distance. As far as the transport properties are concerned, they show a weaker dependence on the polydispersity index. By contrast, results on viscosity and thermal conducitivity show that they are conditioned by the polymer-NP specific interfacial area and the inverse average mass, respectively. These results are in good agreement with previous experimental results. A deeper examination of this intriguing deviation from viscosity predictions in traditional composites, reveals a non-trivial combination of thickening and thinning effects contributing to the final viscosity of the PNC. This thesis also address the influence of the chains’ stiffness on the dynamical and viscous behaviour. An isotropic-to-nematic phase transition is observed, regardless of the NP-monomer interactions, below which a monotonic increase of both properties is observed, whereas orientationally ordered systems dramatically modify them, resulting into a steep increase or a smooth decrease depending on the direction in which they are measured.

Este trabalho descreve a síntese de látices poliméricos híbridos contendo a argila natural Montmorilonita (MMT) por meio da polimerização radicalar controlada via mecanismo de transferência reversível de cadeia por adição-fragmentação (RAFT) em emulsão sem adição de surfatante. Primeiramente, copolímeros anfifílicos com diferentes estruturas e composições, foram preparados por meio da polimerização via RAFT em solução e caracterizados por ressonância magnética nuclear de hidrogênio (RMN 1H) e cromatografia por exclusão de tamanho (SEC). A interação entre os copolímeros sintetizados, chamados de macroagentes RAFT, e a superfície da MMT foi estudada por meio de isotermas de adsorção experimentais, as quais foram ajustadas por modelos teóricos. Os macroagentes RAFT à base de ácido acrílico (AA), acrilato de metil éter poli(etileno glicol) (PEGA) e acrilato de n-butila (BA) apresentaram afinidade pela argila como mostraram as isotermas do \"tipo L\" (Langmuir) obtidas. Os látices híbridos preparados utilizando esses macroagentes RAFT foram analisados por microscopia eletrônica de transmissão em temperatura criogênica (cryo-TEM), que revelou lamelas de MMT decoradas com nanopartículas poliméricas. As isotermas de adsorção dos macroagentes RAFT catiônicos à base de metacrilato de 2-(dimetilamino)etila (DMAEMA), PEGA e BA foram do \"tipo H\" (alta afinidade). Esses macroagentes RAFT possibilitaram a preparação de dispersões estáveis de complexos de MMT/macroagente RAFT, o que foi verificado por espalhamento dinâmico de luz (DLS), e sua utilização na síntese de látices híbridos levou à formação de uma camada polimérica em torno das lamelas de MMT. Os filmes poliméricos nanocompósitos obtidos a partir de látices catiônicos estáveis de poli(metacrilato de metila-co-acrilato de n-butila)/MMT apresentaram melhor estabilidade térmica e melhores propriedades mecânicas do que os filmes poliméricos preparados sem adição de argila como mostraram, respectivamente, os resultados de análise termogravimétrica (TG) e de análise termodinâmico-mecânica (DMA) dos materiais. / This work describes the synthesis of hybrid polymer latexes containing natural Montmorillonite clay (MMT) by reversible addition-fragmentation chain transfer (RAFT)-mediated surfactant-free emulsion polymerization. Firstly, amphiphilic copolymers with different structures and compositions were prepared by RAFT polymerization in solution and characterized by hydrogen nuclear magnetic resonance (1H NMR) and size exclusion chromatography (SEC). The interaction between these copolymers (referred to as macroRAFT agents) and the MMT surface was studied by experimental adsorption isotherms, which were adjusted by theoretical adsorption models. MacroRAFT agents based on acrylic acid (AA), poly(ethylene glycol) methyl ether acrylate (PEGA) and n-butyl acrylate (BA) displayed affinity for MMT as shown by the \"L-type\" (Langmuir) isotherms obtained. The hybrid latexes prepared using these macroRAFT agents were analyzed by transmission electron microscopy at cryogenic temperatures (cryo-TEM), which revealed polymer-decorated MMT platelets. The adsorption isotherms of cationic macroRAFT agents based on 2-(dimethylamino)ethyl methacrylate (DMAEMA), PEGA and BA were of the \"H-type\" (high affinity). These RAFT macroRAFT agents allowed the preparation of stable dispersions of MMT/macroRAFT agents complexes, which was verified by dynamic light scattering analysis (DLS), and their use in the synthesis of hybrid latexes led to the formation of a polymer layer surrounding the MMT platelets. Nanocomposite films obtained from stable cationic latexes of poly(methyl methacrylate-co-n-butyl acrylate)/MMT showed better thermal stability and better mechanical properties than polymer films prepared without addition of clay as shown, respectively, by the results of thermogravimetric analysis (TG) and dynamic mechanical analysis (DMA) of the final materials.