Les membranes à base de liquides ioniques à conduction protonique (PCIL) sont très prometteuses comme électrolytes des piles à combustible haute température (HT- PEMFC) du fait de leur forte conductivité et stabilité à des températures supérieures à 100°C. L'objectif de cette thèse est de réaliser une étude approfondie sur l'évolution de la morphologie et des propriétés fonctionnelles, des membranes à base de liquides ioniques, avec i) la concentration en PCIL, ii) la méthode d’élaboration et iii) la structure chimique du PCIL. Afin de prouver la potentialité de ces membranes dans le HT-PEMFC, des tests préliminaires en pile sont réalisés et les phénomènes de dégradation des PCIL et des membranes en présence de peroxyde d'hydrogène sont étudiés. La première partie de ce travail est focalisée sur la caractérisation des membranes de Nafion® neutralisées avec le triéthylamine (Nafion-TEA) et gonflées avec triflate de triéthylammonium (TFTEA). Il a été montré que dans le Nafion-TEA sec, les cations présentent une organisation de type « string like » à l'interface hydrophobe-hydrophile. L’introduction du TFTEA dans la membrane Nafion-TEA ne détruit pas sa nano-structuration, mais augmente de manière significative la conductivité ionique du système. La deuxième partie de ce travail nous a permis d'établir que les membranes dopées élaborées par coulée-évaporation présentent une meilleure organisation et une meilleure tenue thermomécanique par rapport à celles obtenues par gonflement. La troisième partie de ce travail est focalisée sur l’étude de l'impact de la nature chimique du PCIL sur la morphologie et les propriétés fonctionnelles des membranes de Nafion-TEA. Il a été démontré que les PCILs avec longues chaînes perfluorées ne modifient pas la nano-structuration du Nafion-TEA. Ceci a un impact fort sur les propriétés de conductivité, de sorption d’eau et sur les propriétés thermomécaniques de la membrane. Dans la dernière partie, des Ionomères aromatiques ont été synthétisés afin de remplacer le Nafion-TEA. Malgré la structure similaire de la chaîne latérale des Ionomères aromatiques et du Nafion®, les membranes à base d’Ionomères aromatiques et TFTEA ne présentent aucune nano-structuration. De plus l’effet plastifiant du TFTEA est plus notable dans le cas des Ionomères aromatiques probablement du fait d’une distribution aléatoire des fonctions ioniques dans la membrane polymère. / The polymer electrolyte membranes based on Proton Conducting Ionic liquids (PCIL) are very promising systems for the high temperature-PEMFC technology owing to their good ionic conductivity and stability at temperatures above 100oC. The objective of this thesis work is to achieve a profound study on the evolution of morphology and consequent functional properties of the PCIL based polymer electrolyte membranes in function of: i). concentration of the PCIL, ii). the method of elaboration and iii). chemical structure of the PCIL. To demonstrate the potential of these membranes in HT-PEMFC, preliminary tests have been carried out in the fuel cell stack and degradation phenomena associated with PCILs and membranes in the presence of hydrogen peroxide have been studied. The first part of this work is focused on the characterization of Nafion® membranes neutralized with triethylamine (Nafion-TEA) and swollen with triethylammonium Triflate (TFTEA). It has been shown that Nafion-TEA exhibits a single layer string-like organization of inter-digited Triethylammonium cations at the hydrophobic-hydrophilic interface when in anhydrous state. The introduction of TFTEA into Nafion-TEA membrane does not destroy its nano-structuration but significantly boosts the anhydrous ionic conductivity and hydrophilicity of the system. The second part of this work has permitted us to establish the fact that doped membranes prepared by casting method have better organization and better thermo-mechanical properties compared to those obtained by swelling method. Third part of this work focuses on the impact of the chemical nature of the PCIL on the morphology and functional properties of Nafion-TEA membranes. It has been demonstrated that the PCILs with long perfluorinated chain length do not modify the nano-structuration of Nafion-TEA membranes at all. This has a strong impact on the ion-conducting, water-sorption and thermo-mechanical properties of the membrane. In the last part, aromatic ionomers were synthesized in order to replace Nafion-TEA in such PCIL based system. Despite the similar structure of the side chain of the synthesized aromatic ionomers and Nafion®, the membranes based on aromatic ionomers and TFTEA do not present any nano-structuration. Moreover, the plasticizing effect of TFTEA is more noticeable in the case of aromatic ionomers probably due to a random distribution functions in the ionic polymer membrane.

Les bétons végétaux, composés de particules végétales et d'un liant minéral ou organique, constituent une solution à explorer pour limiter l'impact environnemental du bâtiment. Utilisés principalement pour leurs performances thermiques, ces matériaux suscitent l'intérêt de plusieurs organismes de recherche ainsi que de plusieurs entreprises industrielles. La généralisation de leur utilisation dans la construction ne sera pas possible sans résoudre certains problèmes liés à leurs techniques de mise en œuvre, à leur certification et à leur durabilité. Le présent travail a pour objectif de contribuer à la caractérisation de ces matériaux complexes. Il s'agit en particulier d'étudier les comportements mécanique, thermique et hydromécanique du béton de granulats de bois. La stratégie utilisée consiste à combiner l'expérience et la modélisation pour mieux comprendre les mécanismes mis en jeu. Le module de Young et la résistance en compression ont été mesurés expérimentalement à l'aide de la technique de corrélation d'images numériques. L'évolution de ces propriétés dépend des conditions de conservation, de la durée de séchage ainsi que de la teneur en ciment. En raison de l'orientation aléatoire des granulats de bois, le comportement mécanique du béton est isotrope. Un modèle d'homogénéisation basé sur le schéma autocohérent a été développé pour prédire le module de Young du béton et ses résultats sont très satisfaisants. Les mesures de la conductivité thermique montrent que celle-ci reste constante en conditions endogènes. La modélisation de cette propriété par le schéma autocohérent conduit à des résultats cohérents avec les mesures expérimentales. En conditions de dessiccation, la conductivité thermique dépend linéairement de la densité du béton. L'évolution de la conductivité thermique des granulats de bois et de la pâte de ciment au cours du séchage a été modélisée grâce au schéma de Mori-Tanaka. Ces évolutions ont été intégrées dans le modèle autocohérent qui fournit ainsi des résultats satisfaisants, mais qui pourrait être amélioré si l'on disposait des courbes de sorption/désorption des constituants du béton. Les variations dimensionnelles du béton au cours du temps dépendent des conditions de conservation, mais pas de la direction de mesure, ni de la teneur en ciment. Un modèle reposant sur une combinaison des déformations induites par la désorption de l'eau par des constituants et le transfert d'humidité entre ceux-ci a été proposé et a permis de capturer les tendances des déformations du béton sauf au jeune âge. À l'échelle locale, l'étude a montré que les déformations du béton sont du même ordre de grandeur que celles de la pâte de ciment. Elle a aussi mis en évidence un endommagement partiel de l'interface granulat/liant qui mériterait à être pris en compte dans la modélisation / Environmentally-friendly concretes, made up of plant-based particles and mineral or organic binder, are solutions worth exploring to reduce the environmental impact of buildings. Mainly used for their thermal performance, these materials have aroused interest of many research organisations and industrial companies. Their widespread use in construction is not possible without resolving some technical problems related to their implementation, certification and durability. This work aims to contribute to characterize these complex materials, in particular to study the mechanical, thermal and hydromechanical behaviors of wood-aggregate concrete. Modeling and experiments have been used to understand the complex mechanisms involved. The Young's modulus and the compressive strength were experimentally measured using digital image correlation. The evolution of these properties depends on the conditions of storage, the drying time and the cement content. Because of the random orientation of the wood aggregates, the material exhibits isotropic behavior. A homogenization model based on a self-consistent scheme was developed to predict the Young's modulus. The results were satisfactory. Measurements show that thermal conductivity remains constant under sealed conditions. The modeling of this property with the self-consistent scheme gives results consistent with experimental measurements. In desiccation conditions, the thermal conductivity depends linearly on the density of concrete. The evolution of the thermal conductivity of the wood aggregates and the cement paste during drying was modeled with the Mori-Tanaka scheme. These evolutions were integrated into the self-consistent model, which yielded satisfactory results, but could be improved if sorption/desorption curves of the phases were available. The macroscopic dimensional variations of the wood-aggregate concretes depended on the storage conditions, but not on the measurement direction, nor on the cement content. A model based on the combination of the strains induced by the desorption of water from the phases and the moisture transfer between them was proposed. It allowed us to capture the trends of the strains of our concrete except at early age. At a local scale, the study showed that the strains of concrete were close to those of the cement paste. The study also shed light on a significant damage of the aggregate/binder interfaces, which would deserve to be taken into account into the modeling

The work deals mainly with preparation protocol of nanocomposites. The task of this work is to study structural and procedural parameteres that control the dispersion of nanoparticles in polymer solution to be able to prepare desired spatial organization of nanoparticles. The work resolves the effect of various components such as polymer matrices, nanoparticles and solvent, in which matrices and nanoparticles are blended. Used components control final dispersion state of nanoparticles and it influences also properties of investigated materials such as glass transition temperature, stiffness and rheological properties.

Carbon fiber (CF) must be protected from thermal oxidation for high temperature application because of its low thermo-oxidative stability above 450°C in air. CF is now increasingly being used as a reinforcing material in the construction industry. A thermal and oxidation resistant coating is necessary for CF-reinforced concrete (CFRC) composites in order to satisfy a high level of safety standard in the case of fire. New types of pre-ceramic coatings, such as Tyranno® polymer (Si–Ti based pre-ceramic) and SiO₂ sol–gel, have been deposited on CF filament yarn by means of a wet chemical continuous dip coating method. The results of surface analyses, e.g. scanning electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy, showed the changes in topographical properties of CF caused by the coatings. Thermogravimetric analysis proved that the high temperature (up to 800°C) oxidation stability of CF was considerably improved due to the coatings. Tensile test results indicated that the strength of CF yarn at 20°C was increased by up to 80% with the coatings. Thermo-mechanical properties were also enhanced up to 600°C. CF yarn retains its original strength and elasticity modulus, i.e. the stiffness at 700°C, with a Tyranno® polymer coating.

This thesis is an attempt to understand ways to improve thermo-mechanical and structural properties of nano-structured materials. A detailed study on computational design and analysis of metallic nanowires is carried out. Molecular dynamic simulation method is applied. In particular, FCC metallic nanowires, NiAl, and CuZr nanowires are studied. Various bottom-up approaches are suggested with improved structural and thermo¬mechanical properties. In the first part of the thesis, Cu nanowires are considered. Existence of a novel and stable pentagonal multi-shell nanobridge structure of Cu under high strain rate tensile loading is reported. Such a structure shows enhanced mechanical properties. A three-fold pseudo-elastic-plastic shape recovery mechanism in such nanowires is established. This study also shows that the length of the pentagonal nanobridge structures can be characterized by its inelastic strain. It is also reported that an initial FCC structure is transformed into a new HCP structure. The evidence of HCP structure is confirmed with the help of experimental data published in the literature. Subsequent to the above study, a novel mechanism involving coupled temperature-stress dependent reorientation in FCC nanowires is investigated. A detailed map is generated for size dependent stress-temperature induced solid-solid reorientation in Cu nanowires. In the second part of the thesis, deformation mechanisms in NiAl based intermetallic nanowires are studied. A novel mechanism of temperature and cross-section dependent pseudo-elastic/pseudo-plastic shape and strain recovery by an initial B2 phase of NiAl nanowire is reported. Such a recoverable strain, which is as high as ~ 30%, can potentially be utilized to realize various types of shape memory and strain sensing phenomena in nano-scale devices. An asymmetry in tensile and compressive yield strength behavior is also observed, which is due to the softening and hardening of the nanowires under tensile and compressive loadings, respectively. Two different deformation mechanisms dominated by twinning under tension and slip under compression are found. Most interestingly, a superplastic behavior with a failure strain of up to 700% in the intermetallic NiAl nanowires is found to exist at a temperature of 0.36Tm. Such superplastic behavior is attributed to the transformation of the nanowire from a crystalline phase to an amorphous phase after yielding of the nanowire. In the last part the work, another type of nanowires having Cu-Zr system is considered. A novel stress induced martensitic phase transformation from an initial B2 phase to BCT phase in a CuZr nanowire under tensile loading is reported. It is further shown that such a stress induced martenistic phase transformation can be achieved under both tensile as well as compressive loadings. Tensile-compressive asymmetry in the stress-strain behavior is observed due to two different phase transformation mechanisms having maximum transformation strains of ~ 5% under compressive loading and ~ 20% under tensile loading. A size and temperature dependent tensile phase transformation in the nanowire is also observed. Small nanowires show a single step tensile phase transformation whereas the nanowires with larger size show a two step deformation mechanism via an intermediate R-phase hardening followed by R-phase yielding. A study of energetic behavior of these nanowires reveals uniform distribution of stress over the nanowire cross-section and such stress distribution can lead to a significant improvement in its thermo-mechanical properties. Similar improvement is demonstrated by designing the nanowires via manipulating the surface configuration of B2-CuZr system. It is found that the CuZr nanowires with Zr atoms at the surface sites are energetically more stable and also give a uniform distribution of stresses across the cross-section. This leads to the improvement in yield strength as well as failure strain. An approach to design energetically stable nano-structured materials via manipulating the surface configurations with improved thermo-mechanical properties is demonstrated which can help in fundamental understanding and development of similar structures with more stability and enhanced structural properties. Further ab-initio and experimental studies on the confirmation of the stability of the nanowires via manipulating the surface site is an open area of research and related future scopes are highlighted in the closure.

Magneticky řízené samo-uspořádávání v polymerních nanokompozitech je studováno v této dizertační práci. Strukturování polymerních nanokompozitů pomocí relativně slabých magnetických polí (B=0-50 mT) bylo prokázáno jako praktická metoda pro kontrolu jejích nano a mikrostruktury. Vliv intenzity magnetického pole, množství nanočástic, viskozity a času uspořádávání na výslednou strukturu byl studován v různých systémech jako fotopolymer, polyuretan nebo koloidně dispergované nanočástice v acetonu s malým množstvím rozpuštěného polymeru. Samo-uspořádané struktury – bez aplikace vnějšího magnetického pole vykazují vícekrokovou agregaci nanočástic do uskupení s komplexním tvarem. Magnetické interakce byly označené jako odpovědné za agregaci nanočástic v samo-uspořádaných systémech pomocí výpočtů energii mezi-částicových interakcí. S rostoucím magnetickým polem, magnetické nanočástice jsou rychle uspořádané do jednorozměrných částicových řetězů s vysokým aspektním poměrem a homogenní orientaci v polymerní matrici. S prodluženým časem uspořádaní, tyto struktury postupně rostou z malých submikrometrových struktur do velkých mikroskopických super struktur. Táto metoda vykazuje velký potenciál pro kontrolovanou přípravu široké škály struktur v polymerních nanokompozitech vhodných pro technologické aplikace a také pro fundamentální studie. Magneticky uspořádané polymerní nanokompozity vykazují značnou směrovou anisotropii tuhosti kompozitu nad jeho skelným přechodem přičemž, pod skelným přechodem systému není pozorován žádný efekt. Podélně orientované struktury vykazují větší příspěvek k tuhosti kompozitů. Efektivnost vyztužení vykazuje teplotně závislý průběh a maximum je pozorováno přibližně 60 °C nad skelným přechodem. Struktura magneticky uspořádaného polymerního nanokompozitu byla popsána vícero-úrovňovým hierarchickým modelem materiálu. Mikromechanika byla využitá k popisu směrově závislého vyztužení polymerních nanokompozitů a k popisu teplotně závislé tuhosti hybridních struktur složených z nanočástic a polymeru. Schopnost nést napětí, deformovat se a nenulová tuhost hybridních struktur je odpovědná za vyztužení polymerních nanokompozitů. Přítomnost polymerních přemostění mezi nanočásticemi, které přenášejí napěti skrze magnetické struktury je označená jako nezbytná pro mechanickou odezvu polymerních nanokompozitů a pro tuhost hybridních struktur.