Thèse doctorat : Génie des Matériaux : Villeurbanne, INSA : 2007. / Thèse rédigée en anglais. Titre provenant de l'écran-titre. Contient des références bibliographiques.

Carbon nanotubes have now been a subject of intense research for approaching two decades. Although a short time relative to most conventional materials, much hype about the intrinsic properties of this material has now been substantiated by experiment. The results are conclusive that carbon nanotubes are truly phenomenal materials with highly desirable mechanical, electrical and thermal properties. Furthermore, multiwall carbon nanotubes (MWNTs) have emerged as the most economically viable and abundant form of carbon nanotubes, and therefore the most likely candidate for application. The key materials engineering challenge remains in effectively transferring their properties to macro-scale materials in the form of composites. It is here that research merges with application. This dissertation has therefore been directed to focus on carbon nanotube composites in an applied sense. Here, the state of the art is reviewed, and experimental results of carefully selected composite systems, studied in detail for (1) mechanical, (2) electrical and (3) thermal properties, are presented and discussed. In terms of mechanical properties, the effects of MWNTs for augmentation of the tensile properties of PAN-based carbon fiber, and fatigue performance of poly(methyl methacrylate) are investigated and reported. In MWNT composite PAN-based carbon fiber, the formation of an ordered interphase layer sheathing the nanotubes was observed in fracture surfaces, which indicated a clear importance of their function to template the growth of carbon formation in the PAN-based matrix fiber. These structures open up a route to nano-scale tailorability of the crystallographic morphology of the composite fibers. Large improvements in fatigue performance were observed in MWNT/PMMA composites compared to MWNT/chopped carbon fiber composites, and attributed to the nanometer scale dimensions of the MWNTs enabling them to mitigate submicron damage such as polymer crazing. In terms of electrical and thermal properties, MWNT/epoxy composites were superior to MWNT/carbon black composites. Furthermore, extremely large improvements in the thermal conductivity of epoxy were observed for epoxy-infiltrated aligned MWNT arrays. The alignment of the MWNTs was shown to play a dominant role in enabling the improvement. Finally, these results, in concert with the literature are discussed in terms of the application of carbon nanotubes in engineering materials.

No / Simply melt blended polypropylene/carbon nanotubes composites (PP/CNTs) usually present mechanical deterioration. In this work, multilayered sheet of PP/CNTs with improved tensile property was obtained by solid-phase orientation and hot compression. The initially blended PP/CNTs were highly orientated by employing a constrained slit die and hot compressed under a certain temperature and pressure by stacking eight layers together. The effects of compression temperature and pressure on the tensile property and AC conductivity of the multilayered sheets were examined to explore the evolution of hierarchical crystallization morphology and CNT networks. The multilayered sheet which was hot compressed at 184°C and 5 MPa demonstrated an optimum tensile strength of ∼132.5 MPa and an elongation at break ∼52.7%, respectively, raised by almost 3-fold compared with those initially blended PP/CNTs. By increasing compression temperature and decreasing pressure, the AC conductivity showed an increase of 2 to 4 orders of magnitude. / China Scholarship Council. Grant Number: 201806465028.

Dans la lignée des progrès technologiques récents en électronique, ces dernières décennies ont vu l’émergence d’une variété de systèmes permettant l’interface bioélectronique, allant de la mesure de l’activité électrique émise par l’ensemble du cerveau jusqu’à la mesure du signal émis par un neurone unique. Bien que des interfaces électroniques avec les neurones ont montré leur utilité pour des applications cliniques et sont communément utilisés par les neurosciences fondamentales, leurs performances sont encore très limitées, notamment en raison de l’incompatibilité relative entre les systèmes à l’état solide et le vivant. Dans ce travail de thèse, nous avons étudié des techniques et des matériaux nouveaux permettant une approche alternative et qui pourraient améliorer le suivi de l’activité de réseaux de neurones cultivés in situ et à terme la performance des neuroprothèses in vivo. Dans ce travail, des réseaux de nanofils de silicium et des microélectrodes en diamant sont élaborés pour respectivement améliorer la résolution spatiale et la stabilité des électrodes dans un environnement biologique. Un point important de cette thèse est également l’évaluation des performances de transistors à effet de champ en graphène pour la bio électronique. En raison des performances remarquables et combinées sur les aspects électrique, mécanique et chimique du graphène, ce matériau apparaît comme un candidat très prometteur pour la réalisation d’une électronique permettant une interface stable et sensible avec un réseau de neurones. Nous montrons dans ce travail l’affinité exceptionnelle des neurones avec une surface de graphène brut et la réalisation d’une électronique de détection rapide et sensible à base de transistor en graphène. / In line with the technological progress of last decades a variety of adapted bioelectrical interfaces was developed to record electrical activity from the nervous system reaching from whole brain activity to single neuron signaling. Although neural interfaces have reached clinical utility and are commonly used in fundamental neuroscience, their performance is still limited. In this work we investigated alternative materials and techniques, which could improve the monitoring of neuronal activity of cultured networks, and the long-term performance of prospective neuroprosthetics. While silicon nanowire transistor arrays and diamond based microelectrodes are proposed for improving the spatial resolution and the electrode stability in biological environment respectively, the main focus of this thesis is set on the evaluation of graphene based field effect transistor arrays for bioelectronics. Due to its outstanding electrical, mechanical and chemical properties graphene appears as a promising candidate for the realization of chemically stable flexible electronics required for long-term neural interfacing. Here we demonstrate the outstanding neural affinity of pristine graphene and the realization of highly sensitive fast graphene transistors for neural interfaces.