Nanocomposites graphène/polymères : rôle de la viscoélasticité, mise en oeuvre par assemblage forcé, et étude de l’interface

Abstract : Graphene is an atomically thick, two-dimensional nano-sheet with advanced mechanical, electrical, and thermal properties. As a result, the addition of graphene and graphene derivative nanoparticles to polymer matrices has been a major strategy towards development of new materials in the field of composites. However, from a fundamental point of view, the origins of the advanced properties of graphene-based nanocomposites have been little investigated. In particular, changes in the viscoelastic properties of the polymer matrix due to specific interactions between the polymer and the graphene reinforcing elements can cause higher than expected apparent reinforcement. In addition, there is little work on characterizing the strength of the interface between the graphene used for reinforcement and the polymer matrixes. From a more engineering point of view, the design of polymer nanocomposites made of in-plane oriented graphene to create a two-dimensionally reinforced structure has also not been previously undertaken. The present dissertation is composed of three major works focusing on these problems.The first part focuses on how to use a viscoelastic micromechanics approach to account for the effects of glass transition temperature Tg changes to correct the apparent stiffening of graphene oxide nanocomposites. It is found that graphene oxide stiffens the polymer matrices by increasing the Tg, which significantly modifies their thermo-viscoelasticity. This leads to apparent reinforcements that are not due to the stiffness of the graphene oxide itself, and largely explains anomalously high moduli reported in the literature for such graphene oxide/polymer matrix nanocomposites.The second part focuses on a forced assembly multi-layer co-extrusion method to create films made of alternating layers of neat polymer / oriented graphene nanoplatelet filled polymer. The morphology of the layers (35 ~ 40 nm thick) containing oriented graphene was established by electron microscopy. Mechanical properties of the materials were determined and the two-dimensional stiffening could be related to the oriented graphene nanoplatelets in the layered films. Taking into account the change of Tg, more than 100% intrinsic reinforcement was estimated for 2 wt % of graphene in the nanolayers. The results were analyzed and interpreted via an analytical model based on Mori-Tanaka analysis.The third part focuses on extending a nano-bubble inflation method to the investigation of a novel graphene nano-sandwich with the purpose of investigation of the graphene / polymer interface. At small strains, significant mechanical reinforcement was observed for both graphene-reinforced rubbery and glassy PEMA layers. The interfacial mechanics between graphene and polymer layers was investigated and a “yield-like” interfacial slip was observed in the mechanical response of the nano-sandwich structures.
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Xiguang Li. Nanocomposites graphène/polymères : rôle de la viscoélasticité, mise en oeuvre par assemblage forcé, et étude de l’interface. Mécanique des matériaux [physics.class-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2015. Français. ⟨NNT : 2015ENAM0001⟩. ⟨tel-01138100⟩

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