Preparation And Mechanical Behaviour Of Graphene-based Composites With Controllable Surface And Interface

Recently, owing to excellent mechanical, high electrical and thermal properties, graphene is considered as an attractive material in various fields, the mistery of which have gradually been known by human. Nowadays, the research fields of graphene mainly focus on supercapacity, lithium ion battery, electronic device and polymer nanocomposites that were expected to realize commercialization, while there are still a number of challenges. For example, one of the fatal weakness is that graphene tend to agglomerate once again, due to the high specific surface area and surface energy.Many studies have been reported using various approaches to function the graphene by covalent bond or non-covalent bond for polymer nanocomposites, While how to effective and tunable interphases between the polymer host and the GO sheets not only promote load transfer but also modulate the structure of organic networks that the strength and toughness of composites can be optimized simultaneously is a challenge.Another challenge remains on how to effectively tailor the chemistry, architecture and functionality and thus maintain structural integrity upon large deformation, which is essential to ensure these 3D porous materials to function reliably. Although some control over pore morphologies of these aerogels has been achieved with ice templating, the creation of superelastic, flexible 3D graphene architecture with ideal surface property is not well studied, precluding the ability to tailor mechanical and multi-functional properties of the materials for specific applications (for example, separations, pressure sensors, etc.). More importantly, most previous processing techniques usually involve high GO concentration in aqueous or solvent solution and severe temperature treatment process, which are lengthy and need particular skills. Therefore, it remains a significant engineering and scientific challenge to design and fabricate lightweight porous 3D graphene aerogel materials with tunable microstructures and functionalities for practical applications. These challenges underline the need to develop more facile and low-cost processing technologies that maintain an effective control of the chemistry, architecture and functionality from the nano-level and up. Especially, structural design has to be based on a fundamental understanding of how chemistry determines microscopic architecture and thus affects macroscopic performance.In order to solve these problems, we explore the intereface between polymer and graphene sheets for polymer namocomposites and graphene aerogel composites.(1) Interface design plays a crucial role in developing superior mechanical performance of graphene/polymer nanocomposites. Here, we report a facile approach to the fabrication of advanced polymeric nanocomposites of epoxy by the incorporation of polyetheramine-functionalized graphene oxide (PEA-f-GO). Two types of PEA molecules with different molecular lengths were used to synthesize the PEA-f-GO sheets. The chemical bonds formed between the amine functional groups on the GO surface and the epoxy resin during curing provided strong sheet/matrix interfacial adhesion. The addition of PEA-f-GO was found to produce significant enhancements in the mechanical properties of epoxy, including elastic modulus, tensile strength, elongation at break and toughness. In particular, the PEA-f-GO sheets containing shorter PEA molecules produced higher improvement in strength but smaller increases in both ductility and toughness than those containing longer PEA molecules. For example, at 0.50 wt% filler loading, two nanocomposites showed increases of 63% and 51% in tensile strength and 90% and 119% in toughness as compared to the unfilled epoxy. Our results suggest that the interphases between the GO and the polymer matrix can be tuned by varying the molecular lengths of grafted modifiers, thereby providing a new route for the rational designing and development of the GO-based composite materials.(2) Three-dimensional (3D) graphene-based porous materials with a combination of low density, super elasticity, excellent cyclic mechanical resilience and tunable functionalities can be used in diverse applications. Here we report the fabrication of stable 3D graphene aerogel structures with super compressibility and controllable functionality via a novel and facile silane-assisted assembly processing (at both a low temperature of 80℃ and a low GO concentration of 1.0 mg mL-1 in aqueous solution) that maintains an effective control of the chemistry, architecture and functionality from the nano-level and up. The introduction of silane bonding tunes both the porous microstructure and the surface property of the lightweight aerogel effectively, subsequently providing improved mechanical properties and versatile functionalities (including super compressive elasticity, good electrical conductivity, outstanding cyclic resilient property, stable viscoelastic properties, high level energy absorption capacity, excellent hydrophobicity, remarkable thermal stability and extremely high sensitivity of elasticity-dependent electrical conductivity). This opens up flexible, scalable and low-cost ways to the integration of microscopic two-dimensional graphene sheets into macroscopic 3D cellular networks with tunable hierarchical structures and functionalities, which are expected to have broad implications for novel material design and their applications in numerous fields, such as oil/water separation, sensors, and polymer nanocomposites...