P. Nautiyal, A. Idowu, L. Embrey, J. Bustillos, T. Thomas, C. Zhang, B. Boesl, A. Agarwal
Florida International University,
Keywords: composite, graphene, structural, multifunctional
Summary:Graphene foam, with 3D macroporous architecture, has excellent load bearing capability. As opposed to 2D graphene flakes, incorporation of 3D foam in the material matrix does not require complex dispersion techniques and is not marred with agglomeration challenges. Metallic, polymeric and ceramic composites with graphene foam filler are fabricated and their mechanical properties investigated. Polymer composites based on graphene foam are synthesized by facile dip-coating and mold-casting techniques. Graphene foam addition results in ~300% improvement in the loss tangent of polyimide, indicating excellent energy-dissipation and impact-resistance. The epoxy composite exhibits improved tensile and flexural strength by adding as low as 0.1 – 0.6 wt.% graphene foam. Digital image correlation analysis of the tensile videos shows graphene foam cells restrict the deformation of epoxy, and the graphene branches are responsible for crack-deflection. An ultra-low-density metallic metamaterial based on graphene foam and aluminum is fabricated by electron beam evaporation technique. The composite metamaterial is highly stiff, with spring constant value (~1.13 N/m) comparable to 2D graphene membranes. In-situ indentation inside the electron microscope shows long distance stress-transfer in the metamaterial, making it highly flexible and resistant to localized failure. When subjected to 50 indentation loading-unloading-reloading cycles, the metamaterial exhibits impressive ~98% displacement recovery at the end of each cycle, indicating good fatigue-resistance. A ceramic composite was also fabricated by incorporating 3D foam inside a low temperature ceramic by spark plasma sintering approach. Indentation response of the composite showed a four-fold improvement in load-bearing capacity. Additionally, sub-surface examination by focused ion beam machining shows extensive crack-deflection because of 3D graphene reinforcement. Superior toughness in materials is vital for application in extreme conditions. In addition to mechanical reinforcement, graphene foam is characterized by excellent electrical and thermal transport properties. Graphene foam addition improves the electrical and thermal conductivities of epoxy and PDMS. The enhanced conductivity is exploited for de-icing application in airplane wings using PDMS-graphene foam composite. The deicing efficiency of ~477% is accomplished, with very low required power densities (~0.2 W cm-2). In addition, graphene foam addition improves the tensile strength and elastic modulus of polymers. Simultaneous improvement in electrical and mechanical properties is exploited for developing strain sensors. The epoxy-graphene foam composite is characterized by gauge factor as high as 4.1, twice the value for typical strain-sensor metals, attesting the promise of these polymer composites for motion-sensing. Smart nanocomposites are fabricated by adding graphene foam to a ‘shape-memory’ epoxy. The shape recovery is improved due to heat-transfer pathways provided by graphene foam. Because of shape memory effect, cracks in the material are observed to heal near transition temperature of the polymer. This self-healing behavior is examined at microstructural level by in-situ nanoindentation of the composite inside the electron microscope at elevated temperatures (up to ~70°C). The indents made at room temperature gradually vanish upon sample heating. Self-healing capability is vital for application in extreme conditions. These observations demonstrate that graphene foam is a promising material for engineering multifunctional composites with remarkable properties and performance for a multitude of applications.