Graphite is a unique material which possess excellent electrical, thermal and mechanical properties. Nevertheless, the difficulty exfoliation and dispersing graphene is a major challenge for its commercial applications. Here we report the large-scale production of low density hollow spheres defined by a thin shell of a graphene/polystyrene composite. These spheres are assembled by a thermodynamically driven process of exfoliation of graphite in which graphene sheets exfoliate and spread to stabilize the high-energy interface of water and oil. The sheets thus act as a 2D surfactant and self-assemble to stabilize water-in-oil emulsions that are utilized as polymerization templates. In this study, the much of the styrene continuous phase of the emulsion is replaced by a non polymerizable, volatile organic solvent such as heptane. After polymerization, removal of water results in low density, individual polystyrene coated graphene hollow microspheres. The monomer concentration varied and the mechanical, thermal and electrical properties of the spheres were studied. Additionally, the close packing of the emulsion droplets under the pull of gravity is shown to affect the sphere size and shape. The size distribution and shape-sphericity were determined using dynamic image analysis, and nano indentation was employed to measure mechanical properties such as hardness, stiffness and modulus of these individual spheres.

Hollow microspheres using interfacial trapping of pristine graphene sheets

255th National Meeting (2018)

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