Graphene Functional Composites

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Abstract

Raman spectroscopy is a powerful technique for characterizing carbon materials and their derivatives. In this project, Raman spectroscopy was used to characterize graphene and its composites with the ultimate aim of developing graphene composites for use as wide area strain sensors in structural engineering applications. Model coating systems were made by depositing micromechanically-cleaved graphene onto PMMA substrates. These sensors could sense uniaxial strain to an accuracy of ± 720 microstrain over repeated cyclic deformation. This relatively low accuracy was due to both the strain hardening behaviour of graphene and the interfacial damage that occurred between the graphene and the matrix during the deformation. The interfacial damage led to increasing energy dissipation during each cycle and a build-up of residual stress. The strain sensitivity of micromechanically cleaved graphene deposited on engineering materials like spring steel was also demonstrated. Finally, in order to assess the scale-up potential of the graphene coatings, composites were prepared from solvent- phase exfoliated graphene and commercial graphene nanoplatelets, using either casting or compound mixing methods. In order to achieve large flakes for maximum stress transfer, the solvent phase exfoliation of graphene as a function of sonication time was investigated. The higher the sonication time, the higher concentration of graphene achieved. But presence of large graphite like flakes were evident from the Raman spectroscopy and SEM results, suggesting that low rotation speeds of 500 rpm in NMP was not sufficed enough to remove larger/thicker flakes.

Keyword(s)

Raman spectroscopy; accuracy; graphene composite; strain sensor

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