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Chapter 3 – Raman Spectroscopy of Graphene and Graphene-based Strain Sensors Moreover, due to the asymmetry in graphene lattice caused by uniaxial strain, the band structure of graphene gets disrupted, causing splitting of G256, 265, 270 and 2D band.271, 284, 285 However, the G band splitting was not clear for strains below 0.4 %, rather band broadening was observed (Figure 3.8a,c).256, 265 3.2.6. Stress transfer studies in graphene nanocomposites using Raman Spectroscopy The sensitivity of Raman bands to strain facilitates the study of the interfacial stress transfer between graphene and the matrix in nanocomposites.4 This use of micro- Raman spectroscopy builds upon over 30 years of work in systems such as carbon and polymer fibres.286 Gong et al. carried out the first stress transfer study on graphene using a model experimental composite system comprising of a SLG sandwiched between two polymer layers.32 In this case, as the graphene flake is discontinuous and reinforcing the composite matrix, stress transfer from the matrix to the flake is assumed to take place through a shear stress at the flake/matrix interface as shown in (Figure 3.9a,b). When the system is subjected to axial stress, 𝜎1, parallel to the flake axis, the perpendicular lines drawn to the flake becomes distorted since the Young’s modulus of the matrix is much less than that of the flake. This induces a shear stress at the flake/matrix interface. The axial stress in the flake will build up from zero at the flake ends to a maximum value in the middle of the flake (Shear lag model). The uniform strain assumption means that, if the flake is long enough, in the middle of the flake the strain in the flake equals that in the matrix. Since the flakes have much higher Young’s modulus it means that the flakes carry most of the stress in the composites. Gong et al. produced graphene by MC and subsequent deposition by Scotch tape (Figure 3.9c, d). Raman spectroscopy was then used to map the local strain distribution across the flake and the data fitted to shear-lag theory which had been adapted to a planar filler.32 85PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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