| The reinforcement mechanisms in graphene-based nanocomposites have been studied in this project, which primarily consists of three parts: the size and orientation effects of the graphene-based nano-fillers and their interfacial adhesion with the matrix. Overall Raman spectroscopy has been demonstrated to be a powerful technique to study the graphene-based nanocomposites. The deformation of small size graphene has been followed and a new model has been established to consider both the non-uniformity of strain along the graphene and laser intensity within the laser spot, which interprets the observed unusual Raman band shift well. Additionally, the deformation of monolayer graphene oxide (GO) has been followed for the first time. It appears that continuum mechanics is still valid, and the approximately constant strain distribution along the GO flake suggests a better stress transfer efficiency of GO than that of graphene. The spatial orientation of graphene has been studied based on the Raman scattering obtained from transverse sections of graphene, where the Raman bands intensities show a strong polarization dependence. Based on this, a new model has been established to quantify the spatial orientation of graphene in terms of an orientation distribution function, and the spatial orientation of monolayer graphene has been further confirmed by its surface roughness. This model has been extended to a variety of graphene-based materials and nanocomposites. It is also shown how the spatial orientation of graphene-based fillers affects the mechanical properties of the nanocomposites, through the first determination of the Krenchel orientation factor for nanoplatelets. The findings on both the size and orientation effects have been employed to study the deformation mechanics of bulk GO reinforced nanocomposite films. It has been demonstrated for the first time that the effective modulus of GO can be estimated using the Raman D band shift rate, and this is in agreement with the value measured using conventional mechanical testing. The effective modulus of GO is found to be lower than its Young's modulus, probably due to the mis-orientation, waviness, wrinkling and agglomeration of the GO fillers. |
