Molecular force transfer mechanisms in graphene oxide paper evaluated using atomic force microscopy and in situ synchrotron micro FT-IR spectroscopy.

The mechanical properties of graphene oxide (GO) paper are critically defined both by the mechanical properties of the constituent GO sheets and the interaction between these sheets. Functional carbonyl and carboxyl groups decorating defects, expected to be predominantly sheet edges of the GO, are shown to transfer forces to the in-plane carbon-carbon bonding using a novel technique combining atomic force microscopy (AFM) to mechanically deform discrete volumes of GO materials while synchrotron Fourier-transform infra-red (FTIR) microspectroscopy evaluated molecular level bond deformation mechanisms of the GO. Spectroscopic absorption peaks corresponding to in-plane aromatic C=C bonds from GO sheets were observed to shift during tensile tests. Importantly, FTIR provided information on clear absorption peak shifts from C=O bonds linking along the GO sheet edges, indicating transfer of forces between both C=C and C=O bonds during tensile deformation. Grüneisen parameters were used to quantitatively link the macroscopic FTIR peak shifts to molecular level chemical bond strains, with relatively low bond strains prevalent when applying external forces to the GO paper suggesting probing of hydrogen bonding interactions. We propose a mechanistic description of molecular interactions between GO sheets in the paper from these experiments, which is important in future strategies for further modification and improvement of GO-based materials.