Carbon Trends (Mar 2023)
Investigation of mechanical properties of C70 nanowhiskers through bending and nanoindentation
Abstract
The mechanical properties of C70 nanowhiskers (NWs) grown using the liquid–liquid interfacial precipitation method were investigated through bending and nanoindentation experiments. The results showed the solvated C70NWs exhibited a large elastic deformation with a maximum strain of 2.9% upon bending, similar to solvated C60NWs. However, it should be noted that the C70NWs with a face-centered cubic (FCC) retained a large elastic strain even in structure after desolvation, unlike C60NWs with an FCC-structure which showed a significant decrease in elastic strain after desolvation. This elastic strain preservation in C70NWs after desolvation was also observed in the elastic modulus and hardness measurements obtained during nanoindentation. These results suggest that the mechanical properties of C70NWs are independent of solvation and molecular arrangement. Additionally, the elastic modulus and hardness of the C70NWs before desolvation were 4.21 GPa and 216 MPa, respectively, which were lower than those of C60NWs even after desolvation. This indicates that C70NWs have weak C70–C70 and C70–solvent intermolecular interactions. According to recent reports on elastically flexible molecular crystals, corrugated/interlocked molecular packing that prevents slippage between molecular planes, which causes plastic deformation, is considered a key factor for large elastic deformation, with weak intermolecular interactions acting as structural buffers for the deformation. The ellipsoidal-shaped C70 molecules may have higher interlocked molecular packing and weaker intermolecular interactions in the crystal compared to spherical-shaped C60 molecules. These findings on the effect of molecular shape on the mechanical properties of molecular crystals, including fullerene crystals, provide valuable insight for a comprehensive understanding of these properties.
