Modification of single-walled carbon nanotubes properties through irradiation-induced intertube bonding

Carbon nanotubes (CNT) have extraordinary properties, such as exceptional strength, which are derived from their unique structure. However, the weak Van der Waals (VdW) interactions between adjacent CNTs produce bundled axial properties significantly lower than isolated nanotubes. The VdW interactions lead to low shear strength in bundles which significantly reduces the commercial application of CNTs. The impact of the VdW interactions can be overcome and shear strength improved via irradiation-induced intertube bonds. However, irradiation also produces non beneficial modifications to nanotubes, such as atomic vacancy, which have negative impacts on properties. As such, experimental and computational irradiation of single walled carbon nanotubes (SWNT) was conducted to improve shear strength without significant detriment to other mechanical properties. This involved the optimisation of irradiation duration, electron beam energy and nanotube temperature. Experimentally, irradiation of SWNT identified amorphisation and intertube bonding using electron microscopy and Raman spectroscopy. Electron microscopy revealed that increasing irradiation duration and electron beam energy, increased the transformation of SWNT to amorphous carbon. Increased temperature was observed to improve SWNT structural integrity. Computational irradiation of SWNT produced intertube bonding including a novel “O” shaped bond. Increased irradiation duration and electron beam energy produced more complex bonds, suggesting that these parameters could control bond complexity. Increased nanotube temperature had a significant impact on the reduction of the complexity and stability of intertube bonding as well as atomic vacancy. Irradiation also modified nanotube mechanical properties with pullout capacity increased, tensile capacity decreased and stiffness increased in some cases relative to non-irradiated nanotubes. Complex bonding produced the most significant improvement in pullout and stiffness. In addition, bond complexity did not significantly impact tensile capacity. In summary, creation of irradiation induced intertube bonds can be optimised to significantly improve shear strength without significant detriment to other mechanical properties