On the factors controlling the mechanical properties of nanotube films

We have studied the mechanical and morphological properties of carbon nanotube films prepared from tubes produced by a range of commercial suppliers. We find significant correlations between mechanical parameters (modulus, strength, toughness and ductility) and morphological parameters (porosity and bundle diameter). Both strength and toughness scale linearly with the number of inter-bundle junctions per unit volume as calculated from the porosity and bundle size. Applying a simple model, we can use this data to find the average force and energy required to break a junction to be ∼113 pN and 0.7 eV, respectively. This latter value agrees well with the value of 0.9 eV estimated from the nanotube surface energy, indicating that adjacent bundles are bound predominately by van der Waals interactions.