Elasticity and rigidity percolation in flexible carbon nanotube films on PDMS substrates

The evolution of wrinkles and folds in compressed thin films of type-purified single-wall carbon nanotubes (SWCNTs) on polydimethylsiloxane (PDMS) substrates is used to study the mechanical response of pristine nanotube networks. While the low-strain moduli are consistent with the exceptional mechanical properties of individual nanotubes, the films are remarkably fragile, exhibiting small yield strains that decrease with increasing thickness. We find significant differences in the mechanical response of semiconducting as compared to metallic SWCNT networks, and we use simple scaling arguments to relate these differences to previously determined Hamaker constants associated with each electronic type. A comparison with conductivity measurements performed on identical films suggests more than a two-fold variation in the onset of rigidity vs. connectivity percolation, and we discuss the potential implications of this for both rigid-rod networks and the use of type-purified SWCNTs in flexible electronics.