The role of density in the mechanical response of CNT turfs

Solvent capillary and axial compression can be used to increase the density of as-grown vertically aligned carbon nanotube arrays, herein referred to as turfs. During solvent evaporation, carbon nanotubes cluster together along their vertical growth axis, and axial mechanical compression densifies through compressing tubes into tangled positions and decreasing the empty space between tubes in directions primarily perpendicular to the vertical growth axis. The elastic modulus of the turfs, measured by nanoindentation, is between four to fifteen times higher after densification than that of pristine turfs and scales directly with densification ratio, while the adhesive properties remain unchanged. The electrical conductivity of the densified structure also scales with density. This suggests that multiple methods of post-growth modification of CNT arrays can achieve densified turfs with tailored mechanical properties without corresponding degradation of the electrical contact behavior.