Intermolecular forces in Carbon Nanotubes?
There is known, but poorly understood $\pi-\pi$ stacking. While weak compared to covalent, dipole or ionic interactions, it still beats usual van-der-vaals interactions. 

Carbon nanotubes are, essentially, polycondensed aromatical systems, so they can and would interact with each other as aromatic systems via $\pi-\pi$ stacking