[manus_caerulia]

At a recent poster session I saw a poster on carbon nanotube formation and manipulation that attributed the cluster of the tubes in water to Van Der Waals forces only.  The tubes in question were long, flexible, and would form a compact tangle instead of dissolving in water or ethanol.

While this behavior is expected, I would have expected the cause to be portioning of the hydrophobic tubes.  Is there a unique property of carbon nanotubes that results in such strong Van Der Waals interactions?

I may be mistaken and the two interactions are identical, but the presenter was fairly certain that it was a specific effect and not a solvation effect.

[Yggdrasil]

I would think that the hydrophobic effect would cause the nanotubes to aggregate in aqueous or ethanol solution.  Van der Waals interactions can actually be quite strong, if your surfaces can get very close to each other (remember that vdw forces scale as 1/r⁶, so if you have a really small interparticle distance, you can have some pretty strong vdw interaction).  For example, the vdw forces between a gecko's feet and a wall can hold the entire weight of the animal.  I'm not an expert on this subject, but I would think the regular surfaces of the nanotubes would allow for pretty efficient packing and possibly some fairly strong vdw interactions.  Pi-Pi stacking could also be involved.

[Mitch]

I'm with you, both forces are obviously at work.

[sanderol]

If I read this, the image I get is that the hydrophobic effect causes them to aggregate while the vdW interactions causes them to sick together. These vdW can be quit strong since the CNT's can stack needly, also Pi-Pi can also be involved although these interaction are not fully proven as far as I know (my theses is in this, so I should now )