  Using all atomistic molecular dynamics (MD) simulations we report the
microscopic picture of the nanotube-dendrimer complex for PAMAM dendrimer of
generation 2 to 4 and carbon nanotube of chirality (6,5). We find compact
wrapping conformations of dendrimer onto the nanotube surface for all the three
generations of PAMAM dendrimer. The degree of wrapping is more for
non-protonated dendrimer compared to the protonated dendrimer. For comparison
we also study the interaction of another dendrimer, poly(propyl ether imine)
(PETIM), with nanotube and show that PAMAM dendrimer interacts strongly as
compared to PETIM dendrimer as is evident from the distance of closest approach
as well as the number of close contacts between the nanotube and dendrimer. We
also calculate the binding energy between the nanotube and the dendrimer using
MM/PBSA methods and attribute the strong binding to the charge transfer between
them. Dendrimer wrapping on CNT will make it soluble and can act as an
efficient dispersing agent for nanotube.
