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Abstract
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Atomistic molecular dynamics simulations are
performed on oligomeric polyamide-6,6 chains, composed of 10
chemical repeat units, at a carbon nanotube (CNT) interface. The
effect of surface curvature on the structure and dynamics of polymer
is studied by simulating systems containing CNTs of various
diameters. It is shown that polymer at the CNT interface organizes
into layered structures. The hydrogen bonding in the polymer is
influenced by the CNT surface. In proximity to the CNT surface, the
hydrogen bonds (HBs) are weaker than the corresponding
unperturbed bonds and their density is lower than that of the bulk
sample. On the other hand, over the region where organized layered
structures are formed, stronger HBs with a higher density than that
of the bulk sample are found. An analysis of chain orientation at the
interface shows that the monomers (repeat units) very close to the CNT surface wrap around the tube. However, at distances
corresponding to higher densities than the bulk density, the segments orient parallel to the CNT axis (along the CNT). The
wrapping costs higher energies in the case of smaller diameter CNTs (more curved surfaces). It is shown that while the CNT
surface perturbs the local chain properties up to a distance of ?2 nm from the surface, perturbation in the global chain properties,
such as the radius of gyration, extends to farther distances (a few times the radius of gyration of the unperturbed chain, R0
g). The
chain translation at the interface is found to be anisotropic, depending on the surface proximity and surface curvature. This is due
to the formation of extended conformations (along the CNT), facilitating smoother chain translation parallel to the CNT surface,
compared to that in the radial direction. The magnitude of dynamics deceleration caused by the CNT surface depends on the
surface proximity, surface curvature, and the time scale of the unperturbed dynamical property of interest. The dynamics
decelerates more in the case of l
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