  Using the density functional theory calculations, we show that the oxygen
functional groups exhibit unexpected spontaneously dynamic behaviors on the
interior surface of single-walled carbon nanotubes (SWCNT). Two types of
dynamic oxygen migrations - hydroxyl and epoxy migrations - are achieved by the
breaking/reforming of C-O bond reaction and the proton transfer reaction. It is
demonstrated that the spontaneously dynamic characteristic is attributed to the
sharply reduced energy barrier less than or comparable to thermal fluctuations.
We also observe a stable intermediate state with a dangling C-O bond, which
permits the successive migration of oxygen functional groups. However, on the
exterior surface of SWCNT, the oxygen groups are difficult to migrate
spontaneously due to the relatively high energy barriers, and the dangling C-O
bond prefers to transform into the more stable epoxy configuration. The
spontaneous oxygen migration is further confirmed by the long-distance oxygen
migration, which comprises three hydroxyl migration reactions and one C-O bond
reaction. Our work provides a new understanding of the behavior of oxygen
functional groups on interfaces and gives a potential route to design new
carbon-based dynamic materials.
