حسین اسلامی

Coarse-grained molecular dynamics simulations have been performed to study a nanometric polyamide-6,6 film containing long chains (100 chemical repeat units), in contact with a graphene surface and with vacuum, in a huge simulation box (the distance between the interfaces ? 36 nm) for a long time (70 ns). Compared with atomistic simulations, with limitations in chain length, box size, and simulation time, restricting them to the study of local structural and short-time dynamic properties, this simulation covers a broad range of length scales and captures the long-time relaxation regime of long chains. This enables one to discriminate the interphase thickness for local and global structural properties and to study the interplay between the change in structural and the associated dynamic properties in the interphase compared with the bulk polymer. Our results indicate that the interphase thickness depends on the length scale of particular property of interest for the bulk polymer. At both interfaces a minimum interphase thickness, ?3.0 nm, is associated with local structural properties such as layering of individual superatoms and the hydrogen bonding between amide groups. The interphase thickness, however, extends to an intermediated length of about one radius of gyration, Rg, of the unperturbed polymer (6 nm) and a maximum length of 2Rg in the case of such polymer structural properties as the chain conformations and reach of chains with at least one contact to the interface to the polymer phase, respectively. Accordingly, the time scales for both short- and long-time dynamic properties in the interphase vary (with respect to the corresponding property in the bulk) as a function of distance from the surfaces. The change in time scales, in a 3 nm thick slab parallel to the interfaces, is shown to cover a broad range from 10% to four orders of magnitude. The former change in time scales occurs in the case of such a short-time dynamic property like HB formation (occurri