Structures and dynamics of polyethylene nanostructures with different free surface geometries: nanofilm, nanofiber and nanoparticle

Abstract

Monte Carlo simulations of coarse-grained polyethylene (PE) models were used to compare structural and dynamic properties of polymer chains confined at the nanoscale with different free surface geometries i.e. nanofilm, nanofiber and nanoparticle. All polymer nanostructures, which contain 95 chains of C100H202 were generated by serial reduction of the periodic boundary conditions. For all these nanostructures, the density profiles are hyperbolic, with end bead segregation at the surface. Bulk densities, sizes (thickness/radius) and the interfacial widths are lower, larger and broader for nanofilm, nanofiber and nanoparticle, respectively. The local environment of bond orientation is isotropic in the middle of these nanostructures, but becomes anisotropic near the surfaces. Chain orientation at the surface is also observed and the degree of anisotropy at the whole chain is nanofilm > nanofiber > nanoparticle. Surface energies are calculated directly from the on-lattice energetics and their magnitudes are: nanofilm nanofiber > nanoparticle along the direction of periodic boundaries but this order is reversed for the diffusion along the direction normal to the free surfaces.