Sanjay Misra

Structure and energy of thin films of poly-(1,4-cis-butadiene): A new atomistic approach

SummaryIn this work we study the formation of a thin film in vacuum by collapsing a random parent chain under two-dimensional boundary conditions. The initial random parent chain is obtained from atomistic simulation of bulk amorphous poly-(1,4-cis-butadiene). Films with a thickness of ∼25 Å are obtained for parent chains with 100 monomers. The density drops off sigmoidally over a distance of ∼5 Å near the free surfaces, while in the interior bulk density is obtained. The backbone bonds are randomly oriented in the interior and sharply oriented along the film plane near the free surfaces; the onset of order corresponds roughly with the drop in the mass density from its bulk value. The trans state of the CH2 -CH2 bond is also enriched compared to the bulk, in order for the chain to track the plane of the film more effectively. The difference in the energy of a chain in the amorphous bulk (3D periodic) and in the thin film (2D periodic) allows us to calculate the internal energy contribution to the surface energy; the agreement with the experimental value is reasonable.