intermolecular interactions. The short-range intramolecular interactions make a small contribution, which tends to oppose the effect of the intermolecular interactions on y. This result implies that bonds in the low density surface region can achieve a somewhat greater local intramolecular relaxation than is possible for bonds in the bulk region, as was observed previously by Misra et al .19

There is greater mobility in the surface region of free-standing thin films than in the bulk, both at the level of individual beads and at the level of the translational diffusion of the center of mass of chains of C100H202. This increase in mobility in the surface region is also seen for free-standing thin films that are composed of cyclic chains, C100H200. Therefore the increased mobility is attributed to the lower density in the surface region, and not to the preferential segregation of the ends of the linear chains in the surface region, 24

The computational efficiency of the simulation with the coarse-grained model permits the study of the process by which cohesion of two thin films is obtained with n-alkanes25 Three different time scales are observed for healing of the density profile at the initial interface between the two films, redistribution of chain ends, and complete intermixing of the chains, with the time scale increasing in the order stated.

The behavior described in this section is observed in the simulations of free-standing thin films. Important changes in the static and dynamic properties can occur when the thin film interacts with a single solid wall26 or is confined in a narrow slit between two parallel solid walls.27

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