Molecular dynamics study of the behavior of a single long chain polyethylene on a solid surface
A molecular dynamics simulation has been used in exploring the behavior of a single long chain polyethylene (PE) on a solid surface. We have established how varying the intermolecular (polymer-surface) van der Waals (vdW) interaction force effects the structural and dynamic properties of the polymer chain. For a high intermolecular vdW force, the starting PE chain absorbs on to solid surface, and develops into a stretched monolayerlike structure. However, for a low intermolecular vdW force, segments in the PE chain avoid the surface and fold into a compact lamellalike structure. However, for a moderate intermolecular vdW force, the PE chain forms into a polylayerlike structure where stems align parallel to the surface. Unlike the short chain molecules, the overall conformations developed by the long chain PE possess a degree of intramolecular (intrachain) order. In addition to these, we have systematically analyzed the changes in components of the square of the radius of gyration parallel and orthogonal to the surface, as well as the intermolecular and intramolecular vdW energy of the PE chain when it transforms to monolayerlike, lamellalike, and polylayerlike configurations. Results show that the structural change is in phase with the variation of parallel and orthogonal components of the square of the radius of gyration, and has a corresponding relation with the intermolecular and intramolecular vdW energy. The intermolecular vdW force drags the PE chain lying on the surface and stretching into a loose monolayer. The intramolecular vdW force, rather than any of the other intramolecular interactions, drives the PE chain folding into a compact, ordered lamella.