Modeling of amorphous polymer surfaces in computer simulation

We study surface effects in amorphous polymer systems by means of computer simulation. In the framework of molecular dynamics, we present two different methods to prepare such surfaces. Free surfaces are stabilized solely by van der Waals interactions whereas confined surfaces emerge in the presence of repelling plates. The two models are compared in Various computer simulations. For free surfaces, we analyze the migration of end monomers to the surface. The buildup of density and pressure profiles from zero to their bulk values depends on the surface preparation method. In the case of confined surfaces, we find density and pressure oscillations next to the repelling plates. We investigate the influence of surfaces on the coordination number, on the orientation of single bonds, and on polymer end-to-end vectors. Furthermore, different statistical methods to determine location and width of the surface region for systems of various chain lengths are discussed and applied. We introduce a ''height function'' and show that this method allows the determination of average surface profiles by scanning only the outermost layer of monomers. (C) 1997 Elsevier Science B.V.