Abstract
The thermodynamics based on the interaction of small molecules on a polymer melt surface has been studied by molecular simulations. The melt surface structure of cis-1,4-polyisoprene was constructed using a molecular dynamics simulation technique. The system contained 20 polymer chains and a total of 30,000 carbon atoms. The excess chemical potential and enthalpy terms (average interaction energy between the gas and the polymer) were obtained using a test-particle-insertion method with excluded volume map sampling as a function of the position from the inside to the surface. The thickness of the surface estimated by the density change was 1.3 nm at 373 K. The excess chemical potential showed a minimum and a negative value only at the surface just beyond the position with half of the inside density. These results show the intrinsic properties of the polymer surface which accommodates gas molecules due to adsorption.
