Stochastic dynamics simulations of polymethylene melts confined between solid surfaces

Abstract

Stochastic dynamics simulations of polymethylene chains (CnH2n+2 for n=13, 28, 60) represented by united atom models have been carried out in order to investigate both the equilibrium and dynamic properties of polymer melts confined between flat solid surfaces. The packing manner of monomer segments, segment orientation and local conformations of chains are found to be independent of chain length, and agree very well with the results of the previous Monte Carlo simulations of C13H28 melts. The chains are extremely flattened close to the surface and many molecules assume essentially two-dimensional train configurations even in the case of C60H122 melts. However, the local chain conformations are only slightly affected by the surfaces. The apparent self diffusivities are found to be independent of the distance from the surface as the result of a reduced mobility normal to the surface and an enhanced mobility parallel to the surface. The absolute magnitudes of self-diffusion constants are larger than experimental values, most likely due to the application of united atom model.