Monte Carlo and molecular dynamics simulation of the glass transition of polymers

Abstract

Two coarse-grained models for polymer chains in dense glass-forming polymer melts are studied by computer simulation: the bond fluctuation model on a simple cubic lattice is treated by Monte Carlo methods, and a continuum bead-spring model with a Lennard-Jones potential between the beads is treated by means of molecular dynamics. While the dynamics of the two models differ for short length scales and the associated timescales, the two models behave similarly on mesoscopic spatial and temporal scales. In particular, the mode-coupling theory of the glass transition can be used to interpret the slowing down of the undercooled polymer melt. For the off-lattice model, the approach to the critical point of mode coupling is studied both at constant pressure and constant volume. The lattice model allows a test of the Gibbs-Di Marzio entropy theory of the glass transition to be carried out, and our finding is that although the entropy does decrease significantly, there is no `entropy catastrophe' where the fluid entropy would turn negative. Finally, a forward look at the effects of confinement on the glass transition in thin-film geometry is given.