Aging effects in glassy polymers: a Monte Carlo study

By means of dynamic Monte Carlo simulation the physical aging of a glassy polymer melt is studied. The melt is simulated by a coarse-grained lattice model, the bond-fluctuation model, on a simple cubic lattice. In order to generate glassy freezing an energy is associated with long bonds, which leads to a competition between the energetically favored bond stretching and the local density of the melt at low temperatures. The development of this competition during the cooling process strongly slows down the structural relaxation and makes the melt freeze in an amorphous structure as soon as the internal relaxation time matches the time scale of the cooling rate. Therefore the model exhibits pronounced cooling rate and physical aging effects close to the glass transition. The physical aging of the model occurs on all length scales of a polymer in a self-similar way, which may be expressed by a time-temperature superposition principle for the aging time. For short aging times an Andrade behavior is found for all studied quantities.