The influence of the cooling rate on the glass transition and the glassy state in three-dimensional dense polymer melts: a Monte Carlo study

Abstract

In this Monte Carlo simulation the authors study the glass transition of a dense three-dimensional polymer melt using a lattice model (a bond-fluctuation model on a simple cubic lattice) that was highly optimized for a vector supercomputer. Long bonds are energetically favoured to create a competition between bond energy and packing constraints, which prevents the melt from crystallizing when it freezes. The onset of this freezing can be monitored by the temperature variation of various static quantities that probe both the length scale of a bond vector, such as the mean bond length and mean energy per bond, and that of the whole chain, such as the radius of gyration. As the melt vitrifies, these quantities gradually become independent of temperature in a narrow range around T approximately=0.2 (the temperature is measured in units of an energy parameter, epsilon , introduced in the model Hamiltonian) and their value at low temperatures is strongly influenced by the cooling rate. It is thus possible to infer from these curves the cooling-rate dependence of the freezing temperature Tg. Despite the difference in the detailed dependence of Tg on the cooling rate, the extrapolated value TK coincides with the Vogel-Fulcher temperature T0, obtained from the temperature variation of the diffusion coefficient, within the error bars.