The distribution of the relaxation times as seen by bond fluctuation model

Abstract

The structural relaxation process of an amorphous polymer has been simulated using the Bond Fluctuation Model with a quite simple description of the polymer system. The glass transition, that is apparent when a cooling ramp is simulated, comes as a consequence of chain connectivity and a bond length potential. Annealing of the system at temperatures below the glass transition, in the glassy state, produces a continuous decrease of the total energy of the system at a rate that depends on temperature. The energy evolution is shown to be clearly nonexponential in a certain temperature interval. In this temperature interval, molecular mobility was characterized using different definitions of the relaxation times and calculating a distribution of relaxation times in the system by studying the motions of small regions of the lattice. As annealing temperature decreases the distribution of relaxation times shifts to longer times and slightly broadens. The maxima of the distributions of relaxation times obey the Vogel, Fulcher and Tammann equation.