Bond fluctuation model to describe physical aging in polymeric materials.

The thermal behavior of a polymeric material during a cooling ramp was simulated by means of the bond fluctuation model. By introducing both an intramolecular and an intermolecular potential, if the cooling rate is fast enough, the glass transition occurs, and the states attained at low temperatures can be characterized as disordered glasses. The evolution of the resulting amorphous systems was then studied during isothermal periods both for systems starting as an amorphous liquid and as an amorphous glass. The results show that after a very long annealing time at temperatures above the glass transition, an excess of energy loss appears in the system when compared to the usual glass theory. The Monte Carlo method was used to simulate the physical aging phenomena at long time scales.