Computer simulation of the heterogeneity of segmental dynamics in amorphous polymers

The heterogeneity of local segmental dynamics in a polymer system is analyzed by computer simulation with the Bond Fluctuation Model. A different approach is proposed based on the concept of Dynamically Accessible Volume (DAV) due to the difficulties encountered in the characterization of this heterogeneity by means of the distribution of relaxation times. A DAV value is assigned to each polymer chain as the fraction of cells in its surroundings that could be occupied in one Monte Carlo Step. In this way it is possible to relate the mobility of a chain with the accessible volume around it, due to the relationship between DAV and diffusion coefficient. As temperature decreases in equilibrium the DAV distribution shifts towards lower values, its width decreases and the number of frozen molecules increases. The methodology proposed also provides a way of characterizing the evolution of segmental dynamics distribution in out of equilibrium states below glass transition temperatures.