Geometric distribution of Dynamically Accessible Volume in the Bond Fluctuation Model

The geometry of the Dynamically Accessible Volume, DAV, in polymeric materials has been observed by means of the Bond Fluctuation Model. Simulations were conducted in conditions that yield varying amounts of accessible volume in the lattice, acting on the density of the system, and introducing geometrical restrictions to motion. A parameter has been defined to characterise the connectivity of holes characterising the number and size of hole clusters. The mobility of the accessible cells during athermal simulations has also been characterised concluding that all the holes in the lattice are in motion, contributing to the diffusion of the molecules even for the lowest values of DAV. The number of clusters increases with decreasing DAV reaching a maximum. For values of DAV below that of the maximum number of hole clusters, the diffusion coefficient becomes smaller than that predicted by the quadratic ratio D=γ|DAV|2 The differences in the dynamics of individual molecules and polymer chain systems are studied.