Identification of topological constraints in entangled polymer melts using the bond-fluctuation model

We propose ail algorithm to locate individual entanglements along chains, equilibrated using the bond-fluctuation lattice model. The algorithm identifies entanglements as local deviations of the primitive path from the shortest possible path between beads on a chain that are oil lattice sites. For well-entangled chains (number of beads, N >= 125), the average number of entanglements enumerated using the proposed method is in excellent agreement with the number of entanglements per chain inferred using the ensemble-averaged primitive path length < L-pp > and mean-squared end-to-end distance < R-2 > of the chains, namely Z = < L-pp >(2)/< R-2 >. As an application of this method, we show that the elimination of ail entanglement releases, approximately, one additional entanglement. This implies a value of alpha = 1.03 +/- 0.02 for the dilution exponent relating entanglement density rho(ent) to polymer concentration c via rho(ent) proportional to c(1+alpha) and is consistent with the description of entanglements as binary contacts.