Topological studies of bimodal networks

A new cross-linking algorithm, NETSIM, is described which enables the study of continuously spatially distributed (off-lattice) polymer networks and r eveals some topological features possibly associated with the enhanced mech anical properties seen in certain bimodal elastomer networks. These feature s art;identified based on trends in their occurrence at various mole fracti on and molecular weight combinations and comparison with data found in the literature. A length scale, the linear cross-link spacing, is defined which is associated with these features, to characterize optimal bimodal mixture combinations. NETSIM is unique among cross-linking algorithms in that it e mploys nearest-neighbor periodic boundary conditions to eliminate edge effe cts and reduce the necessary computational size from over 10000 primary cha ins to roughly 1000. Computational size reduction eliminates the need for s ubdivision of the cell, a possible source of bias in results reported in pr evious research. This work also offers, for the first time, computationally determined gel fi action and extent of reaction calculations for various b imodal mixture compositions. For verification, NETSIM results on unimodal s ystems are compared to previous unimodal simulations with good agreement.