Directed diffusion approach for preparing atomistic models of cross-linked epoxy for use in molecular simulations

A directed diffusion approach is used to create atomistic models of cross-linked epoxy. In polymerization based approaches for preparing epoxy model structures, conversions higher than 95% are difficult to achieve due to very slow diffusion of unreacted monomers and cross-linkers in the partially formed network. We overcome this problem by creating very long bonds in the polymerization stage, and then relaxing these to equilibrium values by using a directed diffusion based relaxation strategy. The method minimizes the use of custom code by relying on the in-built functionality in LAMMPS package (Plimpton, S. J. Comput. Phys. 1995, 117, 1-19). The approach allows for near complete conversion (~ 99%) and the thermal and volumetric properties of the structures so prepared show good agreement with experimental data.