A Monte Carlo lattice model for chain diffusion in dense polymer systems and its interlocking with molecular dynamics simulation

The paper reports the development of a Monte Carlo lattice model (cubic F) of polymer chains which is able to access times where the diffusion of the centre-of-mass of the chains is the dominant process, even though the chain lengths are well above that for entanglement. The volume of the model is large when compared with the volume of gyration of the individual molecules. The model incorporates an algorithm, which allows for the possibility of co-operative motions over sections of the chains and increases the time efficiency of the simulation. Both the model and the modifying algorithm have been tested against the known scaling laws.

The model, for shorter chains, is ‘reverse mapped’ into full atomic detail as polyethylene and the shorter time processes simulated using molecular dynamics (MD). The MD model is tested against experimental diffusion data for polyethylene, of the same molecular weight and at the same temperature, and then used to time-calibrate the lattice model.

Both the fine grained MD model and the coarse grained MC model are thus interlocked to cover a time range from the individual atomic motions of MD up to the order of a microsecond, a range of six orders of magnitude.