Molecular dynamics studies of amorphous poly(tetrafluoroethylene)

Force field parameters for amorphous poly(tetrafluoroethylene) (PTFE) and perfluoroalkanes for molecular simulations are developed using four perfluoroalkanes (C3F8, n-C4F10, n-C5F12 and n-C6F14) as reference molecules. Molecular dynamics calculations of the amorphous PTFE are performed under constant temperature and constant pressure conditions. Surprisingly, more than 6 ns calculations are needed to equilibrate the system. The calculated density and the: structure factor are in good agreement with experiment. The concentration of the trans conformation of the backbone corresponds closely to that estimated from a Boltzmann distribution. The determined force field parameters are confirmed to reproduce the realistic amorphous structure of PTFE. The molecular motions of the backbones are investigated by tracing the time evolutions of the dihedral angles and several types of the conformational changes are observed.