STRUCTURE AND MASS-TRANSPORT IN CONSTRAINED POLYMER CRYSTALS VIA MOLECULAR-DYNAMICS SIMULATIONS

To study the plastic deformation of polymer crystals, the structure an d molecular motion in surface-constrained polymethylene crystals conta ining 192 C50H100 chains were followed using molecular dynamics simula tions. Total energy, temperature and density were evaluated as a funct ion of time up to 100 ps. Structure changes, longitudinal and transver se mass transport, changes in setting angle of the zigzag chains and t he concentration and distribution of gauche conformations were noted. Selected chains were followed during the plastic deformation by tracin g their centre-of-mass coordinates and end-to-end distances. The plast ic deformation involves affine expansion and contraction, development of crystallographic fault lines (slip planes), edge dislocations, curv ed lattice planes and longitudinal diffusion of chains out of the crys tal. The time-scale for all these motions is in the picosecond range. The actual chain motion reaches about 10% of the speed of sound.