LANGEVIN DYNAMICS SIMULATIONS OF EARLY-STAGE POLYMER NUCLEATION AND CRYSTALLIZATION

United-atom Langevin dynamics simulations have been performed in an ef fort to understand early-stage polymer crystallization at the microsco pic level. We have modeled the crystallization process by following th e competition between the attraction among nonbonded beads and torsion al energies along chain backbones. We have monitored three processes: spontaneous formation of initial nuclei and their subsequent growth in time by an isolated chain as a function of degree of undercooling, cr ystallization at a growth front as a function of commesurability betwe en the thickness of the growth front and the length of crystallizing c hains, and cooperative crystallization by several chains into lamellae . The details of growth kinetics here have been captured by explicit v isual displays of chain conformations, radius of gyration of labeled c hains and aggregates, local and global orientation order parameters, a nd interaction energies all as functions of time. We observe that the kinetic pathway of lamellar thickening is stepwise and quantized for s mall degrees of undercooling and that the lamellar thickness is invers ely related to the degree of undercooling. The crystallization is foun d to be more efficient if chain length is an integer multiple of the t hickness of the growth front. We have compared several of our key simu lation results with experimentally observed results reported in the li terature and found that the simulations exhibit many salient features of polymer crystallization in dilute solutions. (C) 1998 American Inst itute of Physics.