The effect of local chain stiffness on the mechanism of crystal nucleation in an oligomer melt

While the process by which a polymer crystal nucleates from the melt has been extensively studied via molecular simulation, differences in polymer models and simulated crystallization conditions have led to contradictory results. We make steps to resolve this controversy by computing low-temperature phase diagrams of oligomer melts using Wang Landau Monte Carlo simulations. Two qualitatively different crystallization mechanisms are possible depending on the local bending stiffness potential. Polymers with a discrete bending potential crystallize via a single-step mechanism, whereas polymers with a continuous bending potential can crystallize via a two-step mechanism that includes an intermediate nematic phase. Other model differences can be quantitatively accounted for using an effective volume fraction and a temperature scaled by the bending stiffness. These results suggest that at least two universality classes of nucleation exist for melts and that local chain stiffness is a key determining factor in the mechanism of nucleation.