The correlation of rotational isomers in polyethylene‐like crystals

Abstract

AbstractThe molecular dynamics technique to simulate the behavior of polyethylene crystals, described earlier, is used to study the creation and mobility of rotational isomers of a polyethylene‐like chain in a crystal environment. Both a “gross defect” (formed by perturbation of the cartesian coordinates) and a “kinetic defect” (formed by placing a specific amount of kinetic energy that excites a pure local torsion) are added to the central chain of a polyethylene crystal. The initial dynamic instability quickly forms a more stable, but more or less static defect that, subsequently, moves somewhat along and between neighboring chains, and finally, gets quenched on a time scale of a few picoseconds. Increasing the temperature leads from a highly correlated state to a state where defects are created and quenched statistically (condis state). Increasing the energy input for defect generation leads to the creation of different static defects. The onset of conformational disorder is independent of the initial perturbation. There is a correspondence of the observed defects to the defects proposed for polyethylene based on molecular mechanics calculations, but lifetimes are relatively short.