Molecular Dynamics Simulation of the Nascent Polyethylene Crystallization in Confined Space: Nucleation and Lamella Orientation
SY Chen and W Chen and Y Ren and JY Sun and JD Wang and YR Yang, MACROMOLECULES, 55, 7368-7379 (2022).
Different nascent structures during polyethylene growth can impact the final polymer properties. So far, the evolution of the aggregation structure of nascent polyethylene is still unknown. We have developed a nascent polyethylene model and investigated the effect of confined space on the nucleation and crystallization process. The in situ polymerization characteristics were modeled through the chain-end fixation, temperature gradient, and sidewall setting. We observed a compromise in competition between high undercooling and heterogeneous nucleation in reducing the nucleation free energy, reflecting two nucleation mechanisms for different sidewall settings. Moreover, the contact of sidewall and lamella growth front with different directions had a diverse effect on the development of lamella. The contact of the side face can redress the lamella tilt angle and make its orientation along the Z-axis, while contact of the thickness face is proved to inhibit the increase of the stem length and reduce the thickness of the lamella. The results shed light on the crystallization process of nascent polyethylene and help to explain the role of the polyhedral oligomeric silsesquioxane modification at a microscopic level.
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