Stretching-induced nucleation and crystallization of cyclic polyethylene: Insights from molecular dynamics simulation

YQ Ming and ZP Zhou and J Yang and TF Hao and YJ Nie, EUROPEAN POLYMER JOURNAL, 173, 111232 (2022).

DOI: 10.1016/j.eurpolymj.2022.111232

Stretching-induced nucleation and crystallization of cyclic polyethylene (PE) were investigated by molecular dynamics (MD) simulation. The results show that nucleation and crystallization of cyclic PE are intimately related to the molecular weight of chains and strain rate. We found that there exists a critical molecular weight, below which increasing the molecular weight leads to the increase of crystallization rate and above which increasing the molecular weight leads to the slowdown of crystallization rate. This is caused by the fact that when the chain length is short, it is difficult to form a stable crystal nucleus because of its strong movement ability, while when the chain length is long, it hinders the conformational transformation and orderly arrangement of chain segments due to its reduced movement ability. The more the content of segments with longer conformational ordered segments and higher orientation in the system, the more conducive to the formation of more stable nuclei. Cyclic PE systems tend to form crystal nuclei through intramolecular nucleation with the increases of chain length. In addition, stretching will cause the chains to be disentangled and orderly arranged along the stretching direction to form crystal regions. The crystallization ability of the system will deteriorate with the acceleration of strain rate. This is because when the strain rate is low, it takes a long time to stretch to the same strain, and there is enough time to be stretched, resulting in more stretching of the chains and an increase in the probability of orderly arrangement of chain segments, so it is easier to orientation and crystallization. The opposite is true when the strain rate is high.

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