Molecular dynamics simulations of nucleation details in stretched polyethylene. (8th May 2020)

• Record Type: Journal Article
• Authors: Liu, Zongfa; Zhou, Zhiping; Ming, Yongqiang; Zhang, Shuihua; Hao, Tongfan; Nie, Yijing
• Is Part Of: Polymer. Volume 195(2020)
• Publication Date: 2020-05-08
• Subjects: Molecular dynamics simulations -- Nucleation -- Stretching; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2020.122442
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: Molecular dynamics simulations were performed to investigate the microscopic mechanism of crystal nucleation in stretched polyethylene with different strains. The system consisted of 100 molecular chains, each containing 200 methylene groups. Polymer melts were first stretched to the states with different strains at a high temperature, and then the stretched polymers with different strains were further quenched to a low temperature for isothermal crystallization, respectively. Stretching causes local conformation transition from gauche -conformation to trans -conformation, together with segmental orientation along the stretching direction. Then, highly oriented segments with trans -conformation are further aggregated in local domains, which can be considered as the precursors for subsequent nucleation. During crystallization, most of crystallites originate from the precursors. Furthermore, the detailed process of crystal nucleation is closely related to strain. At low strains, the un-correlated oriented nuclei containing trans -conformation connected by chain-folding appear. At high strains, the oriented nuclei containing trans -conformation with intermolecular alignments connected by ties dominate. Graphical abstract: Image 1 Highlights: Stretch induces the concurrence of local conformation transition and segmental orientation, followed by the aggregation of oriented segments with trans -conformation. During subsequent crystallization at a low temperature, oriented crystallites first appear in the aggregation domains of local segments with trans -conformation. The formation of uncorrelated oriented nuclei is dominant during nucleation in stretched systems with low strains, while connected-network nuclei form during nucleation in these with high strains.