Study by Molecular Dynamics and First-Principles Calculation on the Influence of Length of Molecular Chain and Entanglement of Molecular Chains on the Strength of Amorphous Polyethylene

Abstract

: In order to comprehensively investigate from the effects of the morphology (length and entanglement) of the molecular chain on the strength of polyethylene to its fracture mechanism, molecular dynamics simulation of uniaxial tension using low molecular weight amorphous polyethylene and first-principles calculation of uniaxial tension using methylene trimer were performed. As a result, it was found that when the molecular weight is twice the entanglement molecular weight, the molecular chains can not form a network structure. And the bond stretch had the greatest effect on stress, in contrast, the van der Waals force had negative effect on stress and the effect was larger at lower molecular weights. In addition, it is also found that the decrease in stress after reaching the maximum stress is due to slipping of the molecular chains because the molecular chains donʼt break due to tension. Furthermore, the maximum stress increased with the longer the molecular chain because the entanglement point acted as a resistive force against the tension and because the longer the molecular chain, the higher the number of entanglement points. From the above results, it was clarified that the entanglement works positively for stress, the van der Waals force works negatively, and the entanglement of the molecular chains has a large effect on the strength of polyethylene.