Structure/property relationship of semi-crystalline polymer during tensile deformation: A molecular dynamics approach

TL;DR

This study uses molecular dynamics simulations to explore how temperature, strain rate, and chain length affect the structural and mechanical behavior of semi-crystalline polymers during tensile deformation, revealing temperature-dependent mechanisms and proposing a micro-structure-property model.

Contribution

It introduces a coarse-grained molecular dynamics model to analyze the structure-property relationships in semi-crystalline polymers under tensile stress, highlighting temperature effects and proposing a new hypothetical model.

Findings

Yielding mechanisms differ above and below Tg.

Higher temperature induces melt-recrystallization and crystal destruction.

Microscopic parameters like orientation and trans conformation are closely linked to yield.

Abstract

A coarse-grained molecular dynamics model of linear polyethylene-like polymer chain system was built to investigate the responds of structure and mechanical properties during uniaxial deformation. The influence of chain length, temperature, and strain rate were studied. The molecular dynamic tests showed that yielding may governed by different mechanisms at temperatures above and below Tg. Melt-recrystallization was observed at higher temperature, and destruction of crystal structures was observed at lower temperatures beyond yield point. While the higher temperature and lower strain rate have similar effects on mechanical properties. The correlated influences of time and temperature in the microscopic structures are more complicated. The evolution of microscopic characteristics such as the orientation parameter, the bond length, and the content of trans-trans conformation were calculated from the simulation. The results showed that the temperature have double effects on polymer chains. Higher temperature on one hand makes the chains more flexible, while on the other hand shortens the relaxation time of polymers. It is the interaction of these two aspects that determine the orientation parameter. During deformation, the trans conformation has experienced a rising process after the first drop process. And these microscopic structure parameters exhibit critical transaction, which are closely related to the yield point. A hypothetical model was thus proposed to describe the micro-structure and property relations based the investigations of this study.