Stalled phase transition model of high-elastic polymer

TL;DR

This paper introduces a microscopic model for high-elastic semi-crystalline polymers, explaining their stress-strain behavior and temperature dependence through the tension of chain segments and reversible phase transitions.

Contribution

It presents a novel 1D microscopic model that accounts for the high-elastic behavior and temperature dependence of semi-crystalline polymers, aligning well with experimental data.

Findings

Predicts stress-strain plateau consistent with experiments

Shows temperature dependence of yield stress matches observations

Explains reversible deformation via unfolding of crystalline nuclei

Abstract

The microscopic model of semi-crystalline polymer in high-elastic state is proposed. The model is based on the assumption that, below the melting temperature, the semi-crystalline polymer comprises crystal nuclei connected by stretched chain segments (SCS) with random configuration of monomers. The key factor that stalls the phase transition below the melting temperature is the tension of the SCS. External stress applied to the polymer also shifts the equilibrium and causes unfolding of the nuclei, which enables large reversible deformation of the polymer without loss of integrity. The simple 1D model predicts plateau in stress-strain curve of high-elastic polymer above the yield stress, which agrees with experimental observations. The model prediction for the temperature dependence of polytetrafluoroethylene (PTFE) yield stress in high-elastic state is in satisfactory agreement with experiment.