Phantom chain simulations for the effect of stoichiometry on the fracture of star-polymer networks

TL;DR

This study uses phantom chain simulations to explore how stoichiometry affects fracture behavior in star-polymer networks, revealing that stoichiometry has limited impact on fracture characteristics related to network topology.

Contribution

It extends previous models by investigating the effects of stoichiometry in star-polymer networks through Brownian dynamics simulations, providing more realistic insights.

Findings

Fracture characteristics slightly decrease with increased volume fraction contrast in certain conditions.

Stoichiometry does not significantly affect the relationship between fracture behavior and cycle rank.

Broken bonds and cycle rank show similar dependence on stoichiometry.

Abstract

By phantom chain simulations, it has been recently discovered that the fracture characteristics of star polymer networks with different node functionality and conversion ratios can be described by the cycle rank of the networks [Masubuchi et al., Macromolecules, doi: 10.1021/acs.macromol.3c01291]. However, due to the employed simplifications and idealizations of the examined model networks, the results cannot be cast into realistic systems straightforwardly. For instance, the equimolar reaction was assumed in a limited volume for the binary mixture of star prepolymers. For this issue, the present study investigated the effects of stoichiometry by phantom chain simulations. Examined polymer networks were created from binary mixtures of star prepolymers with various mixing ratios by the end-linking reaction via Brownian dynamics simulations. The networks were stretched with energy minimization until the break. From the mechanical response, strain and stress at break and work for fracture were obtained. These fracture characteristics slightly decrease with increasing the contrast of volume fractions of the binary prepolymer blends when the node functionality is small and the conversion ratio is large. For the other cases, the stoichiometry does not impact the fracture behavior. The number ratio of broken bonds and the cycle rank exhibit similar stoichiometry dependence. Consequently, stoichiometry of prepolymer blends does not disturb the previously reported relationships between the fracture characteristics and the cycle rank.