Understanding creep in vitrimers: Insights from molecular dynamics simulations

Vitrimers offer malleability and recyclability due to covalent adaptable networks, however, they are prone to low-temperature creep. In this work, we investigate the molecular mechanisms of vitrimer creep using molecular dynamics simulations. We model the interplay between dynamic bonding with mechanical loading using a topology-based reaction scheme. The creep behavior is compared against cross-linked epoxies with dynamic reactions to understand the unique aspects related to dynamic bonding. It is found that the free volume that arises from tensile loads is reduced in vitrimers through dynamic bond rearrangement. An important feature that distinguishes the secondary creep behavior between epoxies and vitrimers is the orientation of the dynamic bonds during loading. In vitrimers, the dynamic bonds preferentially align orthogonal to the loading axis, decreasing the axial stiffness during secondary creep, resulting in larger creep strain compared to epoxies. Over longer timescales, such increased strain leads to void growth, resulting in tertiary creep.