Coarse-grained molecular dynamics simulations of slide-ring gels under finite deformation: influence of sliding ring rearrangement on softness and extensibility

Slide-ring (SR) gels are a class of polymer gels known for their unique softness, toughness, and high extensibility. The defining structural feature of SR gels is their figure-of-eight-shaped slidable cross-links, whose sliding dynamics are believed to underpin their mechanical properties. However, the relationship between the sliding mechanics and observed mechanical behavior of SR gels remains unclear because their structure differs considerably from those of conventional fixed cross-link gels and vulcanized rubbers. In this work, we employed coarse-grained molecular dynamics simulations to investigate the mechanical behavior of SR gels up to large deformation. By visualizing the correlated distribution of network strand orientation and stress loading, we found that SR gels under strain exhibit uniform chain orientation and efficient stress dispersion throughout the network, in contrast to gels with fixed cross-links, which display regions of highly oriented and heavily stressed chains. Furthermore, we observed that the distribution of network-strand length changes under deformation, indicating that chains are reconfigured into shorter and longer sections during stretching. Notably, we demonstrated that the finite network-strand length (N_max) determines the finite extensibility of SR gels, corresponding to the maximum elongation ratio (λ_max). These findings provide new insights into the molecular mechanisms driving the high extensibility and toughness of SR gels and offer valuable guidance for designing SR gels with tailored mechanical properties.