Elucidating Nonlinear Stress Relaxation in Transient\nNetworks through Two-Dimensional Rheo-Optics

This study aims to elucidate the\norigin of nonlinear stress relaxation\nbehaviors in transient networks using a systematically controlled\nmodel system consisting of the tetra-armed polyethylene glycols (Tetra-PEG\nslime) in conjunction with two-dimensional rheo-optics observations.\nTransient networks, characterized by their temporary cross-links,\nare extensively utilized in self-healing and robust materials. However,\nthe molecular mechanisms governing their viscoelastic responses to\nlarge deformations have remained elusive. This is primarily due to\nthe heterogeneous structures inherent in conventional transient networks\nand a scarcity of detailed experimental evaluations. By employing\nTetra-PEG slime, which is distinguished by its regular structure with\nuniform strand lengths and functionalities, and the polarization imaging\nmethod, we overcome these obstacles. Our results reveal that the damping\nphenomena observed under large step strains arise from spatially heterogeneous\nrelaxation, predominantly driven by network strand pullout. These\ninsights lay a solid foundation for understanding the intricate rheological\nproperties of transient networks.