Effect of\nRing Mobility on the Dynamics of the Slide-Ring\nGels

Random cross-linking in polymeric gels leads to heterogeneities\nin the obtained network, resulting in poor mechanical properties and\nlimitations of practical applications. To overcome this issue, networks\nwith movable cross-links have been developed. Slide-ring gels (SRGs),\nwhich are polymer networks with cross-links that can slide along the\nnetwork strands, belong to this category. These gels are softer, more\nstretchable, tougher, and with good recovery properties due to the\nsliding of cross-links, which equalizes the applied stress on polymer\nstrands. Although the origin of the excellent mechanical properties\nof these gels has been well-studied, the specific viscoelastic properties\nof slide-ring gels remain ambiguous due to the complexity of controlling\nand detecting the ring mobility. In this study, the development of\na palladium-based slide-ring gel from a metal-coordinated pseudorotaxane\nmotif enables us, for the first time, to control the ring’s\nmobility without changing any other parameters and keeping the overall\nnetwork connectivity. The rheology data of fixed-ring versus free-ring\ngels, analyzed with a tube-based model, reveal that the softness and\nlower elasticity of the slide-ring gels originate from the sliding\nof cross-links, which increases the effective mesh size of the network\nwell above the length of a single polyrotaxane chain. Moreover, we\ndemonstrate the key role played by the entanglements, which limit\nthe sliding distance of the rings. This study thus provides new insights\nfor understanding the peculiar viscoelastic behavior and huge stretchability\nof slide-ring gels, toward the rational design of SRGs with controlled\nproperties.