(Invited) Sliding Dynamics and Mechanical Properties of Slide-Ring Gels

Abstract

To overcome the trade-off relationship between stiffness and toughness of conventional polymer gels with covalent cross-links, introducing dynamical cross-links into polymer network is a promising strategy. A typical example of dynamically cross-linked gels is slide-ring gel, in which polymer chains are cross-linked by rings and the cross-linking points can slide along polymer chains. When slide-ring gels are deformed, the network structure of slide-ring gels is homogenized due to the sliding of the ring molecules, which causes their high deformability [1]. We have recently performed crack propagation tests on slide-ring gels and found that their fracture energy is dominated by the sliding distance of the movable cross-links [2]. In this work, we investigate the relationship between the macroscopic fracture toughness of slide-ring gels and nano-scale sliding dynamics of rings on polymer chains. Slide-ring gels are prepared by cross-linking ring molecules of polyrotaxanes, necklace-like supramolecules consisting of cyclodextrins and polyethylene glycol. The fracture energy of slide-ring gels keeps constant at strain rates below a certain value, and decreases at a high strain rate, where the movable cross-linking points cannot slide and behave like covalent cross-links. From the strain rate dependence of the fracture energy, we have estimated the time scale for the sliding dynamics of cross-links in slide-ring gels.