Viscoelastic behaviors for optimizing self-healing of gels with host–guest inclusion complexes

Abstract

This research showed that the self-healing properties of reversible crosslinked gels with host–guest inclusion complexes depended on the mobility of network chains and the recombination behaviors of reversible complexes, which were affected by changes in the water–glycerol solvent composition. The sticky reptation behaviors of the polymer chains were delayed by the recombination behaviors of reversible bonds. These behavioral characteristics were observed based on a dynamic viscoelasticity. Increasing the glycerol concentration in the mixed solvent decreased the surface tension and increased the mobility of the network chains because the recombination of the complex was slowed by the weak hydrophobic interactions between the host and guest molecules. Consequently, self-healing properties, such as re-adhesion at the cutting surface, were improved by the interdiffusion of polymer chains at the reattached interface. The strong hydrophobic interactions in pure water promoted the formation of complexes within the same cutting surface, thus decreasing the self-healing rates of the mechanical properties. In this study, the solvent was found to be an important parameter for controlling the self-healing properties of reversible crosslinked gels. The competition between the mobility of polymer chains and the recombination behaviors of reversible bonds controlled the self-healing properties of the gels with host–guest inclusion complexes. This study examined how changing the water-glycerol solvent composition affects the self-healing and viscoelastic properties of self-healing gels, which have host-guest inclusion complexes as reversible crosslinks. Increasing glycerol concentration in the mixture solvent reduced hydrophobic interactions between β-cyclodextrin and adamantane, lowering the association constant of host-guest inclusion complexes. The weakened hydrophobic interaction hinders complex recombination and enhances the mobility of the network chains. Consequently, the enhancement of mobility improved the healing ratio because the interfacial diffusion of the chains was promoted at the repair interfaces.