Relation between the Water Content and Mechanical Properties of Hydrogels with Movable Cross-Links

To reveal the synergic effects of movable and reversible cross-links, we fabricated movable cross-linked hydrogels with hydrophobic acetylated cyclodextrins (CDs). The obtained hydrogels showed high toughness based on the broad range of relaxation times achieved by the high mobility of movable cross-links and reversible hydrophobic interaction. The high mobility of movable cross-links resulted from the lack of hydrogen bonds between the triacetylated γCD (TAcγCD) units and main chains. High mobility also occurred because TAcγCD units were not hydrated. The localization of hydration forms hydrophobic domains with the distribution of TAcγCD units. The hydrophobic domains also disperse the stress upon tensile deformation. The low water content (Wc = 15 wt %) achieved further high toughness (36.8 MJ·m–3) by the triple-synergic effects of movable cross-links, reversible hydrophobic interaction, and craze/fibril-like structures upon deformation. The mobility of movable cross-links and the reformation of reversible hydrophobic interaction achieved high self-restoring properties.