Effect of hydrogen bonding strength on the structure and properties of phase-separated hydrogel from gelatin

Dynamic bonded tough hydrogels often contain phase-separated structures that facilitate multiscale energy dissipation. However, the influence of bonding strength on the phase-separated structures and properties of hydrogels has been understudied. In this work, the hydrogen bonding strength within phase-separated gelatin/acrylic acid copolymer hydrogels was modulated by varying the methyl group content in the acrylic acid copolymer. It was found the mechanical properties of the hydrogels are determined by a synergistic effect between water content and hydrogen bond strength. Both weak and strong hydrogen bonds resulted in the hydrogel with high water content and low mechanical strength. It was observed that the chain dense regions within the hydrogels became more condensed and larger with increasing hydrogen bonding strength. The high water content in gels with strong hydrogen bonds is attributed to the formation of condensed chain dense regions, which prevent significant shrinkage of the hydrogel. The combination of high water content and condensed chain dense regions resulted in sparse chain loose regions within the hydrogel, which provided water channels for ion transport, enabling high ionic conductivity even at a reduced water content of 28.9 wt%.