Fig. 6. Theoretical calculation of the mechanical response of the hydrogels.

(A) The synthetic material at the dry state is represented with a cube of dimension, ${\overline{l}}_0$, where eight chains cross-linked at the cubic center extend from the cubic center to each corner of the cube. (B) At the current state, the dimensions of representative volume element (REV) become l₁, l₂, and l₃, due to the solvent absorption, metal ion binding, or mechanical loading. (C) Theoretical prediction of stress-strain curves of HN-PH₁, HN-PH₃, HN-PH₆, HN-PH_3R1, and HN-PH_3R2 when subjected to uniaxial stretching-relaxation. (D) Theoretical prediction of stress-strain curves of HN-PH₁, HN-PH₃, HN-PH₆, HN-PH_3R1, and HN-PH_3R2 when subjected to uniaxial compression-relaxation. (E) Theoretical prediction of stress-strain curves of HN-PH₆ with different concentration of PH₆ when subjected to a uniaxial stretching-relaxation cycle. (F) Theoretical prediction of stress-strain curves of HN-PH₆ with different concentrations of PH₆ when subjected to a uniaxial compression-relaxation cycle. Photo credits: Wenxu Sun, Nanjing University.