Toughening mechanism of tough and self-healing physical hydrogels

Recently, we have developed a new class of tough and self-healing physical hydrogels composed of polyampholytes (PA). Those PA gels possess high toughness, stiffness, fatigue resistance and self-healing. However, the toughening mechanism of these gels is still unclear. In this work, we used real time small-angle X-ray scattering (SAXS) to study the toughening mechanism of PA hydrogels.
We revealed that the high toughness of PA hydrogels is a synergistic effect due to multi-scale energy dissipation. We found that, this class of tough gels have a bicontinuous phase separation structure, consisting of a hard phase network and a soft phase network, of ~100 nm in scale. Upon loading, the microscopic deformation of phase structure is perfectly affine up to a quite large macroscopic uniaxial deformation range, followed by a wide nonaffine regime. In affine deformation regime, the breaking of ionic bonds dissipates energy, while in nonaffine deformation regime, hard phase ruptre dissipate energy.

[1]Cui K, Sun T. L, Liang XB, Nakajima K, Ye, Y. N, Chen L, Kurokawa T, Gong J. P. Multi-scale energy dissipation mechanism in tough and self-healing hydrogels. Physical Review Letters, 2018, 121, 185501.