Tough, self-recovery and self-healing polyampholyte hydrogels

This article reviews the recently developed tough, self-recovery, and self-healing polyampholyte hydrogels. Polyampholyte hydrogels are synthesized using one-step radical copolymerization of cationic and anionic monomers with equal charges at high monomer concentration. The random copolymerization process makes the ionic monomers randomly distributing along the backbones, resulting in the formation of ionic bonds with a wide strength distribution via inter and intra chain complexation in the polymer network, weak bond and strong bonds. The strong bonds serve as permanent cross-linking, integrating the hydrogels to impart the elastic behavior, while the weak bonds can break upon the loading, dissipating energy to give the toughness, and re-form again after unloading to enable the self-recovery behavior. Accordingly, polyampholyte hydrogels have condensed polymers in water (ca 40-50 wt %). They are strongly viscoelastic and have a high toughness (fracture energy of 4000 J/m(2)), a wide range of tuning modulus (0.01 to 8 MPa), 100% self-recovery, and a high self-healing efficiency after cutting.