Multiple Shape Memory, Self-Healable, and Supertough PAA-GO-Fe³⁺Hydrogel

A multiple shape memory and self-healing poly(acrylic acid)-graphene oxide-Fe3+ (PAA-GO-Fe3+) hydrogel with supertough strength is synthesized containing dual physically cross-linked PAA network by GO and Fe3+. The first GO cross-linked hydrogel can be reversibly reinforced by immersing in FeCl3/HCl and pure water and softened by immersing in HCl. The tensile strength is 2.5 MPa with the break strain of 700%. Multiple shape memory capability is found depending on this unique feature, the hydrogel can be fixed in four temporary shapes by adjusting the immersing time in FeCl3/HCl and pure water, and recovered in sequence by immersing in HCl. This hydrogel also exhibits perfect self-healing behavior, the cut as-prepared hydrogel is almost completely healed by immersing in FeCl3/HCl. Besides, the hydrogel shows enhanced electrical conductivity with the presence of GO and Fe3+. This supertough hydrogel provides a new way to design soft actuators.