Self-healing properties of various multivalent cations reinforced Agar-Polyacrylic acid composite double network hydrogels

To obtain hydrogels with tough and self-healing properties, Ca²⁺/Agar-Polyacrylic acid(Ca²⁺/Agar-PAAc), Al³⁺/Agar-PAAc, Fe³⁺/Agar-PAAc composite double network hydrogels reinforced by ionic iron Ca²⁺, Al³⁺, Fe³⁺ cations were prepared by "one-pot" method. The enhancement function of metal ions Ca²⁺, Al³⁺, Fe³⁺, self-repairing properties, self-healing properties of reinforced hydrogels were studied. The tensile strength 320.7 kPa and elongation at break 1 130% of Fe³⁺/Agar-PAAc double network(DN) gels are 12 times and 9 times respectively those of Ca²⁺/Agar-PAAc DN gels. The tensile strength 320.7 kPa of Fe³⁺/Agar-PAAc DN gels is 5 times as large as that of Al³⁺/Agar-PAAc DN gels, elongation ratios of them are the same. Tensile with certain stain was applied to the sample to obtain damaged samples. The mechanical properties of Fe³⁺/Agar-PAAc DN hydrogels can be recovered to 100% of initial state after being soaked in ferric ion solution for 30 min. The mechanical properties of Fe³⁺/Agar-PAAc DN hydrogels can be recovered to 100% of initial state after being put in 50℃ condition for 15 min. By simply placing two hydrogel portions together and allowing enough self-healing time(48 h) for physical interactions to reestablish the network at the interface, the healed Fe³⁺/Agar-PAAc DN hydrogels can be stretched to 800% of initial length. The Fe³⁺/Agar-PAAc DN hydrogels reinforced by Fe³⁺ possess excellent mechanical properties and self-healing properties, without adding any chemicals and external stimuli, both networks possess self-healing properties.