Tunable volume memory poly(acrylic acid sodium) hydrogel by metal ionsd

In this paper, the volume memory effect of poly(acrylic acid sodium) (PAAS) in different salt solutions, such as Na2SO4, MgSO4, Al2(SO[Formula: see text], is investigated. The degree of shrinkage and shrinkage rate is related to the valence of metal ions and the ionic strength of a salt solution. Multivalent ions can chelate with carboxyl groups of PAAS and form a second network in the covalently cross-linked PAAS. The metal–ligand coordination as a physical network significantly increases the ultimate compressive stress, compressive modulus, and fracture strain of the hydrogel. The ultimate compressive stress of the hydrogel chelated by Mg[Formula: see text] ions increases from 35 KPa to 24.1 MPa, an increase of nearly 690 times.