Actuating, shape reconstruction, and reinforcement of galactomannan-based hydrogels by coordination bonds induced metal ions capture

Abstract

Application of abundant hemicelluloses polysaccharides on functional materials are of much interest. In this work, galactomannan (GM) hydrogels were prepared by dual hydrogen bonding interactions with polymerized poly-acrylic acid (AA) and poly-N-isopropylacrylamide (NIPAM). The hydrogels showed a series of novel and distinctive properties through in situ metal ions immersion. Highly improved ductility with a tensile strain of 230% and tensile stress of 390 kPa were exhibited by PAN-GM-Cu and PAN-GM-Fe respectively. More interestingly, the spontaneous metal ions capture into the network successfully actuated the sensitive curving and shape reconstruction behaviors of the hydrogels to varying degrees, which were tuned by the concentration of the metal ions. X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) proved the formation of new coordination bonds between Cu²⁺/Fe³⁺ and carboxylates/hydroxyls groups that reinforced and swelled the networks into different curving states. After the curving, PAN-GM-Cu exhibited more satisfied mechanical properties due to the distinctive morphological distribution of Cu²⁺ on the pores layers of the hydrogels. The intelligent hydrogels proposed in this work would provide new strategies for effective metal ions adsorption, which can be potentially applied on devices actuating, metal ions pollution water treatments, self-reinforcement and shape reconstruction.

Keywords: Galactomannan-based hydrogels; Metal coordination; Reconstruction.