Preparation and Characterization of Low-Voltage Responsive Nanocomposite Shape-Changing Hydrogels/Carbon Nanofibers With Enhanced Mechanical Properties

Abstract

High-voltage responsiveness and poor mechanical properties hindered the practical applications of electro-induced shape-changing hydrogels (EISCHs). In previous work, mechanical properties were improved simply by increasing the degree of crosslinking, which resulted in reduced deformation capacity. Therefore, the nanocomposite technique of reinforcing nondeformable hydrogels' mechanical properties was introduced into EISCHs, resulting in the successful synthesis of Poly (N-isopropylacrylamide-co-5-acrylamido-1,10-phenanthroline bis (1,10-phenanthroline) iron (II))/hydrophilic-treated hydroxylated carbon nanofibers (P(NIPAM-Fe(phen)₃)/HMWCNFs) nanocomposite shape-changing hydrogel that exhibits outstanding mechanical properties, doesn't have its deformation ability weakened and possesses low-voltage responsiveness in this work. The impact of various hydrophilic-treated hydroxylated carbon nanofibers (HMWCNFs) content on hydrogels' structure, swelling, crosslinking, mechanics and electro-induced shape-changing properties was investigated. As the HMWCNFs content increased (0.2%–1.0%), the tensile and compressive strengths increased, marking 6.67 times and 2.91 times rise over hydrogel without HMWCNFs. The deformation ability of P(NIPAM-Fe(phen)₃/HMWCNFs) hydrogel was higher than without HMWCNFs at minimum response voltage 10 V. The physical entanglements and hydrogen bonding between HMWCNFs and polymer chains reduced adhesion energy and provided energy dissipation. HMWCNFs, as a conductive filler, facilitated electron transfer. The hydrogel swelled and shrank due to the transition between 5-acrylamido-1,10-phenanthroline bis (1,10-phenanthroline) iron (II) (Fe(phen)₃) network iron (II) and iron (III) states under low-voltage stimulation.