Effect of H2O and reduced graphene oxide on the structure and rheology of self-healing, stimuli responsive catecholic gels

Abstract

A catechol-containing organogel based on random copolymers of N-isopropylacrylamide (NIPAM) and dopamine methacrylate (NIDO5%) in dimethyl formamide (DMF) was supramolecularly crosslinked by NaBH4 in the presence of reduced graphene oxide (RGO). The focus of the investigations was on the influence of H2O and RGO in the system, which leads to a softening and stiffening, respectively. Whereas RGO tends to restack partially, this tendency was not found in the gels, suggesting a surface coverage of RGO with NIDO5% due to H-bonding and surface crosslinking attributed to the interactions of polar groups of polymer chains with carboxylic and carbonyl groups of RGO sheets proven by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray diffraction and spectroscopy (XRD). While RGO leads to the system becoming more brittle, its presence does not lead to an excessive loss of the self-healing characteristics, but it clearly stabilizes the gel when swollen with H2O, as can be seen from the significantly higher modulus and the retained self-healing behavior.