Incorporation of graphene into photopolymerizable hydrogels of N-acyl glutanamides: Rheological and swelling behavior study of soft nanocomposite materials

Two different respectively N-stearoyl and diacetylenic fatty acyl glutanamide were prepared and employed as both potent low molecular weight hydrogelators (LMWGs). These compounds were able to gelate water at 1.0 wt% of concentration independently of the pH. Due to the presence of two free amino groups on the extremities of the gelator, an aqueous colloidal dispersion of graphene oxide (GO) could be stabilized into the hydrogel matrix simply by ionic bonds. The inclusion of a slightly amount of GO inside the gel networks increased its natural rigidity, confirmed by rheology study. An in-situ reduction of GO afforded after treatment, a semi-transparent hydrogel containing reduced graphene (rGO) that could be easily manipulated without apparent syneresis phenomenon. When the diacetylenic type hydrogel containing GO was irradiated upon UV light, a deep blue coloration change was observed; evidence of an effective photopolymerization. In case of thermal stimulation of the resulted blue polydiacetylene (PDA) hydrogel, the material turned in a red solution precursor of a robust red (PDA) hydrogel at room temperature. This red hydrogel never displayed reversible color change and its swelling behavior was studied at different temperatures. All hydrogels were characterized by different methods such as Field-Emission Scanning Electron Microscopy (FE-SEM) for determining the homogeneity of the gel networks, but also by (FT-IR) Fourier Transform-Infrared spectroscopy and UV–visible measurement.