Green-Solvent-Based Conductive Graphene Ink Prepared via Liquid-Phase Exfoliation of Graphite with Water-Soluble 2,6-Azulene-Based Copolymers as Stabilizers

Liquid-phase exfoliation (LPE) of graphite is a promising strategy to prepare stabilized graphene inks for various applications. However, the stabilizing agents that have been used generally suffer from poor electrical properties, harming the properties of the resulting composites once they are deposited on a surface. In this study, we investigate the use of a water-soluble, conjugated 2,6-azulene-based copolymer as a stabilizing agent for aqueous graphene dispersion. Due to the presence of azulene within the copolymer main chain, the copolymer exhibits proton responsiveness and conductivity in the solid state upon protonation. The LPE process was optimized in a mixture of water and ethanol (1:1), and stable inks can be obtained after 2 h of sonication using a copolymer concentration as low as 0.09 mg·mL–1. The resulting inks were deposited on various surfaces and characterized using Raman spectroscopy, UV–visible spectroscopy, and atomic force microscopy (AFM), which led us to conclude that few- and multilayer graphenes were obtained. Finally, the optimized ink was printed on glossy photographic paper using a modified FDM 3D printer to create printed circuits with a sheet resistance of 60 kΩ·□–1.