Cyclic Liquid-Phase Exfoliation of Electrically Conductive Graphene-Derivative Inks

Advances in electrically conductive inks and printing technology have enabled microelectrodes, chemical sensors, wireless radio frequency identification tags, and bioelectronic circuits to be fabricated on mechanically flexible polymers, paper, and bioresorbable silk. Although conductive polymer and metal-based inks have been used to build functional devices, these materials are often expensive and may involve complicated toxic chemical processes. Recent research has demonstrated that graphene (G), and its derivatives, can be used to create water-based conductive inks. In this paper, an environmentally friendly and cost-effective G-based conductive ink is proposed. The ink is created by using a nontoxic hydrophilic cellulose derivative, Carboxymethyl Cellulose (CMC), to facilitate liquid phase exfoliation and stabilization of naturally hydrophobic G sheets in DI water at high concentrations. It is demonstrated that recycling of nonexfoliated material can produce inks at comparable concentrations. Physical dimensions and defect status of exfoliated G sheets are characterized. Inkjet deposition of thin and thick films is achieved using a binary solvent system and electrical performance of resulting films is investigated. Film morphology is shown to be consistent between thin and thick films. Experiments have demonstrated that G-CMC films of <;700 Ω/sq can be inkjet printed without use of dopants or dangerous solvents.