Emulsifier-Free Graphene Dispersions with High Graphene Content for Printed Electronics and Freestanding Graphene Films

A novel and highly versatile synthetic route for the production of functionalized graphene dispersions in water, acetone, and isopropanol (IPA), which exhibit long-term stability and are easy to scale up, is reported. Both graphene functionalization (wherein the oxygen content can be varied from 4 to 16 wt%) and dispersion are achieved by the thermal reduction of graphite oxide, followed by a high-pressure homogenization (HPH) process. For the first time, binders, dispersing agents, and reducing agents are not required to produce either dilute or highly concentrated dispersions of single graphene sheets with a graphene content of up to 15 g L-1. High graphene content is essential for the successful printing of graphene dispersions by 3D microextrusion. Free-standing graphene films and micropatterned graphene materials are successfully prepared using this method. Due to the absence of toxic reducing agents, the graphene exhibits no cytotoxicity and is biocompatible. Furthermore, the electrical conductivity of graphene is significantly improved by the absence of binders. Flexible microarrays can be printed on different substrates, producing microarrays that are mechanically stable and can be bent several times without affecting electrical conductivity.