A facile route to fabricate stable reduced graphene oxide dispersions in various media and their transparent conductive thin films

In this paper, we demonstrate an easy way to prepare a stable reduced graphene oxide (RGO) dispersion in aqueous or organic media by simple adjustment of the degree of reduction and pH of RGO dispersion, and a subsequent fabrication of transparent conductive RGO thin films on various substrates using a spray coating technique. RGOs were prepared using a hydrazine reducing agent from graphene oxide (GO), which was oxidized from graphite via a modified Hummers' method. The degree of reduction determined the surface properties, such as atomic composition, surface polarity, and potential of RGO platelets. In addition, pH significantly affected the surface potential of graphene dispersion. The fine adjustment of degree of reduction and pH of RGO dispersion made production of fine RGO dispersions in aqueous and organic media such as ethanol and DMF possible without any aid of dispersing agents. The stable RGO dispersion using volatile ethanol medium provided a unique advantage to be spray-coated into uniform transparent conductive RGO thin films on various substrates including silicon wafer, flexible polycarbonate film regardless of their surface properties, and even on non-planar substrates such as round-shaped glassware at room temperature.