ABSTRACT
Aqueous dispersion of graphene is of interest as it affords environmentally safe handling of graphene for coating, composite, electronic, and other materials applications. The dispersion of graphene in water and certain other solvents using surfactants, polymers, and other dispersants is reviewed, and results show that almost completely exfoliated graphene may be obtained at concentrations varying from 0.001 to over 10% by weight in water. The molecular features promoting good dispersion are reviewed and demonstrated. A critical review of optical extinction shows that the visible absorption coefcients of graphene have been reported over the ranges of 7-66 cm2/mg at various wavelengths. We critically present data that prove the higher among these estimates to be good lower bounds to the completely exfoliated dispersion state, with an extinction coefcient of about 100 cm2/mg at 500 nm (80-86 cm2/mg at 660 nm). An inescapable conclusion is that the practice of energetically activating graphene in various solvents with various stabilizers, followed by centrifugation to isolate the “good” dispersion components is ne for producing samples amenable to transmission electron microscopy (TEM) analysis and quantication, but cannot be expected to drive value-added productions of products on the kilogram or higher scale. We also show that nearly complete exfoliation at concentrations of 1%–5% by weight in water is feasible without centrifugation.
