Graphene dispersions

• Visible extinction of graphene at 500 nm is about 50 cm2/mg.
• Careful TEM analysis of dispersed graphene can provide platelet thickness distributions.
• Graphene dispersions in the absence of stabilizer have limited lifetime.
• Surface modification of graphene oxide followed by chemical reduction provides most effective route to conductive coatings.
• Stabilized aqueous dispersions of graphene up to 5% by weight are available.

Aqueous dispersions of graphene are of interest to afford environmentally safe handing of graphene for coating, composite, and other material applications. The dispersion of graphene in water and some other solvents using surfactants, polymers, and other dispersants is reviewed and results show that nearly completely exfoliated graphene may be obtained at concentrations from 0.001 to 5% by weight in water. The molecular features promoting good dispersion are reviewed. A critical review of optical extinction shows that the visible absorption coefficients of graphene have been reported over the ranges of 12 to 66 cm2/mg at various wavelengths. The practice of energetically activating graphene in various solvents with various stabilizers followed by centrifugation to isolate the “good” dispersion components is fine for producing samples amenable to TEM analysis and quantification, but cannot be expected to drive value added production of products on the kg or higher scale. Such approaches lack practical application and often involve 90–99% wasted graphene. However, alternative approaches omitting centrifugation are yielding dispersions 0.5 to 5% by weight graphene, with higher yields likely in the near future. These dispersions yield effective extinctions of about 49 cm2/mg, in conformity with macroscopic optical analysis of single and few layer graphene.

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