Dispersion stability of functionalized graphene in aqueous sodium dodecyl sulfate solutions.

The colloidal stability of functionalized graphene sheets (FGSs) in aqueous sodium dodecyl sulfate (SDS) solutions of different concentrations was studied by optical microscopy and ultraviolet-visible light absorption after first dispersing the FGSs ultrasonically. In up to ∼10 μM SDS solutions, FGSs reaggregated within a few minutes, forming ramified structures in the absence of SDS and increasingly compact structures as the amount of SDS increased. Above ∼10 μM, the rate of reaggregation decreased with increasing SDS concentration; above ∼40 μM, the suspensions were colloidally stable for over a year.

Adsorption of sodium dodecyl sulfate on functionalized graphene measured by conductometric titration.

We report on the adsorption of sodium dodecyl sulfate (SDS) onto functionalized graphene sheets (FGSs) in an aqueous system, measured at broad SDS and FGS concentration ranges by conductometric surfactant titration. At dilute SDS concentrations (<12 μM in bulk solution), there is evidence of a counterion exchange between hydronium ions (from the dissociation of acidic chemical functionalities on FGS) and sodium ions coadsorbing with dodecyl sulfate monomers onto FGSs. We find that, for FGS with a carbon-to-oxygen ratio of ~18, monolayer adsorption of SDS on FGS reaches full surface coverage by ~12 μM SDS.