Achieving high yield of graphene nanoplatelets in poloxamer-assisted ultrasonication of graphite in water

摘要： The role of surfactant (Pluronic? F 127) concentration on the yield and morphological characteristics of graphene nanoplatelets (GNPs) produced from the sonication of aqueous graphene suspensions is investigated in this work. By employing a wide surfactant concentration range (0.1–15 wt%) and sonication power densities up to 420 W L?1 we identify two graphene exfoliation regimes: the first occurs at low sonication power densities (<340 W L?1) and produces GNPs with sizes 200–300 nm, aspect ratios between 70 and 100, and concentrations up 1 mg mL?1. In that regime, the surfactant concentration has no effect on the exfoliation results. In the second exfoliation regime (>340 W L?1), surfactant concentrations greater than 10 wt% produce dramatic increases in GNP yields, namely up to 3.0 mg mL?1, and overall larger GNPs (350–500 nm) with smaller aspect ratios (5–60). We attribute these changes to the onset of a more energy intensive mechanism, termed cleavage. Cleavage involves the separation of graphite clusters in sub-bulk multi-layered graphene entities, as opposed to exfoliation, which involves the separation of individual or few-layer GNPs. Choosing an exfoliation regime by tuning simple process parameters enables control over the yield, size and morphology of the produced GNPs.