Graphene Nanoplatelet Production Through Non-Ionic Surfactant-Assisted Exfoliation of Graphite
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Liquid phase exfoliation of graphite is performed using ultrasonication and shear exfoliation to produce graphene nanoplatelets (GNPs). Ultrasonication is performed using a tip sonicator under power loads ranging from 35-100% amplitude (corresponding to power of 9-36 W) and concentrations of Pluronic® F127 surfactant in water ranging from 1-15 wt%, under batch and sequential addition of surfactant modalities. Shear exfoliation is achieved using a lab scale shear mixer operated with rotor speeds ranging from 1500 rpm to 8000 rpm and Pluronic® F127 concentrations ranging from 1-10 wt%. Ultrasonication exfoliation demonstrated GNP concentrations as high as 3.01 mg·mL-1 at 100% amplitude and 15 wt% surfactant concentration. The average particle sizes of the nanoplatelets, were approximately 200-550 nm for all exfoliation methods as estimated through dynamic light scattering (DLS). Transmission electron microscopy (TEM) characterization revealed particle sizes on the order of hundreds of nanometers in lateral dimension. Ultrasonication resulted in few-layer graphene, with thickness ranging from 4-77 nm as measured by Atomic Force Microscopy (AFM) and aspect ratios of 36-96. Shear mixing generated multi-layer graphene, with thickness ranging from 6-11 nm and aspect ratios of 25-72. Both processes were modeled using dimensional analysis, which revealed that high yields can be achieved beyond specific thresholds of power density input, rotation speed, and surfactant concentration. Based on the results, shear mixing presents itself as a promising method that can be readily scalable above a rotor speed threshold.