Abstract:Prior research into the liquid-phase exfoliation of graphite to produce few-layer graphene has focused primarily on the surface energy matching between graphite and solvent; however, the effect of other solvent properties, such as liquid viscosity, have not been systematically explored. In principle, a higher viscosity solvent should enable the production of graphene and other graphitic nanomaterials by liquid-phase exfoliation at lower shear rates than traditionally used organic solvents of low viscosity, such as N-methyl-2-pyrrolidone (NMP). Thus, at a given shear rate, more material should be exfoliated in the higher viscosity solvent. Hence, graphite suspensions in NMP, benzyl benzoate, and propylene glycol were exfoliated at various shear rates in a rheometer. Exfoliant concentrations were measured by ultraviolet- visual (UV-vis) spectroscopy and quality characterization was performed by Raman spectroscopy and scanning electron microscopy (SEM). Graphite exfoliation in the more viscous propylene glycol solvent resulted in a higher exfoliant concentration than in the less viscous NMP and benzyl benzoate solvents across all shear rates. Benzyl benzoate lowered exfoliant levels, likely due to a poor surface energy match, resulting in particle attraction and aggregation. Characterization showed that at least some of our material is few-layer graphene.
Shear flow behavior and dynamic viscosity of few-layer graphene nanofluids based on propylene glycol-water mixture
