title: Solvent-exfoliated graphene at extremely high concentration.
abstract: We describe three related methods to disperse graphene in solvents with concentrations from 2 to 63 mg/mL. Simply sonicating graphite in N-methyl-2-pyrrolidinone, followed by centrifugation, gives dispersed graphene at concentrations of up to 2 mg/mL. Filtration of a sonicated but uncentrifuged dispersion gives a partially exfoliated powder that can be redispersed at concentrations of up to 20 mg/mL. However, this process can be significantly improved by removing any unexfolaited graphite from the starting dispersion by centrifugation. The centrifuged dispersion can be filtered to give a powder of exfoliated few-layer graphene. This powder can be redispersed at concentrations of at least 63 mg/mL. The dispersed flakes are ~1 μm long and ~3 to 4 layers thick on average. Although some sedimentation occurs, ~26-28 mg/mL of the dispersed graphene appears to be indefinitely stable.
authors.affiliation: School of Physics and CRANN, Trinity College Dublin, Dublin 2, Ireland.
authors.forename: Umar
authors.initials: U
authors.lastname: Khan
authors.forename: Harshit
authors.initials: H
authors.lastname: Porwal
authors.forename: Arlene
authors.initials: A
authors.lastname: O'Neill
authors.forename: Khalid
authors.initials: K
authors.lastname: Nawaz
authors.forename: Peter
authors.initials: P
authors.lastname: May
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Coleman