Size selection of dispersed, exfoliated graphene flakes by controlled centrifugation

In this paper we describe a method to separate an existing dispersion with mean flake length of ~1 μm into fractions, each with different mean flake size

Umar Khan; Arlene O’Neill; Harshit Porwal; Peter May; Khalid Nawaz; Jonathan N. Coleman

2011

Key concepts

Scholarcy highlights

  • Liquid phase exfoliation of graphite to give graphene has received a lot of attention in recent years
  • If one chooses 500 rpm to remove only the crystallites, the result will be the initial supernatant with only small flakes, the redispersed centrifuged sediment with all other flake sizes and a second sediment containing the crystallites
  • The result will be the initial supernatant with only small flakes, the redispersed, centrifuged sediment with medium sized flakes and a second sediment with large flakes and crystallites
  • We have demonstrated that controlled centrifugation can be used to separate graphene flakes by size
  • To achieve this, we first need to determine the baseline flake size distribution achieved using standard dispersion techniques. To do this we sonicated graphite powder in 500ml of NMP in a sonic bath for 168 hrs. This was centrifuged at 500 rpm for 45 minutes and the top 80% of the supernatant pipetted off
  • Centrifugation at a lower rate results in a dispersion of slightly larger flakes and the rejection of the rest. Repeating this procedure a number of times results in the separation of the original dispersion into a number of fractions each with different mean flake length, in this case from ~1 to ~3.5 μm. We have demonstrated this procedure for solvent exfoliated graphene, it could be extended to surfactant exfoliated graphene or otherexfoliated layered compounds

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