Rapid monitoring of graphene exfoliation using NMR proton relaxation.

Graphene is now being produced on an industrial scale and there is a pressing need for rapid in-line measurements of particle size for Quality Assurance and Quality Control (QA/QC). Standardised characterisation techniques such as electron microscopy and scanning probe microscopy can be time consuming and may require pre-processing steps and/or solvent elimination prior to measurements. Herein, we demonstrate the use of nuclear magnetic resonance (NMR) proton relaxation as a powerful method for monitoring the sonication assisted liquid phase exfoliation of graphene. This technique requires little or no sample preparation and the resulting spin-spin relaxation time showed a strong correlation with particle size, exfoliation yield and specific surface area measurements. As the NMR proton relaxation method is rapid, inexpensive, and can potentially be operated in-line, it shows great promise to become a valuable QA/QC method for graphene production methods in liquid.