Flow-induced exfoliation of graphene: understanding colloidal microphysics to produce graphene on the ton scale*

In liquid-phase exfoliation, microparticles of graphite are suspended in a liquid solvent, and the resulting colloidal dispersion is subject to energetic mixing. At a critical value of the local shear rate, layers of graphene are removed from the mother graphite particles. Liquid phase exfoliation is one of the most important production method for graphene, but its microscopic mechanics is incompletely understood. In this talk I will describe our recent work on the theoretical and computational modelling of liquid-phase exfoliation of graphene/graphite, and discuss how our work differ from related investigation on hydrodynamic breakup of colloidal aggregates. We developed two classes of models: a sliding model for relatively rigid nanosheets (Gravelle, Kamal, Botto J. Chem. Phys. 152(10) 2020) and a peeling model for graphene sheets which are able to bend (Salussolia et al., J. Mech. Phys. Solids. 134, 2020). Key conclusions of our work are that only by invoking stress amplification effects due to flow-induced fracture the predicted critical shear rates can become comparable in order of magnitude with the experimental data, and that current estimations of adhesive forces are affected by inacceptable assumptions.