Optimisation of Graphene Production via Liquid Phase Exfoliation

Graphite particles dispersed in a solvent can be exposed to high shear stresses in order to produce graphene in a process called liquid phase exfoliation. Shear stress is commonly understood to be the leading `parameter’, as it overcomes the van der Waals interlayer force and leads to exfoliation. By studying two exfoliation processes with different hydrodynamics, however, it has become apparent that both shear stress {\it and} particle residence time play important roles in production output. In one setup, a thin film flowing over a spinning disc, increasing the rotational speed and/or flow rate leads to an increased radial velocity, thereby directly reducing the amount of time the particles were exposed to the shear. In the second setup, based around Taylor-Couette flow, the influence of both the pump speed and rotational speed of the cylinder have a significant effect on the resultant graphene production rate. Detailed experimental and CFD studies, including DNS of the rapidly rotating thin films and LES of the Taylor-Couette flow, were performed in order to investigate the underlying mechanisms associated with exfoliation and determine the optimal operating points.