Abstract

Liquid-based production and processing techniques of graphene require graphene nanoparticles to be suspended in flowing liquids. Made from just a few atomic layers, the instantaneous dynamics of these plate-like particles in flowing liquids is, experimentally, practically inaccessible. We study theoretically and computationally the micro-hydrodynamics and rheology of dilute suspensions of graphene in a simple shear flow field. In the infinite Péclet number limit, a rigid platelet with the interfacial surface slip properties of graphene does not follow the periodic rotations predicted for classical colloidal particles but aligns itself at a small inclination angle with respect to the flow. This unexpected result is due to the surface slip reducing the tangential stress at the graphene-solvent surface. By analysing the Fokker-Plank equation for the orientational distribution function at all Péclet numbers, we explore how surface slip affects the flow and rheology of graphene suspensions. We find that surface slip can dramatically change the macroscopic behaviour of the suspension. For example, the average orientation of a dilute suspension of platelets is expected to increase for typical slip length values of graphene, and the effective viscosity of the suspension is predicted to drop significantly.