Effective viscosity of a suspension of plate-like particles with slip: MD and continuum theory*

Hydrodynamic slip can align plate-like particles in shear flow if the interfacial slip length (λ) exceeds a length scale comparable to the particle thickness. We investigate the effect of slip on the effective viscosity of a dilute suspension of graphene platelets in shear flow using Molecular Dynamics (MD). Our results show that for a given length over thickness aspect ratio k, the presence of slip induces a surprisingly large reduction in viscosity: the data suggest that at a high Peclet number (Pe>100) and k>10, the viscosity of the suspension is even smaller than that of the bare fluid. To get insights into this unexpected effect, we carried out boundary integral simulations of platelets for which a Navier slip boundary condition is imposed at the fluid-solid boundary. Obtaining trends similar to those in MD, we found that the effect of slip on viscosity becomes stronger for the particles with a larger aspect ratio. However, whether the viscosity is lower than that of the bare fluid or not depends on the threshold values of k, Pe and λ.