Frictional effects on shear-induced diffusion for polydisperse and confined suspensions

The effects of confinement and polydispersity on the shear-induced diffusivity of non-Brownian, neutrally buoyant spheres suspended in a Newtonian fluid are investigated using simulations that incorporate short-range lubrication forces, surface roughness and frictional contacts. Simulations were performed at a fixed volume fraction of 0.45 for multiple values of particle roughness and friction coefficient. Confinement by bounding walls promoted layered structures that suppressed particle mobility and reduced diffusivity, while also diminishing the influence of friction and roughness. In contrast, high polydispersity disrupted layering and enhanced diffusivity, even in confined systems. Polydispersity also led to size-dependent demixing, with smaller particles preferentially migrating towards the walls and exhibiting higher mobility. These results have implications for modelling and controlling transport in suspensions, where confinement and polydispersity alter the effects of friction and roughness on shear-induced diffusion.