A model for short-range interactions in fibre suspensions

This paper introduces a model for short-range fibre-fibre interaction and combines it with the Shaqfeh-Fredrickson result for long-range hydrodynamic interactions. The short-range interactions are assumed to be localised, such that the interaction forces may be taken to act at points on the fibre axes. Only interactions of viscous Newtonian character are explored in this work; the approach, however, may be used to treat more general nonlinear interactions, such as non-Newtonian vicous forces or friction. To simulate the orientation evolution, a convective discretisation technique combined with a modification of the Folgar-Tucker rotary diffusion model is proposed. The rotational parallel-plate geometry is analysed, and transient as well as steady state responses are computed. Experiments are performed on suspensions of polyamide fibres in silicon oil, using a rotational parallel-plate rheometer. It is demonstrated that the effect of fibre volume fraction and aspect ratio are well captured by this theory. Normal force as well as torque is adequately predicted. Other effects, however, such as shear thinning and effect of absolute particle size, are not predicted by the linear theory.