The strange case of shear-thinning in non-Brownian suspensions

Abstract

<h2>Abstract</h2> Shear thinning is generally reported in Brownian suspensions where it is understood to arise from a decrease in the relative contribution of entropic forces. However it has also been often reported in experiments with non-colloidal systems and nominally-Newtonian matrices at high volume fractions. In spite of the generality of the observations, its origin is still a matter of debate and the behaviour is difficult to reproduce in numerical simulations where shear thickening is typically observed instead. Several explanations have been proposed in recent years ranging from hidden non-Newtonian effects in the small interparticle gaps (Vázquez-Quesada et al., Phys. Rev. Lett. 117 (10), 108001 (2016), J. Non- Newt. Fluid Mech. 248, 1-7(2017)), excluded volume effects (Chatté et al. Soft Matter,14, 879-89 (2018)) and variable friction coefficients (Chatté et al.Soft Matter,14, 879-89 (2018); Tanner et al.Rheol. Acta 57:635–643 (2018); Lobry et al. J. Fluid Mech., 860, 682–710 (2019)). Another possibility that has emerged recently is related to slip occurring in the interparticle gaps at the liquid-solid interface (Kroupa et al. Phys. Chem. Chem. Phys., 19, 5979-5984 (2017); Vázquez-Quesada et al., Phys. Rev. Fluids 3 (12), 123302 (2018); Kumar et al.J. Non-Newt. Fluid Mech., 281, 104312 (2020)). In this talk I will review some of these issues and recent theories developed in this context.