Deformation upon impact of a concentrated suspension drop

Abstract

We study the impact between a plate and a drop of non-colloidal solid particles suspended in a Newtonian liquid, paying specific attention to the case when the particle volume fraction, φ, is close to-or even exceeds-the critical volume fraction, φ c , at which the steady effective viscosity of the suspension diverges. We use a specific concentration protocol together with an accurate determination of φ for each drop, and we measure the deformation β for different liquid viscosities, impact velocities and particle sizes. At low volume fractions, β is found to follow closely an effective Newtonian behaviour, which we determine by documenting the low-deformation limit for a highly viscous Newtonian drop and characterizing the effective shear viscosity of our suspensions. By contrast, whereas the effective Newtonian approach predicts that β vanishes at φ c , a finite deformation is observed for φ > φ c. This finite deformation remains controlled by the suspending liquid viscosity and increases with increasing particle size, which suggests that the dilatancy of the particle phase is a key factor in the dissipation process close to and above φ c .