Impact-induced solidlike behavior and elasticity in concentrated colloidal suspensions

Modified drop weight impact tests were performed on $\mathrm{Si}{\mathrm{O}}_2$–ethylene glycol concentrated suspensions. Counterintuitive impact-induced solidlike behavior and elasticity, causing significant deceleration and rebound of the impactor, were observed. We provide evidence that the observed large deceleration force on the impactor mainly originates from the hydrodynamic force, and that the elasticity arises from the short-range repulsive force of a solvation layer on the particle surface. This study presents key experimental results to help understand the mechanisms underlying various stress-induced solidification phenomena.

Figure 1

(a) Viscosity vs shear rate curves for silica particle–ethylene glycol colloidal suspensions; (b) SEM image of silica particles.

Figure 2

Deceleration force, deformation of the suspension (or displacement of the impactor), and impactor velocity vs time for the 65.5 wt % silica suspension under initial impact speeds of (a) $1.07\mathrm{m}{\mathrm{s}}^{-1}$, (b) $1.55\mathrm{m}{\mathrm{s}}^{-1}$, and (c) $2.03\mathrm{m}{\mathrm{s}}^{-1}$.

Figure 3

(a) A summary of deceleration force vs time curves under various impact speeds. (b) Impact stress-strain rate vs strain rate curves of the 65.5 wt % silica suspension.

Figure 4

Deceleration force, deformation of the suspensions (or displacement of the impactor), and impactor velocity vs time for the 69 wt % silica suspension under initial impact speeds of (a) $1.03\mathrm{m}{\mathrm{s}}^{-1}$, and (b) $1.53\mathrm{m}{\mathrm{s}}^{-1}$. The inset in (a) shows a small force peak after the test starts.

Figure 5

(a) Impact stress-strain rate vs strain rate curves of the 69 wt % silica suspension. The arrows indicate the change in the strain rate during the impact test. (b) Deceleration force-strain rate vs interparticle distance curves for 69 wt % suspensions under different initial impact speeds. The figure also indicates that the experimental results can be approximately described by the function $\mathrm{y}=b/\mathrm{x}$ (the curve indicated by “Curve fit” in the figure).

Figure 6

Schematic illustration of the concentrated suspensions under impact. The suspension is represented by a line of particles (of exaggerated size), and the boundary is the bottom of the container.