Experimental Signature of the Pair Trajectories of Rough Spheres in the Shear-Induced Microstructure in Noncolloidal Suspensions

The shear-induced microstructure in a semidilute noncolloidal suspension is studied. A high-resolution pair distribution function in the plane of shear is experimentally determined. It is shown to be anisotropic, with a depleted direction close to the velocity axis in the recession quadrant. The influence of roughness on the interaction between particles is quantitatively evidenced. The experimental results compare well with a model from particle pair trajectories.

Figure 1

Typical image. $\varphi =5\%$. Only the origin particles in the white box are considered.

Figure 2

(a) Pair position vector relative to the local azimuthal flow direction (b) $a_{\mathrm{app}}$ is the apparent radius of the particle.

Figure 3

Pair distribution function in the plane $(\overrightarrow{v},\overrightarrow{\nabla }v)$. $\varphi =5\%$. The approach quadrants are defined by $xy<0$. Up: magnification of the central region.

Figure 4

PDF averaged over the $\rho$ interval [$1.97a$ $2.04a$]. The approach quadrant is $\theta \in [90°,180°]$.

Figure 5

Trajectory from the point $x/a=-10$, $y/a=0.5$, $z/a=0$ for different values of the roughness $ϵa$.

Figure 6

(a) PDF from particle trajectories. The roughness is $ϵ=3\times {10}^{-3}$. Red line: a trajectory in the plane of shear for which contact occurs. (b) AFM image of the particle surface.

Figure 7

Experimental (symbols) and computed (lines) PDF. (a) $g(\rho ,\theta )$ vs $\theta$ ($\circ$) $1.97<\rho <2.04$; ($*$) $2.31<\rho <2.38$; ($-$) $1.93<\rho <2.00$; ($--$) $2.33<\rho <2.40$; (b) $g(\rho ,\theta )$ vs $\rho /a$ ($\circ$) $0<\theta <4.5$; °($*$) $18°<\theta <22.5°$; ($△$) $85.5°<\theta <90$; °; ($-$) $0<\theta <4.5°$; ($--$) $18°<\theta <22.5°$; ($-·$) $85.5°<\theta <90°$.