Flow-induced aggregation of colloidal particles in viscoelastic fluids

The flow-induced aggregation of dilute colloidal polystyrene nanoparticles suspended in Newtonian and viscoelastic solutions is reported. A rheo-optical method has been used to detect real-time aggregation processes via measuring optical absorption or scattering in a quartz Couette cell. The observed absorbance decreases over time are attributed to the flow-induced coagulation. Numerical simulations show that the aggregation processes still follow the Smoluchowski coagulation equation in a revised version. Suspensions in a series of media are studied to evaluate the effect of the media rheological properties on the particle aggregation. The data shows that elasticity reduces the aggregation while the solution viscosity enhances the aggregation processes.

Figure 1

(a) Viscosity and (b) $G^{\prime }$ (solid) and $G^{\prime \prime }$ (hollow) versus shear rate and frequency of the solutions used in the experiments.

Figure 2

Schematic of optical Couette flow apparatus ($r=4.90$ mm, $R=5.00$ mm) [7].

Figure 3

(a) Normalized UV and visible absorption spectra of the AP30-50-2 suspension (the solvent background has been subtracted) experimentally (black line) and simulatively (red dash line). (b) Absorbance (at 250 nm) changes with time in the Couette flow of 282/s experimental (black curve) and simulation (red dots).

Figure 4

The aggregation radius versus time in the AP30-50-2 suspension under the Couette flows with different shear rates.

Figure 5

$ln\left(\kappa \eta \right)$ versus $\sigma$ in the (a) Newtonian and (b) non-Newtonian suspensions.

Figure 6

(a) $\xi$ versus sodium ions concentration in AP30-50-X series suspensions (black squares) and Newtonian suspensions (red dots). (b) $\xi$ versus ${\eta }_m$: black dash line for AP30-50-X series samples and black dot line for AP30-X0-2 series samples; the red dashed line is for Newtonian suspensions and the red circle represents the Newtonian suspension with the same water-glycerol fraction as the AP30-50-X series samples.