Flow-induced structural reponses of attractive colloidal dispersions

Flow-induced structural reponses of attractive colloidal dispersions

Thu, 13/06/2024


Publication of the Physics Laboratory in the Journal of Rheology on April 11, 2024.

In a recent study, a team of scientists led by researchers from the Physics Laboratory of ENS de Lyon (CNRS/ENS de Lyon) focused on the flow-induced responses of colloidal dispersions. Their work provides a better understanding of how colloids structure themselves under the effect of shear, an important step towards understanding this essential process in many industrial applications. Their findings were published in the Journal of Rheology.


The rheological behavior of colloidal dispersions is of paramount importance in a wide range of applications, including construction materials, energy storage systems and food industry products. These dispersions consistently exhibit non-Newtonian behaviors, a consequence of intricate interplays involving colloids morphology, volume fraction, and inter-particle forces. Understanding how colloids structure under flow remains a challenge, particularly in the presence of attractive forces leading to clusters formation. In this study, we adopt a synergistic approach, combining rheology with ultra small-angle X-ray scattering (USAXS), to probe the flow-induced structural transformations of attractive carbon black (CB) dispersions and their effects on the viscosity. Our key findings can be summarized as follow. First, testing different CB volume fractions, in the high shear rate hydrodynamic regime, CB particles aggregate to form fractal clusters. Their size conforms to a power law of the shear rate, ξc∝γ˙−m, with m≃0.5. Second, drawing insights from the fractal structure of clusters, we compute an effective volume fraction ϕeff and find that microstructural models adeptly account for the hydrodynamic stress contributions. We identify a critical shear rate γ∗˙ and a critical volume fraction ϕ∗eff, at which the clusters percolate to form a dynamical network.

The size of the $\xi^*$ aggregates and the $\dot{\gamma}^*$ shear rate at the percolation point allow us to rationalize the flow of attractive colloids into two regimes: the hydrodynamic regime and the elastic regime. (b) In the hydrodynamic regime, the aggregates flow like hard spheres. In the elastic regime, the percolated network already prefigures the properties of the gel formed when the shear rate tends towards zero.
credits: Thomas Gibaud. J. Rheol. 68, 429 (2024)


Attractive carbon black dispersions: Structural and mechanical responses to shear. Julien Bauland, Louis-Vincent Bouthier, Arnaud Poulesquen, and Thomas Gibaud. Journal of Rheology, April 11, 2024.
DOI : 10.1122/8.0000791
Open archive arXiv: 10.48550/arXiv.2403.10262

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