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Soft Matter and Biological Physics


Eur. Phys. J. E 4, 59-68

Systematic study of the settling kinetics in an aggregating colloidal suspension

D. Senis, L. Gorre-Talini and C. Allain.

Laboratoire FAST, Bât. 502 - Campus Universitaire, 91405 Orsay Cedex, France

talini@fast.u-psud.fr

(Received 13 October 1999 and Received in final form 21 April 2000)

Abstract
We present a study of the settling of a strongly-aggregating colloidal suspension. Using well-controlled samples, the different settling behaviours have been systematically investigated according to the values of the volume fraction $\Phi$ of the suspension and of the inclination angle of the cell. In a vertical cell, three velocity regimes are observed. To describe the first and final regimes, we propose a simple 1D model that takes into account the microscopic structure of the gel constituted by a packing of fractal aggregates. The second regime coincides with the opening of fractures within the gel and its description would require a more complex model. When the cell is inclined at an angle $\alpha$ to the vertical, new settling regimes can emerge and an enhancement of the settling velocity can be observed as in usual macroscopic suspensions. Using both our 1D model and arguments similar to the ones used for macroscopic suspensions (PNK model), we propose a description of the influence of inclination that is in good agreement with the experimental data. We also present the various experimental settling behaviours we have observed in a $\Phi$ vs. $\alpha$ diagram that covers the whole range of experimental conditions.

PACS
82.70.Dd - Colloids.
47.20.Bp - Buoyancy-driven instability.
61.43.Hv - Fractals; macroscopic aggregates (including diffusion-limited aggregates).


© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001