BLANC - Blanc

Analysis of Non Isotropic Suspensions Organisation – ANISO

Submission summary

Non-dilute particle suspensions are widely met in nature (biological fluids, clays,...) as well as in industry (cosmetics, food industry, coatings, paints,...). When the particle overall length-scale is of the order of a micron, these suspensions are often referred to as colloids. This length-scale is of major importance since it controls the ability of the suspension to form large-scale structures, because mechanical, thermal and gravitational particle energies are of the same order of magnitude. Such structures can be observed for example in biological tissues or in clays. Colloids made of non-isotropic particles, like disks or fibers, have remarkable mechanical properties due to possible large-scale orientation. For example, under flow conditions, a global particle orientation decreases the effective viscosity of the suspension. Such properties are of major importance for the understanding of landslide triggering. They also enable to design interesting fluids that can be used in various industrial devices (drilling fluids, food industry or cosmetics). The goal of the present project is to analyse these orientation phenomena within flows of colloidal anistropic suspensions, together with their effect on the mechanical properties of the material (viscosity, yield stress - sol/gel transition - viscoelasticity). These analyses will be led on suspensions with particles of various shapes (1D : fibre-like particle, or 2D : disk-like particle), and displaying various anisotropies and size (from a few tens of nanometers to a few microns). A large number of previous studies concerned fiber suspensions. In contrast, suspensions of 2D (disks-like) or 3D objects received much less attention in the past. Because such materials are widely met, especially in minerals, they will therefore be at the core of the present project. In particular it has been recently shown, by most of the members of this project, that generally accepted hypotheses about the structure of these objects (e.g. "house of cards") were inappropriate. New models are therefore to be elaborated. In addition to the particle size and shape, the particle concentration is a key parameter for the understanding of the structural properties of suspensions. Large concentrations lead to a nematic state (preferential large-scale particle orientation) as the free space around the inclusions decreases. Experiments involving specific characterization tools will be developed, according to the optical properties of the medium. For transparent materials, particle orientation mainly lead to birefringence properties. For very turbid media, multiple light diffusion will be an appropriate tool. In all cases, X-rays dispersion at small angle will provide quantitative results which will be used as a reference for the other optical tools. All these non-intrusive measurements will be performed in a flow device enabling simultaneous rheological measurements. Our goal is indeed to model the link between the particle morphology, physico-chemical environment, its average orientation and the mechanical properties of the suspension. Existing models involving spherical particles with multiple hydrodynamic interactions will be re-visited and generalized to non-isotropic objects. For oriented particles, effective theories, partially validated on 1D (fiber) inclusions, will be generalized to 2D objects. Finally, all these approaches will be applied to real flows, like pipe flows or elongational flows.

Project coordination

Christophe BARAVIAN (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 400,000 euros
Beginning and duration of the scientific project: - 48 Months

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