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Interfacial effects in fluid-particles systems

Alban Sauret Surfaces du Verre et Interfaces, UMR 125 CNRS/Saint-Gobain, aubervilliers

The interactions of non-Brownian particles and liquids contribute to the complexity of many environmental, industrial and biological processes, including the preparation and transport of slurry, the contamination of surfaces, and the flow of suspensions. However, the local fluid-particle interactions that are required to describe situations where interfacial forces come into play cannot be captured by classical rheological approaches. In this talk, I will discuss two examples of recent studies in which we address this complex coupling.

I will first consider the flow of a dry granular material on a wet granular susbtrate. This situation is important in industrial blending and geophysical processes, yet it remains poorly understood because of the interplay between the particles, the fluid and interfacial effects. Our experiments show that the wet granular bed grows over time by trapping of the flowing dry particles. The accretion rate exhibits a complex time dependence that we rationalize by accounting for the local mechanisms of grain capture. In the second part of the talk, I will describe thin-film flows of suspensions when the thickness of the liquid layer is comparable to the particle size, which leads to unexpected dynamics. Indeed, in this situation, the particles deform the liquid interface, which modifies the transport of particles and could result in the contamination of the surface and the loss of transported material but also modify the stability of the liquid film.