CE30 - Physique de la matière condensée et de la matière diluée

Flowing dynamics of microscopic granular materials – MicroGraM

Submission summary

Granular and colloidal suspensions share some similarities, as they are both made of an ensemble of individual particles (grains or colloids) dispersed into a liquid. However, granular suspensions are always considered in the athermal regime, where the thermal agitation has no influence at all, whereas colloidal suspensions are often considered in regimes where the thermal agitation dominates every other force, or where the suspensions are very dilute. Therefore, the flowing properties of materials in the intermediate regime, where both thermal forces and contacts between grains play a role, remain largely unexplored.

This experimental project aims to study avalanches dynamics in suspensions of colloidal particles, dense enough to settle and form well-defined piles, but small enough to be sensitive to thermal noise, as an archetype of granular material submitted to a weak (but controlled) external agitation.

The experiments will use microfluidic fabrication techniques, a custom-built horizontal microscope (whose observation plane is vertical), and video-microscopy analysis.

It will focus on the following three main scientific goals:
1) Study the flowing properties of “Brownian granular materials” at different scale, with rotating drum experiments. In particular, identify the transition between the thermal and athermal regimes in avalanche dynamics at the top of a flowing pile, and characterize the rearrangements occurring inside the pile, as a function of the relative amplitude of the thermal agitation with respect to the gravity force.
2) Identify the role of chosen external parameters on the flowing properties of dense colloidal suspensions. In particular, focus on the frictional interactions between the grains (which we can tune in colloidal suspensions), and study the role of polydispersity that induces peculiar behaviors both in macroscopic granular materials and in powder systems.
3) Use the system as a benchmark to gain new insights about granular systems submitted to external perturbations. In particular, reproduce typical geometries used in macroscopic systems to make direct comparison between thermal agitation and other sources of forcing, and identify if mechanical noise sources can really be seen as “effective temperatures” or not.

Project coordination

Antoine Bérut (INSTITUT LUMIERE MATIERE)

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

ILM INSTITUT LUMIERE MATIERE

Help of the ANR 188,384 euros
Beginning and duration of the scientific project: December 2021 - 48 Months

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