Rheology of Granular Rafts

TL;DR

This study investigates the rheological behavior of granular rafts, revealing Bingham-like flow, non-local effects, and quasistatic regions, with experimental and theoretical insights into their complex shear dynamics.

Contribution

It provides the first detailed experimental and theoretical analysis of granular raft rheology, highlighting non-local effects and quasistatic zones in shear flow.

Findings

Rheology exhibits Bingham fluid behavior with diverging viscosity.

Velocity profiles show non-local rheology similar to dry granular materials.

Presence of quasistatic zones near the center of the shear cell.

Abstract

Rheology of macroscopic particle-laden interfaces, called "Granular Rafts" has been experimentally studied, in the simple shear configuration. The shear-stress relation obtained from a classical rheometer exhibits the same behavior as a Bingham fluid and the viscosity diverges with the surface fraction according to evolutions similar to 2D suspensions. The velocity field of the particles that constitute the granular raft has been measured in the stationary state. These measurements reveal non-local rheology similar to dry granular materials. Close to the walls of the rheometer cell, one can observe regions of large local shear rate while in the middle of the cell a quasistatic zone exists. This flowing region, characteristic of granular matter, is described in the framework of an extended kinetic theory showing the evolution of the velocity profile with the imposed shear stress. Measuring the probability density functions of the elementary strains, we provide evidence of a balance between positive and negative elementary strains. This behavior is the signature of a quasistatic region inside the granular raft.