Shear-induced structures in macroscopic dispersions

Abstract

Observations are reported on structures induced in an oscillatorily sheared dispersion of glass spheres in a silicon oil and in a highly viscoelastic fluid (mixture of polyisobutylenes). The shear flow used in these experiments is oscillatory with a frequency ≈ 200 Hz) and has displacement amplitudes of the order of magnitude as the sphere diameter (40 µm).

The interpretation of the structures observed is based on non-linear effects which, even when small, in comparison to the viscous effects, may lead to the irreversible formation of structures over a “long” time, i.e. a time much larger than the period of the shear. A comparison between similar experiments performed with two different suspending fluids (silicon oil, in which the spheres line up perpendicular to the velocity direction; polyisobutylene mixture, in which the spheres line up in the velocity direction) confirm our interpretation.