Oscillons and Propagating Solitary Waves in a Vertically Vibrated Colloidal Suspension

O. Lioubashevski1, Y. Hamiel2, A. Agnon2, Z. Reches2, and J. Fineberg1

1The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

2The Department of Geology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

Received 25 March 1999; revised 8 July 1999

The observation of localized stationary structures, coined oscillons, in granular media has evoked much interest. By parametric excitation of clay suspensions, we demonstrate a hysteretic transition to oscillon-type states in a nongranular medium. When the symmetry of up-down reflection+time translation is lost, these states undergo a transition to propagating localized states previously seen in Newtonian fluids. These observations are in accord with recent theoretical predictions of sufficient conditions for oscillon formation. In addition, a novel measurement technique for the effective suspension viscosity demonstrates their shear-thinning properties.