PHYSICAL REVIEW LETTERS, 2000, 85 (22), 4819

Michel Cloitre,* Régis Borrega,' and Ludwik Leibler

Laboraloire CNRS-ATOFINA, 95, rue Danton, 92303 Levallois-Perret, France

(Received 3 April 2000)

We have studied experimentally the rheological behavior of concentrated suspensions of soft deformable microgels below the yield point. We have found history-dependent effects which are interpreted in terms of aging and rejuvenation phenomena, analogous to those existing in glassy systems. The stress amplitude controls the long-time memory and determines the slow evolution of the suspensions.

PACS numbers :: 83.70.Hq, 61.20.Lc~ 62.20~Fe