Rheological characterization of aging in a concentrated colloidal suspension

Suspensions of soft particles display a rheological transition when their concentration is increased: above a critical concentration, they become pasty and display a yield-stress. We report experiments on silica suspensions in the pasty phase that show how the response of the system to the application of mechanical perturbations depends on its history. Stress relaxation experiments performed after different waiting times clearly show aging taking place in the pasty phase, characterized by an aging exponent of order mu similar to 0.5-0.7. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.