Structural and rheological aging in model attraction-driven glasses by Rheo-SANS.

Abstract

Aging in a model colloidal suspension comprised of particles with a thermoreversible attraction is studied using Rheo-SANS techniques in the attractive-driven glass state. Multiple thermal pathways lead to a common rheological and microstructural aging trajectory, as was observed previously for a thermoreversible gel. SANS measurements of the colloidal glass microstructure as a function of temperature and time during various quench protocols are quantitatively characterized in terms of an effective interaction strength that becomes an order parameter defining the microstructural state of the glass. Using previously validated concepts of a fictive temperature, a semi-empirical, quantitative relationship similar to an Avrami relationship is established between the mechanical aging (elastic modulus) and microstructural aging (order parameter) that is independent of thermal history for the thermal profiles studied herein at long times. Furthermore, shear rejuvenation is studied, and while shear may only partially reduce the degree of structure in the glass, aging upon flow cessation is found to follow a common trajectory when viewed in terms of the microstructural order parameter.