Aging and Glassy Behaviors in a Model Soft Colloidal System

In the vicinity of glass transition, colloidal and molecular systems share similar behaviors. Inspired by temperature jump aging experiments in molecular systems, volume fraction up-jump experiments (induced by temperature down-jumps) were used to study both aging responses and equilibrium dynamics for a thermoresponsive PS-PNIPAM/AA soft colloidal system using light scattering (diffusing wave spectroscopy, DWS). Long-term aging responses were investigated under both equilibrium and non-equilibrium conditions. In the equilibrium state, liquid-to-glass transitions were observed as effective volume fraction increases. For the equilibrium $\alpha $-relaxation processes, the $\alpha $-relaxation time of the samples aged into equilibrium deviate from the Vogel-Fulcher-Tammann (VFT)-type expectations and the super-Arrhenius signature disappears below the glass transition volume fractions. The non-equilibrium aging responses of the samples show decoupling of the $\alpha $-relaxation time and the time for the structural evolution into equilibrium. As a microrheological method, DWS was found to probe the dynamics of the investigated colloidal systems differently from macroscopic rheology when in non-equilibrium regimes.