(243a) Anomalous Rheological Aging of a Model Thermoreversible Colloidal Gel Following a Thermal Quench

In this work, we investigate the aging behavior in a well-studied model system comprised of a colloidal suspension of thermoreversible adhesive hard spheres (AHS) but thermally quenched below the gel transition to much larger depths than previously studied. The aging behavior in the model AHS system is monitored by small amplitude oscillatory shear rheology measurements conducted while rapidly quenching from liquid state at 40°C to a temperature below the critical gel temperature and new, anomalous aging behaviors are observed. Shallow quenches lead to monotonic development of the elastic modulus with time consistent with prior reports for the development of a homogeneous gel (Gordon et al., JOR 2017). However, for deeper quenches, a unique and new phenomenon is reported – namely after an initial rise in the modulus, a reproducible drop in the modulus at a time period of 300 – 1000 s is observed, followed by a plateau in the modulus value. This drop can be gradual or sudden, and the extent of the drop, both depending on the quench depth. After this drop in modulus, the AHS gel evolves toward a quench-path independent state over the experimental timescale. These effects of the extent of quenching on aging behavior is hypothesized to be a consequence of quenching into different underlying thermodynamic states of colloidal gels and the possible influence of the adhesive glass dynamical arrest for the deepest quenches. The research connects homogeneous gelation with heterogeneous gel formation due to phase separation and shows that the extent of quench can be used as an independent parameter to govern the rheological response of the arrested gel.