Quenching and annealing strategies for structural and rheological control of thermoresponsive colloidal gels

Complex thermal processing strategies using annealing and quenching of phase instability have been a conserved motif since antiquity to generate materials with exceptional mechanical properties. However, these strategies have been largely inaccessible to colloidal gels and glasses due to their slow dynamics, difficulties with controlled quenching, and knowledge gaps in the interplay of gelation and phase separation processes. To overcome these challenges, we present studies on model colloids with thermosensitive polymer linkers, in which programmed temperature control provides a facile means to sculpt structure formation, aging and rheology of nascent colloidal gels. Using controlled rate quenches en route to gelation, we show that one can produce gels whose rheological properties vary by orders of magnitude depending on the dwell time in the region of phase instability. Rheo-microscopy establishes the quench-dependent microdynamics of coarsening that underly this control, and is used to inform the design of step-wise quench-anneal-quench protocols for fine control of the length scales of phase separation and rheology in deeply arrested gels. Our results show promise for the design of complex thermokinetic processing strategies to achieve fine-tuned or exotic rheological properties in gelling systems.