Path-dependent rheological and structural properties of binary gels from thermoresponsive soft particles

The interaction potential for colloidal-sized polymer microgels can be switched from soft repulsive to attractive due to a thermoresponsive collapse of the particles, and raising the temperature destabilizes these suspensions, causing aggregation and macroscopic gelation. Particularly interesting is the use of binary mixtures of microgels with different collapse temperature, where the choice of the heat ramp allows for an unprecedented control over the gel structure and the rheological properties. A fast or slow temperature ramp results in either a random binary network through homo-gelation, or a core-shell network through sequential gelation, respectively. The core-shell architecture is shown to enhance the structural integrity of the previously formed single species gel, and the final structure exhibits higher elastic and loss moduli than the compositionally identical random network. We use a combination of linear and non-linear rheology, confocal microscopy and computer simulations to investigate the relationship between kinetic pathway, multi-scale structure and linear and rheological properties, and demonstrate that binary microgel mixtures can controllably and reversibly self-assemble into particle gels with tunable structural and mechanical properties.