Microgel softness alters the dynamics of tracer nanoparticles in supercooled suspensions

The elasticity of polymer microgels governs both their bulk rheological response and the transport of embedded tracer particles. How elasticity and microgel concentration affect the tracer dynamics across different concentration regimes, however, remains incompletely understood. Here, we synthesize dual‐stimuli‐responsive poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-co-PAA) microgels with tunable softness by varying the crosslink density. The microgels undergo a swelling transition near 34°C as they are cooled, and we exploit this transition to modulate microgel concentration in situ. We characterize the dynamics of polystyrene nanoparticles using particle-tracking and differential dynamic microscopy to understand how the softness of the microgels alters the local and collective transport of hard penetrants as the microgel matrix is quenched into supercooled or glassy states. Our results show how elastic compression modulates penetrant transport in microgel networks, which can be applied to the design of biological scaffolds and theranostics.