Suspensions of polymeric nano- and microparticles are fascinating stress-responsive material systems that, depending on their composition, can display a diverse range of flow properties under shear, such as drastic thinning, thickening, and even jamming (reversible solidification driven by shear). However, investigations to date have almost exclusively focused on nonresponsive particles, which do not allow in situ tuning of the flow properties. Polymeric materials possess rich phase transitions that can be directly tuned by their chemical structures, which has enabled researchers to engineer versatile adaptive materials that can respond to targeted external stimuli. Reported herein are suspensions of (readily prepared) micrometer-sized polymeric particles with accessible glass transition temperatures (T g) designed to thermally control their non-Newtonian rheology. The underlying mechanical stiffness and interparticle friction between particles change dramatically near T g. Capitalizing on these properties, it is shown that, in contrast to conventional systems, a dramatic and nonmonotonic change in shear thickening occurs as the suspensions transition through the particles’ T g. This straightforward strategy enables the in situ turning on (or off) of the system’s ability to shear jam by varying the temperature relative to T g and lays the groundwork for other types of stimuli-responsive jamming systems through polymer chemistry.

When sheared sufficiently strongly, suspensions having a large volume fraction of solid particles can exhibit a dramatic increase in viscosity (shear thickening) and even solidify (shear jamming). Investigations to date have almost exclusively focused on rigid, non-responsive particles, which do not allow in situ tuning of shear thickening or jamming. Here we report suspensions of polymeric micron-sized particles with accessible glass transition temperatures Tg) designed to control their non-Newtonian rheology. The underlying mechanical stiffness and interparticle friction between particles change dramatically near Tg. We capitalize on these properties and show that, in contrast to conventional systems, a dramatic and non-monotonic change in shear thickening is observed as the suspensions transition through the particles’ Tg. This behavior enables the in situ turning on or off of shear jamming by varying the temperature relative to Tg, and lays the groundwork for thermally switchable jamming systems.