Leveraging polymer glass transition to access thermally-switchable shear jamming suspensions

Dense suspensions can exhibit discontinuous shear thickening (DST) and shear jamming (SJ) where interparticle frictional interactions play a vital role in constraining the relative particle motions. Recent studies have shown that these constraints as well as the macroscale rheological properties can be tuned by the particle properties, including roughness and surface chemistry. However, most theoretical and experimental studies have considered hard non-deformable particles, and little is known about the role of particle stiffness. In this work, we have developed a strategy for tunning the stiffness in situ by designing and utilizing polymeric particles with accessible glass transition temperatures (T_g). Around T_g, the elastic modulus of particles depends strongly on temperature and changes by ~3 orders of magnitude. We demonstrate that transitioning through T_g of polymer particles has a dramatic and non-monotonic effect on shear thickening and the shear jamming transition can be turned on or off in situ by varying the temperature relative to T_g. This behavior is attributed to the significant change in mechanical stiffness as well as the inter-particle surface friction near T_g. This study lays the groundwork for switchable jamming systems and motivates further research to investigate how polymer dynamics at the interface can affect the constraints on particle relative motions.