(532b) Engineering Stimuli-Responsive Particles for Controlling Dense Suspension Rheology

In polymers, temperature can trigger dramatic changes in the mechanical properties. This has enabled researchers to engineer versatile adaptive materials that can change in mechanical modulus or shape at targeted temperatures, finding applications in adhesives, fabrics and shape-memory materials. However, most applications of temperature-responsive polymers focus on the bulk mechanical properties and there are few examples of utilizing such materials to regulate the non-Newtonian rheological properties of solid particle suspensions. In this work, we demonstrate that stimuli-responsive particles can provide new avenues for regulating the rheological properties of dense suspensions.

In our first system, we designed suspensions that contain particles with accessible polymer glass transition temperatures (Tg). By varying the temperature relative to , the mechanical stiffness and interparticle friction forces can be controlled. This straight-forward strategy enables the in situ turning on (or off) the system’s ability to shear jam. The second system explored consists of sticky particles where the shape is programmable and temperature responsive. We demonstrate that at low temperatures, dense suspensions of anisotropic particles show high yield stress and shear thinning rheology. At elevated temperatures, the anisotropic particles become spherical and the suspension displays low yield stress and mild shear thickening. The results demonstrate how the shape memory effects of the particles can be leveraged to control the yielding behavior. Together, these works lay the groundwork for other types of stimuli-responsive jamming systems through polymer chemistry and help to elucidate how the microscopic single-particle properties can lead up to the changes in macroscopic flow properties.