Shear-Induced Stack Orientation and Breakup in Cluster Glasses of Ring Polymers

Cluster glass-phase ring suspensions exposed to weak shear stress exhibit a stable reorientation of stacks as well as of individual ring polymers with the flow direction and into the flow-vorticity plane. The suspension features shear thinning for a variety of different densities as a result. Under strong shear, a breakup of these clusters takes place, accompanied by a subsequent homogenization of the distribution of centers-of-mass of rings, though their orientational preference is maintained. The flow properties of the system are determined by an interplay between the deformability of the constituent particles of the rings and the response of the anisotropic clusters to shear. We employ mesoscopic simulations to investigate and quantify this behavior as well as to provide an explanation for the underlying mechanism, and we show our findings are qualitatively independent of the consideration or disregard of hydrodynamic interactions. After cessation of shear, the system displays strong memory as regards the stack orientation, although individual rings relax into their equilibrium orientation. Potential applications include the possibility to tune the mechanical properties of the material via molecular architecture and rigidity, as well as the flexibility in creating persisting anisotropies in the material as a result of applied shear.