Dynamics of DNA-bridged particle dumbbells in well-entangled, shear-banding polymer solutions under large amplitude oscillatory shear (LAOS)*

Despite accumulation of experimental evidence for shear-banding flows in highly entangled polymer solutions over the last two decades, the current understanding of the conformational changes that induce shear banding remains incomplete. To elucidate the microscopic dynamics of entangled chains in shear-banding flows, we study the dynamics of DNA-bridged particle dumbbells in the shear-banding flow of well-entangled double-stranded DNA (dsDNA) solutions under LAOS using a rheo-confocal shear cell. First, we confirm that the velocity profiles of the entangled dsDNA solutions become inhomogeneous and strong shear-banding flows arise at high Weissenberg number. We then analyze the translation and orientation of particle dumbbells in the co-existing high- and low-shear rate bands. The orientational distribution of dumbbells exhibits clear difference in the co-existing bands. Moreover, we find that the coupling between sudden reorientation and rapid translational motion of dumbbells occurs exclusively in the high-shear rate band. Quantitative investigation of the spatially distinct dynamics of such dsDNA-bridged dumbbells provides new insights into the microscopic structural origin of shear-banding flows in entangled polymer solutions.