(503b) Visualization of Polymer Dynamics of Highly Entangled Shear-Banding Polymer Solutions Under Large Amplitude Oscillatory Shear (LAOS)

In contrast to well-entangled linear worm-like micelles, where the existence and the origin of shear-banding flows have been well established, the understanding of morphological and conformational changes that accompany shear banding in entangled polymer solutions is still far from complete. Here, we analyze the shear profiles and polymer dynamics of well-entangled double-stranded DNA (dsDNA) under LAOS by combining a custom planar Couette shear cell and a high-resolution confocal microscope. Under LAOS at sufficiently high Weissenberg number (Wi), the velocity profiles display clear evolution from linearity to the shear-banding flows. To investigate the microscopic structural origin of the shear banding, we study the dynamics and distribution of individual dsDNA chains as well as micron-sized passive ellipsoidal tracers. Analysis of the behavior as a function of distance between the plates reveals spatially distinctive features that provide insights into the origin of the two co-existing bands.