Suppressed shear banding in entangled DNA solution by attractive interaction

Shear banding, or strain localization, a narrow zone of intense shearing strain caused by non-homogeneous deformation, is quite ubiquitous in solid and complex fluids. In complex fluids, the existing of shear banding would make conventional rheology difficult to interpret. Especially, in entangled polymer system, the existence of shear banding would overturn the well-known Tube theory. So there is considerable debate over whether shear banding observed in entangled polymers such as Polybutadiene is true or not.We report here just by tuning the attractive interaction between chains, the flow behaviour changes from well-defined banded flow to almost linear flow for the same entangled polymer system. The attractive interaction between polymer chains is gained by grafting short PNIPA (Mw=3k) chains on the DNA main chains with rather low grafting density. The grafting PNIPA doesn’t change the flow behavior of DNA at temperature lower than its LCST while at higher temperature than LCST, the PNIPA undergoes coil-to-globule conformation change and add an attractive interaction on the main DNA chain, which becomes stronger and stronger with temperature. With stronger attractive interaction, the velocity profile becomes almost linear. These observations would help us to understand the mechanism for shear banding in entangle polymer systems on a molecular level and explain why shear banding occurs in some system but not in others