(468e) Experimental Evidence for Shear Banding in Large Amplitude Oscillatory Shear of Entangled DNA Solution.

Combining a planar Couette shear cell with high-resolution confocal microscopy, we investigate the shear profiles of highly entangled DNA solutions undergoing large amplitude oscillatory shear (LAOS). The linear shear profiles of low-concentration solutions transition to wall-slip dominant profiles at high DNA concentrations and ultimately evolve into shear-banded profiles with increasing shear rates or Weissenberg numbers (Wi). We analyze the dynamics of embedded tracer particles in the shear frame, which provide important insights into the microscopic structural changes of shear-banded polymeric solutions. Interestingly, the tracer particles display unusual transient super-diffusivity and enhanced dynamic heterogeneity in the high-shear-rate band. The probability distribution function of particle displacements indicates a Levy-flight-type of motion with power-law decays at large displacements. Such dynamics have also been observed in other shear-banded complex fluids, suggesting a universal feature of shear-banded complex fluids under time-dependent shear.