Shear Banding or Not in Entangled DNA Solutions

An entangled linear double-strand calf thymus DNA solution was used as model entangled polymers in a particle-tracking velocimetric (PTV)/rheometric study to explore the cause of strong shear banding and determine whether shear inhomogeneity was reduced or eliminated when the shear rate was imposed gradually. The entangled DNA solution had a concentration of 11 mg/mL, with glycerol as the solvent. All the rheometric and PTV measurements were carried out at room temperature using a MCR-301 rotational rheometer equipped with a cone-plate of 25 mm diameter and 4° cone angle where the surface roughness due to a black paint was on the order of micrometers. Extensive investigations involving other rates confirmed that the slow rate ramp-up mode or rate quench-down tended to produce approximately linear velocity variation across the gap throughout the stress plateau region in contrast to the shear bands that emerged from startup shear.