Shear banding in semidilute polymeric solutions: Experiments and modeling*

Shear banding is the formation of localized velocity bands with different shear rates, and is observed in semidilute polymer solutions and other soft materials. DNA solutions are convenient model systems owing to their characterization in standard rheometric geometries without edge fracture. Furthermore, their wall slip can be minimized by using glycerol as a solvent. In this talk, we focus on the investigation of shear banding of 13 mg/ml of 115 kbp double-stranded DNA (dsDNA) and 11 mg/ml of 50 kb single-stranded DNA (ssDNA) in glycerol/aqueous buffer solutions and compare the results with our recent works on polyacralymide and polyethylene oxide. The frequency sweep of dsDNA corresponds to that of a soft gel with a small dependence at intermediate frequencies. On the other hand, the behavior of ssDNA is comparable to that of a dense micellar solution having a unique local minimum related to micellar breakage. Due to the much smaller persistence length, ssDNA is more flexible and easily creates small structural units most likely in association with glycerol. The strain sweep of dsDNA is strain thinning and the shear bands are mainly strain-dependent. Early strain stiffening with weak bands is observed for ssDNA followed by a terminal flow regime of the collapsed structure. To summarize our recent activities on shear banding, we will briefly discuss here our mesocopic modeling and simulation efforts in mixed flows (e.g., 4:1 contraction, die extrusion).

References:
N. Germann. Shear banding instabilities in polymeric solutions, Current Opinion in Colloid and Interface Science, submitted.
Th. B. Goudoulas, S. Pan, and N. Germann. Double-stranded and single-stranded well-entangled DNA solutions under LAOS: A comprehensive study, Polymer, 140:240-254, 2018.