Anomalous shear banding revisited with Rheo-NMR and Rheo-USV

• Published in: Rheologica acta Vol. 54; no. 7; pp. 619 - 636
• Main Authors: Kuczera, Stefan, Perge, Christophe, Fardin, Marc-Antoine, Brox, Timothy I., Williams, Martin A. K., Manneville, Sébastien, Galvosas, Petrik
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.07.2015; Springer Nature B.V
• Subjects: Bursts; Characterization and Evaluation of Materials; Chemistry and Materials Science; Complex Fluids and Microfluidics; Fluid dynamics; Food Science; Materials Science; Mechanical Engineering; NMR; Nuclear magnetic resonance; Original Contribution; Polymer Sciences; Shear rate; Shearing; Soft and Granular Matter; Temporal resolution; Velocimetry; Velocity measurement; Vorticity; Rheo-USV; Rheo-NMR; Wormlike micelles; Shear banding; Slip
• DOI: 10.1007/s00397-015-0854-y
• ISSN: 0035-4511

A combined two-dimensional Rheo-NMR velocimetry and two-dimensional Rheo-USV approach is used to further elucidate the flow of a wormlike micellar solution in cylindrical Couette geometries. Recent experimental enhancements for both methods enable a more detailed description of the flow dynamics than available in the past. This enabled us to revisit and investigate shear banded flow utilizing improved spatial and temporal resolution, clearly confirming a departure from a simple lever rule for the micellar solution under study. Both experimental techniques observe different shear rates in the high shear rate band accompanied by a varying position of the interface between bands for different applied shear rates. Furthermore, spatially and temporally resolved velocimetry reveals various flow instabilities. Ultrasound measurements show vorticity undulations with wavelengths that scale linearly with the size of the high shear rate band. For high enough shear rates, the occurrence of turbulent bursts is detected in the USV case. However, no direct evidence of these bursts is found in the NMR measurements for equivalent shear rates, which we attribute so far to differences in the design of the shearing geometries.