Rehab Al-Kaby Mechanical Engineering Doctoral Defense
- Thursday, April 16, 2020 at 1:00pm
- WebEx Meeting number (access code): 498 809 637 Meeting password: 6BwnxkTns34 ia phone +1-855-797-9485 US Toll free
Transient and Steady State Rheo-NMR of Shear Banding Wormlike Micelles
Understanding the correlation between the macroscopic flow field and the microscopic structure and dynamics of the non-Newtonian (complex) fluids is crucial on both fundamental and practical grounds. Among the variety of complex fluids, wormlike micelle (WLM) solutions have become a model system to study an unusual mechanical phenomenon known as shear banding. The shear banding phenomena is simply defined as the splitting of the flow into two macroscopic layers, a high and low shear band bearing different viscosities and local shear rates. In this study, the shear banding of a wormlike micelle (WLM) solution was investigated under steady state and time dependent conditions. The WLM system was a solution of 6 wt. % cetylpyridinium chloride (CPCl) and sodium salicylate (NaSal) in 0.5 M NaCl brine which is well-known for its ability to develop the flow instabilities driven by elasticity.
1D velocity profiles across the 1 mm fluid gap of a concentric cylinder shear cell were recorded every 1 s after shear start-up using Rheo-NMR velocimetry and used to investigate the shear band formation and transition from transient to steady state. Transient and steady state shear banding was observed for a range of shear rates across the stress plateau and the impact of several flow protocols were studied. The evolution of the high, low, and true shear rates, as well as interface position with time after shear startup was used to evaluate changes in the kinetics of shear band formation as a function of applied shear rate and flow protocol. In general, the analysis in this work has the potential to allow a 1D measurement to provide information about the 3D flow.
- Department of Mechanical & Industrial Engineering