In:
Journal of Rheology, Society of Rheology, Vol. 62, No. 5 ( 2018-09-01), p. 1125-1134
Abstract:
In this work, shear band formation following shear startup as a function of flow protocol is investigated in the wormlike micelle (WLM) system of 6 wt. % cetylpyridinium chloride and sodium salicylate in 0.5M NaCl brine in a Couette Rheo-nuclear magnetic resonance (NMR) shear cell. Many applications using WLM solutions occur under time dependent conditions; however, shear banding under time dependent flow protocols is not as well characterized. 1D velocity profiles across the 1 mm fluid gap are recorded every 1 s after shear startup using Rheo-NMR velocimetry and used to evaluate shear banding characteristics, including the shear rates in the low and high shear band, the interface position, and the apparent wall slip as a function of time. The velocity, and therefore the shear banding characteristics, exhibits large temporal fluctuations following an abrupt startup to 12 s−1. Data were decomposed into an average and fluctuation about the average in order to extract the characteristic time scales for the transition of the flow from transient to steady state. In addition, the Fourier transform of time autocorrelation functions was used to quantify the fluctuation frequencies themselves, which are related to the apparent slip at the inner rotating wall and the presence of flow instabilities. This analysis has the potential to allow a 1D measurement to provide information about the 3D flow. Shear startup experiments were also performed for flow protocols with and without preshear. Preshear resulted in different magnitudes of the timescales and a shift in the frequencies of the fluctuation of all shear banding characteristics, emphasizing the importance of shear history on the flow behavior of these WLM solutions.
Type of Medium:
Online Resource
ISSN:
0148-6055
,
1520-8516
Language:
English
Publisher:
Society of Rheology
Publication Date:
2018
detail.hit.zdb_id:
1461060-7
