Worm-like micelles solutions (WLMs) serve as model systems to study the dynamics and non-equilibrium behavior of complex fluids [1-3]. One famous representative is 10% (w/w) cetylpyridinium chloride (CPCl) in 0.5M NaCl solution. Our aim is to further investigate the dynamics of this WLM system using two different methods, namely 2D ultrasonic speckle velocimetry (USV) [4] and Rheo-NMR velocimetry [5].
The anomalous shear banding results reported by Feindel and Callaghan [6] have been further refined. Higher spatial resolution with the Rheo-NMR technique has improved our understanding of the interface position and the variability of the shear rates in the low and high shear rate bands, as a function of the applied shear rate. As with Rheo USV, the interface position does vary with the applied shear rate while the lower shear rate was shown to be much less dependent on the applied shear rate than previously assumed. Consistently, both methods deliver a significant change in the higher shear rate.
We attribute differences between the NMR and USV to instabilities (such as wall slip or elastic instabilities), which may depend on the particularities of the shear geometries. However, the overlap in results may ultimately lead to a more detailed knowledge when studying shear banding fluids with these two complementary methods.
[1] M-A. Fardin and S. Lerouge, Eur. Phys. J. E 35, 91 (2012)
[2] R.L. Moorcroft and S.M. Fielding, Phys. Rev. Lett. 110, 086001 (2013)
[3] M.R. Lopez-Gonzalez et al., Phys. Rev. Lett. 93, 268302 (2004)
[4] T. Gallot et al., Rev. Sci. Instrum. 84, 045107 (2013)
[5] P.T. Callaghan, Rep. Prog. Phys. 62, 599-670 (1999)
[6] K.W. Feindel and P.T. Callaghan, Rheol Acta 49, 1003-1013 (2010)
petrik.galvosas@vuw.ac.nz
