Flow-Induced Structure Change and Flow-Instability of CTAB/NaSal Aqueous Solution in a Two-Dimensional Abrupt Contraction Channel

Abstract

It is known that the CTAB/NaSal aqueous solution forms wormlike micelles when the concentration is higher than a certain value and shows the flow-induced structure change when both the shear rate and shear strain exceed respective critical values. In the present work, the start-up behavior of this surfactant solution in a two-dimensional abrupt contraction channel driven by a constant pressure was investigated. At a low driving pressure, the flow rate increases gradually and reaches an equilibrium state. When the driving pressure is higher than a certain value, the flow rate rises at a certain elapsed time. The elapsed time showing increase in flow rate shortens with increasing driving pressure. In the entry area of the narrow channel, a pair of wedge shape opaque regions appears. From the comparison with the observation in Couette flow of the same solution, it is found the opaque regions are caused by shear induced structure and the viscosity of the regions is higher than the other region. The regions grow up and make the other region with low viscosity narrower. The opaque regions suddenly break and disappear when the flow rate changes. Flow instability is induced by a sudden change of flow states. These phenomena are characteristic of the fluid showing the flow-induced structure change, whereas ordinary polymer solution do not exhibit such behavior.

Rheological characterizations of wormlike micellar solutions containing cationic surfactant and anionic hydrotropic salt

“…Therefore, other potential relaxation time scales from the length/ concentration fluctuation of micelles might also be responsible for the stress response we observed earlier. Investigations of spatial resolution of heterogeneous bands, formation of shear induced structure phase [Ouchi et al (2006a); Takahashi and Sakata (2011)] and localization of stresses at different deformations by rheo-optics [Ouchi et al (2006b); Takahashi et al (2002Takahashi et al ( , 2001] will be considered in the future work to correlate shear stress and flow-birefringence, and flow instability in the CTAB/SHNC system. Concentration fluctuation and shear induced bond formation should be studied to further explore the transient behavior of highly viscoelastic hydrotropic micellar system.…”

Elongational deformation of wormlike micellar solutions

“…A fundamental understanding of material properties as well as the ability to predict changes that occur within the material during processing is extremely important for industrial application. Investigations so far mainly focused on the shear-banding phenomenon [Britton and Callaghan (1997); Britton and Callaghan (1999); Haward and McKinley (2012); Fischer and Challaghan (2001); Salmon et al (2003)], shear-thickening even in dilute solutions [Hu and Matthys (1995); Cappelaere et al (1994); Hartmann and Cressely (1997a); Hartmann and Cressely (1997b); Hartmann and Cressely (1997c); Cressely and Hartmann (1998); Hartmann and Cressely (1998); Wheeler et al (1998); Hu et al (1998); Nowak (2001); Berret and Serero (2001); Azzouzi et al (2005); Vasudevan et al (2008)] and the corresponding shear-induced structure (SIS) [Wheeler et al (1996); Kadoma et al (1997); Ouchi et al (2006a); Ouchi et al (2006b)] using different techniques such as turbidity [Yamamoto and Taniguchi (2012); Schubert et al (2004); Lerouge et al (2008); Herle et al (2005)], flow birefringence [Dehmoune et al (2007); Berret et al (2002); Wunderlich et al (1987); Oda et al (1997); Ouchi et al (2006b)], light scattering [Liu and Pine (1996); Boltenhagen et al (1997)], cryo transmission electron microscopy (cryo-TEM) [Oda et al (1997); Lu et al (1998)], particle image velocimetry …”

Adhesion and Growth Phenomena of Gel-like Materials Induced by Injection of NaSal into Flow of Aqueous Solution of CTAB

“…7-9 and references therein), flow instabilities [10][11][12] , and the emergence of turbid region in various types of flows including Couette flows [13][14][15] , shear flows between parallel plates 16) , capillary flows 17) , flows past a falling sphere 18) , and contraction flows. 19,20) These phenomena are probably relevant to flow-induced gelation of micelles, whereas the relation between these phenomena and flow-induced structures of micelles is not yet clarified. In other experiments, the gelation at the interfaces between a surfactant solution and salts was observed.…”