Shear induced structure

Walkenstrom, P., Windhab, E., and Hermansson, A. M. (1998). Shear-induced structuring of particulate whey protein gels. Food Hydrocolloids 12, 459 68. 

As in PP-based nanocomposite systems, the extended Trouton rule, 3r 0 (y t) = r E (so t), also does not hold for PLANC melts, in contrast to the melt of pure polymers. These results indicate that in the case of P LANC, the flow induced internal structural changes also occur in elongation flow [48], but the changes are quite different in shear flow. The strong rheopexy observed in the shear measurements for the PLA-based nanocomposite at very slow shear rate reflects the fact that the shear-induced structural change involved a process with an extremely long relaxation time. 

Samples are assumed stable (shear-induced structural changes may or may not be part of the study decomposition, evaporation, etc., not allowed). 

If rj is independent of the shear rate y a liquid is called Newtonian. Water and other low molecular weight liquids typically are Newtonian. If rj decreases with increasing y, a liquid is termed shear thinning. Examples for shear thinning liquids are entangled polymer solutions or surfactant solutions with long rod-like micelles. The zero shear viscosity is the value of the viscosity for small shear rates ij0 = lim,> o tj y). The inverse case is also sometimes observed rj increases with increasing shear rate. This can be found for suspensions and sometimes for surfactant solutions. In surfactant solutions the viscosity can be a function of time. In this case one speaks of shear induced structures. 

Tattiyakul and Rao (2000) carefully examined the shearing conditions in studies on starches that reported antithixotropic behavior (Table 4-6). From the data in the table, she suggested that antithixotropic behavior resulted from shear-induced structure formation, that occurred predominantly when the level of shear stress imposed on the sample was less than 120-150 Pa. 

It has often been stated that DR of surfactant solutions is related to their rheological properties. A rise in shear viscosity at a critical shear rate, caused by a shear-induced structure (SIS), viscoelasticity (nonzero first normal stress difference, quick recoil, and stress overshoot), and high extensional viscosity/shear viscosity ratios ( 100) are rheological properties found in many DR surfactant solutions. After reviewing the rheological behavior of many DR surfactant solutions, Qi and Zakin concluded that SIS and viscoelasticity are not always observed in DR surfactant solutions while high extensional/shear viscosity ratios may be a requirement for surfactant solutions to be DR. ... 

Bakker, A. Fasano, J.B. Myers, K.J. Effects of flow pattern on the solids distribution in a stirred tank. I. Chem. E. Symp. Ser. 1994, 136, 1-8. Gadala-Maria, F. Acrivos, A. Shear-induced structure in a concentrated suspension of solid spheres. J. Rheol. 1980, 24, 799-814. 

Liberatore, M. W., PoUauf, E. J., and McHugh, A. J., Shear-induced structure formation in solutions of drag reducing polymers, J. Non-Newtonian FluidMech, 113, 193-208 (2003). 

Gadala-Maria F, Acrivos A (1980) Shear-induced structure in a concentrated suspension of solids spheres. J Rheol 24 799-811... 

Under steady shear, above a critical shear rate, the shear viscosity increases as a new and more viscous phase develops. This shear-induced state is called SIS for shear-induced structure [55] or SIP for shear-induced phase [57] in the literature. 

In the shear-induced state, the solutions are birefringent and exhibit a strongly anisotropic scattering in light and neutron experiments. This anisotropy is compatible with a strong alignment of the shear-induced structures in the flow. 

In the following (Sect. 2.2) we will first provide a list of surfactant molecules that exhibit shear-induced structures in accordance with points 1-5 and then describe the phenomenology of the transition. The rheology (Sect. 2.3), the orientation properties (Sect. 2.4), and the structure of the flow field (Sect. 2.5) for these fluids will then be examined. 

Truong M, Walker L (2002) Quantifying the importance of micellar microstructuie and electrostatic interactions on the shear-induced structural transition of cylindrical micelles. Langmuir 18(6) 2024-2031... 

Oda R, Panizzza P, Schmutz M, Lequeux F (1997) Direct evidence of the shear-induced structure of wormlike micelles gemini 12-2-12. Langmuir 13 6407-6412... 

Keller S, Boltenhagen P, Pine D, Zasadzinski J (1997) Direct observation of shear-induced structures in wormlike micellar solutions by freeze-fracture electron microscopy. Phys Rev Lett 80 2725-2728... 

Butler P (1999) Shear induced structures and transformatirais in complex fluids. Curr Opin Colloid Interface Sci 4 214—221... 

Zhang, H., D. Wang, and H. Chen (2009). Experimental study on the effects of shear induced structure in a drag-reducing surfactant solution flow. Archive of Applied Mechanics 79(8) 773-778. 

Delgado, J. Castillo, R. (2007). Shear-induced structures formed during thixotropic loops in dilute worm-micelle solutions, /. Coll. Int. Sci. 312 481. 

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