- Published on 21 October 2012
A new model provides an alternative description of atomic level gold bonding.While simple Newtonian liquids are structured at the molecular scale, complex fluids are structured at the mesoscopic scale. Shear-banding is a ubiquitous phenomenon in complex fluids. It relates to the formation of regions (bands) with different fluidities and stacked along the velocity gradient direction. Shear banding is a transition towards a heterogeneous state induced by the flow itself. It’s been observed in many systems of practical relevance, including giant (wormlike) micelles, telechelic polymers, emulsions, clay suspensions, colloidal gels, star polymers, granular materials, or foams. Giant micelles, the subject of a recent EPJE Colloquium, are elongated structures resulting from the self-assembly of amphiphilic molecules in aqueous solution. In the past twenty years, shear-banding flows in giant micelles have been probed by various techniques, such as rheometry, velocimetry and flow birefringence. The results collected point to time and space fluctuations that are difficult to explain. Different candidates have been identified, the main ones being wall slip, interfacial instability between bands or bulk instability of one of the bands. In this Colloquium, Fardin and Lerouge present experimental evidence for a purely elastic instability of the high shear rate band as the main origin for fluctuating shear-banding flows.
Instabilities in wormlike micelle systems: From shear-banding to elastic turbulence. M.-A. Fardin und S. Lerouge, Eur. Phys. J. E (2012) 35: 91, DOI 10.1140/epje/i2012-12091-0