Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 16: SYMPOSIUM Driven Soft Matter I
CPP 16.4: Vortrag
Dienstag, 26. Februar 2008, 11:15–11:30, C 130
Experimental investigation of shear banding in wormlike micelles — •Sébastien Manneville1, Lydiane Bécu2, Jean-Baptiste Salmon3, and Annie Colin3 — 1Laboratoire de Physique - Ecole Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon cedex 07, France — 2CNRS - Université du Maine, Avenue Olivier Messiaen, 72085 Le Mans, France — 3Rhodia Lab of the Future - CNRS, 178 avenue du Docteur Schweitzer, 33608 Pessac, France
Under simple shear some complex fluids may separate into bands of widely different viscosities. This phenomenon is known as ``shear banding'' and involves inhomogeneous flows where macroscopic bands bearing different shear rates coexist in the sample. In the last decade, ``wormlike micelle'' solutions have emerged as a model system to study shear banding. Depending on the concentration, these self-assembled surfactant systems constituted of long, cylindrical, semi-flexible aggregates undergo a shear-induced transition from a viscoelastic state of entangled micelles to a state of highly aligned micelles.
In this talk, we will describe two velocimetry techniques, based on dynamic light scattering and ultrasonic velocimetry respectively, that may be used in combination with conventional rheometry to investigate shear banding with high spatial and temporal resolutions. Experimental results will be presented, where shear-banded flows of wormlike micelles are shown to involve complex spatiotemporal behaviors and apparent wall slip. Such observations, confirmed by recent measurements from other groups, raise lots of open questions that we shall address in the last part of the talk.