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Issue 31, 2010
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Ordering fluctuations in a shear-banding wormlike micellar system

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Abstract

We present a first investigation about the non-linear flow properties and transient orientational-order fluctuations observed in the shear-thinning lecithin–watercyclohexane wormlike micellar system at a concentration near to the zero-shear isotropic–nematic phase transition. From rheological measurements the stress plateau was found shifted to very low values of the applied shear rate [small gamma, Greek, dot above] , compared to most of the concentrated living polymer systems reported in the literature. Rheo-small angle neutron scattering (Rheo-SANS) experiments performed in the flow-vorticity plane revealed periodical fluctuations of both the order parameter P2 and the angular deviation ϕ from the vorticity axis as determined from the scattering peaks. The periods of the oscillations were not found to depend on imposed [small gamma, Greek, dot above]. A theoretical model was also developed to explain the oscillatory dynamics of the shear-induced nematic order parameter in terms of the presence of standing waves of the director orientation profile along the circumference of the Couette cell. The experimental results of the periodic order parameter fluctuations together with their theoretical modelling shed significant new insights on the shear banding phenomenon, particularly its microscopic mechanism.

Graphical abstract: Ordering fluctuations in a shear-banding wormlike micellar system

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Publication details

The article was received on 10 Dec 2009, accepted on 12 Apr 2010 and first published on 08 Jun 2010


Article type: Paper
DOI: 10.1039/B926152D
Citation: Phys. Chem. Chem. Phys., 2010,12, 8856-8862
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    Ordering fluctuations in a shear-banding wormlike micellar system

    R. Angelico, C. O. Rossi, L. Ambrosone, G. Palazzo, K. Mortensen and U. Olsson, Phys. Chem. Chem. Phys., 2010, 12, 8856
    DOI: 10.1039/B926152D

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