Is a birefringence band a shear band?

Fischer, Elmar; Callaghan, Paul T.

doi:10.1209/epl/i2000-00552-9

Cited by 64 publications

(83 citation statements)

References 20 publications

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“…This system has been widely studied in the last twenty years [18][19][20][21][22], in particular recently, by Helgeson et al [23,45]. Right after the onset of shear, the bands form, with a flat interface between them.…”

Section: Effects Of the Salt Concentrationmentioning

confidence: 99%

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Interplay between elastic instabilities and shear-banding: three categories of Taylor–Couette flows and beyond

et al. 2012

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In the past twenty years, shear-banding flows have been probed by various techniques, such as rheometry, velocimetry and flow birefringence. In micellar solutions, many of the data collected exhibit unexplained spatiotemporal fluctuations. Recently, it has been suggested that those fluctuations originate from a purely elastic instability of the shear-banding flow. In cylindrical Couette geometry, the instability is reminiscent of the Taylor-like instability observed in viscoelastic polymer solutions. The criterion for purely elastic Taylor-Couette instability adapted to shear-banding flows suggested three categories of shear-banding depending on their stability. In the present study, we report on a large set of experimental data which demonstrates the existence of the three categories of shear-banding flows in various surfactant solutions. Consistent with theoretical predictions, increases in the surfactant concentration or in the curvature of the geometry destabilize the flow, whereas an increase in temperature stabilizes the flow. But experiments also exhibit some interesting behaviors going beyond the purely elastic instability criterion.

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Section: Effects Of the Salt Concentrationmentioning

confidence: 99%

“…Hence a few data in the manuscript concern the concentrated 20% CTAB/D 2 O solution [18][19][20][21][22] and the semi-dilute 10% CPCl/NaSal/brine system [15-17, 24, 25, 39].…”

Section: Samplesmentioning

confidence: 99%

Interplay between elastic instabilities and shear-banding: three categories of Taylor–Couette flows and beyond

et al. 2012

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“…In this contribution, we answer this question by means of spatiallyresolved 2 H NMR spectroscopy 71,72 ( 2 H NMR imaging) as well as spatially-resolved pulsed magnetic field gradient NMR diffusometry 73,74 (diffusion imaging). The large anisotropy of the diffusion tensor in the lamellar phase makes NMR diffusometry a useful tool for probing structural details of the lamellar phase.…”

Section: -4303337mentioning

confidence: 99%

Planar lamellae and onions: a spatially resolved rheo–NMR approach to the shear-induced structural transformations in a surfactant model system

et al. 2011

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The shear-induced transformations between oriented planar lamellae and a state of closely packed multilamellar vesicles (MLVs) in a lyotropic nonionic surfactant model system were studied by the combination of nuclear magnetic resonance (NMR) spectroscopy and diffusometry with magnetic resonance imaging (MRI). 2H NMR imaging confirmed the discontinuous nature of the transition from onions to planar lamellae, revealing the spatial coexistence of both states within the gap of the cylindrical Couette geometry. On the other hand, NMR diffusion measurements in three principal directions and at various values of strain strongly suggest that a multi-lamellar cylindrical or undulated intermediate structure exists during the continuous and spatially homogeneous transition from planar lamellae to MLVs.

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“…It is usually interpreted by a "nucleation-unidirectional growth" process assisted by the pre-transitional fluctuations [10,11,[16][17][18][19][20][21][22] which leads to the coexistence of two defined shear bands related to the isotropic and the shear-induced phases. However, this scenario remains under debate, since the high shear branch of the flow curve, associated to the induced nematic phase, deviates from Newtonian fluid behavior [21,22] and the velocity cartography determined by NMR [23][24][25] suggests that the liquid moves rather as a gel. Finally, in SCLCPs, the coupling model to the pre-transitional fluctuations has to be definitely rejected since the lifetime of these fluctuations is about 10 3 to 10 4 times too short with respect to timescales of the flow [14].…”

Section: Figurementioning

confidence: 99%

Richness of Side-Chain Liquid-Crystal Polymers: From Isotropic Phase towards the Identification of Neglected Solid-Like Properties in Liquids

et al. 2012

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Very few studies concern the isotropic phase of Side-Chain Liquid-Crystalline Polymers (SCLCPs). However, the interest for the isotropic phase appears particularly obvious in flow experiments. Unforeseen shear-induced nematic phases are revealed away from the N-I transition temperature. The non-equilibrium nematic phase in the isotropic phase of SCLCP melts challenges the conventional timescales described in theoretical approaches and reveal very long timescales, neglected until now. This spectacular behavior is the starter of the present survey that reveals long range solid-like interactions up to the sub-millimetre scale. We address the question of the origin of this solid-like property by probing more particularly the non-equilibrium behavior of a polyacrylate substituted by a nitrobiphenyl group (PANO2). The comparison with a polybutylacrylate chain of the same degree of polymerization evidences that the solid-like response is exacerbated in SCLCPs. We conclude that the liquid crystal moieties interplay as efficient elastic connectors. Finally, we show that the "solid" character can be evidenced away from the glass transition temperature in glass formers and for the first time, in purely alkane chains above their crystallization temperature. We thus have probed collective elastic effects contained not OPEN ACCESSPolymers 2012, 4 1110 only in the isotropic phase of SCLCPs, but also more generically in the liquid state of ordinary melts and of ordinary liquids.

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Is a birefringence band a shear band?

Cited by 64 publications

References 20 publications

Interplay between elastic instabilities and shear-banding: three categories of Taylor–Couette flows and beyond

Interplay between elastic instabilities and shear-banding: three categories of Taylor–Couette flows and beyond

Planar lamellae and onions: a spatially resolved rheo–NMR approach to the shear-induced structural transformations in a surfactant model system

Richness of Side-Chain Liquid-Crystal Polymers: From Isotropic Phase towards the Identification of Neglected Solid-Like Properties in Liquids

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