Nuclear magnetic resonance imaging of apparent slip effects in xanthan solutions

Rofe, Craig; Vargas, Lourdes de; Perez‐González, José; Lambert, Robert A.; Callaghan, Paul T.

doi:10.1122/1.550775

Cited by 46 publications

(20 citation statements)

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“…For the onion system, it is found that the location of the interface strongly fluctuates; the mechanism for which is still unclear (Salmon et al 2003d). Interface fluctuations and periodic stress and rate response have been observed to accompany gradient banding in some cases (see, for example, Salmon et al 2003a, d;Herle et al 2005;Callaghan and Gil 2000;Manneville et al 2004a;Hu et al 2002;Rofe et al 1996; Lerouge et al 2006). It is still an open question to what extent dynamical slip-stick phenomena play a role in the observed interface fluctuations.…”

Section: Gradient Bandingmentioning

confidence: 99%

Gradient and vorticity banding

2008

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"Banded structures" of macroscopic dimensions can be induced by simple shear flow in many different types of soft matter systems. Depending on whether these bands extend along the gradient or vorticity direction, the banding transition is referred to as "gradient banding" or "vorticity banding," respectively. The main features of gradient banding can be understood on the basis of a relatively simple constitutive equation. This minimal model for gradient banding will be discussed in some detail, and its predictions are shown to explain many of the experimentally observed features. The minimal model assumes a decrease of the shear stress of the homogeneously sheared system with increasing shear rate within a certain shear-rate interval. The possible microscopic origin of the severe shear-thinning behaviour that is necessary for the resulting nonmonotonic flow curves is discussed for a few particular systems. Deviations between experimental observations and predictions by the minimal model are due to obvious simplifications within the scope of the minimal model. The most serious simplifications are the neglect of concentration dependence of the shear stress (or on other degrees of freedom) and of the elastic contributions to the stress, normal stresses, and the possibility of shear-induced phase transitions. The consequences of coupling of stress and concentration will be analyzed in some detail. In contrast to predictions of the minimal model, when coupling to concentration is important, a flow instability can occur that does not require strong shear thinning. Gradient banding is sometimes also observed in glassy-and gel-like systems, as well as in shear-thickening systems. Possible mechanisms that could be at the origin of gradient-band formation in such systems are discussed. Gradient banding can also occur in strongly entangled polymeric systems. Banding in these systems is discussed on the basis of computer simulations. Vorticity banding is less well understood and less extensively investigated experimentally as compared to gradient banding. Possible scenarios that are at the origin of vorticity banding will be discussed. Among other systems, the observed vorticity-banding transition in rod-like col-loids is discussed in some detail. It is argued, on the basis of experimental observations for these colloidal systems, that the vorticity-banding instability for such colloidal suspensions is probably related to an elastic instability, reminiscent of the Weissenberg effect in polymeric systems. This mechanism might explain vorticity banding in discon-tinuously shear-thickening systems and could be at work in other vorticity-banding systems as well. This overview does not include time-dependent phenomena like oscillations and chaotic behaviour.

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Section: Gradient Bandingmentioning

confidence: 99%

Gradient and vorticity banding

2008

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“…7,8) For non-Newtonian fluids many papers also have been already published. [9][10][11][12][13][14][15][16][17][18][19][20] Migler et al 9) directly measured the local velocity of a sheared polymer melt within 100 nm from the solid surface using evanescent light. They reported that polymers slip at all shear stresses in the absence of strong polymer absorption.…”

Section: Introductionmentioning

confidence: 99%

“…In polymer solutions, the presence of a solid wall may alter the concentration of polymer near the wall, and it causes a low-viscosity layer and apparent slip. 10 17) measured the slip velocity in a tube using NMR (nuclear magnetic resonance) imaging.…”

Section: Introductionmentioning

confidence: 99%

Direct Measurements of Velocity Profiles in Flows of Polymer Solutions through a Rectangular Microchannel with a PDMS Surface

Yasuda

Sugiura

Môri

2006

J. Soc. Rheol., Jpn

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Velocity profiles of polymer solutions were directly measured in a microchannel with rectangular cross sections. The test fluids are 0.2 wt% aqueous solutions of polyacrylamide whose molecular weights are 6 × 10 6 (fluid A) and 1.5 × 10 7 (fluid B). The microchannel was made of PDMS and it was mounted on the glass plate. The velocity profile in the depth direction is discussed as a function of the flow rate and shear stress on the wall. Consequently, for the flows of fluid A, a symmetric profile is observed in the region between the PDMS wall and the glass wall in a low flow rate, but the velocity profile slightly becomes asymmetric with increasing flow rate: the velocity near the PDMS wall is larger than that near the glass wall. For the flows of fluid B, a slightly asymmetric profile is observed even in the low flow rate and a largely asymmetric one in the large flow rate. The PDMS wall significantly affects the velocity profile in the flow of polymer solution through a PDMS microchannel.

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“…Most of this discussion is complicated because no detailed measurements of the velocity profiles in the moving liquid exist, making it difficult to assert what underlies such stress plateaus. In the past few years MRI has been used extensively to study this and has allowed for the detection of wall slip, for instance, in flowing foams and emulsions (Bertola et al 2003), silicone oil-in-water emulsions, xanthan gum, and mayonnaise (Gibbs et al 1996, Johns & Hollingsworth 2007, Rofe et al 1996. Conversely, much effort has been put into the understanding of shear banding, which we discuss below.…”

Section: Mri Rheology Of Complex Fluidsmentioning

confidence: 99%

Some Applications of Magnetic Resonance Imaging in Fluid Mechanics: Complex Flows and Complex Fluids

Bonn

Rodts

Groenink

et al. 2008

Annu. Rev. Fluid Mech.

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Nuclear magnetic resonance imaging of apparent slip effects in xanthan solutions

Cited by 46 publications

References 0 publications

Gradient and vorticity banding

Gradient and vorticity banding

Direct Measurements of Velocity Profiles in Flows of Polymer Solutions through a Rectangular Microchannel with a PDMS Surface

Some Applications of Magnetic Resonance Imaging in Fluid Mechanics: Complex Flows and Complex Fluids

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