Shear thickening in dilute solutions of wormlike micelles

Barentin, Catherine; Liu, Andrea J.

doi:10.1209/epl/i2001-00432-x

Cited by 37 publications

(37 citation statements)

References 39 publications

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“…Here the quiescent state, which consists of well-dispersed, Brownian flexible cylinders, transforms above a critical shear stress to a percolating network (30). The proposed mechanism for the ST is through the aggregation of micelles into bundles due to intermicellar interactions (31) or to the presence of closed micellar loops that form a linked network under shear (32). However, these mechanisms are not likely to be relevant to the flocculated nanotubes presently under study.…”

Section: Resultsmentioning

confidence: 99%

Discontinuous shear thickening in confined dilute carbon nanotube suspensions

Majumdar

Krishnaswamy

Sood

2011

Proc. Natl. Acad. Sci. U.S.A.

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A monotonic decrease in viscosity with increasing shear stress is a known rheological response to shear flow in complex fluids in general and for flocculated suspensions in particular. Here we demonstrate a discontinuous shear-thickening transition on varying shear stress where the viscosity jumps sharply by four to six orders of magnitude in flocculated suspensions of multiwalled carbon nanotubes (MWNT) at very low weight fractions (approximately 0.5%). Rheooptical observations reveal the shear-thickened state as a percolated structure of MWNT flocs spanning the system size. We present a dynamic phase diagram of the non-Brownian MWNT dispersions revealing a starting jammed state followed by shearthinning and shear-thickened states. The present study further suggests that the shear-thickened state obtained as a function of shear stress is likely to be a generic feature of fractal clusters under flow, albeit under confinement. An understanding of the shear-thickening phenomena in confined geometries is pertinent for flow-controlled fabrication techniques in enhancing the mechanical strength and transport properties of thin films and wires of nanostructured composites as well as in lubrication issues.A n increase in viscosity of fluids with increasing flow rate termed as "shear thickening" (ST) is of tremendous interest in basic sciences as well as for many applications which include the design of smart materials like soft body armors and shock absorbers (1). Traditionally, the candidates for shear-thickening fluids have been dense suspensions of Brownian/non-Brownian, nonaggregating, monodisperse spherical or rod-like particles (2-6). This trend is further encouraged by recent experimental and theoretical studies which surmised that a strong ST will not be observed in flocculated suspensions because the attractive interactions that drive flocculation increase the yield stress and mask the ST behavior, leading to a monotonic shear-thinning viscosity curve (7-9). Consistent with this picture, a shear-thinning behavior is always seen, for example, in flocculated suspensions of carbon nanotubes (10, 11).The rheophysics of flocculated suspensions formed by colloidal particles with attractive interactions also raises several interesting issues. A universal jamming phase diagram proposed for attractive particles (12) with particle volume fraction Φ, interparticle attraction U, and stress σ as the control parameters is consistent with the nonequilibrium shear diagram for multiwalled nanotubes mapped out using rheooptical studies (11). Here, the nanotubes, which are entangled at low shear stress to exhibit a solidlike behavior, transform to a liquid-like state by dispersing the nanotubes that align along flow to form a nematic phase above a critical shear stress. However, the feasibility of achieving a reentrant jamming phase behavior by tuning the attractive interactions in these systems has not been examined. In fact, ST behavior was not known for flocculated suspensions until recently, where a modest continuous ST (whe...

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Section: Resultsmentioning

confidence: 99%

Discontinuous shear thickening in confined dilute carbon nanotube suspensions

Majumdar

Krishnaswamy

Sood

2011

Proc. Natl. Acad. Sci. U.S.A.

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“…Model-building attempts have been made from time to time, based for example on shear-induced aggregation or polymerization of rodlike micelles [79]. There are also models that couple a gelation transition to shear bands [80,81], and some that ascribe the shear thickening directly to ionic or electrokinetic phenomena [82]. All these models have drawbacks; for example, aggregation models normally require very high shear rates for onset whereas experimental values are low; thickening is sometimes seen in nonionic micelles [75]; etc..…”

Section: Shear Thickeningmentioning

confidence: 99%

Rheology of giant micelles

Cates

Fielding

2006

Advances in Physics

320

341

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Giant micelles are elongated, polymer-like objects created by the self-assembly of amphiphilic molecules (such as detergents) in solution. Giant micelles are typically flexible, and can become highly entangled even at modest concentrations. The resulting viscoelastic solutions show fascinating flow behaviour (rheology) which we address theoretically in this article at two levels. First, we summarise advances in understanding linear viscoelastic spectra and steady-state nonlinear flows, based on microscopic constitutive models that combine the physics of polymer entanglement with the reversible kinetics of self-assembly. Such models were first introduced two decades ago, and since then have been shown to explain robustly several distinctive features of the rheology in the strongly entangled regime, including extreme shear-thinning. We then turn to more complex rheological phenomena, particularly involving spatial heterogeneity, spontaneous oscillation, instability, and chaos. Recent understanding of these complex flows is based largely on grossly simplified models which capture in outline just a few pertinent microscopic features, such as coupling between stresses and other order parameters such as concentration. The role of 'structural memory' (the dependence of structural parameters such as the micellar length distribution on the flow history) in explaining these highly nonlinear phenomena is addressed. Structural memory also plays an intriguing role in the little-understood shear-thickening regime, which occurs in a concentration regime close to but below the onset of strong entanglement, and which is marked by a shear-induced transformation from an inviscid to a gelatinous state.

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“…On the other hand, Berret et al [11] suggested a shear-induced transition from rodlike to longer, more flexible entangled structures. More recently, Barentin and Liu [13] proposed that the SIS arise through the formation of micellar packages, resulting from counterion-assisted intermicellar attraction.…”

Section: Introductionmentioning

confidence: 99%

“…Wormlike micelles may undergo uniaxial growth upon the addition of salt. As a result, the viscosity of the solution increases, and the micelles form an entangled network [13,31,32]. The decrease in viscosity with further addition of salt, however, is more difficult to explain.…”

Section: Introductionmentioning

confidence: 99%