Letter to the Editor: At last, a true liquid‐phase yield stress

Spaans, Robert D.; Williams, Michael C.

doi:10.1122/1.550684

Cited by 29 publications

(16 citation statements)

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“…Both an apparent yield stress 17 and a long-time stress relaxation modulus that increased with time 18 were observed and interpreted by invoking processes occurring in the interfacial region. It remains, however, to unify the thermal and rheological analyses.…”

Section: Modeling the Interfacial Regionmentioning

confidence: 93%

“…It has even been remarked by the same group 20 that ⌬T g S values were so large that "values of T g S (extracted) from these data should not be taken too seriously" (p. 1081). We are therefore concerned whether the reported 12,17,18 breadth of ⌬T g S for SBS copolymers (where B ϭ any rubbery block) could be an artifact of the data analysis or, as supported by the present interphase model, a reality.…”

Section: Behavior Of ⌬T G and ⌬C P In Block Copolymersmentioning

confidence: 97%

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Probing the interfacial region of microphase-separated block copolymers by differential scanning calorimetry

Spaans

Muhammad

Williams

1999

J. Polym. Sci. B Polym. Phys.

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A region of broad nonlinear curvature is observed in DSC traces of ABA copolymers during temperature sweeps between the glass transition temperatures of the two principal microphases. This curvature is attributed to a smoothly varying composition profile through the interfacial region lying between microphases. The shape of the DSC curve is proposed to be a fingerprint for a given profile. This curvature is, however, shown to be a possible source of uncertainty in precise evaluation of Tg for the microphases and the reported enhanced breadth of these transitions. In addition, microphase separation temperatures are readily identifiable from DSC traces, and their values correspond well to the predictions of Leary‐Williams theory. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 267–274, 1999

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Section: Modeling the Interfacial Regionmentioning

confidence: 93%

Section: Behavior Of ⌬T G and ⌬C P In Block Copolymersmentioning

confidence: 97%

Probing the interfacial region of microphase-separated block copolymers by differential scanning calorimetry

Spaans

Muhammad

Williams

1999

J. Polym. Sci. B Polym. Phys.

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“…', where he presents numerous viscosity versus shear stress curves with viscosity plateaus at low stresses (Barnes 1999). Following the initial publication by Barnes, a number of papers appeared that discuss the definition of yield stress fluids, whether such things existed or not, and how to demonstrate them either way (Hartnett & Hu 1989;Schurz 1990;Evans 1992;Spaans & Williams 1995;Barnes 1999Barnes , 2007. The outcome of this debate has been that the rheology community at present holds two coexisting and conflicting views: (i) the yield stress marks a transition between a liquid state and a solid state and (ii) the yield stress marks a transition between two fluid states that are not fundamentally different-but with very different viscosities.…”

Section: (B) Simple Yield Stress Fluidsmentioning

confidence: 99%

An attempt to categorize yield stress fluid behaviour

Møller

Fall

Chikkadi

et al. 2009

Phil. Trans. R. Soc. A.

243

208

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We propose a new view on yield stress materials. Dense suspensions and many other materials have a yield stress-they flow only if a large enough shear stress is exerted on them. There has been an ongoing debate in the literature on whether true yield stress fluids exist, and even whether the concept is useful. This is mainly due to the experimental difficulties in determining the yield stress. We show that most if not all of these difficulties disappear when a clear distinction is made between two types of yield stress fluids: thixotropic and simple ones. For the former, adequate experimental protocols need to be employed that take into account the time evolution of these materials: ageing and shear rejuvenation. This solves the problem of experimental determination of the yield stress. Also, we show that true yield stress materials indeed exist, and in addition, we account for shear banding that is generically observed in yield stress fluids.

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“…Following these publications, a series of papers appeared discussing the proper definition of yield stress fluids, whether they existed or not, and how to demonstrate either way, e.g. [4][5][6][7][8]. The outcome of this debate has been that the rheology and soft matter communities presently hold two coexisting yet conflicting views: 1) the yield stress marks a transition between a liquid state and a solid state, and 2) the yield stress marks a transition between two fluid states that are not fundamentally different -but with very different viscosities.…”

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confidence: 99%

Origin of apparent viscosity in yield stress fluids below yielding

Møller¹,

Fall²,

Bonn³

2009

Europhys. Lett.

166

132

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Origin of apparent viscosity in yield stress fluids below yieldingMøller, P.C.F.; Fall, A.; Bonn, D. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Abstract -For more than 20 years it has been debated if yield stress fluids are solid below the yield stress or actually flow; whether true yield stress fluids exist or not. Advocates of the true yield stress picture have demonstrated that the effective viscosity increases very rapidly as the stress is decreased towards the yield stress. Opponents have shown that this viscosity increase levels off, and that the material behaves as a Newtonian fluid of very high viscosity below the yield stress.In this paper, we demonstrate experimentally (on four different materials, using three different rheometers, five different geometries, and two different measurement methods) that the low-stress Newtonian viscosity is an artifact that arises in non-steady-state experiments. For measurements as long as 10 4 seconds we find that the value of the "Newtonian viscosity" increases indefinitely. This proves that the yield stress exists and marks a sharp transition between flowing states and states where the steady-state viscosity is infinite -a solid!

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Letter to the Editor: At last, a true liquid‐phase yield stress

Cited by 29 publications

References 0 publications

Probing the interfacial region of microphase-separated block copolymers by differential scanning calorimetry

Probing the interfacial region of microphase-separated block copolymers by differential scanning calorimetry

An attempt to categorize yield stress fluid behaviour

Origin of apparent viscosity in yield stress fluids below yielding

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