Questioning a fundamental assumption of rheology: Observation of noninteger power expansions

Natalia, Irene; Ewoldt, Randy H.; Koos, Erin

doi:10.1122/1.5130707

Cited by 13 publications

(18 citation statements)

References 49 publications

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“…However, a non-cubic and indeed non-integer m 3 in the scaling σ 3 ∼ γ m3 0 has been reported for some materials [7][8][9][10][11]. This was most conclusively demonstrated to be a property of the material tested rather than an instrumental artefact in our previous work [12]. Moreover, a comparison of the materials exhibiting this non-integer scaling points to particle contacts as a potential origin of this peculiar scaling.…”

Section: Introductionsupporting

confidence: 66%

“…In the present paper, we employ MAOS experiments to understand what happens with the particle bonds in capillary suspensions at small deformations. In the previous work, we reported that the third harmonic elastic and viscous stresses scaled in an atypical non-cubical, non-integer manner with the strain for one specific composition of capillary suspension in the capillary state [12].…”

Section: Introductionmentioning

confidence: 95%

“…In the present paper, we report only the power law fits obtained from the third harmonic since they are cleaner and have less uncertainty above σ min . The fitting procedure and an extended discussion about the measurement certainty is described in Natalia et al [12].…”

Section: Capillary Suspensionsmentioning

confidence: 99%

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Particle contact dynamics as the origin for noninteger power expansion rheology in attractive suspension networks

Natalia

Ewoldt

Koos

2021

Journal of Rheology

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In medium amplitude oscillatory shear (MAOS), the cubic scaling of the leading order nonlinear shear stress (σ3 ∼ γ m 3 0 , m3 = 3) is the typical expectation. Expanding on the work by Natalia et al. [J. Rheol., 64(3): 625 (2020)], we report non-cubical, non-integer power law scalings m3 for particle suspensions in two immiscible fluids with a capillary attractive interaction, known as capillary suspensions. Here, we show that distinct power law exponents are found for the storage and loss moduli and these non-integer scalings occur at every secondary fluid concentration for two different contact angles. These compelling results indicate that the non-integer scalings are related to the underlying microstructure of capillary suspensions. Weshow that the magnitude of the third harmonic elastic stress scaling m 3,elastic originates from Hertzian-like contacts in combination with the attractive capillary force. The related third harmonic viscous stress scaling m3,viscous is, therefore, associated with adhesive controlled friction. These observations, conducted for a wide range of compositions, can help explain previous reports of non-integer scaling for materials involving particle contacts and offers a new opportunity to study the importance of the particle bonds and friction in the rheological response under low deformation instead of at very high shear rates.

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Section: Introductionsupporting

confidence: 66%

Section: Introductionmentioning

confidence: 95%

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Particle contact dynamics as the origin for noninteger power expansion rheology in attractive suspension networks

Natalia

Ewoldt

Koos

2021

Journal of Rheology

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“…There has been evidence that percolated nanocomposite polymer systems can exhibit peculiar nonlinear scaling behavior (Kádár et al 2017;Gaska and Kádár 2019). Natalia et al (2020) reported all evidence to date of noninteger power-law expansions for nonlinear viscoelastic properties. Building on previous evidence, Kádár et al (2020b) determined that the onset of unique nonlinear signatures, dubbed 'nonlinear oddities', in the MAOS region matches the electrical percolation threshold of hierarchical reduced graphene oxide (HrGO)-polypropylene (PP) nanocomposites and subsequent percolated network consolidation.…”

Section: Introductionmentioning

confidence: 99%

Phase transitions of cellulose nanocrystal suspensions from nonlinear oscillatory shear

et al. 2022

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Cellulose nanocrystals (CNCs) self-assemble in water suspensions into liquid crystalline assemblies. Here, we elucidate the microstructural changes associated with nonlinear deformations in (2–9 wt%) CNC suspensions through nonlinear rheological analysis, that was performed in parallel with coupled rheology—polarized light imaging. We show that nonlinear material parameters from Fourier-transform rheology and stress decomposition are sensitive to all CNC phases investigated, i.e. isotropic, biphasic and liquid crystalline. This is in contrast to steady shear and linear viscoelastic dynamic moduli where the three-region behavior and weak strain overshoot cannot distinguish between biphasic and liquid crystalline phases. Thus, the inter-cycle and intra-cycle nonlinear parameters investigated are a more sensitive approach to relate rheological measurements to CNC phase behavior.

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“…Although their system should be quite stable, a random strain sweep might have been a good precaution. Changes with time were detected using a reverse sweep in the work of Natalia et al [ 33 ] but keep in mind that once the stress amplitude exceeds the linear limit, changes could be permanent, at least on the time scale of any reasonable experiment.…”

Section: Resultsmentioning

confidence: 99%

Polymer melt rheology: Advantages of frequency sweeps using randomly selected frequencies*

Shaw

2021

Polymer Engineering & Sci

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Measurement of the viscoelastic properties of polymer solids, melts, and solutions is broadly practiced. The so‐called “frequency sweep” appears in thousands of publications, with data covering up to five decades of frequency to reveal, for example, the relative molecular size of a polymer. To perform these experiments, the frequency range is typically “swept” from high to low frequency or vice versa. Unfortunately, this confounds frequency with run time. This is more than annoying; time effects can result in serious mistakes in the interpretation of the data. Fortunately, the confounding can be eliminated by simply running the frequencies in random order, which converts the time trend to random error. Described here is how this can be done and shows via modeling that the result can not only show that time effects are present but can be analyzed to show the time rate of change of the sample. This analysis is demonstrated using two real examples: loss of solvent from poly(dimethyl siloxane) gum and gelation of porcine gelatin. This method compares well with the multiwave technique, but does not require any special software or adjustments of amplitude with frequency or harmonic spacing of the frequencies.

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Questioning a fundamental assumption of rheology: Observation of noninteger power expansions

Cited by 13 publications

References 49 publications

Particle contact dynamics as the origin for noninteger power expansion rheology in attractive suspension networks

Particle contact dynamics as the origin for noninteger power expansion rheology in attractive suspension networks

Phase transitions of cellulose nanocrystal suspensions from nonlinear oscillatory shear

Polymer melt rheology: Advantages of frequency sweeps using randomly selected frequencies*

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