Large amplitude oscillatory shear of pseudoplastic and elastoviscoplastic materials

Ewoldt, Randy H.; Winter, Peter; Maxey, Jason; McKinley, Gareth H.

doi:10.1007/s00397-009-0403-7

Cited by 324 publications

(198 citation statements)

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“…The values of e 3 /e 1 and v 3 /v 1 are now much larger than they were for the case in which γ 0 =1. The positive value of e 3 /e 1 can be attributed towards an intra-cycle strain stiffening in this material (Ewoldt et al, 2008(Ewoldt et al, , 2010. It is the appearance and growth of these higher harmonics that lead to the progressive deviation of the shear stress magnitude mea- One interesting aspect of figure 12 (d) is the appearance of a more enhanced even harmonic at ω = 2ω d in the imaginary part of the discrete Fourier transform of the stress response.…”

Section: Large Amplitude Regime -Laosmentioning

confidence: 88%

“…Large amplitude oscillatory shear (LAOS) is used to progressively deform the material deeper into the nonlinear regime and probe the onset of shear-banding behavior in the absence of substantial secondary flows and wall slip. We also use the LAOS framework developed in previous work (Cho et al, 2005;Ewoldt et al, 2008Ewoldt et al, , 2010 to connect local kinematic measurements with nonlinearities in the bulk rheology, and show that the onset of shear banded velocity profiles closely coincides with the growth of nonlinearities in the bulk viscoelastic response. Similar behavior has recently been explored using some of the microstructural constitutive models that have been proposed for describing the rheology of shear banding systems (Adams and Olmsted, 2009;Zhou et al, 2010), providing an opportunity in the future for comparing experimental data with theoretical predictions.…”

Section: Introductionmentioning

confidence: 93%

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Rheo-PIV of a shear-banding wormlike micellar solution under large amplitude oscillatory shear

et al. 2012

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We explore the behavior of a wormlike micellar solution under both steady and large amplitude oscillatory shear (LAOS) in a cone-plate geometry through simultaneous bulk rheometry and localized velocimetric measurements. First, particle image velocimetry is used to show that the shear banded profiles observed in steady shear are in qualitative agreement with previous results for flow in the cone-plate geometry. Then under LAOS, we observe the onset of shear-banded flow in the fluid as it is progressively deformed into the non-linear regime -this onset closely coincides with the appearance of higher harmonics in the periodic stress signal measured by the rheometer. These harmonics are quantified using the higher order elastic and viscous Chebyshev coefficients e n and v n , which are shown to grow as the banding behavior becomes more pronounced. The high resolution of the velocimetric imaging system enables spatiotemporal variations in the structure of the banded flow to be observed in great detail. Specifically, we observe that at large strain amplitudes (γ 0 ≥ 1) the fluid exhibits a 3-banded velocity profile with a high shear rate band located in-between two lower shear rate bands adjacent to each wall. This band persists over the full cycle of the oscillation, resulting in no phase lag being observed between the appearance of the band and the driving strain amplitude. In addition to the kinematic measurements of shear banding, the methods used to prevent wall slip and edge irregularities are discussed in detail, and these methods are shown to have a measurable effect on the stability boundaries of the shear banded flow.

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Section: Large Amplitude Regime -Laosmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 93%

Rheo-PIV of a shear-banding wormlike micellar solution under large amplitude oscillatory shear

et al. 2012

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“…Despite the clear evidence in this early literature and reiteration in recent publicationsthat absence of even harmonics does not necessarily mean the absence of slip (Ewoldt et al, 2010, Hyun et al, 2011; the presence or absence of even harmonics is still commonly used as a defining parameter (Renou et al, 2010, Ozkan et al, 2012. More recent work has been carried out investigating wall-slip during LAOS in a variety of suspensions.…”

Section: Slip During Oscillatory Shearmentioning

confidence: 99%

“…Lissajous-Bowditch (L-B) curves are a common method for qualitatively interpreting the results of LAOS tests from either Fourier-Transform (FT) or Chebyshev analysis (Ewoldt et al, 2010). The stress waveforms can be replotted as stress against strain (elastic L-B curve) or stress against strain rate (viscous L-B curve) (Ewoldt et al, 2010, Hyun et al, 2011, Mewis and Wagner, 2011.…”

Section: Slip During Oscillatory Shearmentioning

confidence: 99%

“…The stress waveforms can be replotted as stress against strain (elastic L-B curve) or stress against strain rate (viscous L-B curve) (Ewoldt et al, 2010, Hyun et al, 2011, Mewis and Wagner, 2011. On an elastic L-B curve in the linear viscoelastic region, where the stress response is sinusoidal, the curves are elliptical as shown in …”

Section: Slip During Oscillatory Shearmentioning

confidence: 99%

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Rheology of soft particle suspensions

Shewan¹

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The purpose of this work is to investigate the effect of particle elasticity on suspension rheology and flow. Non-colloidal (~ 10 µm) spherical agarose microgels suspended in water are used as a model system. The advantage of these microgels is that they are manufactured to a specific elastic modulus, ranging from 8 to 300 kPa, determined from the modulus of an agarose gel disk. This is in contrast to routinely studied colloidal microgels where the particle modulus cannot be established. Colloidal microgel modulus and specific volume are variable as they are responsive to suspension conditions (such as, pH, temperature and osmotic pressure). Using experimental rheology, an investigation was carried out into the liquid and solid-like behaviour of agarose microgel suspensions. Suspension concentration regimes from dilute to densely packed were investigated to show explicitly the effect of particle modulus on rheology, which becomes increasingly more significant with increasing phase volume. In addition, particle modulus is shown to influence two shear flow characteristics -slip and shear thickening.To interpret suspension viscosity as a function of phase volume the model, developed by Maron and Pierce (1956) and popularised by Quemada (1977) (MPQ model), is applied. This model is based on a scaling relation of the pair distribution function and predicts the critical phase volume at which the viscosity tends to infinity, corresponding to when spherical particles are randomly close packed (φ rcp ).Commonly, it is used empirically by free fitting of experimental data to obtain the critical phase volume. In this work, a method has been developed to use the MPQ model in accordance with its theoretical basis by independently predicting φ rcp from the particle size distribution. It is shown that this theoretical form of the MPQ model, with no adjustable parameters, results in an accurate prediction (within experimental uncertainty, ± 5 %) of the viscosity-phase volume relationship for hard spheres. In addition, alterations in suspension microstructure (for example, through particle aggregation) or rheological artefacts (such as, particle migration) are readily identified by plotting the MPQ model in a linear form.In contrast to hard spheres, the phase volume of agarose microgels is difficult to define accurately. The approach typically used in literature, and used here, is to iii define the specific volume from dilute suspension viscosity. This approach can be corroborated using the theoretical viscosity-phase volume model validated with hard sphere suspensions. The specific volume of agarose microgels is easily defined at φ rcp using the particle size distribution. From this approach it is discovered that, in the viscous regime, below φ rcp , particle elasticity does not explicitly affect suspension viscosity. However, it is shown that particle elasticity has an indirect effect on viscosity at phase volumes between ~ 0.4 and φ rcp due to limited re-swelling during microgel preparation procedures.When microgels c...

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Rheological Measurements

2013

Encyclopedia of Polymer Science and Technology

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Rheology is the science to study the flow and deformation of matter. It becomes an important field in material science and engineering, food, biotechnology, and so on. The objects in rheological study are not the ideal solid and ideal fluid, which can be described by the Hookean elastic model and the Newtonian viscous model, respectively. Instead, the rheological study often focuses on materials that can exhibit viscous, elastic, and plastic behavior under different flow conditions. They are often termed as complex fluids or soft matter, which include polymers, gels, suspensions, emulsions, biofluids, foods, inks (1). In contrast to hydrodynamics, which often accounts for the complex flow behavior of simple fluids, simple geometry is utilized in rheological measurements to understand the rather complicated relationship between the mechanical input and output of complex fluids. The real flow fields encountered in many applications (such as polymer extrusion, injection molding, blow molding, fiber spinning, inkjet printing, coating) are rather complicated (2). It becomes a problem whether the rheological measurements that performed under simple flow fields are useful in understanding the complicated flow behaviors of complex fluids. Fortunately, it has been proved in many examples that the properties determined from simple rheological measurements are sufficient to quantify the material parameters in various constitutive equations, which have been used widely and successfully to simulate the flow behaviors in polymer processing (3-11). The most frequently used simple flow fields are simple shear flow and simple extensional flow.The simplest geometry that defines the simple shear is two infinite parallel plates separated by a distance h. The liquid is set between two plates with one plate moving parallel to the other (Fig. 1). In reality, when the length L and the width B are much larger than the gap h, the flow in the center regime resembles the flow between two infinite plates. It means that the edge effects are ignored in most experimental shear geometries. In rheological measurements, the flow between two plates should be laminar. Moreover, it is usually assumed that the velocity across the gap satisfies a linear profile. As shown in Fig. 1, if the bottom plate is fixed and the upper plate moves horizontally with the velocity V, the fluid velocity varies linearly from 0 at the bottom plate to V at the upper plate if the no-slip boundary condition is satisfied. The linear velocity profile generates a constant velocity gradient, which is known as the shear rate. Then, the flow field between two parallel plates is homogeneous in the shear rate. The homogeneous assumption is nontrivial in the rheological tests since the actual velocity

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Large amplitude oscillatory shear of pseudoplastic and elastoviscoplastic materials

Cited by 324 publications

References 35 publications

Rheo-PIV of a shear-banding wormlike micellar solution under large amplitude oscillatory shear

Rheo-PIV of a shear-banding wormlike micellar solution under large amplitude oscillatory shear

Rheology of soft particle suspensions

Rheological Measurements

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