Deviation of Velocity Gradient Profiles from the “Gap Loading” and “Surface Loading” Limits in Dynamic Simple Shear Experiments

Schrag, John L.

doi:10.1122/1.549445

Cited by 95 publications

(54 citation statements)

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“…For oscillatory experiments, gap loading conditions may be confirmed by ensuring that the shear wavelength (k s ) is at least greater than 10 h, where h is the geometry gap. The shear wavelength can be estimated as [28] …”

Section: Resultsmentioning

confidence: 99%

i-Rheo: Measuring the materials' linear viscoelastic properties “in a step”!

Tassieri

Laurati

Curtis

et al. 2016

Journal of Rheology

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We present a simple new analytical method for educing the materials' linear viscoelastic properties, over the widest range of experimentally accessible frequencies, from a simple step-strain measurement, without the need of preconceived models nor the idealization of real measurements. This is achieved by evaluating the Fourier transforms of raw experimental data describing both the time-dependent stress and strain functions. The novel method has been implemented into an open access executable "i-Rheo," enabling its use to a broad scientific community. The effectiveness of the new rheological tool has been corroborated by direct comparison with conventional linear oscillatory measurements for a series of complex materials as diverse as a monodisperse linear polymer melt, a bimodal blend of linear polymer melts, an industrial styrene-butadiene rubber, an aqueous gelatin solution at the gel point and a highly concentrated suspension of colloidal particles. a)

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Section: Resultsmentioning

confidence: 99%

i-Rheo: Measuring the materials' linear viscoelastic properties “in a step”!

Tassieri

Laurati

Curtis

et al. 2016

Journal of Rheology

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“…This value is significantly above the value of 62.7 • ± 1.0 • obtained using an SMT rheometer (ARES-G2 in the present study) and displays a high degree of uncertainty reflective of the large deviation of the positions of the GP roots. The deviation in the root positions (±6.9 • ) should alert the experimentalist to inadequacies in the GP acquisition procedure, which may be caused by several experimental issues, for example; sample mutation Mours andWinter, 1994); sample inertia (Schrag, 1977); evaporation of the sample (Hellström et al, 2015); under/over/asymmetric loading (Ewoldt et al, 2015) or instrument inertia. In the present study, the effect of inaccurate instrument inertia calibration has been isolated by careful experimental design and data verification (see Sec.…”

Section: Resultsmentioning

confidence: 99%

“…Gelatin samples were loaded onto the rheometer at 34 • C before the upper geometry was lowered into place and the test commenced at which point the temperature was quenched to the test temperature. To satisfy the gap loading condition (Schrag, 1977), which ensures that the velocity gradient across the geometry gap is uniform thus confirming negligible sample inertia effects, a shearing gap of 150 µm was used. Inertia correction studies were completed using 2.5 wt.…”

Section: Cmt Rheometersmentioning

confidence: 99%

An enhanced rheometer inertia correction procedure (ERIC) for the study of gelling systems using combined motor-transducer rheometers

et al. 2017

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The rheological characterisation of viscoelastic materials undergoing a sol-gel transition at the Gel Point (GP) has important applications in a wide range of industrial, biological, and clinical environments and can provide information regarding both kinetic and microstructural aspects of gelation. The most rigorous basis for identifying the GP involves exploiting the frequency dependence of the real and imaginary parts of the complex shear modulus of the critical gel (the system at the GP) measured under small amplitude oscillatory shear conditions. This approach to GP identification requires that rheological data be obtained over a range of oscillatory shear frequencies. Such measurements are limited by sample mutation considerations (at low frequencies) and, when experiments are conducted using combined motor-transducer (CMT) rheometers, by instrument inertia considerations (at high frequencies). Together, sample mutation and inertia induced artefacts can lead to significant errors in the determination of the GP. Overcoming such artefacts is important, however, as the extension of the range of frequencies available to the experimentalist promises both more accurate GP determination and the ability to study rapidly gelling samples. Herein, we exploit the frequency independent viscoelastic properties of the critical gel to develop and evaluate an enhanced rheometer inertia correction procedure. The procedure allows acquisition of valid GP data at previously inaccessible frequencies (using CMT rheometers) and is applied in a study of the concentration dependence of bovine gelatin gelation GP parameters. A previously unreported concentration dependence of the stress relaxation exponent (α) for critical gelatin gels has been identified, which approaches a limiting value (α = 0.7) at low gelatin concentrations, this being in agreement with previous studies and theoretical predictions for percolating systems at the GP.

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“…The oscillatory shear rheology of water was measured with an apparent G' > G" suggesting solid-like behaviour. This low viscosity fluid was subsequently shown to be outside of the measurable range for oscillatory shear rheology in parallel plates as a standing wave can be set up in low viscosity fluids which interferes with the result (Schrag, 1977). Amplitude sweeps were completed to determine a stress value which was within the linear viscoelastic region (LVR) across the range of frequencies measured.…”

Section: Oscillatory Shear Rheologymentioning

confidence: 99%

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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Deviation of Velocity Gradient Profiles from the “Gap Loading” and “Surface Loading” Limits in Dynamic Simple Shear Experiments

Cited by 95 publications

References 0 publications

i-Rheo: Measuring the materials' linear viscoelastic properties “in a step”!

i-Rheo: Measuring the materials' linear viscoelastic properties “in a step”!

An enhanced rheometer inertia correction procedure (ERIC) for the study of gelling systems using combined motor-transducer rheometers

Rheology of soft particle suspensions

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