The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
John M. Dealy - One of the best experts on this subject based on the ideXlab platform.
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use of a sliding plate Rheometer to measure the first normal stress difference at high shear rates
Rheologica Acta, 2007Co-Authors: Junke Xu, Stéphane Costeux, John M. Dealy, Mark N De DeckerAbstract:The use of a sliding plate Rheometer (SPR) to determine the first normal stress difference of molten polymers and elastomers at high shear rates is demonstrated. The simple shear flow in this instrument is not subject to the flow instabilities that limit the use of rotational Rheometers to shear rates often below 1 s−1. However, issues of secondary flow and wall slip must be addressed to obtain reliable data using an SPR. A highly entangled, monodisperse polybutadiene and a commercial polystyrene were the polymers studied. The inclusion of the polystyrene made it possible to compare data with those obtained by Lodge using a stressmeter, which is an instrument based on the measurement of the hole pressure. The data from the two instruments are in good agreement and are also close to the predictions of an empirical equation of Laun based on the storage and loss moduli.
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a high pressure sliding plate Rheometer for polymer melts
Journal of Rheology, 1999Co-Authors: Francois Koran, John M. DealyAbstract:A high-pressure sliding plate Rheometer has been developed to investigate the effect of pressure on the rheological behavior of molten polymers and elastomers. The new Rheometer operates at pressures up to 70 MPa and temperatures up to 225 °C. The sample is subjected to simple shear, and the resulting shear stress is measured locally using a shear stress transducer. This design eliminates the inhomogeneities in pressure and shear rate that occur in high pressure capillary and slit Rheometers. Preliminary evaluation of the new instrument was carried out using a linear low density polyethylene. Viscosity curves were generated at pressures ranging from atmospheric pressure to 70 MPa, and the pressure coefficient of viscosity was determined. Experiments were also carried out in step strain and large amplitude oscillatory shear, demonstrating the new Rheometer’s use to study the nonlinear viscoelastic behavior of molten polymers. Finally, this instrument was used to study strain-induced crystallization.
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frequency response of a shear stress transducer installed in a sliding plate Rheometer
Journal of Rheology, 1998Co-Authors: John M. Dealy, Ranjit S JeyaseelanAbstract:A number of laboratories are currently using sliding plate Rheometers equipped with shear stress transducers to study the nonlinear viscoelasticity and slip of molten polymers. In making such measurements, it is sometimes essential to know to what degree the dynamic response of the shear stress transducer itself is influencing the output signal. Experiments should be designed to minimize this effect, but some attenuation and phase shift is inevitable because of the presence of polymer inside the transducer. We have measured the dynamic response of a shear stress transducer in situ in a sliding plate Rheometer for two molten polyethylenes. We have also developed a model for the transducer response. In oscillatory shear experiments above a frequency of 1 Hz, the amplitude ratio and phase lead are significant for both materials studied.
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An In-line Melt Rheometer for Molten Plastics
International Polymer Processing, 1994Co-Authors: B. I. Nelson, T. O. Broadhead, W. I. Patterson, John M. DealyAbstract:Abstract An in-line Rheometer designed for use as a sensor for closed-loop control of melt processing operations has been previously described. This instrument can measure the true viscosity of a melt stream over a range of shear rates. In order to evaluate its performance in processing applications the Rheometer was mounted on a twin-screw extruder. A chemical degradation process was used to introduce changes in the molecular weight distribution, and thus the viscosity of a polypropylene resin, and these changes were monitored using the Rheometer. For rapid replacement of melt in the zone of controlled shear in the Rheometer, flow simulations indicated that it would be advantageous to operate the Rheometer in a cyclic mode. A stochastic process identification technique based on a pseudorandom binary signal was used to determine the parameters of a first-order plus deadtime model of the process. In order to estimate the portion of the system response due to Rheometer dynamics, residence time distributions...
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nonlinear viscoelasticity of concentrated polystyrene solutions sliding plate Rheometer studies
Journal of Rheology, 1992Co-Authors: Nicole Raymond Demarquette, John M. DealyAbstract:Because of the degree to which the linearity and polydispersity of polystyrene samples can be controlled in laboratory polymerizations, the rheological properties of melts and solutions of this polymer have been extensively studied. However, in previous work the maximum strain or strain rate was limited to small values due to edge effects in the rotational Rheometers used. We used a sliding plate Rheometer equipped with a shear stress transducer and a birefringence apparatus to measure simultaneously the shear stress and the third normal stress difference, N3 (≡σ11−σ33), during step strain, start‐up of steady shear, and exponential shear. Depending on the strain history, the maximum strain achieved was between 20 and 80. The steady‐state shear stress in steady shear flow was found to be nearly independent of shear rate over a range of shear rates with a strong suggestion of a maximum, a phenomenon predicted by the Doi–Edwards theory. The relaxation modulus for the shear stress was found to be superposable...
Dongyang Sun - One of the best experts on this subject based on the ideXlab platform.
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High-shear rate rheometry of micro-nanofibrillated cellulose (CMF/CNF) suspensions using rotational Rheometer
Cellulose, 2018Co-Authors: Saumil Sudhir Vadodaria, Amaka J. Onyianta, Dongyang SunAbstract:Suspensions of cellulose micro- and nanofibrils are widely used in coatings, fibre spinning, 3D printing and as rheology modifiers where they are frequently exposed to shear rates > 104 s−1, often within small confinements. High-shear rate rheological characterisation for these systems is therefore vital. Rheological data at high-shear rates are normally obtained using capillary and microfluidic Rheometers, which are found in relative scarcity within research facilities compared to rotational Rheometers. Also, secondary flows and wall depletion prevalent at such high-shear rates often go unnoticed or unquantified, rendering the measurement data unreliable. Reliable high shear rate rheometry using rotational Rheometers is therefore desirable. Suspension of TEMPO-oxidised CMF/CNF was tested for its high-shear rate rheological properties using parallel plate geometry at measurement gaps 150–40 µm and concentric cylinder at 1 mm gap. The errors from gap setting, radial dependence of shear stress and wall depletion were quantified and accounted for. Viscosity data from 0.1 to 30,000 s−1 shear rates was constructed using both geometries in agreement. Possibilities of secondary flows, radial migration of fluid and viscous heating were ruled out. Steady shear flow data of CMF/CNF suspension from 0.1 to 30,000 s−1 obtained using rotational Rheometer
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high shear rate rheometry of micro nanofibrillated cellulose cmf cnf suspensions using rotational Rheometer
Cellulose, 2018Co-Authors: Saumil Sudhir Vadodaria, Amaka J. Onyianta, Dongyang SunAbstract:Suspensions of cellulose micro- and nanofibrils are widely used in coatings, fibre spinning, 3D printing and as rheology modifiers where they are frequently exposed to shear rates > 104 s−1, often within small confinements. High-shear rate rheological characterisation for these systems is therefore vital. Rheological data at high-shear rates are normally obtained using capillary and microfluidic Rheometers, which are found in relative scarcity within research facilities compared to rotational Rheometers. Also, secondary flows and wall depletion prevalent at such high-shear rates often go unnoticed or unquantified, rendering the measurement data unreliable. Reliable high shear rate rheometry using rotational Rheometers is therefore desirable. Suspension of TEMPO-oxidised CMF/CNF was tested for its high-shear rate rheological properties using parallel plate geometry at measurement gaps 150–40 µm and concentric cylinder at 1 mm gap. The errors from gap setting, radial dependence of shear stress and wall depletion were quantified and accounted for. Viscosity data from 0.1 to 30,000 s−1 shear rates was constructed using both geometries in agreement. Possibilities of secondary flows, radial migration of fluid and viscous heating were ruled out. Steady shear flow data of CMF/CNF suspension from 0.1 to 30,000 s−1 obtained using rotational Rheometer
Saumil Sudhir Vadodaria - One of the best experts on this subject based on the ideXlab platform.
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High-shear rate rheometry of micro-nanofibrillated cellulose (CMF/CNF) suspensions using rotational Rheometer
Cellulose, 2018Co-Authors: Saumil Sudhir Vadodaria, Amaka J. Onyianta, Dongyang SunAbstract:Suspensions of cellulose micro- and nanofibrils are widely used in coatings, fibre spinning, 3D printing and as rheology modifiers where they are frequently exposed to shear rates > 104 s−1, often within small confinements. High-shear rate rheological characterisation for these systems is therefore vital. Rheological data at high-shear rates are normally obtained using capillary and microfluidic Rheometers, which are found in relative scarcity within research facilities compared to rotational Rheometers. Also, secondary flows and wall depletion prevalent at such high-shear rates often go unnoticed or unquantified, rendering the measurement data unreliable. Reliable high shear rate rheometry using rotational Rheometers is therefore desirable. Suspension of TEMPO-oxidised CMF/CNF was tested for its high-shear rate rheological properties using parallel plate geometry at measurement gaps 150–40 µm and concentric cylinder at 1 mm gap. The errors from gap setting, radial dependence of shear stress and wall depletion were quantified and accounted for. Viscosity data from 0.1 to 30,000 s−1 shear rates was constructed using both geometries in agreement. Possibilities of secondary flows, radial migration of fluid and viscous heating were ruled out. Steady shear flow data of CMF/CNF suspension from 0.1 to 30,000 s−1 obtained using rotational Rheometer
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high shear rate rheometry of micro nanofibrillated cellulose cmf cnf suspensions using rotational Rheometer
Cellulose, 2018Co-Authors: Saumil Sudhir Vadodaria, Amaka J. Onyianta, Dongyang SunAbstract:Suspensions of cellulose micro- and nanofibrils are widely used in coatings, fibre spinning, 3D printing and as rheology modifiers where they are frequently exposed to shear rates > 104 s−1, often within small confinements. High-shear rate rheological characterisation for these systems is therefore vital. Rheological data at high-shear rates are normally obtained using capillary and microfluidic Rheometers, which are found in relative scarcity within research facilities compared to rotational Rheometers. Also, secondary flows and wall depletion prevalent at such high-shear rates often go unnoticed or unquantified, rendering the measurement data unreliable. Reliable high shear rate rheometry using rotational Rheometers is therefore desirable. Suspension of TEMPO-oxidised CMF/CNF was tested for its high-shear rate rheological properties using parallel plate geometry at measurement gaps 150–40 µm and concentric cylinder at 1 mm gap. The errors from gap setting, radial dependence of shear stress and wall depletion were quantified and accounted for. Viscosity data from 0.1 to 30,000 s−1 shear rates was constructed using both geometries in agreement. Possibilities of secondary flows, radial migration of fluid and viscous heating were ruled out. Steady shear flow data of CMF/CNF suspension from 0.1 to 30,000 s−1 obtained using rotational Rheometer
Anke Lindner - One of the best experts on this subject based on the ideXlab platform.
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Serpentine channels: micro-Rheometers for fluid relaxation times
Lab on a chip, 2013Co-Authors: Josephine Zilz, Christof Schäfer, Christian Wagner, Robert J. Poole, Manuel A. Alves, Anke LindnerAbstract:We propose a novel device capable of measuring relaxation times of viscoelastic fluids as small as 1 ms. In contrast to most Rheometers, which by their very nature are concerned with producing viscometric or nearly-viscometric flows, here we make use of an elastic instability that occurs in the flow of viscoelastic fluids with curved streamlines. To calibrate the Rheometer we combine simple scaling arguments with relaxation times obtained from first normal-stress difference data measured in a classical shear Rheometer. As an additional check we also compare these relaxation times to those obtained from Zimm theory and good agreement is observed. Once calibrated, we show how the serpentine Rheometer can be used to access smaller polymer concentrations and lower solvent viscosities where classical measurements become difficult or impossible to use due to inertial and/or resolution limitations. In the absence of calibration, the serpentine channel can still be a very useful comparative or index device.
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Serpentine channels: micro -- Rheometers for fluid relaxation times
arXiv: Soft Condensed Matter, 2013Co-Authors: Josephine Zilz, Christof Schäfer, Christian Wagner, Robert J. Poole, Manuel A. Alves, Anke LindnerAbstract:We propose a novel device capable of measuring the relaxation time of viscoelastic fluids as small as 1\,ms. In contrast to most Rheometers, which by their very nature are concerned with producing viscometric or nearly-viscometric flows, here we make use of an elastic instability which occurs in the flow of viscoelastic fluids with curved streamlines. To calibrate the Rheometer we combine simple scaling arguments with relaxation times obtained from first normal-stress difference data measured in a classical shear Rheometer. As an additional check we also compare these relaxation times to those obtained from Zimm theory and good agreement is observed. Once calibrated, we show how the serpentine Rheometer can be used to access smaller polymer concentrations and lower solvent viscosities where classical measurements become difficult or impossible to use due to inertial and/or resolution limitations. In the absence of calibration the serpentine channel can still be a very useful comparative or index device.
Ranjit S Jeyaseelan - One of the best experts on this subject based on the ideXlab platform.
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frequency response of a shear stress transducer installed in a sliding plate Rheometer
Journal of Rheology, 1998Co-Authors: John M. Dealy, Ranjit S JeyaseelanAbstract:A number of laboratories are currently using sliding plate Rheometers equipped with shear stress transducers to study the nonlinear viscoelasticity and slip of molten polymers. In making such measurements, it is sometimes essential to know to what degree the dynamic response of the shear stress transducer itself is influencing the output signal. Experiments should be designed to minimize this effect, but some attenuation and phase shift is inevitable because of the presence of polymer inside the transducer. We have measured the dynamic response of a shear stress transducer in situ in a sliding plate Rheometer for two molten polyethylenes. We have also developed a model for the transducer response. In oscillatory shear experiments above a frequency of 1 Hz, the amplitude ratio and phase lead are significant for both materials studied.
