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Author index ►Premanarayani Menon, Yin Yin Teo, Misni Misran

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Effect of diethylaminoethyl-dextran coated liposomes on the rheological properties of carbopol gel

Appl. Rheol.28:6 (2018) 62616 (6 pages) ►

Liposomal gel has played an important role in administration of drugs via topical and transdermal routes. Incorporation of liposome into gel not only has overcome the liquid nature of liposomal dispersion but also helped to preserve the original structure of liposome. In this study, we formulated a liposomal gel consisting of Carbopol gel and a diethylAminoethyl dextran (DEAE-DX) coated liposome. The effect of coated and non-coated liposomes on the rheological properties of Carbopol gel was investigated. The rheological results indicated that incorporation of liposomes into Carbopol gel modified the viscoelastic and flow behaviour of the gel significantly. Apart from that, liposomal gel consisting of DEAE-DX coated liposomes exhibited more solid-like behavior compared to the non-coated liposomal gel. Incorporation of DEAE-DX coated liposomes increased the yield stress of liposomal gel compared to non-coated liposomes. This supports the findings obtained from the amplitude and frequency tests whereby addition of DEAE-DX enhanced the rigidity of the gel so that the resultant gel was more resistant to flow.► Cite this publication as follows:

Menon P, Teo YY, Misran M: Effect of diethylaminoethyl-dextran coated liposomes on the rheological properties of carbopol gel, Appl. Rheol. 28 (2018) 62616.

The oscillatory shear rheological behaviors of a polyolefin plastomer (POP) at various temperatures were exAmined within its linear viscoelastic (LVE) regime. The apparent storage modulus, loss modulus, complex modulus, complex viscosity, and phase angle of POP at various temperatures are all found gap dependent, revealing that wall slip occurred under the applied oscillatory shear with the shear stress amplitude controlled constant. All Han plots and van Gurp-Palmen (vGP) plots of POP samples overlapped each other at various gaps at a certain temperature, suggesting that a time-gap-superposition (TGS) is valid with all the apparent angular frequency dependent storage modulus and loss modulus of POP at various gaps shifted to their master curves at a selected reference gap. This indicates that the wall slip can be understood as adding a dashpot in series to POP sample only with the apparent relaxation time multiplied by a shift factor. By TGS, a method to determine the wall slip length b and the actual oscillatory shear rheology of the fluids was consequently established. The results showed that the obtained b is dependent on temperature and wall slip made it possible to extend the experimental angular frequency range to lower frequencies. Further analysis revealed that wall slip did not influence the Arrhenius viscosity dependence of POP on temperature, while the viscous flow activation energy decreased.► Cite this publication as follows:

Li J, Wang L, Yu D, Christiansen JdC, Jiang S: Wall Slip of Polyolefin Plastomers under Oscillatory Shear, Appl. Rheol. 28 (2018) 33226.

The performance of modern slurry dewatering equipment is essentially dependent on the efficiency of compression. Shear yield stress as an index of flowability and compressibility is affected by suspension properties, while the presence of reagents may be significant. In this work, the effect of fine fraction, pH, flocculant, and collector concentration on the shear yield stress of copper flotation tailings at concentrators placed at Sarcheshmeh and Shahrebabak (Iran) were exAmined. Slump and settling tests were utilized to investigate the shear yield stress and compressibility of suspension. A pilot scale column was also employed to investigate the compressibility of suspension. Results indicated that shear yield stress increase, while compressibility decrease with flocculant concentration and fine fraction. It was found that the shear yield stress steadily increased with pH. Furthermore, in the presence of collectors the shear yield stress was reduced, while the compressibility enhanced.► Cite this publication as follows:

Garmsiri MR, HajiAminShirazi H: The effect of suspension properties on shear yield stress and compressibility of the suspension of copper flotation tailings, Appl. Rheol. 28 (2018) 15721.

Bacterial cultures, when under appropriate conditions, will grow into a biofilm. This weak hydrogel, composed of a complex conglomeration of bacterial clusters and extrapolymeric substances, serves to protect and insulate the bacteria from mechanical disturbances and environmental perturbations that may include antibiotics. Measuring the bulk rheology of the biofilm provides a quantitative description of the macroscopic structural integrity of the soft solid, which can be used to evaluate the efficacy of techniques that are often directed at their removal or prevention. Techniques for measuring the rheology of biofilms vary significantly, ranging from filtering or scraping the biofilm from its growth medium to attempting to grow the biofilm directly on the geometry of the rheometer. In this study, we developed a protocol for measuring the bulk rheology of a biofilm that was grown in a liquid medium. By keeping the biofilm intact from its growth phase through its rheological measurement, this method allows the mechanical strength of the biofilm to be probed without compromising its integrity. Presented in the form of case studies, the results from this study confirmed the gel-like structure of the biofilm of the wild-type strain of Pseudomonas aeruginosa (PAO_{1}). The flexibility of this protocol was shown by varying the incubation time of the biofilm from 4 to 9 days, providing a bulk elastic modulus that varied over two orders of magnitude and a yield stress that varied by an order of magnitude. Finally, in an attempt to demonstrate the fragility of biofilm, measurements were also taken on samples that were simply transferred from their incubated Petri dish to the rheometer. Results from the mechanical robustness of the biofilm are highlighted to emphasize the importance of understanding and addressing the mechanical strength of the biofilm system before attempting to remove the bacterial contAmination through chemical or mechanical means.► Cite this publication as follows:

Daalkhaijav U, Walker TW: Developing a Nondestructive Technique for Measuring Bulk Rheology of Pseudomonas Aeruginosa Biofilm, Appl. Rheol. 27 (2017) 64033.

Rheological investigations are reported for pure polyolefin and its clay-nanocomposites to establish structure-properties relationship with respect to filler concentration. Flow birefringence is performed through an engineering geometry slit-die to obtain centerline principal stress difference during elongational flow. The centerline stress profile of clay-nanocomposite revealed additional viscoelastic nature even at low silicate concentrations whereas at the slit entrance no exceptional strain hardening was reported. Effects of higher filler concentrations are further exAmined during the simple shearing flow where non-terminal low frequency strain hardening only at maximum concentration of clay exhibited pseudo solid like response with improved dynamic moduli. The increase in damping coefficient with increasing clay concentration shows polymernanocomposites are more strain sensitive. The Wagner exponential damping function could adequately describe the timestrain separability at all clay concentrations studied. The results of this investigation reveal that the polymers are time-strain separable at all clay concentrations during elongational and simple shearing flows. But different molecular orientations are possible according to layers alignment along the flow direction.► Cite this publication as follows:

Mudasir M, Ahmed R: An Explanation of Structure-Property Relationships for Polymer/Clay-Nanocomposites through Melt Flow Birefringence and Damping Function, Appl. Rheol. 27 (2017) 53700.

The Couette flow of a model yield-stress fluid with slip at the walls, a 0.12% Carbopol® 940 microgel, was analyzed in this work by simultaneous rheometrical and particle image velocimetry measurements (Rheo-PIV). The Rheo-PIV technique was first tested in the analysis of the Couette flow of a Newtonian fluid and then used to determine the velocity and shear rate distributions of the microgel across gap. A reliable and full description of the different flow regimes occurring in the steady Couette flow of yield-stress fluids with slip at the rheometer walls was obtained, which includes rigid body-like motion at stresses below the yield one, rigid body-like motion and shear flow at stresses above the yield one, as well as pure shear flow once the shear stress at the outer cylinder overcomes the yield value. Slip occurred at both cylinders, which were made up of hydrophobic (inner) and hydrophilic (outer) materials, respectively. The slip velocity values measured at both walls increased along with the shear stress and the trends of these dependencies deviated from the predictions of the hydrodynamic and elastohydrodynamic lubrication mechanisms of slip in the flow of soft deformable particle dispersions [1]. Besides, the yield stress was determined with good accuracy from the velocity profiles, as well as the location of the yielded and non-yielded regions for each flow condition. Finally, the consistency of the obtained velocity profiles was tested by comparison with a theoretical prediction for the Couette flow problem of a Herschel-Bulkley fluid without slip.► Cite this publication as follows:

Medina-Banuelos EF, Marin-Santibanez BM, Perez-Gonzalez J, Rodriguez-Gonzales F: Couette flow of a yield-stress fluid with slip as studied by Rheo-PIV, Appl. Rheol. 27 (2017) 53893.

In primary cementing of an oil well, the oil-based drilling mud (lubricant) is displaced by sequential pumping of an aqueous surfactant 'spacer' fluid, and then the aqueous cement slurry. The cement sets to seal the annular space between the geological formation and the steel wellbore casing. In the displacement process, there will be some intermixing of the fluids. Compatibility between the drilling mud, the spacer, and the cement slurry is necessary to achieve successful zonal isolation. In this study, steady shear and dynamic oscillatory shear were used to investigate the changes in rheology that occur as a result of this inter-mixing. For the steady shear measurements the Herschel-Bulkley model shows good agreement with measured stress-strain data, accurately capturing the yield stress and the plastic viscosity over the range of shear rates from 0.75 to 520 s^{-1}. The vis-coelastic properties, which are related to the microstructure of the slurry were exAmined by using dynamic oscillatory shear and it was demonstrated that this measurement could be utilized to evaluate the compatibility. Moreover, a close relationship between yield stress and storage modulus was observed, which enabled a correlation relating the steady shear and the dynamic oscillatory results.► Cite this publication as follows:

Choi M, Prudhomme RK, Scherer GW: Rheological evaluation of compatibility in oil well cementing, Appl. Rheol. 27 (2017) 43354.

Shortenings are examples of soft viscoelastic materials with important mechanical functions in baking applications. To fully understand their mechanical functionality, it is essential to correlate material microstructure with rheological behavior. We investigated commercial shortenings designed for various applications, with emphasis on those intended for use in lAminated doughs. The microstructure of lAminating shortenings was characterized by well-defined crystallites arranged in a layer-like fashion, whereas all-purpose and cake shortenings exhibited more distorted crystallites packed in a more heterogeneous manner. Oscillatory and creep shear behavior demonstrated that all shortenings acted as viscoelastic solids, but lAminating shortenings had higher viscosities at .rest. in the linear regime. Recovery in the nonlinear regime showed that lAminating shortenings had lower fractional recovery associated with pronounced plastic irreversible deformations. Extrusion tests also in dicated higher viscous dissipation for lAminating shortenings. It is argued that the unique layered microstructure is partly responsible for the increased viscous and plastic flow of lAminating shortenings, aspects that dictate the ability of these products to endure mechanically demanding processes without apparent catastrophic failure.► Cite this publication as follows:

Macias-Rogriguez B, Marangoni A: Bakery shortenings: structure-mechanical function relations, Appl. Rheol. 27 (2017) 33410.

It has been proposed that hydrogen bonding plays a role in promoting the electrospinnability of some materials. In this work, the significance of non-covalent interactions in the electrospinnability of aqueous sugar solutions (i.e. mono- and disaccharide) was investigated as a function of carbohydrate concentration. The electrospinnability of concentrated aqueous solutions of glucose, fructose, and sucrose was studied by physicochemical and rheological characterization methods, and by subsequently exAmining the resulting morphology via scanning electron microscopy. The results on the electrospinning of concentrated saccharide solutions indicated the significance of non-covalent interactions on the electrospinning of these systems. Electrospinnability models based on critical concentration and visco-elasto capillary theories were compared with the experimental results. It is shown that visco-elasto capillary theory has the closest correlation with the experimental data. The electrospinnability of highly concentrated saccharide solutions appears to be directly related to the density and intermolecular bonding capacity of the solution.► Cite this publication as follows:

Lepe PGT, Tucker N, Watson AJA, LeCorre-Bordes D, Fairbanks AJ, Staiger MP: The electrospinnability of visco-elastic sugar solutions, Appl. Rheol. 27 (2017) 35703.

In modern intensive care a comprehensive solution for monitoring the coagulation status or blood clotting problems is currently not available, because fast reliable detection of all bleeding-based disorders (coagulation, fibrinolysis, platelet function) cannot be conducted with a single medical device. This situation calls for a comprehensive technical solution, which we think possible to be solved with a rheological piezo-based system. Rheological measurements provide valuable information on the viscoelastic properties of complex fluids. Here, we compared the performance of a commercially available rheological industrial device using shear stress (Kinexus Pro, Malvern) with that of a piezo-based research measuring system (piezoelectric axial vibrator, PAV) applying squeeze flow to sample fluids. Comparative measurements using different xanthan concentrations (0.1 to 5%) were carried out at 25 and 37 °C. At higher concentrations (1, 2, and 5%), there was an overlapping frequency range and a consistent range of the viscous and elastic shear viscosity for both systems, allowing direct comparisons. Specifically the lower concentrations of 0.1, 0.2, and 0.5% xanthan could be used to assess the possibility of both systems to measure blood coagulation, as those concentrations correspond approximately to the viscosity of human blood. Measurement of blood coagulation was then also tested with the PAV. Measurement repeatability was assessed performing blood coagulation measurements over time at different frequencies (10, 100, 300, and 1000 Hz). The middle frequencies of 100 and 300 Hz provided the most repeatable results for blood. Afterwards the activated clotting time (ACT) was performed with PAV at 300 Hz. The piezo-based measuring system was able to differentiate between various heparin blood concentrations (1, 2, and 3 IU/ml). In this study the reliability, repeatability and limitations of the piezo system were exAmined. Our initial results showed that the piezo system can be used to assess blood coagulation, but further studies are necessary to confirm these promising results. The aim of a fast, small and reliable point-of-care system may be possible with this type of rheological device.► Cite this publication as follows:

Kunnkattu S, Gross T, Stoppelkamp S, Knieps J, Remmler T, Fennrich S, Wendel HP, Rauch N: Potential of a piezo-based measuring method (PAV) as a haemostasis monitoring system compared to a rotational rheometer , Appl. Rheol. 27 (2017) 13540.

DLS Microrheology involves tracking the time dependent motion or mean square displacement of dispersed tracer particles of known size using Dynamic Light Scattering (DLS) in order to determine viscoelastic properties of the dispersion medium. The viscoelastic moduli are calculated using a generalised form of the Stokes-Einstein equation which requires Fourier Transformation of the MSD. An alternative approach for estimating the viscoelastic moduli uses a modified algebraic form of the generalized Stokes-Einstein equation, which employs a power law expression to describe the local change in MSD with time. Since the mean square displacement is linearly related to the creep compliance, it can be shown that the same algebraic approach can also be applied to creep measurements made on a rotational rheometer, giving access to the low frequency moduli in a fraction of the time required for oscillatory testing. Furthermore, the quality of the conversion process can be improved by fitting a Burgers model to the time domain data prior to conversion thus minimising errors associated with local differentiation, which is fundamental to the conversion approach.► Cite this publication as follows:

Duffy JJ, Rega C, Jack R, Amin S: An algebraic approach for determining viscoelastic moduli from creep compliance through application of the Generalised Stokes-Einstein relation and Burgers model, Appl. Rheol. 26 (2016) 15130.

The core of activated sludge monitoring lies in the biological analyses. Anyway, the knowledge of sludge physical characteristics is crucial for a proper management of WWTPs (Waste Water Treatment Plants). One of these physical features is viscosity that, notwithstanding its valuable role has not yet become a routine analysis. This study exAmined the evolution of rheological properties of two sludges alongside the .purification route. (from the biological reactor up to the sludge treatments). It could been shown that sludges behaved like non-Newtonian fluids and dry solids content strongly affected viscosity values, which reached relatively high values. Microscopic observation of flocs was carried out. Both the sludges revealed similar features, in particular an over-proliferation of filamentous bacteria. This work showed how rheological measurements can be a tool to obtain information on microbiological composition of activated sludge and how it could be related to settleability properties.► Cite this publication as follows:

Papa M, Pedrazzani R, Nembrini S: Should rheological properties of activated sludge be measured?, Appl. Rheol. 25 (2015) 24590.

As a fundamental rheological property, shear yield stress is used to assess the flowability of suspensions. Slump test is a cheap and quick experiment which is commonly used to estimate shear yield stress on-site. It has been generally believed that, cylinder height to diameter ratio and lifting velocity has no effect on the slump test results. In this work, the sensitivity of the slump test to the height to diameter ratio and lifting velocity of cylinder was investigated. Projections on the top surface of suspension column after the slump test were also analyzed. Results indicated that, the effect of cylinder height to diameter ratio is negligible in the low range of shear yield stress, while it is remarkable in the high range. It was deduced that, using a cylinder with dimension ratio in the range of 0.83 to 1.15 is more reliable. Furthermore, it is shown that the lifting velocity of cylinder has a significant effect on the results. A high lifting velocity could introduce a great error in estimation particularly in a large height to diameter ratio.► Cite this publication as follows:

Garmsiri M, HajiAminShirazi H, Yarahmadi M: An analysis of the influence of cylinder dimension ratio and lifting velocity on the slump test results, Appl. Rheol. 25 (2015) 23416.

Studies have shown that rheology of asphalt mastic plays an important role in pavement performance, specifically for the case of recycled asphalt pavement (RAP) mastics which contains mostly aged binder. This study determines the rheological properties of RAP mastics and a comparison is conducted with the no-RAP binder. Influence of RAP fines on rutting and cracking performances is also studied. A performance grade PG 70-22 binder is mixed with varying percentages (10, 20, and 40%) of crushed stone (no-RAP) and RAP fines to prepare mastics. Dynamic Shear Rheometer testing is conducted to measure the complex shear modulus G^{*}, and phase angle δ of these mastics at high and intermediate temperatures through frequency sweep. Bending Beam Rheometer test is conducted at low temperatures (-10 C, -16 C, and -22 C) to measure the stiffness S and relaxation (m-value). Direct Tension Test is conducted to compute the failure strain at -22 C. Results show an improvement in rutting with the addition of RAP fines (increase in G^{*}/sinδ), a decline in low-temperature cracking resistance (increase in S). Addition of RAP fines up to 20% does not affect the fatigue resistance of the mastics adversely. However, fatigue cracking of 40% RAP mastic is shown to be high (increase in G^{*}sinδ). 40% RAP mastic shows a smaller failure strain than the virgin binder and 40% no-RAP mastic, which indicates that mastics containing RAP are more susceptible to low-temperature cracking. To characterize the viscoelastic properties of the RAP mastics, the G^{*}master curve is constructed at 22 C reference temperature. RAP mastics. master curves follow the sigmoidal function irrespective of %RAP in mastics. However master curves do not show any significant difference between RAP mastics and no-RAP mastics.► Cite this publication as follows:

Mannan UA, Islam M, Weldegiorgis M, Tarefder R: Experimental investigation on rheological properties of recycled asphalt pavement mastics, Appl. Rheol. 25 (2015) 22753.

The rheological properties of diamond (< 10 nm) in silicone oil (PDMS) were analyzed using steady shear and oscillatory shear measurements. Unlike micron sized diamond suspensions these suspensions were non Newtonian and showed strong viscoelastic behavior without the electric field applied. Furthermore these nanodiamond mixtures showed sigmoidal behavior for their apparent viscosity as the shear rate is increased without the electric field applied. When the electric field was applied the apparent viscosity of the mixtures increased by an order of magnitude at lower shear rates. The effects of electric field and concentration on diamond rheology are both exAmined. The rate of shear thinning for the mixtures is high when the applied electric field is high. At high shear rates for the mixture the electric field does not have much effect. The flow curve was described by the Herschel-Bulkley model. Yield stress values obtained from the model gives an important relationship between yield stress, electric field and concentration, that is τ ∝Eand where 0.8 <^{n}n< 1.3.► Cite this publication as follows:

McIntyre C, Pereira A: Electrorheology of nanodiamond/PDMS nanofluids in steady and oscillatory shear, Appl. Rheol. 24 (2014) 63471.

This study addresses the Taylor-Galerkin/pressure-correction solution of industrial high-speed reverse roller coating flow associated with thin-film paint-coatings of strip-steel. Novel aspects lie in the inclusion of the dynamic wetting line and flow analysis due to surface tension and inelastic rheology effects, via shear-thinning and lowering high shear viscosity levels. The main aim of the study is to predict the zonal flow influences by exAmining viscous flow structures around the meniscus, nip and wetting line regions, conveyed via streamline and shear rate patterns, surface distributional lift and localised nip-pressures. The majority of this study focuses on the secondary nip-vortex and its influences on the contact point and dynamic wetting line. This aspect of the flow provides the driving mechanism for the onset of instabilities, which governs the entire process and tends to determine the consistency of the film thickness at the outflow. Positive peak-pressures tend to increase with decrease in nip-gap size. At low nip-gap size, negative peak pressures are observed around the substrate-wetting line contact region. At higher speed-ratios, positive peak pressures are seen to increase with less recirculation apparent around the contact zone. Significantly and upon surface tension increase, the dynamic wetting line is sucked further inwards towards the nip-gap, stimulating a localised wetting line-foil third vortex structure, which causes an apparent reduction in film-leakage thickness.► Cite this publication as follows:

Echendu S, Tamaddon-Jahromi H, Webster M: Modelling Reverse Roll Coating flow with dynamic wetting lines and inelastic shear thinning fluids, Appl. Rheol. 23 (2013) 62388.

In this work, bentonite suspension and mixtures containing 5 wt% of bentonite and 0.1 and 0.5 wt% of carboxymethyl cellulose (CMC) were investigated in terms of their rheology and hydrodynamic behaviour in pipe flow. All fluids exhibited non- Newtonian rheological behaviour that can be well described by the three parameters Herschel-Bulkley model. The axial velocity distribution was determined using ultrasonic pulsed Doppler velocimetry technique. In the lAminar regime the flow parameters were predicted by integration of the constitutive rheological model used. In the turbulent flow, the Dodge and Metzner model was applied to fit the experimental data. The measurements of the friction factor showed a small amount of drag reduction for the pure bentonite suspension, whereas for the polymer.clay blend the drag reduction was more important.► Cite this publication as follows:

Benslimane A, Bekkour K, Francois P: Effect of addition of Carboxymethylcellulose (CMC) on the rheology and flow properties of bentonite suspensions, Appl. Rheol. 23 (2013) 13475.

Dynamic oscillatory and creep tests are two common rheological methods used to determine viscoelastic properties. In the food industry, these tests are generally performed in the linear viscoelastic region, providing information on food structure and behavior over a range of timescales. However, this small-strain testing gives an incomplete picture of structural deformation and breakdown. Nonlinear oscillatory and creep testing, on the other hand, may yield a more complete fingerprint of food structural behavior. In this study, whey protein isolate (WPI)/k-carrageenan gels with different structures were studied under large amplitude oscillatory shear (LAOS) and creep tests to determine the impact of structure on nonlinear oscillatory and creep behavior, and to exAmine correlations between nonlinear oscillatory and creep parameters. Evaluated structural types comprised a homogeneous protein gel, a bicontinuous gel, in which both WPI andk-carrageenan exhibited a continuous network, and a carrageenan continuous gel. Creep data were fit to 4-element Burgers models for further analysis, and the predicted compliance values were found to be in agreement with experimental data (R^{2}≥ 0.90). Carrageenan continuous gels showed the greatest degree of nonlinearity under LAOS (25 % strain), while homogeneous gels displayed the least. Nonlinear oscillatory data was found to correlate (R^{2}> 0.7, p < 0.05) with parameters used in the 4-element Burgers model. Hence, nonlinear viscoelastic behavior among materials may be evaluated by both creep data and nonlinear oscillatory data. However, nonlinear oscillatory data gives a quantitative measure of the type and extent of nonlinear behavior, while creep data indicates only the presence of nonlinear behavior. By combining information on structural behavior derived from nonlinear oscillatory and creep data, it is possible to determine nonlinear behavior over a wide range of timescales, yielding insight into structural deformation and breakdown under application of stress or strain at different rates.► Cite this publication as follows:

Melito HS, Daubert CR, Foegeding EA: Creep and large amplitude oscillatory shear behavior of whey protein isolate/.-carrageenan gels, Appl. Rheol. 22 (2012) 63691.

Generally, fly ashes (FA) could function as either semi-reinforcing or non-reinforcing fillers in polymeric systems, depending on particle size, specific surface areas and surface chemistry of FA particles. Typically, FA particles are spherical with smooth surfaces having significant influences on viscoelastic and mechanical properties. Additionally, the presence of heavy metals in FA particles could play role on degradation process of rubber molecules to some extent. In this article, the storage instability and thermal aging properties of FA filled natural rubber (NR) compounds were focused via changes in viscoelastic responses. Results obtained reveal that the storage duration of FA filled NR compounds leads to decreases in elastic modulus and molecular weight, particularly in the compounds with high FA loading. By replacing NR with polyisoprene (IR) containing no non-rubber substances, the storage stability is significantly enhanced. It is believed that the presence of metal ions in both FA and non-rubber substances in NR could catalyze the degradation process of rubber molecules. Such degradation process could effectively be suppressed by the addition of Amine-based antioxidant.► Cite this publication as follows:

Saowapark T, Sae-oui P, Sombatsompop N, Sirisinha C: Storage Instability of Fly Ash Filled Natural Rubber Compounds, Appl. Rheol. 22 (2012) 55414.

The T-bar rheometrical tool (Brookfield Engineering Laboratories, Inc.) is a slender rod which is placed in a material and rotated horizontally about its short axis by a vertical shaft. The torque on the shaft from lAminar flow of material around the rod is determined by the material.s rheological properties. T-bar experiments for a Newtonian liquid are shown to agree closely with existing theory. For yield stress materials an approximation is derived for the torque on a rotating T-bar which is supported by experiments on a range of materials. The torque for very slow rotational speed is insensitive to boundaries beyond a few T-bar diameters and is shown to correlate with the material.s yield stress and other non-Newtonian parameters. A stepdecrease in torque for each half-revolution of the T-bar was shown by some materials and possible origins of this effect are discussed.► Cite this publication as follows:

Anderson VJ, Meeten GH: Interpretation of T-bar tool measurements for yield stress materials, Appl. Rheol. 22 (2012) 55370.

Ultrasonic Velocity Profiling with Pressure Drop (UVP+PD) is a technique, which allows the measurement of the shear rate dependent viscosity non-invasively in a lAminar pipe flow. To assess the performance of different data processing approaches for the extraction of the rheometric values, model fluids are characterized under well defined flow conditions created with a piston setup. Considering the shear rate range available in the pipe flow, a good quantitative agreement is found between the in-line measurements and the off-line measurements made with a rotational rheometer► Cite this publication as follows:

Birkhofer B, Debacker A, Russo S, Ricci S, Lootens D: In-line rheometry based on ultrasonic velocity profiles: comparison of data processing methods, Appl. Rheol. 22 (2012) 44701.

We constructed a macroscopic model illustrating behavior of a single entanglement knot of macromolecules in a melt and exAmined its behavior at different deformation rates. A model consists of flexible elastic strips, which are tied in a granny knot (modeling not a real geometrical form of entanglements but their behavior at relatively easy sliding). This scheme models the situation when elastic energy exceeds the energy of the Brownian motion. The behavior of a knot chosen for modeling is different at low and high deformation rates. In the previous case knots disentangle as predicted by the .tube. model, elastic strips slip out a knot and this is an illustration of flow. In the latter case, knots tighten up, further extension of strips leads to the increase in stresses up to breakup of a strip. This effect imitates the transition from the flow to the rubbery-like behavior of polymer melts, when flow becomes impossible due to the formation of quasi-permanent entanglements. The general dimensionless correlation for the process under discussion has been proposed.► Cite this publication as follows:

Malkin A, Semakov A, Kulichikhin V: Macroscopic modeling of a single entanglement at high deformation rates of polymer melts, Appl. Rheol. 22 (2012) 32575.

In this study the steady flow viscosity, complex viscosity and relative viscosity of PP/FeSi composite melts with filler contents up to x =0.7 (70 vol.%) of spherical Iron Silicon (FeSi) microparticles (in 10 vol.% steps) with diameter of d < 106 mm have been investigated. Plate-plate and capillary rheometry at different shear rate and angular frequency in the range from 0.12 to 16000 s-1 (rad/s) were used. The results show an inflection point at high filler contents x ≥ 0.4 (40 vol.%) and low shear rates (< 1 s-1) caused by particle/particle interactions.With increasing shear rate and angular frequency the typical shear thinning flow behaviour of polymer melts was found for all investigated filler contents. The viscosity increases with increasing filler content at constant shear rate and angular frequency.Time-temperature-superposition (TTS) and Cox-Merz relation were fulfilled at filler contents up to x =0.3 (30 vol.%). The results of complex viscosity were normalized to a superimposed master curve. The three parameter of the new modified Carreau model were calculated for PP melt and shifted by two factors depending on the filler content. Based on these modifications, the complex viscosity was calculated for each filler content up to x =0.3. The complex viscosity graphs were reduced to a general master curve of the investigated PP/FeSi composites up to x =0.3. Finally, the relative viscosity of the exAmined composites shows the best fit to the Quemada model► Cite this publication as follows:

Kirchberg S, Ziegmann G: Effect of Spherical Iron Silicon (FeSi) Microparticles on the Viscosity Behaviour of Polypropylene Melt, Appl. Rheol. 21 (2011) 35495.

This article reports viscosity data on a series of colloidal dispersions collected as part of the International Nanofluid Property Benchmark Exercise (INPBE). Data are reported for seven different fluids that include dispersions of metal-oxide nanoparticles in water, and in synthetic oil. These fluids, which are also referred to as 'nanofluids,' are currently being researched for their potential to function as heat transfer fluids. In a recently published paper from the INPBE study, thermal conductivity data from more than 30 laboratories around the world were reported and analyzed. Here, we exAmine the influence of particle shape and concentration on the viscosity of these same nanofluids and compare data to predictions from classical theories on suspension rheology.► Cite this publication as follows:

Venerus DC, Buongiorno J, Christianson R, Townsend J, Bang I, Chen G, Chung S, Chyu M, Chen H, Ding Y, Dubois F, Dzido G, Funfschilling D, Galand Q, Gao J, Hong H, Horton M, Hu L-W, Iorio CS, Jarzebski AB, Jiang Y, Kabelac S, Kedzierski MA, Kim C, Kim J-H, Kim S, McKrell T, Ni R, Philip J, Prabhat N, Song P, VanVaerenbergh S, Wen D, Witharana S, Zhao X-Z, Zhou S-Q: Viscosity measurements on colloidal dispersions (nanofluids) for heat transfer applications, Appl. Rheol. 20 (2010) 44582.

The present work deals with the study of the rheological behaviour of PVC (polyvinylchloride) pastes containing particles of ~ 150 μm in diameter obtained by polymerization in suspension.The rheological properties of the PVC pastes were characterized by creep experiments using 6-bladed vane geometry. The pastes show a very small compliance and a very narrow linear domain. The effects of temperature, of interstitial liquid and of saturation level of the wet paste were studied in detail and it was found that they significantly modify the creep behaviour. Other techniques allowed us to characterise rearrangements of the particles under load, in compression, by their oedometric modulus and by the failure stresses measured using a shear box. A very high oedometric modulus was measured (20 MPa) and by application of the Mohr-Coulomb criterion the internal friction coefficient (μ ~ 0.6) and the cohesion of the materials were deduced.We conclude from this investigation that the interfacial properties of the grains play a major role in the behaviour of the wet pastes under shear or in compression. The paper illustrates the difficulties in measuring the rheological and the structural properties of jammed systems made from non-ideal (real) particles and reveals the key parameters in studying such media.► Cite this publication as follows:

Rabia A, Djabourov M, Feuillebois F, Lasuye T: Rheology of wet pastes of PVC particles, Appl. Rheol. 20 (2010) 11961.

Aggregation, heterogeneous flows, and complex particle geometries all pose challenges in rheology. This paper uses squeeze flow rheometry techniques to exAmine a case, where all of these played a role. The applicability of some squeeze theories is tested, and the ability to predict results based on suspension theories is exAmined. The squeeze flow data is shown to deviate from Stefan's Law [Stefan J, Sitz. Kais. Akad. Wiss. Math. Nat. Wien 69 (1874) 713-735]. The suspension rheology deviated from predicted theory, but by taking into account particle effects such as aggregation the fit to the empirical Maron-Pierce equation [Maron SH and PE Pierce, J. Coll. Sci. 11 (1956) 80-95] could be understood. The conclusions of this study show how using only squeeze flow techniques the synergistic nature of these effects can be better understood.► Cite this publication as follows:

McIntyre EC, Filisko FE: Squeeze Flow Rheology of Zeolite Suspensions, Appl. Rheol. 19 (2009) 44322.

In practice, while placing concrete in a formwork by pumping, the pressure generated by the pump is not controlled. In order to enhance the safety on the worksite, and in view of the current economic and ecologic arguments, it would be useful to dispose of an equation able to predict pressure losses based on the rheological properties of the concrete and the pipe configuration. This paper describes the derivation of an extended version of the Poiseuille formula, for shear-thickening materials with a yields stress, described by the modified Bingham equation. This formula is applied to flow-tests with self-compacting concrete. The results prove the applicability of this extended Poiseuille formula, showing that the flow is occurring in lAminar regime, with no significant wall slip.► Cite this publication as follows:

Feys D, Verhoeven R, DeSchutter G: Extension of the Poiseuille formula for shear-thickening materials and application to Self-Compacting Concrete, Appl. Rheol. 18 (2008) 62705.

The lubricated semi-hyperbolic die has been proposed as a technique for generating uni-axial extensional flow and, hence, as a device for measuring elongational viscosity. Two methods for extracting extensional viscosity data for polymer melts in lAminar flow from this device have been proposed and are evaluated here. Following the approach proposed by Collier and coworkers, values of the transient extensional viscosity, η_{c}^{+}, obtained from a non-lubricated semi-hyperbolic (SHPB) die for several polyethylene (PE) melts were found to be considerably higher than values obtained by means of the Münstedt type device. Furthermore, the values of η_{c}^{+}obtained from the SHPB die were considerably higher than the strain averaged values of η_{c}^{+}which Everage and Ballman proposed would be obtained from a lubricated SHPB. The pressure drop across a SHPB die was estimated assuming resistance was all due to wall shear (using the lubrication approximation) for two PE resins. In the case of low density PE (LDPE) the values agreed to within 20% of the measured values suggesting that shear effects at the die wall were dominating the pressure drop and not extensional stresses. An analysis was carried out which showed that in the presence of lubrication the conditions for which the values of η_{c}^{+}obtained from the SHPB would be relatively accurate (Hencky strains > 5.0).► Cite this publication as follows:

Baird DG, Huang J: Elongational Viscosity Measurements Using A Semi-Hyperbolic Die, Appl. Rheol. 16 (2006) 312.

Of the torsional drag-flow experiments, the hands-down winner for simplicity and ease of use is that using parallel- plate fixtures. This geometry is highly flexible, allowing custom modification of plate size and material, and is easily adaptable for optical use and the application of electric fields. However, its nonuniform flow is a major encumbrance for measuring nonlinear response. In 1987, Cross and Kaye offered a simple and clever solution for this problem, which essentially states that one assumes the sample is Newtonian, but the shear rate assigned to the observed ''Newtonian'' viscosity is 3/4ths of the rim shear rate . This shift factor arises from the use of Gaussian integration over radius of the nonlinear stress profile. Recent re-exAmination of the Cross-Kaye rule indicates that there may be a more accurate rule of thumb with the shift factor being 0.8 instead of 0.75 (4/5 instead of 3/4). However, for complex materials, the real question is how much useful information is covered up by this approach vs. the traditional differentiation of the integral to account for the stress profile. We have attempted to answer this question using a selection of nonlinear measurements on an AB block copolymer solution that is rheologically complex.► Cite this publication as follows:

Shaw MT, Liu ZZ: Single-point Determination of Nonlinear Rheological Data from Parallel-Plate Torsional Flow, Appl. Rheol. 16 (2006) 70.

Conventional methods often impose difficulties when measuring the viscosity of fluids containing particles or fibres, e.g. tomato paste or fruit preparations, mainly due to the narrow gaps of the viscometer. In order to solve these problems different geometries have been developed, e.g. different mixer systems and wide gap double concentric cylinders. However, these can not be evaluated assuming a constant shear rate throughout the fluid. In this study, three different kinds of mixer systems have been studied; a small and a large paddle and a helix. For the mixer systems an average shear rate must be determined and a quotient between torque and shear stress must be found. In addition, a wide gap double concentric cylinder (DCC) was exAmined and evaluated using two different methods. When evaluating the mixer systems a method based on the Couette analogy has been used successfully for a number of complex fluids, including prepared sauces and fruit samples containing particles of different size. The DCC has been evaluated using a numerical as well as an approximate method, both giving results of good accuracy. All systems had the limitation that no consistent results were obtained for tomato paste. However, when starch was added to the diluted tomato paste dispersion, satisfying results were once again obtained.► Cite this publication as follows:

Roos H, Bolmstedt U, Axelsson A: Evaluation of New Methods and Measuring Systems for Characterisation of Flow Behaviour of Complex Foods, Appl. Rheol. 16 (2006) 19.

Polymer melts can be mixed with many monomers, plasticizers, antistatics or foAming additives. Properties of such mixtures can change during blending because of chemical reactions like polymerization or crosslinking. The process may be carried out either in stirred tanks, extruders or in motionless mixers. In this paper we focused on the mixing time and the diffusion time of reagent, plasticizer and polymer thanks to rheological tools, and on the way how rheological properties can be studied during chemical reaction in polymer blending. The concept of rheoreactor and Couette analogy were introduced since we have a reactor on our disposal that can mix solution and measure rheological properties without taking sample. This apparatus appears to be an appreciable tool in complement of internal mixers that are specific to polymer blending. For example, we show the importance of the competition between mixing time and reaction time for reactive systems.► Cite this publication as follows:

Lacoste C, Choplin L, Cassagnau P, Michel A: Rheology Innovation in the Study of Mixing Conditions of Polymer Blends during Chemical Reaction, Appl. Rheol. 15 (2005) 314.

The effect of high ac electric fields upon a liquid crystalline polymer solution, poly(n-hexyl isocyanate) in p-xylene, is exAmined. The results show that the solutions exhibit an increase in rheological properties proportional to the strength of the field at concentrations well below those exhibiting liquid crystalline behavior. The effects of frequency and field strength are exAmined as a means to explain this previously unreported phenomenon.► Cite this publication as follows:

Menna TJ, Filisko FE, Lynch RA: Effect of Electric Fields on the Rheological Properties of the Isotropic Phase of phic/p-Xylene Solutions, Appl. Rheol. 15 (2005) 172.

The answer to this provocative question is .no.! This is demonstrated by experiment and analysis for two very different materials . a highly concentrated emulsion and an 8%v/v Kaolin clay suspension. The flow curves of both materials clearly showed a low shear Newtonian asymptote and a pseudoplastic domain. The difference in the accuracy of the fitting equations relates mainly to the low shear rate domain. While the Cross equation is adequate over the full flow curve, the power law and the Herschel-Bulkley equations are clearly inadequate for the low shear rate range. These equations as well as the direct numerical method (using the Rabinowitsch- Weissenberg integral) were used for the calculation of the lAminar pipe flow transport characteristics and the results were compared with experimental pipe flow data. It was shown that in all cases the maximum error did not exceed 5%, which is quite acceptable for engineering design, indicating that the choice of the flow curve fitting equation was unimportant.► Cite this publication as follows:

Malkin AY, Masalova I, Pavlovski D, Slatter P: Is the Choice of Flow Curve Fitting Equation Crucial for the Estimation of Pumping Characteristics?, Appl. Rheol. 14 (2004) 89.

A short synopsis of the recently proposed reptation models based on the Doi and Edwards. tube concept is provided. Specifically, a critical exAmination of a number of theories like the .simplified. Mead-Larson-Doi model, the Ötinger model and the .Double Convection Reptation. model of Marrucci and coworkers has been performed. These models have been chosen due the fact that are computationally tractable as they mimic the chain dynamics in the tube using unconnected portions of the chain in a mean field way. Overall, we find each of these models to be equally competitive barring a few exceptional cases, where it is suspected that certain critical assumptions, made during the formulation of the model could lead to inaccurate predictions under transient or Lagrangian unsteady settings.► Cite this publication as follows:

Gigras PG, Khomami B: An Evaluation of Single-Segment Reptation Theories for Linear Entangled Polymeric Systems, Appl. Rheol. 14 (2004) 22.

Previous studies involving rheological measurement of semi-solid foods have reported a large amount of data variability, but have focused little on understanding the cause of such variability. This project exAmined whether differences in normal force have an effect on the variability of rheological measurements. Experimental methods focused on error introduced during sample loading; specifically whether normal force application during loading influenced the storage (G.) and loss (G.) moduli of semi-solid and liquid foods. Samples were loaded to 5 or 20 N between the parallel plates of a TA-1000N rheometer and tested immediately. For all semi-solid products tested, normal force application during sample loading did significantly affect oscillatory parameters, with G. and G. measurements increasing up to 50 % with greater normal force. However, loading normal force did not significantly influence the parameters measured for the liquid sample. This suggests that differences in normal force during loading could be a significant source of data variability during rheological measurement of semi-solid products.► Cite this publication as follows:

Pearce MAD, Bellmer DD: Data Variability in Rheological Measurement of Semi-Solid Foods: Effects of Loading Normal Force, Appl. Rheol. 12 (2002) 282.

In the case of some highly viscous fluids, or thick pastes (such as those exhibiting high yield stress and/or high plastic viscosity), neither rotational nor tube type viscometers are suitable for rheological characterisation. Due to their capacity for generating and maintaining high torque or high rates of rotation, kneaders and mixers can often engender shear rates in excess of those of conventional rotational viscometers. Often these devices are instrumented, to measure and record the rate of rotation of the mixing blades and the related torque on the shaft turning the blades. The major problem facing users of these mixers lies in data interpretation, specifically in relating rate of rotation and torque data to shear rate and shear stress respectively. If it were possible to obtain such relationships, useful rheological data could be generated with instrumented mixers. This work outlines the experimental and analytical techniques required to convert pertinent data from the Ika Visc MKD 0.6-H60 instrumented kneader into useful rheological quantities. The kneader is calibrated using a Newtonian fluid and the calibration successfully tested with other Newtonian fluids, as well as on shear thinning solutions. The possibility of using a constant factor, a, which accounts for both the geometric complexity of the mixing chamber, and non-ideal fluid flow properties, is exAmined. It is shown that a is not constant, but depends on the non-Newtonian flow indices. At moderate and high rates of kneading blade rotation, calibration was not reliable and results are based on rates of rotation from 0 - 8rpm for the slower of the two mixing blades (0-16rpm for the quickly rotating blade). A number of assumptions and empirical relationships are utilised for this technique. The approximate nature of the technique necessitated by their use is more than offset by providing us with a potentially important outcome in that the capacity for collecting rheological data available to the interested scientist or engineer has been enhanced. A robust calibration technique has been developed, which is not, in principle limited to the specific equipment utilised for our analysis.► Cite this publication as follows:

Kealy T, Tiu C: Calibration of a Commercial Kneader for Rheological Applications, Appl. Rheol. 12 (2002) 241.

A numerical study is conducted on the behaviour of yield stress fluids in a mixing vessel equipped with anchor agitator in lAminar regime. It is shown that extending a standard Carreau model of shear thinning fluid is a suitable practice. Validations versus Couette flow analytical solution are satisfactory. Main features of local hydrodynamics and global power consumption are described for a 2D flow. Significant changes in the flow pattern are observed for low inertia and high yield stress and the results are considered as guidelines for further laboratory experiments.► Cite this publication as follows:

Marouche M, Anne-Archard D, Boisson HC: A Numerical Model of Yield Stress Fluid Dynamics in a Mixing Vessel, Appl. Rheol. 12 (2002) 182.

We exAmine the validity of the slump test for predicting the yield stress of polymeric suspensions and mineral suspensions. First we propose a modification of this test: in order to make measurements on fluids with high yield stress (of the order of several hundreds of Pascal) we add a mass at the sample top. From detailed observations of the slump in time we show that, for polymeric suspensions (hair gel and sewage sludges), two critical stresses can be distinguished which almost exactly correspond to the two critical stresses (respectively corresponding to a regime change and to the asymptotic slump) observed in rheometry during creep tests. Thus the slump test appears as a practiceful and relevant means to determine the intrinsic properties of these fluids. For mineral suspensions it is shown that the flow abruptly stops after a short time, a behaviour in agreement with the results of rheometrical tests carried out by progressively decreasing the applied stress. In that case the slump also appears to significantly depend on the procedure and cannot be related to a single property of the material.► Cite this publication as follows:

Baudez J-C, Chabot F, Coussot P: Rheological Interpretation of the Slump test, Appl. Rheol. 12 (2002) 133.

A frequent task undertaken by quality-control personnel in typical consumer-goods factories is the measurement of the viscosity of liquid products. The problem often faced in this task is how to strike the correct balance between the complete rheological characterisation of the non-Newtonian properties of the liquid of interest which requires expensive, sophisticated equipment and can be quite time-consuming and the dictates of production pressures that demand, as near as possible, an instant decision, and one usually based on a single number. Here we consider the rheological issues that arise in such a debate, which is aimed at finding what adequate characterisation would require. We will investigate the implications of liquids products being non-Newtonian for two of the most commonly encountered viscometers in factory quality laboratories, i.e. the simple dip-in rotating spindle viscometer of the Brookfield type (with its different forms and many imitations) and the more sophisticated concentriccylinder- type device typified by the Haake Rotovisco VT 550 range. Each is capable of giving a single-number answer for viscosity, but the implications of understanding this single number are different in each case, with the dip-in viscometer being in an infinite sea of liquid and the concentric-cylinder situation being narrow gap. We also investigate when the infinite sea of the dip-in viscometer is effectively infinite and when is a concentric- cylinder geometry really narrow gap? We will use the power-law model throughout our discussions.► Cite this publication as follows:

Barnes HA: An examination of the use of rotational viscometers for the quality control of non-Newtonian liquid products in factories, Appl. Rheol. 11 (2001) 89.

Distributive fluid mixing in lAminar flows is studied using the concept of concentration distribution mapping matrices, which is based on the original ideas of Spencer & Wiley [1], describing the evolution of the composition of two fluids of identical viscosity with no interfacial tension. The flow domain is divided into cells, and large-scale variations in composition are tracked by following the cell-average concentrations of one fluid using the mapping method of Kruijt et al. [2]. An overview of recent results is presented here where prototype two- and three-dimensional timeperiodic mixing flows are considered. Efficiency of different mixing protocols are compared and for a particular example the (possible) influence of fluid rheology on mixing is studied. Moreover, an extension of the current method including the microstructure of the mixture is illustrated. Although here the method is illustrated making use of these simple flows, more practical, industrial mixers like twin screw extruders can be studied using the same approach.► Cite this publication as follows:

Anderson PD, Meijer HEH: Chaotic mixing analyses by distribution matrices, Appl. Rheol. 10 (2000) 119.

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Senge B, Schwarzlos M, Blochwitz R, Annemuller G: Rheological Examination of Mashing in Brewery Process, Appl. Rheol. 6 (1996) 11.

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Mewes D, Gruber U: Theoretical Examination of the Calendering of Polymers, Appl. Rheol. 1 (1991) 152.

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