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Katarina Dimic-Misic, Kari Vanhatalo, Olli Dahl, Patrick GaneAuthor index ►
Rheological properties comparison of aqueous dispersed nanocellulose derived from a novel pathway-produced microcrystalline cellulose or by conventional methods
Appl. Rheol. 28:6 (2018) 64474 (15 pages) ►
Novel-produced never-dried and dried microcrystalline cellulose (MCC) was previously compared with a commercial MCC. The novel MCC was shown to be a suitable starting material for producing cellulose nanofibrils, in turn having similar molecular weight Mw, crystallinity, and particle size comparable to those from sequentially enzymatic and mechanically treated softwood sulphite pulp, but at lower cost. The study here presents a rheological parameterisation of the aqueous suspension throughout the process, aimed at delivering a correlation between specific surface area, at equal material particle size, and adsorptive coupling between neighbouring cellulose particles and interstitial water under flow. We conclude that combining dynamic viscosity with an independent measure of particle size provides a suitable quality control of MCC-derived cellulose nanofibrils, obviating the need for individual property-raw material relationships to be evaluated, and this principle may provide a generalised method for use in the production of cellulose nanofibrils.► Cite this publication as follows:
Dimic-Misic K, Vanhatalo K, Dahl O, Gane P: Rheological properties comparison of aqueous dispersed nanocellulose derived from a novel pathway-produced microcrystalline cellulose or by conventional methods, Appl. Rheol. 28 (2018) 64474.
In this research, a fully developed steady flow of a third-grade fluid in a pipe under an externally applied magnetic field with convection on wall is investigated. The governing equations including momentum and energy in the form of partial differential equations are reduced to ordinary differential equations which are solved numerically by using a finite element method (FEM) as part of the FlexPDE software package. For validity, the results are compared with the 4th order Runge-Kutta method. The effect of different physical parameters such as the non-Newtonian parameter, the Biot number, the Hartmann number, the Eckert number on the dimensionless velocity profiles, the dimensionless velocity gradient profiles, the dimensionless temperature profiles, and the dimensionless gradient temperature profiles have been discussed. It is concluded that by increasing the non-Newtonian parameter and Hartman number the dimensionless velocity, the velocity gradient, the temperature and temperature gradient profiles reduce and thus the heat transfer of fluid flow, the shear stress and the skin friction on the pipe wall decrease. Increasing the Biot number caused a decrease of the temperature and a more uniform dimensionless temperature profile of the fluid within the pipe. Besides, with a decrease of the Prandtl number, the dimensionless temperature decreases inside the pipe. In fact, the dimensionless temperature profile becomes flat. For this reason, the dimensionless temperature gradient decreases on the pipe wall which causes the reduction of the heat transfer rate on the pipe wall. Further, by increasing the Eckert number, the dimensionless temperature of the fluid within the pipe and the heat transfer from the fluid to the pipe wall increases. Applying the FlexPDE software for solving governing equations numerically seems to lead to appropriate and reasonable results.► Cite this publication as follows:
Javanmard M, Taheri MH, Ebrahimi SM: Heat Transfer of Third-Grade Fluid Flow in a Pipe Under An Externally Applied Magnetic Field with Convection on Wall, Appl. Rheol. 28 (2018) 56023.
An approach of Nelson and Ewoldt [Soft Matter 13 (2017) 7578] to create a viscosity model of the Herschel-Bulkley type in order to use only parameters with the potential of containing fluid information has been extended to be applied to drilling fluids using current industry standard procedures. The commonly used Herschel-Bulkley consistency parameter k is found inadequate in describing fluid properties properly as it has a unit dependent on n. Hence, the model is not optimum for digitalisation. The Herschel- Bulkley model is re-written and base its parameters directly on the yield stress and the additional or surplus shear stress at a pre-determined shear rate releVant for the flow situation to be considered. This approach is also applicable for Power-Law models.► Cite this publication as follows:
Saasen A, Ytrehus JD: Rheological Properties of Drilling Fluids - Use of Dimensionless Shear Rates in Herschel-Bulkley Models and Power-Law Models, Appl. Rheol. 28 (2018) 54515.
In the last decades, one of the most critical issues concerning the control on the processing, structure and properties of nanocomposites is related to the dispersion of nanofiller in the polymer matrix and internal interactions resulting in percolation. In this study, we investigate the rheological behavior in oscillatory and steady shear flow of poly(lactic) acid based nanocomposites incorporating 0 - 12 wt% graphene nanoplates (GNP) and multi-walled carbon natotubes (OH-MWCNT). The effect of the filler contents and aspect ratio on the viscosity and viscoelastic response is evaluated. Three rheological techniques are used for estimation of rheological percolation threshold. Due to different aspect ratio and state of dispersion of GNP and MWCNTs the percolation threshold differs significantly for both compositions φ ≤ 1.5 wt% for MWCNT/PLA and φp ≤ 5 wt% for GNP/PLA. The larger the aspect ratio of nanofiller, the lower is the rheological percolation threshold. The visualized structure by TEM analysis confirms the rheological predictions for both type composites. The index of flow was estimated by the power law slope of the flow curves and a better dispersion was assumed for MWCNTs in comparison with GNPs due to the surface modification. Based on the rheological percolation threshold and the flow index, nanocomposites were classified in three groups: Newtonian, percolated composites and elastic solids. Both characteristics are used to select the printing parameters for the three groups of nanocomposites, suitable for fused deposition modeling (FDM).► Cite this publication as follows:
Ivanova R, Kotsilkova R: Rheological study of poly(lactic) acid nanocomposites with carbon nanotubes and graphene additives as a tool for materials characterization for 3D printing application, Appl. Rheol. 28 (2018) 54014.
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.
In petroleum drilling, aqueous Polyanionic Cellulose solutions (PAC) are often used as a drilling fluid model system in experimental laboratory studies to investigate cuttings transport. Cuttings transport refers to the transportation of drilled-off solids out of the wellbore. In these studies, PAC solutions are typically assumed to behave purely viscous, i.e. they do not show timedependent/ thixotropic and/or viscoelastic properties. In this study, a rheological characterization of PAC has been performed in combination with an evaluation of time scales characterizing the fluid to verify the conventional assumption of a purelyviscous fluid. It is found that PAC solutions are generally not purely viscous: They feature viscoelastic behavior on time scales of the order of 0.01 to 1 s, such as normal stress differences, as well as thixotropic behavior on larger time scales of the order of 10 to 1000 s because of their polymeric microstructure. If simplified to a purely viscous fluid, the degree of uncertainty in representing the measured apparent shear viscosity may increase by an order of . 75 to 90 % depending on the releVant time scale. When obtaining flow curves, a sufficiently long measurement point duration (sampling time for a particular torque reading) is required to ensure that the liquid microstructure has reached its dynamic equilibrium at the desired shear rate. Due to their polymeric nature, PAC solutions feature Newtonian viscosity plateaus at both low and high shear rates. For modeling purposes, the application of a Cross/Carreau material function is recommended because it both best describes the flow curve data and minimizes extrapolation errors compared to the conventionally used Power Law material function.► Cite this publication as follows:
Busch A, Myrseth V, Skjetne P, Khatibi M, Johansen ST: Rheological characterization of polyanionic cellulose solutions with application to drilling fluids and cuttings transport modeling, Appl. Rheol. 28 (2018) 25154.
Visco-plasticity characterized by yield stress is an important rheological property of composite propellant suspensions. The yield stress along with viscosity affects various unit operations in propellant processing as well as the quality of final product. The characterization of yield stress of propellant suspensions using direct measurement techniques, such as forced falling ball and slump test is described. The slump test is a simple and quick measurement tool with applicability at processing site whereas forced ball drop is useful for measurement of very high yield stress. The yield stress measurement of propellant suspension of four different compositions with varying particle size and volume fraction using above methods is reported and results are compared with Vane geometry of rotational rheometer. Further, the yield stress behavior was studied for the propellant compositions with increasing solid loading. The dependence of yield stress of the studied propellant compositions on the reduced packing fraction φ/φm of solids is established and expressed by a mathematical correlation. In addition, effect of vibration on yield stress was also studied using slump test.► Cite this publication as follows:
Dombe G, Yadav N, Lagade R, Mehilal M, Bhongale C: Studies on Measurement of Yield Stress of Propellant Suspensions using Falling Ball and Slump Test, Appl. Rheol. 27 (2017) 45262.
The overall objective of this work was to explore the rheology of an adVanced performance xanthan gum, which is able to endure the shear and turbulent flows typically found in high-shear mixers or even homogenizers. A further goal was the development of a rheological experimental setup that can be used to gain information about the structural recovery after applying a given shear stress. A fast structural recovery after cessation of shear is essential for a wide range of practical applications. The high zero shear viscosity, strong shear thinning response along with a fast drop of viscosity with shear time and structural recovery support the applications of this xanthan gum as thickening agent and stabilizer. The rheological characterization focused on the influence of xanthan gum concentration (0.15 – 0.40%(m/m)) on the dynamic viscoelastic properties, steady shear and thixotropic behavior, and kinetics of structural recovery.► Cite this publication as follows:
Carmona JA, Calero N, Ramirez P, Munoz J: Rheology and structural recovery kinetics of an advanced performance xanthan gum with industrial application, Appl. Rheol. 27 (2017) 25555.
Graphene/polymer nanocomposites are the latest trends in materials science in the recent years, but the technology of their preparation plays a crucial role in obtaining reliable materials with repeatable and enhanced properties. Up to now, there are many unresolved problems in controlling the dispersion of the graphene filler and the corresponding influence on the properties of the final nanocomposite materials. In the present study, we apply rheological methods for controlling the quality of the graphene dispersion. We prepare and characterize epoxy/graphene nanodispersions with graphene contents varying from 0.05 to 1 wt% and explore the effect of different mixing regimes on the dynamic moduli and viscosity, thus assessing the degree of the dispersion. The rheological percolation threshold and relaxation time spectra are determined, in order to evaluate the internal structure of the nanodispersions. The relaxation spectrum is highly efficient to probe the effects of interfaces and interconnections on the relaxation dynamics of molecules in nanodispersions. Rheological results combined with transmission electron microscopy (TEM) observations confirm that the low frequency dynamic viscosity and moduli strongly increase, with increasing the degree of dispersion due to the exfoliation of graphene sheets. The rheological percolation threshold was found at very low concentration depending from the processing conditions. The weight of the relaxation spectra is strongly shifted to higher values, compared to the neat epoxy resin and this effect is much stronger around and above the rheological percolation threshold.► Cite this publication as follows:
Ivanov E, Velichkova H, Kotsilkova R, Bistarelli S, Cataldo A, Micciulla F, Bellucci S: Rheological behavior of graphene/epoxy nanodispersions, Appl. Rheol. 27 (2017) 24469.
This paper investigates the influence of limestone crushed sand dust (LCSD) on rheological properties of cement mortar based on crushed sand (CS) with different mineralogical nature (limestone and siliceous). A LCSD with a specific surface BET of 1470 m2/kg was used at different content replacement by mass of sand (0, 5, 10, 15, and 20 %). The water-cement ratio (W/C) and the cement content were kept constant for all mixes. The results show that the slump decreased as well as the flow time, the yield stress and the viscosity of mortar increased with the increase in LCSD content. Thus, the mortar based on limestone crushed sand (LS) has a low loss of rheological properties compared with a mortar based on siliceous crushed sand (SS). Yet, for 0 % of LCSD, it was found that the rheological properties are nearly equal for both CSs. The use of superplasticizer (Sp) significantly improves the workability and rheological properties. However, the rheological behavior of mortar has been strongly affected by increasing the volume concentration of CS whereas the effect of CS on fresh mortar presents significantly greater disadVantages compared with rolled sand (RS).► Cite this publication as follows:
Safiddine S, Debieb F, Kadri E, Menadi B, Soualhi H: Effect of crushed sand and limestone crushed sand dust on the rheology of cement mortar, Appl. Rheol. 27 (2017) 14490.
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.
Dispersions of acid hydrophobized hydrolysis lignin in light crude oil, industrial oil, and diesel fuel were found to demonstrate the transition from Newtonian to non-Newtonian behavior with shear-thinning and thixotropy within the increase in lignin concentration. Lignin-in-diesel fuel dispersions were shown to have the smallest apparent viscosity while lignin-in-industrial oil dispersions have the highest one and the sharpest drop of viscosity with shear rate increasing. At the same time, relative viscosity demonstrates the inverse dependence: It is highest for lignin-in-diesel fuel suspensions. Calculation of parameters based on microrheological model of elastic flocs with generalized Casson equation allowed determining of the parameters k and A that describe hydrodynamic interaction between separated particles and their aggregates under flow, parameter FA, characterizing the force impeding the break of aggregates and numbers of particles in the floc for different systems as the dependence of shear stress. The explanation based on a higher affinity of diesel fuel to lignin unlike industrial oil and light crude oil as dispersing medium has been given.► Cite this publication as follows:
Savitskaya T, Reznikov I, Grinshpan D: Rheological Behavior of Lignin Based Dispersions Intended for Composite Fuel Production, Appl. Rheol. 26 (2016) 63476.
Dispersion quality has a large influence on the resulting properties of filled polymers, hybrids and nanocomposites in general. Reducing the Van der Waals forces and therefore, matching the refractive index between the filler and the matrix should improve dispersion in hybrid materials. However, in this case the usual light-based techniques cannot be used to assess dispersion quality. In this work, dispersions containing silica nanoparticles and a solvent mixture of 1-butanol and benzyl alcohol were analysed by rheological methods. The refractive index of the solvent was changed by varying the mixing ratio, and thus the effect of index difference on the filler-matrix interaction was investigated. In agreement with theory, a stronger gel network was observed when the refractive index of filler and solvent were matched. If the difference in refractive index of the two materials became too large, particles and solvent interaction was reduced, and agglomerates were formed. This resulted in a weaker gel network.► Cite this publication as follows:
Frohlich KA, Mitrentsis E, Clemens F, Hoffmann B, Michaud V, Graule T: Assessment of the Dispersion Quality of refractive index-matched nanodispersions, Appl. Rheol. 26 (2016) 65050.Tom C. B. McLeish (Ed.)
Obituary Alexei Likhtman (1971-2015)
Appl. Rheol. 25:6 (2015) 53-54 ►
Alexei Likhtman, a leading scientist in Theoretical Soft Matter Physics, has died aged 44
Born in 1971 into a family with strong scientific tradition, Alexei was educated in Moscow. He was awarded a Diploma in Physics with honours from the Physics Department of Moscow State University (MGU) in 1994. He remained at MGU for his PhD research, supervised by Professor Alexander Semenov. The topic, his first foray into polymer physics, was the calculation of the extraordinary ordered nanoscale patterns of chemical separation that are spontaneously generated within polymer melts whose molecules contain extended regions of different chemistry but joined together. These systems maintained a lifelong fascination for Alexei, as did the collaboration with the experimental group in Crete that the Russians worked with closely. The relationship with Crete remained strong and close until the end of Alexei's life. A more important lifelong partnership also began in Moscow - it was as students there that Alexei and Katrina met and married in December 1990. The family grew after their daughters Sonya and Asya were born while Alexei was working on his PhD thesis. Helping to look after two little girls however did not stop him from producing a high quality piece of work. Till the end of his days Alexei remained a loving, committed, hands on dad, always reliable and extremely loyal to his family. The family stayed in Moscow for two more years, with Alexei as a Scientific Fellow at Moscow State University, before moving to the U.K, in 1998, where he took up a position as a Research Assistant in the Department of Applied Mathematics at Leeds University, where Semenov, now his colleague, had also moved. That initial one year position marked the beginning of family's long life in the UK
Alexei stayed at Leeds from 1998 until 2007: in 1999 he moved to the Department of Physics and Astronomy, where he worked on theories of fast flow of entangled polymer melts, including theory and simulations of the convective constraint release model, supervised by Professor Tom McLeish, and working collaboratively with Prof. Scott Milner at an ex tended international workshop at the Kavli Institute of Theoretical Physics in Santa Barbara. In 2002, Alexei’s research had developed to the point where he was awarded an AdVanced EPSRC Fellowship, which he held from 2002-2005 in the School of Physics and Astronomy. In this period, Alexei worked on developing new models of polymer dynamics, simultaneous description of rheology, neutron spin-echo, neutron scattering, diffusion, dielectric spectroscopy and NMR experiments, the theory of chemical reactions in polymers and computer simulations. This work has been recognized in many ways, including the best paper award of the Journal of Rheology (2006). From 2005-2007 Alexei held his Fellowship in the Department of Applied Mathematics, also as University Fellow, supervising a team of three postdoctoral researchers working on molecular simulations of polymer melts, slip-links model of entanglements and experimental rheology. Although a theoretician, he worked with experimental colleagues in different laboratories and performed experiments himself, learning and questioning every single detail. As a result, he personally developed the most reliable experimental protocol for measuring the flow properties of polymer melts yet found by the Leeds lab. For an experimentalist, it was a treat to interact with Alexei in this context, a unique experience that led to improved experiments. Co-supervising a PhD student, Richard Graham, the two formulated a now-celebrated non-linear but easily-computable mathematical model for the flow of linear polymers of well-defined length (the ROLiE-Poly model).
He worked hard not only on brilliant new theoretical science, but on making this accessible to others. For example, his foresight and energy led to the creation, with long-time colleague Jorge Ramirez, of a free software tool (called REPTATE) that enabled experimental scientists in universities and industry to sort their polymer flow data and compare it quickly and efficiently to theoretical models, greatly accelerating fundamental research and its application.
In May 2007, Alexei moved to the Department of Mathematics and Statistics at the University of Reading, as Professor of Mathematical Physics. There, together with Prof. Mark Matsen, he created a new group of theoretical polymer physics and within a few years had put Reading ‘on the map’. The group focused on the microscopic foundations of the tube theory and using a blend of theory and multi-scale simulation to dig deeper, and with more care, into the underlying physics than any other group in the world. A testimony of Alexei’s brilliance is his unique ability to bridge concepts and methodologies from different fields. He did so in his recent simulation work by using concatenated ring polymers to study polymer entanglements.
Alexei achieved enormous academic distinction, and his achievements came remarkably quickly – testament to his brilliance as a scientist. Several theoretical works on the linear and non-linear viscoelasticity of entangled polymers carry his name, including the famous Likhtman-McLeish model (2002) for slow flows (which was 90% Likhtman) and the GLaMM model (2003) for fast flows (with Graham and Milner). His AdVanced EPSRC Fellowship came at the age of 31, and he was appointed Professor of Mathematical Physics in Reading at the age of just 35. Yet while undoubtedly successful himself, Alexei was equally proud of the many achievements of the group he developed. For example, in September this year he spoke glowingly of how two poster prizes out of three available at the Institute of Physics Polymer Physics Biennial Conference were won by post-doctoral researchers from his team. In the same month, he was appointed as the first Mercator Fellow of the Freiburg-Strasbourg-Basel-Mulhouse International Research Training Group on 'Soft Matter Science'. He enjoyed a productive visit to Strasbourg, during which he described himself as "feeling like a PhD student again" (possibly partly due to the position that his former PhD supervisor, Semenov, now holds there!). This is typical of his modesty and enthusiasm.
Alexei was one of those wonderful scientists who remind us that just because something is obvious, doesn't make it true. Alexei would challenge every idea that we had at Leeds – including the ones that we thought were obviously true. But the way in which he demolished your ideas was so kind and so surgically precise that it always felt good somehow. He was a particularly vociferous critic of the bad habit that much of the polymer rheology community had got into, of presenting theory together with data from just one technique, then subtly altering the parameters when data from a different technique was brought into comparison. A wonderful paper from 2005 compared his remarkable ‘slip-link model’ to data on rheology, NMR and diffusion measurements simultaneously. He leaves us a permanent reminder that you learn more from theory when it disagrees with experiment and that an experimentalist should have a good grasp of theory and vice versa.
Alexei was a wonderful colleague, and all those who were lucky enough to work with him benefitted immensely from his enthusiasm, support and wisdom. Alexei was an intellectual powerhouse, a truly curious mind, a wonderfully creative thinker, a brilliant teacher at undergraduate and graduate levels, with academic gravitas way beyond his years, yet completely ap proachable, modest and always friendly in a natural way that charmed anybody who met him. The superb group he built in Reading and the quality of people he brought in reflect his vision and sense of commitment.
He was hugely supportive of those for whom he felt he had a responsibility. His dedication to his PhD students and his research team went well beyond professional duty. He sought to provide a family-like environment for the group, especially supportive for those who were far from home. He presented himself as an exemplary reference figure for all the young people in his group, full of energy and full of life. In this continuous work of hospitality and welcome he was supported by his family, to whom he was utterly devoted as husband and father.
Alexei was so much more than an academic and an intellectual. He truly enjoyed life and always managed to combine professional activities with hobbies and family activities. He did so last summer when he visited friends with his family following a workshop and seminar. He had a passion for so many things ranging from sports (especially swimming and hiking) to photography. A truly happy, free spirited man, full of energy and passion for things he did, he had as infectious a love of life as a tireless desire to find scientific truth. He was a great admirer of nature and outdoors with real care about the world and people around him. He was a great friend, a funny, spirited, yet always serious person, and his daily passionate presence, his enthusiasm for science, his warm friendship, will be sorely missed.
Alexei died on 11 October 2015 following a fall while hiking in Maryland, USA. He is survived by his wife Katrina, and their two daughters, Sonya and Asya.
► Cite this publication as follows:
McLeish TCB: Obituary Alexei Likhtman (1971-2015), Appl. Rheol. 25 (2015) 53.
An experimental and numerical investigation of the rotational rheometry of yield-stress materials is performed, using waterbased Carbopol dispersions. The flow and fluid characterization in different rheometer geometries, namely the smooth Couette, the grooved Couette, and the Vane-in-cup are analyzed. The bi-dimensional flow governing equations are solved numerically, using the finite volume method and Fluent software (Ansys Inc.). The viscoplastic behavior of Carbopol dispersions is modeled using the Generalized Newtonian constitutive equation with the regularized viscoplastic viscosity function proposed by de Souza Mendes and Dutra [1], herein called SMD function. The flow pattern and the presence of apparent wall slip in rheometric measurements of yield-stress materials are investigated and discussed.► Cite this publication as follows:
Marchesini FH, Naccache MF, Abdu A, Alicke AA, deSouzaMendes PR: Rheological characterization of yield-stress materials: Flow pattern and apparent wall slip, Appl. Rheol. 25 (2015) 53883.
Measurements and modeling of rheological properties of a high viscosity silicone oil (polydimethylsiloxane, PDMS) at high frequency are reported. The linear viscoelastic properties are measured by small amplitude oscillation shear (SAOS) tests with a rotational rheometer. Furthermore, Diffusing Wave Spectroscopy (DWS) is used, which expands the angular frequency range of the measured loss and storage moduli up to 105 rad/s, in a temperature range of 20 - 70 C. Good agreement between both methods is found in the overlapping frequency region, especially at higher temperatures. The DWS data show that the elastic modulus stays dominant and increases with frequency, without a second cross-over point up till 108 rad/s. Flow curves, measured with rotational and with capillary rheometry up to a shear rate of 7.6 × 104 s-1, show shear thinning behavior, which implies nonlinear viscoelasticity. Comparison of the dynamic and complex viscosity shows that the Cox-Merz rule is valid in a frequency range spanning six orders of magnitude. A multi-element White-Metzner model is proposed as a constitutive equation, which accurately describes the nonlinear viscoelastic properties, including the decrease of the loss and storage moduli during amplitude sweeps in oscillatory shear measurements.► Cite this publication as follows:
Kokuti Z, vanGruijthuijsen K, Jenei M, Toth-Molnar G, Czirjak A, Kokavecz J, Ailer P, Palkovics L, Volker AC, Szabo G: High-frequency rheology of a high viscosity silicone oil using diffusing wave spectroscopy, Appl. Rheol. 24 (2014) 63984.
The aim of this study is to propose a theoretical frame that is able to lead someone to an appropriate way of modeling cement-based material extrusion. It clearly appears that different extrusion scenarios may occur. Cement-based materials are viscoplastic materials that may undergo drainage during an extrusion process carried out at low velocity. Four material behaviors can be encountered: perfect plastic, viscoplastic, frictional plastic (with evolving properties) and frictional viscoplastic (that has never been reported in the literature as drainage occurs when ram velocity is low and thus when viscous effects can be neglected). In this work, criteria are proposed to choose the more releVant way to model extrusion. Then, models are proposed for the possible extrusion scenarios.► Cite this publication as follows:
Perrot A, Rangeard D, Melinge Y: Prediction of the ram extrusion force of cement-based materials, Appl. Rheol. 24 (2014) 53320.
It is well known that the shear and shear rate are not uniform in the azimuthal flow within the gap between parallel concentric disks - perhaps the most versatile among the geometries used in rheometry. This flow inhomogeneity represents a disadVantage, because the data analysis becomes intricate. Typically the stress is calculated at the rim with the assumption that it varies linearly with the radial coordinate, and then a correction is applied. This correction may be very large, depending on the nature of the sample, type of test, and range of parameters. While for steady-state shear flow different methods for correcting the stress are available, for transient flows they are rather scarce and in some cases unavailable. In this work we analyze in detail the stress correction for the main rheometric experiments, and discuss when it is needed. To this end, we performed different tests with a commercial hair gel and a polyacrylamide solution. For oscillatory flows, a simple equation to correct the stress amplitude is obtained in terms of the amplitudes of the torque and shear rate.► Cite this publication as follows:
deSouzaMendes PR, Alicke AA, Thompson RL: Parallel-plate geometry correction for transient rheometric experiments, Appl. Rheol. 24 (2014) 52721.
Starch-based adhesives play a releVant role in paperboard production and are becoming more and more interesting, for different uses, because they are based on renewable biopolymers. Starch modifications or additive addition are becoming frequent to obtain the macroscopic properties desired for specific uses. In this paper the effects of the addition of four different tannins on a typical adhesive, adopted for corrugated paperboard production, were investigated by using fundamental rheological techniques, both in dynamic and steady conditions. It was found that tannins increase the onset of starch gelatinisation, estimated as the knee point of the storage modulus in a dynamic temperature ramp test, and decrease the steady shear viscosity. This is due to the interactions between tannin and starch that affect the gelatinisation and retrogradation reactions weakening the starch network. Even though a partial reinforcement effect was also observed, owing to the polymeric nature of tannin components, a lower consistency, with respect to the neat adhesive, was found for all modified samples. Tannin has shown itself able to modify technological properties such as gelatinization temperature and viscosity, since the specific results are determined by the nature and amount of tannin; therefore it could be used to adapt adhesive characteristics to specific applications, potentially improving starch-based adhesive competitiveness with respect to different adhesives.► Cite this publication as follows:
Marino R, Giovando S, Gabriele D: Effect of tannin addition on the rheological properties of starch-based adhesives, Appl. Rheol. 24 (2014) 46138.
Phase-separable particulate-containing gel structures constitute complex fluids. In many cases they may incorporate component concentration inhomogeneities within the ensemble matrix. When formulated into high consistency suspensions, these can lead to unpredictable time-dependent variations in rheological response, particularly under shear in simple parallel plate and cylindrical rotational geometries. Smoothing function algorithms are primarily designed to cope with random noise. In the case studied here, namely nanocellulose-based high consistency aqueous suspensions, the system is not randomised but based on a series of parallel and serial spatial and time related mechanisms. These include: phase separation, wall slip, stress relaxation, breakdown of elastic structure and inhomogeneous time-dependent and induced structure re-build. When vacuum dewatering is applied to such a suspension while under shear, all these effects are accompanied by the development of an uneven solid content gradient within the sample, which further adds to transitional phenomena in the recorded rheological data due to spatial and temporal differences in yield stress distribution. Although these phenomena are strictly speaking not noise, it is nevertheless necessary to apply releVant data smoothing in order to extract apparent/process viscosity parameters in respect to averaging across the structural ensemble. The control parameters in the measurement of the rheological properties, to which smoothing is applied, are focused on parallel plate gap, surface geometry, shear rate, oscillation frequency and strain variation, and relaxation time between successive applications of strain. The smoothing algorithm follows the Tikhonov regularisation procedure.► Cite this publication as follows:
Dimic-Misic K, Nieminen K, Gane PA, Maloney T, Sixta H, Paltakari J: Deriving a process viscosity for complex particulate nanofibrillar cellulose gel-containing suspensions, Appl. Rheol. 24 (2014) 35616.
Rheological and electrical properties of polymeric nanoparticle solutions and their influence on the rheological and electrical properties of red blood cell (RBC) suspensions have been studied. Poly(acrylic acid) macromolecules of different architecture and molecular weight were used: (i) a new core.shell type star polymer whose interior forms hyperbranched polystyrene bearing arms of poly(acrylic acid) with molecular weight Mn = 56 920 Da and (ii) linear polyacrylic chains with average molecular weights Mn = 6000, 20000, and 225000 Da. The polymers dissolved in physiological solution with weight concentrations 1 mg/ml and 0.2 mg/ml were used for the experiments. Under physiological conditions the star-shaped macromolecules present spherical nanoparticles while the linear poly(acrylic acid)s adopt an extended chain conformation close to rod-like particles. The apparent viscosity of the nanoparticle solutions and RBC suspensions in the presence and absence (the control) of nanoparticles were measured using a rotational viscometer Contraves Low Shear 30 (LS 30) at a steady flow at shear rates from 0.0237 to 94.5 s-1 and temperature 37 C. A method, based on the measurement of dielectric properties of dispersed systems in Couette viscometric blood flow was applied. A concurrent measurement system and data acquisition system implied into the Contraves LS 30 were used to quantify the electrical conductivity. The main adVantage of this technique is that blood is subjected to a uniform shearing field in a Couette rheometric cell as well as the information about the mechanical and electrical properties of the fluid is obtained in parallel. The results show that rheological and electrical properties of the nanoparticle solutions and RBC suspensions, namely their electrical conductivity and apparent viscosity, are dependent on the shear rates, shape, concentration and molecular weight of the polymers. Key► Cite this publication as follows:
Antonova N, Koseva N, Kowalczuk A, Riha P, Ivanov I: Rheological and electrical properties of polymeric nanoparticle solutions and their influence on RBC suspensions, Appl. Rheol. 24 (2014) 35190.
This paper presents the development of a Vane rheometer to estimate mortar plastic viscosity and yield stress. The rheological parameters were developed from measurements using a procedure to convert the Vane torque and rotational velocity data into shear stress versus shear rate relationships. The used procedure considered the locally sheared material as a Bingham fluid and computed the characteristic shear rate from Couette analogy. The apparatus was tested with three experimental programs in which many rheological parameters of mortar compositions were calculated. The obtained results validated the rheometer test procedure and confirmed that the test results are reproducible.► Cite this publication as follows:
Soualhi H, Kadri E, Ngo T, Bouvet A, Cussigh F, Kenai S: A new vane rheometer for fresh mortar: development and validation , Appl. Rheol. 24 (2014) 22594.
This paper provides a new model to evaluate the yield stress of suspensions, slurries or pastes, based on the release of a finite volume of material onto a horizontal surface. Considering the height (h) and the radius (R) of the sample at the flow stoppage, two asymptotic regimes, where h > R or h < R, lead to different analytical models that allow the determination of yield stress. Experimental observations show typical sample shape at stoppage between slump (h > R) and spread (h < R). Based on these observations, we have developed a new analytical model to evaluate accurately the yield stress of materials in this intermediate regime. The validity of this model was evaluated from data obtained using various Carbopol(c) dispersions. The yield stress measured with the proposed model was compared with the yield stress evaluated from shear flow curves obtained with roughened plate/plate geometry fitted to the Herschel-Bulkley model. Results show the releVance of the proposed model which that can be applied in the range between models used for the two asymptotic regimes.► Cite this publication as follows:
Pierre A, Lanos C, Estelle: Extension of spread-slump formulae for yield stress evaluation, Appl. Rheol. 23 (2013) 63849.
The main objective of this study is to get insight into the dynamic behavior of viscoplastic drop in impingement process in which the Capillary number is greater than one. In numerical analysis, Volume Of Fluid (VOF) approach was used for capturing the liquid-gas interface. Two different drop shapes (spherical and tear shapes) were used to investigate the drop morphology in an impingement process. According to the results, the numerical results concerning the tear shape drop showed proper agreement with experimental reports (mean deviation of 16 %) in different impact velocities. The flow field was discussed during the impact process in terms of its effect on apparent viscosity and spreading length. Influence of contact angle, consistency, power law index, and surface tension variations on spreading parameter (ratio of contact diameter on the substrate to equivalent initial drop diameter) were investigated. Furthermore, three different rheological models (consisting of Herschel-Bulkley, Casson, and Robertson-Stiff) were employed to study the effects of rheological models on simulation outcomes.► Cite this publication as follows:
Noroozi S, Tavangar S, Hashemabadi S: CFD Simulation of Wall Impingement of Tear Shape Viscoplastic Drops Utilizing OpenFOAM, Appl. Rheol. 23 (2013) 55519.
► Cite this publication as follows:
Goodyer S: Advances in Non-Newtonian Fluid Mechanics (INFFM Annual Conference 2013), Appl. Rheol. 23 (2013) 236.
► Cite this publication as follows:
Anderson PD, VanPuyvelde P: 8th Annual European Rheology Conference (ERC 2013), Appl. Rheol. 23 (2013) 235.
We discuss the possibility of using penetrometry technique for measuring the yield stress of concentrations made of grains immersed in a colloidal phase, such as concrete or muds. In that aim we used model materials made by suspending glass beads at different concentrations in a kaolin-water paste. We then show that a uniform shear stress develops along the object (plate or cylinder) beyond the entrance length. This shear stress plotted versus the object velocity exhibits a shape similar to the flow curve of the material determined from rheometry. For materials exhibiting the typical flow curve of a simple yield stress fluid, i.e. at bead concentrations smaller than 30 %, the stress associated with an inflection point located at low velocities of this curve appears to correspond to the material yield stress. At larger concentrations of beads the suspensions have a more complex behaviour likely affected by its granular nature at a local scale and the possibility of migration or frictional effects, so that neither conventional rheometry nor penetrometry provide releVant data. We conclude by describing two practical penetrometry techniques for precisely measuring the yield stress of simple pastes.► Cite this publication as follows:
Tikmani M, Boujlel J, Coussot P: Assessment of penetrometry technique for measuring the yield stress of muds and granular pastes, Appl. Rheol. 23 (2013) 34401.
The flow of complex fluids is routinely encountered in a variety of industrial manufacturing operations. Some of these operations use rheological methods for process and quality control. In a typical process operation small quantities of the process fluid are intermittently sampled for rheological measurements and the efficiency of the process or the quality of the product is determined based on the outcomes of these measurements. The large number of sample-handling steps involved in this approach cost time and cause inconsistencies that lead to significant variability in the measurements. These complications often make effective process/ quality control using standard rheometric techniques difficult. The effectiveness of control strategies involving rheological measurements can be improved if measurements are made online during processing and sampling-steps are eliminated. Unfortunately, online instruments capable of providing sufficiently detailed rheological characterisation of process fluids have been difficult to develop. Commercially available online instruments typically provide a single measurement of viscosity at a fixed deformation rate. This dependence on a single pre-determined shear rate restricts these instruments from identifying changes in the product or the process, especially if the viscosity at the pre-determined shear rate remains unaltered during these changes. We introduce an Online Rheometer (OLR) that uses small amplitude oscillatory squeeze flow to measure the viscoelastic properties of process fluids in-process and in real time under typical processing conditions. We demonstrate that with an appropriate measuring geometry and amplitude of oscillation, the frequency response of typical non-Newtonian fluids can be accurately measured in a process pipe. We also compare our results with other techniques that are typically used for process rheometry, critically evaluating the utility of the OLR technology for adVanced process and quality control.► Cite this publication as follows:
Konigsberg D, Nicholson TM, Halley P, Kealy TJ, Bhattacharjee PK: Online process rheometry using oscillatory squeeze flow, Appl. Rheol. 23 (2013) 35688.
Simulations are performed to investigate the flow of a shear-thinning, non-Newtonian fluid in a collapsed elastic tube and comparisons are made with experimental data. The fluid is modeled by means of the Bird- Carreau viscosity law. The computational domain of the deformed tube is constructed from data obtained via computer tomography imaging. Comparison of the computed velocity fields with the ultrasound Doppler velocity profile measurements show good agreement, as does the adjusted pressure drop along the tube.s axis. Analysis of the shear rates show that the shear-thinning effect of the fluid becomes releVant in the crosssections with the biggest deformation. In fact, the maximum shear rate is about a factor of thirty larger than its corresponding maximum value in the undeformed tube, and the viscosity is reduced by a factor of two. The effect of the shear-thinning behavior has also been compared with identical simulations carried out for a Newtonian fluid.► Cite this publication as follows:
Tanner FX, Al-Habahbeh AA, Feigl KA, Nahar S, Jeelani SJA, Case WR, Windhab EJ: Numerical and Experimental Investigation of a Non-Newtonian Flow in a Collapsed Elastic Tube, Appl. Rheol. 22 (2012) 63910.
The measurement of elongational viscosity still evokes a series of problems in comparison with the relatively well-established measurement of shear viscosity. Recently new techniques have appeared enabling measurement of elongational viscosity with the samples for which the aspect ratios of their geometrical shapes (i.e. length vs. width (diameter)) can attain moderate values, i.e. not necessarily of a longitudinal character as in the case of earlier techniques. The aim of this contribution is to experimentally demonstrate the invariantness of transient uniaxial elongational viscosity measured with respect to a rectangular shape and thickness of LDPE samples using a SER Universal Testing Platform fixed in an Anton Paar MCR 501 host system. The width of the samples was varied within the range 2.1-12.7 mm and thickness altered within 0.1-1 mm. An adVantage of fixing polymer samples directly to both drums (if possible) over the application of clamps is documented.► Cite this publication as follows:
Filip P, Svrcinova P: Measurement of elongational viscosity of polymer melts using SER Universal Testing Platform, Appl. Rheol. 22 (2012) 14776.
A high torque Vane rheometer is used to measure the yields stress of cement-based materials. It is shown that this apparatus is suitable for the evaluation of the yield stress of various concretes and mortars in the fresh state in comparison with slump tests realized with ASTM Abrams cone. Then, the rheological properties (yield stress and shear flow behaviour) of a homogeneous kaolin clay suspension are studied with the apparatus and favourably compared with other rheometers and geometries.► Cite this publication as follows:
Estelle P, Lanos C: High torque vane rheometer for concrete: principle and validation from rheological measurements, Appl. Rheol. 22 (2012) 12881.
Viscoelastic properties are traditionally measured using sophisticated instrumentation, and the high cost of these rheometers may limit utility. This research attempts to enable viscometers that can provide a torque-time response, with Vane attachment and a recommended cup size, to measure viscoelastic properties. Phase angles and shear moduli of model systems (gelatin and polyacrylamide gels) were calculated using torque-time response and deformation zone concept. The methods were applied to data obtained from Brookfield YR-I viscometer and the calculated values were compared with the data obtained from oscillatory testing on a stress controlled rheometer. The methods were improved in several areas by testing different cup sizes, rotational speeds, and viscometers and correcting torque-time responses to obtain most accurate results possible. The developed method, along with the torque-time response obtained from the viscometer, was capable of measuring viscoelastic parameters for the tested materials and further development could design a new quality control device directed towards viscoelastic property measurement.► Cite this publication as follows:
Tanjore D, Daubert CR: A vane-in-cup approach to measure viscoelastic properties of gelatin gels through torque-time responses from Brookfield YR-I viscometer, Appl. Rheol. 21 (2011) 63172.Evan Mitsoulis
Hellenic Society of Rheology meeting (HSR 2011)
Appl. Rheol. 21:4 (2011) 245-245 ►
► Cite this publication as follows:
Mitsoulis E: Hellenic Society of Rheology meeting (HSR 2011), Appl. Rheol. 21 (2011) 245.
Strain rate frequency superposition (SRFS) has been suggested as new method to extend the frequency range for assessment of the complex storage modulus G* of soft glassy materials to lower frequencies. The basic idea is that relaxation processes in such fluids are accelerated by an external shear field, analogous to the effect of a temperature shift in polymer melts and solutions. Master curves for G' and G'' are constructed from the apparent modulus data determined from non-linear oscillatory shear experiments. Here we validate the SRFS principle for the first time by independent experiments and also demonstrate its limitations.We compare SRFS results to directly measured G', G'' at frequencies down to 10-3 rad/s and creep experiments lasting up to 104 s for a variety of gel-like fluids, including polymeric thickener solutions, a highly concentrated w/oemulsion, and wormlike micellar surfactant solutions, as well as a weakly viscoelastic non-Brownian suspension of glass beads. Good agreement between SRFS data and directly measured G', G'' values for the thickener solutions, the emulsion as well as the suspension. Apparent viscosity data obtained from creep experiments and absolute values of the complex viscosity in the low frequency limit agree fairly well for these fluids. But the method fails for the wormlike micellar solutions and this could be due to non-uniform flow or due to flow-induced structural changes. Finally,we demonstrate that the combination of SRFS, rotational rheometry, and adVanced high frequency rheology methods allows for a broad bandwidth characterization of complex fluids spanning an unprecedented frequency range of about eleven decades.► Cite this publication as follows:
Kowalczyk A, Hochstein B, Stahle P, Willenbacher N: Characterization of complex fluids at very low frequency: experimental verification of the strain rate-frequency superposition (SRFS) method, Appl. Rheol. 20 (2010) 52340.
Results are presented aiming to determine whether wall slip occurs while performing rheological measurements of Carbopol solutions and bentonite dispersions at different concentrations using a standard oil-field Couette-type viscometer with two gap sizes. Yield stresses using a Vane rheometer were also determined and compared to those obtained by extension of the experimentally-derived rheological curves at the Couette viscometer.The results show that, if preparation procedures are followed as suggested for Carbopol solutions and by API standard for drilling fluids, simulating either the pre-shearing in the rig mud pumps or in the bit nozzles during drilling operations, wall slip does not occur, with a good agreement of the rheograms and of the yield stresses determined for both gap sizes of the Couette viscometer and by the Vane rheometer. No slip occurs also for CMC solutions which exhibited pseudoplastic power-law behavior.► Cite this publication as follows:
Kelessidis VC, Hatzistamou V, Maglione R: Wall slip phenomenon assessment of yield stress pseudoplastic fluids in Couette geometry, Appl. Rheol. 20 (2010) 52656.
A new magnetocell, based on a plate-plate twin gap with housing and integrated online flux density measurement, allows for a reliable rheological characterization of magneto¬rheological fluids (MRF). Various modifications introduced into the commercial magnetocell version MRD180/1T (Physica/Anton Paar), distinctly improve the homogeneity of the magnetic flux density distribution and broaden the range of accessible shear rates in a MCR501 rheometer up to more than 3000 s-1. The new design has been licensed to the manufacturer, to provide a commercial twin gap magnetocell. Fixed volume dosing of MRF yields an improved reproducibility of flow curve measurements, as required for the design of technical devices like MR clutches and MR brakes. The twin gap magnetocell enables the mimicking of MRF response releVant for clutch and brake applications, like shear rate or shear stress step or ramp testing, and drive cycle testing.The dynamic shear stress response to changes of flux density and/or shear rate may be characterized. Testing of MRF is possible for brake applications under constant holding torque conditions in the pre-yield regime. MRF creep and recovery for various imposed shear stresses may be monitored as a function of time. Comparison with a concentric cylinder pilot clutch underlines the validity of the shear stress versus flux density characteristic as determined with the twin-gap magnetocell.► Cite this publication as follows:
Gabriel C, Kieburg C, Laun HM: Clutch and brake related testing of magnetorheological fluids using the BASF twin gap magnetocell, Appl. Rheol. 20 (2010) 41778.
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.
Surface rheological properties affect the dynamics of vesicles, nanoparticles, emulsion droplets, foam bubbles, polymer microcapsules, liquid jets, living cells, lung avioli, thin liquid films, and many other multiphase systems. Surface rheology is therefore releVant for a wide range of disciplines in the areas of physics, chemistry, engineering, biology, and medicine. Currently used descriptions of surface rheology have a number of limitations, and in particular are hard to generalize to the large deformation regime. Data are often analyzed with constitutive equations based on straightforward generalizations of models developed for describing bulk phase rheology. Since the latter are in general designed to describe incompressible materials, they are not guaranteed to describe highly compressible interfaces correctly. Here we discuss a unified approach to surface rheology based on nonequilibrium thermodynamics (NET) that provides a consistent set of balance and constitutive equations for the unambiguous determination of surface rheological parameters, both near and far beyond equilibrium. A closer integration of experimental surface rheology and multiphase nonequilibrium thermodynamics would clearly be beneficial for both disciplines.► Cite this publication as follows:
Sagis L: Rheology of complex fluid-fluid interfaces: a unified approach based on nonequilibrium thermodynamics, Appl. Rheol. 20 (2010) 24380.
We propose a viscosity model accounting for experiments of emulsions of two immiscible liquids at arbitrary volume fractions. The model is based on a recursive-differential method formulated in terms of the appropriate scaling variable which emerges from an analysis of excluded volume effects in the system. This variable, called the effective filling fraction, incorporates the geometrical information of the system which determines the maximum packing and reduces to the bare filling fraction for infinitely diluted emulsions. The agreement of our model for the viscosity with experiments and previous theories is good for all the range of volume fractions and viscosity ratios.► Cite this publication as follows:
Mendoza CI, Santamaria-Holek I: Rheology of concentrated emulsions of spherical droplets, Appl. Rheol. 20 (2010) 23493.
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.
► Cite this publication as follows:
Gahleitner M: Advances in Polymer Science and Technology (APST 01), Appl. Rheol. 19 (2009) 362.
Rheological characterisation of mortar is complicated by phenomena of slip, the formation of shear bands and depletion. At relatively low solid fractions a typical Couette geometry and a medium-size mixer-type rheometer were used to determine flow curves. At higher solid fractions a large-size coaxial cylinder rheometer with multiple blade Vane geometry was used up to the point where slippage occurred. The viscosity as a function of concentration responds to the Krieger-Dougherty law, when a mortar is considered as a suspension of sand in a matrix of binder slurry. The limits of this description corresponds to a critical solid fraction above which air is entrapped during the mixing procedure: air content measurements demonstrate this phenomenon. A clear relationship between mortar and slurries was established, based on the measured properties of both binder and sand particles, and on the Farris model for polydisperse suspensions. Intrinsic viscosity can be used as a tool to evaluate shape characteristics of the binder particles. A procedure for mixture optimisation of mortars using this model is demonstrated for the case of a trimodal mortar.► Cite this publication as follows:
Hendrickx R, Rezeau M, VanBalen K, VanGemert D: Mortar and paste rheology: concentration, polydispersity and air entrapment at high solid fraction, Appl. Rheol. 19 (2009) 52550.
The combined effect of charged addition and molecular weight, Mw, on the thermal gelation and gel dissolution of poly(Nisopropylacrylamide) chains was explored by using Rheological techniques. The synthesized charged derivative is poly(N-isopropylacrylamide co-Acrylic acid). The rheological behavior of the two macromolecules is clearly different: the thermal gelation of the high Mw and charged macromolecule is much more accentuated. This suggests that the gelation at high temperatures only occurs when the inter polymer aggregate distance is sufficiently short to allow polymer bridging; this situation can be achieved by different approaches, such as increasing polymer concentration and increasing polymer persistence length and polymer Mw.► Cite this publication as follows:
Antunes FE, Gentile L, Tavano L, OlivieroRossi C: Rheological characterization of the thermal gelation of poly(N-isopropylacrylamide) and poly(N-isopropylacrylamide)co-Acrylic Acid, Appl. Rheol. 19 (2009) 42064.
► Cite this publication as follows:
Yeo L, Chang H, Wen W: Advances in Microfluidics and Nanofluidics (Hong Kong, 2009), Appl. Rheol. 19 (2009) 175.
► Cite this publication as follows:
Sarraf H: High performance ceramics by advanced colloidal processing (PhD thesis summary), Appl. Rheol. 19 (2009) 119.
Steady state and transient rheological behaviours of a one-coat render mortar are considered experimentally using a shear rheometer equipped with the Vane geometry.The flow curves performed at controlled shear-rates exhibit highly pronounced minima, which is attributed to shear localization and strong thixotropy. This latter property is further investigated separately by considering the temporal growth of the apparent stress at very low shear-rate, reflecting the material's microstructure rebuild up following shearing at different high shear rates. It is found that rebuilding characteristic time is roughly independent upon shear history, indicating that this is a material parameter. The influence of water dosage rate on the rheological behaviour is considered. As expected, apparent viscosity and yield stress decrease with increasing kneading water amount. The rebuilding up kinetics is found to be non sensitive to water dosage rate, suggesting that the material's processability would be preserved when changing this parameter, although significant creeping may be expected at high water dosage rates.► Cite this publication as follows:
Kaci A, Chaouche M, Andreani P-A, Brossas H: Rheological behaviour of render mortars, Appl. Rheol. 19 (2009) 13794.
Rheological properties of elastomeric nanocomposites with organically modified Montmorillonite clays, as possible replacements or supplements to classical active fillers, such as carbon black or silica, have been intensively studied in recent years. Possessing large specific surface areas acquired through the melt-mixing processes of elastomeric intercalation and subsequent filler exfoliation, the clay particles have indeed proved to be highly eligible reinforcing and thermally stabilizing ingredients for application in elastomers. In fact, their performance has shown to be in many respects superior to that of classical fillers, particularly owing to some unusual, though beneficial, exhibited properties. Namely, apart from uncommonly high surface activity, manifested by creation of a host of Van der Waals type secondary linkages with elastomer molecules, the main curiosity of clay filler is its dissipative action. Using dynamic mechanical functions under different deformational and temperature conditions, as means for rheological characterization of nanocomposites, the foregoing nano-scale traits are clearly reflected in substantial stiffness at low strains and, unexpectedly, dwindling energy loss with increasig filler content and/or decreasing temperature. Besides, rheological analysis of this kind, together with appropriate theoretical grounds, has enabled elucidation of peculiar conduct, as well as macroscopic insight into the very nature of secondary interactions in elastomers.► Cite this publication as follows:
Susteric Z, Kos T: Rheological Idiosyncrasies of Elastomer/Clay Nanocomposites, Appl. Rheol. 18 (2008) 54894.
Technical fibre flows are normally flocky but have theoretically mainly been treated as individual fibre flows. The reason for this can only be understood through the subject's historic development. In Part 1 of this investigation the origin of fibre flow research was traced to the beginning of the 19th century, and was followed through its formative years at the first half of the 20th century up to about WWII. This second and final part takes us up to about the 1960s when the present main theoretical research tradition had been firmly established. An example of an alternative approach is given. Finally, some suggestions for future work are adVanced. In Appendix methods of characterising the inner geometry of technical fibre suspensions are discussed.► Cite this publication as follows:
Bjorkman U: The Nonlinear History of Fibre Flow Research: Part 2. Continuation, Reflections and Suggestion, Appl. Rheol. 18 (2008) 34694.
A new procedure is described to convert the Vane torque and rotational velocity data into shear stress vs shear rate relationships. The basis of the procedure consists in considering locally the sheared material as a Bingham fluid and computing a characteristic shear rate from Couette analogy. The approach is first applied to experimental Vane data of Newtonian fluid, then used to process Vane experimental data of non-Newtonian and yield stress materials. Results, which are favourably compared with torsional flow, show that the approach correctly predicts the rheological behaviour of the materials investigated.► Cite this publication as follows:
Estelle P, Lanos C, Perrot A, Amziane S: Processing the vane shear flow data from Couette analogy, Appl. Rheol. 18 (2008) 34037.
The XVth International Workshop on Numerical Methods for Non-Newtonian Flows (XVth IWNMNNF 2007) was held on the island of Rhodes, Greece, in June 6 - 10, 2007. Since their inception in 1979, in Providence, Rhode Island, USA, the workshops are rotated biennially between North America and Europe. This was the first time the meeting was held in Greece. Rhodes Island was a proper destination, as the meetings have come a full circle after almost 30 years of frantic activity, which have seen workshop meetings in castles, lakes, islands, seasides. Rhodes, as the capital of the Dodecanese Islands, combines all of the above, and has been a place of tourism and holidays since antiquity. The XVth IWNMNNF was by all measures a truly international event, drawing around 60 scientists and engineers from 18 countries around the world. The Workshop included a plenary lecture by Roger Tanner, from University of Sydney, Australia, and 7 thematic sessions. [more]► Cite this publication as follows:
Mitsoulis E, Mavrantzas VG: Numerical Methods for Non-Newtonian Flows - XVth IWNMNNF 2007, Appl. Rheol. 17 (2007) 354.
Rheo-optics is a method that allows the analysis of optical properties, like birefringence and dichroism under steady and oscillatory shear. It is possible to correlate macroscopic mechanical responses with induced microscopic changes in the material. We describe how this method was improved several fold and implemented on a commercially available setup. However, the here presented ideas are applicable to any rheo-optical setup, based on modulation of the laser light. Additionally it does not need a lock-in amplifier and therefore reduces the costs of the setup.► Cite this publication as follows:
Klein C, Venema P, Sagis L, vanDusschoten D, Wilhelm M, Spiess HW, vanderLinden E, Rogers SS, Donald AM: Rheo-optical Measurements using Fast Fourier Transform and Oversampling, Appl. Rheol. 17 (2007) 45210.
Rheology is commonly used as a tool for analytics and quality control in latex technology. As soon as flow becomes essential for the structure measured in a scattering experiment we call it scattering from shear-ordered dispersions or rheologic scattering. In this paper it is shown that the structure of concentrated dispersions can with adVantage be studied by scattering experiments. Theoretical and experimental aspects as well as examples of small-angle synchrotron x-ray and neutron scattering from colloidal dispersions, presented in the paper, are closely related to rheology.► Cite this publication as follows:
Versmold H: Scattering from shear-ordered dispersions, Appl. Rheol. 17 (2007) 11412.
In this paper, by means of AdVanced Rheometric Expanded System (ARES), oscillatory and steady shear behavior of binary mixtures of a quaternary ammonium based ionic liquid [Me3NC2H4OH]+[Zn2Cl5]- with ethanol (EtOH) were determined at 25 C and 25-50 C, respectively. The effects of shear rate, temperature and concentration on viscosity were elucidated sufficiently. It was found that the solutions show pseudo-plastic behavior at low shear rate and Newtonian property at higher shear rate. The addition of EtOH caused a substantial decrease in viscosity of the ionic liquid and the viscosity of binary mixtures could be described by an exponential equation. Arrhenius Equation and Power Law equation were applied to describe the respective effects of temperature and shear rate on viscosity. Activation energy derived from Arrhenius equation decreased with increasing the EtOH fraction in the mixture.► Cite this publication as follows:
Li Q, Wu G, Liu Y, Luo Y: A rheological study of binary mixtures of Ionic Liquid [Me3NC2H4OH]+[Zn2Cl5]- and ethanol, Appl. Rheol. 16 (2006) 334.
In this paper we describe the rheological behaviour of Ca2+-induced cold-set gels of whey protein mixtures. Coldset gels are important applications for products with a low thermal stability. In previous work [J. Agric. Food Chem. 54 (2006) 4229], we determined the state diagram for whey protein mixtures that were heated for 10 h at pH 2 at 80°C. Under these conditions, the major whey protein, β-lactoglobulin (β-lg), forms fibrils. When whey protein mixtures are heated at protein concentrations in the liquid solution regime of the state diagram, cold-set gels can be formed by adding Ca2+ ions at pH 7. We studied the rheological behaviour of cold-set gels for various sample compositions for whey protein mixtures. When keeping the total whey protein concentration constant, the elastic modulus, G., for the cold-set gels decreased for increasing α-lactalbumin and bovine serum albumin ratios, because less material (blg fibrils) was available to form a gel network. In the cold-set gels the interactions between the β-lg fibrils induced by the calcium ions are dominant. The β-lg fibrils are forming the cold-set gel network and therefore determine the gel strength. α-Lactalbumin and bovine serum albumin are not incorporated in the stress-bearing structure of the gels.► Cite this publication as follows:
Bolder S, Hendrickx H, Sagis L, vanderLinden E: Ca2+-induced cold-set gelation of whey protein isolate fibrils, Appl. Rheol. 16 (2006) 258.
When two biopolymers are mixed together, they will normally phase separate to give two distinct phases. If the biopolymers are gelled during this phase separation, for instance by reducing the temperature, one phase is trapped in this other one and an emulsion-like composite structure is obtained. In this study, we investigated the effect of volume fraction and droplet size of this dispersed phase on the mechanical properties of maltodextrin/ agarose gel composites, where agarose is the dispersed phase. Mechanical properties of the different composites were investigated under large deformation using a rheometer with a Vane geometry. These composites were also observed by confocal microscopy, allowing conclusions to be drawn regarding the microstructural origins of the observed mechanical behaviour.► Cite this publication as follows:
Loret C, Frith WJ, Fryer PJ: Mechanical and structural properties of maltodextrin/agarose gel composites, Appl. Rheol. 16 (2006) 248.
In this contribution, a brief review is given of the dynamics of emulsions in microconfined shear flow. The interest in confined flow is triggered by the increasing importance of microfluidic applications in the processing industries. In a first part, some important aspects of confinement on single droplet dynamics are highlighted. The validity of the conclusions drawn from this part are subsequently applied to more concentrated systems. It is shown that microconfined emulsions can exhibit rich dynamics, and can display some peculiar morphologies.► Cite this publication as follows:
Vananroye A, VanPuyvelde P, Moldenaers P: Morphology development during microconfined flow of viscous emulsions, Appl. Rheol. 16 (2006) 242.
The measurement of the shear rheology of concentrated particulate suspensions is important to a range of mixing, pumping and flow operations. The use of a four or six bladed Vane attached to a rheometer in an open cup is a popular technique to achieve a rheological characterisation. A problem occurs in the use of automated software with a number of rheological devices for yield stress materials. A torque auto zero default causes the torque at the start of a test to be ignored, and can result in significant errors and underestimation of the yield stress or rheological response of the suspension. The potential effect of using a torque auto zero default is demonstrated for a concentrated particulate suspension of nickel laterite.► Cite this publication as follows:
Fisher DT, Boger DV, Scales PJ: Measurement errors in yield stress rheometry that arise from torque auto zero, Appl. Rheol. 16 (2006) 206.
The effect of viscoelasticity on multilayer polymer extrusion is discussed. In these coextrusion processes predetermined patterns are created with a remarkable breadth of complexity even in geometrically simple dies via elastic rearrangements caused by the second-normal stress differences. A computational method is offered, based on the mapping method, which quantitatively describes the flow-induced patterns. Besides that the results are esthetically beautiful, they are also releVant for practice, since process and die design optimization is now possible. Not only to minimize interface distortion, but potentially also to deliberately create new processes and products based on this flow-induced patterning of polymers.► Cite this publication as follows:
Anderson PD, Dooley J, Meijer HEH: Viscoelastic effects in multilayer polymer extrusion, Appl. Rheol. 16 (2006) 198.
The purpose of this paper was to re-evaluate the novel rheological method of Crosby et al. [J. Rheol. 46 (2002) 401] to characterise long chain branching (LCB) in polyethylenes (PE) using the rheology of concentrated solutions. The feasibility of this dilution method centred on knowing the class of branched material and the molecular tube theory-based technique for the determination of two topological parameters (n, bU), where n is the number of entanglements between branch points while bU is the probability of meeting a branch point when tracing along the molecule from a random monomer against the direction of polymerisation. This paper proposes new possible approaches to calculate the two topological parameters (n, bU) set for metallocene polyethylenes (mPE), and their ambiguity discussed, as the results are dependent on the approach taken, though the previous authors mentioned only one. In addition, their approach requires an input value of LCB/1000C obtained from the standard analytical solution (SEC-V or SEC-LALLS) methods, hence, until now, without proper demonstration of the potential adVantage of the dilution rheology method for LCB characterisation, as the main premise of their published article was to characterise the degree of LCB via rheological measurements without recourse to other methods of LCB characterisation.► Cite this publication as follows:
Chai CK, Ang SC: An Evaluation of Dilution Rheology for the Characterization of Long Chain Branching of Polyethylenes, Appl. Rheol. 16 (2006) 90.
The Impact Factor of a journal is a quantitative way of assessing its worth and releVance to the academic community it serves. Many librarians see the ratio between Impact Factor and price as a suitable yardstick by which to measure the value of their collections. In addition, the research assessment exercises which, in many countries, are now being carried out on a more formal basis mean that authors submitting original research must publish it in a journal with the highest perceived worth possible in order to secure future funding, job promotions and peer recognition. It has been suspected [T. Opthof, Cardiovasc. Res. 33 (1997) 1; J. Stegmann, Nature 390 (1990) 550], however, that a particular author's impact is not much related to the journals in which her/he publishes. As will be demonstrated in this letter, the impact of articles published in rheological journals is largely influenced by criteria such as length of article, number of authors, number of cited references.► Cite this publication as follows:
Kroger M: Publication Specific Impact of Articles Published by Rheological Journals, Appl. Rheol. 15 (2005) 406.
Exponential integral functions were fitted to relaxation data obtained from tensile and shear loading of an asphalt-sand mixture at different temperatures. This approach yields a better fit to the experimental data than the traditional Prony series and provides physical insight into essential characteristics of the relaxation processes that govern the asphalt-sand mixture. We expect that using this model beyond the time range covered by the experimental data would result in a significantly better representation of the material behavior than would extrapolation of the Prony series fit.► Cite this publication as follows:
Koenigsberg W, Selverian JH: Zone Method for Representing Relaxation Characteristics of Viscoelastic Materials, Appl. Rheol. 15 (2005) 160.
A new model for mean velocity profile of turbulent water flow with added drag-reducing surfactants is presented in this paper. The general problem of drag due to frictional resistance is reviewed and drag reduction by the addition of polymers or surfactants is introduced. The model bases on modified Prandtl's mixing length hypothesis and includes three parameters, which depend on additives and can be evaluated by numerical simulation from experimental datasets. The adVantage of the model in comparison with previously reported models is that it gives uniform curve for whole pipe section and can be determined for a new surfactant with less necessary measurements. The use of the model is demonstrated for surfactant Habon-G as an example.► Cite this publication as follows:
Krope A, Krope J, Lipus LC: A Model for Velocity Profile in Turbulent Boundary Layer with Drag Reducing Surfactants, Appl. Rheol. 15 (2005) 152.
There is often a need to perform rheological tests on dilute polymeric liquids at a time long after their initial preparation, for example if a more sensitive or novel method of measuring a material property (such as uniaxial/ biaxial extensional viscosity or second normal-stress differences) becomes available. An inexpensive method of storing such fluids which prevents any form of deterioration (e.g. bacteriological) would therefore be of great value. This study explores the potential of freezing as that storage process by investigating whether the freezethaw process itself leads to rheological changes. The rheological properties of three polymeric liquids: 0.25 % xanthan gum, 0.125% polyacrylamide and a 0.1 %/0.1 % carboxymethylcellulose / xanthan gum blend commonly used in non-Newtonian fluid flow studies were determined in both shear and oscillation before and after a freeze-thaw process. Within the uncertainty of the rheometer used, the rheological properties of the polymers studied were found to be unaffected by the freeze-thaw process leading to the conclusion that this storage method is indeed a practical possibility.► Cite this publication as follows:
Escudier MP, Clement-Evans J, Poole RJ: Freezing as a Storage Process for Aqueous Polymer Solutions, Appl. Rheol. 15 (2005) 90.
The term |G*|/(1-(1/tand sind)) has been suggested as one of the best candidates for the replacement of the Superpave specification parameter |G*|/sind, which has been found to be inadequate in rating polymer-modified binders for high temperature performance grading. This refinement of the Superpave specification parameter evolved through a theoretical derivation based on fundamental concepts. It was shown to be more sensitive to the variations in the phase angle d than the original Superpave specification parameter. It thus described the unrecovered strain in the asphalt binders more accurately, and hence related to actual field performance data. This article provides a comprehensive treatise of the parameter |G*|/(1-(1/tand sind)) giving details of its derivation, salient features that are attributed to its success, comparison with actual field performance data for validation and a one-on-one comparison with the existing parameter |G*|/sind. It is shown that for all available field data, the parameter |G*|/(1-(1/tand sind)) does a better job in correlating with the rutting behavior than the parameter |G*|/sind for unmodified as well as modified asphalts. Since it is obtained in the same manner as the parameter |G*|/sind through the determination of |G*| and d from a stress-controlled or strain-controlled dynamic shear rheometer, it means that no retraining of technicians and staff is required and implementation for the use of this parameter is immediate, thereby saving enormous amount of time and money. This parameter has the further adVantage of being in a form easily adaptable to modeling, and thereby directly applicable for pavement design purposes.► Cite this publication as follows:
Shenoy A: A Comprehensive Treatise of the High Temperature Specification Parameter |G*|/(1-(1/tan d sin d)) for Performance Grading of Asphalts, Appl. Rheol. 14 (2004) 303.Evan Mitsoulis
Hellenic Society of rheology: HSR 2004 Athens, Greece
Appl. Rheol. 14:5 (2004) 266 ►
► Cite this publication as follows:
Mitsoulis E: Hellenic Society of rheology: HSR 2004 Athens, Greece , Appl. Rheol. 14 (2004) 266.
The aim of this paper is to present a new phenomenological rheological model suitable for the description of a wide class of viscoelastic fluids. Classical phenomenological models predict the relation shear viscosity vs. shear rate (or shear stress) for shear-thinning (or thickening) materials exhibiting smooth monotonous passage from the first - upper (lower) - Newtonian plateau to the second - lower (upper) - one. However, present state of non- Newtonian materials used in practice (ranging from aqueous surfactant solutions, bituminous materials, associative polymers, polymer thickeners, lacquers and gels, to some special disperse systems, etc.) evokes the need to describe this - for many materials non-monotonous - relation in the corresponding way, i.e. through the sufficiently simple phenomenological model with a moderate number of parameters. A six-parameter model enabling description of not only monotonous but also non-monotonous course of shear viscosity function against shear rate (stress) is proposed including physical characterisation of the parameters. This model describes not only extreme points (maximum or minimum) but also a possible appearance of intermediate Newtonian plateau or its indication. The meaning and influence of the individual six parameters is documented on the experimental data published in the literature. There is a good agreement of the model proposed with many different experimental data representing different rheological behaviour. The applicability of this model for a wide class of viscoelastic materials is its principal adVantage over the hitherto published phenomenological models.► Cite this publication as follows:
David J, Filip P: Phenomenological Modelling of Non-Monotonous Shear Viscosity Functions, Appl. Rheol. 14 (2004) 82.Dr. J.H. Watson
The Diabolical Case of the Recurring Yield Stress
Appl. Rheol. 14:1 (2004) 40-45 ►
The yield stress has, since its conception, been a source of fierce and often acrimonious debate. This review article deals with the issue, looking at problems related to the meaning of the definition, timescale of the observation, whether the yield stress is a property of concentrated suspensions or is linked to the strength of coherent network structures. We discuss the problematic nature of how to measure the yield stress, directly or indirectly, and examples of the Vane geometry are given. Throughout, absolutist and realist theories and evidence are presented and a consensus is finally drawn. Rheologists should embrace the consequences of the absolutist and realist theories and apply them to their everyday world - whatever the timescale!► Cite this publication as follows:
Watson JH: The Diabolical Case of the Recurring Yield Stress, Appl. Rheol. 14 (2004) 40.Peter Van Puyvelde, Paula Moldenaers
Sunny Rheology School in Leuven
Appl. Rheol. 13:6 (2003) 317 ►
► Cite this publication as follows:
VanPuyvelde P, Moldenaers P: Sunny Rheology School in Leuven, Appl. Rheol. 13 (2003) 317.Evan Mitsoulis
PPS 2003 Europe/Africa Regional Meeting
Appl. Rheol. 13:6 (2003) 316 ►
► Cite this publication as follows:
Mitsoulis E: PPS 2003 Europe/Africa Regional Meeting, Appl. Rheol. 13 (2003) 316.
Red blood cell aggregation (RBCa) is a sensitive inflammation marker. RBCa determination from erythrocyte sedimentation rate, ESR, is used since long, but is unspecific unless corrected for hematocrit, Ht. Whole blood viscosity measurement at low shear rate is also sensitive to RBCa but is cumbersome to apply. To investigate whether electrical blood impedance, being sensitive to spatial red cell distribution, can be a good alternative to determine RBCa in low shear conditions. Blood was collected from 7 healthy volunteers. From each 16 different samples were prepared with 4 different Ht.s and with 4 different fibrinogen concentrations. Viscosity was measured at low shear rate (4.04 s-1) with a rotational viscometer at 37.C. Electrical blood impedance was measured during similar shear conditions and temperature in a specially designed cuvette. ESR was determined according to Westergren. A logarithmic increase of viscosity as well as of capacitance, Cm, is seen when fibrinogen rises and an exponential increase when Ht rises. However, ESR shows a logarithmic decrease with increasing Ht and an exponential increase when fibrinogen rises. The viscosity could be accurately described using an exponential model. Under similar low shear conditions and temperature in-vitro, either whole blood viscosity or electrical blood capacitance reflect red blood cell aggregation due to fibrinogen and Ht variation in a similar way.► Cite this publication as follows:
Pop GAM, Hop WJ, Moraru L, vanderJagt M, Wuak J, Dekkers D, Chang Z, Gijsen FJ, Duncker DJ, Slager CJ: Blood Electrical Impedance Closely Matches Whole Blood Viscosity as Parameter of Hemorheology and Inflammation, Appl. Rheol. 13 (2003) 305.
Novel approach to rheological modelling of a fly ash-water mixture is proposed. The model is first tested against the available experimental data for a corn starch-water, a glass beads-water and a fly ash-water mixture and then used taking the adVantage of available CFD code for a calculation of major and minor losses. Numerical results for Quadratic model are compared with results for Power law.► Cite this publication as follows:
Marn J, Ternik P: Use of Quadratic Model for Modelling of Fly Ash-Water Mixture, Appl. Rheol. 13 (2003) 286.
Polymer modified asphalt is an highly temperature sensitive material. To obtain the master curves of dynamic material functions, for this material, it is necessary to perform the testing over the temperature interval from - 30.C to at least 90.C. Since in this temperature range the polymer modified asphalt undergoes the transition from a glass-like to a Newtonian-like material, the benefit of using three testing geometries is studied here. The geometries used were: torsion bar (for the low temperatures), plate-plate (for the mid range temperatures) and bob and cup (for the high temperatures). The adVantage of the combination of these three geometries is discussed. Stress and strain controlled rheometers were used to conduct all dynamic experiments. Master curves obtained by these geometries cover up to 20 decades of the reduced frequency.► Cite this publication as follows:
Polacco G, Vacin OJ, Biondi D, Stastna J, Zanzotto L: Dynamic Master Curves of Polymer Modified Asphalt from Three Different Geometries, Appl. Rheol. 13 (2003) 118.
► Cite this publication as follows:
DeCesare G: Third International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (3rd ISUD), Appl. Rheol. 12 (2002) 309.
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.
The Vane geometry with a large gap is used to determine the Newtonian, non-Newtonian and viscoelastic properties of complex fluids. We show that when this geometry is carefully characterized, it can be used for precise rheometry. A novel effective cylinder approximation is used to obtain the shear rate and shear stress factors. The effective radius is found to be close to the height of the triangle formed by joining the tips of adjacent blades. This result differs significantly from that of previous work. Flow visualization has been used to confirm that the stream lines bend towards the centre between the blades. These factors can be used to determine the flow curves of non-Newtonian liquids, using Krieger.s power law expansion. The standard procedure for using the Vane to determine the yield stress is also carefully investigated and alternative procedures are suggested.► Cite this publication as follows:
Baravian C, Lalante A, Parker A: Vane rheometry with a large, finite gap, Appl. Rheol. 12 (2002) 81.
A method has been proposed for quantitative characterization of the flow behaviour of fluids, which is an important problem of applied rheology. Particle Image Velocimetry technique has been used for visualization and measurement of the velocity field. The rheometric study of the fluid is aimed at determining the character of the flow and its dynamic viscosity. It is shown that the experimental data obtained for the velocity field and the viscosity are necessary and sufficient for determining the shear stress field at each point of the flow bulk. The major part of the investigations are performed using a Newtonian fluid (epoxy resin), but some data for the non- Newtonian fluid (solution of xantan) are shown too. The flow is produced by gravity in a system of tubes (a barrel and a capillary) with different round crossections. The possibility of further improvement of the combined rheo-optical method is shown.► Cite this publication as follows:
Ivanov Y, Kavardjikov V, Pashkuleva D: Combined Method for Quantitative Characterisation of Fluid Flow, Appl. Rheol. 11 (2001) 320.
► Cite this publication as follows:
Lä, uger J, Raffer G: Physica advanced Peltier system PTD150 (Pat. Pendt.). Making the temperature control with a Peltier system accurate, Appl. Rheol. 11 (2001) 281.
The Microsoft Excel Solver tool is a very simple but powerful procedure, even in the hands of the mathematically disadVantaged. It has very good application for quickly fitting experimental flow-curve data to non-Newtonian flow models with any number of parameters, and can cope with data from a number of sources. Examples are given for a range of industrially important examples ranging from standard non-Newtonian liquids, through detergent solutions to gels, pastes, and filled polymer melts, often measured on different viscometers.► Cite this publication as follows:
Roberts GP, Barnes HA, Mackie C: Using the Microsoft Excel `solver' tool to perform non-linear curve fitting, using a range of non-Newtonian flow curves as examples, Appl. Rheol. 11 (2001) 271.
To overcome difficulties (slip, sample disturbance) associated with traditional sensors, a semi-empirical method was developed to allow the use of a 4-bladed Vane sensor in small strain oscillatory testing. It was assumed that the Vane sensor acted as a bob with an acting radius, RV, different from the actual radius of the Vane (0.02005 m). To solve for RV, the complex modulus obtained using a concentric cylinder sensor from reference viscoelastic fluid, was set equal to the complex modulus equation for Vane sensor. RV values were grouped into three phase shift ranges from 5° to less than 16°, from 16° to less than 60°, and from 60° to 90° and they were 0.01883, 0.01869, and 0.01850 m, respectively. These values were used in the calculation of viscoelastic properties of eight commercial food products, which resulted in complex modulus values within 15% of those obtained using a concentric cylinder sensor. Results showed that this particular Vane and cup system can be used to directly measure the storage and loss moduli of viscoelastic material and phase shift within the upper frequency value of 6.28 rad/s. Above 6.28 rad/s, there is an inconsistency in phase shift angles measured using Vane method. This method is ideal for testing thixotropic food systems because disturbance is minimal during sample loading, giving more accurate viscoelastic measurements.► Cite this publication as follows:
Junus S, Briggs JL: Vane sensor system in small strain oscillatory testing, Appl. Rheol. 11 (2001) 264.
► Cite this publication as follows:
Richtering W: The Colloidal Domain where physics, chemistry, biology and technology meet (D.F. Evans, H. Wennerstrom), Appl. Rheol. 11 (2001) 177.
► Cite this publication as follows:
Ivanov Y: Balkan seminar on rheology and 9th national workshop on rheology (Sofia/Bulgaria), Appl. Rheol. 11 (2001) 156.
An electrorheological fluid (ERF) (magnetorheological fluid - MRF) is a particulate suspension which shows a dramatic increase in flow resistance upon application of an external electric (magnetic) field. In both systems, the fundamental physical process is believed to be that the field induces polarization of each particle with respect to the carrier material, and the resulting interparticle forces cause elongated aggregates of particles to form in the field direction. While recent years have witnessed the appearance of several applications using these tunable flow properties, optimal use of this technology is still hindered by our incomplete understanding of the underlying mechanisms. This paper surveys our current understanding of several of the key issues governing the rheological behavior of MRF and ERF, with particular focus on recent progress made in important areas such as the behavior under high fields, sedimentation, temperature dependence, effect of wall surface conditions, and adVances made in developing practical modelling strategies.► Cite this publication as follows:
See H: Mechanisms of magneto-and electro-rheology: Recent progress and unresolved issues, Appl. Rheol. 11 (2001) 70.
Previous studies have documented the presence of increased red blood cell aggregability in patients with ischemic heart and brain diseases. We adapted a simple slide technique and image analysis to reveal the state of erythrocyte adhesiveness/aggregation (EAA) in the peripheral blood of 206 such patients and in 174 controls. A significant (P<0.0001) correlation was noted between the EAA state and both fibrinogen concentrations and erythrocyte sedimentation rate in the whole cohort. Noteworthy was a highly significant increment in the EAA state in a subgroup of 49 patients who had normal fibrinogen concentrations when compared to matched healthy controls. This was also the case in 82 patients who had a normal erythrocyte sedimentation rate. Thus, the EAA assay appears to have the adVantage of revealing the presence of acute phase response sticky proteins not detected by either the erythrocyte sedimentation rate or clottable fibrinogen in some patients with a documented ischemic vascular disease.► Cite this publication as follows:
Zeltser D, Rotstein R, Rogowski O, Fusman R, Shapira I, Prochorov V, Bornstein NM, Roth A, Keren G, Avitzour D, Arber N, Eldor A, Berliner S: The erythrocyte adhesiveness/aggregation test (EAAT) in the peripheral blood of patients with ischemic heart and brain disease with normal fibrogen concentrations, Appl. Rheol. 10 (2000) 231.
► Cite this publication as follows:
GlennIII TA, Keener KM, Daubert CR: A Mixer Viscometry Approach to Use Vane Tools as Steady Shear Rheological Attachments, Appl. Rheol. 10 (2000) 80.
► Cite this publication as follows:
Mitsoulis E: Computational Rheology with Integral Constitutive Equations, Appl. Rheol. 9 (1999) 198.
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