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Hansong Zhang, Zhide Hu, Hua Yan, Jianjian Yang, Fanghao Niu
The influences on field-induced chains by nonmagnetic microstructures inside the magnetorheological fluids Based on PTFE-oil organogel

Appl. Rheol. 28:5 (2018) 53921 (12 pages)

Polytetrafluoroethylene (PTFE) micropowders were used to prepare PTFE-oil organogel. Carbonyl iron particles were dispersed in this organogel to fabricate magnetorheological fluids. The main aim of this paper is to investigate the influences on fieldinduced chains by non-magnetic microstructures inside these organogel-based MRFs. The field-induced anisotropy of MRFs between first normal stress differences to shear stresses and dynamic modulus reveal that organogel widen the non- Newtonian elastic range of MRFs as long as the non-magnetic particles content is appropriate. Both theoretical and experimental results of static and dynamic normal forces indicate that normal forces are influenced by magnetic and non-magnetic microstructures comprehensively. The dynamic normal forces are lower than static ones under low magnetic field strength while the phenomenon becomes opposite in the presence of high strength magnetic field. Moreover, a 3ITT test of normal forces exhibits a significant time-dependent behavior of the normal forces. The investigations of recovery ratio demonstrate that the non-magnetic microstructures help field-induced chains to recover at relatively low magnetic field strength but hinder this structural recovery at high magnetic field strength. Finally, a new investigation method on amplitude-dependent normal forces is introduced showing a four-region behavior as a function of strain amplitude, which reflects the internal microscopic evolution of MRFs and cOuld be a proper way to study the influences on field-induced chains by non-magnetic particles.

Cite this publication as follows:
Zhang H, Hu Z, Yan H, Yang J, Niu F: The influences on field-induced chains by nonmagnetic microstructures inside the magnetorheological fluids Based on PTFE-oil organogel, Appl. Rheol. 28 (2018) 53921.

Maryam Mudasir, Riaz Ahmed
An Explanation of Structure-Property Relationships for Polymer/Clay-Nanocomposites through Melt Flow Birefringence and Damping Function

Appl. Rheol. 27:5 (2017) 53700 (11 pages)

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

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

Myoungsung Choi, Robert K. Prudhomme, George W. Scherer
Rheological evaluation of compatibility in oil well cementing

Appl. Rheol. 27:4 (2017) 43354 (9 pages)

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

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

F.M. Leon-Martinez, P. F. de J. Cano-Barrita
Yield stress of mortars in rotational and oscillatory shear experiments usinag a ball measuring system

Appl. Rheol. 27:4 (2017) 45838 (11 pages)

This study compared the flow curve fitting and oscillatory strain sweep methods to determine the yield stresses of Portland cement mortars using a ball measuring system (BMS). The tests were performed in two stages. In the first stage, the responses from a BMS with ball diameters of 8, 12, and 15 mm were compared to those from conventional cone-plate geometry with two different polymer dispersions. In the second stage, thirty-five mortars were prepared with 10 wt% of the cement replaced by silica fume. Five water-to-binder ratios and seven concentrations of a polycarboxylate-based superplasticizer were selected. An 8-mm diameter ball was selected for use in mortar production due to the smaller drag that it produced. The results indicated an increase in the linear viscoelastic region due to a reduction in the water-to-binder ratio and/or an increase in the superplasticizer concentration. In oscillatory tests, the dynamic yield stress was related to the stability of the cement paste and the strengths of the internal links between the cement particles. The flow and Herschel-Bulkley yield stresses result were not statistically different. Therefore, flow stress calculations cOuld be carried out using either of these methods. An amplitude sweep test performed using the BMS may be an alternative method of studying the rheology of cement-based materials.

Cite this publication as follows:
Leon-Martinez FM, Cano-Barrita PFdJ: Yield stress of mortars in rotational and oscillatory shear experiments usinag a ball measuring system, Appl. Rheol. 27 (2017) 45838.

Eakasit Sritham, Sundaram Gunasekaran
Rheological and Microstructure Evaluations of Amorphous Sucrose-Maltodextrin-Sodium Citrate Mixture

Appl. Rheol. 27:4 (2017) 43102 (10 pages)

Rheological properties and the mechanical relaxation behavior of rubbery amorphous sucrose-maltodextrin-sodium citrate systems were studied at room temperature using the small amplitude oscillatory shear test in the frequency range of 0.1 - 150 Hz. The system with high sucrose concentration exhibited viscous-dominant relaxation, while the system with high maltodextrin concentration exhibited elastic-dominant relaxation. The addition of sodium citrate cOuld retard molecular mobility presumably due to its molecular interaction with sucrose rather than with maltodextrin. The technique was capable to detect changes in molecular process even with a small variation in the matrix components. Evidences obtained with scanning electron micrographs suggested the possible effect of sodium citrate to interfere with molecular interactions in the system with high maltodextrin concentration, i.e. the system tended to be more brittle.

Cite this publication as follows:
Sritham E, Gunasekaran S: Rheological and Microstructure Evaluations of Amorphous Sucrose-Maltodextrin-Sodium Citrate Mixture, Appl. Rheol. 27 (2017) 43102.

Silju-John Kunnkattu, Theresia Gross, Sandra Stoppelkamp, Juvano Knieps, Torsten Remmler, Stefan Fennrich, Hans Peter Wendel, Nicole Rauch
Potential of a piezo-based measuring method (PAV) as a haemostasis monitoring system compared to a rotational rheometer

Appl. Rheol. 27:1 (2017) 13540 (11 pages)

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.

Katja A. Fröhlich, Eleni Mitrentsis, Frank Clemens, Botho Hoffmann, Véronique Michaud, Thomas Graule
Assessment of the Dispersion Quality of refractive index-matched nanodispersions

Appl. Rheol. 26:6 (2016) 65050 (10 pages)

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.

Sven Pieper, Hans-Joachim Schmid
Guard ring induced distortion of the steady velocity profile in a parallel plate rheometer

Appl. Rheol. 26:6 (2016) 64533 (7 pages)

The shape and fracture of the free surface frequently limits the measuring range and impedes the use of optical velocimetric techniques in parallel plate and cone plate setups. To prevent this, various kinds of edge guards are often employed. In the present study, we elucidate how an edge guard distorts the steady velocity profile in a parallel plate setup. To this end, we analyzed the velocity field of a strongly shear-thinning fluid, a Newtonian fluid and a set of suspensions via particle image velocimetry in a parallel plate device. Several guard ring sizes were studied. The distortion is described by a simple three parameter model. These parameters are mostly constant for different fluids and suspensions with particle volume fractions below 45%. With increasing radius, the guard ring.s influence approaches a limiting value that we attribute to the influence of the fluid surrounding the gap. Our results indicate a limiting ratio of the difference between plate radius and guard to gap size that shOuld always be exceeded. In the presence of a guard ring, even Newtonian fluids do not exhibit a constant shear rate for most radial distances within the gap. This distortion of the velocity field challenges the simple superposition approach of unguarded device and guard influence that is prevalent in the literature.

Cite this publication as follows:
Pieper S, Schmid H: Guard ring induced distortion of the steady velocity profile in a parallel plate rheometer , Appl. Rheol. 26 (2016) 64533.

Joseph Assaad, Yehia Daou
Use of the equivalent mortar phase to assess thixotropy of fresh SCC - Prediction of interfacial bond strength between successive placement lifts

Appl. Rheol. 26:4 (2016) 42759 (10 pages)

Self-consolidating concrete (SCC) is very sensitive to delays or stoppages between successive lifts during casting, especially given that vibration is prohibited with this highly flowable type of concrete. The investigation reported in this paper seeks to quantify the effect of mixture proportioning on thixotropy along with the resulting effect on interfacial bond strength of hardened material that cOuld result from successive lifts. The suitability of the equivalent mortar phase to simplify testing protocols and appropriately predict SCC properties was given particular attention; the concrete-equivalent-mortar (CEM) mixtures are derived from SCC by eliminating the coarse aggregate fraction and replacing it by an equivalent quantity of sand having equal surface area. Tests results have shown that SCC and CEM mixtures prepared with combinations of increased cement content, silica fume, and/or viscosity-modifier led to higher levels of thixotropy. Yet, the responses determined using SCC were higher by around 1.6 times than those of CEM, given the differences in unit weight and air content between both materials. Good correlations are established between thixotropy and interfacial bond strengths of SCC and CEM mixtures. Key words:

Cite this publication as follows:
Assaad J, Daou Y: Use of the equivalent mortar phase to assess thixotropy of fresh SCC - Prediction of interfacial bond strength between successive placement lifts, Appl. Rheol. 26 (2016) 42759.

Bin Yu, Yuanjing Chen, Qinghua Liu
Experimental study on the influence of coarse particle on the yield stress of debris flows

Appl. Rheol. 26:4 (2016) 42997 (13 pages)

Former studies show that the coarse particle plays a very important role in the determination of the yield stress of fluid-solid mixtures such as debris flows. The characteristics of the coarse particle in these mixtures include particle size, gradation, shape, and type of material. To assess the influence of these coarse particles on the yield stress the concept of equivalent volumetric solid concentration C is introduced. The equivalent concentration can be derived from the volumetric solid concentration by considering the particle size, gradation, shape, and type of material. Laboratory experiments to determine the yield stress of various mixtures were conducted to calibrate the coefficients of these coarse particle characteristics. A yield stress phenomenological expression is proposed using the refined volumetric solid concentration (equivalent concentration), which cOuld be calibrated by the experiments in this study. The validation of this phenomenological expression with data from literature shows good agreements, especially for higher volumetric concentrations of the sediments.

Cite this publication as follows:
Yu B, Chen Y, Liu Q: Experimental study on the influence of coarse particle on the yield stress of debris flows, Appl. Rheol. 26 (2016) 42997.

Jingsi Zhang, Simon J Haward, Zhigen Wu, Xiaohu Dai, Wenquan Tao, Zhuo Li
Evolution of Rheological Characteristics of High-solid Municipal Sludge during Anaerobic Digestion

Appl. Rheol. 26:3 (2016) 32973 (10 pages)

Rheological characterization of high-solid sludge is a fundamental requirement for optimizing the mixing and transport of high-solid sludge during anaerobic digestion in waste water treatment systems. We investigate the time evolution of physicochemical properties and rheological characteristics of high-solid digested sludge with total solids (TS) 15−20 wt.% during anaerobic digestion. A series of experiments are carried out over a period of 26 days during the operation of an anaerobic sequencing batch reactor. In equilibrium flow curves, high-solid digested sludge exhibits shear thinning behavior with a yield stress. Strong viscoelastic behavior is exhibited in the linear and non-linear regimes in dynamic and creep tests. A critical shear stress is found in the equilibrium flow curve, which accounts for the viscoelastic property. To accurately model the flow curves, a piecewise Herschel-Bulkley function separated by the corresponding critical shear rate is proposed. The digestion time plays an important role in determining the rheological behavior. Longer digestion times lead to a decreased yield stress in creep tests, and a decreased viscosity and a reduced critical shear stress in the steady flow curve. In addition, the storage modulus G' and the loss modulus G'' are reduced as digestion proceeds, leading to a shorter linear viscoelastic regime. Moreover, we find that the storage modulus G' varies linearly with the concentration of total organic matter in the sludge, suggesting that G' cOuld be used as a new control parameter for monitoring of the anaerobic digestion process.

Cite this publication as follows:
Zhang J, Haward SJ, Wu Z, Dai X, Tao W, Li Z: Evolution of Rheological Characteristics of High-solid Municipal Sludge during Anaerobic Digestion, Appl. Rheol. 26 (2016) 32973.

Heiko Stettin
Resonances in oscillatory rheometry

Appl. Rheol. 26:2 (2016) 24246 (12 pages)

Resonance phenomena are discussed in detail. The influence of significant parameters as the moment of inertia and the measuring constants are enlightened and verified with measurements. It is shown that resonance frequencies weekly depend upon the moment of inertia and strongly on the geometrical coefficient of the measuring system. Both parameters form the configuration constant. If a measuring system is replaced, the moment of inertia changes little but the configuration constant changes more. Thus resonance frequencies can be shifted some decades. The comparison between the developed formalism and measurements gives good results for different rheological measuring modes. Even at pronounced resonances measurements provide proper results. The formalism can be used for the simulation of measuring values. However, deformation oscillations along the rotating axis generate resonances of higher order at higher frequencies. These phenomena contribute systematically errors and shOuld be avoided.

Cite this publication as follows:
Stettin H: Resonances in oscillatory rheometry, Appl. Rheol. 26 (2016) 24246.

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.

Magda Nystrom, Waqas Muhammad, Margareta Bulow, Olle Ekberg, Mats Stading
Effects of rheological factors on perceived ease of swallowing

Appl. Rheol. 25:6 (2015) 63876 (9 pages)

This study is a contribution to the understanding of how rheological properties of a fluid influences swallowing, especially people suffering from swallowing disorders (dysphagia). Our hypothesis was that fluid elasticity contributes to safe and pleasant swallowing. In the present study three food grade model fluids with specific rheological properties were developed and used: a Newtonian fluid with constant shear viscosity, an elastic Boger fluid with constant shear viscosity and a shearthinning fluid which was elastic and had rate dependent shear viscosity. By comparing the swallowing of these model fluids the specific rheological effects cOuld be distinguished. Sensory analysis of the perceived ease of swallowing was performed by a panel of healthy individuals, and by a group of dysphagic patients. The swallowing of the latter group was also characterized by videoflouroscopy and the transit times in the mouth and pharynx were determined. The hypothesis was confirmed by dysphagic patients who perceived swallowing easier for the elastic model fluids. A sensory panel of healthy individuals cOuld not distinguish differences in swallowing, likely because their swallowing functions well and is an involuntary process. Quantitative videofluoroscopic measurements of swallowing transit times for the dysphagic patients suggested that fluid elasticity contributed to easy and safe swallowing, but the effect was not statistically significant due to the large spread of type of swallowing disorder.

Cite this publication as follows:
Nystrom M, Muhammad W, Bulow M, Ekberg O, Stading M: Effects of rheological factors on perceived ease of swallowing, Appl. Rheol. 25 (2015) 63876.

Willy Mbasha, Irina Masalova, Rainer Haldenwang, Alexander Malkin
The yield stress of cement pastes as obtained by different rheological approaches

Appl. Rheol. 25:5 (2015) 53517 (11 pages)

Different rheological methods for yield stress estimation of cement pastes during initial hydration were used and results were compared. These methods include measuring of the hysteresis loop, flow curves (recalculated to the same time of hydration) and large amplitude oscillating strain (LAOS). Experiments were performed with four Ordinary Portland Cements from one manufacturer, produced at different factories and one polycarboxylate acid based superplasticiser (SP). The yield stress values obtained by constructing flow curves is the only method which gives information about the evolution of the rheological properties, reflecting structure evolution of cements pastes. It was shown that the yield stress values established by the LAOS method and that calculated from the flow curves are similar while the values found from the downward part of the hysteresis loops are much lower. Differences in the yield stress values obtained by various methods are related to the different states of the material corresponding to the kinetics of hydration. The hysteresis loops provide information about thixotropic characteristics of the material including characteristic times of rebuilding and the rate of yield stress evolution of cements. The rheological properties are very sensitive to the chemical and physical differences of the cements and cOuld be used for their characterization.

Cite this publication as follows:
Mbasha W, Masalova I, Haldenwang R, Malkin A: The yield stress of cement pastes as obtained by different rheological approaches, Appl. Rheol. 25 (2015) 53517.

Yi Chen, Xianggang Li, Guangsheng Zeng, Wenyong Liu
The influence of continuous shear, shear history and relaxation on the rheological behavior of SiO2/glycerine suspensions

Appl. Rheol. 25:4 (2015) 44806 (9 pages)

Suspensions of SiO2 microspheres in glycerine exhibit drastic shear-thickening behavior under steady shear and dynamic oscillatory shear test. The rheological behavior of suspensions agrees with the modified Cox-Merz rules as the dynamic oscillatory rheological behavior at low frequency cOuld be reasonably interpreted in terms of the steady shear behavior. As new insight, the effect of shear history and the relaxation on the rheological behavior was investigated in detail. The result showed that under continuous shear, the viscosity decreases after a 'pulse': The degree of decrease is directly proportional to the shear rate. Similar phenomenon is also found under the continuous stress and dynamic oscillatory shear rate sweep. The shear history shows a non-negligent effect on the rheological behavior, the suspensions with higher viscosity show a lower viscosity under the same shear rate. Moreover, the relaxation time of suspensions shows the direct dependency on the initial viscosity, while the volume fraction of suspensions also affect the relaxation time. For more enlapsed times, also longer relaxation times are needed for the suspensions with lower volume fraction and higher initial viscosity.

Cite this publication as follows:
Chen Y, Li X, Zeng G, Liu W: The influence of continuous shear, shear history and relaxation on the rheological behavior of SiO2/glycerine suspensions, Appl. Rheol. 25 (2015) 44806.

J. J. Duffy, A. J. Hill, S. H. Murphy
Simple method for determining stress and strain constants for non-standard measuring systems on a rotational rheometer

Appl. Rheol. 25:4 (2015) 42670 (6 pages)

There is often a necessity to measure, or at least estimate, true viscosity values using non-standard measuring systems on a rotational rheometer. This may be to replicate a mixing or manufacturing process on a lab scale, to keep a sample dispersed and uniform during a measurement or to measure some rheological property that wOuld be difficult or impossible with a standard configuration. Such measurements can be made easily enough, but without a process for converting torque to shear stress and angular velocity to shear rate only these raw data variables can be reported. In this paper a simple and novel empirical method for determining strain/strain rate C1 and stress C2 constants for non-standard measuring systems on a rotational rheometer is presented. This method uses relative torque measurements made with a Newtonian and non-Newtonian material and their corresponding power law fitting parameters to determine C1 and C2 using a non-linear regression analysis. Equilibrium flow curves generated for two non-Newtonian fluids using two non-standard mixing geometries show very good agreement with data generated using a standard cone and plate configuration, therefore, validating the approach.

Cite this publication as follows:
Duffy JJ, Hill AJ, Murphy SH: Simple method for determining stress and strain constants for non-standard measuring systems on a rotational rheometer , Appl. Rheol. 25 (2015) 42670.

Hesam Taheri, Dirk Stanssens, Pieter Samyn
Rheological characteristics of a waterborne organic nanoparticle dispersion

Appl. Rheol. 25:3 (2015) 32889 (12 pages)

Organic nanoparticles of poly(styrene-co-maleimide) or SMI were synthesized in aqueous dispersion with a maximum concentration of 35 wt.% and are favorably applied in industrial coating processes. In order to evaluate the further processability and flow behavior of these nanoparticle dispersions, general rheological characterization under creep, oscillatory and rotational testing was done by applying various shear stresses, shear rates and frequencies on an air-bearing cylindrical rheometer. Creep tests at different stresses show that the nanoparticle dispersions behave like a viscous material. The crossover of G' and G'' according to oscillatory experiments also demonstrates a transition to viscoelastic behavior at high frequency. The sensitivity of shear-viscosity behavior to concentration and temperature of the dispersions has been evaluated. In parallel, the influences of gap size, repeatability and water evaporation have been statistically evaluated and cOuld be successfully controlled. By comparing oscillatory and rotational rheometry data, flow curves under low shear rates were reconstructed.

Cite this publication as follows:
Taheri H, Stanssens D, Samyn P: Rheological characteristics of a waterborne organic nanoparticle dispersion, Appl. Rheol. 25 (2015) 32889.

Matteo Papa, Roberta Pedrazzani, Stefano Nembrini
Should rheological properties of activated sludge be measured?

Appl. Rheol. 25:2 (2015) 24590 (6 pages)

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

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

M.R. Garmsiri, H. Haji Amin Shirazi, M.R. Yarahmadi
An analysis of the influence of cylinder dimension ratio and lifting velocity on the slump test results

Appl. Rheol. 25:2 (2015) 23416 (8 pages)

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

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

Yi Chen, Weijian Xu, Yuanqin Xiong, Yue Peng, Chang Peng, Zhengliang Ou
Shear-Thickening Behavior of Precipitated Calcium Carbonate Particles Suspensions in Glycerine

Appl. Rheol. 25:1 (2015) 12466 (8 pages)

For developing a new composite material owning shear-thickening characteristic, the rheological behaviors of nano-sized precipitated calcium carbonate (PCC) particles with irregular sharp in glycerine were investigated systematically by means of steady and dynamic rheometry. The results showed that the concentrated PCC suspensions exhibit a strong shear-thickening behavior under both steady and dynamic oscillatory shear when the volume fraction of PCC above the threshold (about 41 %). In steady shear tests, the critical shear rate decreases and the maximum viscosity in shear thickening region increases dynamically with the increase of volume fraction. While, for suspensions with different volume fractions, the similar critical stress for the onset of shear thickening is found. In dynamic strain sweep at different fixed frequencies, with the increase of fixed frequency, the complex viscosity of suspensions decreases slightly, while the critical strain for shear-thickening shifts to lower value. The dynamic oscillatory rheological behavior of suspensions at low frequency (w < 100 rad/s) cOuld be reasonably interpreted in terms of the steady shear behavior. For the suspensions with same volume fraction, it was interestingly found that the critical dynamic shear rate equaled to the product of critical strain and frequency cOuld agree well with the critical shear rate in steady shear. Moreover, the rheological behavior of PCC suspensions shows excellent reversibility and reproducibility.

Cite this publication as follows:
Chen Y, Xu W, Xiong Y, Peng Y, Peng C, Ou Z: Shear-Thickening Behavior of Precipitated Calcium Carbonate Particles Suspensions in Glycerine, Appl. Rheol. 25 (2015) 12466.

Idowu T. Dosunmu, Subhash N. Shah
Steady shear and dynamics properties of drag reducing surfactant solutions

Appl. Rheol. 25:1 (2015) 12539 (10 pages)

The rheological behavior of oilfield surfactants (Aromox™ APA-T and APA-TW) at various concentrations was studied using steady shear and dynamic testing. The results showed that the solutions exhibit non-Newtonian behavior at all concentrations, with their rheological character influenced by the temperature and ionic content of the base fluid. Temperature was observed to have a significant effect on viscosity and dynamic data. The apparent viscosity at different temperatures cOuld be reduced to a single master curve using horizontal and vertical shift factors. However, satisfactory scaling cOuld not be attained for the dynamic or viscoelastic data. Molecular scaling using characteristic time for data at different concentrations proved unsuccessful due to the strong non-Newtonian character of surfactant solutions. Scaling relations between rheological parameters and concentration indicated the presence of long micelles in APA-T solutions. APA-TW solutions, on the other hand, contained branched micelles.

Cite this publication as follows:
Dosunmu IT, Shah SN: Steady shear and dynamics properties of drag reducing surfactant solutions, Appl. Rheol. 25 (2015) 12539.

Jonathan J. Stickel, Jeffrey S. Knutsen, Matthew W. Liberatore
Connecting large amplitude oscillatory shear rheology to unidirectional shear rheology and application to biomass slurries

Appl. Rheol. 24:5 (2014) 53075 (10 pages)

Large amplitude oscillatory shear (LAOS) rheology is often performed in order to complement steady simple shear (SSS) rheology, i.e., probe rheological properties of materials that cannot be not observed with SSS alone. However, it is difficult to measure the SSS rheology of some problematic materials due to fracture and ejection, and LAOS may alleviate these issues, at least partially. Therefore, it is of interest to obtain SSS rheology information from LAOS measurements. We show that a constitutive modeling approach may be used to unify the analysis of LAOS data obtained from different viscometric geometries and modes of control and that the LAOS data may be used to predict SSS profiles. A model elastoviscoplastic material, a Carbopol solution, was used to validate the approach experimentally. LAOS rheometry of problematic biomass slurries was also performed, and the SSS profiles for the slurries were predicted with more confidence than cOuld be obtained from SSS measurements directly.

Cite this publication as follows:
Stickel JJ, Knutsen JS, Liberatore MW: Connecting large amplitude oscillatory shear rheology to unidirectional shear rheology and application to biomass slurries, Appl. Rheol. 24 (2014) 53075.

Rosamaria Marino, Samuele Giovando, Domenico Gabriele
Effect of tannin addition on the rheological properties of starch-based adhesives

Appl. Rheol. 24:4 (2014) 46138 (10 pages)

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.

Hsiao Wei Tan, Misni Misran
Effect of chitosan-modified fatty acid liposomes on the rheological properties of the polysaccharide-based gel

Appl. Rheol. 24:3 (2014) 34839 (9 pages)

Incorporation of liposome into gel is the most common approach for the preparation of topical and transdermal liposomal formulation, due to the ability of liposome to improve the drug deposition and permeation rate within the skin. In this study, the liposomal gel consisted of iota-carrageenan, carboxymethyl cellulose, and chitosan-coated-oleic acid liposome were prepared. The effect of liposomes on the rheological properties of the iota-carrageenan-carboxymethyl cellulose mix gel was evaluated. The rheological result indicated that the presence of the chitosan-coated-oleic acid liposomes in the gel had modified the viscoelastic and flow characteristics of the gel. The input energy from the oscillatory test cOuld be stored more effectively in the elastic component of the liposomal gels, as compared to the original gel itself. This result showed that the liposomal gels exhibited greater elasticity and were more solid-like when compared with the original gel system. The complex viscosity of the liposomal gels was slightly higher than the original gel. The complex viscosity of the liposomal gels was also found to decrease with increasing frequency, indicating the shear thinning behavior of the liposomal gels. The lower Power Law Index (PDI) of the liposomal gels indicated a greater shear thinning behavior and better spreadability.

Cite this publication as follows:
Tan HW, Misran M: Effect of chitosan-modified fatty acid liposomes on the rheological properties of the polysaccharide-based gel, Appl. Rheol. 24 (2014) 34839.

Alain Ponton, Claire Meyer, Guillaume Foyart, Luc Aymard, Karim Djellab
Structural and thermomechanical investigation of lyotropic liquid crystal phases doped with monodisperse microparticles

Appl. Rheol. 24:1 (2014) 14147 (7 pages)

We present a study of the structural and thermomechanical properties of lyotropic phase in the quasi ternary system made of Cetylpyridinium chloride (CPCl)/hexanol/salt water (0.9% by mass) with and without cobalt microparticles. Phase transition temperatures of the structural sequence isotropic L1/nematic calamitic Nc,/hexagonal H have been determined by differential scanning microcalorimetry. Temperature induced developable domains in hexagonal phase H and disclinations in calamitic nematic phase Nc were observed in crossed polar optical microscopy in confined geometry. A rheological study of calamitic nematic phase Nc highlighted structuring effect of cobalt microparticles from a concentration of 2% to be demonstrated by an increase in viscosity and viscoelastic moduli. This cOuld be explained by a stabilization of disclinations.

Cite this publication as follows:
Ponton A, Meyer C, Foyart G, Aymard L, Djellab K: Structural and thermomechanical investigation of lyotropic liquid crystal phases doped with monodisperse microparticles, Appl. Rheol. 24 (2014) 14147.

M. Soutrenon, V. Michaud, J-A.E. Manson
Influence of processing and storage on the shear thickening properties of highly concentrated monodisperse silica particles in polyethylene glycol

Appl. Rheol. 23:5 (2013) 54865 (9 pages)

The shear thickening behavior of concentrated suspensions can be exploited to dissipate energy during impact or shear loading. To preserve the consistency of the thickening behavior in practical applications, particle concentration, and dispersion shOuld be kept within very close bounds over time. In this article, we analyze the influence of the processing methods and storage conditions on the rheological properties of shear thickening fluids (STF) based on monodisperse suspensions of silica particles in polyethylene glycol. Particle dispersion linked to processing method and time strongly influences the value of the critical shear rate and storage in contact with air and humidity is responsible for a change in particle concentration. Encapsulating the suspensions in silicone is proposed as a solution to preserve their rheological properties over time.

Cite this publication as follows:
Soutrenon M, Michaud V, Manson JAE: Influence of processing and storage on the shear thickening properties of highly concentrated monodisperse silica particles in polyethylene glycol, Appl. Rheol. 23 (2013) 54865.

Shuyun Wu
Shear and Elongational Rheology of Partially Hydrolyzed Polyacrylamide Used for EOR

Appl. Rheol. 23:5 (2013) 53800 (7 pages)

Rheological properties are one of the primary considerations in selecting a fluid for using in chemical flooding enhanced oil recovery (EOR) operations. In this work, the rheological behavior of partially hydrolyzed polyacrylamide (HPAM) used for EOR was characterized by different techniques like steady shear flow and uniaxial elongation in capillary breakup experiments. Particular attention was focused on the main parameters affecting flow behavior of solutions, such as polymer concentration, molecular weight and molecular weight distribution. The shear rate dependence of viscosity for HPAM solutions cOuld be described by the Carreau model. Elastic model was used to fit the rheological results obtained by transient uniaxial extensional technique, which enabled to evaluate relaxation time. The results indicated that the elasticity of HPAM solutions was dominated by molecular weight. Shear viscosity at higher shear rates was mainly influenced by polymer concentration, which was not an important factor determining relaxation time. For HPAM solutions, increasing of molecular weight distribution led to a decrease in shear viscosity, and vice versa for elongational viscosity and relaxation time. In addition, it was found that there was direct proportional relationship between first normal stress difference and elongational viscosity.

Cite this publication as follows:
Wu S: Shear and Elongational Rheology of Partially Hydrolyzed Polyacrylamide Used for EOR, Appl. Rheol. 23 (2013) 53800.

M. Guettari, I. Ben Naceur, G. Kassab, A. Ponton, T. Tajouri
Temperature and concentration induced complex behavior in ternary microemulsion

Appl. Rheol. 23:4 (2013) 44966 (7 pages)

Viscosity measurements were performed in water/AOT (sodium bis(2-ethylhexyl) sulfoccinate)/isooctane microemulsions as a function of temperature between 25 C and 55 C, molar ratio Wo = water/AOT ranging from 3 to 45 and three values of AOT/isooctane volume fractions (Φm = 0.1, 0.15, and 0.2). It was shown that microemulsions behaved as Newtonian fluids in the studied range of shear rate. For a critical molar ratio, Woc, the corresponding viscosity, ηoc, was shown to be constant with temperature but dependent on the micellar concentration. For Wo < Woc, the solutions behaved as simple fluids and the temperature dependence of viscosity was described by an Arrhenius law. The total activation energy was found to be dependent on W with a maximum for Wo = 5. A correlation between the microscopic structure of the reverse micelles and the total activation energy was proposed. However, a complex fluid behavior was observed for Wo > Woc, where the viscosity increased with temperature. For some values of Wo, the viscosity reached a maximum, which cOuld be explained by attractive interdroplet interactions and formation of droplet clusters.

Cite this publication as follows:
Guettari M, BenNaceur I, Kassab G, Ponton A, Tajouri T: Temperature and concentration induced complex behavior in ternary microemulsion, Appl. Rheol. 23 (2013) 44966.

Thanunya Saowapark, Pongdhorn Sae-oui, Narongrit Sombatsompop, Chakrit Sirisinha
Storage Instability of Fly Ash Filled Natural Rubber Compounds

Appl. Rheol. 22:5 (2012) 55414 (9 pages)

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

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

Deepti Tanjore and Christopher R. Daubert
A vane-in-cup approach to measure viscoelastic properties of gelatin gels through torque-time responses from Brookfield YR-I viscometer

Appl. Rheol. 21:6 (2011) 63172 (11 pages)

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.

Yan Meng, Joshua Otaigbe
Mechanism of unexpected viscosity decrease of polymer melts by low-Tg inorganic phosphate glass during processing

Appl. Rheol. 21:4 (2011) 42654 (11 pages)

We report unprecedented non-Einstein-like viscosity decrease of polymer melts by special low glass transition, Tg, inorganic tin fluorophosphate glass (Pglass) that is remarkably counter to widely accepted dispersions, suspensions, and composites theories. The well dispersed low-Tg Pglass dramatically decrease the polymer melt viscosity while increasing its Young's modulus in the solid state at low loading (<2%) however decreasing with high loading (>2%), making the hybrid Pglass/polymer solid material stronger yet easier to process in the liquid state. Disruption of the Nylon 6 melt dynamics, strong physicochemical interactions, and submicrometer nanophase separation (proved by rheometry, FTIR, DSC, SEM, NMR and XRD) are thought to be responsible for this experimental fact. This finding shOuld beneficially impact our ability to prepare lower viscosity, very highly filled Nylon 6 melts from already existing materials and polymer processing methods such as injection molding and extrusion, making the simple strategy potentially widely applicable in a number of applications such as thinner barrier resistant thin films, composites, and membranes for heterogeneous catalysis.

Cite this publication as follows:
Meng Y, Otaigbe J: Mechanism of unexpected viscosity decrease of polymer melts by low-Tg inorganic phosphate glass during processing, Appl. Rheol. 21 (2011) 42654.

Tereza Moravkova, Petr Stern
Rheological and textural properties of cosmetic emulsions

Appl. Rheol. 21:3 (2011) 35200 (6 pages)

A set of 31 cosmetic emulsions, as the most frequent cosmetic dispersions, comprising lotions and creams (o/w, w/o), was analyzed by rheological procedures (RheoStress 300, Thermo Fischer Scientific) and by sensory profiling. The power law model was used for pseudoplastic body lotions and the Herschel-Bulkley model for viscoplastic creams to get basic rheological parameters (apparent viscosity, consistency parameter, yield stress value, plastic viscosity and flow behaviour index). The content of TiO2 in sun lotions probably caused better agreement with viscoplastic creams. Rheological analysis proved to be more suitable for the storage stability testing of the emulsion than sensory evaluation. Psychorheology was applied as a suitable complex method. Rheological parameters were compared to sensory texture attributes (removing from a package, ease of spreading, skin feel and thickness). Almost 60% of relationships among rheological and sensory parameters were statistically significant (P = 0.05). Considering relationships only between rheological and sensory characteristics (with each other), 46 % were statistically significant (P = 0.05). In the case of apparent viscosity and removing the lotion from a bottle the relationship was reliable enough (correlation coefficient 0.91) to estimate the sensory attribute by fast rheological measurement. The other statistically significant relationships (correlation coefficients proved that the sensory texture acceptability of a cosmetic emulsion cOuld be partly predicted by rheological analysis.

Cite this publication as follows:
Moravkova T, Stern P: Rheological and textural properties of cosmetic emulsions, Appl. Rheol. 21 (2011) 35200.

Yannick Manon, Dominique Anne-Archard, Jean-Louis Uribelarrea, Carole Molina-Jouve, Luc Fillaudeau
Physical and biological study of cell cultures in a bioreactor: on-line and off-line rheological analyses

Appl. Rheol. 21:3 (2011) 35167 (11 pages)

Rheological behaviour of culture broth stands as a fundamental parameter in bioprocess performances because it affects simultaneously the heat and mass transfer as well as the flow pattern. On-line measurements of rheological behaviour are hardly compatible with the operating condition with respect to accurate and stringent conditions imposed by cell culture strategy. Our scientific and technical objectives are (i) to develop and identify an experimental device enabling on-line rheometry and (ii) to discuss and compare on-line and off-line measurements. In this aim, a bioreactor was equipped with a derivation loop including a specific on-line rheometric device as well as additional physical and biological measurements (specific density, mass flow rate, electrical conductivity, pH,pO2 and temperature) during microbial cell cultures. In a first time, friction curves of calibrated ducts were established with Newtonian and non-Newtonian shear-thinning fluids. In a second time, axenic cultures with two microorganisms (bacteria and yeast exhibiting different sizes) were investigated in pure oxidative culture in order to produce biomass under high cell concentrations: ~ 40 to 110 gCDW/l for E. coli (bacteria) and ~ 75 to 105 gCDW/l for Y. lipolytica (yeast). Cell broths exhibited Newtonian behaviour for E. coli and shear-thinning behaviour for Y. lipolytica, which were both dependant on biomass concentration. On-line and off-line rheological measurements are consistent for E. coli and Y. lipolytica, but significantly differed. On-line estimated viscosity appears higher than off-line apparent viscosity. Several assumptions in relation with microorganism physiology and metabolism (size, morphology, surface properties, concentration, biological activity) cOuld be formulated in agreement with scientific literature. On-line rheology brings new insight to investigate complex interaction between physical and biological phenomena.

Cite this publication as follows:
Manon Y, Anne-Archard D, Uribelarrea J, Molina-Jouve C, Fillaudeau L: Physical and biological study of cell cultures in a bioreactor: on-line and off-line rheological analyses, Appl. Rheol. 21 (2011) 35167.

Anne-Laure Koliandris, Elisabeth Rondeau, Louise Hewson, Joanne Hort, Andrew J. Taylor, Justin Cooper-White, Bettina Wolf
Food grade Boger fluids for sensory studies

Appl. Rheol. 21:1 (2011) 13777 (11 pages)

The effect of shear viscosity on taste and mouthfeel perception has been extensively studied; however, the effect of extensional viscosity on sensory perception has been mostly neglected. This may be important as in-mouth processing is complex and probably best described as a superposition of shear and extensional flow characteristics. Fluid mechanics researchers interested in separating elastic effects from viscous effects use Boger fluids and this approach was adopted here to investigate the effect of fluid elasticity on sensory perception. For the first time, two food grade Boger fluids based on glucose syrup and aqueous solutions of maltodextrin as solvents and xanthan gum as high molecular weight polymer were formulated. The elasticity of the Boger fluids was characterised in rotational shear rheometry, in a filament break-up device and in microcontraction flow. Saltiness perception and mouthfeel of the Boger fluids and samples corresponding to the respective solvent were analysed. Surprisingly, there were no significant differences. Hypotheses attributing this finding to the intrinsic properties of the samples are discussed. A major study wOuld be required to gain in-depth understanding of the sensory properties of these fluids as their flow properties are very different from typical liquid foods.

Cite this publication as follows:
Koliandris A, Rondeau E, Hewson L, Hort J, Taylor AJ, Cooper-White JJ, Wolf B: Food grade Boger fluids for sensory studies, Appl. Rheol. 21 (2011) 13777.

Anne Kowalczyk, Bernhard Hochstein, Philipp Stahle, Norbert Willenbacher
Characterization of complex fluids at very low frequency: experimental verification of the strain rate-frequency superposition (SRFS) method

Appl. Rheol. 20:5 (2010) 52340 (10 pages)

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.

Donald G Baird, Tung W Chan, Christopher McGrady, Syed M Mazahir
Evaluation of the use of a semi-hyperbolic die for measuring elongational viscosity of polymer melts

Appl. Rheol. 20:3 (2010) 34900 (12 pages)

The semi-hyperbolic (SHPB) die with and possibly without wall lubrication has been proposed as a device for measuring the elongational viscosity of polymeric fluids. Using numerical simulation under the condition of complete wall slip, it was found for two polyethylenes (LDPE and LLDPE) that the calculated elongational viscosity values agreed well with strain-averaged values, < ηe >, obtained from independent measurements in stretching type rheometers. This is in agreement with the original hypothesis of Everage and Ballman (E-B). Numerical simulations showed that the Baird and Huang (B-H) approach for calculating < ηe >, which accounts for the shear stress due to geometric considerations in the presence of complete slip, agreed with data better than did the E-B approach. Numerical simulations using varying degrees of wall slip indicated that reasonable values of < ηe > cOuld be obtained using the B-H approach with wall slip levels which cOuld be most likely reached using a coating such as a flouroelastomer. The numerical simulations provided an explanation as to why the elongational viscosity values determined in the SHPB die for resins such as LDPE, which are extensional-strain hardening, are less sensitive to wall slip than non-strain-hardening resins such as LLDPE.

Cite this publication as follows:
Baird DG, Chan TW, McGrady C, Mazahir SM: Evaluation of the use of a semi-hyperbolic die for measuring elongational viscosity of polymer melts, Appl. Rheol. 20 (2010) 34900.

Leonard Sagis
Rheology of complex fluid-fluid interfaces: a unified approach based on nonequilibrium thermodynamics

Appl. Rheol. 20:2 (2010) 24380 (8 pages)

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.

Noemi Baldino, Lucia Seta, Massimo Migliori, Domenico Gabriele, Bruno de Cindio, Giuseppe Chdichimo
Rheological modelling of plaster deposition for painting restoration

Appl. Rheol. 20:2 (2010) 23110 (9 pages)

This paper reports on the result of rheological modelling of plaster deposition for paintings restoration. A typical plaster recipe was changed in order to check the effect of water level on rheological properties, both performing oscillatory tests and measuring plaster viscosity at two different temperatures. A model based on momentum balance on a vessel-nozzle geometry for a shear thinning fluid was set-up to simulate the deposition process and numerical results were compared to experimental data. A good agreement was found for moderate deposition times. At high process time, due to phase-separation in plaster, a loss in matching between the simulation and experimental point was found, because the modelling assumption of 'pseudo-homogeneous' behaviour does not apply anymore. Simulations allowed operating charts to be prepared reporting the deposited plaster volume as a function of the main process variables (temperature and pressure) and rheological properties of the plaster. This model cOuld effectively support the development of an automatic deposition system able to recognise the filling volume over the painting surface and to control autonomously feeding of the plaster from a vessel through the deposition nozzle

Cite this publication as follows:
Baldino N, Seta L, Migliori M, Gabriele D, deCindio B, Chdichimo G: Rheological modelling of plaster deposition for painting restoration, Appl. Rheol. 20 (2010) 23110.

Dmitry Borin, Piotr Nikrityuk, Stefan Odenbach
On the magnetic field influence on the viscosity of liquid GaInSn with suspended solid particles

Appl. Rheol. 19:6 (2009) 61995 (7 pages)

Experimental and numerical studies have been undertaken to check the influence of a magnetic field on the viscosity of liquid GaInSn with suspended solid particles.The rheological investigations show a significant change of the slope of the measured flow curves between the situation B = 0 and 0.02 T. By means of numerical simulations of the flow in the presence of Lorentz forces it cOuld be shown that the influence of magnetohydrodynamic damping of the flow reduces the measured changes but does not annihilate them. As conclusion a 15 % change of viscosity of the melt in a magnetic field with B = 0.02 T cOuld be fixed.

Cite this publication as follows:
Borin D, Nikrityuk P, Odenbach S: On the magnetic field influence on the viscosity of liquid GaInSn with suspended solid particles, Appl. Rheol. 19 (2009) 61995.

Rolando Curvale, Carlos Cesco
Intrinsic viscosity determination by 'single-point' and 'double-point' equations

Appl. Rheol. 19:5 (2009) 53347 (6 pages)

"Single-point" equations used for intrinsic viscosity determination are greatly used when working with synthetic polymer solution systems. In this work we have applied them to a biological macromolecule in a bovine serum albumin (BSA)/water system. Almost all single-point equations are available and errors can be lowered. However, we have detected a systematic bias in the estimations provided by "single-point" methods. To overcome it we propose a "double-point" method which gives lower estimation errors for this system. This novel method is not system specific and cOuld be applied to other polymeric solution.

Cite this publication as follows:
Curvale R, Cesco C: Intrinsic viscosity determination by 'single-point' and 'double-point' equations, Appl. Rheol. 19 (2009) 53347.

Ernest Carl McIntyre, Frank E. Filisko
Squeeze Flow Rheology of Zeolite Suspensions

Appl. Rheol. 19:4 (2009) 44322 (8 pages)

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

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

Shiva Amirkaveei
A Comparison of the Rheology of four Wheat Flour Doughs via a Damage Function Model

Appl. Rheol. 19:3 (2009) 34305 (9 pages)

The basic rheological properties of two Persian wheat flours - Tajan (11 % protein) and Back Cross Roshan (8 % protein) and two Australian wheat flours-JANZ (12.9 % protein) and Rosella (8.6 % protein) have been characterized.These properties have been interpreted via a damage function model. All samples cOuld be reasonably well described by the damage function model with a power-law relaxation spectrum. Although the shear stresses in the Australian samples were higher, the relaxation parameter G(1) and power-law exponent p for the Australian varieties were lower than those for the Persian samples and the damage functions were different. Since protein contents were different, this indicates that the amount of protein is not the sole determinant of softness in the samples. The damage function f was also calculated for all samples. This function gives a measure of the softening due to working or kneading of the samples at a given strain level.

Cite this publication as follows:
Amirkaveei S: A Comparison of the Rheology of four Wheat Flour Doughs via a Damage Function Model, Appl. Rheol. 19 (2009) 34305.

A. Kaci, M. Chaouche, P.-A. Andreani, H. Brossas
Rheological behaviour of render mortars

Appl. Rheol. 19:1 (2009) 13794 (8 pages)

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.

Dimitri Feys, Ronny Verhoeven, Geert De Schutter
Extension of the Poiseuille formula for shear-thickening materials and application to Self-Compacting Concrete

Appl. Rheol. 18:6 (2008) 62705 (11 pages)

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

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

Hamid Shahnazian, Stefan Odenbach
New driving unit for the direct measurement of yield stress with a stress controlled rheometer

Appl. Rheol. 18:5 (2008) 54974 (7 pages)

Investigations of rheological properties of ferrofluids have shown strong changes of the viscosity in magnetic fluids with an applied magnetic field. The change of the viscosity . the magnetoviscous effect . can theoretically be described with chain and structure formation under the influence of a magnetic field. Moreover, the formation of these structures leads to the appearance of viscoelastic effects or other non-Newtonian features like yield stress in ferrofluids with an applied magnetic field. With a shear rate controlled rheometer . as it as been used in former experiments . the yield stress cOuld not be investigated directly. Therefore the results concerning a field dependent yield stress based on an extrapolation of shear controlled measurements. For the direct investigations of the yield stress, a dedicated stress controlled rheometer is required, allowing direct investigations of the magnitude and field dependence of this effect. In this work the design of the stress controlled rheometer with its main parameters has been described in detail. The rheological investigations with differently composed fluids show that the stress controlled rheometer enables direct measurements of even small yield stresses in ferrofluids as well as large effects like they are found in magnetorheological fluids (MRF).

Cite this publication as follows:
Shahnazian H, Odenbach S: New driving unit for the direct measurement of yield stress with a stress controlled rheometer, Appl. Rheol. 18 (2008) 54974.

Velichko Hristov, John Vlachopoulos
A Study of Entrance Pressure Loss in Filled Polymer Melts

Appl. Rheol. 17:5 (2007) 57191 (9 pages)

The influence of the molecular structure of the polymer matrix and filler loading on the entrance pressure loss of polyethylene/ wood flour composites has been investigated in this research by means of a capillary rheometer equipped with an orifice die. The entry flow of talc- and glass-filled polyethylene composites has been investigated as well. It was found that the entrance pressure loss of wood filled polyethylene composites greatly increased with increasing the wood flour loading. Talc and solid glass spheres also increase the entrance pressure loss, however not as much as wood flour. It was also observed that composites based on narrow molecular weight distribution (MWD) resins exhibited larger entrance pressure loss than the broad MWD and branched polyethylene based ones. It was concluded that measurements of the entrance pressure loss reveal some interesting features of the polymer-filler interactions and cOuld provide significant insights in the processing of highly filled polymer melts.

Cite this publication as follows:
Hristov V, Vlachopoulos J: A Study of Entrance Pressure Loss in Filled Polymer Melts , Appl. Rheol. 17 (2007) 57191.

Mustapha M. Ould Eleya, Sundaram Gunasekaran
Rheology of fluid foods for dysphagic patients

Appl. Rheol. 17:3 (2007) 33137 (9 pages)

Pre-thickened beverages and barium sulfate suspensions are used in the treatment and diagnosis of dysphagia. These liquids are labeled nectar consistency (NC), honey consistency (HC) etc.These labels are rather misleading and do not represent the actual rheological character of the liquids.We carefully investigated the rheology of these liquids to assist both in their formulation and use for dysphagic patients. Steady state flow properties, thixotropy, dynamic response, and creep recovery behavior were investigated for six beverages and two barium sulfate suspensions. All samples exhibited a shear-thinning behavior. The flow curves of all samples followed both Herschel-Bulkley and Casson models. HC barium sulfate suspension exhibited higher yield stress, σ0, and higher storage modulus, G', than their fluid food counterparts. In contrast, NC barium sulfate suspension had lower σ0, and G' than some of the liquid food counterparts. Frequency spectra of NC samples were similar to that of a macromolecular solution with both G' and loss modulus, G'', increasing with frequency; whereas those of HC samples were similar to that of a gel with a little dependency of G' and G'' over frequency. Stress sweep experiments showed that the linear viscoelastic region of fluid foods and barium sulfate suspensions extended up to 1 and 10 Pa, respectively. Thus, significant differences exist in the rheological properties of both pre-thickened and videofluoroscopy fluids currently used for diagnosis and treatment of dysphagia.

Cite this publication as follows:
OuldEleya MM, Gunasekaran S: Rheology of fluid foods for dysphagic patients, Appl. Rheol. 17 (2007) 33137.

Qianmei Li, Guozhong Wu, Yaodong Liu, Yingshe Luo
A rheological study of binary mixtures of Ionic Liquid [Me3NC2H4OH]+[Zn2Cl5]- and ethanol

Appl. Rheol. 16:6 (2006) 334-339

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.

Donald G. Baird, J. Huang
Elongational Viscosity Measurements Using A Semi-Hyperbolic Die

Appl. Rheol. 16:6 (2006) 312-320

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

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

Peggy Courtois, Rammile Ettelaie, Jianshe Chen
Numerical Studies of Transport Properties in Heterogeneous Food Systems

Appl. Rheol. 16:5 (2006) 275-286

The current computer simulation based study aims to elucidate the complex role that the state of aggregation and morphology of the food materials plays in determining their transport behaviour. Using Brownian dynamic simulations, applied to colloidal systems, we simulate the compression of two different dense layers of nanoparticles (with reversible and irreversible bonds), at interface, at three different compression rates. We determine the desired transport coefficient for these structures using a novel technique, originally proposed by Torquato and Kim (1990). This method allows us to consider complex structures in our study, for which calculations of effective transport coefficients using conventional methods, like finite elements and finite difference, wOuld be relatively difficult. We first validate our algorithm by comparing its results with those of exact calculations, for different regular lattices. Our results are in excellent agreement with the theory. The variation in the transport coefficient of nano-particle monolayers during the compression, are also correlated with the build up of stress and changes in the structure of the films.

Cite this publication as follows:
Courtois P, Ettelaie R, Chen J: Numerical Studies of Transport Properties in Heterogeneous Food Systems, Appl. Rheol. 16 (2006) 275.

Paolo Perona
Bostwick Degree and Rheological Properties: an Up-to-date Viewpoint

Appl. Rheol. 15:4 (2005) 218-229

The correlation between the Bostwick degree and the static rheological properties of yield stress food fuids is first revisited and then reformulated in this work. The role of the yield stress in the free surface flow of the Bostwick test is studied using dimensional analysis. Results from experiments on 48 different samples of yield stress fluids are considered and included to check the adequacy of the proposed correlation. Asymptotic dynamic behaviour is also presented and discussed as a mechanism of complete self similarity with respect of the dimensionless time. This approach wOuld seem to support the opinions in favor of the yield stress as a key parameter, and thus offers an interesting new viewpoint useful to both future experiments on the Bostwick test and studies of 'dam-break' like dynamics.

Cite this publication as follows:
Perona P: Bostwick Degree and Rheological Properties: an Up-to-date Viewpoint, Appl. Rheol. 15 (2005) 218.

William Koenigsberg, John H. Selverian
Zone Method for Representing Relaxation Characteristics of Viscoelastic Materials

Appl. Rheol. 15:3 (2005) 160-171

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.

Joachim Götz, Hartmut Balzer, Ruth Hinrichs
Characterisation of the Structure and Flow Behaviour of Model Chocolate Systems by Means of NMR and Rheology

Appl. Rheol. 15:2 (2005) 98-111

In order to characterise the structure and flow behaviour of model chocolate systems Nuclear Magnetic Resonance (NMR) and rheometry were used to determine the T1 - and T2 - NMR relaxation times and their corresponding flow functions. T1 and T2 characterise the molecular mobility of fluids and correlate with both the zeroshear- rate and infinity viscosity of various chocolate model systems (determined with rotational rheometry and capillary rheometry). Based on this correlation, NMR provides the possibility to determine characteristic viscosities of chocolate masses by means of NMR-relaxation experiments. The viscosities of chocolate masses are important process parameters, as they are used for quality control of the production process. An online process viscosimetry via T2 relaxation wOuld allow the installation of an efficient process control and, thus, a process automation. This NMR application with comparatively short measuring times is especially interesting for disperse systems where the use of conventional rheometric techniques may cause large errors. The only prerequisite for the measurement of the viscosities using NMR is a previous calibration. This was performed with the help of rotational and capillary rheometry. The NMR self-diffusion experiments are especially appropriate to characterise the influence of emulsifiers on the structure and the flow behaviour of chocolate masses.

Cite this publication as follows:
Gotz J, Balzer H, Hinrichs R: Characterisation of the Structure and Flow Behaviour of Model Chocolate Systems by Means of NMR and Rheology, Appl. Rheol. 15 (2005) 98.

M.P. Escudier, J. Clement-Evans, R.J. Poole
Freezing as a Storage Process for Aqueous Polymer Solutions

Appl. Rheol. 15:2 (2005) 90-97

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.

E. Alanis, G. Romero, C. Martinez, L. Alvarez, C. Mechetti
Characteristic Times of Microstructure Formation in Electrorheological Fluids determined by Viscosity and Speckle Activity Measurements

Appl. Rheol. 15:1 (2005) 38-45

Viscosity measurements of a suspension of cornstarch in silicone oil, at several concentrations and subject to different electrical field strengths, were conducted. An increase in the apparent viscosity, in correlation with the field strength, which is characteristic of the so-called electrorheological fluids (ERF), was observed. For a given field intensity, the value of the viscosity increases rapidly in the first seconds after the application of the electric field, and then it increases slowly until it finally approaches a saturation value. This behaviour of the apparent viscosity has been related to the microstructure formation due to interactions between dipoles induced by the electric field. Characteristic times, related to structure formation after application of an electric field, are investigated by means of diffuse light transmission and speckle-pattern activity measurements. Two characteristic times were found that shOuld be related to the state of aggregation of the suspended particles: orientation of the non-isotropic particles and later chain formation. These results agree reasonably with that obtained from electrorheological measurements. Microscopic observations of structure formation are also reported.

Cite this publication as follows:
Alanis E, Romero G, Martinez C, Alvarez L, Mechetti C: Characteristic Times of Microstructure Formation in Electrorheological Fluids determined by Viscosity and Speckle Activity Measurements, Appl. Rheol. 15 (2005) 38.

J.P. Plog, W.-M. Kulicke, C. Clasen
Influence of the Molar Mass Distribution on the Elongational Behaviour of Polymer Solutions in Capillary Breakup

Appl. Rheol. 15:1 (2005) 28-37

Commercially available, blended methylhydroxyethyl celluloses with similar weight-average molar masses but varying molar mass distributions were characterized by different techniques like steady shear flow and uniaxial elongation in capillary breakup experiments. The determined relaxation times t were then correlated with the absolute molar mass distribution acquired via SEC/MALLS/DRI (combined methods of size-exclusion-chromatography, multi angle laser light scattering and differential refractometer). In order to describe the longest relaxation time of the polymers in uniaxial elongation via integral mean values of the molar mass distribution, defined blends of polystyrene standards with varying molar mass distributions were characterized. The obtained data was scaled via different moments of the molecular weight distribution and cOuld be correlated with the results obtained for the methylhydroxyethyl celluloses.

Cite this publication as follows:
Plog JP, Kulicke W-M, Clasen C: Influence of the Molar Mass Distribution on the Elongational Behaviour of Polymer Solutions in Capillary Breakup, Appl. Rheol. 15 (2005) 28.

Lourdes Zumalacarregui, Miguel Vazquez, Tania Estevez, Ana Aguilera, Eugenio Hardy
Rheological Studies of Interferon Creams

Appl. Rheol. 14:5 (2004) 251-255

The determination of flow curves and the apparent viscosity curves at 28°C of creams containing human leukocyte alpha interferon as active principle is presented in this paper. These creams are used for the treatment of papiloma virus and herpes simplex. It is demonstrated that their behaviour corresponds to a thixotropic fluid. The Herschel-Bulkley model parameters are presented and discussed as an indicator of the grade of thixotropy. Apparent viscosity plotted as a function of shear rate and storage time allows defining the time period in which the samples recover their initial structure. Additionally it was concluded that for determining the quality of the product, the acceptance limit of the viscosity shOuld be specified for a given shear rate.

Cite this publication as follows:
Zumalacarregui L, Vazquez M, Estevez T, Aguilera A, Hardy E: Rheological Studies of Interferon Creams, Appl. Rheol. 14 (2004) 251.

J.M. Valverde, A.T. Perez, A. Castellanos, R.E. Viturro
Rheological Testing of Xerographic Liquid Inks: A Need for Printing Technology

Appl. Rheol. 14:4 (2004) 190-196

Rheological properties of xerographic liquid inks of different concentrations of solid particles have been tested. Generally we have found that viscosity decreases with increasing shear rate, i.e. the system is pseudoplastic as corresponds to the break down of aggregated particles by the applied shear. The viscosity of inks may vary in orders of magnitude depending on solids concentration, reaching up values of ~ 108 Pas for solids concentration of 40 wt%. The existence of a yield critical stress has been discussed and we estimate that it increases exponentially with solids concentration. We have looked for possible differences in the rheological behavior of ink samples obtained either diluting more concentrated inks or drying less concentrated ones. Concentration and dilution of xerographic inks do not change their rheological properties meaning that the microscopic structure of the concentrated dispersion is broken (when diluting) and recovered (when drying) reversibly. On the other hand processed ink (previously subjected to high mechanical and electrostatic stresses) behaves differently than non-processed ink. The properties of processed inks are not totally recovered when diluting, manifesting itself in a higher effective apparent viscosity. This result shOuld be of main concern to liquid ink based printing technologies, for which elimination of waste by recycling processed ink is a major goal.

Cite this publication as follows:
Valverde JM, Perez AT, Castellanos A, Viturro RE: Rheological Testing of Xerographic Liquid Inks: A Need for Printing Technology, Appl. Rheol. 14 (2004) 190.

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.

Piyush G. Gigras, Bamim Khomami
An Evaluation of Single-Segment Reptation Theories for Linear Entangled Polymeric Systems

Appl. Rheol. 14:1 (2004) 22-32

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

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

G.A.M. Pop, W.J. Hop, M. van der Jagt, J. Quak, D. Dekkers, Z. Chang, F.J. Gijsen, D.J. Dunncker, C.J. Slager
Blood Electrical Impedance Closely Matches Whole Blood Viscosity as Parameter of Hemorheology and Inflammation

Appl. Rheol. 13:6 (2003) 305-312

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.

Ben Hanson, Martin Levesley, John Fisher
Using Self-Sensing Techniques to Produce a Small, Robust, Inexpensive Rheometer

Appl. Rheol. 13:5 (2003) 242-250

Self-sensing is the technique of using a transducer to both actuate and sense concurrently, therefore eliminating the need for separate sensors. A sensorless rheometer cOuld be much smaller, simpler and more robust than traditional designs. One application where such a rheometer wOuld be desired is the in-situ measurement of curing bone cement in orthopaedic surgery. A set of equations was developed that models the relationship between force, motion and back-e.m.f. generation for a class of electromagnetic actuators. This enables velocity, displacement and force to be self-sensed from voltage measurements only. This self-sensing was validated on a conventional linear electromagnetic actuator, and a small rotary moving magnet device, which was designed to be a small self-sensing rheometer. The accuracy of the estimation was assessed and shown to compare favourably with measured data. The actuators were then used to construct simple rheometers to measure bone cement. Rheological models were used to calculate storage and loss moduli and dynamic viscosity from the self-sensed values of displacement, velocity and torque. The accuracy of these self-sensing rheometers was verified against a traditional rheometer using a silicone fluid and a polyethylene oxide solution. The self-sensing rheometers were used to characterise acrylic bone cements during curing, reinforcing and extending upon previous results. The elimination of sensors meant that it was possible to produce a small, inexpensive rheometer with a very simple structure. This indicates there is potential to develop small rheo-transducers for certain applications.

Cite this publication as follows:
Hanson B, Levesley M, Fisher J: Using Self-Sensing Techniques to Produce a Small, Robust, Inexpensive Rheometer, Appl. Rheol. 13 (2003) 242.

Jerker Jäder, Lars Järnström
The Influence of Thickener Addition on Filter Cake Formation During Dewatering of Mineral Suspensions

Appl. Rheol. 13:3 (2003) 125-131

A novel method to continuously measure the rate of build-up of an immobilised layer (apparent filter cake) was demonstrated for three mineral suspensions containing carboxymethyl cellulose and polymer latex. These suspensions were designed to be similar to those normally used as coating colours within the paper industry. The instrumentation was based on a rheometer equipped with units for controlling (and measuring) the normal forces acting on the rotating upper plate and precise measurements of the gap height in parallel.plate geometry. The bottom plate in the measurement cell was perforated and connected to vacuum, giving the driving pressure for flow through the filter. The technique shOuld so far be taken as a qualitative, but is an attractive method for measuring filtration in thin films under controlled shear rate. The technique enables the apparent filter cake height to be calculated at any time during dewatering of the coating colours.

Cite this publication as follows:
Jä, der J, Jarnstrom L: The Influence of Thickener Addition on Filter Cake Formation During Dewatering of Mineral Suspensions, Appl. Rheol. 13 (2003) 125.

I. Eriksson, U. Bolmstedt, A. Axelsson
Evaluation of a helical ribbon impeller as a viscosity measuring device for fluid foods with particles

Appl. Rheol. 12:6 (2002) 303-308

The traditional methods of measuring viscosity with rotational viscometers, i.e. cone-plate and concentric cylinder systems, are often not suitable for suspensions. To be able to measure viscosity on suspensions mixer viscometers have been developed. In this study a new design of a helical ribbon impeller has been evaluated and the Metzner-Otto approach has been used to calibrate the impeller. Different kinds of food products were studied. The Metzner-Otto parameter obtained from tomato products was lower than those obtained from starch products. The study showed that the Metzner-Otto parameter varied but seemed rather to be dependent on the composition of the food material than on the flow behaviour index. The impeller cOuld handle high concentration of quite large particles. This type of helical ribbon impeller viscometer is thus recommended for rheological studies of suspensions with high concentration of particles.

Cite this publication as follows:
Ericksson I, Bolmstedt U, Axelsson A: Evaluation of a helical ribbon impeller as a viscosity measuring device for fluid foods with particles, Appl. Rheol. 12 (2002) 303.

Melissa J.Daniels Pearce, Danielle D.Bellmer
Data Variability in Rheological Measurement of Semi-Solid Foods: Effects of Loading Normal Force

Appl. Rheol. 12:6 (2002) 282-288

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

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

Tim Kealy, Carlos Tiu
Calibration of a Commercial Kneader for Rheological Applications

Appl. Rheol. 12:5 (2002) 241-251

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

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

Karim Bekkour, Nadja Kherfellah
Linear Viscoelastic Behavior of Bentonite-Water Suspensions

Appl. Rheol. 12:5 (2002) 234-240

Bentonite are extensively used materials in a wide range of applications. Creep and oscillatory shear experiments in the linear viscoelastic domain were carried out on bentonite-water suspensions at different solid fractions. It was found that bentonite dispersions exhibit important viscoelastic behavior which cOuld be represented by the generalized Kelvin-Voigt mechanical model. It is well known that an exhaustive study of colloidal dispersions may require the determination of its viscoelastic properties over a wide frequency scale. Unfortunately, due to microstructure changes, the experiments are limited in time. In order to avoid such limitation, oscillatory data were deduced from creep curves - without actually vibrating the clay dispersions - because a periodic experiment at frequency w is qualitatively equivalent to a creep test at time 1/w. That is, it was possible to complete the dynamic response in the low-frequency range using data obtained from the transient response in creep.

Cite this publication as follows:
Bekkour K, Kherfellah N: Linear Viscoelastic Behavior of Bentonite-Water Suspensions, Appl. Rheol. 12 (2002) 234.

Tomas Honek, Berenika Hausnerova, Petr Saha
Temperature dependent flow properties of powder injection moulding compounds

Appl. Rheol. 12:2 (2002) 72-80

The temperature dependent flow properties of highly filled polymer compounds intended for production of hard-metal parts by powder injection mOulding (PIM) technology were studied. The pure binder based on polyethylene, ethylene and butyl acrylate block copolymer and paraffin, and its compounds with hard-metal carbide powder (up to 55 vol. %) were prepared by melt mixing at 180.C. The flow properties were investigated at the temperature range from 140.C to 200.C using capillary rheometer operating flow at a constant piston speed. The measure of temperature sensitivity of PIM compounds, activation energy of shear flow, decreases with powder loading and shear rate. The Arrhenius relation for these materials is only valid in the stable flow region. At the temperatures above 170.C the compounds filled with 45 vol. % carbide powder and higher exhibit an unstable flow of pressure oscillations type at the shear rates above 103 s-1. The onset of pressure oscillations is strongly affected by temperature. The relation between critical shear stress for the onset of pressure oscillations and temperature is non-linear.

Cite this publication as follows:
Honek T, Hausnerova B, Saha P: Temperature dependent flow properties of powder injection moulding compounds, Appl. Rheol. 12 (2002) 72.

R. Muller, M. Bouquey, F. Mauguiere, G. Schlatter, C. Serra, J. Terrisse
Rheology of reactive polymer blends: separation of mixing and reaction steps

Appl. Rheol. 11:3 (2001) 141-152

The crosslinking reaction in various types of polymer blends was followed by rheological measurements. Miscible polymers with controlled glass transition temperature, chain length and number of functional units per chain were synthesized by bulk radical copolymerization. Other experiments were carried out on immiscible systems based on commercial polymers. Blends were either prepared in a batch mixer or directly in the parallel-plate geometry of a rotational rheometer. Due to the low glass transition or melting temperature of most blend components, it was usually possible to separate the mixing step which was carried out at low temperature from the crosslinking reaction which was followed by small amplitude dynamic measurements at higher temperatures. The influence of several parameters on the reaction was studied, in particular : the reaction temperature, the amount of shear during the mixing step (or mixing time), the number of functional units per chain in each blend component and the blend composition. For the miscible blends, a master curve for the dependence of the elastic modulus G’ as a function of reaction time cOuld be drawn for different functionalities and blend compositions.

Cite this publication as follows:
Muller R, Bouquey M, Mauguiere F, Schlatter G, Serra C, Terrisse J: Rheology of reactive polymer blends: separation of mixing and reaction steps, Appl. Rheol. 11 (2001) 141.

Chenxu Yu, Sundaram Gunasekaran
Correlation of dynamic and steady viscosities of food materials

Appl. Rheol. 11:3 (2001) 134-140

Eight commercial foods representing a wide range of viscosities (i.e. honey, condensed milk, mayonnaise, tomato ketchup, cream cheese, yogurt, process and Mozzarella cheeses) were investigated. Their steady shear viscosity and dynamic complex viscosity were determined by rheological measurements at two temperatures using a Bohlin-CVO rheometer. Based on experimental data, shear rate dependence of steady flow apparent viscosity and frequency dependence of dynamic viscosity was established and compared. It was determined that for condensed milk, tomato ketchup and mayonnaise, a modified Cox-Merz relation cOuld be established. For cream cheese, a generalized Cox-Merz relation was proposed; and for yogurt, a deviation from the Cox-Merz rule was found. For Mozzarella and process cheeses a sharp drop in steady shear viscosity was noticed between 1~10 s-1 shear rate range. The Cox-Merz rule was not applicable for these cheese samples.

Cite this publication as follows:
Yu C, Gunasekaran S: Correlation of dynamic and steady viscosities of food materials, Appl. Rheol. 11 (2001) 134.

T. Neidhöfer, M. Wilhelm, H.W. Spiess
Fourier-transform-rheology on linear polystyrene melts

Appl. Rheol. 11:3 (2001) 126-133

Large amplitude oscillatory shear (LAOS) was applied to a linear polymer melt in order to study the mechanical harmonic generation in the nonlinear regime. In the nonlinear regime mechanical harmonics at 3w1, 5w1, etc. are generated under oscillatory shear with a shear frequency w1. These higher harmonics can be analysed with respect to frequencies, amplitudes and phase if the time data of the torque is Fourier transformed. This experimental method (FT-Rheology) permits therefore to quantify the mechanical nonlinearities if sinusoidal shear rates are applied. This article describes the basic idea of this experimental method as well as the application to different anionically polymerized polystyrene melts. The dependence of the nonlinear, rheological properties with respect to the molecular weight Mn, the applied strain g0, the frequency w1 and the temperature was investigated. In addition to simple nonlinear theories we cOuld also observe even harmonics at 2w1, 4w1, etc. in the FT-rheology spectra. The appearance of even harmonics was correlated with the appearance of a more complex nonlinear behaviour.

Cite this publication as follows:
Neidhö, fer T, Wilhelm M, Spiess HW: Fourier-transform-rheology on linear polystyrene melts, Appl. Rheol. 11 (2001) 126.

Howard A. Barnes
An examination of the use of rotational viscometers for the quality control of non-Newtonian liquid products in factories

Appl. Rheol. 11:2 (2001) 89-101

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

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

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