Flow Curve Measurements Research Articles

Influence of rheology on mixing homogeneity and mechanical behavior of twin-pipe 3D printable concrete

The twin-pipe pumping technology has been developed for the stiffening control of 3D printable concrete, which is achieved by pumping two different mixtures separately and blending these mixtures using a static mixer before extrusion. The combination of the two mixtures undergoes a significant phase transition in the static mixer from liquid to solid due to accelerated hydration. The phase transition, as well as the mechanical performance of hardened elements, is strongly influenced by the mixing homogeneity of the mixtures. In this study, we examine how the rheological behavior of the two mixtures being combined in the static mixer affects the mixing homogeneity. The rheological behavior was studied by performing flow curve measurements using a dynamic shear rheometer. To characterize the mixing homogeneity, polished cross-sections of 3D-printed elements were prepared and characterized using an innovative macropixel-based image analysis procedure. Specifically, the image analysis-based procedure involves identifying the two mixtures by applying color segmentation, followed by the Poole index method to assess the mixing homogeneity. The results indicate that a low yield stress, especially for the main constituent mixture of which the flow rate is higher than the second constituent mixture, is advantageous to achieve a higher mixing homogeneity. The viscosity or the viscosity ratio of the two constituent mixtures is found to have a minor influence on the mixing homogeneity.

Rheological investigation on the associative properties of poly(vinyl alcohol) solutions

We report intrinsic viscosity and flow curve measurements on a set of five industrial poly(vinyl alcohol) (PVOH) samples, with varying degree of hydrolysis, molecular weight, and concentration in two solvents: water and dimethyl sulfoxide (DMSO). Aqueous poly(vinyl alcohol) solutions exhibit clear features of associative polymers, and the hydroxyl-carbonyl hydrogen bonds seem to dominate polymer chain associations. We propose a “sticky-blob” model, applicable to any associating polymer solution with many stickers inside each correlation blob, which predicts the concentration dependence of the specific viscosity and the chain relaxation time in the entanglement regime. When PVOH polymers are dissolved in DMSO, a strong hydrogen bond acceptor, chain-chain associations are fully prevented for all relevant degrees of hydrolysis. The specific viscosity and the relaxation time of the chain recover the expected concentration dependences for nonassociating flexible polymers in DMSO. The same concentration dependences are exhibited by literature data on 100% hydrolyzed PVOH in water, as the acetate content, dominating interchain associations, is zero. Comparing entangled aqueous and DMSO solutions at the same concentration enables the experimental measure of the time delay due to associations as the ratio between the terminal relaxation time of solutions in water and DMSO. The concentration dependence of such a time delay was also captured by the simple sticky-blob model introduced in this work.

Characterization of slurries for lithium-ion battery cathodes by measuring their flow and change in hydrostatic pressure over time and clarification of the relationship between slurry and cathode properties

Hypothesis: It is important to elucidate the effect of the particle dispersion/aggregation state of electrode slurries on resulting electrodes for the development of superior lithium-ion batteries. Many studies have been conducted to characterize cathode slurries for lithium-ion batteries; however, the particle dispersion state of cathode slurries remains unclear. This study investigates the rheological behavior and the packing ability of the cathode slurries for obtaining a denser electrode with lower electric resistance.Experiments: In addition to the conventional flow curve measurement, we measured the changes in the hydrostatic pressure of the slurries with time to evaluate their packing ability. The relationship between the properties of the cathode slurries and those of the as-cast cathodes was also investigated.Findings: It was found that a slurry in which acetylene black powder forms a network structure, with sufficient strength and the ability to rapidly recover after breaking, yields a cathode with comparatively high density and comparatively low volume resistivity. It was also found that the normalized settling time of a cathode slurry determined from its change in hydrostatic pressure over time correlates well with both the density and volume resistivity of a resulting as-cast cathode.

A Novel Method of Flow Curve Measurement for Magnetic Fluid Based on Plane Poiseuille Flow

Accurate measurement of the flow curves of magnetic fluid under a uniform field has always been a challenge. In this article, a novel method is proposed to measure the flow curve of magnetic fluids based on plane Poiseuille flow. The measuring system was built and its performance was compared with that of a commercial rheometer. Flow curves of magnetic fluid with different zero-field viscosity were tested under various field strengths. This novel method facilitates direct observation of the flowing behaviors of magnetic fluid under different stresses. By examining the variation trend of viscosity under certain constant stress, a more reliable method to determine the dynamic yield stress of magnetic fluid was used. The dynamic yield stress of the magnetic fluid measured by the new method was larger than the value obtained by the fitting, which is more reliable from an engineering point of view.

Rheological properties of concentrated allophane, halloysite, and kaolinite suspensions

This study investigated the rheological properties of concentrated suspensions of allophane, halloysite, and kaolinite, which are representative of a series of weathering products of volcanic glass and feldspar minerals in volcanic rocks and deposits, to elucidate the mechanism of landslide generation involving these materials. All suspensions generally showed shear thinning during flow curve measurements, as represented by a steady decrease of viscosity with increasing shear strain rate from 0.1 to 1000 s−1. A difference among them was that the kaolinite suspension showed unstable flow behavior at high solid concentration, and the halloysite suspension had a similar behavior at low solid concentration. The shear stress at the beginning of flow—which represents the yield stress of the suspension—showed a power law correlation with the solid volumetric fraction, and that for kaolinite agreed well with previous static yield stress measurements. The stress of the halloysite suspension deviated from the power law curve at solid fraction < ~0.15. Dynamic viscoelasticity tests indicated that all suspensions showed a power law correlation between the modulus value and solid fraction. The crossover strain (when a solidlike-to-liquidlike transition occurs) of the kaolinite suspension was almost constant within the investigated solid fraction range, whereas that of the halloysite suspension decreased noticeably at solid fraction < ~0.15. Overall, the allophane suspension had the weakest strength and lowest resistance to oscillatory strain at a given solid fraction condition. The rheological properties of halloysite observed here may be related to the occurrence of flow-like, long-distance landslides in volcanic areas containing weathered tephra.

Non-Invasive Rheo-MRI Study of Egg Yolk-Stabilized Emulsions: Yield Stress Decay and Protein Release.

A comprehensive understanding of the time-dependent flow behavior of concentrated oil-in-water emulsions is of considerable industrial importance. Along with conventional rheology measurements, localized flow and structural information are key to gaining insight into the underlying mechanisms causing time variations upon constant shear. In this work, we study the time-dependent flow behavior of concentrated egg-yolk emulsions with (MEY) or without (EY) enzymatic modification and unravel the effects caused by viscous friction during shear. We observe that prolonged shear leads to irreversible and significant loss of apparent viscosity in both emulsion formulations at a mild shear rate. The latter effect is in fact related to a yield stress decay during constant shearing experiments, as indicated by the local flow curve measurements obtained by rheo-MRI. Concurrently, two-dimensional D-T2 NMR measurements revealed a decrease in the T2 NMR relaxation time of the aqueous phase, indicating the release of surface-active proteins from the droplet interface towards the continuous water phase. The combination of an increase in droplet diameter and the concomitant loss of proteins aggregates from the droplet interface leads to a slow decrease in yield stress.

Synthesis and rheological characteristics of high viscosity linear polysiloxane carrier fluid-based magnetorheological fluids

This study addresses the synthesis and field-dependent rheological characteristics of novel magnetorheological fluids (MRFs) using high viscosity linear polysiloxanes (HVLPs) as a carrier fluid. First of all, the components and preparation of novel HVLP-based MRFs (HVLP MRFs) were explained in detail and the microscopic images of each component were taken by using scanning electron microscope (SEM). Four HVLP MRF samples with different particle volume fractions of 10, 15, 20, and 26 vol% in the same HVLP carrier fluid viscosity of 800 Pa·s were synthesized to investigate the particle concentration effect on their field-dependent rheological properties. In order to understand the effect of the carrier fluid viscosity, two more HVLP MRF samples with different HVLP viscosities of 140 and 440 Pa·s in the same particle concentration of 26 vol% were also fabricated. In addition, the temperature effect on HVLP MRFs was studied by using the sample with 26 vol% in particle concentration and 140 Pa·s in HVLP viscosity under different operating temperatures of 25 °C, 40 °C, 55 °C and 70 °C. The flow curve measurements of shear stress versus shear rate in the magnetic fields were conducted by using controlled shear rate (CSR) test method with a commercial parallel-plate type rotational rheometer. From the flow curves, the field-dependent rheological properties of HVLP MRFs including static and dynamic yield stresses and the dynamic range (ratio of field on to field off yield stress) were obtained. These material characteristics were then examined as a function of varying particle concentration, varying carrier fluid viscosity, and varying temperature. A conventional commercial MRF (i.e. Lord MRF-126CD) was adopted for comparison study and its rheological properties under different temperatures were also measured and compared with those of HVLP MRFs. Using HVLP carrier fluids, it was demonstrated that the HVLP MRFs exhibited much greater suspension stability than the conventional commercial MRF.

Operando observation of concentrated SiO2 suspensions by optical coherent tomography during flow curve measurements: The relationship between polymer dispersant structures and surface interactions

HypothesisFlow curve measurement is commonly used to characterize the flow behavior of concentrated suspensions. However, dynamic changes in the suspension inner microstructures under highly sheared conditions have not been correctly understood even though they strongly affect the measured shear stress. We hypothesize that the real particle dynamics during shearing could be effectively revealed by a systematic investigation that combines macroscopic flow curve measurements with operando microstructural observation employing an optical coherent tomography (OCT) apparatus and surface interaction measurements with the colloidal probe atomic force microscopy (AFM) method. ExperimentsThe model system was spherical SiO2/toluene suspensions stabilized by polyethyleneimine (PEI) partially complexed with different fatty acids. Inner structures of the suspensions during flow curve measurements were observed by the OCT technique. The surface-surface interactions in toluene were analyzed using the colloidal probe AFM method. FindingsOperando OCT observations revealed that during flow curve measurements, the suspensions can have completely different microscopic flow modes depending on the fatty acid species complexed to PEI and the solid concentrations. These microscopic flow modes could not be recognized using the typical flow curve measurements alone. The different flow modes can be explained by surface interactions measured by the colloidal probe AFM method.

Rheological response of entangled isotactic polypropylene melts in strong shear flows: Edge fracture, flow curves, and normal stresses

Isotactic polypropylene (iPP) melts are industrial semicrystalline polymers whose processing typically involves strong shear flows. The study of the rheological response of iPP melts, well beyond the linear viscoelastic limit, is limited by edge fracture, which manifests in rotational rheometers. In this work, we used a reflection polariscope under shear to detect the onset shear rate at which edge fracture is observed for various rotational rheometry fixture diameters. The onset shear rate for edge fracture was found to correlate with the zero-shear viscosity, thereby enabling the prediction of edge fracture by only knowing the zero-shear viscosity; a quantity that is easier to measure compared to the second normal stress difference. Edge fracture is then mitigated by using a cone-partitioned plate, which enabled the study of the first normal stress difference, and in combination with capillary rheometry, allowed the measurement of flow curves with a very well-resolved shear thinning region. For strongly polydisperse iPPs at high shear rates, we found that viscosity scales as the −0.7 power of the shear rate, while primary normal stress difference scales as the square root of the shear rate. The dependence of the shear thinning of iPPs on polydispersity was then unravelled, offering a broad set of data to develop and test molecular models.

Understanding the effects of processing conditions on the formation of lamellar gel networks using a rheological approach

Lamellar gel networks are multiphase systems which form the basis of many cosmetic and pharmaceutical cream products, thanks to their superior stability compared to typical oil-in-water emulsions, and highly desirable rheological properties inferred by the interconnected structure. There has previously been considerable interest in the formulation of lamellar gel networks, but little interest has been given to the effects of processing conditions on the formation of the desired structure, or the possibility for process optimisation through understanding power consumption. The evolution of the microstructure of an incipient lamellar gel network during processing was investigated by varying the temperature, vane speed and time using a rheometer equipped with a four-bladed vane in cup geometry. Torque and vane speed measurements were recorded at 2 Hz for the duration of the experiment, from which apparent viscosity (taken at a reference shear rate of 200 s−1) and power input were calculated. Samples were then characterised by yield stress and flow curve measurements to determine the impact of processing conditions on the final product microstructure. Increasing vane speed increased the maximum apparent viscosity achieved and yield stress of the sample, and reduced the time taken to reach the peak apparent viscosity. However, the increased power requirements from the higher vane speed were not counteracted by shorter processing times. Increasing the temperature reduced the rate of apparent viscosity increase but did not affect the yield stress of the final lamellar gel network, offering a reduction in power consumption due to a lower apparent viscosity for the majority of the process.

High pressure rheological studies of methane hydrate slurries formed from water-hexane, water-heptane, and water-decane multiphase systems

High pressure rheological properties of methane hydrate slurries entail the high-pressure rheometer that can deliver a suitable mixing to form in situ methane hydrate from the multiphase system. However, the hydrate formation was extremely challenging in conventional cup and bob geometry due to its plane surface. In this work, modified Couette geometry has been used in a high pressure rheometer to study in situ formation and dissociation of methane hydrate slurries formed from multiphase water-hexane (C6H14), water-heptane (C7H16) and water-decane (C10H22), with varying water-to-liquid hydrocarbon ratios (50:50, 30:70 v/v). Rheological properties such as viscosity, flow curve measurements, viscoelastic properties have been measured during hydrate formation and dissociation. Transient viscosity measurements are carried out at 10 MPa and 275.15 K at a shear rate of 1000 s−1. It was observed that the viscosity increases significantly during hydrate induction. Viscosity profile has shown bobbing behavior during the course of hydrate formation indicating in situ morphological changes (agglomeration and breakage of hydrate crystals) during hydrate formation. Flow curves indicate strong shear thinning behavior. Viscosity profile of methane hydrate slurries were also observed for each case during the hydrate dissociation using thermal stimulation. The peak in the viscosity has been identified near hydrate equilibrium condition during dissociation. Dynamic viscoelastic properties indicate solid behavior of methane hydrate slurries. The present study provides significant contribution on the rheology of methane hydrate slurries formed from multiphase systems in the context of flow assurance applications.

High Field MicroMRI Velocimetric Measurement of Quantitative Local Flow Curves.

Performing rheo-microMRI velocimetry at a high magnetic field with strong pulsed field gradients has clear advantages in terms of (chemical) sensitivity and resolution in velocities, time, and space. To benefit from these advantages, some artifacts need to be minimized. Significant sources of such artifacts are chemical shift dispersion due to the high magnetic field, eddy currents caused by the pulsed magnetic field gradients, and possible mechanical instabilities in concentric cylinder (CC) rheo-cells. These, in particular, hamper quantitative assessment of spatially resolved velocity profiles needed to construct local flow curves (LFCs) in CC geometries with millimeter gap sizes. A major improvement was achieved by chemical shift selective suppression of signals that are spectroscopically different from the signal of interest. By also accounting for imperfections in pulsed field gradients, LFCs were obtained that were virtually free of artifacts. The approach to obtain quantitative LFCs in millimeter gap CC rheo-MRI cells was validated for Newtonian and simple yield stress fluids, which both showed quantitative agreement between local and global flow curves. No systematic effects of gap size and rotational velocity on the viscosity of a Newtonian fluid and yield stress of a complex fluid could be observed. The acquisition of LFCs during heterogeneous and transient flow of fat crystal dispersion demonstrated that local constitutive laws can be assessed by rheo-microMRI at a high magnetic field in a noninvasive, quantitative, and real-time manner.

Impact of methodological artifact on digested sludge flow curve measurement

Inconsistent experimental procedures have been used to characterize sludge rheology in literature. This often has resulted in proposing different rheological models for sludge as well as non-comparable data. Any collected rheological data needs to be interpreted considering the methodology used for its collection because otherwise they cannot be used by engineers for design and troubleshooting. This paper intends to shed light on the influential parameters during data collection procedure to produce a reliable and reproducible data.This paper systematically investigates the impact of different geometries, preshear, equilibrium, rest and storage time on flow curve measurement for digested sludge in the range of 2.3 to 6% total solid and recommends a reliable procedure for reproducible sludge flow curve measurements. While the magnitude of impacts is different, we found all factors are significantly dependent on the sludge solid concentration. Besides, the method of the development of the protocol can be utilized to develop appropriate protocols for rheological characterization of any other sludge. The customization highlights are:•Selecting the geometry according to the sludge solid concentration.•Allocating an equilibrium time at each point of flow curve according to the sludge solid concentration.•Flow curve data requires to visually inspected for instabilities.

Development and Progress of Innovative Rotational-Type Viscometer with Electromagnetically Spinning Method

Rotational-type viscometers are the most representative methodology in the rheometry, and commonly used in flow curve measurement, creep test, and dynamic viscoelastic spectroscopy. From the view point of measurement accuracy, however is some cases, the rotational-types are inferior to the capillary-types especially in measuring less viscosity than 1 mPa·s. Recently, the authors developed a series of viscosity measurement systems based on the electromagnetically spinning (EMS) method, which can provide both the rotational-type's versatility and the capillary-type's accuracy. In addition, these EMS systems have advantages of a perfectly sealed condition as well as a disposable usage so that they will break new ground for rheometry. In this paper, we introduced the noteworthy features of each of the EMS series, and showed some interesting results by rheometry in lowly viscous fluids.

Essential refinements of spherical nanoindentation protocols for the reliable determination of mechanical flow curves

Understanding and linking mechanical properties obtained by spherical indentation experiments to uniaxial data is extremely challenging. Since the first attempts in the early 20th century numerous advances gradually allowed to expand the output of indentation tests. Still, the extraction of flow curves from spherical nanoindentation has not yet been fully established, as tip shape problems and size effects impede a straight-forward implementation. Within this study, we show new calibration procedures originating from fundamental geometrical considerations to account for tip shape imperfections. This sets the base for strain-rate controlled tests, which in turn enables us to measure rate-dependent material properties either with constant strain-rate or by strain-rate jump tests. Finally, experimental evaluation of the constraint factor in consideration of the mechanical properties and induced strain enables the extraction of flow curves. Testing materials with refined microstructures ensures the absence of possible size-effects. This study contributes to a significant improvement of current experimental protocols and allows to move flow curve measurements from single spherical imprints one step closer to its implementation as a standard characterization technique for modern materials.

Physicochemical, functional and rheological investigation of Soymida febrifuga exudate gum

Acacia gum is a well-known and most used exudate gum. High solubility with low viscosity is one of the best property of this gum. Many studies were conducted to find out a substitute for acacia gum but very few gum had shown properties as good as acacia gum. The exudates collected from Soymida febrifuga also shows high solubility with low viscosity as acacia gum. Purified Soymida febrifuga gum (SFG) was characterised for physicochemical, functional, rheological and thermal properties. The FTIR spectra of SFG revealed a typical trend of polysaccharides. The monosaccharide composition of the gums indicated the presence arabinose, galactose, and ribose. Element composition of SFG shows resemblance with AG. However, the molecular weight of SFG is less than the AG. The rheological outcome was derived from flow curve measurements of gum at different concentrations and temperatures. Alikeness was observed in Viscosity profile of both the gums. SFG shows semblance with AG and can be use in food and pharmaceutical industry.

Influence of shear rheometer measurement systems on the rheological properties of microfibrillated cellulose (MFC) suspensions

Flow curve and viscoelastic measurements were performed on microfibrillated cellulose (MFC) suspensions of different solids content using both cylinder and cup (smooth and rough) as well as vane in cup geometries. To compare the data quantitatively from amplitude sweep measurements and dynamic flow curves several descriptors were newly introduced to parameterize the observed two-zone behaviour separated by a transition region. It was observed that the cylinder cup geometries are prone to erroneous effects like slip, wall depletion and/or shear banding. However, those effects were not observed when the MFC suspension was not stressed beyond the dynamic critical stress (yield) point, i.e. when still in the linear viscoelastic regime. The vane in cup system on the other hand, seems to be less affected by flow inhomogeneities. By following the rheological properties as a function of the MFC suspension solids content, it could be shown that the global property trends remained alike for all investigated measurement systems, despite the presence of erroneous effects in some geometries. The observed effects were linked to recent model hypotheses in respect to the morphology of MFC suspensions under changing shear situations.

Comparative study of Acacia nilotica exudate gum and acacia gum

Over 900 species of Acacia trees are found on earth, most of them produce gums. Acacia nilotica (Babul tree) is one of the major gum-yielding acacia species found in he Indian subcontinent. A. nilotica gum was collected from Maharashtra, India and characterised for its proximate analysis, physicochemical, functional, rheological and thermal properties. These properties further were compared with commercially available Acacia gum (AG). The sugar composition of the gums indicated the presence of arabinose, galactose, and rhamnose in ANG and AG. FTIR spectrums revealed the typical trend of polysaccharides for both the gums, however, the difference was observed in fingerprint region. The rheological outcomes were derived from flow curve measurements of gums at different concentrations and temperatures. Investigations of the flow curves of both gums revealed the diminutive difference in viscosity profile. The concentration difference in the monosaccharides of polysaccharides and proximate analysis of gums could be the responsible for the difference in rheological and thermal properties of gums. However, ANG shows good resemblance with AG and can be substituted for numerous applications in food and pharmaceutical industry.

Development of grouts for consolidation of old renders

A study was conducted on the development of lime based grouts for consolidation of renders and plasters detached from the support. The aim is to develop grouts that should be compatible with the pre-existing materials and allow the restoring of the adherence of coatings to the background. Special attention was paid to the rheological behaviour of the grouts and to other features of the fresh state. The role of components such as binders, aggregates and admixtures used in the formulations was tested through an outlined series of mechanical and physical tests. In terms of hardened state properties, a set of basic requirements (related to strength and capillarity) were evaluated and a test for adhesion loss measurement was developed in order to test the ability of developed grouts to restore adhesion of coating layers.The rheological behaviour was evaluated through a distinct procedure, which involved the test with a specific speed profile (dwell profile). The dwell profile allows studying the rheological behaviour along measuring time, making possible to observe changes in rheological parameters in mortar suspensions, through the measurement of flow curves along the time test. The dwell profile allowed obtaining the rheological parameters (viscosity and yield stress) according to the Bingham model.Grouts based on lime, fine sand and metakaolin together with the right amount of water and admixtures were developed and adjusted in order to be used in consolidation works of old renders.

Preparation and characterization of nanodispersions of yttria, yttrium aluminium garnet and lutetium aluminium garnet

Refractory and chemically inert nanoparticulate solids like yttria, yttrium aluminium garnet or lutetium aluminium garnet are notoriously difficult to disperse in aqueous solution, although such dispersions might prove useful for 2D- and 3D-printing, deposition of films or other shaping procedures for ceramic green bodies. This work reports on experiments to prepare such dispersions from nanopowders, using a range of selected carboxylic acids as ligands for electrostatic charging and stabilization of the various nanomaterials. The assessment of the system properties achieved combines ζ-potential and viscosity (flow curve) measurements in the resulting colloidal systems. Calculations of the molecular electrostatic potential of the ligands were used to correlate the molecular structure of the ligands and their capability to dock to the surface of the solid particles. The colloid chemical data received have then been interpreted on this background; citric acid and polyacrylic acid have been identified as the most attractive dispersants.