Showing papers on "Rheometer published in 2020"

The Rheology Handbook: For users of rotational and oscillatory rheometers

Abstract: Official Full-Text Publication: Rheological characterization of gel-in-oil-in-gel type low amplitude oscillatory shear rheology and creep recovery measurements. with the effects of rheology, the science of deformation and flow behavior. Rheology Handbook: For Users of Rotational and Oscillatory Rheometers PDF. Rotational (oscillatory) rheometers (referred to in road engineering as Dynamic Rheometers – DSR) are complex devices designed to characterize rheological.

Operating windows for oscillatory interfacial shear rheology

Abstract: Interfacial rheology becomes important when surface active species such as surfactants, particles, or proteins are present in sufficient quantities at liquid-liquid interfaces and interact between them. Interfacial rheometry measurements are challenging for various reasons. The mechanical response of the thin interface is often weaker compared to that of bulk materials and so one is often measuring close to the lower force and torque limits of rheometers, hence signal-to-noise ratios merit closer attention. In addition, the role of both instrument and sample inertia is more important for interfacial rheometry compared to bulk rheometry. Effects of misalignment and imperfections of the measurement geometries lead to effects of surface and line tension. Finally, peculiar for interfacial rheometry is the need to deconvolute the contributions of flow and deformation in the surrounding phases from that at the interface. Whereas some of these aspects have received attention in previous works, a clear and unambiguous view on the operating limits of interfacial rheometers has been missing. In the present work, we investigate the different experimental challenges and develop a generic methodology, which provides a clear definition of the operating limits of various interfacial rheometers including the interfacial needle shear rheometer, the double wall ring, and the bicone geometries. We validate this methodology by investigating the limitations defined intrinsically by the instrument as well as the ones emerging from the properties of the interface of interest for an interface composed of fatty alcohols which represents a challenging test case. The results provide cautionary examples and clear guidelines for anyone measuring interfacial rheology with these direct rheological techniques.Interfacial rheology becomes important when surface active species such as surfactants, particles, or proteins are present in sufficient quantities at liquid-liquid interfaces and interact between them. Interfacial rheometry measurements are challenging for various reasons. The mechanical response of the thin interface is often weaker compared to that of bulk materials and so one is often measuring close to the lower force and torque limits of rheometers, hence signal-to-noise ratios merit closer attention. In addition, the role of both instrument and sample inertia is more important for interfacial rheometry compared to bulk rheometry. Effects of misalignment and imperfections of the measurement geometries lead to effects of surface and line tension. Finally, peculiar for interfacial rheometry is the need to deconvolute the contributions of flow and deformation in the surrounding phases from that at the interface. Whereas some of these aspects have received attention in previous works, a clear and unambi...

reptate rheology software: Toolkit for the analysis of theories and experiments

Abstract: We present a new, free, and open source reptate (rheology of entangled polymers: toolkit for analysis of theory and experiment) software package for viewing, exchanging, and analyzing rheological and associated data. The main idea of reptate is to propose a powerful and user-friendly platform, which can be installed on the same computer as, e.g., the rheometer and which makes comparing experiments with classical, or latest, theories easy—without the need for a theoretician. The new reptate software offers full compatibility with different operating systems (Windows, Mac, and Linux). We demonstrate the use of reptate by reproducing predictions of recently published articles, from entangled, monodisperse, and polydisperse linear chains to branch-on-branch polymer systems in linear and nonlinear rheology regimes.

Interlaboratory study on rheological properties of cement pastes and reference substances: comparability of measurements performed with different rheometers and measurement geometries

Abstract: This paper presents the results of an interlaboratory study of the rheological properties of cement paste and ultrasound gel as reference substance. The goal was to quantify the comparability and reproducibility of measurements of the Bingham parameters yield stress and plastic viscosity when measured on one specific paste composition and one particular ultrasound gel in different laboratories using different rheometers and measurement geometries. The procedures for both in preparing the cement paste and carrying out the rheological measurements on cement paste and ultrasound gel were carefully defined for all of the study’s participants. Different conversion schemes for comparing the results obtained with the different measurement setups are presented here and critically discussed. The procedure proposed in this paper ensured a reasonable comparability of the results with a coefficient of variation for the yield stress of 27% and for the plastic viscosity of 24%, despite the individual measurement series’ having been performed in different labs with different rheometers and measurement geometries.

A novel method to characterise asphalt binder at high temperature

Abstract: The current experimental method used in Europe to characterise asphalt binder at high temperature is based on the Ring & Ball softening point. However, for modified binders it was demonstrated that...

Experimental Investigation and Performance Evaluation of Modified Viscoelastic Surfactant (VES) as a New Thickening Fracturing Fluid

Abstract: In hydraulic fracturing, fracturing fluids are used to create fractures in a hydrocarbon reservoir throughout transported proppant into the fractures. The application of many fields proves that conventional fracturing fluid has the disadvantages of residue(s), which causes serious clogging of the reservoir’s formations and, thus, leads to reduce the permeability in these hydrocarbon reservoirs. The development of clean (and cost-effective) fracturing fluid is a main driver of the hydraulic fracturing process. Presently, viscoelastic surfactant (VES)-fluid is one of the most widely used fracturing fluids in the hydraulic fracturing development of unconventional reservoirs, due to its non-residue(s) characteristics. However, conventional single-chain VES-fluid has a low temperature and shear resistance. In this study, two modified VES-fluid are developed as new thickening fracturing fluids, which consist of more single-chain coupled by hydrotropes (i.e., ionic organic salts) through non-covalent interaction. This new development is achieved by the formulation of mixing long chain cationic surfactant cetyltrimethylammonium bromide (CTAB) with organic acids, which are citric acid (CA) and maleic acid (MA) at a molar ratio of (3:1) and (2:1), respectively. As an innovative approach CTAB and CA are combined to obtain a solution (i.e., CTAB-based VES-fluid) with optimal properties for fracturing and this behaviour of the CTAB-based VES-fluid is experimentally corroborated. A rheometer was used to evaluate the visco-elasticity and shear rate & temperature resistance, while sand-carrying suspension capability was investigated by measuring the settling velocity of the transported proppant in the fluid. Moreover, the gel breaking capability was investigated by determining the viscosity of broken VES-fluid after mixing with ethanol, and the degree of core damage (i.e., permeability performance) caused by VES-fluid was evaluated while using core-flooding test. The experimental results show that, at pH-value ( 6.17 ), 30 (mM) VES-fluid (i.e., CTAB-CA) possesses the highest visco-elasticity as the apparent viscosity at zero shear-rate reached nearly to 10 6 (mPa·s). Moreover, the apparent viscosity of the 30 (mM) CTAB-CA VES-fluid remains 60 (mPa·s) at (90 ∘ C) and 170 (s − 1 ) after shearing for 2-h, indicating that CTAB-CA fluid has excellent temperature and shear resistance. Furthermore, excellent sand suspension and gel breaking ability of 30 (mM) CTAB-CA VES-fluid at 90 ( ∘ C) was shown; as the sand suspension velocity is 1.67 (mm/s) and complete gel breaking was achieved within 2 h after mixing with the ethanol at the ratio of 10:1. The core flooding experiments indicate that the core damage rate caused by the CTAB-CA VES-fluid is ( 7.99 % ), which indicate that it does not cause much damage. Based on the experimental results, it is expected that CTAB-CA VES-fluid under high-temperature will make the proposed new VES-fluid an attractive thickening fracturing fluid.

Low-temperature performance grade characterisation of asphalt binder using the dynamic shear rheometer

Abstract: Currently, the bending beam rheometer (BBR) test is the standard method for evaluating the low-temperature performance grade (PG) of asphalt binders. Despite its use, there are limitations with the...

Localized transient jamming in discontinuous shear thickening

Abstract: We report direct measurements of spatially resolved surface stresses over the entire surface of a dense suspension during discontinuous shear thickening (DST) using boundary stress microscopy (BSM) in a parallel-plate rheometer. We find that large fluctuations in the bulk rheological response at the onset of DST are the result of localized transitions to a state with very high stress, consistent with a fully jammed solid that makes direct contact with the shearing boundaries. This jammed solidlike phase (SLP) is rapidly fractured, producing two separate SLPs that propagate in opposite directions. By comparing the speed of propagation of the SLPs with the motion of the confining plates, we deduce that one remains in contact with the bottom boundary and the other remains in contact with the top. These regions grow, bifurcate, and eventually interact and decay in a complex manner that depends on the measurement conditions (constant shear rate vs constant stress). In a constant applied stress mode, BSM directly reveals dramatic stress fluctuations that are completely missed in the standard bulk rheology.

Rheology by Design: A Regulatory Tutorial for Analytical Method Validation.

Abstract: The increasing demand for product and process understanding as an active pursuit in the quality guideline Q8 and, more recently, on the draft guideline on quality and equivalence of topical products, has unveiled the tremendous potential of rheology methods as a tool for microstructure characterization of topical semisolid dosage forms. Accordingly, procedure standardization is a dire need. This work aimed at developing and validating a methodology tutorial for rheology analysis. A 1% hydrocortisone cream was used as model cream formulation. Through a risk assessment analysis, the impact of selected critical method variables (geometry, temperature and application mode) was estimated in a broad range of rheological critical analytical attributes-zero-shear viscosity, upper-shear thinning viscosity, lower-shear thinning viscosity, infinite-shear viscosity, rotational yield point, thixotropic relative area, linear viscoelastic region, oscillatory yield point, storage modulus, loss modulus, and loss tangent. The proposed validation of the approach included the rheometer qualification, followed by the validation of numerous operational critical parameters regarding a rheology profile acquisition. The thixotropic relative area, oscillatory yield point, flow point and viscosity related endpoints proved to be highly sensitive and discriminatory parameters. This rationale provided a standard framework for the development of a reliable and robust rheology profile acquisition.

Universal viscosifying behavior of acrylamide-based polymers used in enhanced oil recovery

Abstract: Conventional polymers used in enhanced oil recovery (EOR) are acrylamide-based copolymers of very high molecular weight. Their viscosity in aqueous solution depends on various physicochemical parameters such as monomer composition, concentration, average molecular weight, polydispersity, salinity level and ionic composition, temperature, etc. Moreover, solutions are non-Newtonian; they exhibit low-shear Newtonian plateau viscosity at a low-shear rate followed by a shear thinning region at a higher shear rate. In the absence of a predictive model, for any new polymer grade or lot, any new or slightly varying field condition, it is necessary to perform a whole set of viscosity measurements at varying concentrations, which is tedious, time-consuming, and not valuable. Flow curves (viscosity vs shear rate) were measured on a great number of polymer solutions in various physicochemical conditions (variation of the polymer microstructure, monomer composition, molecular weight, brine salinity, and temperature). The flow curves in dilute nonentangled, semidilute nonentangled, and semidilute entangled regimes were modeled by only two adjustable parameters: the intrinsic viscosity [ η ] and the relaxation time in the dilute regime λ d. The zero-shear viscosity η 0 (more specifically, the specific viscosity η s p) and the power law index n obey master curves that are solely functions of the overlap parameter C [ η ]. The relaxation time λ depends on C [ η ] and the relaxation time in the dilute regime λ d. All these results are consistent with predictions for a neutral polymer in a good solvent. By using these master curves, intrinsic viscosity of any polymer/brine system can be easily obtained at various temperatures from a single measurement in the semidilute regime in which viscosity is higher than water, and classic rheometers are very sensitive. The whole flow curve η ( γ ˙ ) can be predicted at any concentration, temperature, and molecular weight. For any unknown polymer/brine system, the determination of λ d enables us to determine the viscosimetric average molecular weight M of the polymer. Finally, by using the additive property of the intrinsic viscosity of binary solutions, a method is proposed to evaluate the molecular weight of field samples. Polymer physics is today considered well described and well known. However, the beauty and the usefulness of this physics have been partly ignored by the EOR community up to now. This study gives a methodology to predict the viscosifying behavior and the molecular weight of any acrylamide-based copolymer/brine system. By attributing the molecular weight rather than a viscosity value, on-site and lab quality control will be greatly improved.

Dramatic effect of oxide on measured liquid metal rheology

Abstract: Liquid metals have long been treated as Newtonian liquids, but several researchers have recently indicated that some metals may shear thin. While apparent shear thinning can be caused by surface oxidation, the reports of shear-thinning metals were investigated using cup and bob type rheometers, which are expected to only be weakly impacted by the surface contamination effects. We show here that even small amounts of oxide on the surface of liquid metals can cause dramatic changes to the measured viscosity of the sample. Using a Searle-type rotational rheometer, we measured the viscosity of eutectic gallium indium and tin in a low-oxygen environment. When either metal is slightly oxidized, the measured viscosity increases by orders of magnitude and the liquid displays erroneous shear-thinning behavior. When the oxide is removed via an active flux, the measured viscosity is Newtonian. The results outlined here provide insight into the difficulties of measuring the viscosity of easily oxidized liquids and confirm that liquid metals are likely best described as Newtonian liquids at all measured shear rates.

A methodology for adding thixotropy to Oldroyd-8 family of viscoelastic models for characterization of human blood

Abstract: Recent work modeling the rheological behavior of human blood indicates that blood has all the hallmark features of a complex material, including shear-thinning, viscoelastic behavior, a yield stress, and thixotropy. After decades of modeling only the steady state blood data, steady state models, such as the Casson, Carreau–Yasuda, and Herschel–Bulkley models, have been developed. The advancement and evolution of blood modeling to transient flow conditions now has renewed interest. Using recently collected human blood rheological data from a strain-controlled rheometer, we show and compare a new modeling effort using the Oldroyd-8 viscoelastic framework as a foundation. This foundation is enhanced with the application of a recent thixotropic framework recently published to model elastic and viscoelastic contributions from the microstructure to three Oldroyd-8 families of models: the corotational Jeffreys model, the convected Maxwell model, and the Oldroyd 4-constant model. The elastic and viscoelastic stress contributions from the microstructure are then linearly superimposed with the viscoelastic backbone solution for stress given by the Oldroyd-8 family of models. Demonstrated here is a parametric analysis, model comparison, and a comparison of the new approaches made using the ability to predict large amplitude oscillatory shear and uni-directional large amplitude oscillatory shear flow. The new family of models can solve components of the full stress tensor, making them ideal for use with a future conformation tensor to evolve, model, and better understand the effects of the microstructure of human blood. In addition, there is now a methodology to model the normal forces of blood.

Improved rheometry of yield stress fluids using bespoke fractal 3D printed vanes

Abstract: To enable robust rheological measurements of the properties of yield stress fluids, we introduce a class of modified vane fixtures with fractal-like cross-sectional structures. A greater number of outer contact edges leads to increased kinematic homogeneity at the point of yielding and beyond. The vanes are 3D printed (3DP) using a desktop stereolithography machine, making them inexpensive (disposable), chemically compatible with a wide range of solvents, and readily adaptable as a base for further design innovations. To complete the tooling set, we introduce a textured 3DP cup, which attaches to a standard rheometer base. We discuss general design criteria for 3DP rheometer vanes, including consideration of sample volume displaced by the vanes, stress homogeneity, and secondary flows that constrain the parameter space of potential designs. We also develop a conversion from machine torque to material shear stress for vanes with an arbitrary number of arms. We compare a family of vane designs by measuring the viscosity of Newtonian calibration oils with error <5% relative to reference measurements made with a cone-and-plate geometry. We measure the flow curve of a simple Carbopol yield stress fluid and show that a 24-armed 3DP fractal vane agrees within 1% of reference measurements made with a roughened cone-and-plate geometry. Last, we demonstrate use of the 24-armed fractal vane to probe the thixo-elastoviscoplastic response of a Carbopol-based hair gel, a jammed emulsion (mayonnaise), and a strongly alkaline carbon black-based battery slurry.

Viscoelastic properties of flexible and rigid polymers for turbulent drag reduction

Abstract: The relation between the drag reduction (DR) performance of several water-soluble polymers and their viscoelastic properties was investigated. Polymers with a flexible molecular structure including three grades of polyacrylamides (PAM), and a polyethylene oxide (PEO) were investigated. Xanthan gum (XG) and carboxymethyl cellulose (CMC), each with a rigid molecular structure, were also considered. The rheology was characterized using steady shear-viscosity measurement, capillary break-up extensional rheometer (CaBER), and small-amplitude oscillatory shear measurement at the concentration of the drag-reduced solution. To isolate the effect of shear viscosity, the concentration of the polymers was adjusted to produce solutions with a similar shear viscosity at high shear rates. Using pressure drop measurements in a turbulent pipe flow, the DR of each polymer solution was determined. With identical high-shear-rate viscosities, the flexible PAM solutions resulted in an initial DR of 50–58%, while the initial DR of PEO was 44%, and the rigid polymers provided the least DR of 12%. The rigid polymers demonstrated negligible degradation of DR over a period of 2 h. Of the flexible polymers, PAM showed moderate degradation, while the DR of PEO quickly diminished after 20 min. Drag reduction correlated with extensional viscosity and Weissenberg number obtained from CaBER. A strong correlation was not observed between DR and the viscoelastic moduli obtained from small-amplitude oscillatory shear. The large mechanical degradation of PEO was associated with a continuous extensional thickening, in which extensional viscosity increased with decreasing strain rate until the filament broke up.

Analysis of the complex rheological properties of highly concentrated proteins with a closed cavity rheometer

Abstract: Highly concentrated biopolymers are used in food extrusion processing. It is well known that rheological properties of biopolymers influence considerably both process conditions and product properties. Therefore, characterization of rheological properties under extrusionrelevant conditions is crucial to process and product design. Since conventional rheological methods are still lacking for this purpose, a novel approach is presented. A closed cavity rheometer known in the rubber industry was used to systematically characterize a highly concentrated soy protein, a very relevant protein in extruded meat analogues. Rheological properties were first determined and discussed in the linear viscoelastic range (SAOS). Rheological analysis was then carried out in the non-linear viscoelastic range (LAOS), as high deformations in extrusion demand for measurements at process-relevant high strains. The protein showed gel behavior in the linear range, while liquid behavior was observed in the nonlinear range. An expected increase in elasticity through addition of methylcellulosewas detected. The measurements in the non-linear range reveal significant changes of material behavior with increasing strain. As another tool for rheological characterization, a stress relaxation test was carried out which confirmed the increase of elastic behavior after methylcellulose addition.

Pipe rheology of microfibrillated cellulose suspensions

Abstract: The shear rheology of two mechanically manufactured microfibrillated cellulose (MFC) suspensions was studied in a consistency range of 0.2–2.0% with a pipe rheometer combined with ultrasound velocity profiling. The MFC suspensions behaved at all consistencies as shear thinning power law fluids. Despite their significantly different particle size, the viscous behavior of the suspensions was quantitatively similar. For both suspensions, the dependence of yield stress and the consistency index on consistency was a power law with an exponent of 2.4, similar to some pulp suspensions. The dependence of flow index on consistency was also a power law, with an exponent of − 0.36. The slip flow was very strong for both MFCs and contributed up to 95% to the flow rate. When wall shear stress exceeded two times the yield stress, slip flow caused drag reduction with consistencies higher than 0.8%. When inspecting the slip velocities of both suspensions as a function of wall shear stress scaled with the yield stress, a good data collapse was obtained. The observed similarities in the shear rheology of both the MFC suspensions and the similar behavior of some pulp fiber suspensions suggests that the shear rheology of MFC suspensions might be more universal than has previously been realized.

Preparation and characterization of natural rubber bio-based wood adhesive: effect of total solid content, viscosity, and storage time

Abstract: Natural rubber (NR) grafted by methyl methacrylate (MMA) was used to produce bio-based wood adhesive. The effect of total solid content (%TSC) at 55, 57, and 60%, represented as 55NR-g-MMA, 57NR-g-MMA, and 60NR-g-MMA, respectively, and the effect of storage time on lap shear strength were investigated. It was found that contact angle sharply decreased from 95° for NR to approximately 65° for all of NR-g-MMAs. Because the MMA groups were incorporated into various NR-g-MMA samples and the highest relative amount of grafted MMA was obtained by 57-NR-g-MMA which is determined by peaks intensities ratio between wave number at 1725 (C=O stretching) and 1450 (CH2 stretching), investigated by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). These influences resulted in an increase in storage modulus (E′), whereas tanδ was decreased as compared to that of NR, characterized by dynamic mechanical analyzer (DMA). In addition, the apparent viscosity performed by plate-and-plate rheometer trended to increase with total solid content and storage time. However, the highest lap shear strength was achieved by 57NR-g-MMA. It means that the lap shear strength was not only governed by viscosity as well as total solid content, but the amount of grafted MMA also plays an important role.

Intra-Cycle Elastic Nonlinearity of Nitrogen-Doped Carbon Nanotube/Polymer Nanocomposites under Medium Amplitude Oscillatory Shear (MAOS) Flow.

Abstract: This study seeks to unravel the effect of carbon nanotube’s physical and chemical features on the final electrical and rheological properties of polymer nanocomposites thereof Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized over two different types of catalysts, ie, Fe and Ni, employing chemical vapor deposition Utilizing this technique, we were able to synthesize N-CNTs with significantly different structures As a result, remarkable differences in the network structure of the nanotubes were observed upon mixing the N-CNTs in a polyvinylidene fluoride (PVDF) matrix, which, in turn, led to drastically different electrical and rheological properties For instance, no enhancement in the electrical conductivity of poorly-dispersed (N-CNT)Ni/PVDF samples was observed even at high nanotube concentrations, whereas (N-CNT)Fe/PVDF nanocomposites exhibited an insulative behavior at 10 wt%, a semi-conductive behavior at 20 wt%, and a conductive behavior at 27 wt% In terms of rheology, the most substantial differences in the viscoelastic behavior of the systems were distinguishable in the medium amplitude oscillatory shear (MAOS) region The stress decomposition method combined with the evaluation of the elastic and viscous third-order Chebyshev coefficients revealed a strong intra-cycle elastic nonlinearity in the MAOS region for the poorly-dispersed systems in small frequencies; however, the well-dispersed systems showed no intra-cycle nonlinearity in the MAOS region It was shown that the MAOS elastic nonlinearity of poorly-dispersed systems stems from the confinement of N-CNT domains between the rheometer’s plates for small gap sizes comparable with the size of the agglomerates Moreover, the intra-cycle elastic nonlinearity of poorly-dispersed systems is frequency-dependent and vanished at higher frequencies The correlation between the microstructure and viscoelastic properties under large shear deformations provides further guidance for the fabrication of high-performance 3D-printed electrically conductive nanocomposites with precisely controllable final properties for engineering applications