Degree Of Shear Thinning Research Articles

Effect of xanthan gum on stability and rheological behavior of O/W emulsion

Oil-in-water emulsions were prepared by homogeneous emulsification using glycerol stearate (and) PEG-100 stearate (A165) as emulsifier and xanthan gum (XG) as thickener. The effects of oil and XG content on the stability and flow behavior of emulsion were studied by polarizing microscope and rheometer. The hydrogen bonding interaction between xanthan gum molecules was studied by molecular dynamics simulation, and then the interaction between xanthan gum and emulsifier was further studied. The results showed that when there is no xanthan gum and the emulsifier content is 3%, the oil content increased, the particle size decreased. When the oil content is constant, the emulsion particle size decreases at first and then increases with the XG content increasing, which is due to the accumulation of XG and emulsifier on the oil-water interface, and the interfacial film thickens. The flow behavior of O/W emulsion can be described by a power law function. The emulsion without XG is Newtonian fluid at low oil content, and when the oil content increased, it was transformed into non-Newtonian fluid. The viscosity and consistency index increased with the increase of XG, which is due to the hydrogen bond between XG and emulsifier. However, the flow behavior index decreased greatly, the degree of shear thinning of emulsion enhanced. XG increased the viscosity of the mobile phase, under shear force, the deformation degree of droplets and the degree of shear thinning were different. This study can provide a reference for further regulating the stability and flow characteristics of skin care emulsion.

Rheology of Suspensions Thickened by Cellulose Nanocrystals.

The steady rheological behavior of suspensions of solid particles thickened by cellulose nanocrystals is investigated. Two different types and sizes of particles are used in the preparation of suspensions, namely, TG hollow spheres of 69 µm in Sauter mean diameter and solospheres S-32 of 14 µm in Sauter mean diameter. The nanocrystal concentration varies from 0 to 3.5 wt% and the particle concentration varies from 0 to 57.2 vol%. The influence of salt (NaCl) concentration and pH on the rheology of suspensions is also investigated. The suspensions generally exhibit shear-thinning behavior. The degree of shear-thinning is stronger in suspensions of smaller size particles. The experimental viscosity data are adequately described by a power-law model. The variations in power-law parameters (consistency index and flow behavior index) under different conditions are determined and discussed in detail.

Synthesis, optimization, and characterization of precipitation derived starch nanoparticles from guinea seeds

Guinea starch nanoparticles (GS-SNP) were developed using ultrasound and nanoprecipitation techniques. The physicochemical, thermal, structural, morphological, pasting, and rheological properties of GS-SNP were examined and compared with native starch. The particle size of GS-SNP was 391.50–206.00 nm, with a PDI of 0.35–0.23 and a zeta potential of −37.5 to −13 mV. The amylose content of GS-SNP increased with a decrease in relative crystallinity, and a VH-type crystalline structure was observed. The GS-SNP were in round shape with some self-aggregated granules. The water and oil absorption capacity, solubility, and gelatinization temperature of GS-SNP increased, but the swelling power was restricted. The viscosity of the GS-SNP dispersion remained almost constant throughout the heating but slightly increased after cooling. A higher degree of shear thinning was observed due to a fluid-like gel network and weak gel structure. The optimum conditions were: 50 % amplitude, 30 min time, and a starch to ethanol ratio (1:4) with 85 % maximum desirability. Overall, the findings suggest that GS-SNP have promising potential for application in a liquid system where viscosity of the system cannot be significantly influenced by temperature.

Effects of MHD and thermal radiation on non-Newtonian fluid with Cattaneo–Christov heat over a stretching flow surface

In this study, we are investigating the flow of an incompressible Williamson fluid using a Cattaneo–Christov heat flux model, with consideration for a magnetic Reynolds number that is not high. This fluid flows over a linearly stretched 2-D surface and is affected by a magnetic field, thermal radiation-diffusion, and heat generation. To model the Williamson flow, we apply a boundary layer approximation and develop the ordinary differential equations. The system of differential equations is transformed into a system of ordinary differential equations using a suitable transformation. We utilize the Iterative Runge–Kutta fourth-order scheme to numerically solve the boundary conditions associated with the nonlinear, dimensionless ordinary differential equations. Graphical representations of the results are employed to analyze the impact of physical properties on velocity, temperature, and concentration, with the numerical results presented in tabular form. Upon comparing our findings with previously published results, we have found them to be in good agreement. The velocity decreases as the Williamson fluid factor gradually increases. Williamson fluids are recognized for their shear thinning behavior, wherein viscosity decreases as the shear rate increases. However, higher parameter values can lead to increased fluid viscosity, potentially reducing the degree of shear thinning. This phenomenon results in a more uniform viscosity profile across varying shear rates, contributing to a reduced velocity distribution within the fluid.

Processing of Aqueous Graphite–Silicon Oxide Slurries and Its Impact on Rheology, Coating Behavior, Microstructure, and Cell Performance

The mixing process is the basis of the electrode microstructure, which defines key cell performance indicators. This work investigated the effects of varying the energy input within the mixing procedure on slurry rheology, coating behavior, mechanical and electrical properties of dry electrodes and electrochemical performance of cells fabricated from these negative electrodes. Energy input differences were achieved by varying the solids content within the mixing procedure; however, the final total solids content of the slurries was always the same. The slurries, produced with graphite and silicon oxide as active materials and carboxymethylcellulose (CMC) and styrene-butadiene rubber as binders, showed large differences in flow behavior which were explained by changes in CMC adsorption and mechanical degradation because of increasing energy input. Low shear viscosity and the degree of shear thinning decreased with increasing energy input, resulting in a narrower stability window for slot-die coating. The resistance between the electrode and current collector decreased as more CMC was adsorbed on the active material. Electrode adhesion drastically dropped at the highest energy input, presumably due to a change in SBR distribution. Despite these variations, all fabricated pouch cells demonstrated excellent electrochemical performance and a slight trend of increased charge capability was observed in cells prepared with higher energy input.

Rheological properties of cement-based slurry and evaluation of rheological model: Influence of particle size and shape

With the continuous development of mineral admixtures and additives, the influence of various factors on the rheological properties of cement-based slurry remains unclear. In this study, the effects of particle size, particle shape, shear rate, and time on the rheological properties were analyzed. The rheological curves were determined using an RST-SST rheometer and fitted with the Bingham model, Modified Bingham model and Herschel-Bulkley model, respectively. The rheological parameters were evaluated. The results showed that the effect of particle size on the rheological properties is much greater than that of the particle shape. The small particle size is evidently affected by the shear rate, and the rheological parameters increase with time. The three rheological models can well describe the samples containing microfine cement (MC), fly ash (FA) and calcium carbonate whisker (CaCO3 whisker). The sample containing nano-silica (nano-SiO2) requires special analysis. The yield stress predicted by the Bingham model is the highest, whereas that predicted by the Herschel–Bulkley model is the lowest. The plastic viscosity predicted by the Bingham model is lower than that predicted by the modified Bingham model. The rheological index (n) of the Herschel–Bulkley model can effectively characterize the degree of shear thinning. The three rheological models demonstrate their characteristics and advantages, and an appropriate rheological model should be selected to evaluate the rheological parameters according to the requirements. The research aims to provide theoretical support for the analysis of rheological properties and the selection of rheological models.

Rheology of self-compacting concrete containing silica fume and recycled aggregates

Rheology of Self-Compacting Concrete (SCC) containing selected silica fume dosages (0% (control mix), 5%, 10% and 15%) in a binary binder has been investigated using the flow-curve test protocol implemented on a co-axial cylinder rheometer. At each silica fume dosage, coarse recycled concrete aggregate volumetric replacement levels were 0%, 50% and 100%. Calibration of selected flow models with the measured flow data showed that rheology transitioned from shear thickening to shear thinning as the silica fume dosage increased from 0% to 15%, other mix constituents remaining unchanged. Similar flow behaviour was noted in the SCCs made with the recycled concrete aggregates (SCRACs) across all replacement levels though for a given silica fume dosage, degree of shear thinning decreased with increasing contents of the coarse recycled aggregates. The experimental results have been used to propose a workability box containing bounds for acceptable rheology of the SCCs and the SCRACs.

Effects of Dispersion Medium on Surface Tension and Rheological Behavior of Pectin and Guar Gum Based Thickeners Used in Treatment of Dysphagia

Dysphagia is a complex condition as each individual may have unique swallowing difficulties and sensitivities. Experimental studies investigating the effects of dispersion media on thickeners can contribute to the development of customized thickening agents. Understanding how the dispersion environment affects the surface tension and rheological behavior of thickeners can lead to improved patient safety, comfort, and overall treatment efficacy by helping healthcare professionals make informed decisions when selecting appropriate thickening agents and optimizing their use in clinical practice. In this study, the effects of dispersion medium (water and lemonade) on the surface tension and rheology of thickened liquids prepared with pectin or guar gum-based thickening powders have been investigated. The rheological behaviors of the samples are determined at room temperature at the shear rate ranges of 10-100 s-1 using a rotary viscometer. Obtained data are modeled by Power Law and Herschel Bulkley. Both pectin and guar gum thickeners exhibit shear thinning behavior, meaning that their viscosity decreases under shear stress. The dispersion medium influences the degree of shear thinning observed. The low surface tension of this medium raises wetting and improves the dispersion of thickeners, resulting in faster dissolution and better mixing. This can be beneficial for the treatment of dysphagia as it allows for easier swallowing and better texture of thickened fluids.

Effect of jet-cooking on rheological properties of navy bean flour suspensions

Navy beans are a gluten-free pulse containing great heathy sources for human beings. In this work, we compared the rheological properties of untreated navy bean flour suspensions (UNBFS) and jet-cooked navy bean flour suspensions (JCNBFS). Jet-cooking is a direct-contact heating process employing high-temperature and high-pressure steam for producing food and beverage products. We found that the linear rheological properties of 8% (wt.%) UNBFS exhibited viscoelastic fluid behavior; while 10% (wt.%) UNBFS displayed viscoelastic fluid/solid cross-over behavior; but 12% (wt.%) UNBFS displayed weak viscoelastic solid behavior. Unlike UNBFS, all three (8%, 10%, and 12%) (wt.%) jet-cooked navy bean flour suspensions (JCNBFS) displayed linear rheological properties having viscoelastic solid gel-like behaviors. The rheological properties of JCNBFS were strongly dependent on the concentration of the suspensions. The non-linear viscoelastic properties of the three suspensions of UNBFS exhibited similar viscosity shear thinning behavior. The degree of shear thinning was slightly reduced both at very low and high shear rates. The non-linear rheological properties of the three suspensions of JCNBFS also displayed shear thinning behaviors. The viscosity curves of the JCNBFS were much steeper than those of the UNBFS. This demonstrates that JCNBFS possessed greater shear thinning capacity than UNBFS. Both linear and non-linear rheological property studies for UNBFS and JCNBFS revealed that jet-cooking processing alters the molecular structures of navy bean flours’ starch and proteins, which would influence the navy bean flour suspensions’ properties. The results of this work will be useful to develop new food products from navy beans.

Ultrasonication for preparing high-performance phase change material nano-emulsions: Optimization and characterization

This work was aimed to optimize the formulation of phase change material nano-emulsions by ultrasonic emulsification that has not been investigated systematically. The optimization was performed using response surface methodology on two response parameters, average droplet size and apparent viscosity, and three independent variables including ultrasonic amplitude (X1), treatment time (X2), and surfactant content (X3). The significance of three variables on both droplet size and apparent viscosity followed the order of X3 > X1 > X2. At the optimal variable levels (X1 = 58 %; X2 = 9 min; X3 = 8 wt%), the droplet size of 118.2 nm and apparent viscosity of 7.3 mPa·s were predicated by the regression model and also well verified by experiments. The 25 wt% phase change nano-emulsion formed by ultrasonication exhibited the best emulsion stability and the lowest apparent viscosity compared with those formulated by high-energy rotor-stator homogenizer and low-energy method of phase inversion temperature. In addition, the rheological behavior associated with the average droplet size and the solid/liquid state of phase change material was illustrated numerically for the first time. In general, a threshold of 170–180 nm was found for the transition of liquid-in-water emulsions from a shear-thinning non-Newtonian fluid to a Newtonian fluid in the shear rate range of 0.6–73 s−1. All solid-in-water suspensions showed shear-thinning fluid behavior, though the shear-thinning degree was dramatically reduced to a flow behavior index of about 0.95 as the particle size was below 100 nm. These findings may be useful for designing high-performance phase change material nano-emulsions with long service life, high energy storage capacity, and low pumping power consumption for applications.

Rheology of non-Brownian particle suspensions in viscoelastic solutions. Part II: Effect of a shear thinning suspending fluid

The shear rheology of particle suspensions in shear-thinning polymeric fluids is studied experimentally using parallel plate measurements and numerically using fully resolved, 3D finite volume simulations with the Giesekus fluid model. We show in our experiments that the steady shear viscosity and first normal stress difference coefficient of the suspension evolve from shear-thickening to substantially shear-thinning as the degree of shear-thinning of the suspending fluid increases. Moreover, in highly shear-thinning fluids, the suspension exhibits greater shear-thinning of the viscosity than the suspending fluid itself. Our dilute body-fitted simulations show that in the absence of hydrodynamic interactions, shear-thinning can arise from the particle-induced fluid stress (PIFS), which ceases to grow with increasing shear rate at low values of β (solvent viscosity ratio) and finite values of α (the Giesekus drag coefficient). In a Giesekus suspending fluid, the polymers surrounding the suspended particle are unable to stretch sufficiently at high Weissenberg numbers (Wi) and the reduced polymer stress results in a lower PIFS. When coupled with the shear-thinning stresslet, this effect creates an overall shear-thinning of the viscosity. We then explore the effects of particle-particle interactions on the suspension rheology using immersed boundary simulations. We show that multiparticle simulations are necessary to obtain the shear-thinning behavior of the per-particle viscosity of suspensions in shear-thinning fluids at moderate values of β. Particle-particle interactions lead to a substantial decrease in the PIFS and an enhancement of the shear-thinning of the stresslet compared to the single particle simulations. This combination leads to the shear-thinning of the per-particle viscosity seen in experiments. We also find that very low values of β and finite values of α have opposing effects on the per-particle viscosity that can lead to a nonmonotonic per-particle viscosity versus shear rate in a highly shear-thinning fluid. Overall, the addition of rigid particles to highly shear-thinning fluids, such as joint synovial fluid, leads to increased viscosity and also increased shear-thinning at high shear rates.

Study on the Physical and Chemical Properties of Cement-Based Grout Containing Coal-Fly Ash.

To study the physical and chemical properties of grout containing fly ash, Class II fly ash was used as a mineral admixture and mixed with silicate cement to produce grout, and the rheological properties, strength properties, hydration properties, and microscopic mechanism were studied. The results of the study showed the following. The incorporation of fly ash reduced the thixotropic area of the composite cement slurry, which facilitated pumping in the pipeline conveying process. The inclusion of fly ash reduced the yield stress and plastic viscosity of the cement paste, but the rheological index increased and then decreased with the increase in fly ash, and the composite paste had the lowest degree of shear thinning at 30% fly ash inclusion. The incorporation of fly ash reduced the hydration exothermic rate and total hydration exothermic amount of the composite slurry and prolonged the hydration induction period, but the promotion effect of fly ash on the hydration rate of cement was obvious at 10% fly ash admixture. The admixture of fly ash increased the empty volume of the composite slurry, but the effect on the most probable aperture was not significant, and the porosity of the system increased, resulting in a decrease in compressive strength. The effect of adding fly ash on the hydration products was reflected mainly by the C-S-H gel produced by cement hydration and the change in calcium alumina and Ca(OH)2. Fly ash does not directly participate in the hydration reaction of cement, but it can promote cement hydration and increase the reaction rate of cement. By analyzing the rheological properties, mechanical properties, and hydration properties of fly ash composite cement paste, the comprehensive analysis found that the rheological properties are excellent when the fly ash admixture is 20-30%, and the water-cement ratio can be reduced to improve the strength without affecting the pumping demand.

Motion of a Taylor bubble in a realistic shear-thinning fluid

<h2>Abstract</h2> This talk will focus on the motion of a gaseous Taylor bubble in a capillary tube. Although the dynamics of a bubble in a Newtonian liquid has been the subject of several studies since the seminal works Taylor and Bretherton, the case where the fluid exhibits a shear-thinning behaviour is much less understood. To fill this gap, we derive a lubrication model in the film region to identify the scaling laws for the bubble speed and the film thickness as a function of the Ellis number and the degree of shear-thinning. Our model identifies a universal scaling law for the effective viscosity that accounts for the interplay of the zero-shear-rate and shear-thinning effects. After discussing the features of the front and rear menisci, we present an analysis of the recirculation vortexes ahead of the bubble. In the final part of the talk, we show the results of recent numerical simulations that validate the proposed theory and suggest a strategy to account for the effect of finite capillary numbers on the scaling law for the film thickness in the case of shear-thinning fluids.

Analysis of pulsatile shear-thinning flows in rectangular channels

We present an analysis of pulsatile shear-thinning flows in two-dimensional channels. Characteristic viscosity is determined based on steady-state analysis of non-Newtonian flows and is used to non-dimensionalize the flow system by introducing the non-Newtonian Womersley number. Numerical analyses on various Carreau fluids reveal the existence of master curves related to the amplitude and phase lag of the flows, where the shape of the master curve is determined by the degree of shear-thinning. Furthermore, the pulsatile flow dynamics can be predicted accurately using pre-computed master curves, thus predicting shear-thinning pulsatile flow dynamics without explicit transient computations.

Structure, physicochemical, functional and in vitro digestibility properties of non-waxy and waxy proso millet starches

The structural, physicochemical, gel textural, rheological, and in vitro digestibility properties as well as their relationships of non-waxy proso millet starch (NPMS) and waxy proso millet starch (WPMS) were evaluated by taking normal corn starch (CS) and potato starch (PS) as controls. Proso millet starch was mostly polygonal or spherical, with an A-type crystalline structure. Proso millet starch contained more short-branched chains (DP 6–24) compared with CS and PS. WPMS possessed higher crystallinity and more short-range ordered structures than NPMS. NPMS displayed higher pasting temperature, retrogradation rate and shear thinning degree, and lower gelatinization temperature and enthalpy than WPMS. The hardness and chewiness of starch gel formed by NPMS were higher than those of WPMS. All starch samples exhibited shear thinning behavior in the steady-flow test and typical elastic solid behavior in the dynamic rheological test. Moreover, NPMS was considered a potential formula for functional foods, with its lower rapidly digestible starch (RDS) and higher resistant starch (RS) contents than WPMS, CS, and PS. This paper revealed the influence of amylose content and structure on the physicochemical properties of different proso millet starch.

Polyelectrolyte solutions in Taylor-Couette flows

Taylor-Couette (TC) flow is ideal for studying the flow behavior of complex solutions due to the wide variety of available hydrodynamic flow states. For non-Newtonian solutions, the presence of polymers in solution changes the solution rheology, which in turn modifies accessible flow states. While significant prior work exists on the effects of elasticity and shear thinning of polymer solutions on TC flow, the effects of changes in polymer chain conformation on these properties and the resultant changes in the TC flow states have not been extensively studied. Here, we have explored the effects of changing polymer chain conformation of polyelectrolyte solutions on laminar and turbulent TC flow by using a quasi-static ramp protocol to vary the inner cylinder rotation rates. The ionic strength of the cationic polyacrylamide (CPAM) solution was varied to modify the equilibrium polymer equilibrium conformation and solution rheological properties. In general, as the increasing solution ionic strength increases polymer chain flexibility and decreases elasticity and degree of shear thinning, there is a shift toward more Newtonian-like flow behavior. Additionally, the effects of co- and counter-rotation of the cylinders on the stability of flow states were observed as a function of solution ionic strength, and phase diagrams of the resulting flow states were mapped as a function of the inner and outer cylinder Reynolds numbers. It was found that co-rotation of the cylinders stabilizes some of the polymer-influenced flow states, while counter-rotation de-stabilizes flow states.

Motion of a confined bubble in a shear-thinning liquid

Abstract

Local velocity of thermoresponsive colloidal gels in rate-driven flow

The interplay between flow and attractive interactions in colloidal gels results in complex particle trajectories and velocity profiles that are not evident from bulk rheological measurements. We use high-speed confocal microscopy to investigate the local velocity of a low volume fraction (ϕ = 0.20) thermogelling nanoemulsion system as it flows through a cylindrical capillary at temperatures below and above the gel point. The nanoemulsions are composed of poly(dimethyl siloxane) droplets in a continuous phase of sodium dodecyl sulfate, de-ionized water, and a gelator molecule, poly(ethylene glycol diacrylate). The trajectories of fluorescent polystyrene tracer beads in the oil-rich domains are tracked using two-dimensional image processing. While the velocity profiles agree with those computed from rheometry measurements for nanoemulsion suspensions below the gel point temperature, increasing attractive interactions above the gel point results in statistically significant deviations. Specifically, the velocity measurements indicate a higher yield stress and a larger degree of shear thinning than expected from bulk rheology measurements, resulting in a more plug-shaped velocity profile as temperature and associated interdroplet attraction increase. These deviations from theoretical predictions are likely due to structural heterogeneity. Confocal microscopy images show that small, fluidized clusters are found in high shear rate regions near the capillary walls, while large dense clusters form in low shear rate regions closer to the center of the capillary.

Characterization of vortical structures in T-shaped branches depending on shear-thinning

The characteristics of vortical structures in T-shaped branches with respect to the shear-thinning effect are numerically investigated using a power-law fluid model. By varying the power-law index n, we observe three different flow structures, namely, steady-, harmonic-, and turbulent-like regimes. The time-averaged and instantaneous vortical structures are examined for different values of the local Reynolds number. In the steady regime, stationary vortical structures form near the corners of the T-shaped branch. As n decreases, the vortical structures oscillate back and forth, giving rise to the harmonic regime. Decreasing n further, we observe the turbulent-like regime. In this regime, the vortical structures are torn off near the tips of the vortices and small-scale structures are vigorously generated, constituting more violent behavior than in the harmonic regime. If the local Reynolds number near the wall and near the cores of the vortical structures reaches a critical value, the flow structure becomes turbulent-like after the bifurcation of the T-shaped branch. In addition, the modal characteristics of the vortical structures are analyzed using dynamic mode decomposition with respect to the degree of shear-thinning. As shear-thinning appears in the flow, various high-frequency modes with small-scale vortical structures are observed, and their energies are evenly distributed. This supports the present observation of the vortical structures depending on shear-thinning and -thickening.

Global and local statistics in turbulent emulsions

Abstract