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Hypothesis Waterborne polyurethane (WPU) is a common colloidal dispersion that can aggregate in the aqueous phase to form nanoparticles with hydrophobic polyurethane chains as the core and hydrophilic ionic groups as the shell. Considering their structure and pH-responsive functional groups, WPU nanoparticles could be ideal particulate emulsifiers for preparing pH-responsive Pickering high internal phase emulsions (HIPEs). Experiments A series of anionic WPU with different content of 2,2-bis(hydroxymethyl)propionic acid (DMPA) side chains were synthesized via a polyaddition reaction. The DMPA content, size, ζ-potential, and interfacial behaviors of WPU were then investigated. Furthermore, the effects of particle concentration, internal phase fraction (ϕ), oil type, and pH values on the Pickering HIPEs’ morphology, stability, and rheological behaviors were systematically studied. Finally, we demonstrated the emulsification–demulsification process of WPU-stabilized Pickering HIPEs and discussed its mechanism. Findings Oil-in-water (O/W) Pickering HIPEs with tailored morphology and excellent pH-responsiveness were prepared from anionic WPU nanoparticles. The WPU concentration, ϕ, and oil type had a large impact on the formation and mean droplet size of the WPU-stabilized emulsions. Rheology analysis demonstrated that the strictly limited movement of droplets endowed the WPU-stabilized HIPEs with high stability, shear sensitivity, and excellent thixotropic recovery. By simply changing the aqueous-phase pH value, the WPU-stabilized HIPEs could undergo more than ten emulsification-demulsification cycles, as the physical and interfacial properties of WPU nanoparticles were pH-dependent. The excellent performance of the WPU-stabilized pH-responsive Pickering HIPEs exhibited their potential practical applications, such as for oil transportation and recovery, emulsion polymerization, and heterogeneous catalysis.

The 3D printing thixo-forming process is a method that utilizes semisolid thixotropic feedstock for layer extrusion by controlling feedstock viscosity below the complete melting temperature of metallic alloys to form a 3D structure. The process of producing metallic feedstock has a significant impact on alloy microstructure, which is critical for the material’s printability. This study aims to propose a semisolid heat treatment processing window of Pb-40% Sn alloy for use as feedstock billets for a variety of extruder nozzles (sizes 1–3 mm) during the 3D printing thixo-forming process. Firstly, Pb-40% Sn alloys were cold deformed to reduce the specimens’ diameters. Semisolid treatments for deformed specimens were performed at a variety of semisolid heating temperatures and three separate holding times (2, 5, and 10 min). The microstructure of semisolid feedstock specimens was then investigated. The temperature and time of the semisolid heating processing window of Pb- 40% Sn alloy were optimized to feedstock specimens and thixo-extruding processes with different printed output sizes. Therefore, the proposed semisolid heat treatment processing window was a promising approach to pave the way for the low-cost manufacturing of AM, which yields higher printing rates and improved scalability of printed lines. Additionally, this approach allows for a versatile manufacturing route for producing 3D metal parts with maximum density and intricate geometries as a result of the ability to tailor the microstructure.

In present work, a film forming gel (FFG) was developed through ingenious amalgamation of polymers: Pullulan, Terminalia catappa and Carbopol®971P ® for cutaneous delivery of clotrimazole (CTZ) employing D-optimal mixture design. The developed FFG possess pseudoplastic, viscoelastic, thixotropic characteristics leading to good spreadability (35.71 ± 1.72 g·s, work of shear; 452.73 ± 8.23 g, firmness). Upon solvent evaporation, FFG converted in situ into bioadhesive film (81.90 ± 3.24 g) leading to longer residence on skin surface, prolonged delivery and ~1.3 fold enhanced CTZ skin retention as compare to commercial cream as evident from biopharmaceutical analysis, which is ideal for skin infections treatment. The simulation analysis suggested ≥10 μg/mL (MIC against C. albicans) CTZ concentration maintained for 2 times the days in rat skin as well as human skin as compared to commercial cream. Overall, the developed FFG system ascertained to be promising delivery system for treatment of chronic skin conditions.

Paste slurry exhibits significant thixotropy, which has a significant influence on the slurry pipeline transportation resistance. This paper proposes a novel test method for the thixotropy of paste slurry, which can ensure that the slurry reaches flow equilibrium during the test. Accordingly, the influences of the solid mass concentration, cement-to-tailings ratio, and temperature on thixotropy were studied by employing a control variable method, and the influences of the above three factors on the stress overshoot and rheological parameters were evaluated. The results revealed that the solid mass concentration and temperature have significant influence on the thixotropy. Moreover, with an increase in the solid mass concentration, the time required for the slurry to reach flow equilibrium decreases. The cement content and temperature are proportional to the significance of the stress overshoot, and the change in dynamic yield stress can be considered an indicator for the effective quantification of thixotropy. In the continuous shearing cycles, the maximum apparent viscosity at the start of shearing significantly decreases on the time axis. The solid mass concentration has a significant influence on the minimum apparent viscosity in the slurry flow process, whereas the cement-to-tailings ratio and temperature have no significant influences.

Several authors have studied the effect of particle shape and size on cuttings transport and have reported different, often contradictory, results. The thixotropic nature of the drilling is seldom considered. This study investigates the effects of particle shape and size on cuttings carrying capability of thixotropic fluids in an attempt to better understand the underlying process. Flow equations are based on the mixture approach and are numerically solved using the CFD methodology. Turbulence is modeled using the buoyant k-epsilon model. A relative velocity equation is developed to model the slip between non-spherical particles and thixotropic fluid. It is concluded that in horizontal annuli, cuttings transport does not have a one to one relationship with particle size and/or particle shape. Instead, cuttings transport has a power-law relationship with the ratio of the product of particle shape and flow rate, and particle size i.e. (sphericity x velocity)/particle diameter.

Aims at improving the utilization rate of red mud and preparing a low-cost grouting material for underground engineering, the ultrafine red mud was adopted to prepare a slag-red mud based grout, and its fresh and hardened state properties were investigated comparing with the coarse red mud. The results showed that the incorporation of red mud could prolong the setting time and decrease the viscosity and thixotropy of slag-based geopolymeric grout, and ultrafine red mud has a better decrement effect. Ultrafine red mud has an enhancement effect on the slurry stability. The mechanical strength decreased with the adoption of red mud, while the ultrafine red mud has a higher mechanical strength than coarse red mud. The microstructure analysis showed that red mud plays a filling role in the geopolymerization process, and mechanical activation could increase the reactivity of red mud, furthermore, the iron component in ultrafine red mud could take part in the geopolymerization process. The results shed light on the utilization of red mud and the application of geopolymer in grouting engineering.

Waxy crude oil emulsion has thixotropic properties at the temperature near gel point, which is a macro-mechanical characterization of the structure failure and recovery of waxy crude oil emulsion. In this paper, the thixotropic behaviors of waxy crude oil emulsion near gel point were studied using hysteresis loop formed by stress linear increase and decrease, as well as the structural recovery characteristics. The influence of the loading conditions and water content on the thixotropy of waxy crude oil emulsion were analyzed with hysteresis loop area. The concept of “structural recovery” was introduced to study the degree of structural recovery after different stewing, and influencing factors were taken into account. Results have shown that for waxy crude oil emulsion, the failure to fully restore of the structure after lysis is the cause of the formation of hysteresis loop, and the loading conditions will not affect the strength of thixotropy and the degree of structural recovery. Additionally, the dispersed phase droplets weaken the thixotropy and structure recovery characteristics of waxy crude oil emulsion, and the greater the water content, the weaker the thixotropy. The findings can help to better understand the safe and economic operation of waxy crude oil-water pipeline transportation.

Compounding is a safe method to avoid limitations of a singular gel. Here, composite gels were prepared with konjac glucomannan (KGM) and gum arabic (GA) and evaluated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), water solubility index (WSI), water absorption index (WAI), texture profile analysis (TPA) and rheological analysis. The gel stratified when GA concentration ≥ 2.5%. FTIR indicated that the interactions of KGM and GA were mainly related to hydrogen bonds and acetyl groups, and the solution separated from gels only included GA and water molecules. The microstructures became denser and contained smaller holes at high GA concentrations as seen by SEM. WSI and WAI both increased with GA increasing. Hardness and springiness dropped when GA concentration increased from 0 to 2.0%, but they increased when GA increased from 2.0% to 4.0%. Rheological analysis showed the gels were non-Newtonian pseudoplastic fluids, with anti-thixotropy (GA ≤ 3.5%) and thixotropy (GA ≥ 4.0%). Furthermore, the gels could be classified as non-covalent gels, with higher gel strength at high GA concentrations. The non-covalent linkages included hydrogen bonding and hydrophobic interaction, and hydrogen bonding held the dominated status. Therefore, KGM and GA have antagonistic and synergistic effects.

In this paper, the impact of different substitution levels of cress seed gum (CSG, 0, 5, 10, and 15%) and sucrose (SUC, 0, 5, and 10%) on the rheological properties, textural attributes, syneresis, FTIR and microstructure of native wheat starch (NWS, 4%) gel was investigated. According to the rheological tests, the NWS-CSG and NWS-CSG-SUC gels showed thixotropic behavior and all the samples exhibited shear-thinning flow behavior. Increasing the CSG substitution level up to 15% elevated the apparent viscosity, consistency coefficient whereas the SUC substitution with NWS reduced these values. The higher apparent viscosity, consistency coefficient, and stronger pseudoplastic behavior were obtained for NWS-CSG-SUC gel than NWS gel. The addition of CSG greatly decreased hardness and consistency from 140 to 55.5 g and from 6.9 to 3.0 mJ, respectively during storage at 4 °C for 14 days; while in the presence of SUC these values slightly decreased. After storage, syneresis of NWS and NWS-10%SUC gels increased by 46.78% and 32.11%, respectively; whereas it decreased 19.88% for NWS-15%CSG gel. The SEM images showed that the mixed gels had a denser structure with a smaller pore size. The results indicated that CSG had positive effect in modifying the properties of NWS-SUC mixed gels.

Stereolithography process is predominated by vat based printers, which require the use of low viscosity materials. In this study, a configuration derived from tape casting is used, which allows for printing viscous materials. The role of layer thickness and casting shear rate on the dimensional control, surface roughness, and microstructure texture of printed objects were investigated. This included an examination of the thixotropic and flow behaviors of a highly concentrated alumina suspension. The results showed that the adhesion between layers improved using a high energy dose with thicker layers, but the lateral resolution was reduced. The surface roughness improved using thinner layers with low energy dose at fixed cure depth to layer thickness ratio. The applied shear rates showed no effect on dimensional control.

Texture is one of the main characteristics involved in the acceptance of yogurt and must be monitored for the quality control of the product and for the adequate layout of the processing units. However, the determination of these properties requires expensive equipment, such as rotational rheometers, inaccessible to many industries. Thus, the modeling of artificial neural networks (ANNs) was applied to predict the texture properties of yogurt (output) based on changes in formulation and process conditions (inputs). Non-fat yogurts were produced with different centrifugation conditions and concentrations of protein and enzyme transglutaminase. Three models were developed: ANN-TPA to predict the properties obtained in the analysis of the texture profile (TPA), and ANN-TIX and ANN-VIS to predict thixotropy and viscosity, respectively. The enzymatic and protein variables had an impact of 46.3% and 53.6%, respectively, on the response of ANN-TPA. The shear rate had an impact of 83.7% and 86.0% on the thixotropy and apparent viscosity, respectively. The ANNs were able to predict responses with good precision (R2 >0.95) and low root mean square error (RMSE), showing their potential to be used as a tool to predict the properties of yogurt.

In this paper, the effect of increasing shear rate was studied on the viscosity of shear thickening fluid (STF). It was observed that the viscosity as well as the severity of shear thickening increased with the shear rate. The recovery rate ratio for STF at 25 °C was measured as 88.54% after 30 s, in three interval thixotropy test. Mathematical modeling was also done with the existing viscosity function of STF at 25 °C. It was observed that the viscosity obtained from mathematical model was in good match with the experimental data. For the validation of numerical simulation results, a 3D model of cone and plate was generated in ANSYS FLUENT. A user defined function (UDF) with all the chemical and physical properties of STF was used in 3D model at 25 °C. It was found that STF with UDF depicted similar results as obtained from experimental results, showing shear thinning at low shear rates and shear thickening beyond the critical shear rate. Critical viscosity obtained from experimental, mathematical model and numerical simulation was 0.653 Pa.s at critical shear rate of 10 s−1. Post shear thickening viscosity of 30.017 Pa.s was achieved for experimental and mathematical model and 30 Pa.s for numerical simulation.

The uncontrollable printed structure and poor toughness of three dimensional (3D) printed cement composites hamper their application in buildings. In this study, the polypropylene (PP) and polyvinyl alcohol (PVA) fibers were introduced into the 3D printed calcium sulphoaluminate cement composites (CSACCs) to achieve the stable shape retention and high mechanical strength by controlling the rheological parameters. Experimental results show that the PP and PVA fibers enlarge the linear viscoelastic region (LVR) and increase the elastic modulus of CSACCs. Moreover, these two fibers clearly increase the yield stress and improve the thixotropy of CSACCs in the fiber content of 0.50–1.25%. The relationship between the rheological parameters and structure deformation is revealed by the radar map, and it indicates that the printed structure deformation is improved by controlling the coupling rheological parameters. Furthermore, both PP and PVA fibers are beneficial to the improvement of toughness in the 3D printed CSACCs, and the optimal contents are 0.75 and 1.00%, respectively. In conclusion, developing the 3D printed fiber-reinforced CSACCs with the controllable rheological parameters is significant for improving the printed structures and toughness, which shows a considerable potential in buildings.

We develop highly concentrated vinyltriethoxysilane-coated zirconium oxide/acrylate composites with various nano-to micro-particle ratios as three-dimensional printing materials for use in a supportless stereolithography process. The incorporation of nano-particles with micro-particles at certain particle volume ratios resulted in densely packed network structures that generate good particle dispersion as well as a uniform particle distribution. Structural deformation and time-dependent structural recovery were analyzed by the three interval thixotropy test. We found sustained solid-like behaviors in the composites composed of 50:50 and 30:70 nano-particle to micro-particle ratios. Phase diagrams using structural deformation parameters confirm that the 50:50 and 30:70 composite's structure contributes to their good colloidal stability and printability. The addition of nano-particles also enhances the total heat release during the curing process due to improved light scattering, and the amount of heat release affects the degree of photo-polymerization in the printing material.

The catalyst layers of proton exchange membrane fuel cells are usually fabricated by (1) mixing catalyzed carbon black, ionomer solution, and solvents to form an ink, (2) coating this ink by spraying or transferring from decal to a membrane or gas diffusion layer, and (3) drying. During the mixing stage, dispersion methods, such as ball milling and sonication, are employed to homogenize the ink and prevent agglomeration of solid ingredients. The present study focused on the first step of fabricating the catalyst layer and conducting a rheological investigation on catalyst inks. The viscosity and thixotropy of inks that were prepared by ball milling and sonication, respectively, were measured, and some major factors affecting the change in the viscosity were analyzed. The catalyst layer inks exhibited pseudoplastic fluid behavior, which was clearly non-Newtonian, and their viscosity decreased with stress rate. The results indicated that the ionomer solution plays a decisive role in the dispersion of carbon-supported catalysts. Hence, homogeneous ink cannot be formed without the ionomer solution. The viscosity of the ink was dependent on the solid content ratio and the dispersion method used, while the dispersion time and amplitude were less critical. Ball milling and sonication methods result in inks with different rheological characteristics. Rheological data indicate that the thixotropic recovery of the ink prepared by ball milling is faster in comparison to that prepared by sonication.

Injectable bone cement combined with minimally invasive surgery has attracted much attention in recent years due to its rheological properties directly influencing its convenience and effectiveness in clinical applications. This study systematically investigates the influence of particle size distribution on the rheological, injectability, and anti-washout properties of borosilicate bioactive glass bone cement (BSBGC). Meanwhile, the setting time is also evaluated. Furthermore, a rheological model is proposed that describes the flow behaviour of BSBGC. Rheological results indicated that all the BSBGC samples exhibited non-Newtonian fluid behaviour, with thixotropic and shear-thinning properties. The BSBGC sample prepared via ball milling for 24 h (designated as CBM24) presented the largest thixotropic loop area, confirming that CBM24 has the greatest thixotropy. Particle size distribution greatly influenced the sol-gel time point, elastic and loss moduli, and viscosity of the BSBGC. Based on rheological results, four models (Ostwald–de Waele (Power law), Bingham, Herschel–Bulkley, and Casson) were selected and applied to fit the experimental data. It was found that the Power law and Herschel–Bulkley models were the most suitable for modelling the flow behaviour of the BSBGC, with the CBM24 sample having the greatest fitting proximity under the Power law model. Injectability test results showed that all BSBGC samples could be easily injected. Anti-washout test results indicated that CBM24 presented the most stable structure based on having the best anti-washout properties. Moreover, CBM24 had a reasonable initial and final setting time.

This paper investigates the rheological properties of methylcellulose-silica-ionic liquid nanocomposite (2-MCPS-MC) on the rheological properties (apparent viscosity (AV), plastic viscosity (PV), yield point (YP), 10-s gel strength, 10-min gel strength, and thixotropy according to API requirements) of water-based mud, and comparing these properties with the properties of the silica-free methylcellulose (MC) as drilling fluid additive. The physicochemical properties of the MC and 2-MCPS-MC compounds were studied using 1H NMR, FTIR, Raman-spectroscopy, XRD, FE-SEM, AFM, and TGA. By FE-SEM and AFM, it is proven that the silica had an excellent dispersion in a spherical shape on the MC polymer. Three samples were prepared: the first is the commercial water-based mud, while the second and the third samples are MC and 2-MCPS-MC, respectively. The samples of MC were prepared in four concentrations (2%, 1.5%, 1.0% and 0.5% by weight). Throughout the test, density remained at 7.6 (lbs/gal) for mud fluid and 8.5 (lbs/gal) for MC and 2-MCPS-MC at pH 9.0. The results confirmed that the optimum concentration of MC and 2-MCPS-MC, which meet the required API code, was between 1 and 1.5%. The addition of 2-MCPS-MC to water-based mud enhances filtration properties. Response surface technique (RSM) with central composite design (CCD) was also used to optimize the drilling fluid properties to achieve the optimal response to AV, PV, YP, Gl, and Thixotropic using a Design expert software. The results obtained by RSM showed consistency between the experimental and theoretical data.

Cemented paste backfill (CPB), an engineered mix consisting typically of tailings, cement and water, has become a regularly used structural material in most mines worldwide. The performance of the CPB structure is dependent both on the quality of each constituent and the rheological behavior of fresh CPB during placement into mined-out voids. A connection between the backfill's rheological behavior and the structural changes governing thixotropy and structural breakdown can provide a better understanding of the different yield stress-viscosity results. In this study, the mineral admixture effect on rheological properties of fresh CPB slurry is studied by considering a combined assessment of time dependency and thixotropy. A total of three mineral admixtures such as fly ash (FA), granulated blast furnace slag (Slag) and silica fume (SF) were used for the preparation of CPB material. The rheological parameters, mainly yield stress and plastic viscosity, were examined by the Bingham model. Results indicate that the thixotropy of fresh CPB decreases with FA dosage, while the addition of Slag and SF gives lower thixotropy values at early ages, and a higher rate of thixotropy acquisition at a later age. A partial replacement of cement with FA leads to an increase in the static deformability and significant improvement in fluidity of CPB, and a plot of thixotropy versus plastic viscosity results in a linear correlation between them. Moreover, the addition of slag particles reduces the yield stress and plastic viscosity of CPB, while SF-containing CPB exhibits improved yield stress and lower plastic viscosity. Plotting thixotropy versus plastic viscosity generates a poor linear relation for SF- and Slag-containing CPB slurries. The findings of this study will be useful in the lucrative design, efficient operation and safe production of early-age CPB material.

Hypothesis The rheology of complex suspensions, such as nuclear waste slurries at the Hanford and Savannah River sites, imposes significant challenges on industrial-scale processing. Investigating the rheology and connecting it to the agglomerate morphology and underlying particle interactions in slurries will provide important fundamental knowledge, as well as prescriptive data for practical applications. Here, we use suspensions of nano-scale aluminum oxyhydroxide minerals in the form of boehmite as an analog of the radioactive waste slurry to investigate the correlation between particle interactions, agglomerate morphology, and slurry rheology. Experiments A combination of Couette rheometry and small-angle scattering techniques (independently and simultaneously) were used to understand how agglomerate structure of slurry changes under flow and how these structural changes manifest themselves in the bulk rheology of the suspensions. Findings Our experiments show that the boehmite slurries are thixotropic, with the rheology and structure of the suspensions changing with increasing exposure to flow. In the slurries, particle agglomerates begin as loose, system-spanning clusters, but exposure to moderate shear rates causes the agglomerates to irreversibly consolidate into denser clusters of finite size. The structural changes directly influence the rheological properties of the slurries such as viscosity and viscoelasticity. Our study shows that solution pH affects the amount of structural rearrangement and the kinetics of the rearrangement process, with an increase in pH leading to faster and more dramatic changes in bulk rheology, which can be understood via correlations between particle interactions and the strength of particle network. Nearly identical structural changes were also observed in Poiseuille flow geometries, implying that the observed changes are relevant in pipe flow as well.

The non-homogeneous flow of a thixotropic fluid around a settling sphere is simulated. A four-parameter Moore model is used for a generic thixotropic fluid and discontinuous Galerkin method is employed to solve the structure-kinetics equation coupled with the conservation equations of mass and momentum. Depending on the normalized falling velocity $U^{*}$, which compares the time scale of structure formation and destruction, flow solutions are divided into three different regimes, which are attributed to an interplay of three competing factors: Brownian structure recovery, shear-induced structure breakdown, and the convection of microstructures. At small $U^{*}( \ll 1)$, where the Brownian structure recovery is predominant, the thixotropic effect is negligible and flow solutions are not too dissimilar to that of a Newtonian fluid. As $U^{*}$ increases, a remarkable structural gradient is observed and the structure profile around the settling sphere is determined by the balance of all three competing factors. For large enough $U^{*}(\gg 1)$, where the Brownian structure recovery becomes negligible, the balance between shear-induced structure breakdown and the convection plays a decisive role in determining flow profile. To quantify the interplay of three factors, the drag coefficient Cs of the sphere is investigated for ranges of $U^{*}$. With this framework, the effect of the destruction parameter, the confinement ratio, and a possible nonlinearity in the model-form on the non-homogeneous flow of a thixotropy fluid have been addressed., 28 pages, 16 Figures, accepted manuscript at Applied Mathematical Modeling

Ice-containing cemented paste backfill (ICPB) is a novel type of backfill material that has both the advantages of traditional CPB and the underground cooling function. The pipeline transport characteristics of ICPB need to be investigated to promote its application, which are influenced by the rheological properties. The objective of this study is to investigate the rheological properties of ICPB by means of experimental and computational fluid dynamics (CFD) methods. The rheological parameters were measured using a rheometer and the slump test was performed in a cylinder slump. A calculation model that considered the slump mold lifting and the ice particle phase change was established to simulate the cylindrical slump. The results indicate that the ICPB behaved as a Bingham fluid. The yield stress, plastic viscosity, and thixotropy increased with an increase in the ice/water ratio and concentration, while the cylindrical slump decreased under the same variation. The simulation results of the cylindrical slump were compatible with the experimental results. Furthermore, the numerical study indicates the slump increased when the test temperature was increased from 285 K to 305 K. The results found in this study can be used as a reference for the pipe design of ICPB.

The paper describes the data on unusual rheological properties of detonation nanodiamonds (DND) hydrosols and presents the fractal model explaining such behavior. The hydrosols of DND with particles size of 4–5 nm and concentration range of 1.1–7.3 wt% with negative (ζ 0) electrokinetic potentials have been studied by rotational viscometry, small-angle X-ray scattering, nuclear magnetic resonance and Cryo Electron Tomography. Remarkable hysteresis of viscosity and thixotropic effect demonstrate the sol-gel transition at very low concentrations of the DND: 4–5 wt% for ζ > 0 and 5–6 wt% for ζ

Hydration of the seeds of chan (Hyptis suaveolens (L.) Poit) produces a mucilage that exudes and agglutinates on the surface; the mucilage is difficult to separate from the seed. This study proposes a new strategy for the extraction of hydrated mucilage using the surface response methodology (RSM) and polynomial equations for the optimization of the mucilage extraction by mechanical agitation (MA) and ultrasound-assisted extraction (UAE). The results of the solid:liquid extractions were fitted to a second-order polynomial model for the optimization; the evaluation of the experimental response variables included the yield, viscosity, thixotropy, flow behavior index, consistency coefficient, glass transition temperature, melting temperature, enthalpy and heat capacity. The predicted values of the viscosity, thixotropy, glass transition temperature and melting temperature were significantly different (p

Hypothesis Electrorheological fluid (ERF) is a kind of suspension or colloid composed of fine particles and insulating oil as continuous phase. The second miscible liquid phase with less affinity to the particles than the continuous phase is expected to influence particles aggregation, assembly and spanning mesostructures. Hence, it should be possible to tune the rheological and electrorheological properties and stability by the addition of second miscible liquid with different chain length and substituents. Experiments We developed a giant ERF (GERF) with a binary liquid phase (BLP) by the addition of alkane to the silicone oil continuous phase. We studied the shear stress and viscosity under different shear rates, thixotropy and particle size distributions of these suspensions and characterized the concentration variation of GERFs under quiescent conditions by measuring the backscattering light intensity variation through vertical scanning. Findings The dispersed particle size distribution is broadened, which produces higher static yield stress and lower zero-field viscosity than those of a single-liquid-phase GERF. The ER efficiency is much higher with the addition of alkane, reaching 10656, which is 1.8 times larger than that of single-liquid-phase suspensions. We performed 100-day stability testing and found that the GERF with 1-phenyldodecane showed excellent stability and performance.

Magnetorheological fluids (MR Fluid) have magnetic particles suspended in them and as a result of which they show a tendency to change their behavior in the presence of an applied magnetic field. Inverse thixotropy or sometimes called Rheopexy is property of fluid in which the fluid’s viscosity increases with time as it is sheared at a constant rate. MR Fluid, like any other smart fluids, has a large particle size and as a result, it has a tendency in which the suspended particles tend to settle due to the gravitational pull and form hard cake due to agglomeration. This leads to the case in which the fluid loses its property of changing the viscosity with change in magnetic field because there are no particles left suspended in the fluid that can be aligned under the influence of magnetic field. To measure the sedimentation or settling rate of MR fluid, it is necessary to measure particle concentration at various time intervals and at different height of the fluid. In this article, various methods are illustrated with their advantages and limitations, which can provide help in generating the fluid concentration profile.

Smart materials such as Magnetorheological Fluids (MRF) have become sought-after material in wide ranging applications due to the ability to change properties in a controlled manner under application of stimulation such as a variable current, magnetization, heat, force, stress and deformation. Magnetorheological fluids in the rheological fluid domain has found use due to its ability to change its shear strength based on the applied magnetic field. Magnetorheological fluids are composed of magnetizable micron sized iron particles and a non-magnetizable base/ carrier fluid. The shear strength of commercially available MRF varies from 0 to 100kPa under the effect of the magnetic field. In a valve mode, the Magnetorheological damper (MR Damper or MRD), the MR fluid flows between two-fixed poles, which are parallel to each other. When the fluid flows between them, due to the applied magnetic field the magnetic particles align themselves in a chain form (on state) which is easily reversible when the field is removed (off state). Physical change of the fluid from liquid to semi-solid is controlled by the magnetic field, which makes the fluid a reliable member in active vibration control applications. In this study, two types of magnetizable particles (Carbonyl iron (CI) and Electrolytic iron (EI)) are taken and characterized using an Anton Paar MCR 702 rheometer set-up, in on and off states. To overcome issues like sedimentation, agglomeration and corrosion of the MR fluid, the iron particles are coated with natural gum like guar and xanthan, to the carrier fluid grease and other thixotropic additives are added. The addition of grease and thixotropic additives will inhibit the microbiological degradation of natural gum over an extended period. These engineered MR fluids are then used to analyze the performance of designed and developed stand-alone MR damper, which is tested using an electro-dynamic shaker. The response and damping performance of the MR Damper is analyzed with controlled changes in variables including percentage of additives in MR fluid & magnetization values

[EN] In this study, the viscosifiers for diesel oil drilling fluid were prepared using Tunisian clay modified with cationic surfactant for five concentration levels from 0.5 to 4.0 times the cationic exchange of purified clay (CEC). The organo-modified clay samples were characterized by X-ray diffraction (XRD), Infrared spectroscopy (FTIR), scanning electron micrography (SEM) and specific surface area (BET model). Oil–clays suspensions were investigated using polarized light optical microscopy (PLOM) and double cone rheometer. The influence of surfactant concentration on rheological properties of suspensions is related to the different microstructures development which depend on surfactant arrangement in the interlayer of clay. The results showed the growth of yield stress and consistency coefficient as the surfactant concentration is increased and the best behaviors were observed for the 3.0 CEC concentration. This sample was tested for two weight percents (5 and 10 wt%), the higher Herschel Bulkley parameters (τ 3.6 Pa, K = 0.397 and n = 0.85) were found for the organoclay at 10 wt%. The latest sample has the high thixotropy loop area so can be used as viscosity enhancer for the oil drilling fluid., The authors would like to thank the Faculty of Sciences of Gabes and the Tunisian Ministry of Higher Education and Sci-entific Research for its help in financing internship in Spain

This study aims to develop a new formulation of a sauce by incorporation of air in the oil phase. First, the effect of mono- and diglyceride (MDG) concentration (2, 6, and 10 wt.%), whipping speed (1100, 3200, and 5400 rpm) and time (up to 60 min) on foam properties were studied. The desired foam (overrun ≥ 60%) achieved by oil containing 10 wt.% MDG at 3200 rpm for 10 min. Optical micrographs showed stable air bubbles (20–25 μm) even after six months of storage. Then this foam was used to produce an aerated reduced-fat sauce. For purposes of comparison, aerated sauce, along with commercial full- and reduced-fat sauces, was analyzed by measuring the rheological properties, stability, and color. The power-law equation was used to model the behavioral features (R2 = 0.99). Compared with the full-fat sauce, the consistency coefficient (K) of aerated and reduced-fat sauces was more close to each other, and their flow behavior index (n) was higher. Overall samples showed shear-thinning thixotropic flow behavior. Also, aerated sauce showed acceptable stability and lightness (L*). These findings affirm the potential of nonaqueous foam for the production of reduced-fat sauces, which could be meet consumers’ and marketing requirements.

The study sets out to evaluate the thixotropy of conventional concrete containing rheology modifiers using various methods of rotational rheometry. Five mixes were examined: the control, two mixes with viscosity modifying agent (VMA) and superplasticiser (SP) respectively, a mix with combined viscosity modifying agent and superplasticiser (VMA + SP) and the last mix with an increase in water content. These mixes were formulated to achieve concrete with varying rheological properties. Tests were carried out to examine the evolution of rheology parameters (static yield stress, dynamic yield stress and plastic viscosity), thixotropy index, shear thinning and thickening, flocculation properties, torque decay pattern (with a subsequent drop in apparent viscosity), and hysteresis loop. Results show that conventional concrete known to be a shear thinning and thixotropic material, can possess anti-thixotropic (rheopexy) and shear thickening properties depending on the condition pre-history, resting time, shearing rate and inclusion of rheology modifiers. These factors also influence the magnitude of the thixotropy but not necessarily the evolution of thixotropy. Inclusion of VMA in conventional concrete had only slight influence (both increasing and decreasing depending on the method of measurement) on its thixotropic behaviour while the inclusion of SP, VMA + SP and increased water considerably influenced concrete’s thixotropic behaviour in a similar pattern. However, each rheology modifiers had its unique influence. VMA significantly improves the evolution of concrete’s viscosity; inclusion of SP tends to result in a rheopectic concrete; addition of VMA + SP and pre-shearing of concrete may result in an unstable thixotropy, while SP can initially dominate the thixotropic behaviour of concrete containing both VMA and SP, VMA’s influence may later surpass that of SP; more water in concrete tends to result in a lesser rate of thixotropic structure breakdown.

Shear history exerts a great impact on the rheological properties, and thus the consolidation and construction quality of concrete. This study experimentally investigated the time-dependent rheological behavior of cementitious pastes under continuously shear mixing. A parameter describing the disappearance of shear thinning at the decelerating curve was proposed. Results indicate that continuous shear mixing could not effectively hinder the development and evolution of thixotropy and yield stress of cementitious pastes over time. After continuously shear mixing for a while, the critical shear rate corresponding to the disappearance of shear thinning increased. Cementitious pastes tended to exhibit shear thinning behavior at relatively lower shear rate ranges. At higher shear rates, the rheological behavior of cementitious pastes after continuously shearing was strongly dependent on the composition of cementitious materials. The evolutions of rheological properties after continuously shearing were associated with the physical nature and chemical hydration of cementitious pastes.

This paper presents a novel rheological thixotropy model that specifically appertains to the characterisation of materials that are suitable for 3D printing of concrete (3DPC). The model accounts for both physical and chemical influences on a material’s microstructure, denoted by R t h i x (re-flocculation) and A t h i x (structuration) respectively. Rheological analyses are performed on a reference material with varying superplasticizer (SP) and nano-silica (nS) dosages in order to determine their effects on the aforementioned parameters. Specific focus is placed on the re-flocculation thixotropy mechanism. The advantages of adding nanoparticles to concrete for 3DPC is practically validated by printing circular hollow columns until failure occurs. The result is supported by the thixotropy model, which is applied to the materials that are used for the 3DPC tests. It is concluded that, for this study, R t h i x is a better measure of thixotropy behaviour that is suitable for 3DPC than A t h i x .

Egg yolk plays a crucial role in mayonnaise making. As an emulsifier, egg yolk controls the texture and stability of mayonnaise. Freezing extends the shelf-life of the yolks, however it causes gelation which negatively alters the functional properties of the yolk including its emulsifying ability. At 10% wt/wt concentration, sucrose and sodium chloride are effective gelation inhibitors that have been widely used over the years. Recently, it was found that hydrolyzed egg yolk proteins (HEY) can prevent egg yolk gelation at only 5% (wt/wt) concentration, nevertheless further research is still needed to evaluate the resulting yolk characteristics. In this study, frozen-thawed yolk products containing 5% HEY, 10% salt, and 10% sugar were used as emulsifiers in mayonnaise. Rheological properties (i.e. firmness, thixotropy, yield stress, stability), heat stability, and particle size distribution were characterized and compared to those of mayonnaise prepared with fresh yolk without additives and fresh yolk containing 5% HEY. Results showed that the mayonnaise prepared with frozen-thawed HEY yolk has very high heat stability as well as comparable rheological properties, texture and microstructure to the mayonnaise formulated using fresh yolk.

The rheological behavior of low-calcium fly ash suspensions in activating solutions of colloidal silica and alkali hydroxide is investigated. The study is aimed at relating the rheological behavior of alkali-silicate activated low-calcium fly ash (AAF) suspensions with Portland cement paste suspensions. The yield stress and the viscosity of the AAF suspensions increase with the alkalinity of the colloidal solution, which is due to changes in the surface charges on fly ash particles with the change in the ionic medium. Increasing the alkalinity results in a less negative zeta potential of fly ash in the alkaline solution of colloidal silica and an increase in the yield srtess of the AAF suspension. The thixotropic behavior in AAF suspensions is associated with structure breakdown to a finely dispersed suspension of particles produced by shearing. Energy measurements indicate a very slow change in the internal particle structure with age at room temperature. A comparison of AAF suspensions is presented with suspensions of Portland cement in water, which are proportioned for similar physical flow characteristics and yield stress. AAF suspensions have a larger solid fraction than the cement suspensions in water of comparable yield stress. The zeta potential of cement particles in water is less negative when compared to fly ash in alkaline-silicate solutions. The AAF suspensions of comparable yield stress exhibit a significantly higher viscosity than the cement suspensions in water. Cement paste and AAF suspensions exhibit a rate dependent yield response. Cement paste suspensions exhibit a threshold strain rate for minimum yield stress. In AAF suspensions there is a continuous decrease in the yield stress at lower strain rates. The thixotropic behavior in cement paste is influenced by chemical ageing which produces a rapid recovery of yield stress. In comparison, there is very little ageing at room temperature in the AAF suspensions and a very slow recovery of yield stress after shearing.

Camellia-oil based oleogels were structured at a constant tea polyphenol-palmitate (Tp-palmitate) particles concentration of 2.5% (m/v) and varying citrus pectin concentration of 1.5, 2.5, 3.5 and 4.5% (m/v) using emulsion-templated method. Optical and laser confocal microscope were used to observe the microstructure of emulsions, dried products formed by freeze-drying the emulsions, and oleogels obtained by further shearing the dried products. Series of rheological measurements were performed to evaluate effects of citrus pectin concentration on the gel strength of emulsions and oleogels. The texture of dried products, and the oil binding capacity, oxidative stability and potential application of oleogels were characterized, respectively. Results revealed that citrus pectin concentration had significant effects on the physical properties of emulsions, dried products and oleogels due to the reinforcement from the interactions and entanglements of polymer. With the increase in the citrus pectin concentration, the stability and viscoelasticity of the emulsions increased, the hardness of the dried products with more compact structure became larger, and the oil binding capacity and gel strength of the oleogels enhanced. Oleogels displayed a high gel strength of G′ > 17,000 Pa and a good thixotropic recovery when the citrus pectin concentration was higher 1.5% (m/v). The polyphenol-rich oleogels had high anti-oxidative activity. The hedonic score in overall quality of cakes prepared with oleogels replacement of butter and that of cakes with butter were 21.49–27.58 and 32.03, respectively. This research gave a reference for preparing oleogels with food-approved polymer and provided more information for their potential application as substitution of solid fats.

Effects of molecular weight (MW), charge density (CD) and structure of polyacrylamide (PAM) on conditioning of excess sludge (ES) and ozonized sludge (OS) with/without ferric salt pretreatment (FSP) were investigated by orthogonal experiment. Rheological and morphological analyses were conducted to elucidate conditioning mechanism of ES and OS. OS had smaller particle size, worse filterability, lower flowability and more evident thixotropy than ES, and required FSP before conditioning. Orthogonal experiment showed that the optimal conditioner was PAM with medium MW and cross-linked structure for ES, and high MW and linear structure for OS after FSP, respectively. The specific resistance of filtration and capillary suction time were reduced to (1.2 ± 0.1) × 1012 m/kg and 25.8 ± 1.9 s for OS after FSP and optimized PAM conditioning, and particle size increased from 30.3 for OS to 269.7 μm after conditioning. The limiting viscosity, structural strength and thixotropy of conditioned OS were lower than conditioned ES, but greatly enhanced by FSP. Morphological analyses confirmed that ozonation cracked microbial cells of sludge, and FSP obtained more porous structure and reinforced floc strength of PAM conditioned OS.

Waxy crude oil presents poor flowability and complicated rheological behaviors near and below its gelation temperature. In recent years, high voltage direct current electric field has emerged as a novel approach to significantly reduce the viscosity of waxy crude oil below its wax appearance temperature, but the effect of electrical treatment on the structural behaviors of gelled waxy crude oil remains unknown. In the present study, the viscoelasticity, yielding behavior, and thixotropy of gelled waxy crude oil experienced electrically-treatment were investigated over a range of electrical field strength of 0–0.8 kV/mm and treatment temperature between the wax appearance temperature and the pour point. We demonstrate for the first time that the structural strength of gelled waxy crude oil can be significantly weakened after electrical treatment below its wax appearance temperature. The magnitude of the reduction increases with the electric field strength increasing and treatment temperature decreasing. However, no significant influence was found on the wax appearance temperature, wax disappearance temperature, and the amount of precipitated and dissolved wax, revealing the phase equilibrium of wax in crude oil not affected. The investigation of the wax crystal microscopy shows that the wax crystals in the electrically-treated waxy gels are generally larger, and have larger aspect ratio and boundary box fractal dimension, which indicates that the size and morphology of wax crystals are varied by the influence of the electrical treatment.

In considering the adverse nutritional and flavor consequences of thermal pasteurization on fruit juices, freshly squeezed and unpasteurized fruit juices, commonly called raw juices, are of increasing demand as they are served in bars, restaurants and at home. Apparently, due to lack of controlled processing regime as did in a juice factory, the raw juice often undergoes a rapid phase separation and is at the risk of microbial unsafety. To this end, an attempt of cold ultrasound treatment (CUT, 87.52 W/cm2, 10 °C) was implemented to a raw tomato juice up to 30 min. Appreciatively, the physical stability, nutritional value and microbial safety substantially improved. On a CUT time scale, cloud stability and total phenolic content continuously increased; the total plate count was adversely altered; the rheological parameters (viscosity, thixotropy and shear-thinning tendency) and total carotenoids obtained shared a parabolic changing pattern but peaked at 15 min and 10 min, respectively. Finally, the ascorbic acid sharply increased at an earlier stage (5 min), and then remained stable throughout the whole process. Notably, the occurrences of these improvements are of spatial-temporal nature and resulted from different cavitation induced stress fields. At the initial stage, CUT chiefly worked via the mechanical field with the particles in pulp phase, making them smaller and releasing the soluble materials into serum phase. When the particles larger than approximately of 160 μm were completely disintegrated, the CUT entered its second stage and mainly functioned in the serum phase via both mechanical and chemical fields. As a result, the serum pectin and carotenoids were depolymerized and degraded, respectively. The present results are valuable in uncovering the mechanism and kinetics underlying the ultrasound treatment of fruit juices and the present CUT is highly recommended due to its high maneuverability and excellent performance.

The sesame oil-in-water Pickering emulsions using cellulose nanofibers (CNF) as the emulsifier were prepared for the rheological study, aiming at establishing relationship between emulsion viscoelasticity and morphology. A droplet cluster structure forms in those systems due to multicomponent properties of sesame oil and fibrillar structure of CNF. Its deformation and relaxations result in weak strain overshoot behavior in large amplitude oscillatory shear (LAOS) flow, but not affect the scaling behavior of small amplitude oscillatory shear (SAOS) responses. The relaxation time scales can be evaluated by creep of emulsions. This structure can evolve during ramp shear flow, rearranged and oriented at the higher flow rates, which has evident influence on the thixotropic behavior of emulsions. The mechanisms of evolution and relaxations of droplet cluster structure are traced through rheo-optical way. This work presents some interesting results and paves a possible way to control morphology and viscoelasticity of edible Pickering emulsions.

Rapid Visco Analyzer (RVA) is a reliable viscometer that is commonly utilized to measure the pasting properties of starch. The conventional model of RVA can only determine starch pasting properties at heating temperatures up to 95 °C, which thus cannot evaluate the performance of starch related to high-temperature processing, such as retorting, jet-cooking and extrusion. In this study, RVA 4800 ‒ the latest model of the viscometer having high-temperature capability ‒ was deployed to determine the pasting properties of representative waxy, normal and high-amylose starches of 1.8–69.7% amylose contents at heating temperatures of 95–140 °C. As the temperature increased from 95 to 140 °C, the pasting temperatures and peak viscosities of most waxy and normal starches remained unchanged, but their holding strengths and final viscosities decreased, which could be attributed to thixotropic breakdown and thermal degradation of starch molecules. Consequently, the paste adhesiveness or gel hardness of most waxy and normal starches was reduced at higher temperatures. By contrast, heating at temperatures above 120 °C completely gelatinized wrinkled pea and high-amylose maize starches, allowing the starch granules to swell for viscosity development and subsequent gel formation. Matrix structures of the freeze-dried starch pastes and gels were observed under scanning electron microscope to elucidate how the changes at granular and molecular levels at the tested cooking temperatures influenced the pasting and gelling properties of different starches. This research offered new insights into the relationships between the thermal properties, pasting properties and gelling ability of various starches at heating temperatures of 95–140 °C by using RVA 4800.

This work presents a comparative study of the effects of nanosilica particles on the fresh state properties of a Portland cement paste designed for 3D printing. Cement pastes were prepared with different solid substitutions of cement by pozzolanic particles and their yield stress was measured after different resting times. Rheological results were used to obtain the rate of thixotropic buildup of each paste, which was used to compute the parameters of an ideal 3D printing process (layer height, time to extrude one layer, and horizontal velocity). Results obtained for nanosilica were compared with results from other three commonly used pozzolanic nano and micro particles (microsilica, metakaolin and nanoclay). All pozzolanic particles studied were capable of increasing both the initial yield stress and the rate of thixotropic buildup of cement paste through different mechanisms; nevertheless, these increases did not translate directly into a more efficient 3D printing process due to the limitations imposed by the need to avoid cold joints between layers. It was concluded that even though nanosilica particles are more efficient thickeners for cement paste than the other particles studied, their effect is constrained by the maximum and minimum printing velocities. Additional chemical accelerators should be considered to reach the full potential of nanosilica as a structural buildup agent.

Rheological behaviour of the mushy zone is dependent on the microstructure and related to parameters such as temperature, shear rate and shear strain/time. However, constitutive modelling of the rheological behaviour is difficult due to the diversity of the parameters. This study focuses on the influence of the microstructure and the above parameters on the rheological behaviour of partially solidified A356 alloy and establishing a constitutive model accordingly. During solidification, the evolution of α-Al phase leads to the changes of the apparent viscosity of mushy zone. Steady-state viscosity and peak viscosity measured by rotational rheometry reveal the thixotropy of the mushy zone. The thixotropic strength is found to increase with increasing shear rate and decreasing temperature. The peak viscosity, as well as the steady-state viscosity, is found to obey a power law model and is modelled using the power law model with the coupling of temperature and shear rate. Furthermore, a constitutive model with temperature, shear rate, shear tress and shear strain/time as parameters which describes the rheological behaviour of the mushy zone of partially solidified A356 alloy accurately and completely is established. Comparing with previously reported experimental results, the FEM simulation employing the constitutive model works well in enabling visualization of the viscoelastic filling process of A356 alloy in mushy zone. The constitutive model provides a solution for characterizing the forming behaviour of other mushy zone/semi-solid aluminium alloys with corresponding rheological parameters.

The effect of calcium ions (Ca2+) on the rheological behavior, gel properties, and microstructure of Ca2+–Mesona blumes polysaccharide (MBP) gels was evaluated by using rheological, X-ray diffraction, and microstructure analysis. Ca2+ caused significant changes in the viscosity, elasticity, thixotropy, and thermal properties of MBP. Ca2+ increased the crystallinity of the Ca2+–MBP gel system, and induced new diffraction peaks appeared at approximately 12.4°. Microstructure analysis of Ca2+-MBP gels showed that Ca2+ could promote the formation of gel networks. The gel network became dense, and the surface became smooth. In the presence of Ca2+, electrostatic interactions played an important role in promoting gel formation and maintaining the three–dimensional structure of the gels. Based on the observed rheology–structure relationship, a general “egg box” gelling mechanism for Ca2+/MBP aqueous mixtures was proposed.

Pickering High Internal Phase Emulsions (HIPEs) stabilized by food-grade particles have received considerable attention. In this work, we first demonstrated the use of chitosan-caseinophosphopeptides (CS-CPP) nanocomplexes as particulate emulsifiers to stabilize the interface of natural oils and water. For this purpose, we developed the CS-CPP nanocomplexes through electrostatic interactions and demonstrated their application in the formation of stable Pickering HIPEs. The microstructures, e.g., interfacial frameworks, of the CS-CPP nanocomplexes partition between the continuous phase and interfacial region, and the states of the droplets of Pickering HIPEs were visualized by confocal laser scanning microscopy (CLSM) and an optical microscope. The compressed droplets in Pickering HIPEs formed a percolating 3D-network framework that endowed emulsions with viscoelastic, self-supporting, and ideal thixotropic features. In addition, the gelatinous state of Pickering HIPEs combined with robust and compact CS-CPP nanocomplexes formed an interfacial layer around the droplets, thus depressing the oxidation of linseed oil. The contents of primary and secondary oxidation products in HIPEs were lower than that in bulk oil and emulsions stabilized by surfactants. An in vitro gastrointestinal (GI) model was constructed to characterize the lipid oxidation, lipid digestion and curcumin bioaccessibility of Pickering HIPEs. Interestingly, this route enhanced the bioaccessibility of curcumin from 20.49% (bulk oil) to 49.21% (Pickering HIPEs). This work offers a facile method to develop Pickering HIPEs by food-grade particles, which help to fill the gap between the performance of CS-CPP nanocomplexes-stabilized Pickering HIPEs and potential applications as oral delivery systems of nutraceuticals.

Concrete, mortars, and grouts in fresh state can be pumped, sprayed and now even printed with additive manufacturing. For this type of materials, the knowledge of flow properties is crucial for adequate control during its applications. The thixotropy of cementitious materials must be taken into account due to the benefits of the change of viscosity especially in self-levelling applications. In this study, a rheological approach is used to characterize the thixotropy of a cement paste and to study both the physical and chemical thixotropies. White Portland cement pastes to cement ratios of 0.25. 0.34, 0.40 and 0.46 were prepared. For all pastes a commercial high range water reducing admixture (HRWRA) was used in concentrations of 0.04%, 0.120% and 0.360% and for samples with 0.360% concentration, the same mixes have been done with the addition of a commercially available viscosity modifying admixture (VMA). Results show that by measuring the viscosity over-time it is possible to uncouple the contribution of the chemical and physical thixotropy. An empirical mathematical model has been proposed in order to identify physical and chemical aging over time, finding that in the first instants the physical aging grows exponentially, followed by a linear growth ascribed to chemical aging. The addition of additives only affects the physical aging but does not interfere with chemical thixotropy. This approach could be suitable to predict and control the thixotropy of cement pastes and mortars.

Invert emulsion fluids stabilized by organoclays are important for applications in thixotropic fluids and petrochemical industry, especially in the field of oil extraction. Among these applications, improvement of the rheological properties of invert emulsion fluids at high temperatures lacks detailed study. In the current work, three different organoclays, including organo-sepiolite (OSEP), organo-hectorite (OSHCA) and organo-montmorillonite (OMMT) were prepared through chemical modification of unmodified clays using DODMAC. The results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that DODMAC is not only adsorbed on the surface of particles, but also inserted into the layers of OMMT and OSHCA. For OSEP particles, DODMAC can only be adsorbed on the surface of particles. Interestingly, the results of optical microscopy and rheology indicate that the OSHCA particle-stabilized invert emulsion fluid provides better rheological properties than the other two organoclays at high temperature. Such high rheological properties is ascribed to the weak flocculation of OSHCA particles. Due to its nonreactive Mg−OH surface groups, OSHCA maintains the rheology of high-temperature aged invert emulsions by reconstructing weak flocculation structure. On the other hand, on the particle surface of OMMT and OSEP, Al−OH may react with OH− under alkaline conditions, which will destroy the weak flocculation due to increased repulsion interaction. These results clearly shed light on the relationship between the performance of invert emulsion at high aged temperature and particle weak flocculation, and also are beneficial to the applications which need stable emulsion at high temperature.

Blending with non-starch hydrocolloids is a crucial method to modify the processing properties of native starch. However, few comprehensive studies investigated the effects of inulin on the properties of rice starch (RS). In this research, we used three types of inulin with different degrees of polymerization (DP), namely, short-chain inulin (SI, DP 10), and long-chain inulin (LI, DP > 23), to investigate the effects of inulin on the pasting, thermal, and rheological properties of RS and to provide the foundation for the application of inulin in RS-based food. Inulin addition increased the pasting temperature of RS and decreased all viscosity indices, including the peak, final, breakdown, and Setback viscosities of RS. Compared with LI, SI and MI exerted stronger influence on the viscosity indices of RS. The gelatinization temperature levels of the RS–inulin blends were higher than that of starch alone. The RS and RS–inulin blends exhibited a shear-thinning property, and stress–shear hysteresis loops were observed during shear. Thixotropy followed the order RS > RS-LI > RS-MI > RS-SI. Dynamic viscoelasticity results indicated that the RS and RS–inulin blends displayed weak gel-like behavior. Replacement of RS with LI and MI evidently increased the elastic properties more than the viscous properties of the RS–inulin blends.

Understanding the rheological characteristics of sludge is important for design and operation of water and wastewater treatment units including stirrers, mixers, pumps, and separators. Studying the rheological characteristics of real sludge involves health risks and complexity due to opaque nature of sludge and its time evolution caused by microbial activity and aging. Researchers have applied various simulants such as clay, minerals, and gels to prepare synthetic sludge and to perform a lab-scale study on rheological properties and flow behaviour of real sludge. Some of previous studies have ignored the stability and rheological characteristics of simulant fluids, which might lead to less reliable results. Therefore, selection of a safe, cheap and stable alternative that can mimic rheological behaviour of real sludge is still open and challenging. The proposed study examined the pH sensitivity, zeta potential characteristics and rheological properties of sodium carboxymethyl cellulose, polyethylene glycol, sodium alginate, and xanthan gum as popular model fluids with different concentrations (0.1, 0.5, 1, 1.5, 2, and 3 wt%) in details. A comparison of rheological properties of these fluids with the rheology of different types of sludge indicated that xanthan gum is a preferred simulant fluid that mimic the behaviour of sludge for the shear rate below 100 s−1. Analysis of zeta potential and pH sensitivity indicates that xanthan gum is also a resistant solution to pH changes and agglomeration. In addition, it replicates sludge behaviour in terms of viscosity, flow curve, and Herschel–Bulkely parameters. Nevertheless, xanthan gum does not support thixotropy and viscoelastic characteristics of sludge.

Symmetric diketopyrrolopyrrole derivatives with N,N-diHexyl, N,N-diOctyl, N,N-diDecyl and N,N-diDodecyl alkyl chain were synthesized and characterized. The effects of alkyl chain length, which attached to the central core of diketopyrrolopyrrole were studied on physical properties of the synthesized dyes. Then, in addition to the effects of various solvents with different polarity on photophysical properties of the synthesized materials, their emission intensities were investigated by changing their concentration in alkyd resin, maleic resin and in the mixture of two resins in organic varnish formulation. Consequently, obtained optimum concentrations of the dyes (%1 wt) and the best ratio of resin (60:40) were investigated to obtain maximum emission intensity and the color coordinates (Lab) of fabricated organic films. The organic varnish formulation with %0.2 wt concentration with N,N-diHexyl dye was performed and applied as Fluorescent security film. Moreover, the optimal fluorescent dye content was used in the red, blue and yellow formulation of pigmented organic varnish (as the three main colors) and fluorescent emission and their color coordinates were evaluated under visible and ultraviolet light sources. The effect of organic film shade on the fluorescent emission was also studied and fluorescent pigmented varnishes (yellow, red and blue) have high, medium and low fluorescence intensity, respectively. Finally, the effects of alkyl chain length on rheological properties such as viscosity, thixotropy, temperature effect and dynamic parameters of pigmented and non-pigmented organic varnish formulation were investigated. Rheological modification efficiency in formulation increases with increasing dye concentration and length of the alkyl chain.

The rheological properties of water based MWCNT nanofluids are investigated at five different low volume concentrations (0.0047%, 0.0238%, 0.0571%, 0.1428%, 0.2381%) and five low temperatures (275 K, 277 K, 279 K, 281 K, 283 K) by a novel experimental method in the present study. The present methodology combines the 3ITT test and the DSO test. Measurements show that the nanofluids are featured with clear thixotropy and shear thinning behaviors when the concentration is above 0.0571%. It is further shown that the thixotropy becomes less obvious as the concentration lowers implying a stronger Newtonian fluid characteristic. Therefore the concentration of 0.0571% can be regarded as the critical point quantifying the transition from Newtonian to non-Newtonian and this critical concentration is independent of temperature. It is also observed that relative viscosity increases slightly with temperature at medium shear rate. Moreover, temperature sweep measurement suggests that the viscosity decreases with temperature firstly and it increases beyond a critical temperature, which can be curbed by raising the shear rate for solutions with concentration lower than 0.0571%. The dependency of the relative viscosity of the MWCNT nanofluids on shear rate, temperature and concentration is obtained and a new and accurate correlation is developed for engineering application.

Coke ash (CA) from the dust collection station of coking plants has a high carbon content and can be used as a fuel feedstock for secondary uses, avoiding environmental pollution. In this study, CA was blended with diesel oil and water to prepare a coke emulsion slurry (CES) synfuel in the presence of primary alcohol ethoxylate (AE) and polycarboxylate dispersant (PC) for gasification or combustion, as an efficient method for the utilization of CA. The effects of the particle size distribution of CA, oil to water ratio (O:W) and temperature on the slurryability of CES were investigated, and properties, such as rheology, thixotropy and stability, of CES were examined. The results showed that with a decrease of CA particle size, its slurryability is greatly improved. The apparent viscosity of CES increased when the oil content and the CA content (ω) increased. The maximum value of ω in the CES declined incrementally in oil proportion, ranging from ω = 74 wt% for the coke-water-slurry (CWS) to ω = 62 wt% at CES with O:W = 1:3. Furthermore, the higher the temperature was, the lower the apparent viscosity of the slurry. CES and CWS both exhibited non-Newtonian pseudoplastic fluid behaviour. Its pseudoplasticity and thixotropy also increased as the ω of CES rose. The oil content and ω had a great influence on the stability of CES. The dispersion behaviour and stabilization mechanism were revealed by the contact angle, zeta potential measurements and optical microscope image. Overall, this study provided a direct and efficient utilization method for CA.