Rheological Behavior Of Suspensions Research Articles

Fractional modelling of salinity/temperature-dependent shear rheological behavior including stress overshoot for bentonite clay suspensions

Based on the experimental studies of thixotropic behavior of bentonite clay suspensions at different salinities and temperatures, a complex nonlinear rheological phenomenon was firstly discovered in our previous work [Yin et al., Eng. Geol, 295(2021): 106,435], which exhibits multi-stage stress responses including stress overshoot and power-law flow behaviors. Motivated from this observation, in this work, a variable-order viscoelastic element and a novel viscoplastic element are combined to simultaneously characterize the complex multi-stage stress response of suspensions, where the former is used to describe stress overshoot and the latter is applied to characterize power-law flow behavior. The model is further employed to describe salinity/temperature-dependent rheological behavior of suspensions, where the criteria for model parameters are established. The results indicate that fractional order can be regarded as an index to identify the flow behavior where the order evolution exhibits three stages corresponding to the multi-stage flow behavior of bentonite suspensions. Applications of the proposed fractional model at different salinities and temperatures further validate the predictability and efficiency.

Role of Mixing Method and Solid Content on Printability of Alumina Inks for Stereolithography 3D Printing Process

Additive manufacturing of ceramics via stereolithography method is a promising way to fabricate high-resolution ceramic parts with complex geometry, which is hard to obtain with traditional ceramic shaping methods. In order to shape the ceramics with the Digital Light Processing (DLP), a mixture of photocurable resin and ceramic powders, called ink, must be prepared. In this paper, the printability of the Alumina-glass inks, with different solid contents were prepared by two mixing methods, having long and short mixing durations. In order to evaluate the printability of inks, the rheological behavior of suspensions was investigated, and printing parameters such as curing time and layer thickness were changed. The ceramic-resin suspensions were prepared via 24-hour ball-milling and 10,000 rpm mechanical homogenizing. The suspension containing 60 wt% solid content and prepared by mechanical homogenizing showed the best stability with 8% sedimentation within 4 days and the lowest viscosity of 1.37 Pa·s at shear rates of 30 s-1, exhibiting a suitable viscosity for DLP printing. Therefore, a mechanical homogenizer can be a promising and quick method for mixing by providing simultaneously appropriate rheology and printability.

Fibers Effects on Contract Turbulence Using a Coupling Euler Model

Fiber additive will induce the rheological behavior of suspension, resulting in variation in velocity profile and fiber orientation especially for the non-dilute case. Based on the fluid-solid coupling dynamics simulation, it shows that the fiber orientation aligns along the streamline more and more quickly in the central turbulent region as the fiber concentration increases, especially contract ratio Cx > 4. However, fibers tend to maintain the original uniform orientation and are rarely affected by the contract ratio in the boundary layer. The fibers orientation in the near semi-dilute phase is lower than that in the dilute phase near the outlet, which may be the result of the hydrodynamic contact lubrication between fibers. The orientation distribution and concentration of the fibers change the viscous flow mechanism of the suspension microscopically, which makes a velocity profile vary with the phase concentration. The velocity profile of the approaching semi-dilute phase sublayer is higher than that of the dilute and semi-dilute phases on the central streamline and in the viscous bottom layer, showing weak drag reduction while the situation is opposite on the logarithmic layer of the boundary layer. The relevant research can provide a process strategy for fiber orientation optimization and rheological control in the industrial applications of suspension.

Screening method for producing suitable spray-dried HA powder for SLS application

Screen methods are time-saving tools, assisting the establishment of a new process or technique for laboratory and industrial scale. This paper presents a step-by-step approach to use spray drying (SD) for obtaining hydroxyapatite (HA) powder, with suitable characteristics to be used as a filler in a polymer matrix, for selective laser sintering (SLS) processing. The proposed method consists of adjusting the departing HA suspension and SD processing parameters, briefly discussing relevant elements that must be considered. Suspension's rheological behavior and spray-dried powder morphological features were investigated, serving as selection criteria for the favorable set-up. Variations on slurry feed and atomization pressure of SD processing parameters have allowed obtaining different powder characteristics. A major influence of atomization pressure variation was identified, a greater pressure value resulted in smaller particle size. Desirability function was employed to determine the optimal SD processing parameters, in other words, conditions that made it possible to obtain spherical particles with the proposed mean diameter in the range of 15 to 25 μm, with narrow particle size distribution.

Stability, rheological behaviors, and curing properties of 3Y–ZrO2 and 3Y–ZrO2/GO ceramic suspensions in stereolithography applied for dental implants

The combination of yttria-zirconia (3Y–ZrO2) and stereolithography (SLA) is essential for forming alternative bioceramics for complex, custom-designed dental implants. In addition, suitable bioceramic suspensions are preconditions for such fabrication using SLA technology. In this study, 3Y–ZrO2 and 3Y–ZrO2/graphene oxide (GO) powders dispersed in ultraviolet curable acrylic-based resins are developed. A sedimentation experiment is performed to evaluate various ratios of monomers and dispersants to ensure good stability and dispersion of the suspensions. The hydrophobic structures of KH560 are introduced on the surfaces of ceramic powders, representing better wettability performances with 40 vol% NPG2PODA and 60 vol% Di-TMPTA. Moreover, the effects of premixed solvents and solid contents on the rheological behaviors of suspensions are investigated to confirm shear thinning and pseudo plasticity, with the experimental results fitting the Krieger–Dougherty curves. Further, the cure depth and width of the ceramic suspensions are studied, the results of which show that the penetration depth and critical exposure of the 3Y–ZrO2 (3Y–ZrO2/GO) pastes are 17.2 ± 0.50 μm and 4.80 ± 0.62 mJ/cm2 (11.8 ± 1.20 μm and 22.80 ± 9.34 mJ/cm2), respectively. The addition of GO results in a sharp increase in critical exposure, which intensifies the light scattering and hinders the curing of the ceramic paste. The research is expected to serve as a technical guide for the fabrication of ceramic suspensions for dental implants using SLA technology.

Influence of wet foam stability on the microstructure of ceramic shell foams

In this study, recycled ceramic shell particles from the mold used in precision casting, which consists of coating a wax model with several layers (shell) of mullite and zirconia particles of different sizes, were used as raw material to prepare stable wet-foams by direct foaming and gelcasting using ovalbumin. The control of suspension parameters, such as pH, dispersant concentration, solids concentration and stirring velocity, can influence the foam stability against destabilization mechanisms (such as drainage, coalescence, and Ostwald ripening), optimizing the final properties of the cellular ceramic structures. The rheological behavior of suspensions and the gel point temperature of foams was also evaluated. The evolution of the bubbles-sizes (as a function of time) into the wet foam structure was analyzed by Axio Vision LE and ImageJ software. The fired ceramic shell foam (1550 ​°C, 2 ​°C/min, for 2 ​h) exhibited porosities higher than 80%, characterized by a highly interconnected network of spherical pores, with sizes ranging from 518 ​± ​29 to 1088 ​± ​103 ​μm and compressive strength of 0.9 ​± ​0.2 ​MPa. The morphological features and mechanical strength of the obtained foam indicating the possibility that it could be employed as low-cost replacement for radiant porous burners applications.

Correlating inter-particle forces and particle shape to shear-induced aggregation/fragmentation and rheology for dilute anisotropic particle suspensions: A complementary study via capillary rheometry and in-situ small and ultra-small angle X-ray scattering

HypothesisUnderstanding the stability and rheological behavior of suspensions composed of anisotropic particles is challenging due to the complex interplay of hydrodynamic and colloidal forces. We propose that orientationally-dependent interactions resulting from the anisotropic nature of non-spherical sub-units strongly influences shear-induced particle aggregation/fragmentation and suspension rheological behavior. ExperimentsWide-, small-, and ultra-small-angle X-ray scattering experiments were used to simultaneously monitor changes in size and fractal dimensions of boehmite aggregates from 6 to 10,000 Å as the sample was recirculated through an in-situ capillary rheometer. The latter also provided simultaneous suspension viscosity data. Computational fluid dynamics modeling of the apparatus provided a more rigorous analysis of the fluid flow. FindingsShear-induced aggregation/fragmentation was correlated with a complicated balance between hydrodynamic and colloidal forces. Multi-scale fractal aggregates formed in solution but the largest could be fragmented by shear. Orientationally-dependent interactions lead to a relatively large experimental suspension viscosity when the hydrodynamic force was small compared to colloidal forces. This manifests even at low boehmite mass fractions.

Influence of Oxidation Degree of Graphene Oxide on the Shear Rheology of Poly(ethylene glycol) Suspensions

This work studies the influence of the concentration and oxidation degree on the rheological behavior of graphene oxide (GO) nanosheets dispersed on polyethylene glycol (PEG). The rheological characterization was fulfilled in shear flow through rotational rheometry measurements, in steady, transient and oscillatory regimes. Graphene oxide was prepared by chemical exfoliation of graphite using the modified Hummers method. The morphological and structural characteristics originating from the synthesis were analyzed by X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and atomic force microscopy. It is shown that higher oxidation times increase the functional groups, which leads to a higher dispersion and exfoliation of GO sheets in the PEG. Moreover, the addition of GO in a PEG solution results in significant growth of the suspension viscosity, and a change of the fluid behavior from Newtonian to pseudoplastic. This effect is related to the concentration and oxidation level of the obtained GO particles. The results obtained aim to contribute towards the understanding of the interactions between the GO and the polymeric liquid matrix, and their influence on the suspension rheological behavior.

Design of Optimal Organic Materials System for Ceramic Suspension‐Based Additive Manufacturing

Ceramic suspension is a basic ingredient for various ceramic processing, and designing a ceramic suspension system is important to secure material processability in various applications. Especially when engineering ceramics, a highly loaded ceramic suspension is essential to fabricate dense ceramic bodies for proper mechanical properties. However, as solid loading increases, the viscosity of ceramic suspension keeps increasing and shows a shear‐thickening behavior under a shear condition, which makes suspension formulation a challenging issue of interest. Herein, a strategy to design highly loaded ceramic suspension with optimal organic materials system is given based on the systematic correlation between solubility parameter of organic materials system and rheological processability of highly loaded ceramic suspensions. Especially with silicon nitride suspension that generally suffers from inferior rheological processability, a trend between solubility parameter of organic dispersing media and rheological behavior of suspensions is defined as a material selection guideline. Based on this selection strategy, a photocurable monomer is selected as an optimal dispersing media and directly applied to prepare highly loaded silicon nitride suspension (≈51 vol%) showing low viscosity and a shear‐thinning behavior. The designed ceramic suspension is successfully applied to a photocuring‐based additive manufacturing process, the digital light processing, for fabrication of various 3D silicon nitride shapes.

Stability of oil well olefin drilling fluids: solid–liquid sedimentation and rheological characterization

Oil wells drilling processes are a crucial step in petroleum exploration and drilling fluids are an important player in this operation. Both solid–liquid sedimentation stability and appropriate rheological characteristics are significant and desirable aspects for drilling fluid. In this context, this study aimed at analyzing the stability of olefin drilling fluids, differentiated by calcium carbonate additive, related to solid–fluid interaction sedimentation and rheological behavior. Rheology, gravitational, and batch sedimentation experimental tests were performed as both time and function position. A low viscosity viscometer was used for the rheological characterization, and gamma-ray attenuation, a nondestructive technique, was applied to quantify the local volumetric solids concentration in sedimentary regions. The results showed a shear-thinning behavior and thixotropic effects in these fluids and the influence of calcium carbonate in the sedimentation profile. The thickened suspension showed higher values of apparent viscosity and lower sedimentation rates than the non-thickened system. Thus, the formulation of drilling fluids affected the solid–liquid separation process and the rheological behavior of suspensions; and, for that sense, it should be appropriated for drilling exploration.

Functional and Rheological Properties of Yam (<em>Dioscorea rotundata</em>) Mucilage

The objective of the present study was to evaluate the functional and rheological properties of mucilage of Hawthorne bread of yam ( Dioscorea rotundata ). The extraction of mucilage was performed by continuous bubbling method and then its functional (solubility at 30 to 70°C, water absorption index, water solubility index, swelling capacity, stability and clarity of the paste, oil absorption capacity, emulsifier activity, stability of emulsion, total phenols and antioxidant capacity) and rheological (stationary test and viscoamilogram) properties were evaluated. The results indicate a greater solubility (96.96% to 30°C and 88.76% to 70°C) and stability of emulsion (68.89%); however, total phenol content and antioxidant capacity lower to other mucilage, possibly due to the extraction method employed (bubbling). The method that best represented the rheological behavior of suspensions of mucilage of yam was that of Oswald de Waele, categorizing it as dilatant fluid (n>1) and the viscoamilogram demonstrates the low starch content in mucilage, showing a setback of 11.43 mPa.s, which indicates high stability of this polymer. The functional properties show the potential of mucilage as emulsifier and its easy inclusion in food matrices.

Microscopic relationship between colloid–colloid interactions and the rheological behaviour of suspensions: a molecular dynamics-stochastic rotation dynamics investigation

ABSTRACTWe investigate the dependence of the shear viscosity of suspensions of spherical colloids as a function of the volume fraction of the suspension, the colloid–colloid interactions and the shear rate. We couple molecular dynamics to describe the motion of the colloids with stochastic rotation dynamics (MD–SRD) for the fluid environment by means of stochastic collisions, in order to incorporate hydrodynamics effects leading to non-newtonian responses. The shear viscosity is computed using non-equilibrium simulations by imposing explicit velocity gradients. The impact of the colloid–colloid interactions is examined by modelling the inter-colloid pair potential with a repulsive power law, that allows interpolating different degrees of colloidal softness. The general rheological behaviour of our suspensions can be described with a Krieger–Dougherty like equation, which must be corrected to account for the variations in the maximum packing fraction and non-equilibrium effects arising from the flux of momentum imposed to the suspension, which appear when varying the softness of the inter-colloidal interactions. We further show evidence for non-newtonian behaviour at high Péclet numbers, characterised both by shear thinning and shear thickening, and thus demonstrate these effects can be successfully captured using MD–SRD methods.

Gel-casting of transparent magnesium aluminate spinel ceramics fabricated by spark plasma sintering (SPS)

In this paper, a transparent magnesium aluminate spinel ceramic was fabricated through the newest colloidal gel casting method, using a synthetic powder with the average particle size of 90nm and Isobutylene-Maleic Anhydride (ISOBAM) additive. ISOBAM served as both a dispersant and a gelation agent to achieve a dense body. Also, the suspension rheological behavior was optimized by the solid loading of 85wt%, the additive content of 0.7wt%, and the gelation time of 350s. This led to a green body with a density equal to 65% of theoretical density and the green strength of 14.48MPa. The results revealed that the reduction of porosity and the uniform distribution of pores in the green body (smaller than half of the initial powder particle size, 35nm), as accompanied by spark plasma sintering (SPS), resulted in the final body density of 99.97%, as well as the high in-line transmittance of 86.7% at the wavelength of 1100nm.

Effect of composition on rheological behavior of iron oxides produced by hydrothermal method

The aim of the present work was to investigate the rheological properties of different iron oxides (Fe3O4, NiFe2O4, ZnFe2O4 and Ni0.5Zn0.5Fe2O4) aqueous suspensions. The oxides were produced through mixing the respective metallic sulfates within a closed isothermal reactor at 100°C and at pH ≈12, in an oxidant environment (provided by H2O2 0.63% w/v). The reactor was coupled with an adequate real-time data (RTD) acquisition system enabling measurement of temperature, pH and pressure. Obtained RTD data showed that once the isothermal conditions are reached, the pressure slowly decreases over time, which is a result of O2 consumption through oxidation of Fe2+ to Fe3+. To characterize the suspensions as a function of temperature and shear rate, the steady rheology was used. The results revealed that the effect of temperature on viscosity of all suspensions was insignificant while steady rheology showed pseudoplastic behavior for all ferrites. The magnitude of viscosity and pseudoplasticity turned out to be in agreement with the hydrodynamic diameters of particles complying with the order: NiFe2O4>Fe3O4>Ni0.5Zn0.5Fe2O4>ZnFe2O4. Finally, the rheological behavior of suspensions was attributed to the concentration of OH groups on the surface of particles and this hypothesis was effectively supported by DRX, FTIR and TGA/DTA measurements.

Rheological behaviors of nanosilica suspensions with different dispersion levels prepared by the bead milling technique

The different dispersion levels of silica nanoparticles in organic suspensions were deliberately fabricated using the bead milling technique by controlling the milling time. The dispersion level was confirmed by the dynamic light scattering technique, the transmission electron microscopy, the stability of the suspensions as well as the optical properties of the coatings made from the suspensions. The rheological behaviors of the suspensions were investigated by the steady and dynamic shear tests. It was found that larger agglomerations had a stronger impedence for suspension to flow, leading to a higher viscosity and stiffness. Some important rheological parameters were correlated with the dispersion levels of the suspensions and the reasonable explanation was discussed.

Effect of compatibiliser on rheological behaviour of straw fibre/low density polyethylene composites

Rheological behaviour of suspensions of straw fibre in low density polyethylene (LDPE) melts was investigated at a certain temperature over a wide range of frequencies using a plate rheometer operated in dynamic mode. The viscoelastic of composite melt changed gradually with the straw fibre content increasing, for example at the low frequency region the slope of the G′ decreased from 1.67 of the plain LDPE to 0.889 of 50 wt-% straw fibre plastic composite. The addition of compatibiliser doubled the tensile strength, and the relaxation time reduced from 405 to 214 s. It was observed that the presence of compatibiliser may be attributed to improve interaction between the polymer and filler, which reduces the resistance of the agglomeration of straw fibres, lessening the relaxation time. Consequently, the straw fibre plastic composite is easier to produce.

Rheological Measurements for Indicating Structural Changes in selected Soil Catenas of European Experimental Fields

Characterization of soil degradation and changes of soil quality are of great importance. The effects of the mismanagement in Puch experimental station (Germany), the differences between bio and conventional agriculture in the plots of Basilicata and Tuscany (Italy) and the effect of vegetation cover in Santomera field (Spain) were studied by rheological measurements. The rheological parameters were measured in suspensions containing as much water as equilibrium sediment can be retained during long standstill, introduced by Czibulya et al. (2010) as the water content of soil suspension in corresponding state (WCSSinCS). Rheological parameters were determined under soil relevant conditions (low shear, high viscosity), where surface properties of soil particles and composition of aqueous phase governed rheological behavior of suspensions, and were compared with parameters related to the organic matter content of soils such as total organic carbon (TOC), soil organic matter content (OM) and humic substances carbon (Chum) values measured within a European specific targeted research project (acronym: INDEX-GOCE-CT-2003505450) and it was explored that the flow ability of soil suspensions in corresponding state is influenced by liquefying and solidifying effects. The higher WCSSinCS indicates better water holding capacity of soils liquefies suspensions, since the number of particles in the unit volume of suspensions decreases. The increase of organic matter content can induce higher shear resistant aggregation structure only if adequate Ca 2+ -ion is available. The ratio of organic matter content to that of Ca 2+ -ion is also high, but its liquefying effect comes out for lack of Ca 2+ ions.

The Effect of Polymer Content on the Non-Newtonian Behavior of Acetaminophen Suspension

Acetaminophen is used as an analgesic and antipyretic agent. The aim of the study was evaluation of the effect of different polymers on rheological behavior of acetaminophen suspension. In order to achieve controlled flocculation, sodium chloride was added. Then structural vehicles such as carboxymethyl cellulose (CMC), polyvinyl pyrrolidone (PVP), tragacanth, and magnesium aluminum silicate (Veegum) were evaluated individually and in combination. Physical stability parameters such as sedimentation volume (F), redispersibility (n), and growth of crystals of the suspensions were determined. Also, the rheological properties of formulations were studied. The results of this study showed that the combination of suspending agents had the most physical stability and pseudoplastic behavior with some degree of thixotropy. Viscosity of suspensions was increased by adding NaCl 0.02%. Presence of PVP is necessary for improving rheological behavior of suspensions by NaCl. This may be related to the cross-linking between the carbonyl group in the PVP segment and Na+ ions.

Room-temperature injection molding of aqueous alumina-polyvinylpyrrolidone suspensions

Abstract Room-temperature injection molding, a novel, environmentally benign ceramic processing method, produced dense, near-net shape alumina rings by utilizing unique flow properties of aqueous, highly loaded (>50 vol.%) ceramic suspensions with ≤5 vol.% polyvinylpyrrolidone (PVP) dispersed using Darvan 821A. The rheological behavior of suspensions along with microstructural and mechanical properties of resulting specimens were evaluated by varying PVP content to determine the optimal composition for forming. Parallel-plate rheometry revealed that suspensions containing ≤5 vol.% PVP were yield pseudoplastic at room temperature, which facilitated processing without heating or complex chemical reactions. Alumina rings with high green densities (>60% true density (TD)) were machined before binder removal, and increasing PVP content was observed to enhance green machinability. After binder burnout and sintering, bulk densities were ∼98%TD with

Foaming performance of aqueous albumin and mullite-albumin systems used in cellular ceramic processing

Abstract Bovine serum albumin (BSA) solutions (5, 10 and 15 vol%) and stabilized aqueous mullite (40 vol%)–BSA (5, 10 and 15 vol%) suspensions were foamed by mechanical stirring at 2300 rpm. The colloidal and rheological behaviors of suspensions were studied by measuring zeta potential and shear flow properties, respectively. The foaming performance of aqueous systems was evaluated by characterizing the foaming capacity and the foam stability by volume and electrical conductivity measurements. Overrun % was considered as a measure of the foaming capacity, while the variation of this parameter, the foam wetness ( Φ FW ) and the foam density stability ( FDS % ) with the stand time and the time to half collapse ( t 1/2 ) were evaluated in order to study the stability of foamed systems. Median bubble diameters, bubble size distribution widths and bubble shape factors as a function of time were determined by analyzing images captured by confocal laser-scanning microscopy (CLSM). The results related to the stability of foamed systems were used to evaluate the global destabilization mechanism of these systems, analyzing, in particular, the influence of the solid particles in the protein foam. The obtained results are useful for studying the shaping of cellular mullite green bodies from the thermogelation of foamed aqueous ceramic-protein suspensions.