Increasing Shear Rate Research Articles

Enhanced performance of a self-propelled flexible plate by a uniform shear flow and mechanism insight

The hydrodynamics of a two-dimensional self-propelled flexible plate in a uniform shear flow is explored using a penalty-immersed boundary method. The leading edge of the plate is enforced into a prescribed harmonic oscillation in the vertical direction but free to move in the horizontal direction. It is found that as the shear rate increases, the input power, the propulsive velocity, and the efficiency increase. This finding means that the plate enables to get substantial hydrodynamic benefits from the shear flow. Using the force decomposition method based on the weighted integral of the second invariant of the velocity gradient tensor, the hydrodynamic force exerted on the plate is decomposed into a body-acceleration force, a vortex-induced force, and forces due to viscous effects. The results show that the body-acceleration force is the main driving force of the self-propelled motion, and that it is almost invariant with the shear rate. The vortex-induced force offers a significant contribution to the drag, and it decreases with the shear rate. The viscous friction force provides a pure drag, and it increases with the propulsion velocity. Further investigation on the vortex evolution and the vortex-induced force shows that the incoming shear flow destroys the trailing-edge vortex that sheds during the downward half period and, therefore, reduces the vortex-induced drag, which is the reason for the enhanced propulsive performance in the shear flow. The result obtained in this study provides new insight into the self-propulsion mechanism in complex incoming flows.

Influence of mold cavity thickness on electrical, morphological and thermal properties of polypropylene/carbon micromoldings

Abstract In this work, a comparative study on the electrical conductivity (σ) and thermal properties of polypropylene (PP)/carbon microparts with different part thickness (namely, 0.85 and 0.50 mm) is reported. Two different types of carbon filler (i.e., CNT and CB) were adopted to study the efficacy of different carbon fillers in improving the σ of PP/carbon microparts. In general, the σ of 0.85 mm thickness microparts were higher than the 0.50 mm thickness microparts, regardless of the carbon filler type and testing directions. This suggested that higher shearing conditions that prevailed in the microinjection molding (μIM) process were unfavorable for the formation of intact conductive pathways in corresponding moldings, albeit the distribution of carbon fillers turned better with increasing shear rates, as confirmed by morphology observations. Differential scanning calorimetry results showed that prior thermomechanical histories (including melt blending and μIM) experienced by the polymer melts had an influence on the thermal behavior of subsequent moldings. Also, there existed a strong shear flow-induced crystallization of polymer chains during μIM because the crystallinity of microparts was higher than that of feed materials.

Effects of Crude Oil Properties and Dispersant on the Microstructure and Viscosity of Seawater-in-Oil Emulsions

This study examines the effects of crude oil properties and dispersant concentration (Corexit 9500) on the evolution of bulk viscosity, viscoelastic properties, and microstructure of salt water-in-crude oil emulsions. Microscopy, followed by machine-learning-based analysis, provides the size and spatial distribution of the seawater droplets. The crude oils include light Bakken, Alaskan North Slope (ANS), and Louisiana oils, and medium to heavy Platform Henry, Cold Lake, and Platform Gina oils. The light and medium oils entrain water up to 80% by volume, and the heavy oils, up to 25%. The droplet sizes and distance between them decrease with increasing viscosity, with small droplets clustering around larger ones. The Bakken- and ANS-based emulsions are unstable, but all of the emulsions evolve in time. All exhibit a non-Newtonian behavior, with the viscosity decreasing with increasing shear rate. The storage modulus is higher than the loss modulus for light oils, and vice versa for heavy oils. Trends of their nondimensional viscosity are collapsed onto two power laws as a function of the Ohnesorge number involving the properties of the original oil, and the size or distance between droplets. For light oils, the power law exponent decreases with increasing capillary number based on the rheometer shear rate and increases for heavy oils. At high shear rates, the exponents converge to the same value, 0.45, suggesting that the oil viscosity becomes the property that defines the emulsion rheology. The present findings are consistent with previously published data. Premixing the emulsions with dispersant causes separation of most of the water from the light oils, leaving only sparse droplet concentrations. In contrast, owing to slow diffusion rate, only a small fraction of the seawater is extracted from the heavy oil emulsions. Hence, the sparse light oil emulsions become Newtonian, but the heavy ones remain non-Newtonian.

Effects of traditional Chinese exercise on vascular function in patients with Alzheimer's disease: A protocol for systematic review and network meta-analysis of randomized controlled trials.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with an insidious onset, usually characterized by memory impairment, visual-spatial skill impairment, executive dysfunction and personality behavioral changes. Studies have confirmed that vascular dysfunction may precede AD pathological changes and can present as vascular malformations, atherosclerosis, and impaired self-regulation, and can affect oxidative stress and amyloidosis. Therefore, it is important to improve or prevent vascular dysfunction in AD patients. Regular exercise can effectively inhibit the production of reactive oxygen species during the occurrence of AD and can improve the reduction of cerebral blood flow due to AD. Previous studies have shown that exercise can achieve superior clinical results in improving vascular function in AD patients. Therefore, we hypothesize that traditional Chinese exercises (TCEs) may have a good clinical effect in improving vascular function in patients with AD. We will search "PubMed," "the Cochrane Library," "Embase," "Web of Science," "CINAHL," "ProQuest Dissertations and Theses," and "ProQuest-Health & Medical Collection," "CNKI," "SinoMed," "VIP," and "Wanfang Data" to find randomized controlled trials of the effects of TCEs on AD vascular function from the creation of the database to the present, including at least 1 indicator in carotid intima-media thickness (cIMT), middle cerebral artery mean flow velocity (MFV), blood indicators [Heme Oxidase-1 (HO-1), angiopoietin I (Ang I), vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor, matrix metalloproteinase-9 (MMP-9)], and arterial stiffness [(Ankle Brachial Index (ABI), pulse wave velocity (PWV)]. For the included literature, Excel 2019 will be used for data extraction and collection. For the indicators that can be netted for network meta-analysis, Surface Under the Cumulative Ranking for each exercise modality will be calculated with the help of Stata 16.0 and rank, where the higher the SUCRA score, the higher the ranking. For the indicators that cannot be netted, Review Manager 5.4 will be used for meta-analysis will be performed to evaluate the improvement effect of TCEs on AD patients. This meta-analysis will further determine the efficacy and safety of TCEs on vascular function in AD patients. In this study, randomized controlled trials of the effects of TCEs on vascular function in AD patients will be selected to provide evidence-based medical evidence for promoting the application of TCEs by observing the order of advantages and disadvantages of various exercise modalities through network meta-analysis.

Physicochemical and Rheology Properties of Ice Cream Prepared from Sunflower Oil and Virgin Coconut Oil

In the last decade, increasing trends towards the consumption of healthier foods have forced processors of high-fat products (ice cream) to shift their formulations to higher proportions of unsaturated or “healthier” fats. Vegetable oils such as sunflower oil and VCO can be used as a substitute for milk fat, milk solids not fat (skim milk powder), sweeteners, stabilizers and emulsifiers, and mineral water in making ice cream. A study was carried out to determine the effects of the use of the ratio of sunflower oil: virgin coconut oil with palm fruit as a stabilizer in the production of ice cream on physicochemical properties (pH, proximate, overrun, viscosity, and melting rate). The use of palm fruit is based on the content of galactomannan in palm fruit. Premium ice cream with five different ratios of SO and VCO (15:0), (10:5), (7.5:7.5), (5:10), (15:0). The ice cream production involves mixing, pasteurization, homogenization, aging, and freezing. The physicochemical result shows ice cream sample with a ratio SO:VCO (5:10) obtained good physical properties, the lowest first-time drop/ shape retention, and a low melting rate compared to the others. The rheological behavior of ice cream is the non-Newtonian fluids with a pseudoplastic behavior. The apparent viscosity decreased with increasing shear rate.

Fatigue in a class of viscoelastic solids

We study fatigue (weakness induced by cyclic loading) in a viscoelastic body described by a generalization of the Kelvin-Voigt constitutive relation, employing a novel damage initiation criterion developed by Alagappan et al. [13-15]. The main premise is that damage is a consequence of the inhomogeneity of the material which leads to some locations in the body being naturally weaker, say for instance due to the density being lower and the material moduli depending on the density and decreasing with density, leading ultimately to failure at that location. This approach has been used successfully for polymers, elastomers and concrete subject to monotonic loading. In this study, we consider the initiation of damage due to cyclic loading, which is referred to as fatigue. Since the body under consideration is viscoelastic, it dissipates energy in each cycle which leads to an increase in temperature. We shall not take the effect of the temperature of the material moduli, instead we assume that the material moduli depend on the density and the rate of dissipation. In the case of our specific study the shear modulus of the material depends on the density and dissipation (in the case of the constitutive relation considered the shear rate), and the structure of the shear modulus is such that it decreases with decrease in density and decreases with increase in dissipation (tantamount to the assumption that it decreases with increasing shear rate for the constitutive relation under consideration) leading to damage of the material. We find that after sufficient number of cycles, the body under consideration undergoes significant loss in load carrying capacity due to fatigue.

Virgin coconut oil oleogel: gelation mechanism, rheological, structural and thermal properties

SummaryA monocomponent oleogel was prepared by combining virgin coconut oil (VCO) with stearic acid (SA) as a structuring agent. The results showed that higher gelator concentrations significantly enhanced the oil binding capacity. The microstructural and thermodynamic properties revealed that higher SA content resulted in a stronger gel network structure. The rheological properties confirmed the pseudoplastic or shear thinning nature of oleogels, as viscosity decreased with increasing shear rate. Moreover, the temperature sweep test emphasised that SA concentration influenced the gelling point. Additionally, Fourier transform infrared spectroscopy (FTIR) spectra documented that oleogelation occurred due to the physical interaction of oleogel components as a result of a supramolecular assembly of the gelator. Collectively, the obtained results suggested that solid fat alternatives can be prepared from VCO, which will pave the way for the production of healthy bakery products to promote health benefits through straightforward oil structuring techniques.

Influence of Normal Stiffness and Shear Rate on the Shear Behaviors and Acoustic Emissions Characteristics of Artificial Rock Joints

Understanding the asperity damage behaviors of joints during shearing is critical for evaluating the stability of deep underground engineering structures. In this paper, we prepared plaster joints and used them for direct shear tests under different normal stiffness (0–7 MPa/mm) and various shear rate (0.5–20 mm/min) conditions. The effects of normal stiffness and shear rate on mechanical behavior and AE characteristics were studied. With the increase of normal stiffness, the damaged area of the surface of the joint and the weight of the damaged, rough body basically show a linear increase. With the increase of the shear rate, the peak shear stress and the final shear stress of the joint are non-linearly decreased (the decrease rate at the shear rate of 0.5–5 mm/min is much larger than that at the shear rate of 5–20 mm/min), more local cracks appear on the surface of the joint, and the dilatancy of the joint slightly decreases. More than 60% of the acoustic emission signals in the shearing process of the joint are concentrated in the post-peak phase. With the increase of normal stiffness, the cumulative number of acoustic emission impacts and cumulative energy both increase. With the increase in shear rate, the accumulated acoustic emission impact number decreases, and the accumulated AE energy tends to increase when the shear rate is 0.5–5 mm/min and decreases when the shear rate increases to 5–20 mm/min.

INVESTIGATION OF RHEOLOGICAL PROPERTIES OF A NANOCOMPOSITE OF SUPERPARAMAGNETIC IRON OXIDE NANOPARTICLES WITH POLYETHYLENE GLYCOL

This paper presents the results of a new investigation of the rheological properties of a nanocomposite of superparamagnetic iron oxide nanoparticles (SPIONs) with polyethylene glycol (PEG). The surface of the nanocomposite had no electrical charge and the SPIONs were coated with the polymer. The investigations were performed at different temperatures and the results were compared on different rheological parameters. The steady-state behavior of samples was observed at 20 °C and 40 °C and a small increase of viscosity versus shear strain, shear rate or time was revealed at 60 °C. Moreover, the shear stress increase was observed with the increase of shear rate and shear strain. The slopes of the corresponding changes were higher at 20 °C and decreased with the increase in temperature. The torque values increased with shear strain and time. The same phenomenon concerning the different slopes at different temperatures was observed for the torque-shear strain and torque-time variations. These results showed that the rheological properties of the nanocomposite depended on the temperature and could change with the temperature increase. An advantage of this study was that the comparative investigation of the rheological properties of nanocomposite at different temperatures was carried out. The other advantage was that the effect of the coating of the SPIONs with the polymer was observed in the obtained results. This new investigation of the nanaocomposite of SPIONs-PEG coated with PEG can provide comparative data for more investigations of the surface charged SPIONs coated with this polymer. These studies can provide information for a further investigation of the effect of the surface charge of SPIONs in the polymeric matrix on their rheological properties.

Frequency-dependent viscosity of salmon ovarian fluid has biophysical implications for sperm-egg interactions.

Gamete-level sexual selection of externally fertilising species is usually achieved by modifying sperm behaviour with mechanisms that alter the chemical environment in which gametes perform. In fish, this can be accomplished through the ovarian fluid, a substance released with the eggs at spawning. While the biochemical effects of ovarian fluid in relation to sperm energetics have been investigated, the influence of the physical environment in which sperm compete remains poorly explored. Our objective was therefore to gain insights on the physical structure of this fluid and potential impacts on reproduction. Using soft-matter physics approaches of steady-state and oscillatory viscosity measurements, we subjected wild Atlantic salmon ovarian fluids to variable shear stresses and frequencies resembling those exerted by sperm swimming through the fluid near eggs. We show that this fluid, which in its relaxed state is a gel-like substance, displays a non-Newtonian viscoelastic and shear-thinning profile, where the viscosity decreases with increasing shear rates. We concurrently find that this fluid obeys the Cox-Merz rule below 7.6 Hz and infringes it above this level, thus indicating a shear-thickening phase where viscosity increases provided it is probed gently enough. This suggests the presence of a unique frequency-dependent structural network with relevant implications for sperm energetics and fertilisation dynamics. This article has an associated ECR Spotlight interview with Marco Graziano.

Measuring Thrombus Stability at High Shear, Together With Thrombus Formation and Endogenous Fibrinolysis: First Experience Using the Global Thrombosis Test 3 (GTT-3).

Thrombus formation in a severely stenosed artery is initiated by high shear activation of platelets, with soluble platelet agonists, such as ADP and thromboxane, playing only a secondary role in the growth and stability of the thrombus. Conventional platelet function tests, however, assess only the soluble agonist-dependent pathway of platelet aggregation. As the thrombus evolves, its stability and ability to withstand dislodgement by arterial flow will determine whether complete and persistent vessel occlusion will occur. The Global Thrombosis Test (GTT), an automated point-of-care technique, simulates the formation of thrombus in whole blood under high shear flow (shear rate >12 000 s-1) and measures the time for occlusive thrombus formation and spontaneous, endogenous thrombolysis/fibrinolysis. The latest GTT-3 model subjects the growing thrombus to upstream pressure, resembling that in a medium-sized artery, and provides an additional assessment of thrombus stability and fibrinolysis rate. It can be used in 3 programs, including a new "hypershear" mode, whereby repetitive cycles of pressure are applied to the growing thrombus, increasing shear rate to ∼22 000 s-1, such as that in patients on mechanical circulatory support. In addition to assessing the risk of arterial thrombosis, the GTT-3 could be used to assess the impact of antithrombotic medications on thrombus stability at high shear. Although current antiplatelet medications target the biochemical axis of platelet aggregation (soluble agonists) and also increase bleeding risk, novel shear-selective antiplatelet therapies may prevent thrombosis while preserving hemostasis. Future studies are needed to assess the usefulness of assessing thrombus stability on cardiovascular and pharmacological evaluation.

Energy and velocity of sliding of edge and screw dislocations in austenite and Hadfield steel: Molecular dynamics simulation

The sliding of edge and screw dislocations in Hadfield steel and in pure HCC iron (austenite) depending on temperature and deformation rate was studied by the method of molecular dynamics. The complete dislocation appears in the present model immediately in the form of a split into a pair of partial Shockley dislocations separated by a packing defect. The distance between partial dislocations is several nanometres. As the shear rate increases, this distance decreases. According to the data obtained, the energies of edge and screw dislocations in steel are higher than in pure austenite. The energy of the total edge dislocation in γ-iron and Hadfield steel averages 2.0 and 2.3 eV/Å, helical – 1.3 and 1.5 eV/Å respectively. Dependences of the sliding velocity of the edge and screw dislocations on the shear rate and temperature were obtained. The sliding velocity of the edge dislocation is in all cases higher than the screw one, which is explained by the difference in the propagation velocity of longitudinal and transverse waves in the material. With an increase in the shear rate, the sliding speed increases to a certain limit, depending on the propagation velocity of the corresponding elastic waves. At low and normal temperatures, the sliding velocity of dislocations in Hadfield steel is significantly (about one and a half times) lower compared to pure HCC iron. In pure iron, the sliding velocity of dislocations decreases with increasing temperature. However, for Hadfield steel, this dependence is nonmonotonic: as the temperature increases to about 500 K, the dislocation rate increases. That is probably due to the intensification of diffusion of impurity carbon atoms; then, as in iron, it decreases.

Nanostructured Lipid Carriers (NLC)-Based Gel Formulations as Etodolac Delivery: From Gel Preparation to Permeation Study.

Topical administration of drug is an attractive alternative to the oral administration as it provides a reduction in adverse reactions and an enhancement of therapeutic effects. The use of lipid carriers in hydrogel structures makes it possible to introduce lipophilic substances in a dissolved form. In this study, an NSAID from the BCS class II, etodolac (ETD), was used. The nanostructured lipid carriers (NLC) obtained with ETD were incorporated into semi-solid forms (gels). Hydrogels with the suspended drug and oleogel were also prepared for comparison purposes. The obtained gels were tested in terms of pH, viscosity, rheological, mechanical, and bioadhesive properties. The release and permeation through membranes were also studied. All tested formulations were characterized by a pH below 7, which ensured the physiological state of the skin. The viscosities of all gels decreased with increasing shear rate, indicating non-Newtonian behavior. The fastest ETD release was observed for NLC with a Carbopol base (formulation F1); a similar result was noticed in the permeation test. The developed gel formulations containing ETD-NLC dispersion and Carbopol or Poloxamer as gelling agents were stable and possessed beneficial pharmaceutical properties.

Chemically functionalized graphene oxide with N‐phenyl‐p‐phenylenediamine as efficient tribo‐ and rheological modifier for lubricating oil

AbstractNanoadditive with multifunctional properties holds commercial importance in the lubricant industry. Herein, GO‐N‐PPDA was synthesised as nanoadditive by functionalizing graphene oxide (GO) using N‐phenyl‐p‐phenylenediamine and characterised by Fourier transform infrared spectroscopy, X‐ray diffraction analysis, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy analysis. The antioxidant behaviour of GO‐N‐PPDA was analysed by 2,2‐diphenyl‐1‐picryl‐hydrazyl‐hydrate. The nanoparticles dispersed mineral base oil (N‐250) in 0.2%, 0.4%, 0.6% (w/v) concentrations were evaluated for tribological, rheological and thermophysical analysis by ASTM methods. The flow behaviour of the nanolubricant shows shear thickening behaviour with an increase in shear rate. In contrast, tribological results indicate a significant reduction in wear scar diameter and coefficient of friction to the base oil. Furthermore, GO‐N‐PPDA shows improved thermophysical properties compared with the mineral base oil. Thus, GO‐N‐PPDA shows multifunctional behaviour in terms of viscosity index, pour point, antioxidant activity, rheology and tribological properties.

Examining rheological behavior of CeO2-GO-SA/10W40 ternary hybrid nanofluid based on experiments and COMBI/ANN/RSM modeling

In this study, the rheological behavior and dynamic viscosity of 10W40 engine oil in the presence of ternary-hybrid nanomaterials of cerium oxide (CeO2), graphene oxide (GO), and silica aerogel (SA) were investigated experimentally. Nanofluid viscosity was measured over a volume fraction range of VF = 0.25–1.5%, a temperature range of T = 5–55 °C, and a shear rate range of SR = 40–1000 rpm. The preparation of ternary-hybrid nanofluids involved a two-step process, and the nanomaterials were dispersed in SAE 10W40 using a magnetic stirrer and ultrasonic device. In addition, CeO2, GO, and SA nanoadditives underwent X-ray diffraction-based structural analysis. The non-Newtonian (pseudoplastic) behavior of ternary-hybrid nanofluid at all temperatures and volume fractions is revealed by analyzing shear stress, dynamic viscosity, and power-law model coefficients. However, the nanofluids tend to Newtonian behavior at low temperatures. For instance, dynamic viscosity declines with increasing shear rate between 4.51% (at 5 °C) and 41.59% (at 55 °C) for the 1.5 vol% nanofluid. The experimental results demonstrated that the viscosity of ternary-hybrid nanofluid declines with increasing temperature and decreasing volume fraction. For instance, assuming a constant SR of 100 rpm and a temperature increase from 5 to 55 °C, the dynamic viscosity increases by at least 95.05% (base fluid) and no more than 95.82% (1.5 vol% nanofluid). Furthermore, by increasing the volume fraction from 0 to 1.5%, the dynamic viscosity increases by a minimum of 14.74% (at 5 °C) and a maximum of 35.94% (at 55 °C). Moreover, different methods (COMBI algorithm, GMDH-type ANN, and RSM) were used to develop models for the nanofluid's dynamic viscosity, and their accuracy and complexity were compared. The COMBI algorithm with R2 = 0.9995 had the highest accuracy among the developed models. Additionally, RSM and COMBI were able to generate predictive models with the least complexity.

Single-polymer dynamics of starch-like branched ring polymers in steady shear flow

The stretching dynamics and dynamical behaviors of individual branched ring polymer (BRP), a coarse-grained model for some types of the starch, in steady shear flow are studied by using a hybrid mesoscale simulation approach that combines multiparticle collision dynamics with standard molecular dynamics. By analyzing the stretched configuration of BRPs, we find the polymer size increases nonmonotonically with increasing branch length. Meanwhile, the decrease of the alignment angle of the stretched configuration of BRPs follows a universal power law during the first downward phase as the shear rate increases. Constructing the three-dimensional surface of the polymer's ring backbone and tracing the temporal fluctuations of the surface's normal vector along the simulation trajectory, the tumbling and tank-treading motion are clearly reflected by periodic and non-periodic changes of the normal vector. Interestingly, these temporal changes are much more regular than that of the gyration tensor. Thus, a novel cross-correlation function, which is the correlation between fluctuations of the normal vector along the flow direction and the velocity-gradient direction, is proposed to analyze the tumbling motion that usually coexists with the tank-treading motion. This function can naturally address the fails of traditional method that analyzing the tumbling motion by determining the correlation of temporal fluctuations of the gyration tensor Gαα. By analyzing the dynamical behaviors of BRPs, diverse dependences of the tumbling frequency ωTB and tank-treading frequency ωTT on the shear rate γ̇ are observed at a wide range of shear rates and polymer sizes. Furthermore, our simulations also reveal that the tank-treading motion is more stable than the tumbling motion for small-branch-size BRPs but the tumbling motion is more stable than the tank-treading motion for large-branch-size BRPs.

Effects of temperature and shear conditions on lamellar-to-onion transition in nonionic surfactant/water systems

The effects of temperature and shear conditions on the lamellar-to-multilamellar vesicle (MLV) phase transition were elucidated using rheometry (Rheo)–small-angle light scattering (SALS) measurements for a system comprising C12E4.2 (a nonionic surfactant containing distributed ethylene oxide; 40 wt%) and water (60 wt%). Small-angle X-ray scattering (SAXS) measurements indicated that the bilayer d-spacing widened up to 30 °C, and further increasing the temperature caused the bilayer to fluctuate more easily. Rheo–SALS measurements indicated that the C12E4.2 viscosity increased, and a cloverleaf pattern appeared, as previously reported for other CnEm systems, indicating a phase transition. The decrease in vesicle size with increasing shear rate was slower than that reported for the non-distributed system. In a conventional dynamic phase diagram prepared in the shear-rate–temperature space, regions appeared in which temperatures and shear rates required for the phase transition were inconsistent. When a shear-stress-controlled flow was applied, the shear stress magnitude required for the phase transition increased continuously with increasing temperature. Furthermore, critical shear strains comparable to those measured for the shear rate control were obtained for different temperatures. These results suggest that the bilayer fluctuated more easily with increasing temperature, requiring more energy for the phase to transition, as indicated by the stress ramp measurements. Therefore, the temperature-dependent bilayer kinetics determined the conditions required for the phase transition, and shear stress magnitudes required for the phase transition must also be considered in CnEm systems.

Stabilisation, rheology and application of aqueous suspensions of oxidised vs. non-oxidised SiC powder

The study aimed at evaluating the stabilisation and rheological properties of aqueous suspensions (30 vol%) of pristine (non-oxidised) and oxidised fine SiC powders which were stabilised either with NaOH or TMAH (tetramethylammonium hydroxide). The extensive oxidation of the SiC powder surface was confirmed by the results of XPS and FT-IR analyses. The optimal amount of a given dispersant depended, according to the results of zeta potential measurements, on a pH range guaranteeing formation of a stable suspension. This effect allowed the authors to propose a mechanism of stabilisation of the SiC suspensions. Herein, the maximum amount of silanol groups is formed on the SiC particles surface in the pH range of 9.5–11 which then adsorb Na+ or TMA+ cations, thus creating a favourable system of electrostatic interactions. In turn, it increases the electrostatic repulsion between SiC particles and improves the stabilisation of the suspensions and their rheological characteristics. An increase in the surface oxidation of the SiC particles leads to reducing the repulsive forces between the powder particles. Apparent viscosity of the suspensions made of SiC UF10 powder, regardless of the type and amount of the fluidizer, is very low (5–10 mPa s) and shows a slight increase as the shear rate increases. The oxidation of the SiC powder changes the rheological characteristics of the suspensions, which may be caused by their rapid sedimentation. Stability of the prepared SiC suspensions was also assessed by casting them into a plaster mould and then by sintering and characterisation of the resulting samples.

Pickering Emulsions Stabilized by Chitosan/Natural Acacia Gum Biopolymers: Effects of pH and Salt Concentrations

In this study, chitosan (CT) and naturally occurring acacia gum (AG) blends were employed as emulsifiers to form a series of emulsions developed from diesel and water. Effects of pH level (3, 5, 10, and 12) and various NaCl salt concentrations (0.25-1%) on the stability, viscosity, and interfacial properties of CT-(1%)/AG-(4%) stabilized Pickering emulsions were evaluated. Bottle test experiment results showed that the stability indexes of the CT/AG emulsions were similar under acidic (3 and 5) and alkaline (10 and 12) pH media. On the other hand, the effects of various NaCl concentrations on the stability of CT-(1%)/AG-(4%) emulsion demonstrated analogous behavior throughout. From all the NaCl concentrations and pH levels examined, viscosities of this emulsion decreased drastically with the increasing shear rate, indicating pseudoplastic fluid with shear thinning characteristics of these emulsions. The viscosity of CT-(1%)/AG-(4%) emulsion increased at a low shear rate and decreased with an increasing shear rate. The presence of NaCl salt and pH change in CT/AG solutions induced a transformation in the interfacial tension (IFT) at the diesel/water interface. Accordingly, the IFT values of diesel/water in the absence of NaCl/CT/AG (without emulsifier and salt) remained fairly constant for a period of 500 s, and its average IFT value was 26.16 mN/m. In the absence of salt, the addition of an emulsifier (CT-(1%)/AG-(4%)) reduced the IFT to 16.69 mN/m. When the salt was added, the IFT values were further reduced to 12.04 mN/m. At low pH, the IFT was higher (17.1 mN/M) compared to the value of the IFT (10.8 mN/M) at high pH. The results obtained will help understand the preparation and performance of such emulsions under different conditions especially relevant to oil field applications.

Rheology of oil-based nitrogen foam at shallow reservoir conditions: Experiment and evaluation

Exhibiting as a combination of viscous, elastic, and plastic behavior, rheology is a branch of physics and is majorly concerned with continuum mechanics for flow characterizations, particularly non-Newtonian flow like foam. However, most existing studies of foam rheology are primarily focused on water-based foam, while oil-based foam rheology lacks adequate understanding, plus few comprehensive experimental analyses have been done. This study, for the first time, investigates the rheological behavior of oil-based nitrogen foam with full foam quality and shallow reservoir conditions through a newly-designed visualized capillary rheometer. Basically, the effects of foam quality and shear rate on foam morphology and apparent viscosity were elucidated, and the foam rheology at different temperatures and pressures was evaluated. More specifically, with increasing shear rate, the apparent viscosity of nitrogen foam decreases in a concave-down parabola pattern. With the foam quality of 86 %, the apparent viscosity of the foam flow is found to reach its maximum value, 58.4 mPa·s, at the flow rate of 4 mL/min, temperature of 25 °C and pressure of 5 MPa. The foam flow gradually becomes uniform and dense and the apparent viscosity elevates with increasing foam quality up to 86 %. After that, the foam flow tends to be slug flow and its stability becomes worse with linearly-decreasing apparent viscosity. With increasing pressure, the apparent viscosity and consistency coefficient increase, which result in the increase of rheological index and decrease of non-Newtonian property. The temperature effects on the foam flow are absolutely opposite but stronger in comparison to pressure effects as aforementioned. In addition, the rheological equations of nitrogen foam are determined by fitting the consistency coefficient and rheological index with foam quality. Overall, thorough investigations of the rheology of oil-based nitrogen foam would be of great importance for foam theory and practice.