Rheological Changes Research Articles

Seasonal changes in blood rheology in little ground squirrels.

The annual cycle of small ground squirrels (Spermophilus pygmaeus) consists of 2 periods: wakefulness (spring-autumn) and hibernation (winter). During the active period, ground squirrels breed (spring), accumulate fat reserves (summer) and prepare for hibernation (autumn). We suppose that the rheological properties of blood and the deformability of erythrocytes can change in different seasons of the animal's wakefulness period to adequately provide tissues with oxygen. The aim of this study was to identify possible adaptive changes in erythrocyte deformability and erythrocyte indices in ground squirrels during their active period. The deformability of erythrocytes was studied by ektacytometry in an osmotic gradient. It was found that in spring, after the arousal of ground squirrels, erythrocytes have the highest deformability (El_max), hydration (O_hyper), water permeability (El_min) and osmotic stability (∆O). In summer, compared with spring, the deformability of erythrocytes decreases, and the average volume of erythrocytes (MCV) also decreases. In autumn, before hibernation, the integral deformability of erythrocytes, their hydration, as well as the range of osmotic stability of erythrocytes increases relative to the summer period. In summer and autumn, in contrast to spring, the average concentration of hemoglobin in the erythrocyte (MCHC) increases. At low shear stress (1 Pa) in summer and autumn, osmoscan becomes a pronounced polymodal form, indicating a change in the viscoelastic properties of ground squirrel erythrocyte membranes. Thus, for the first time, we discovered seasonal variability in the deformability of ground squirrel erythrocytes, which is consistent with the spring-summer activity of animals and preparation for hibernation.

2D stationary computational printing of cement-based pastes with time-dependent rheology

Additive manufacturing is rapidly emerging as a potentially transformative technology for the construction industry. Many technical hurdles, however, are yet unresolved including the formulation of robust, standardized cement-based printing pastes. To hasten the development of rheologically sound materials for printing, a combined experimental and computational approach has been taken. A new, efficient strategy for computational printing was recently introduced. The new method, 2-D Stationary Computational Printing (2D-SCP), has been shown to map well to experimental print outcomes. Here, the 2D-SCP strategy was extended to include time-dependent rheological effects due to hydration-related structuration. The time-domain rheological properties of cement-based printing pastes were determined from experimentally measured static yield stress values. As a benchmark, a tubular form was used for printed objects. The numerical models were then validated by comparing the polished sections of the printed objects with that produced using the 2D-SCP model. The importance of structural build-up and related rheological changes i.e. static yield stress, on 3D printing of the experimental cement pastes was quantified. The obtained results show high fidelity between 2D-SCP prints and experimental objects. This newly developed computational printing strategy can assist in targeting optimal paste design for 3D printing applications.

Correlating 3D printing performance with sol-gel transition based on thermo-responsive k-carrageenan affected by fructose

Thermo-responsive food inks occupy an important part of 3D food printing materials. A great challenge of their accurate 3D printing is to ensure sol-gel transition is adapted to 3D printing process. In this study, k -carrageenan (KG) incorporated with fructose (0–30%, w/v) was selected as a representation of thermo-responsive inks, and their interactive mechanism was investigated. Sol-gel transition and rheology were correlated with 3D printing process in terms of extrusion stage, formation stage, and self-supporting stage. Results indicated that fructose addition increased ink's gelation temperature (Tg) and affected printing temperature selection. During extrusion stage, ink in sol-state with a low viscosity was desirable to enable proper extrudability. While, during formation stage, sol-gel transition speed (gelation time) was important for extruded ink to solidify to avoid continuous spreading. Increased elastic modulus (G′) with fructose addition was beneficial for printed structures to be self-supportable during self-supporting stage. Low field nuclear magnetic resonance (LF-NMR) indicated that water mobility was increasingly restricted with addition of fructose. Hydrogen bond, hydrophobic and electrostatic interactions all significantly affected the KG/fructose ink. Scanning electron microscopy (SEM) suggested that fructose addition resulted in a denser network structure. This study would provide insights on 3D printing of thermo-responsive food inks by correlating with sol-gel transition. • 3D printing behavior was correlated with sol-gel transition process. • 3D printing was divided into three stages and correlated with rheology change. • Fructose addition increased Tg, gelation speed and resultant 3D printing behavior.

Nondestructive rheological measurements of biomaterials with a magnetic microwire rheometer

Programmable hydrogels, such as thiolated hydrogels, are frequently used for tissue engineering and drug delivery applications, because they offer the ability to control gelation, degradation, and adhesion. Understanding how the mechanical properties of these materials change during these processes is essential as they directly impact cell fate and delivery efficacy. The rheology of hydrogels has been quantified primarily via bulk rheological methods. While such methods are effective, they require large sample volumes and result in the destruction of the sample; therefore, responses to multiple stimuli must be recorded across many different samples. We have developed a magnetic microwire rheometer that can characterize the rheology of small sample volumes while maintaining the integrity of the sample, such that the material response to a range of stimuli can be recorded for a single sample. This capability enables insights into time-dependent rheological changes, such as gelation and degradation, and can be applied to characterize dynamic in situ systems that are the basis for tissue scaffolding, drug delivery vehicles, and other important biological applications.

Recyclability of additively manufactured bio-based composites

As the flexibility, efficiency, and application space of additive manufacturing continues to grow, many have begun to investigate more sustainable feedstocks as well as options for the end of life of additively manufactured parts. This study examines the effects of mechanical recycling on additively manufactured parts from bio-based feedstock. Articles were printed on the Big Area Additive Manufacturing (BAAM) system at the Oak Ridge National Laboratory using poly (lactic acid)/wood flour (PLA/WF) pellets. These parts were shredded and granulated, and the granulate was fed directly back into the BAAM system for re-printing, skipping the costly and energy-intensive steps of extrusion and pelletization. The chemical, mechanical, thermal, and rheological changes to PLA/WF before and after recycling were investigated. Additionally, the energy savings from directly printing granulate on the BAAM system without extrusion and pelletization is reported. It is shown that PLA/WF is an excellent candidate for recycling of large format additively manufactured parts, and value of these parts can be reclaimed while saving cost and energy through mechanical recycling.

Effect of Fibrillization pH on Gelation Viscoelasticity and Properties of Biofabricated Dense Collagen Matrices via Gel Aspiration-Ejection.

Reconstituted hydrogels based on the self-assembly of acid-solubilized collagen molecules have been extensively used as in vitro models and precursors in biofabrication processes. This study investigated the effect of fibrillization pH-ranging from 4 to 11-on real-time rheological property changes during the gelation of collagen hydrogels and its interplay with the properties of subsequently biofabricated dense collagen matrices generated via automated gel aspiration-ejection (GAE). A contactless, nondestructive technique was used to characterize the temporal progression in shear storage modulus (G', or stiffness) during collagen gelation. There was a relative increase in G' of the hydrogels from 36 to 900 Pa with an increase in gelation pH. Automated GAE, which simultaneously imparts collagen fibrillar compaction and alignment, was then applied to these precursor collagen hydrogels to biofabricate native extracellular matrix-like densified gels. In line with viscoelastic properties, only hydrogels fibrillized in the 6.5 < pH ≤ 10 range could be densified via GAE. There was an increase in both fibrillar density and alignment in the GAE-derived matrices with an increase in gelation pH. These factors, combined with a higher G' in the alkaline precursor hydrogels, led to a significant increase in the micro-compressive modulus of GAE-densified gels of pH 9 and 10. Furthermore, NIH/3T3 fibroblast-seeded GAE-derived matrices densified from gels fibrillized in the pH range of 7 to 10 exhibited low cell mortality with >80% viability. It is anticipated that the results of this study can be potentially applicable to other hydrogel systems, as well as biofabrication techniques involving needles or nozzles, such as injection and bioprinting.

Rheological Changes During the Atrial Fibrillation

Rheological Changes During the Atrial Fibrillation

Effect of Gamma Radiation on the Processability of New and Recycled PA-6 Polymers.

The growing quantities of plastic waste have raised environmental concerns, with almost a quarter of disposed plastics being sent to landfill. This has motivated research efforts into various recycling technologies to ease dependence on fossil resources, increasing circularity. Irradiation of various kinds, such as electron beam, beta and gamma rays, has been studied in the past as a way of revamping end-of-life polymer properties. The present work focuses on the effects of gamma radiation on the processability of new and recycled polymers, which is intimately linked with their rheological properties. In this study, both virgin and recycled polymers were irradiated under different radiation doses and the effects of the radiation on their viscosity assessed and compared. Results were analyzed making use of different theoretical relationships, and the causes of the changes in rheology were investigated by means of various characterization techniques, such as GPC, FTIR, EPR and DSC. Finally, the rheological curves of all samples were fitted to the Ostwald-de Waele relationship and the dependence of its parameters on the absorbed dose fitted to a function.

Controlling ettringite precipitation and rheological behavior in ordinary Portland cement paste by hydration control agent, temperature and mixing

The influence of ettringite precipitation on the rheological properties during the initial and the induction period of ordinary Portland cement (OPC) hydration is examined by combining quantitative X-ray diffraction (QXRD), thermogravimetry (TG), calorimetry, penetration test method and 1H-TD-NMR. This allows a good overview about mineralogical changes during hydration and conclusions about their effect on rheological and microstructural changes within the paste. The reaction kinetic are controlled either by varying curing temperature or by an organic additive, which allows adjustment of the initial aluminate reaction while delaying the silicate reaction for hours. A significant correlation of ettringite content and rheological behavior due to structural build-up of the paste is observed in all investigated systems. The potential influence of ettringite content on structural build-up of the paste is found to be comparable to the effect of solid volume fraction on rheology (viscosity & yield stress).

Physicochemical and rheological properties of skim milk with different added zinc salts

Physicochemical and rheological changes in skim milk after the addition of soluble zinc salts, zinc acetate (Zn(OAc)2), zinc sulphate (ZnSO4) and zinc gluconate (ZnGlu) at 20 °C were investigated. Addition of zinc salts resulted in a significant decrease in pH, and the solution pH from lowest to highest at the same concentration was ZnSO4 < ZnGlu < Zn(OAc)2. The colloidal phase zinc concentration increased the most when Zn(OAc)2 was added. At low concentrations of added zinc salts (<20 mmol L−1) the zinc + skim milk solutions did not gel at 20 °C for 3 h (final G′ <1 Pa). Gelation was observed when 22.5 mmol L−1 Zn(OAc)2 was added to skim milk, while it was necessary to add 30 mmol L−1 ZnSO4 and ZnGlu to achieve a final G′ >1 Pa, followed by increasing final G′ with increasing concentrations of added zinc salts. Higher colloidal phase zinc concentrations resulted in a stronger gel at 20 °C.

THERMAL CONDUCTIVITY, RHEOLOGY AND ELECTRICAL CONDUCTIVITY OF WATER AND ETHYLENE GLYCOL BASED NANOFLUIDS WITH COPPER AND ALUMINUM PARTICLES

Nanoparticles are mesoobjects that occupy an intermediate position in size between ordinary molecules and macroscopic particles. Suspensions with nanoparticles, called nanofluids, are also specific mesoscopic suspensions. Today it is known that their thermophysical and mechanical properties are not described by classical theories. The unusual properties of these dispersed fluids make them extremely popular in a wide variety of applications. However, successful use of nanofluids involves the prediction of their properties, which in turn requires systematic studies. This paper presents an experimental study on the thermophysical properties of water and ethylene glycol based nanofluids with aluminum and copper particles. The thermal conductivity, rheology and electrical conductivity of nanofluids were systematically studied. The weight concentration of nanoparticles varied from 2.5 to 20%. It was shown that the thermal conductivity of these nanofluids significantly exceeds that of nanofluids with oxide particles. Its higher values are determined by the size of the nanoparticles and the thermal conductivity of the base fluid. The nanofluids studied are either pseudoplastic or viscoplastic. Their rheology is determined by the concentration and size of nanoparticles. The smaller the size of nanoparticles and the higher their concentration, the more likely the change in rheology is. Correlation curves were constructed for the rheological parameters of nanofluids versus the concentration and size of nanoparticles. It was found that the electrical conductivity of nanofluids increases almost linearly with increasing nanoparticle concentration and strongly depends on the nanoparticle size. The electrical conductivity mechanisms of nanofluids were discussed. The speed of sound in a nanofluid and its dependence on particle size were measured.

Anomalous glucose-responsive rheological changes in a boronic acid-modified hyaluronan.

Herein, we report anomalous glucose (Glc)-responsive gelation/solation in 3-aminophenylboronic acid-modified hyaluronic acid. With 5-20 mM Glc, gelation occurred, resulting in the formation of crosslinks via Glc, which could reversibly bind to the two boronic acid sites. Solation was induced at Glc concentrations of >80 mM.

Strong effect of fluid rheology on electrokinetic instability and subsequent mixing phenomena in a microfluidic T-junction

When two fluids of different electrical conductivities are transported under the influence of an electric field, the electrokinetic instability (EKI) phenomenon often triggers in a microfluidic device once the electric field strength and conductivity gradient exceed some critical values. This study presents a detailed numerical investigation of how the rheological behavior of a fluid obeyed by the non-Newtonian power-law constitutive relation could influence this EKI phenomenon in a microfluidic T-junction. We find that as the fluid rheological behavior changes from shear-thickening (n &amp;gt;1) to shear-thinning (n &amp;lt;1), the EKI phenomenon is significantly influenced under the same conditions. In particular, the intensity of this EKI phenomenon is found to be significantly higher in shear-thinning fluids than in Newtonian and shear-thickening fluids. Also, the critical value of the applied electric field strength for the inception of this EKI phenomenon gradually increases as the fluid rheological behavior progressively moves from shear-thinning to shear-thickening. The corresponding mixing phenomenon, often achieved using this EKI phenomenon, is also notably higher in shear-thinning fluids compared to Newtonian and shear-thickening fluids. A detailed analysis of both the flow dynamics and mixing phenomena inside the microdevice is presented and discussed in this study. To perform so, we also employ the data-driven dynamic mode decomposition technique, considered one of the widely used reduced-order models to analyze a dynamical system. This analysis facilitates a better understanding of the EKI-induced chaotic convection and mixing phenomena inside the microdevice. We observe that the spatial expanse and intensity of the coherent flow structures differ significantly as the power-law index changes, thereby providing valuable insight into certain aspects of the underlying flow dynamics that, otherwise, are not apparent from other analyses.

Impact of Different Enzymatic Processes on Antioxidant, Nutritional and Functional Properties of Soy Protein Hydrolysates Incorporated into Novel Cookies.

Soy protein concentrate (SPC) was hydrolyzed using several commercial food-grade proteases (Alcalase, Neutrase, papain, Everlase, Umamizyme, Flavourzyme) and their combination to obtain promising ingredients in the manufacture of functional bakery products. In all cases, the hydrolysis caused nutritional, sensory, and rheological changes in SPC, as well as protein structural changes like increased surface hydrophobicity and content of exposed SH groups with the magnitude of these changes depending on enzyme specificity. The hydrolysis with the combination of Neutrase and Flavourzyme (NeuFlav) increased essential amino acid content by 9.8% and that of Lys by 32.6% compared to SPC. This hydrolysate showed also significant antioxidant activities including ABTS and superoxide anion scavenging activity and metal-chelating ability. The addition of all hydrolysates in wheat flour decreased water adsorption and increased development time to some extent due to gluten network weakening, but also decreased the rate of starch retrogradation, contributing to the increase of the shelf-life of bakery products. The NeuFlav tasted less bitter than other hydrolysates, while E-nose provided a discrimination index of 93 between control and hydrolysates. It appeared that the addition of the NeuFlav hydrolysate in a cookie formulation improved protein content and nutritional quality and directed to its higher general consumer acceptability than cookies formulated with only wheat flour.

Validation of empirical changes to asphalt specifications based on phase angle and relaxation properties using data from a northern Ontario, Canada pavement trial

Polymer modified asphalt is generally accepted to provide positive benefit/cost outcomes in terms of extending pavement service life. It has recently been claimed that higher modification levels perform better. A 13-year-old pavement trial in Ontario, Canada is providing valuable insights on this issue. Dynamic shear rheometer (DSR) tests were conducted to monitor rheological changes upon oxidative aging. Gelled binders exhibit more solid-like response leading to less ability to relax thermal stress, and hence an accelerated decay in performance. This was further verified from relaxation spectra calculated from stress relaxation data. A test section constructed with a gel-type binder containing 7 % styrene-butadiene-styrene (SBS) modifier has a predicted service life of 23 years, nearly the same as the control which was tainted with recycled engine oil bottoms (REOB). In contrast, sol-type 3.5 % SBS modified binder and straight-run Cold Lake asphalt binder are expected to last around 60 % longer at 36 and 38 years, respectively. Conclusions from this study reiterate that current specifications fail to correlate with field performance. Improved binder grading is possible by limiting the slope of the phase angle master curve between 30° and 45°.

Graphene oxide dispersion in epoxy resin prepared by direct phase transfer from ethanol: Rheology and aging

Graphene oxide addition to epoxy still presents challenges related to attaining optimized dispersion in scale-up production. Herein, the synthesis of high-quality GO by exfoliation in ethanol enabled the spontaneous phase transfer of GO from solvent to epoxy resin to produce a masterbatch with 1.5 wt.% GO content. Nanocomposites with 0.25 wt.%, 0.50 wt.% and 0.75 wt.% nanofiller contents were obtained by masterbatch dilution in epoxy resin. The results reveal the presence of a partial cross-linked network in these nanocomposites associated with the presence of GO, even without the use of a hardener. Thermogravimetric analysis showed the influence of GO on the oxidative decomposition mechanism of epoxy resin, whose behavior was assigned to strong interactions in the GO-epoxy interphase. Furthermore, the rheological behavior changes demonstrate the high quality of the GO dispersion in the resin obtained in this work. The nanocomposites showed high viscosity increases over time and pseudoplastic behavior, which was completely different from the neat epoxy resin. Aged nanocomposites without hardener present a first chemically cross-linked layer of epoxy to GO (∼ 10% for nanocomposite at 0.50 wt.% GO content) and a supramolecular coating interacting and entangled with these structures (> 40% of epoxy chains for EP-GO50).

Improving Alkali Polymer Flooding Economics by Capitalizing on Polymer Solution Property Evolution at High pH

Summary Alkali polymer (AP) flooding is a promising enhanced oil recovery (EOR) method to increase oil recovery from reactive oils. It is essential to carefully select the alkali and polymer type and concentration to optimize incremental oil recovery. In addition to the conventional laboratory tests for polymer flooding, the effects of the high pH on the polymer and its evolving properties over time need to be investigated. Consideration of near-wellbore and reservoir effects is key in designing the process. We are showing how understanding and taking advantage of the polymer performance in a high pH environment allow for cost reduction and increase in injectivity and incremental oil recovery for AP projects. The polymer performance was evaluated for AP flooding of the Matzen field (Austria). Evaluations included changes in polymer rheology during aging at high pH conditions, phase behavior tests, and single-/two-phase corefloods with aged and nonaged polymer solutions. In addition, adsorption of the aged polymer and interfacial tension (IFT) were measured. The aging was studied in anaerobic conditions at reservoir temperature and through an accelerated method at elevated temperatures. The accelerated method developed earlier for neutral pH range provides a possibility to run aging at elevated temperatures in a short time frame and transfer the data to reservoir temperature to give information on the long-term performance. The transfer takes place through a conversion factor derived from the first-order kinetics of acrylamide hydrolysis in pH 6–8. In the present work, the applicability of the accelerated method is evaluated for elevated pH by determining the degree of polymer hydrolysis over time via nuclear magnetic resonance and linking it to viscosity performance at various temperatures. The AP conditions in the Matzen AP flooding project (pH &amp;gt; 10) lead to an increased initial rate of polymer hydrolysis of the tested hydrolyzed polyacrylamide (HPAM) by a factor of 100 compared to hydrolysis at a neutral pH level. This resulted in a rapid increase in a polymer solution viscosity of 160% compared with initial conditions within days at a reservoir temperature of 49°C, after which the viscosity leveled off. Accelerated aging experiments at higher temperatures predict long-term stability of the increased viscosity level for several years. Single-phase injection test in a representative core confirmed the performance of the aged solution compared to a nonaged solution at the same polymer concentration. The retention of polymers is reduced in AP conditions compared with traditional neutral pH conditions, 19 vs. 48 µg/g in the static adsorption test, respectively. Two-phase coreflood tests showed increased polymer viscosity at reservoir conditions. The displacement efficiency of the aged and nonaged polymer solution was similar, confirming the potential for cost savings using lower polymer concentration. This is leading to an improved injectivity and makes use of the increased polymer viscosity down in the reservoir through hydrolysis. The current work combines multiple aspects that should be considered in the proper planning of AP projects—not only improvements in polymer viscosity performance due to water softening but also long-term effects due to increased pH. Additionally, these aspects are combined with changes in adsorption properties. The results show that the design of AP projects will benefit from the holistic approach and understanding the changes in polymer rheology with time. The costs of AP projects can be reduced owing to the lower required polymer concentrations for the same displacement efficiency and reduced retention of polymer. An efficient design of AP projects takes good injectivity of nonaged polymers and the aging of the polymer solutions in alkali into account. Overall, we aim to reduce the polymer concentration—which is a key cost driver—compared with a nonaged application. We show that for AP effects, these effects should be evaluated to improve the economics.

On the evolution of oil-separation properties of lubricating greases under shear degradation

The bleed rate of a grease may change over time due to degradation of the thickener microstructure and a decrease in oil content, as oil is released from the grease. In this work, the bleed properties—quantified by the permeability—of five types of lubricating greases are studied. Controlled shear ageing is performed using a grease worker. It is shown that the bleed rate does not change significantly in a grease worker at room temperature, as opposed to changes in rheology and microstructure. This is explained using a permeability model. It is shown, via a comparison with rolling bearings results, that ageing grease in a grease worker is too mild to yield significant changes in the permeability of lubricating greases.

Numerical analysis of lubricated point contacts using the Finite Area Method

Validation of a contact model which is sensitive to the elastoplastic deformation of asperities and rheological changes to the lubricant properties is presented. The contact model was derived using a two-dimensional variant of the Finite Volume Method, the Finite Area Method, and was implemented in foam-extend, an OpenFOAM fork. The contact lubrication model combines a modified Reynolds equation incorporating a cavitation algorithm, a deterministic contact model and a thermal contact model. The final model can be used to analyse lubricant flow and cavitation, changes of lubricant properties, including changes due to temperature variations and non-Newtonian effects, and asperity contact of rough surfaces. The cumulative validation of the aforementioned models was performed on two ball-on-disc test cases, which use two different types of oil (Turbo T9 and T68 oils). The numerical results were validated against experimental measurements for ball-on-disc tribological experiments found in the literature and available numerical data.

Rheological changes in melts and magmas induced by crystallization and strain rate

This review highlights the rheological and phase proportions variation induced by cooling events from superliquidus temperature (melt) to subliquidus temperatures. It provides a comprehensive view of the rheological response of magmatic systems undergoing dynamic cooling and shear deformation. The two main parameters which are of importance to model the rheological properties of such crystallizing systems and which are simultaneously poorly investigated so far are crystallization and strain rates. The response to relatively high deformation rates results in shear thinning behavior in partly crystallized systems under variable shear rate and it should be considered in magmatic processes. Due to the sluggish crystallization of SiO 2 -rich melts, data are mainly available for mafic systems, which does not allow a general reappraisal. An attempt to model available literature data for less evolved systems in dynamic scenarios and a comparison with MELTS algorithm approach (thermodynamic equilibrium conditions) is provided. Since there are difficulties in comparing experimental data gained using different methodologies, we focus mainly on data obtained with the concentric cylinder technique. This highlights the fact that a general experimental protocol is needed in order to compare and model viscosity data to predict the dynamic rheological evolution for volcanic rocks.