Wide Range Of Shear Rates Research Articles

Two-species model for nonlinear flow of wormlike micelle solutions. Part II: Experiment

Applications often expose wormlike micelle solutions to a very wide range of shear and temperature conditions. The two-species model presented in Part I [Salipante et al., J. Rheol. 68 (2024)] describes the nonlinear rheology over a wide range of shear rates. Here, we compare the model predictions to measurements using a combination of microcapillary and rotational rheology to measure the viscosity of surfactant solutions across seven decades of shear rate and five decades of viscosity. The effect of temperature is studied between 20 and 60 °C for different surfactant concentrations. Model parameters are determined from both small-amplitude shear measurements and fitting to the nonlinear data. Under shear stress, the model predicts due to hindered combination kinetics that the average micelle length decreases from several micrometers to a few hundred nanometers. At sufficiently high stress, the micelle shear rheology exhibits a transition from entangled wormlike behavior to a dilute rod rheology in agreement with the model. Transient stress-growth measurements exhibit a large overshoot, which is rather well predicted by the model with hindered combination rate. Microcapillary flow birefringence also is adequately predicted by the model, confirming the accuracy of its predicted micelle lengths and exhibiting a marked change in stress-optic response at the transition between entangled polymers and dilute rods. The relaxation of retardance after flow cessation follows model predictions that include micelle-micelle interactions, which are sensitive to the rotational diffusivity and length. These methods can be applied broadly to explore relationships between composition and performance.

Two-species model for nonlinear flow of wormlike micelle solutions. Part I: Model

We develop a rheological model to approximate the nonlinear rheology of wormlike micelles using two constitutive models to represent a structural transition at high shear rates. The model is intended to describe the behavior of semidilute wormlike micellar solutions over a wide range of shear rates whose parameters can be determined mainly from small-amplitude equilibrium measurements. Length evolution equations are incorporated into reactive Rolie-Poly entangled-polymer rheology and dilute reactive-rod rheology, with a kinetic exchange between the two models. Although the micelle length is remarkably reduced during flow, surprisingly, we propose that they are not shortened by stress-enhanced breakage, which remains thermally driven. Instead, we hypothesize that stretching energy introduces a linear potential that decreases the rate of recombination and reduces the mean micelle length. This stress-hindered recombination approach accurately describes transient stress-growth upon start-up shear flow, and it predicts a transition of shear viscosity and alignment response observed at high shear rates. The proposed mechanism applies only when self-recombination occurs frequently. The effect of varying the relative rate of self-recombination on the rheology of wormlike micelles at high shear rates is yet to be explored.

Shear-driven stability of a rigid particle in yield stress fluids

The stability of a rigid particle in yield stress fluids, comprised of soft particle glasses (SPGs), is investigated in shear flow under an applied external force, such as weight, using particle dynamics simulations. Results provide the critical force threshold, in terms of the dynamic yield stress and the flow strength, required to initiate sedimentation of the rigid particle over a wide range of shear rates and volume fractions. The streamlines of the SPGs show local disturbances when the rigid particle settles. The form of these disturbances is consistent with the microdynamics and microstructure response of the neighboring soft particles of the sedimenting rigid particle. Sedimenting particle induces non-affine displacement to the suspensions at low shear rates and high applied forces, while these dynamical events are localized and suppressed at high shear rates. Stability diagrams, which provide the conditions of the sedimentation of the rigid particle, are presented in terms of the applied force and the shear rate. These individual stability diagrams at each volume fraction map onto a universal stability diagram when the external force is scaled by the dynamic yield stress and shear rate with a ratio of the solvent viscosity to the low-frequency modulus of the SPGs.

The rheological behavior of aqueous magnetic fluids over a wide range of shear rates

Abstract A rheological measurement system was constructed to investigate the rheological behavior of magnetic fluids under a wide range of shear rates, and its feasibility was verified. The system is capable of measuring a shear rate range spanning five orders of magnitude, with a maximum shear rate of 106 s−1. It was utilized to study the time required for aqueous magnetic fluids in a magnetic field to reach a steady state, taking into account the coupling effect of the flow field and magnetic field. Additionally, the time needed for the magnetic fluids to return to their initial state after demagnetization was also measured. Based on these measurements, the rheological behavior of magnetic fluids with varying concentrations and magnetic field directions was studied. Results indicate that the residence time of the magnetic fluids in the magnetic field and the de-magnetization time have almost no effect on their viscosity. When the magnetic field direction is perpendicular to the flow direction, regardless of concentration, aqueous magnetic fluids exhibit shear thinning behavior; when it is parallel to the flow direction, high-concentration aqueous magnetic fluids show shear thickening, while low-concentration ones behave as Newtonian fluids. In this study’s shear rate range, no Newtonian regions were found in either high- or low-shear rate regions.

Optimizing the injection molding process for thermally and electrically conductive, carbon fiber and carbon nanotube‐reinforced poly(lactic acid) hybrid composites with enhanced mechanical properties

AbstractWe produced poly(lactic acid) (PLA) matrix carbon fiber and carbon nanotube‐reinforced hybrid composites with enhanced thermal conductivity (0.48–0.59 W/mK) and electrical conductivity (0.35–0.97 S/cm). The conductive fillers greatly decreased the toughness, which was compensated with oligomeric lactic acid (OLA). Since fillers and plasticizers greatly alter the flow and thermal properties of the material as well, it was necessary to optimize several parameters of the injection molding process that were predetermined based on theoretical considerations. Based on oscillatory shear rheometry, we explored the rheological behavior of the materials in a wide temperature and shear rate range for the optimum injection molding temperatures, injection volume rates. We showed that by adding 15 wt% OLA as a plasticizer to the composites, the optimal processing temperature decreased by 45–135°C. This remarkable change illustrates the need for rheological studies of PLA compounds. The injection molded hybrid composites containing 5% oligomeric lactic had a tensile strength, modulus of elasticity, and work of fracture higher by 41%, 10%, and 150%, respectively, compared to samples without OLA.

Rheological Property Modification of a Molten-State Polyamide through the Addition of an α-Olefin-Maleic Anhydride Copolymer.

The rheological properties of a polyamide (PA) resin with low crystallinity were modified by melt-mixing it with a small amount of an alternative α-olefin-maleic anhydride copolymer as a reactive compound. Because PA has a low melting point, rheological characterization was performed over a wide temperature range. Owing to the reaction between PA and the alternative α-olefin-maleic anhydride copolymer, the blend sample behaved as a long-chain branched polymer in the molten state. The thermo-rheological complexity was obvious owing to large flow activation energy values in the low modulus region, i.e., the rheological time-temperature superposition principle was not applicable. The primary normal stress difference under steady shear was greatly increased in the wide shear rate range, leading to a large swell ratio at the capillary extrusion. Furthermore, strain hardening in the transient elongational viscosity, which is responsible for favorable processability, was clear. Because this is a simple modification method, it will be widely employed to modify the rheological properties of various polyamide resins.

Microfluidic Rheology: An Innovative Method for Viscosity Measurement of Gels and Various Pharmaceuticals.

Measuring the viscosity of pharmaceutical dosage forms is a crucial process. Viscosity provides information about the stability of the composition, the release rate of the drug, bioavailability, and, in the case of injectable drug formulations, even the force required for injection. However, measuring viscosity is a complex task with numerous challenges, especially for non-Newtonian materials, which include most pharmaceutical formulations, such as gels. Selecting the appropriate shear rate is critical. Since viscosity in many systems is highly temperature-dependent, stable temperature control is necessary during the measurement. Using microfluidics technology, it is now possible to perform rheological characterization and conduct fast and accurate measurements. Small sample volumes (even below 500 µL) are required, and viscosity determination can be carried out over a wide range of shear rates. Nevertheless, the pharmaceutical application of viscometers operating on the principle of microfluidics is not yet widespread. In our work, we compare the results of measurements taken with a microfluidic chip-based viscometer on different pharmaceutical forms (gels, solution) with those obtained using a traditional rotational viscometer, evaluating the relative advantages and disadvantages of the different methods. The microfluidics-based method enables time- and sample-efficient viscosity analysis of the examined pharmaceutical forms.

Rheological Behavior Features of Feedstocks with a Two-Component Wax–Polyolefin Binder Compared to Analogs Based on Polyoxymethylene

Despite the large number of studies devoted to different compositions of polymer binders for PIM technology, the actual task is still a comparative analysis of the properties of different types of binders to determine their advantages and disadvantages and optimize the compositions used. In this regard, this study aims at the identification and comparative analysis of the rheological properties of the most demanded feedstocks with binders based on polyoxymethylene and a wax–polyolefin mixture under the condition of using identical steel powder filler. The rate of change in the volume fraction of the liquid phase of the binder in the compared feedstocks with temperature change was determined by the calculation–experimental method. As shown, the temperature dependence of the viscosity of feedstocks with a binder based on a polymer blend depends on factors with variable power, i.e., the viscosity change with temperature occurs by different mechanisms with their relaxation spectra. Thus, the principle of temperature–time superposition for feedstocks with multicomponent binders is not applicable, and the study of the viscosity of such materials should involve a wide range of shear rates and temperatures using experimental methods. Capillary rheometry was used to measure the flow curves of feedstocks based on polyoxymethylene and wax–polyolefin binders. The analysis of flow curves of feedstocks showed that feedstocks with a binder of solution–thermal type of debinding have significantly lower viscosity, which is an advantage for molding thin-walled products. However, their difference of 1.5 times sensitivity to the shear rate gradient leads to their lower resistance to “jets” and liquation of components because of shear rate gradients when molding products with elements of different cross-sectional areas.

Vibrorheology of fresh cement-based materials with different compaction energy

Vibration is commonly applied to the placement of cement-based materials to improve their fluidity and compactness. Appropriate compaction could ensure the designed performance by preventing the formation of voids and cavities within a structure. In recent years, the application of vibration has been extended to the rheology control of 3D printable concrete as well. While previous studies have reported on the effective radius of compaction and rheological changes in cement-based materials induced by poker-type vibrators, there has been limited in-depth research on the rheological behavior beyond this effective radius, particularly in relation to the compaction energy. This study investigates the rheological behavior of a cement-based material under controlled vibration energy across a wide range of shear rates. A novel device is proposed for the precise control of compaction energy, in terms of the energy transfer rate per unit volume (power density) of vibration, and the vibrorheology under various power densities is measured. Experimental results reveal that viscosity at a low shear rate decreases proportionally to power density, while vibration has negligible effects on viscosity at a high shear rate. Furthermore, a correlation between power density and normalized yield stress is established, along with the effects of varying water-to-cement ratios. The study also discusses the influence of the vibration frequency on the effective radius of the poker-type vibrator.

Influence of shear deformation on the formation of dynamic structure in protic ionic liquids. Representation of the temperature dependence of viscosity within the framework of Angell’s fragility concept

The rheological properties of a liquid containing two types of basic centers and hydroxyl groups (BGE-Im), as well as protic ionic liquids (ILs) derived from it, were studied in a wide range of shear rates (γ̇) (10−6–103 s−1) at various temperatures from 10 to 50 °C. Viscosity (η) of the BGE-Im does not depend on the scanning direction of shear stress (σ), i.e. this compound behaves like a Newtonian fluid over the entire range of σ. The dependence log η (1/T) of BGE-Im in Arrhenius coordinates is linear. Protonation of basic centers of BGE-Im leads to a strong increase in the viscosity of ILs obtained on its basis, and the temperature dependence of the viscosity of these ILs is described by the Vogel–Fulcher–Tammann (VFT) equation. It has been established that in the region of low shear rates, the viscosity of the ILs increases with decreasing shear rate, which leads to the appearance of a yield stress (σY). This indicates the formation of a fluctuation rheopectic structure in the ILs. In this sense, ILs are heterogeneous systems and their behavior is similar to that of highly concentrated suspensions and emulsions. For the first time, a quantitative comparison between the parameters of the VFT equation, the fragility (according to Angell’s model) of ILs, the relative coordination number of ILs molecules and the rheological yield stress characterizing the shear-induced fluctuation rheopectic structure of ILs has been made and the relationship between these characteristics has been shown.

Rheological properties of water-based amino acid ionic liquids

The rheological properties and zero-shear viscosity of water-based lubricants (WBLs) containing amino acid ionic liquids (AAILs) were investigated using both equilibrium (EMD) and non-equilibrium molecular dynamics (NEMD) simulations. We also performed experimental measurements to validate the simulations. The simulations demonstrated that adding AAIL additives to water increased both the shear viscosity and zero-shear viscosity. We added tetrabutylphosphonium (P4444) as a cation and three different amino acids, serine (Ser), lysine (Lys), or phenylalanine (Phe), as anions. We varied the AAIL concentration from 5 to 10 wt. % for tetrabutylphosphonium-serine (P4444-Ser) ionic liquid additives, showing that AAILs increased water viscosity by 68%–125%, depending on concentration. The P4444-Ser WBLs also exhibited a significantly higher first normal stress difference than water, meaning they could support more load in lubrication. The improved rheology persisted over a wide range of shear rates up to ∼1011 s−1. We have extracted full rheological parameters by fitting data into Cross, Carreau–Yasuda, and Eyring models, including zero-shear viscosity and critical shear rates of onset shear thinning. The experimental values of zero-shear viscosity were close to zero-shear viscosity results obtained from fitting NEMD results to these models, demonstrating the high fidelity of the molecular model. We explored the formation of hydration shells around amino acid anions as a marker for low friction behavior. These findings suggest that AAIL WBLs can be potentially low-friction and biodegradable lubricants in tribological applications.

Whole Blood Viscosity Reference Intervals and Its Correlation with Hematology and Serum Chemistry in Cats Using Scanning Capillary Method

Whole blood viscosity, a hemorheological factor, is currently used for diagnosis, as it is correlated with various vascular diseases that are difficult to diagnose early with a general blood test. It was determined that it was necessary to set reference intervals for further studies and utilization of whole blood viscosity in cats, a representative companion animal, and this study was conducted. Fifty healthy cats were recruited for the study, and whole blood viscosity, complete blood count, and serum chemistry tests were performed. The reference intervals of whole blood viscosity were 15.169 to 43.684 cP at a shear rate of 1 s−1 reflecting diastole, and 3.524 to 5.544 cP at a shear rate of 300 s−1 reflecting systole. Red blood cells, hematocrit, hemoglobin, white blood cells, and neutrophils in the complete blood count, and total protein, albumin, globulin, and cholesterol in the serum chemistry were significantly correlated with whole blood viscosity. The results of this study set the reference intervals of whole blood viscosity for healthy cats in a wide shear rate range that has not yet been fully established, and its correlation with other blood indicators investigated.

The influence of alkyl ammonium modifiers on the microstructure and high-pressure rheology of sepiolite-vegetable oil dispersions

In the context of environmental sustainability, the drilling industry faces new challenges resulting in the study and development of new drilling fluids based on eco-friendlier components to replace harmful mineral oils. Organic modified sepiolite dispersed in oil is an excellent additive to provide suitable rheological properties at low concentrations. The present study investigates the effect of alkyl ammonium modifiers on the microstructure and rheological properties of sepiolite-vegetable oil dispersions under high-temperature (up to 140 °C) and high-pressure (up to 2000 bar) conditions. Organo-sepiolite, prepared using a high-shear processing method and containing surfactant with alkyl chains longer than 12 carbon atoms, exhibited a high degree of surface adsorption and thermal resistance. All modifiers developed a stable fibrous structure in the dispersion. This structure maintained the pseudoplastic behavior in a wide range of shear rate, temperature and pressure without reaching an apparent yield stress. These dispersions showed suitable rheological and thermal properties to develop sustainable drilling fluids.

Relative Influences of Inertia and Polymeric Viscoelastic Effects on Nusselt Numbers within Rotating Couette Flows

In past investigations of elastic instabilities and elastic turbulence, almost no attention has been devoted to the effects and influences of inertial phenomena. Within the present investigation, Nusselt number data are provided to illustrate the relative influences of inertia and polymeric viscoelastic phenomena within a rotating Couette flow (RCF) environment. Data are provided from experimental measurements of local surface heat transfer characteristics for different flow passage heights, one radial position, and different values of disk rotational speed for polyacrylamide polymer concentrations ρ of 0 ppm, 100 ppm, 150 ppm, and 300 ppm. With this approach, data for a wide range of shear rate γ˙ values, Weissenberg numbers, and first normal stress difference values are provided. Nusselt number data are provided as dependent upon a newly developed P′ parameter, equal to ReEI/Re0.22, which collapse into a single distribution over the range of P′ values considered which range from 0 to about 182. Such characteristics indicate that the P′ parameter provides an appropriate means to simultaneously account for the relative influences of inertia and polymeric viscoelastic effects. The use of such a power law dependence for Re additionally gives P′ values which are dominated by ReEI values when the Weissenberg number Wi is greater than the elastic instability transition onset value. The experimental conditions associated with this value correspond to the change from inertia domination (with buoyance influences) to polymeric viscoelastic domination which occurs for shear rates in the vicinity of 11 to 12 s−1. For Weissenberg numbers greater than the onset value, Nusselt numbers associated with H = 5 mm are generally the highest values measured, with magnitudes that steadily increase with γ˙. Associated Nusselt numbers become as high as about 3.0, whereas zero-shear rate values (obtained with zero rotation) are in the vicinity of 1.0. At lower Weissenberg number magnitudes (below the transition onset value), Nusselt numbers cover a wide range of values as experimental conditions and configuration are varied, as a consequence of the complicated and simultaneous influences of inertia, buoyancy, and dilute polymer presence.

A General Deep Learning Method for Computing Molecular Parameters of a Viscoelastic Constitutive Model by Solving an Inverse Problem.

Prediction of molecular parameters and material functions from the macroscopic viscoelastic properties of complex fluids are of great significance for molecular and formulation design in fundamental research as well as various industrial applications. A general learning method for computing molecular parameters of a viscoelastic constitutive model by solving an inverse problem is proposed. The accuracy, convergence and robustness of a deep neural network (DNN)-based numerical solver have been validated by considering the Rolie-Poly model for modeling the linear and non-linear steady rheometric properties of entangled polymer solutions in a wide range of concentrations. The results show that as long as the DNN could be trained with a sufficiently high accuracy, the DNN-based numerical solver would rapidly converge to its solution in solving an inverse problem. The solution is robust against small white noise disturbances to the input stress data. However, if the input stress significantly deviates from the original stress, the DNN-based solver could readily converge to a different solution. Hence, the resolution of the numerical solver for inversely computing molecular parameters is demonstrated. Moreover, the molecular parameters computed by the DNN-based numerical solver not only reproduce accurately the steady viscoelastic stress of completely monodisperse linear lambda DNA solutions over a wide range of shear rates and various concentrations, but also predict a power law concentration scaling with a nearly same scaling exponent as those estimated from experimental results.

A versatile and customizable low-cost printed multipass microrheometer for high-throughput polymers rheological experimentation

We report the design of a multipass microrheometer that can be fully customizable at a low cost and reasonable time, which allows us to perform experiments rapidly and in a broad range of shear rates (i.e., from 0.1 to 100 s−1), using small amounts of material (i.e., just some milligrams). Additionally, the low-cost approach opens for an easy parallelization of the setup that makes it suitable for high-throughput rheological experimentation of polymer melts (HT-Rheo-E). The novel rheometer consists of a microchannel (i.e., a microcapillary or a microslit) in which the fluid flows driven by two controlled millimetric pistons (diameter of 2 mm). Two piezoelectric miniaturized pressure sensors are placed at the microchannel entrance and exit to record the pressure drop across the capillary during the motion. The current work reports the design of the rheometer with two different cross sections of the microchannel, i.e., circular and rectangular, and measurements of the shear viscosity with a Newtonian and a non-Newtonian polymer over a wide range of shear rates using less than 1 g of sample. We demonstrate that the current multipass microrheometer can measure viscoelastic properties of polymers by applying an oscillatory flow. The printed setup is of potential interest for applications in quality control in industrial production, in natural systems (such as starch-based mixtures) and academic research where rapid and repeated measurements using limited milligrams of polymer are required (e.g., biological systems).

HEMORHEOLOGICAL MODELS APPLIED TO DATA ANALYSIS IN GROUPS OF PATIENTS AND IN HEALTHY SUBJECTS

An overview of some mathematical models describing the rheological behavior of blood is done. Several known models were used to describe the non-Newtonian rheological properties of blood. The parameters of two of the simplest models — the power law and the Herschel–Bulkley law were used to analyze the differences between the microrheological and micromechanical characteristics of blood in a group of patients with diabetes mellitus type 2 (T2DM) and in healthy subjects. The experiments were carried out with Low Shear 30 (LS 30) Contraves viscometer in a wide range of shear rates. All experimental data were statistically processed using the Mann–Whitney U-test for intergroup comparison of independent variables, as well as the t-test. The Statistica program was used for statistical processing. The results obtained are compared with the hemorheological models from other disease states.

Scavenging of polystyrene microplastics by sediment particles in both turbulent and calm aquatic environments

Microplastic particles (MP) are emerging pollutants ubiquitously distributed in all aquatic environments, remaining in suspension in the water column or deposited in sediment beds. MP are suspended in the water column along with other particles with whom they might interact. The current study presents the results of slow-settling MP (Polystyrene) scavenged by fast-settling sediment particles. The study covers a wide range of salinities (from freshwater to saltwater) and shear rates (from calm to mixing ecosystems). In calm regions, the scavenging by fast-settling sediment particles produces the greatest removal of MP from the water column (42 % of MP in suspension), thus increasing the MP pollution of sediment beds. In contrast, turbulence reduces the settling of MP and sediment particles (72 % of MP remain in suspension), causing more pollution than in calm regions.Although salinity increased the buoyancy of MP, the scavenging by sediment has been found to overcome the increase in buoyancy. Consequently, MP are transported to the sediment bed independently on the salinity. Therefore hotspots of MP contamination in aquatic environments need to consider both the MP and sediment interaction and the local mixing of the water column.

Analyzing and Predicting the Viscosity of Polymer Nanocomposites in the Conditions of Temperature, Shear Rate, and Nanoparticle Loading with Molecular Dynamics Simulations and Machine Learning

Predicting the viscosity (η) of polymer nanocomposites (PNCs) is of critical importance as it governs a dominant role in PNCs' processing and application. Machine-learning (ML) algorithms, enabled by pre-existing experimental and computational data, have emerged as robust tools for the prediction of quantitative relationships between feature parameters and various physical properties of materials. In this work, we employed nonequilibrium molecular dynamics (NEMD) simulation with ML models to systematically investigate the η of PNCs over a wide range of nanoparticle (NP) loadings (φ), shear rates (γ̇), and temperatures (T). With the increase in γ̇, shear thinning takes place as the value of η decreases on the orders of magnitude. In addition, the φ dependence and T dependence reduce to the extent that it is not visible at high γ̇. The value of η for PNCs is proportional to φ and inversely proportional to T below the intermediate γ̇. Using the obtained NEMD results, four machine-learning models were trained to provide effective predictions for the η. The extreme gradient boosting (XGBoost) model yields the best accuracy in η prediction under complex conditions and is further used to evaluate feature importance. This quantitative structure-property relationship (QSPR) model used physical views to investigate the effect of process parameters, such as T, φ, and γ̇, on the η of PNCs and paves the path for theoretically proposing reasonable parameters for successful processing.

Multivariable Rheological Models for Commercial Polypropylene with High Molar Masses

AbstractThis work investigates the fitting performance of conventional rheological models and the development of multivariable rheological models to reproduce experimental rheological data of different industrial grades of linear isotactic polypropylene (iPP) having high mass average molar masses, Mm (164–404 kg mol−1), at three temperature values (180–220 °C) over a wide range of shear rates (10−1–104 s−1). A shear thinning behavior is found in all investigated conditions. However, a low shear rate primary Newtonian plateau for a short shear rate range is only identified for the smallest Mm among those investigated, and for higher Mm such primary plateaus are even found at shorter shear rate range. Among the investigated models, only Cross and Carreau–Yasuda models are effective to reproduce the data for a specific PP grade. Two modified models are proposed that incorporate three variables. In the modified Cross Model, it has been shown that the characteristic time (λ) between the Newtonian plateau at the low shear rates and the shear‐rate range with shear‐thinning behavior depends exponentially on the Mm, and it does not depend on the temperature. Both proposed models fit very well with the experimental data with shear thinning behavior for a wide range of Mm.