Rheologica Acta最新文献

In this paper, we propose a novel method to classify battery slurries using echo state network (ESN) model with real-time pressure and flow rate signals during circulating channel flows. To collect the signal, a closed circuit flow system with a pump, pressure sensors, and flow rate sensors is installed. The slurries with different states are prepared by two methods: long-term circulation and dispersant content control. Sensor signals are collected while the slurries are flowing through the pipe system. The collected signals show distinctive chaotic fluctuating patterns for different slurries, which are assumed to reflect the states of the slurries. The hidden state of the ESN is generated from these collected data, which are then split into training and test data. Consequently, the ESN can effectively distinguish the slurries by the output (label). We also analyze the accuracy of the network, based on training time and output averaging time. This study demonstrates that the states of the slurries can be detected from the fluctuating flow signals. We argue that the manufacturing process of any complex fluid can be optimized with this approach.

Hemorheology is the study of blood flow and the mechanical stresses and kinematics involved. The Casson constitutive equation is a popular and simple model used to describe the steady shear rheology of blood, with only two parameters that specify an infinite shear viscosity and a yield stress that depend on blood physiology. Previous literature has identified hematocrit and fibrinogen concentration as the two most important physiological factors that affect blood flow, but previous parameterizations of the Casson model may not be reliable due to the use of non-standardized data sets. This study uses machine learning and the largest standardized dataset to improve the parameterization of the Casson model with respect to hematocrit and fibrinogen concentration for healthy individuals. The study also employs machine learning to identify a potential additional factor, the mean corpuscular hemoglobin (MCH), that may affect blood rheology. The proposed approach demonstrates the potential for machine learning to improve the connection between physiology and blood rheology with possible implications in cardiovascular diagnostics.

Rheological analysis is an important tool to investigate the structural characteristics of materials widely used in the biomedical field, such as polymer solutions, colloids, and hydrogels. In this work, we studied the rheological properties of a colloidal system composed of carboxymethyl cellulose (CMC) and Laponite, both biocompatible materials. Rheological properties of CMC/Laponite aqueous dispersions are influenced by electrostatic interactions and hydrogen bonds between the silanol (Si–O) groups of Laponite and hydroxyl (-OH) of CMC. It was found that the effect of Laponite rheological behavior is strongly affected by CMC concentration, resulting in weak or strong gels. Adding CMC reinforces the blended network, increasing the storage (left({G}^{^{prime}}right)) and loss (left(G''right)) moduli, as well as viscosity. CMC/Laponite gels presented strong shear-thinning and thixotropy due to structural rearrangements when subjected to shear stresses. Moreover, time sweep tests revealed that adding CMC inhibited Laponite aging.

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Surfactant-water mixtures display a complex rheological behaviour, with changes in parameters such as viscosity and moduli of several orders of magnitude as a consequence of phase changes, depending on their concentration and temperature: this criticism heavily affects different industrial processes. In our work, linear rheological behaviour of aqueous mixtures of a commercial anionic surfactant, sodium lauryl ether sulphate, is investigated in a range of temperature (30–60 °C) and surfactant concentration (20–72%wt) of technological relevance. Four phases with different texture are identified by polarised light microscopy: micellar, hexagonal, cubic and lamellar, all showing a shear-thinning behaviour. Rheological parameters of cubic phase show a net jump in a relatively narrow temperature range, suggesting a temperature-induced phase change. The systematic analysis of the rheological behaviour of this widely used surfactant system, reported here for the first time, can be of fundamental support for many industrial applications.

Graphical Abstract

Samples of two commercial low-density polyethylene melts were investigated with respect to their fracture behavior in controlled uniaxial extensional flow at constant strain rate in a filament stretching rheometer. In order to assess the possible influence of grain boundaries on fracture, the samples were prepared by three different types of pre-treatment: by compression molding of (1) virgin pellets used as received, (2) pellets homogenized in a twin-screw extruder, and (3) pellets that were milled into powder by cryogenic grinding under liquid nitrogen. The elongational stress growth data were analyzed by the Extended Hierarchical Multi-mode Molecular Stress Function (EHMMSF) model developed by Wagner et al. (Rheol. Acta 61, 281-298 (2022)) for long-chain branched (LCB) polymer melts. The EHMMSF model quantifies the elongational stress growth including the maximum in the elongational viscosity of LDPE melts based solely on the linear-viscoelastic relaxation spectrum and two nonlinear material parameters, the dilution modulus G_D and a characteristic stretch parameter ({overline{lambda}}_m). Within experimental accuracy, model predictions are in excellent agreement with the elongational stress growth data of the two LDPE melts, independent of the preparation method used. At sufficiently high strain rates, the fracture of the polymer filaments was observed and is in general accordance with the entropic fracture criterion implemented in the EHMMSF model. High-speed videography reveals that fracture is preceded by parabolic crack opening, which is characteristic for elastic fracture and which has been observed earlier in filament stretching of monodisperse polystyrene solutions. Here, for the first time, we demonstrate the appearance of a parabolic crack opening in the fracture process of polydisperse long-chain branched polyethylene melts.

In this work, we investigate the large amplitude oscillatory shear (LAOS) behavior of white-wheat, wholegrain-wheat and chickpea flour doughs experimentally and theoretically. In order to accurately model the LAOS behavior of those doughs, it was important to study their linear viscoelastic as well as stress relaxation behaviors. We analyzed the linear viscoelastic behavior theoretically through the single spring-pot model, the fractional Maxwell model (FMM) and the fractional Kelvin-Voigt model. We found that the FMM is best suited to describe the LVE of the doughs we investigated. The damping function form was chosen based on stress relaxation and strain sweep experiments. We found that the Soskey-Winter (SW) equation is suitable for accurately describing the damping behavior of doughs. The LAOS experimental results were obtained at a set of strain amplitude and frequency values to build the Lissajous-Bowditch curves in Pipkin space. We modeled the LAOS stress response using the Kay-Bernstein Kearsley and Zapas (K-BKZ) model coupled with the FMM and SW models. The SW parameters were optimized for each dough by fitting the LAOS Lissajous-Bowditch curves in Pipkin space. The obtained fits to LAOS stress response were very good and illustrate that the FMM-SW-K-BKZ model provides an excellent description of the LAOS behavior of the different variety of doughs examined in this work. Moreover, the study shows that LAOS Lissajous-Bowditch curves provide characteristically different shapes for wheat and chickpea flour doughs.

The colloidal suspension of magnesium lithium phyllosilicate (MLPS), a synthetic clay that shows complex rheological behaviors, is a promising analogue for natural soft clay. The significant thixotropy of MLPS colloidal suspension controls the solid-liquid transition and affects the application of the material. In this work, the thixotropic yielding behaviors of MLPS with concentrations of 3, 4, 5, and 6 wt% were investigated utilizing rheological testing methods. The static and dynamic yield stresses measured by different methods were analyzed and compared. The flow curves of shear rate ramp tests show inapplicability in determining yield stresses due to shear banding, while the yield stresses obtained by shear stress ramp and oscillatory shear tests exhibit satisfactory consistency. Coupled with a structural kinetics equation, a thixotropic visco-plastic model incorporating static and dynamic yield stress was established to describe the thixotropic yielding behavior of MLPS suspension. The model parameters were conveniently determined via shear ramp tests and step change in shear rate tests with good fitting performance, and the concentration-dependent characteristics of the parameters were also discussed. Based on model prediction and experimental results, the interactions between shear stress, shear rate, and microstructure were analyzed in steady and transient states.

A Pom-Pom polymer with q_a side chains of molecular weight M_w,a at both ends of a backbone chain of molecular weight M_w,b is the simplest branched polymer topology. Ten nearly monodisperse polystyrene Pom-Pom systems synthesized via an optimized anionic polymerization and a grafting-onto method with M_w,b of 100 to 400 kg/mol, M_w,a of 9 to 50 kg/mol, and q_a between 9 and 22 are considered. We analyze the elongational rheology of the Pom-Poms by use of the hierarchical multi-mode molecular stress function (HMMSF) model, which has been shown to predict the elongational viscosity of linear and long-chain branched (LCB) polymer melts based exclusively on the linear-viscoelastic characterization and a single material parameter, the so-called dilution modulus G_D. For the Pom-Poms considered here, we show that G_D can be identified with the plateau modulus ({G}_{N}^{0}={G}_{D}), and the modeling of the elongational viscosity of the Pom-Poms does therefore not require any fitting parameter but is fully determined by the linear-viscoelastic characterization of the melts. Due to the high strain hardening of the Pom-Poms, brittle fracture is observed at higher strains and strain rates, which is well described by the entropic fracture criterion.

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