Rheologica Acta最新文献

The rheological behaviour of a polymer was investigated by performing numerical simulations in complex flow and comparing them to experiments. For our simulations, we employed a Smoothed Particle Hydrodynamics scheme, utilising an integral fractional model based on the K-BKZ framework. The results are compared with experiments performed on melt-state isotactic polypropylene under medium and large amplitude oscillatory shear. The numerical results are in good agreement with the experimental data, and the model is able to capture and predict both the linear and the non-linear viscoelastic behaviours of the polymer melt. Results show that equipping SPH with an integral fractional model is a promising approach for the simulation of complex polymeric materials under realistic conditions.

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Dairy fouling consists in the accumulation of whey proteins and minerals on equipment walls. While heat-induced protein denaturation is a primary cause, fouling also occurs below the denaturation threshold (≈ 70 °C). This leads to a renewed interest in other driving forces influencing fouling mechanisms. In this wake, this study investigates the role of shear on the formation of whey protein deposits under sub-denaturation temperature and concentrated conditions. We compared morphology and rheological behavior of shear-induced and unsheared structures formed at 15 and 20 wt% protein concentrations. While unsheared gel-like deposits were compact and stiff, shear led to the formation of weaker, more porous, and highly crosslinked structures. This effect was more pronounced at higher concentrations, where shear counteracted heat-induced aggregation, resulting in an alternative structural organization. These findings provide new insights not only into whey protein gelation but also into dairy fouling mechanisms, highlighting a concentration-dependent shear effect.

Graphical Abstract

Tribological components such as bearings and gears sustain a tremendous external load and operate at high relative speeds. For hydrodynamically lubricated contacts, subject to these extreme conditions, the lubricating fluid film exhibits non-Newtonian characteristics. In particular, when the ratio of fluid relaxation time to the flow residence time, i.e., the Deborah number ((varvec{De})), becomes appreciable, viscoelastic effects emerge. In this work, we model the effect of viscoelasticity using the viscoelastic Reynolds equation (VR) in cylindrical coordinates under the ultra-dilute limit in which the solvent concentration in terms of viscosity is larger than the polymeric contribution. As such, the velocity field remains Newtonian and the polymer stress constitutive relation is further simplified. We examine the effect of fluid viscoelasticity on the load carrying capacity for two geometries; (i) a conical configuration (that could be aligned or misaligned) and (ii) a flat surface embedded with different kind of textures. Our results show that viscoelasticity can enhance the load carrying capacity in both cases. Small errors in alignment strongly affect the trend in the load versus (varvec{De}) and a strong nonlinear trend emerges exhibiting load both saturation and diminishment. Introducing pockets in the surface further improves the load bearing capability beyond the Newtonian values. However, numerical simulation of such textured configurations is challenging and, unlike the inclined asymmetric cone, large values of the Deborah number could not be reached.

We investigated structure–rheology relationships in oil-in-water Pickering emulsions stabilized by hydrophilic fumed silica (Aerosil) with a cationic co-emulsifier (didodecyldimethylammonium bromide, DDAB). A systematic composition matrix (Aerosil 2–6 wt%; DDAB 1–9 mg per 3 mL oil) decouples particle from surfactant effects. Optical microscopy and SEM/EDS confirm silica-armored droplets; morphological stability requires sufficiently high particle loading and modest DDAB, whereas low Aerosil or very low DDAB leads to merged “lakes”. Steady flow shows strong shear-thinning and a pronounced first-interval effect: the initial high-rate sweep erases the rested structure, after which start-up curves become reproducible. Oscillatory tests establish weak-gel signatures (G’ > G”, weak frequency dependence), with strain sweeps revealing a clear elastic plateau and a G” peak near yield. Increasing Aerosil elevates the modulus scale, broadens the linear-viscoelastic window, and delays softening; increasing DDAB at fixed particle fraction softens the emulsion and advances yielding. Multiple-interval thixotropic tests (miTT) quantify flow-history memory: the recovered small-amplitude moduli G’(γ̇_prev) and G”(γ̇_prev) decrease monotonically with prior shear rate, recover only partially between pulses, and—when normalized—show greater resilience at higher Aerosil but heightened sensitivity with surplus DDAB. These insights provide a practical formulation window for tunable, robust emulsions.

We present an experimental microfluidic platform capable of reconstructing full three-dimensional trajectories of single particles in viscoelastic fluids by exploiting oscillatory flow. The system combines synchronized high-speed imaging from orthogonal perspectives with a custom-fabricated square microchannel and optical correction techniques, enabling high-resolution, time-resolved observation of particle dynamics. The device is applied to study the migration of spherical particles in Polyethylene Oxide solutions, providing the first complete measurements of particle trajectories in such flows. The effects of initial particle position, flow rate, oscillation period, and fluid rheology are systematically analyzed.

The poor low-temperature flowability of waxy crude oil poses significant challenges for pipeline transportation. To address the issue, this study systematically investigates the potential of graphene materials as novel flow improvers, utilizing steady and dynamic rheology in conjunction with microstructural characterization techniques. Rheological analyses demonstrate that graphene at an optimal concentration of 400 ppm reduces the viscosity of the oil by 23.43% and lowers the pour point by 5.1 ± 0.5 °C in oil with 7.4 wt% wax. The graphene weakens the gel structure’s strength, decreasing the thixotropic loop area by 22.63% and the critical shear stress from 63 Pa to 16 Pa. The addition of graphene substantially reduced the median wax crystal length from 39.15 μm to 18.77 μm and enhanced structural disorder. These findings establish a relationship between graphene modification, wax crystal evolution, and improved flowability, thereby providing fundamental insights into the application of graphene for enhancing the flow assurance of waxy crude oil in pipeline transportation.

The present study reports a quantitative analysis of the gelation kinetics and mechanical behaviour of chitosan-based hydrogels chemically crosslinked with glyoxal. Time-resolved mechanical spectroscopy (TRMS) was coupled with non-parametric generalised additive models (GAM) to accurately model the evolution of viscoelastic moduli and determine statistically key parameters at the gel point, including gel time (t_g), gel stiffness (S), and relaxation exponent (Δ). The effect of polymer and crosslinker concentrations on these parameters was established with the use of GAM and validated by multivariate linear regression, yielding interpretable parametric models. In a similar way, a detailed statistical analysis of oscillatory and uniaxial compression measurements of fully gelled hydrogels in both swollen and dry states revealed distinct trends in mechanical response: crosslinker concentration enhanced stiffness in the swollen state but exhibited a saturation effect in the dry state. Convolutional neural network (U-Net) analysis of scanning electron microscopy (SEM) images was, finally, able to provide structural insight correlating pore morphology with mechanical properties. The findings demonstrate the utility of statistical learning tools in increasing knowledge of the mechanical and morphological properties of hydrogels.

Graphical Abstract

Magnetorheological (MR) fluids exhibit field-dependent rheological behavior arising from the reversible formation of particle chains under applied magnetic fields. Predicting the static yield stress of these systems remains a central challenge in their modeling and design. This work presents a closed-form analytical expression for the yield stress of MR fluids, derived from a particle-scale formulation that incorporates multipolar magnetic interactions and microstructural descriptors. The model explicitly accounts for the average number of interparticle contacts and the inclination angle of the chains relative to the internal magnetic field within the suspension, based on a simple microstructural hypothesis involving chain-like aggregates. A mechanical stability criterion is also formulated by identifying a critical inclination angle, (theta _{textrm{c}}), below which chains remain stable under the combined influence of magnetic attraction and hydrodynamic shear. This condition is obtained from force and torque balance at the chain–particle level and is applicable over a wide range of experimental conditions. Model validation is performed through complementary comparisons: the yield stress predicted by the model is directly contrasted with experimental data, while the corresponding chain inclination angles reconstructed from these measurements are compared with theoretical predictions of (theta _{textrm{c}}). The results show that the formulation captures observed trends and outperforms classical dipolar approaches across diverse particle sizes, magnetic properties, and field strengths, with confirmed applicability up to (phi lesssim 0.20). Additionally, an analysis of competing interparticle forces reinforces the assumptions underlying the model and its domain of applicability.

In this article, we provide a brief perspective on recent developments in the study of shear thickening in dense suspensions. We give a rapid overview of the state of the art and discuss current models aiming to describe this particular rheology. Although most of the experiments and simulation studies are conducted in “ideal” flows, where the sample is confined without an open boundary condition, we have decided to highlight more realistic flow conditions. We further provide an overview on how to relate the recently proposed constitutive models to these more practical flow conditions like pipe flow or flow down an incline.