The morphology of immiscible polymer blends generated during twin-screw extrusion depends on the deformation history of the dispersed phase and on the matrix rheology. Here, this effect is investigated numerically in a two-dimensional, co-rotating, fully intermeshing batch twin-screw extruder. A Newtonian dispersed phase is considered, while the matrix is modeled as Newtonian, a Generalized Newtonian Fluid (GNF) accounting for shear thinning, and a Generalized Newtonian Fluid with Flow-Type dependence (GNFFTy), which combines shear thinning in shear-dominated regions and elongational thickening in extension-dominated regions. Velocity-gradient histories along tracer trajectories are used in a morphology model including droplet deformation, breakup, filament stretching, and coalescence. The three rheologies give similar gross flow structures but different local viscosity fields. The GNF model reduces viscosity in high shear regions, whereas GNFFTy predicts localized viscosity enhancement in extensional screw-screw gaps. These differences affect breakup, showing that shear-rate-based morphology predictions may miss topology-dependent viscosity effects.
Waxy oils exhibit complex rheological behavior at low temperatures. This crystallization process, and consequently the resulting morphology and gel strength, is highly sensitive to the thermal history imposed on the material. While previous studies have documented the influence of the initial cooling temperature ( T_i ) on the gelation of crude oils, this work demonstrates for the first time in the open literature that T_i also significantly affects the rheological response of formulated waxy oils. Morphological analysis shows that increasing T_i leads to a transition from a dense network of numerous small crystals to a sparser structure composed of fewer, larger crystals. To explain this behavior, we propose a hypothesis based on the persistence of subcritical molecular self-assembly precursors in the solution. We suggest that T_i dictates the number density of these precursors, which subsequently act as nucleation sites, thereby defining the connectivity and mechanical strength of the wax crystal network.
This study examines the rheology of two cereal- and pulse-based batter suspensions with differing nutritional profiles. These batters, composed of soft-deformable particles, show distinct flow behaviour compared to well-studied hard-particle dispersions. We explore the effects of particle size, concentration, and temperature on their rheology. Both batters exhibit stress–strain and viscosity–concentration responses consistent with the Berli-Quemada (BQ) model. Yield stress obtained from BQ model fit is found to be prominent for suspensions of concentration higher than 20
We introduce i-Rheo-Indent, a transformation-based methodology for determining the linear viscoelastic properties of soft solids directly from macroscale indentation experiments. By combining force-relaxation and indentation-depth measurements with direct time-to-frequency transformations, the method recovers the complex shear modulus, G^*(ω ) , over a broad frequency range without requiring oscillatory excitation or predefined constitutive models. The methodology addresses key limitations of conventional rotational rheometry, where compressional forces required to maintain sample–tool contact may alter the measured response through stress stiffening and interfacial artefacts. Stress-relaxation indentation experiments were performed using a rigid truncated-conical indenter, with the geometry explicitly incorporated into the constitutive formulation. The approach was validated across hydrogels, polydimethylsiloxane elastomers, anatomical modelling materials, and industrial soap bar formulations. Good agreement with oscillatory rheometry was obtained over a broad frequency range, while improved consistency with capillary rheometry was observed for highly structured soft solids under Cox–Merz comparison. These results establish i-Rheo-Indent as a simple, rapid, and robust methodology for broadband rheological characterisation of soft solids.
We derive analytical solutions for the fully coupled, incompressible, steady, fully developed Poiseuille flow of a suspension of non-Brownian, short, rigid fibers in the presence of wall slip. The flow geometry considered is either a two-dimensional planar channel (slit) or an axisymmetric circular pipe (nozzle). The rheology of the matrix is modeled as a power-law generalized Newtonian fluid. The two-way coupling between the velocity field and the fiber-induced extra stress is incorporated explicitly into the momentum balance. Fiber orientation is described using a second-order orientation tensor formulation that accounts for finite-aspect-ratio fibers and fiber–fiber interactions, together with a hybrid closure approximation for the fourth-order orientation tensor. Closed-form analytical expressions for the velocity and pressure fields are derived for both geometries, while the orientation tensor associated with the hybrid closure is obtained numerically. The analysis shows that wall slip is necessary for the two-way coupling to produce non-trivial modifications to the pressure drop and velocity profiles. Under these conditions, the fiber-induced extra stress leads to a significant increase in the pressure drop required to sustain a prescribed volumetric flow rate, while the velocity profile is only weakly affected. The resulting solutions are also used to investigate parametrically the effects of the material parameters on the pressure and velocity profiles.
Inter-fiber interactions in concentrated fiber suspensions give rise to complex rheological behavior. In this study, we investigated how hydrodynamic and contact interactions contribute to the transient and oscillatory responses of a concentrated fiber suspension by using shear-reversal-based experimental protocols. The pseudo-steady-state viscosity immediately after shear reversal exhibited a concentration dependence consistent with the scaling predicted by a theory of long-range hydrodynamic interactions over the concentration range examined, supporting the interpretation that fiber-fiber contact contributions were substantially suppressed after reversal. The stress overshoot characteristic of fiber suspensions was also observed under large-amplitude oscillatory shear (LAOS), producing a pronounced deviation from the correspondence based on the Cox-Merz rule at intermediate strain amplitudes. In the LAOS-SR experiments, when the reverse strain accumulated after the preceding flow reversal within the LAOS cycle was smaller than the characteristic overshoot strain, the subsequent SR response exhibited a sigmoidal transition rather than an overshoot. At low strain amplitudes, hydrodynamic interactions provided the dominant contribution, revealing the strain-dependent nature of inter-fiber interactions. Based on these findings, parallel superposition, in which a small-amplitude oscillation was superposed on steady shear, was used as a probe to extract hydrodynamic and contact contributions. Under high-frequency small-amplitude oscillation, shear reversal occurred within each cycle, and a low-viscosity regime associated with the suppression of contact interactions was observed together with cycle-by-cycle transient changes. These results show that the rheology of concentrated fiber suspensions is governed by both fiber orientation and inter-fiber interactions, and provide new insight into how orientation and contact formation are coupled in such systems.
Parallel superposition flows have been examined in the rheology literature since 1965; they consist of simultaneously applied steady shear and oscillatory flows. One interesting result found from the study of parallel superposition flows has been reportedly negative values of the dynamic moduli. This apparently unphysical result has led to some speculation regarding its origin. In this work, we provide mathematical and experimental evidence showing that negative moduli are potentially due to the oscillatory signal being distorted by inclusion of the steady shear component in the Fourier analysis. However, the moduli can be easily corrected to restore physical meaning.
Optimally windowed chirp-based rheometry (OWCh) enables rapid acquisition of linear viscoelastic spectra and has become an increasingly popular alternative to conventional discrete frequency sweep measurements, particularly for time-evolving materials. However, the accuracy of chirp-based protocols is sensitive to instrumental and signal-processing artefacts that can distort the recovered complex modulus. In this work, we demonstrate that timestamp-induced phase offsets produce a frequency-dependent rotation of the complex modulus, causing crosstalk between the storage and loss moduli. Further, when OWCh measurements are undertaken using a combined motor transducer rheometer the phase offset and instrument inertia are intrinsically coupled such that the inertial effect, which is typically assumed to affect only the storage modulus, leaks into the loss modulus. Analytical modelling reveals a cubic frequency scaling of the resulting loss modulus error. Using numerical examples and experimental measurements obtained on multiple rheometers and materials, we show that conventional inertia correction is insufficient to recover the true material response when phase offsets are present. We further introduce a practical calibration procedure that enables phase correction to be performed prior to inertia correction, restoring quantitative agreement between chirp-based and frequency sweep measurements. These results establish a physically consistent correction sequence for chirp-based rheometry and provide a robust framework for chirp-only rheometry.
Human saliva is a complex biological fluid whose rheological and interfacial characteristics are crucial for oral lubrication, bolus formation, swallowing, and sensory perception. Despite its importance, the degree of intra-individual variability in saliva structure and rheological behavior under controlled sampling conditions remains inadequately defined. In this study, unstimulated whole human saliva collected from a single donor over five consecutive days under standardized routine was examined in its uncentrifuged (UN – UWHS) and centrifuged state (C – UWHS). Particle size analysis revealed pronounced day-to-day variability, while centrifugation consistently reduced the contribution of larger populations. Extensional rheometry showed strong fluctuations in filament thinning dynamics, with relaxation times ranging from 0.2 to 6.2 s in native saliva and decreasing to 0.002–0.04 s after centrifugation. In contrast, shear viscosity exhibited lower variability, although native saliva consistently displayed higher viscosity and more pronounced shear-thinning behaviour. Size exclusion chromatography (SEC) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) revealed multiple macromolecular populations, while confocal microscopy indicated that saliva foam is stabilized by a protein-rich interfacial layer. Overall, the results demonstrate that saliva is a dynamic viscoelastic colloid with substantial intra-individual variability even under controlled sampling conditions. These findings are relevant for improving experimental reproducibility in saliva rheology studies and for guiding the development of biomimetic saliva substitutes for xerostomia.
Magnetorheological (MR) fluids exhibit field-dependent yield stress and viscosity, enabling their use in adaptive damping, braking, and clutch systems. However, precise rheological characterisation remains difficult due to issues such as fluid loss from centrifugal forces, non-uniform magnetic fields, and deformation of measurement gaps under magnetic loading. This work introduces the design, magnetic optimisation, and experimental validation of a new concentric cylindrical magnetorheometer that overcomes these challenges. The proposed device features an enclosed geometry to prevent fluid loss, a fixed-radius shear design to maintain consistent shear rates, and an optimised magnetic circuit to provide uniform flux distribution without creating normal magnetic forces. Magnetic circuit modelling, supported by finite element simulations, confirms enhanced field uniformity and efficiency. Rheological testing with custom-prepared MR fluids demonstrates the instrument’s capability to measure dynamic yield stress under varying magnetic field strengths, rotor–stator material combinations, particle concentrations, and gap sizes. Results show a strong link between magnetic material configuration and yield stress, significant increases in yield stress with higher carbonyl iron particle content, and performance reductions at larger gap sizes. The device’s accuracy and repeatability make it a reliable platform for advanced MR fluid research and application development at high shear rates.
It is increasingly common to use self-thinning of slender fluid filaments to infer the rheological properties of complex fluids under uniaxial extensional flow. These techniques require precise control over how filament thinning is triggered, as implemented in methods such as dripping-onto-substrate (DoS) and the commercial capillary-breakup extensional rheometer (CaBER), together with high-speed imaging to resolve rapid thinning dynamics. Here, we introduce the Stringimeter, a low-cost and modular capillary-driven thinning platform that integrates CaBER-like and DoS-like configurations within a single adaptable framework. The system combines moderate-speed imaging (up to 420 frames/s) with a temporal superposition strategy that increases the effective sampling rate and reduces reliance on expensive high-speed cameras. Validation with Newtonian fluids and polymer solutions demonstrates reliable extraction of elastocapillary timescales as low as τ _EC≈ 6 ms, corresponding to a polymer relaxation time of λ =τ _EC /3≈ 2 ms within the Oldroyd–B model. The open-source architecture enables broad adaptability and, by maintaining a total system cost of approximately 1
Fluid gels are suspensions of gelled particles dispersed within a continuous liquid phase, formed by applying shear during gelation. Although widely used to functionalise materials across industries, controlling and tuning their rheological properties through particle design remains a major challenge due to the significant coupling between formulation variables, gelation kinetics, and shear-induced micro structuring. In this work, we demonstrate that mixtures of κ-Carrageenan (κ-C) and Locust Bean Gum (LBG) enable precise and predictable tuning of fluid gel rheology by simply adjusting the LBG/κ-C ratio at a fixed total hydrocolloid concentration (1 wt
Aqueous solutions of hydrolyzed polyacrylamide polymer (HPAM) are now regularly used to support excavation in underground construction, e.g., trenches and pile bores, because of their high viscosity and shear-thinning nature. To ensure excavation stability, it is crucial to maintain the high fluid viscosity and therefore to be able to measure it accurately on site. In this work, two tests commonly used in civil engineering are assessed, i.e. the Fann viscometer and the Marsh funnel. These tests measure viscosity in different ways; the Fann viscometer uses a torque measurement, while the Marsh funnel measures the discharge time for a fixed flow volume. We employed high-resolution computational fluid dynamics (CFD) techniques to simulate both test processes and assessed the extent to which the test predictions by the standard measurement protocols can capture the rheological parameters. The results suggest that the Fann viscometer is reliable at very low shear rates; however, inertial effects lead to an overestimation of apparent viscosity at high rotational velocities. Though a correction factor can be successfully applied to correct Fann viscometer data in the case of Newtonian fluids, it is unlikely that a single correction factor can be used for HPAM fluids. The Marsh funnel time is very sensitive to the infinite-shear-rate viscosity for HPAM fluids. This presents a challenge to its use as an in-situ quality control measure as the infinite-shear-rate viscosity is similar for HPAM with different concentrations. The critical assessment offered in this work supports the development of new experimental approaches for quality control when polymer fluids are used in ground engineering construction projects.
Creep ringing is typically analyzed using canonical models like the Kelvin-Voigt or Jeffreys models. Such analysis is used to remove inertial artifacts and estimate model parameters, viscoelastic moduli, and creep compliance J(t). We investigate the accuracy of the J(t) inferred by such analysis for materials with nontrivial retardation spectra. To this end, we introduce Glacier – a program that predicts how inertia modifies J(t). We generate synthetic data with generalized linear models and fit them with canonical models to study model-specification error. We find that the error in fitting data is correlated with the error in predicting J(t), although the latter is larger and widely dispersed. Application to the Rouse model illustrates that a visually good fit to ringing oscillations does not guarantee accurate recovery of J(t) beyond the fitting window or viscoelastic moduli far from the ringing frequency.
Oscillatory amplitude sweeps are essential for determining linear viscoelastic properties of asphalt binders because selection of unsuitable amplitudes can lead to measurement mistakes, material failure and misinterpretation. This study provides extended information and guidelines about the procedure and analysis of amplitude sweeps for asphalt binders. Different rheological parameters to identify the linearity limit are discussed together with recommended shear amplitude values from current international technical Standards. A large set of amplitude sweep tests is performed in the dynamic shear rheometer (DSR) to reveal the effects of test temperature, test frequency, aging state, binder type, test geometry and control mode (shear stress vs. shear strain) on amplitude sweep results and linearity limit. A systematic analysis including considering of the harmonic distortion of the materials sinusoidal response signals allow selection of best suitable shear amplitudes for different test conditions. Test temperature shows the highest influence on the suitable shear amplitudes, with a proposed increase of one decade for a temperature increment of 30 °C. Finally, recommended shear amplitude values were derived and presented in nomograms in function of the temperature for different binder grades in fresh and in RTFOT + PAV-aged states.
To clarify the influence of molecular structure on interfacial behaviors of extended surfactants, interfacial rheological properties of three extended surfactants with different ionic heads (C8P10E5C and C8P10E5S) and different hydrophobic tails (C8P10E5C and phP10E5C) were investigated by the droplet analysis method. The effects of adsorption time, interfacial pressure, oscillating frequency, and concentration on the dilational modulus and phase angle of C8P10E5C, C8P10E5S, and phP10E5C were determined. Results indicate that interfacial films of these three extended surfactants exhibit predominantly elastic behavior. The modulus and phase angle of C8P10E5C and C8P10E5S with different ionic heads exhibit little variation at variable experimental conditions, indicating that different ionic heads have a negligible effect on interfacial film properties. At low interfacial pressures, the adsorption layer is in a local thermodynamic quasi-equilibrium state with negligible intrinsic relaxation processes. At high interfacial pressures, the diffusion exchange process may play a more important role in the interfacial film of C8P10E5C. Compared to C8P10E5C, phP10E5C with a different hydrophobic group maintains a higher dilational modulus over a wider concentration range due to its rigid phenyl groups. Compared to ionic heads, hydrophobic tails exert a more pronounced influence on the interfacial rheological behavior of extended surfactants. These findings are expected to contribute to the rational design of extended surfactants with a short hydrophobic group.
In this study, carbon black (Ketjen Black) suspensions were employed as model non-Newtonian particulate systems to investigate shear-history-dependent structural reconstruction dynamics using a rheo-impedance approach. Slurries dispersed with poly(vinylpyrrolidone) (PVP) of different molecular weights and concentrations exhibited pronounced shear-thinning behavior, and both the magnitude of shear thinning and the power-law index strongly depended on dispersant concentration and molecular weight. Step shearing tests revealed that particle networks disrupted under high shear were rebuilt after shear cessation. Under steady shear conditions, a clear inverse correlation was observed between the relative viscosity ηr and the total electrical resistance RT, indicating that both responses reflect the same underlying particle-network structure through mechanical connectivity and electrically effective particle contacts. However, during the recovery process after shear cessation, the temporal evolutions of mechanical and electrical responses did not coincide. The recovery of the electrical network was delayed relative to that of the mechanical network, demonstrating decoupled recovery dynamics governed by distinct characteristic time scales. These findings highlight that structural rebuilding in non-Newtonian particulate suspensions cannot be described by a single kinetic process, but instead involves time-scale separation between mechanical network formation and electrically effective contact reformation. The rheo-impedance method provides a complementary tool for probing thixotropic structural reconstruction and offers new insight into the dynamics of particle-network rebuilding under shear.
This study establishes systematic design guidelines for organogels by exploring stepwise side-chain substitution and core skeleton geometry. While our previous work focused on functional comparisons between hetero-type molecules and physical mixtures, this study investigates how incremental replacement of oleyl chains with 2-ethylhexyl (2C8) chains dictates the balance between solubility and self-assembly. We demonstrate that the core skeleton (pyromellitamide (PMDA-R), its hydrogenated analogue (HPMDA-R), or butane tetracarboxamide (BT-R)) is the primary determinant of the rheological fingerprint. Quantitative scaling analysis reveals that although different skeletons produce comparable network mesh sizes, intrinsic fiber rigidity governs macroscopic gel strength. These findings provide a robust strategy for predictable engineering of supramolecular architectures, shifting the focus from simple functional proof to comprehensive structural design for advanced material control.
The effect of liquid crystallinity on the rheological properties of ethylcellulose solutions in the isotropic phase has been examined using four solvents. Double-logarithmic plots of dynamic viscoelasticity at different temperatures can be superposed with each other by the combination of arbitrary horizontal and vertical shifts. However, it has been found that some plots are superposed in the framework of the conventional time-temperature superposition principle and the other needs further shifts. Accordingly, it is asserted that the isotropic phase consists of two categories and what should be called semi-isotropic phase lies between full-isotropic and liquid crystal phases. The conditions for respective phases with respect to the ethylcellulose concentration and temperature have been mapped out as a consequence of rheological analysis. The feature of the semi-isotropic phase is pictured by the local alignment of ethylcellulose chains precedent to the formation of a cholesteric liquid crystal, which would contribute to the reduction of chain entanglement. The zero-shear viscosity as well as the plateau modulus in the full-isotropic phase can be scaled by the concentration with an exponent that is independent of the solvent, while at the same time it is revealed that ethylcellulose chains exhibit specific interaction with each solvent. The rheological behavior of full-isotropic concentrated solutions can be characterized by that of semiflexible chains in the tightly-entangled regime.
