Understanding the flow behaviors of supercooled liquids presents a major challenge in liquid-state physics due to the strong nonlinearity and rich phenomena. To unravel this complexity, we introduce the concept of local configurational relaxation time τ LC , which allows us to embody the solid-liquid duality, proposed by Maxwell for phenomenologically describing materials’ response to external load, at the particle level. The spatial distribution of τ LC in flow is heterogeneous. Depending on the comparison between the local mobility measured by τ LC and the external shear rate, the shear response of local regions is either solidlike or liquidlike. In this way, τ LC plays a role similar to the Maxwell time. By applying this microscopic solid-liquid duality to different conditions of shear flow with a wide range of shear rates, we describe the emergence of shear thinning in steady shear and predict the major characteristics of the transient response to start-up shear. Furthermore, we reveal a clear structural foundation for τ LC and the solid-liquid duality associated with it by introducing an order parameter extracted from local configuration. Thus, we establish a framework that connects microscopic structure, dynamics, local mechanical response, and flow behaviors for supercooled liquids. Finally, we rationalize our framework in terms of activations from energy basins that are facilitated by shear. This model illustrates how local structure, convection, and thermal activation collectively determine τ LC . Notably, it predicts two distinct response groups, which well correspond to the microscopic solid-liquid duality.

Rheological tests (low-amplitude oscillatory shear, creep and creep recovery, and steady shear rate) were used to evaluate the 3D concrete printing (3DCP) performance of fiber-reinforced cementitious composites (FRCC). UHMWPE fibers were modified to increase hydrophilicity and functionality. FRCC with hydrophilic or hydrophobic fibers, with or without nanoclay, was assessed for extrudability and buildability. Hydrophilic fibers significantly enhanced microstructural rigidity, followed by hydrophobic fibers and nanoclay, evidenced through an increase of storage modulus by 115.29%, 59.37%, and 49.49%, respectively. The combined inclusion of hydrophilic fibers and nanoclay developed the stiffest, strongest, and stable solid-like microstructure with 211.52% enhanced storage modulus, 87.20% lowered creep compliance, 100% elastic recovery, and the highest viscoelastic yield stress, as compared to a simple cement/water mixture. Hydrophobic fibers with nanoclay also improved storage modulus and yield stresses, enabling effective buildability and extrudability. Certain FRCC compositions succeeded in 3DCP extrusion tests due to higher storage modulus and optimal yield stresses. The tensile strength and ductility of printed samples containing hydrophilic fibers improved due to stronger fiber-matrix bonding, as reflected by 40% higher first-crack strength, 19% higher ultimate tensile strength, and 50.27% enhanced strain capacity as compared to samples with hydrophobic fibers. The addition of nanoclay further improved the matrix strength in both cases. However, the ductility of FRCC containing hydrophilic fibers with nanoclay decreases by more than 50% compared to FRCC with only hydrophilic fibers, likely due to insufficient water availability to satisfy the demand of both water-absorbing components in the FRCC system. Overall, FRCC containing hydrophilic fibers without nanoclay is found to be the most effective option for 3DCP performance, demonstrating superior rheological behavior, tensile strength, and ductility.

This study systematically investigates the complex nonlinear rheological behavior of magnetorheological fluids (MRFs) and greases (MRGs) through comparative experiments under two shear modes (steady-state shear and large-amplitude oscillatory shear) at room temperature. Results demonstrate that during steady-state shear tests, the apparent viscosity of both materials decreases with the increasing shear rate, exhibiting shear-thinning behavior at high shear rates that aligns with the Herschel–Bulkley constitutive model. Throughout the logarithmically increasing shear rate range, the viscosity and shear stress of MRF consistently exceed those of MRG. Under low-frequency, large-amplitude oscillatory shear (LAOS) conditions, both materials display pronounced viscoelasticity and hysteresis. At higher current levels, the maximum shear stress of MRF surpasses MRG, but its hysteresis loops exhibit reduced smoothness. The Bouc–Wen model accurately characterizes the nonlinear hysteresis of both materials, with model parameters successfully identified via a genetic algorithm. This work establishes a universal framework for the dynamic mechanical response mechanisms of magnetorheological materials, providing theoretical guidance for designing and predicting the performance of smart damping devices.

Microswimming cells and robots exhibit diverse behaviours due to both their swimming and their environment. One key environmental feature is the presence of a background flow. While the influences of select flows, particularly steady shear flows, have been extensively investigated, these only represent special cases. Here, we examine inertialess swimmers in more general flows, specifically general linear planar flows that may possess rapid oscillations, and impose weak symmetry constraints on the swimmer (ensuring planarity, for instance). We focus on swimmers that are inefficient, in that the time scales of their movement are well separated from those associated with their motility-driving deformation. Exploiting this separation of scales in a multiple-time-scale analysis, we find that the behaviour of the swimmer is dictated by two effective parameter groupings, excluding mathematically precise edge cases. These systematically derived parameters measure balances between angular velocity and the rate of strain of the background flow. Remarkably, one parameter governs the orientational dynamics, whilst the other completely captures translational motion. Further, we find that the long-time translational dynamics is solely determined by properties of the flow, independent of the details of the swimmer. This illustrates the limited extent to which, and how, microswimmers may control their behaviours in planar linear flows.

Hydrodynamic flows are often generated in colloidal suspensions. Since colloidal particles are frequently used to construct stochastic heat engines, we study how the hydrodynamic flows influence the output parameters of the engine. We study a single colloidal particle confined in a harmonic trap with time-periodic stiffness that provides the engine protocol, in the presence of an externally applied steady linear shear flow. The nature of the flow (circular, elliptic, or hyperbolic) is externally tunable. In the quasistatic limit, the work done by the flow field is shown to dominate over the thermodynamic (Jarzynski) work done by the trap, if there is an appreciable deviation from the circular flow. The work by the time-dependent trap is the sole contributor only for a perfectly circular flow. The work done by the elliptic flow is positive whereas in the case of hyperbolic flows, in the limit of low trapping strength, it can be negative, so as to allow for harnessing the work from the flow field. We also study an extended model, where a microscopic spinning particle (spinor) is tethered close to the colloidal particle, the latter being the working substance of the engine, such that the flow generated by the spinor influences the dynamics of the colloidal particle. We simulate the system and explore the influence of such a flow on the thermodynamics of the engine. We further find that for larger spinning frequencies, the work done by the flow dominates and the system cannot produce thermodynamic work.

We numerically investigate the steady shear rheology of mixtures of active and passive Brownian particles, with varying fractions of active components. We find that even a small fraction of active dopants triggers fluidization with comparable efficiency to fully active systems. A combined parameter, active energy, given by the dopant fraction multiplied by the propulsion speed squared controls the steady shear rheology and glass transition of the active-passive mixtures. These results together provide a quantitative strategy for fine-tuning the mechanical properties of a soft material with small amounts of active dopants.

In this study, we propose an analytical framework to characterize rheological behavior under general superimposed flows, where steady shear is combined with oscillatory shear of arbitrary magnitude and orientation. Building upon the sequence of physical processes approach, the framework remains valid within flow conditions where the newly defined superposition number (Su) is less than or equal to 1. Its applicability was demonstrated through simulations of a model colloidal gel, a representative elastoviscoplastic material with complex rheological responses. The analysis captured rheological evolutions across a broad range of steady shear rates, offering interpretations closely connected to microstructural transitions—from the quiescent state to shear-induced densification and subsequently to rejuvenation and eventual fluidization. Distinct interference effects were observed in parallel superposition, where constructive and destructive interactions between steady and oscillatory shear produced two deltoids in the Cole–Cole plot. In contrast, orthogonal superposition, without such interference, resulted in a single deltoid. Overall, the proposed framework offers a powerful tool for superposition rheology, particularly for materials exhibiting complex structural and rheological transitions driven by flow-induced anisotropy.

Shaping suspensions: Stabilizing anisotropy in viscoelastic media using oscillations.

ABSTRACTComposites of sodium alginate (Alg) and carboxymethyl chitosan (CMCS) are used to 3D print tissue scaffolds, but the rheological properties and printability of these composites remain underreported, resulting in time‐consuming trial‐and‐error printing. This study investigates these properties to rigorously design the 3D printing process. Dynamic shear tests characterize viscoelastic and frequency‐dependent properties, while steady shear tests assess the apparent viscosity and temperature‐dependent viscosity. A novel approach based on mass flow rate models guides the printing of two‐layer scaffolds for printability analysis. Brightfield microscopy and printability indexes quantify the deviations between printed and designed scaffolds, defined as printability. Results show that Alg predominantly directs the rheological properties. At 4% w/v Alg, the addition of < 3% w/v CMCS reduces elasticity, contrary to the trend where increasing CMCS increases elasticity. CMCS improves the thermal resistance of the composites, while Alg reduces it. Of the composites printed, a 4% w/v Alg + 1% w/v CMCS formulation most accurately replicates the designed scaffold, and adding CMCS improves scaffold printing repeatability by at least threefold compared to Alg‐only solutions. These findings provide a framework that informs the preparation and performance of Alg‐CMCS composites with tunable properties, advancing scaffold bioprinting for tissue engineering.

In this work, we investigate the transient rheological behavior of two soft glassy materials: a clay dispersion and a silica gel, emphasizing their unconventional shear stress buildup behavior under conditions of constant imposed strain. For both materials, the elastic modulus and static yield stress undergo time-dependent evolution or aging. In addition, following an intense period of preshearing (i.e., shear rejuvenation or destructuration), the material relaxation time is observed to show a stronger than linear dependence on the sample age, indicative of hyperaging dynamics. We show that these features are consistent with nonmonotonic steady-state flow curves characterized by a local stress minimum. When a steady shearing flow is suddenly ceased, and the total imposed sample strain is held constant, both materials show an initial relaxation of the shear stress, followed by a period of shear stress buildup, resulting in a local minimum in the evolution of shear stress with time. For the clay dispersion, the intensity of these effects increases at higher preshear rates, whereas for the silica gel, the effects are largely independent of the preshear rate. We also propose a simple time-dependent linear Maxwell model that qualitatively predicts the experimentally observed trends in which the shear stress buildup is directly related to a monotonic increase in the elastic modulus with time, giving keen insight into this peculiar phenomenon.

Linear and non-linear rheological assessments of long-term stable water-in-water emulsions made with starch- basil seed gum mixtures.

The effect of wheat bran soluble dietary fiber on the digestion characteristics of noodles.

Background: Knee osteoarthritis (KOA) is a degenerative joint disorder marked by cartilage degradation, synovial inflammation, and altered synovial fluid (SF) rheology, resulting in pain and impaired joint function. Intra-articular hyaluronic acid (IA-HA) injections aim to restore SF viscoelasticity and improve lubrication; however, their efficacy may be potentiated when combined with physiotherapy (PT). This monocentric observational study evaluated whether the addition of a multimodal PT program to IA-HA therapy enhances SF rheologic properties compared to IA-HA alone. Methods: A total of 52 patients (aged 47–61) with radiographically confirmed moderate KOA (Kellgren–Lawrence grade 2) were enrolled. Patients were assigned to a pilot group (PG; n = 37) receiving IA-HA (Kombihylan®, 3 MDa) combined with a multimodal PT protocol, or a control group (CG; n = 15) receiving IA-HA alone. The PT program included ten sessions of transcutaneous electrical nerve stimulation, low-level laser therapy, therapeutic ultrasound, progressive exercise, and cryotherapy. SF samples were collected immediately after the first injection and again at six weeks, then analyzed rheologically using the Kinexus Pro+ rheometer. Viscosity parameters were assessed via steady and oscillatory shear tests. Results: At baseline, both groups demonstrated comparable SF viscosity profiles. After six weeks, the PG exhibited significantly higher shear viscosity values across all measured percentiles and reduced variability in rheological parameters, suggesting a more stable intra-articular milieu. Rheometric analysis indicated enhanced SF viscoelasticity, potentially mediated by reduced inflammation and stimulation of endogenous HA synthesis. In contrast, the CG showed inconsistent viscosity changes, reflecting variable responses to IA-HA monotherapy. Conclusions: Combining IA-HA with multimodal PT significantly improves SF rheological properties in moderate KOA patients compared to IA-HA alone. These findings support the role of mechanical stimulation in enhancing joint lubrication and homeostasis, offering a more consistent and effective approach to viscosupplementation.

Jammed suspensions of soft particle glasses (SPGs) exhibit intriguing rheological response under different shear flows, such as stress overshoot in start-up shear and Herschel–Bulkley behavior in steady shear. However, the fundamental link between microscopic processes and macroscopic (bulk) behavior remains elusive. To address this, we employ large-scale 3D simulations of model SPGs to study the impact of shear-induced microstructural rearrangements on particle stress distributions. These rearrangements cause significant changes in stress distribution, consequently influencing the overall stress and bulk rheology of the system. The characteristics of stress distribution, including its width and peak, are found to be influenced by factors such as particle volume fraction, applied shear rate, and system history. Building upon previous works, we introduce a thermodynamic model that offers insights into the particle stress distribution in SPGs, providing a microscopic basis for understanding bulk rheology. Furthermore, we present a self-consistent model based on the advection–diffusion equation, which describes the evolution of particle stress distribution in SPGs under steady shear. Our findings emphasize the importance of stress distributions in elucidating bulk rheology and highlight the utility of thermodynamics as a valuable tool for modeling these complex materials.

ABSTRACTIn this study, lithium stearate and fumed silica co‐thickened grease with po‐ly(sodium‐4‐styrenesulfonate) (PSSNa) additive was synthesised and characterised for application as an automotive lubricant, including for the potential use in an electric vehicle (EV). Oscillatory shear and steady shear rheological tests confirmed that the sample exhibited appropriate shear thinning required in greases. Fumed silica was found to increase thermal stability. Additionally, the conductivity of the synthesised grease was higher than the threshold conductivity required to avoid electrical arcing and static charge buildup (4 × 10−12 S/cm). The tribo‐pair lubricated with LSFSPNa grease demonstrated a significant improvement in tribological performance, with the coefficient of friction reduced by approximately 65% compared to commercial grease, decreasing from 0.31 to 0.11. The wear volume showed a tenfold reduction, accompanied by a substantial decrease in surface roughness (Ra), which dropped from 0.81 μm with commercial grease to 0.17 μm with LSFSPNa grease. At the same time, the synthesised grease exhibited better copper corrosion resistance. Overall, the synthesised grease was found to be compatible for EV applications in terms of rheology, friction reduction, copper corrosion resistance, conductivity, and thermal stability.

Ultrasonic homogenization is an emerging technique with significant potential to modify the structure and functionality of food ingredients. This study evaluated the effect of ultrasonic homogenization on the rheological behavior and physical stability of aqueous dispersions of flaxseed fiber. Flax mucilage, with health-promoting and techno-functional properties, is of growing interest in several industries. The samples were subjected to different ultrasonic treatments, varying in amplitude (from 40 to 100%) and duration (from 2 to 20 min), with and without preliminary rotor–stator homogenization. The rheological properties were analyzed using small-amplitude oscillatory shear (SAOS) tests and steady shear flow curves. Physical stability was assessed by multiple light scattering. The results revealed that short treatment under ultrasonic homogenization had minimal impact on the viscoelastic parameters and viscosity, regardless of the amplitude used. However, longer treatments significantly reduced both values by at least one order of magnitude or more, indicating the occurrence of microstructural degradation. The relevance of this research lies in its direct applicability to the development of functional foods, since it is concluded that control of the ultrasonic homogenization process conditions must be carefully selected to retain the desirable rheological properties and physical stability.

We analyze the nonlinear shear and elongational rheology of six nearly monodisperse polystyrene pom-pom systems with different molecular weights of backbone and different numbers and molecular weights of side arms. Startup viscosity and apparent normal stress growth in shear flow as well as startup viscosity in elongational flow of pom-poms with strongly entangled side arms can be described consistently by the Hierarchical Multi-mode Molecular Stress Function (HMMSF) model. The modeling is based on the linear-viscoelastic characterization of the pom-poms in shear flow and accounts for dilution of the shorter relaxation modes by hierarchical relaxation of the longer modes. Dynamic dilution is characterized by a specific dilution modulus. For pom-poms with more than five entangled side arms, the dilution modulus is equal to the plateau modulus, and therefore the modeling of the nonlinear shear and elongational rheology of the pom-poms does not require any fitting parameter. We also show that pom-poms with weakly entangled or unentangled side arms can be considered as quasi-linear polymers with the slowly relaxing backbone chains being permanently diluted by the fast relaxing side arms. Pom-poms with entangled vs unentangled backbones show remarkably different features of steady shear and elongational viscosities resulting from different interplay of orientation and stretch of backbone chains.

Aiming toward the magnetorheological characterization of whole human blood, we evaluated the suitability of our experimental setup for steady shear measurements with low-viscosity fluids. Previous measurements with a rotational rheometer equipped with a magnetorheological cell returned low and inconsistent apparent-viscosity values. In this work, a parametric study was conducted, experimentally and numerically, to evaluate the possible error sources and define an experimentally reliable window. Steady shear measurements were carried out with Newtonian fluids using two geometries: parallel-plates at different gap heights and cone-plate. A clear decrease in measured viscosity with parallel-plate gap reduction was found, along with a slight overestimation of the cone-plate. Numerical results corroborated the experimental observations, pointing toward a small inclination of the bottom plate (between 0.1° and 0.3°). The numerical study has also shown that geometry non-parallelism can lead to significant flow alterations, particularly for cone-plate geometries where contraction/expansion flow can be generated, critically deviating from the canonical Couette flow and provoking non-negligible errors. Additional experimental and numerical work was conducted to evaluate the effects of the non-parallelism on magnetorheological measurements. The geometrical asymmetry results in severe alterations of the microstructural dynamics, possibly leading to an underestimation of the magnetorheological response. This work has shown that geometry non-parallelism can have critical repercussions on simple shear flows, with fundamentally different implications from a general gap-error, and can be identified through comparative measurements with Newtonian fluids in different geometries (parallel-plates and cone-plate).

Film-forming solutions were prepared using Tara gum (TG), with glycerol (GL) as a plasticizer and orange peel powder (OP) as a filler. A TG stock solution (10 g/L) was initially prepared to facilitate homogenization, from which appropriate dilutions were made to obtain final concentrations of 0.6%, 0.8%, and 1.0% (w/v). GL (30% and 50%) and OP (0%, 20%, and 50%) were incorporated based on the dry weight of TG, meaning their amounts were calculated relative to TG content to ensure consistent formulation ratios. Rheological parameters, including the flow behavior index, consistency coefficient, storage modulus (G'), and loss modulus (G″), were characterized via steady shear and oscillatory rheometry. Mechanical properties, such as the Young's modulus, tensile strength, and elongation at break, were also evaluated. A strong positive correlation (R2 = 0.840) was observed between G' and the Young's modulus, indicating that solutions with higher internal network strength yield films with greater stiffness. The synergistic interaction between TG and OP was critical: TG primarily enhanced stiffness and mechanical reinforcement, whereas OP improved structural cohesion and stability. GL functioned as a plasticizer, increasing film flexibility while reducing stiffness. These interactions led to a reduction in film solubility by up to 62.43%, particularly in formulations without orange peel powder. In contrast, mechanical strength increased by up to 50.21% in films containing orange peel powder, as those without it exhibited significantly lower tensile strength. Flexibility, expressed as elongation at break, was enhanced by up to 78.86% in formulations with higher glycerol content. Barrier properties were also improved, demonstrated by decreased water vapor permeability and increased hydrophobicity, attributed to the TG-OP synergy. A regression model (R2 = 0.928) substantiated the contributions of TG to stiffness, OP to matrix reinforcement, and GL to flexibility modulation. This study underscores the pivotal role of rheological behavior in defining film performance and presents a novel analytical framework applicable to the design of sustainable, high-performance biopolymeric materials.

Nanofluids—engineered suspensions of nanometer-sized particles—have attracted significant attention due to their reportedly enhanced thermal properties, making them promising candidates for advanced heat transfer applications. However, despite extensive studies, uncertainties remain regarding the magnitude and origin of these effects, limiting their practical implementation. To address this, we present a comprehensive study on nanofluid formulations based on the commercial refrigerant HFE-7500, incorporating surfactant-stabilized dispersions of several metal oxide and nitride nanoparticles. We measured key physicochemical properties, including zeta potential, particle size, viscosity, and thermal conductivity. Our results show that while the nanofluids exhibited high stability, their particle sizes in suspension were significantly larger than the primary nanoparticle sizes measured by TEM. Notably, alumina-based suspensions demonstrated the greatest enhancement, exhibiting approximately 10–15% increases in thermal conductivity as a function of volume percentage. These surpassed the 5–10% improvements observed with other metal oxides, an effect that may be linked to their comparatively larger particle sizes. However, the observed enhancements were lower than some previously reported values that claimed anomalously high thermal conductivity increases. Furthermore, steady shear viscosity increased with particle concentration, showing enhancements of 10–20%, which suggests a potential trade-off for practical implementation. Our findings refine the understanding of nanofluid behavior in refrigerants and establish a foundation for optimizing their performance in thermal management applications. However, viscosity increases must be carefully considered when designing next-generation nanofluids for real-world use.