Rheologica Acta最新文献

By considering the rotationality of shear flow, we distinguish between tube segments created by reptation before the inception of shear flow and those created during flow. Tube segments created before inception of shear flow experience both stretch and orientation, while tube segments created after inception of flow are not stretched, but are only aligned in the flow direction. Based on this idea, the Rotation Zero Stretch (RZS) model allows for a quantitative description of the start-up of shear flow and stress relaxation after step-shear strain experiments, in agreement with data of polystyrene long/short blends and corresponding polystyrene 3-arm star polymers investigated by Liu et al. (Polymer 2023, 281:126125), as well as the shear viscosity data of poly(propylene carbonate) melts reported by Yang et al. (Nihon Reoroji Gakkaishi 2022, 50:127–135). In the limit of steady-state shear flow, the RZS model converges to the Doi-Edwards IA model, which quantitatively describes the steady-state shear viscosity of linear polymer melts and long/short blends. The assumption of “non-stretching” of tube segments created during rotational flow is therefore in agreement with the available experimental evidence. Three-arm star polymers behave in a similar way as corresponding blends of long and short polymers confirming the solution effect of the short arm in asymmetric stars. The analysis of step-shear strain experiments reveals that stress relaxation is at first dominated by stretch relaxation, followed at times larger than the Rouse stretch relaxation time by relaxation of orientation as described by the damping function of the Doi-Edwards IA model. The RZS model does not require any nonlinear-viscoelastic parameter, but relies solely on the linear-viscoelastic relaxation modulus and the Rouse stretch relaxation time.

Graphical Abstract

This research investigates the interactions between Carbopol® and zinc microparticles and their role in the stabilization of zinc within the framework of zinc slurry–air redox flow batteries (Zn-air RFBs). The study explores the potential of yield stress fluids, particularly PAA (Carbopol®) microgels, as stabilizers for zinc particles during battery operation, and regarding sedimentation in particular. Two effects that can limit the effectiveness of PAA yield stress in stabilizing the suspension are examined in this study. First is the ionic strength and pH that can evolve during the slurry formulation. The second effect is associated to zinc polymer interactions that can develop during the suspension preparation. Using methodologies based on rheometry and UV–Vis spectroscopy, the research identifies that the primary stabilization challenge is the adsorption of Carbopol® microgels onto zinc surfaces, which significantly influences the gel’s yield stress. These insights contribute to an enhanced understanding of the physical chemistry of the suspending fluid, facilitating the development of more efficient and stable Zn-Air RFBs.

The flow through a 4:1 planar contraction has  been investigated using different rheological models having the same shear viscosity, namely, the inelastic Carreau-Yasuda model (CY), the enhanced Bautista-Manero-Puig (eBMP), and the exponential version of the Phan-Thien/Tanner (PTT). Noticeable discrepancies were observed with the CY model and the eBMP in terms of the velocity profiles along the centerline and in the exit channel (near the end of the geometry) normal to the flow direction. Transient planar extensional viscosity shows a large effect on vortex dynamics although the effect of transient and steady elongation on pressure drop seems negligible. Simulation results allowed gathering that pressure drop is largely influenced by the shear-thinning behavior of the fluid, noticeably affected by elasticity, and less by extensional viscosity.

Graphical Abstract

The transient rheological behaviour of semi-dilute kaolinite clay suspensions is investigated. Specifically, the flow curve hysteresis and step shear rate tests are used to investigate the shear behaviour of kaolinite suspensions. We found that there is a coupling effect between thixotropy and slip that dominates this transient rheological behaviour. It appears that the onset of solid-like slip in the system is a function of wall roughness and interfacial phenomena between the particles of the suspension and the wall. The coupled phenomena of slip and thixotropy are investigated using the application of sandpaper, varying the gap, and using different geometries. To illustrate the importance of slip in this system, we propose a Coupled Thixotropy and Slip (CTS) model that couples a thixotropic Structure Parameter Model (SPM) to an existing slip model.

We have found that the unique particle properties of fly ash can be applied to the modification of shear thickening fluid. In this paper, rheological properties and microscopic thickening mechanism of fly ash/silicon-based shear thickening fluid (subsequently abbreviated as FA/SiO₂-STF) are studied. Ultrasonic technology and mechanical stirring method were used to prepare FA/SiO₂-STF with different mass fractions of fly ash, and then rheometer was used to carry out steady-state rheological testing for FA/SiO₂-STF, and 4%FA/SiO₂-STF dynamic rheological test and temperature sensitivity testing, respectively. The thickening mechanism of FA/SiO₂-STF was analyzed by scanning electron microscope. The rheological test results show that the FA/SiO₂-STF with 4% fly ash content exhibits remarkable shear thickening effect. Finally, the relationship between the viscosity and shear rate of FA/SiO₂-STF is numerically described by a mathematical model, which can accurately reflect the viscosity thickening effect.

Flow-induced disentanglement (FID or CCR-D) and chain tumbling are two molecular mechanisms typically observed in non-equilibrium molecular dynamics simulations of entangled polymer melts under fast shear. As regards quantitative performance, classical tube models exhibit limitations at fast rates presumably due to the negligence of the aforementioned mechanisms. CCR-D or tumbling inclusion is reported in some revised tube models. For example, in Desai–Larson’s (DL) work (J Rheol 58:255–279, 2014), which focuses on uniaxial elongation, FID is coupled to the alignment and stretch status of the chains. In Costanzo et al. (Macromolecules 49:3925–3935, 2016), tumbling is accounted for via incorporation of a semi-empirical tumbling function in the stretch equation. Nevertheless, CCR-D is neglected. Here, we include tumbling in the DL differential constitutive set and we assess its performance at shear and relaxation following shear. Model predictions are compared against data on various polystyrene melts as obtained by a cone-partitioned-plate fixture.

We suggest a new interpretation for pH-dependent temporal evolution in the microstructure and rheology of silica suspensions based on interparticle interactions, which differs from the conventional explanation including the catalytic effect of hydroxyl ions and charges. The temporal evolution of silica suspensions under various pH conditions was investigated through rheometry and diffusing wave spectroscopy (DWS) analysis. The transition from liquid to solid was observed to be the most rapid at pH 5 compared to other pH conditions (pH 3, 7, 9). This phenomenon could not be adequately explained by the conventional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory that predicts the liquid-to-solid transition occurs more rapidly at the lower pH condition due to the lower surface charge. As an alternative, we employed an elaborated DLVO theory that additionally considers the hydration force, arising from the hydrophilic nature of the silica surface. The pH dependency was interpreted using the elaborated DLVO theory, which showed that the strong short-range nature of the hydration force significantly reduced the attraction range at pH 3, leading to the retardation and decline in structural and rheological development. The impact of pH and resulting alterations in interparticle interaction on the microstructure were further investigated using rheological scaling theory.

Graphical Abstract

Liquid crystalline polymer (LCP) solutions undergo uniaxial elongation in fiber spinning, yielding highly oriented fibril-structured fibers with enhanced orientation and mechanical properties. This study explores how initial fiber orientation and Frank elasticity influence the dynamics and stability of the isothermal spinning process for LCP solutions. The simplified Larson-Doi mesoscopic model is employed, capable of capturing elastic stress emerging from domain structure evolution. Two main factors, inlet orientation and the Ericksen number as a parameter representing Frank elasticity, significantly affect steady-state fiber orientation profiles and the onset of draw resonance instability, as determined through linear stability analysis. The sensitivity of spinline flow to a sinusoidal disturbance is assessed using the frequency response method. Changes in stability onset concerning these two main factors are reasonably correlated with the extensional behavior of the LCP solution in the spinline and the results of the frequency response.

Graphical Abstract

This work investigates transient non-colloidal suspension flows in cone-and-plate, plate-plate, and cylindrical geometries to assess particle motion’s impact on viscosity measurement. Mass and momentum conservation equations model the two-phase liquid–solid flow, with both phases treated as continuous in an Euler-Euler approach. Findings demonstrate rheometric flow induces particle motion, affecting suspension homogeneity and viscosity measurement over time. Both buoyancy and inertia effects drive particle motion, with buoyancy dominating at low shear rates and inertia at high shear rates. Particle volume fractions, shear rates, and liquid viscosity notably influence viscosity measurements. Measurements with concentric cylinders are the least affected by particle motion. Additionally, we propose a time limit and a critical Reynolds number in which particle motion does not affect the measurement of the suspension viscosity.