Korea-Australia Rheology Journal最新文献

In this study, we systematically investigate the rheological behavior and microstructure formation of the anode slurries containing silicon (Si), carbon black (CB), and carboxymethyl cellulose (CMC) from the perspective of interactions between the constituent components, aiming to provide a fundamental understanding of the dispersion characteristics of Si-based anode slurries. The CMC adsorbs onto both particles (CB/Si) but has different effects on the inter-particle interactions (CB–CB and Si–Si). It stabilizes the CB particles through electro-steric interactions, whereas it agglomerates the Si particles through bridging interactions, in aqueous medium. In the meanwhile, the CMC selectively adsorbs onto CB particles among the two particles. Therefore, at a CMC content lower than the optimum graft density where CB particles are adsorbed and saturated by CMC, it acts as a dispersant in the slurries. However, at a higher content, the CMC that remains after adsorption on CB particles adsorbs onto Si particles and acts as a flocculant for the particles in the slurries. The origin of selective adsorption is understood in terms of the driving forces for adsorption and the surface energy analysis. We anticipate our findings provide a useful guideline for the Si slurry design in terms of its dispersion and contribute to the development of Si anode technology.

Vortex growth is related to the extensional thickness viscosity of polymer melts flowing through contractions, whereas the shear thinning viscosity results in no significant vortex. The nonlinearity of extensional viscosity in relation to molecular architectures and additive composition compositions is usually more sensitive than shear viscosity. Recently, the proposed GNF-X (Generalized Newtonian Fluid eXtended) of the weighted shear/extensional viscosity has been incorporated in the state-of-the-art CFD (computational fluid dynamics) framework to show the extension-induced vortex growth. Using GNF-X, it is important to investigate the conflicting role of shear thinning and extensional thickening on vortex sizes in 3D (three-dimensional) contraction flow simulations for branched and filled polymers melts. In particular, one demonstrates that the long-branched polymers and fiber-filled polymers strongly increase the vortex size, which is consistent with the related experimental observations.

To study the overall rheological characteristics of the silicone oil-based ferrofluid, a chemical co-precipitation method was adopted for preparation, and transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) were used for characterization. The average size of Fe₃O₄ magnetic particles was 10.4 nm and the saturation magnetization of the ferrofluid was 5.98 emu/g. Then, the fluidity, magnetoviscous effect and viscoelasticity of the ferrofluid were studied using a rotational rheometer. The results showed obvious shear thinning of the silicone oil-based ferrofluid under an external magnetic field, and the yield stress of the ferrofluid could not be accurately obtained by fitting the flow curve with an H–B model at a continuous shear rate. A strong magnetoviscous effect could be observed at different shear rates and temperatures. The magnetoviscous parameter R increased with the increase of temperature and its variation decreased with the increase of shear rate. Moreover, based on the magnetic particle chain model and the viscosity–temperature characteristics of the base carrier liquid, different mechanisms of temperature influence on the magnetoviscous effect were analyzed. Finally, a discussion of the microstructure evolution mechanism of the ferrofluid in the modulus changing with frequency was presented through the viscoelastic analysis of the silicone oil-based ferrofluid.

In this work, a numerical model is carried out to investigate the magneto-hemodynamics of blood driven by an oscillating pressure gradient and exposed to a uniform magnetic field and an external body acceleration. The non-Newtonian nature of blood was taken into account using a time-dependent thixotropic model. Incompressible, axisymmetric, and laminar flow assumptions were used to simplify the non-linear partial differential equations. The velocity field and wall shear stress distribution are numerically solved using the finite difference method. The analytical solution of the velocity distribution of a fully developed pulsatile flow of a Newtonian fluid is used to validate the numerical solution. Further research is done into how structural traits, the average of the pressure gradient, body acceleration, and the magnetic field affect the magneto-hemodynamic properties of blood. The findings indicate how the various characteristics taken into account affected the blood's magneto-hemodynamic behavior in arteries.

The rheological property of cathode slurry is commonly influenced by coating speed and mixing temperature, thereby leading to its storage stability and coating uniformity. In this study, the effect of the temperature of slurry on the rheological behaviors is investigated under various shear rates and temperatures based on steady and dynamic tests as well as theoretical models. In the flow experiments, the thixotropic behavior of the slurry is observed at all temperatures tested, and it is reduced with the increase in temperature. The experimental data is captured well by rheological models, and the model parameters are evaluated under the combined effects of shearing and temperature, resulting in two generalized state equations for the description of the flow properties of the slurry. In addition, microstructural rearrangement and polymeric entanglement at high temperatures cause viscosity and modulus to change, giving rise to complex rheological behavior in creep and oscillatory shear. Compared with slurry at 25 and 40 °C, both storage and loss moduli are dependent on oscillatory strain in the range of 0.1–1000% at 65 °C. The difference in characteristic strain corresponding to yielding and strain stiffening behavior is only observed at high temperatures, whereas relaxation times were independent of temperature in the oscillatory shear test. Understanding the effect of the temperature of slurry on rheological behaviors will be useful for improving the manufacturing efficiency of electrodes.

Three different types of carbon materials [carbon nanotubes (CNTs), carbon black (CB), and carbon fibers (CFs)] were incorporated into polyvinylidene fluoride (PVDF) as single fillers or hybrid fillers (CNT/CB and CNT/CF) via solution blending. The physical properties of the hybrid filler systems such as the electrical, thermal, morphological, and rheological properties were compared to those of the single filler systems. Images of the PVDF composites containing hybrid fillers obtained by a field-emission scanning electron microscope showed that CB appeared to be embedded between highly entangled nanotubes, promoting their debundling in the PVDF matrix. The hybrid filler systems of CB and CF with 0.5 wt% nanotubes were electrically conductive from the corresponding content of 1 wt%, showing maximum values from 5 wt% CB and 10 wt% CF. In the hybrid filler systems, the extent of the increase in crystallization temperature (Tc) in the presence of CB or CF was more prominent at a lower CNT content of 0.5 wt%. In the hybrid systems of CB with 0.5 wt% nanotubes, the melting peak for the β phase was generated from 1 wt% CB and its intensity increased with CB content. On the contrary, the hybrid filler systems of CF with nanotubes did not provide a new peak. Regarding the rheological properties, the complex viscosity (η*) of PVDF/CNT0.5/CB increased with CB content, a pattern similar to that of the single filler system of CB. On the contrary, the presence of CF with 0.5 wt% nanotubes slightly increased η* with CF content, while that with 1 wt% nanotubes notably increased η*, exhibiting a sharp increase at 10 wt%.

This paper presents an experimental investigation of the effect of electro-osmosis on lubricating the interface between the cement paste-based material and metal wall. A new experimental apparatus was developed and set up in this study. Two scales of cement paste-based materials were used and tested: cement paste and mortar. Tests performed were as follows: (i) range of potential difference varies from 5 to 30 V; (ii) range of metallic plate slope varies from 7° to 15°. The pre-movement time was reduced and the sample velocity was increased by increasing the potential difference and the slope. The rheological properties of two mixtures were determined to identify the characteristics of the fluid film at the interface that plays an important role in lubricating the sample. The permeability coefficient for managing the contact lubrication was also determined in this study.

Recently, consumers have shown a growing interest in polymeric products that offer high aesthetic and comfort features, along with superior engineering performance. In response to this demand, we conducted a study on metallic polymer composites, utilizing metal fillers and polymers. To create these composites, micro-sized aluminum flakes and nano-sized spherical aluminum powder were combined with aliphatic polyketone. Furthermore, an ion-beam irradiation process was employed to enhance the surface properties of the products, including surface hardness, modulus, and glossiness. The compounding process was carried out using a twin-screw extruder, and disk-shaped specimens were prepared through injection molding. Subsequently, nitrogen ion-beam irradiation was applied to the prepared specimens. Comprehensive analysis was performed to evaluate the mechanical, aesthetic, structural, and morphological properties of these metal-like composites.

The present study dealt with the evaluation of the particulate aggregation in a suspension of multi-walled carbon nanotubes using fractal theory and rheological properties including thixotropy. The multi-walled carbon nanotubes are dispersed in Newtonian glycerol in the concentration range between 0.2 and 0.45 wt%. Rheological measurement was performed for the suspension at various dispersion times up to 300 min. The suspension showed thixotropy, shear-thinning behavior, and yield stress. It also exhibited plateaus of storage modulus in frequency and strain sweep tests. As the dispersion time increases, thixotropy, low-shear viscosities, and yield stress increase, and then their increasing rates slow down. Suspension’s electrical conductivity also showed similar behavior as that of thixotropy with the dispersion time. Viscoelastic behavior was combined with a fractal concept to provide the fractal dimensions of the flocs in the suspension at various dispersion times. The fractal dimension tends to decrease with the dispersion time. Conclusively it is interpreted that as the dispersion proceeds flocs become smaller and chain-like, then the reduced and thinned flocs build the wider range of network structures at rest state.

Characterized by high strength to unit weight, poly(ethylene terephthalate) (PET) remains one of the most widely used engineering plastics, hence the attention to its associated waste and recycling technology development has been paid from academic and industrial perspectives. Herein, we investigate the mechanical degradation of PET through degradative compounding process cycles and the effect of chain extender (Joncryl^® ADR 4468) to prevent molecular degradation of PET during melt processing. They are characterized based on rheological and mechanical measurements. Characterization of the bottle-grade PET samples reveals low viscosity and crystallinity owing to isophthalic acid units within the PET copolymer structure over PET homopolymer. Mechanical shear and thermal impact by virtue of the increase in rotor speed and temperature are employed to study the degradation of the PET samples. Both samples respond to degradation in successive processing cycles with as much as 70% decrease in their complex viscosity and moduli. The molecular weight of PET copolymer accordingly decreases from 23,400 to 8010 g/mol. Chain scission arising from thermo-mechanical degradation results in high crystallinity by more than five folds in the processed PETs. Attributed to recoupling of the degraded short chains, the chain extender compensates with the increase in viscosity and moduli up to 20% whilst serving to increase crystallinity but almost ineffective in appreciating mechanical performance with barely any significant variation in tensile strength and elongation at break. This study shows that mechanical shear is verified to impact a pronounced degradation on PET more than thermal action on the samples.