Korea-Australia Rheology Journal最新文献

The behavior of drops in the emulsion is significant in transport phenomena and the oil and the petrochemical industry. In this study, the behavior of drops that are close to each other was investigated. These drops were studied at two viscosity ratios (0.5 and 0.9, which are the viscosity ratio of drops to fluid) and six capillary numbers (0.05, 0.11, 0.17, 0.42, 0.28, and 0.36). The results demonstrate the effect of drops on each other at a range of volume fractions. Also, at capillary numbers of 0.42, 0.82, and 0.36, there were volume fractions at which drops stuck to each other and broke after combining. In contrast, the single drop at these new capillary numbers after merging was not broken. At the capillary number of 0.84, and volume fraction of 0.001495, the drops did not stick to each other, but they were broken under the influence of each other. For each capillary number, a specified volume fraction was achieved, at which the drops behave as a single drop. Therefore, in each capillary number, a volume fraction can be found so that in volume fractions less than that, drops behave individually and do not interact with each other.

Poly(2-cyano-p-phenylene terephthalamide) (CY-PPTA) has garnered significant interest as a promising precursor for super p-aramid fibers because of its organosolubility in N,N-dimethyl acetamide/lithium chloride (DMAc/LiCl) while conserving the superior properties of the resultant fibers. However, CY-PPTA has been reported to exhibit abnormal phase behavior owing to the strong dipole–dipole interactions induced by the cyano groups. Herein, we rheologically study the isotropic phases of CY-PPTA/DMAc solutions with respect to the concentration and temperature and compare them with those of CY-PPTA/sulfuric acid (H₂SO₄) solutions. In the isotropic region, the CY-PPTA solutions yield a higher power-law exponent of the dynamic viscosity (η') versus concentration of 6.0 (ηʹ ~ c^6.0) in the DMAc system than that in H₂SO₄ (ηʹ ~ c^3.2). Moreover, the CY-PPTA/DMAc solutions exhibit a lower critical solution temperature (LCST) behavior with increasing temperature, in contrast with the upper critical solution temperature in H₂SO₄. Consequently, the viscosity and exponent of the CY-PPTA/DMAc solutions increase at elevated temperatures. As shown by the Cole–Cole plot, the heterogeneity in the DMAc system becomes worse. The LCST of the CY-PPTA solution is ascribed to the intermolecular interactions between the highly polar cyano groups, which are negligible in H₂SO₄.

Pipeline transport at high Reynolds number can result in significant turbulent losses. One of the most effective methods for turbulent drag reduction is adding a very small amount of polymer drag-reducing agent to the pipeline. However, due to the complex interaction between polymers and turbulence, turbulence models incorporating polymer additives remain to be studied and developed. In the present work, we investigated the turbulence model using Reynolds averaged numerical simulation (RANS) to describe polyacrylamide drag reduction flow. A low-Reynolds-number k–ε model in turbulent flow has been developed by considering the concentration and type of polymers, which can be applied for polymer drag reduction prediction in the pipe. Mean velocity profile U_f, turbulent intensity, turbulent kinetic energy k, and turbulent dissipation rate ε in the regions of viscous sublayer, buffer layer and logarithmic layer have been predicted with various concentration θ, Reynolds number Re, degradation degrees, and changing laws of these factors have been revealed with wall distance. The developed turbulence model showed a good capability to qualitatively forecast mean velocity profile, turbulent intensity, turbulent kinetic energy, and turbulent dissipation rate, and the prediction error between the experimental and simulated values falls along the y = x curve, which can be used for the investigation and prediction of varies water-soluble, oil-soluble polymers in turbulent drag reduction flow in pipes with other parameters such as pipe diameter, pipe length, and the Reynolds number.

There have been developed a number of algorithms for the determination of relaxation spectrum from viscoelastic data. When viscoelastic data are given by stress relaxation test, the relation between relaxation spectrum and relaxation modulus can be transformed to that of Laplace transform. Hence, calculation of relaxation spectrum from relaxation modulus is a problem of inverting Laplace transform. Among various mathematical methods for inverse Laplace transform, the Post–Widder formula has been chosen by a number of researchers. However, they did not solve the problem by use of advance numerical technic but used low-order approximations. We suggest a new numerical algorithm which can calculate higher order solutions. In principle, the order of the Post–Widder formula is not limited in our algorithm.

A cylinder rotating in an off-center position across a microchannel is known to generate a net flow for highly viscous Newtonian fluids. The mechanism is also known to be a viable option for the transport of viscoelastic or viscoplastic fluids albeit with a slight drop in performance. In the present work, the applicability of this mechanism is numerically investigated for the transport of (inelastic) time-dependent fluids obeying the structural-based Quemada model. By numerically solving the equations of motion, it is predicted that viscous micropumps can be used for the transport of thixotropic fluids although the obtained numerical results suggest that there exists a critical thixotropy number (a dimensionless number related to the fluid’s natural time) at which the flow rate is at its lowest value. It is shown that the critical thixotropy number can be avoided from the response of the fluid by properly choosing the geometrical parameters of the device. The general conclusion is that viscous micropumps can be deemed as an efficient mechanism for the transport of thixotropic fluids in microfluidic systems provided that the thixotropy number is sufficiently small, i.e., the fluid is strongly thixotropic. The device is predicted to be more suitable for anti-thixotropic fluids.

Liposomes have emerged as pivotal entities in the field of therapeutics, particularly in the domain of protein and vaccine administration. Hence, the development of novel liposomal formulations has garnered considerable interest. Liposomal delivery systems are considered advantageous as medication carriers, especially in the field of dermatology, owing to their moisturizing and restorative characteristics. Nevertheless, a significant drawback in the utilization of liposomes in topical applications is the inherent fluidity of the formulation, which might result in leakage following delivery to the skin surface. The use of liposomes inside the gel matrix, while maintaining the integrity of the vesicles, presents a potentially appealing method for topical administration. The primary objective of this work is to develop a liposomal-loaded gel formulation and assess its in vitro release characteristics as well as its rheological profile, including viscoelastic properties and flow behaviour. This study incorporated two different types of drugs, namely hydrophilic (specifically diphenhydramine hydrochloride) and hydrophobic (namely curcumin), inside its formulations. A liposome, composed of a long alkyl chain lipid such as DPPC with a chain length of 16, was synthesized using the thin film hydration process and subsequently integrated into a carbopol gel. It is noteworthy that the introduction of diphenhydramine hydrochloride (DPH) resulted in a substantial decrease in the elastic modulus and cohesiveness of the liposomal gel. Conversely, the incorporation of curcumin-loaded liposomal gel led to an increase in critical strain and cohesiveness when compared to the plain liposomal gel. In contrast, the liposomal gel containing DPH and curcumin demonstrated a reduced release rate compared to the plain liposomal gel, spanning a duration of 48 h. The in vitro release studies offer the potential for the utilization of liposomal gels as a sustained delivery system.

The capability of a polymer to be molded by the injection molding process is referred to as its moldability. Injection molding technicians typically estimate moldability using a parameter known as the Melt Flow Index (MFI), but this metric can be misleading as it reflects the polymer’s ability to flow under specific conditions that may differ considerably from those encountered during injection molding. A more relevant parameter is the flow length, which represents the distance a polymer travels in a thin, cold mold cavity during the injection molding process. In this study, three types of commercial polypropylene were injection molded in cavity and the flow lengths were measured based on injection pressure and temperature. The outcomes were then compared to the polymer’s rheological properties. The findings indicate that the MFI is not a reliable indicator of polypropylene’s moldability. An empirical equation is suggested to predict polypropylene’s flow length as a function of injection pressure.

The rheological behavior of anode slurries for lithium-ion batteries, containing both natural and synthetic graphite as active material, was investigated with a focus on the different graphite morphologies. When the solid content is low, slurries containing synthetic graphite with a discotic shape display greater viscoelasticity than slurries containing natural graphite with a relatively more spherical shape. This result is attributed to the anisotropic geometry and interparticle force of the synthetic graphite. When the solid content is high, slurries comprising synthetic graphite exhibit lower viscoelasticity than slurries containing natural graphite. Tap density and sedimentation experiments reveal that, due to discotic shape and surface-to-surface attraction, synthetic graphite aggregates to a more densely packed aggregate than natural graphite. Consequently, in conditions of high solid contents where graphite has a greater chance of formation of densely packed aggregates, it is expected that synthetic graphite will have a more compact aggregate structure and a smaller effective volume. The smaller viscoelasticity of synthetic graphite slurries at more concentrated regions, where the effective volume of clusters plays more important role than in dilute regions, is attributed to the surface-to-surface aggregated structure of the synthetic graphite and the resulting small effective volume. Although the effective volume fraction of the graphite aggregates is reduced, slurries made of synthetic graphite demonstrate significant strain stiffening. Our findings suggest that the strain stiffening observed may originate from the anisotropic morphology, which possesses a significant surface area and is accompanied by jamming and high friction.

The settling stability of magnetorheological fluid (MRF) is an important aspect of magnetorheological research and an important indicator of MRF quality. The discrete element method (DEM) was proposed to study the multi-particle settling process of particles dispersed in silicon oil with different iron powder content, particle size, base viscosity, and added magnetic field. Then by preparing MRF, the zero-field viscosity, dynamic magnetic field viscosity, and settling stability of various MRF were measured and analyzed. The results show that the average kinetic energy of MRF settling decreases as particle content, particle size, and base fluid viscosity increase. With 50% iron powder content, 300 nm particle size, and 5% bentonite additive, MRF has the highest viscosity under zero field; under a dynamic magnetic field, the larger the particle size, the larger the viscosity; the MRF settling rate decreases by 18% with a change in iron powder content, decreases by 22.5% with a change in particle size to 300 nm, and decreases by 22% with a change in bentonite content. Under the application of a magnetic field, MRF hardly settles. The final experimental and simulation results are comparable, indicating that the MRF settlement characteristics can be predicted to some extent with the help of DEM simulation.