Korea-Australia Rheology Journal最新文献

Magnetorheological (MR) elastomer is classified as a smart material whose mechanical properties, such as stiffness, natural frequency, and damping capacity are tunable and controllable under the influence of magnetic field. This tunability makes it suitable for various engineering applications that require adjustable devices. Generally, MR elastomer contains magnetic particles and a matrix. Iron particles are typically used as magnetic particles in MR elastomer because of their low residual magnetism and high magnetization. Nevertheless, iron particles are prone to oxidation in a practical environment that can weaken the effectiveness of MR elastomer in terms of its field-dependent viscoelasticity. As an alternative, MR elastomer contains cobalt particles that offer better oxidative resistance and favorable electrical properties, yet their properties under oxidation have not been explored. In this work, we conducted an oxidation process using diluted 5vol% hydrochloric acid (5 vol% HCl). Two different magnetic particles (iron particles and cobalt particles) were used and tested to identify the better filler for MR elastomer subjected to oxidation conditions. The characterizations of magnetic particles were accomplished using high-resolution field emission scanning electron microscopy and energy dispersive X-ray spectroscopy (HR-FESEM and EDS) to observe the morphology and elemental compositions, and X-ray diffraction (XRD) to determine the crystallinity of magnetic particles. In addition, Fourier-transform infrared (FTIR) analysis was conducted to identify the molecular compounds of the MR elastomers. A vibrating sample magnetometer (VSM) was also utilized to obtain magnetic properties and a rheometer to measure rheological properties. The oxidation on the layer of the magnetic particles undoubtedly affected the MR elastomers’ properties showing the degradation of magnetic properties and rheological properties (storage modulus and loss modulus) for both iron particles and cobalt particles. However, cobalt particles exhibit greater oxidation resistance. It is shown that MR elastomers with cobalt particles showed a higher storage modulus and loss modulus compared to MR elastomers with iron particles both before and after oxidation. Specifically, MR elastomers with cobalt particles and MR elastomers with iron particles showed a decrement of the MR effect by 119.36% and 139.26%, respectively.

Graphical Abstract

It is well known from existing literature that the molecular constitutive models face convergence issues in CFD simulations at higher flow rates. Hence, this article investigates the viability of a numerically efficient approximation that potentially replaces such models by a GNF-based approach, by closely mimicking flow and stress profiles. As a test case, we use the flow of polymer solutions, modelled by FENE-P, around a sphere. Note, the FENE-P is frequently used as a constitutive model for polymer solutions. First, the flow fields predicted by FENE-P are compared with an equivalent GNF model (with the Carreau-Yasuda serving as the representative GNF in this study). Despite efforts to align the viscosity-shear rate dependence and thus creating equivalent models, the GNF model exhibits notable shortcomings, particularly due to neglect of chain stretching, especially near the stagnation points. Subsequently, an attempt is made to address this limitation by introducing extensional components to the local viscosity. Various inelastic models exist in literature for this aspect, among which the most recent one, the GNF-X formulation [Journal of Rheology 64, 493 (2020)] is selected. However, this formulation predicts significantly large stresses at the stagnation regions relative to FENE-P as well as fails to exhibit the asymmetry in stress and flow profiles. Consequently, we propose appropriate corrections to be added (termed as GNF-XM), which enables successful predictions. The asymmetry and drag coefficients from the GNF-XM agree well with the predictions from FENE-P across all flow rates. Notably, being inelastic and easier to converge, computational times are significantly lower than those for FENE-P, particularly at higher flow rates. This suggests a promising, highly efficient GNF-based approximation to FENE-P, with potential applicability to other complex constitutive models. Note, such an inelastic model would be helpful for polymer processing applications, particularly for faster design estimates. The corrections are physical in origin and independent of the details of the GNF-X formulation, which can be added to any given inelastic mixed-viscosity formulation.

Graphical abstract

We investigated a composite hydrogel composed of bovine serum albumin (BSA) and xanthan gum (XG). Using small-amplitude oscillatory shear (SAOS) and large-amplitude oscillatory shear (LAOS) tests, we explored the effects of both BSA and XG concentrations on the BSA-XG composite hydrogel across linear and nonlinear deformation length scales. In the SAOS tests, an increase in XG concentration, at a constant BSA content, resulted in a linear increase in the storage modulus (({G}^{prime})) and loss modulus (({G}^{{prime}{prime}})) of the hydrogel. The power-law viscoelastic frequency dependence of the BSA-XG hydrogel increased with higher XG concentrations, indicating a denser crosslinking network. The LAOS behavior, analyzed through storage modulus (({G}^{prime})) and loss modulus (({G}^{{prime}{prime}})) via Fourier transform rheology, revealed that the critical yielding strain amplitudes decreased as the XG concentration increased. Additionally, intra- and intercycle analyses were performed using Lissajous plots in conjunction with the stress decomposition method, stiffening and thickening ratios, and the sequence of physical processes technique. Strong elastic strain-stiffening was identified as the dominant nonlinear behavior at large strain amplitudes. Moreover, at higher XG concentrations, the strain-stiffening response was better preserved beyond the first critical yield strain amplitude. Fourier transform infrared spectra confirmed that the unfolding and crosslinking intensity of BSA was proportional to the XG concentration.

Graphical abstract

We investigated the effect of surfactant concentration on the rheological behavior of suspensions containing multi-walled carbon nanotubes (MWNTs) dispersed in N-methyl-2-pyrrolidone (NMP) mixed with nonionic surfactant, polyoxymethylene sorbitan monooleate (Tween 80). The surfactant concentration ranged from 0 to 10 wt.% relative to the MWNT particles. As the surfactant concentration increased, the shear viscosities initially decreased, reaching a minimum at 6 wt.%, and then increased. Similar trends were observed in the behavior of the yield stress and the power-law index. In oscillatory shear tests, storage modulus increased with the surfactant concentration up to 6 wt.% and then decreased. Aggregation structure was analyzed using a scaling theory, based on the suspension’s elasticity obtained from linear viscoelastic measurements. The dependence of elastic modulus on MWNT concentration at different surfactant concentrations provided fractal dimension of average aggregate. It was found that the addition of surfactant lowered the fractal dimension of average aggregates from 1.9 to 1.2–1.3. The fractal dimension at the surfactant concentration of 6 wt.% showed slightly lower values than those of 2 wt.% and 10 wt.%. which is the same trend as the rheological properties. These findings were further supported by a UV–visible-NIR spectroscopy method, which measured the light absorbance of individual MWNTs in diluted suspensions. The UV–visible-NIR spectroscopy analysis showed maximum absorbance at a surfactant concentration of 6 wt.%, indicating optimal dispersion of the MWNTs. This behavior aligned with the observed trends in shear viscosity and fractal dimension.

Graphical Abstract

The study aims to analyse the importance of electroosmotic force on the solute dispersion in a microchannel where the carrier fluid is defined by non-Newtonian Casson rheology. The Electric-double layer (EDL) is considered near the channel walls. Flow unsteadiness due to the electric force leads to a highly non-linear momentum equation, which is solved using a regular perturbation method. However, Gill’s generalized dispersion technique is used to discuss the solute dispersion mechanism. The velocity profile, along with the advection, dispersion coefficients and mean concentration, is discussed with different rheological and controlled parameters. The impact of key control parameters, i.e., thickness of the EDL, yield stress, and Péclet number, on the dispersion coefficient, advection coefficient, and mean concentration is examined. A wide range of parameters is considered based on the experimental and physical database from different literatures. Although the transport coefficients are evaluated analytically, numerical tests have also been conducted, producing results that match very well. The existence of electroosmotic force (higher Debye–Hückel electro-osmotic parameter, κ) raises the advection coefficient, and this impact is more noticeable for lower κ values. The dispersion coefficient ((K_{2})) diminishes nonlinearly with increasing κ and eventually converges to a specific value with larger κ. The mean concentration variation is more pronounced at lower values of κ, showing a 50% increase as κ rises from 10 to 50, while the variation is only 7% when κ changes from 50 to 100. Understanding dispersion phenomena controlled by electroosmotic force and pulsatility is a challenging task, mainly due to its nonlinearity, and as a result, this area has not been extensively explored. This type of study may have wide applications in biomedical engineering, human blood flow analysis, and beyond. The present simulation will thus be valuable in understanding mass transfer processes.

Graphical abstract

Schematic diagram of the proposed geometry

This article describes a new rheological model that considers the structural changes of Simple Yield Stress Fluid (SYSF). These fluids exhibit an elastic behavior below a threshold stress and non-Newtonian viscous behavior governed by a model similar to the generalized Casson model proposed by Benhadid et al. [1] above the yield stress. This model represents the complex rheological behavior of SYSFs across the whole shear rate range while taking into account the structural changes found in this type of fluid. This approach is based on the development of a generic model that will encompass most classical models as particular cases by describing the complete flow curve of viscoplastic (VP) materials with an extension to ElastoViscoPlastic fluids (EVP). Thus, the apparent viscosity determined from the proposed model describes a smooth flow curve without discontinuities, where the yield stress is clearly expressed with a maximum Newtonian viscosity (viscosity at zero shear rate (eta_{0})), which approaches a Newtonian viscosity (eta_{infty }) at high shear rates.

Graphical abstract

We propose a systematic method to solve viscoelastic model for viscometric flows. The method is to generalize integration factor for tensor differential equation. If the analytical solution for viscometric flow exists, then it is easier to check the validity of the constitutive equation than use of numerical solution. Our ansatz gives the analytical solutions of quasi-linear viscoelastic models, such as the upper-convected, lower-convected, and corotational Maxwell models, because they become sets of linear ordinary differential equations for viscometric flows such as simple shear and elongational flows. We expect that the integration factor method can improve the numerical algorithms for nonlinear viscoelastic models and we are in preparation of a new numerical algorithm based on the integration factor method.

Graphical abstract

In this study, low-reflective multilayer films (LRMFs) and high-reflective multilayer films (HRMFs) were designed and manufactured using colorless polyimide (CPI) as a low refractive index layer and Si₃N₄ as a high refractive index layer. A numerical simulation was conducted to design a nanolayered structure with different reflectivity characteristics at specific wavelengths. Rheological analysis was performed to determine a solution concentration needed for coating CPI at the nanoscale via the wet process. A layer of 89 nm was found to be formed stably using a 5wt% CPI solution at 5000 rpm. The results revealed that LRMFs exhibited less than 1% reflectivity at the central wavelength, while HRMFs showed more than 40% reflectivity at the central wavelength. Morphological analysis confirmed that the designed nanostructures were successfully fabricated. This research has provided a new way to fabricate optical film through the wet process.

Graphical abstract

Complex chemical reactions and hydrodynamic dispersion feature in many aspects of hemodynamics. Motivated by examining the reactive phase change dispersion in perfusion, a mathematical study is presented for solute dispersion in incompressible laminar blood flow through a straight circular capillary with a permeable wall (enabling lateral movement across the vessel fenestrations in perfusion and associated with the presence of the endothelial layer). The boundary condition at the vessel wall is considered a reversible phase exchange process based on first-order chemical kinetics. Darcy’s law is deployed to feature the permeability nature of the capillary. A multiple-scale asymptotic analysis is developed, and a non-dimensional transverse averaged “macro-transport” equation for convective diffusion–dispersion is derived. Expressions are then presented for the advection coefficient and Taylor dispersion coefficient. Numerical evaluation of the impact of key control parameters i.e., permeability parameter, pressure parameter, retention parameter (α), Damköhler number (Da) on dispersion coefficient, advection coefficient and leading order concentration of the solute is conducted, and solutions are visualized graphically both for small and large times. The novelty of the present work is, therefore, the collective consideration of complex wall permeability and pressure difference in addition to boundary reaction and Darcian body force effects. The analysis shows that the dispersion coefficient is initially enhanced gradually with an increment in the retention parameter with its initial small value and thereafter exhibits a smooth decay. The hydrodynamic dispersion coefficient markedly decreases with higher values of the permeable parameter. A higher magnitude of dispersion coefficient is computed at the vessel inlet and then decreases towards the outlet. A boost in the leading order concentration of the solute is computed at small times but is stabilized and eventually remains invariant with time. The axial velocity is found to depend strongly on the axial position in the capillary. A displacement in concentration peaks is also observed which is attributable to advection along the axial direction, and the decreasing peaks with respect to time are due to the diffusion of the solute from the fluid phase to the vessel wall. Generally, it is also observed that retention enhances the chemical reaction effect, leading to a greater loss of solute over time. The simulations are relevant to chemo-hemodynamics and also may find applications in drug delivery (pharmacodynamics).

Graphical abstract

Poly(ionic liquid)s are ion-containing polymers possessing ionic liquid structures on their repeating units. Owing to the unique physicochemical properties of ionic liquids, many existing studies have found that the properties of poly(ionic liquid)s are distinct from those of conventional ion-containing polymers, such as poly(sodium styrene sulfonate). A lot of scientific efforts have been made to understand the relationship between the chemical structure and the material properties of poly(ionic liquid)s, and several good review papers are available in the literature. The aim of this short review is to summarize key results on the viscoelastic properties of poly(ionic liquid)s in solution. We discuss in detail the counterion condensation and the charge screening in poly(ionic liquid) solutions.

Graphical Abstract