Korea-Australia Rheology Journal最新文献

During the drying of droplets containing colloidal particles under rapid drying conditions, particle accumulation near the interface leads to the formation of a skin layer. The resulting stress, arising from the high particle concentration, can induce mechanical instabilities and cause undesirable final morphologies. In this study, we investigate particle-scale dynamics during colloidal droplet drying using the lattice Boltzmann method. The mean squared displacement of particles within the skin layer reveals that the drying process proceeds through four distinct stages. In particular, a sharp increase in particle mobility is followed by a burst-like inward motion, characterized by the sudden displacement of particles beneath the droplet surface, which serves as a precursor to subsequent microstructural evolution. To elucidate the underlying mechanisms of this inward motion, local stress and structural features are examined. We show that the burst-like inward motion emerges collectively once the average surface stress reaches a critical threshold, primarily initiating along the grain boundaries of crystallized particle domains. These results provide a comprehensive understanding of structural evolution within drying droplets and clarify the relationship between morphological changes and stress buildup in the skin layer, which remains difficult to access through direct experimental observation.

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Rheology of foods is a necessary tool for quality control and carries importance in processing, stability, and packaging. In this study, two different viscosity-modifiers, industrially used hydrocolloids, guar gum and algae-derived carrageenan, were investigated in various amounts for tomato sauces having different solid contents. Using both hydrocolloids is the novelty of this study, namely, guar gum is a thickener and stabilizer and has role on managing many health problem symptoms; carrageenan integrates with other food ingredients to attain ideal rheological qualities and extends the shelf life of products. The rheology of tomato sauce was examined with linear and non-linear rheological models such as Bingham and Herschel–Bulkley, the rheological parameters were determined and discussed. The optimization of the effective parameters, such as shear yield stress, plastic viscosity, consistency, and flow index was evaluated by Response Surface Methodology, which includes both the statistical and mathematical methods used in processes those are sensitive to the multiple variable effects. In this research, the Box–Behnken experimental design was applied by using ANOVA-supported Design Expert software. The rheological results showed that the Herschel–Bulkley model was found to be a more appropriate model than the Bingham model due to its highest regression coefficients. Design Expert analyses produced quadratic models for each response chosen. Storage and stability tests conducted at optimum conditions from RSM (minimum shear yield stress—71.11 Pa and shear-thinning behavior—n: 0.44) demonstrated that tomato sauces preserved both their resistance to deformation and flow consistency during extended cold storage periods.

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A cosmetic formulation can penetrate its polymer packaging material through direct contact, resulting in changes in the physical properties of the container and visible deformation, thereby incurring significant economic and industrial losses. Therefore, understanding the mechanisms underlying formulation-promoted container deformation is essential for the development of preventive material strategies. In this study, we investigated the effect of a water-in-oil (W/O) emulsion on three types of polymer containers: polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET), under accelerated conditions (45 °C, 80% relative humidity). The physical properties and morphologies of each polymer container were analyzed following long-term storage, revealing that continuous infiltration of the emulsion resulted in the plasticization of the crystalline regions of the PE container, leading to volumetric expansion, whereas the PP container exhibited bending deformation owing to the plasticization of its amorphous regions. In contrast, the PET container exhibited no noticeable changes in either its physical properties or appearance, presumably because of the high chain rigidity conferred by the aromatic PET structure. Overall, this study reveals that the long-term migration of a cosmetic emulsion into a polymer container depends on its intrinsic material characteristics, thereby providing a systematic morphological mechanism for the deformation phenomena.

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Particle deposition in microfluidic channels can lead to clogging and performance degradation. Despite extensive studies on flow and particle transport, it is still unclear how changes in flow features caused by viscosity and channel geometry influence deposition behavior. In this study, we investigate particle deposition in expansion–contraction microchannels by varying fluid viscosity and cavity length using microfluidic experiments and numerical simulations. With the cavity length fixed at 150 μm, the viscosity of the glycerin solution is increased by increasing the glycerin concentration from 40 to 70 wt%. As viscosity increases, particle deposition decreases in the straight regions (both upstream and downstream), whereas it increases in the cavity region. To interpret these trends, two-dimensional steady-state flow simulations are conducted to analyze velocity field, wall shear stress, recirculation region, and stagnant flow region. Furthermore, at fixed fluid viscosity, the cavity length is varied from 50 to 200 μm, along with a contraction channel corresponding to an infinite cavity length. Varying cavity length produced a non-monotonic deposition trend with a minimum at 150 μm, which is associated with geometry-dependent changes in local flow structure, such as recirculation region. These findings suggest that viscosity and channel geometry influence particle deposition and provide practical guidance for controlling deposition in microchannel-based processes.

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This study numerically investigates the mixing of thixotropic fluids in a groove-embedded partitioned pipe mixer (GPPM). The fluid is modeled using the Moore structure-kinetics model, in which viscosity depends on a structure parameter ((lambda)), governed by the competition between shear-induced breakdown and structural recovery. A parametric analysis is performed over wide ranges of the thixotropy number (Th) and destruction parameter (({k}_{d})) at Reynolds numbers of (text{R}text{e}=0.1) and 10, for two plate aspect ratios, (alpha =1) and 2. The coupled evolution of the structure parameter, flow field, and scalar transport is analyzed to clarify the mechanisms responsible for mixing enhancement and suppression. The results show that Th controls the overall degree of structural degradation, whereas ({k}_{d}) determines the spatial nonuniformity of (lambda). In creeping flow ((text{R}text{e}=0.1)), mixing is primarily geometry-dominated and thixotropy reduces homogenization. At (text{R}text{e}=10), however, the coupling between inertia and thixotropy gives rise to strongly non-monotonic behavior. For (alpha =1), mixing deteriorates at intermediate Th and improves only at the highest Th examined. For the higher aspect ratio ((alpha =2)), inertia does not consistently enhance mixing; instead, it reduces mixing performance near (text{T}text{h}approx 1). Quantification using the intensity of segregation demonstrates that mixer designs optimized for Newtonian fluids do not necessarily ensure efficient mixing of thixotropic materials. These findings highlight the critical role of thixotropy in the design of static mixers.

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It is a well-established fact that vibration of a vessel in the vertical direction increases the settling velocity of large solid particles in yield-stress liquids obeying the Bingham model. In the present work, using the lattice Boltzmann method (LBM) we numerically show that in shear-thinning, yield-stress fluids obeying the Casson model the response of a circular solid particle settling in a finite-sized vibrating vessel is non-monotonic and exhibits four different settling regimes. Specifically, starting from a low dimensionless frequency of S = 0.8, the settling velocity of the particle progressively increases by vibrating the vessel until a critical frequency of S = 3.9 is reached. Beyond this critical frequency, the settling velocity of the particle starts decreasing until another critical frequency, roughly S = 4.7, is reached. Beyond this frequency, the settling velocity of the particle again increases up to roughly S = 7 beyond which it approaches an asymptotic value. By plotting the yielded zones and viscosity profiles it is shown that competition between yield stress effects with shear-thinning effects combined with the effects of the sidewalls is responsible for such complex settling behavior, not reported before. For particles that are already stuck in yield stress materials, our numerical results show that the amplitude needed to unblock such particles (at any given frequency) is larger for Casson fluid as compared with Bingham fluid. Since both fluid models have the same critical yield number, this finding highlights the importance of the rheological model adopted to represent particulate systems such as foodstuffs.

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A solid particle settling in a vessel filled with viscoplastic fluids obeying the Casson model exhibits non-monotonic behavior depending on the frequency of the vessel (S) and yield stress of the fluid (Y). The non-monotonic effect is attributed to a competition between yielding (low frequencies), side-wall effects (intermediate frequencies) and shear-thinning (high frequencies).

In battery manufacturing, electrode slurries are transported through pipelines to the coating step. During pipe-flow transport, slurry microstructures can evolve and degrade electrode quality and manufacturing productivity. Conventional off-line tests inherently rely on sampling, which introduces time delay and can yield biased results because the slurry is spatially non-uniform and prone to inhomogeneity. To address these limitations, we construct a laboratory-scale pipe-flow system and directly probe undiluted electrode slurries using in-line electrochemical impedance spectroscopy (EIS) during flow. The in-line EIS distinguishes dispersant-content variations as small as 0.05 wt%. Normalization by a characteristic frequency enables quantitative comparison with conventional off-line EIS result, and the composition-dependent characteristic frequencies remain comparable despite differences in geometry. An equivalent circuit modeling (ECM) links impedance parameters to CMC-driven microstructural transitions. Below the CMC level that saturates surface adsorption, conductive particles agglomerate and the resistance decreases. Above this threshold, excess CMC remains free in the continuous phase, and the effective diffusion length scale decreases with diffusion coefficient changes, consistent with modified ionic transport. Regime-specific ECM trends remain consistent between in-line and off-line data, indicating that the pipe-flow spectra encode composition-dependent microstructural information. Power-law analyses from Ultra-small-angle neutron scattering (USANS) and rheological characterizations independently support these interpretations. Overall, this study demonstrates that in-line EIS measures high-solid slurries reliably under flow and enables real-time, structure-sensitive monitoring in industrial slurry processes.

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Conventional viscoelastic characterization of thermoplastic amorphous polymers employs rotational rheometer above the glass transition temperature (T_g) and Dynamic Mechanical Analysis below T_g. This work proposes a Single-Pellet Molding (SPM) method that enables comprehensive viscoelastic characterization across both regimes using a single rotational rheometer. The SPM procedure involves introducing a single polymer pellet into a custom mold seated on the lower plate, compressing the pellet with the upper plate, and molding a cylindrical sample between the parallel plates. This approach offers a critical advantage for thermally and oxidatively sensitive polymers, as sample preparation can be completed in air at temperatures below the trimming threshold without requiring an inert gas atmosphere. Whereas conventional preprocessing (requiring chamber opening for trimming) introduces cooling-induced artifacts to both sample and shaft geometry, that may lead to human error, the SPM method fundamentally eliminates these sources of uncertainty. SPM enables reproducible QC testing across T_g for Cyclo olefin copolymer (COC), addressing recycling limitations critical to smartphone camera lens production scraps. Validation experiments comparing SPM to traditional trimming procedures, using 5 mm diameter parallel plates, demonstrate a 69% improvement in reproducibility (relative standard deviation: 3.52% → 1.09%). By directly measuring and calibrating both the thermal expansion coefficient and torsional compliance of the measuring tool, we confirm continuous acquisition of consistent viscoelastic data from the polymer melt temperature through sub-T_g region using a single instrument. The method significantly reduces measurement time, requires minimal sample mass (10–20 mg), eliminates nitrogen gas costs, and enables low-temperature measurement without thermal degradation. We anticipate immediate industrial applicability for rapid, economical material characterization in development and quality verification workflows.

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This study investigates the flow behaviour and phase stability of bituminous binders modified using a composite system of Styrene Butadiene Rubber (SBR) and nano-sized calcium carbonate (CaCO₃). Multiple binder formulations were developed with varying SBR contents (3%, 4% and 5%) while keeping Nano-CaCO₃ constant at 4% to evaluate their effectiveness in improving high-temperature performance and blend homogeneity. The experimental program included conventional binder tests (penetration, softening point, and ductility), rotational viscosity at 135 °C, Superpave rutting parameter assessment (G*/Sin δ), failure temperature determination, and Multiple Stress Creep and Recovery (MSCR) testing. Results demonstrated that composite modification significantly reduced penetration values while increasing softening point and viscosity, indicating enhanced stiffness and rutting resistance. MSCR results showed notable reductions in non-recoverable creep compliance (Jnr) and improvements in elastic recovery (R%), particularly at higher SBR dosages. The modified binders also exhibited increased failure temperatures, reflecting improved thermal resistance. Among all formulations, 4S + 4C and 5S + 4C binders provided superior rutting resistance but exhibited elevated viscosity exceeding recommended workability limits. Overall, the SBR/Nano-CaCO₃ composite system effectively enhances asphalt binder mechanical performance and phase stability, offering a promising approach for pavement applications.

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In this study, the injection molding process of a polyphthalamide (PPA)-based thermoplastic polymer package was optimized for application in high-temperature and high-humidity smart farm environments. A numerical three-dimensional flow analysis was conducted to predict the shrinkage behavior under varying packing pressure, mold temperature, injection pressure, melt temperature, and packing time. The predicted results were applied using an orthogonal array, and the Taguchi method was employed to determine the influence of each factor and identify the optimal conditions. As a result, melt temperature and packing time were found to have the most significant statistical impact on shrinkage. Under the optimized conditions (packing pressure of 140 MPa, mold temperature of 90 ℃, injection pressure of 140 MPa, melt temperature of 280 ℃, and packing time of 20 s), the minimum shrinkage value (signal-to-noise ratio = − 12.36 dB) was achieved. The theoretical and experimental shrinkage results obtained from the optimized processing conditions were in excellent agreement.

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