Search Results (164)

An analytical study is conducted on unsteady, one-directional magnetohydrodynamic (MHD) flows of electrically conducting, incompressible, and viscous fluids, where the viscosity varies with pressure following a power-law relationship. The flow takes place within a planar channel and is driven by the lower plate, which moves along its own plane with an arbitrary, time-dependent speed. The effects of gravitational acceleration are also considered. General exact formulas are derived for both the dimensionless velocity of the fluid and the resulting non-zero shear stress. Moreover, these are the only general solutions for the MHD motions of the fluids considered, and they can produce precise solutions for any motion of this type for respective fluids. The proposed analytical method leads to simple forms of analytical solutions and can be useful in the study of other cases of fluids with viscosity depending on pressure. As an example, solutions related to the modified Stokes’ second problem are presented and confirmed through graphical validation. These solutions also help highlight the impact of the magnetic field on fluid dynamics and determine the time needed for the system to achieve a steady state. Graphical representations indicate that a steady state is reached more quickly and the fluid moves more slowly when a magnetic field is applied. Full article

This study develops highly flexible, biodegradable polymer blends using bio-based polyhydroxyalkanoate (PHA) polymers for Fused Deposition Modeling (FDM) 3D printing. A Design of Experiment (DoE) approach optimized blend compositions by varying crystallinity levels of three PHAs, processed via twin-screw extrusion. Rheological analysis revealed that PHA blends exhibited 30–50% lower viscosity than PLA at low shear rates, ensuring improved processability. Tensile testing confirmed favorable mechanical properties, with elongation at break exceeding 2000%, significantly surpassing PLA (29%). Differential scanning calorimetry (DSC) indicated partial miscibility and crystallinity reductions of up to 50%, influencing printability. Optimized 3D printing parameters demonstrated minimal warping for blends with crystallinity below 18%, ensuring high-dimensional stability. During home composting tests, PHA blends showed significant degradation within two months, whereas PLA remained intact. Scanning electron microscopy (SEM) confirmed microbial degradation. Cytotoxicity tests demonstrated that the blends were non-toxic, supporting applications in tissue engineering. These findings highlight the potential of PHA-based blends as sustainable, high-performance materials for biomedical, packaging, and environmental applications. Full article

This study investigated the effects of electron beam radiation on the room-temperature and high-temperature mechanical properties of two ethylene-vinyl acetate (EVA) copolymers, designated EVA 206 and EVA 212. These copolymers had varying vinyl acetate (VA) contents (6 wt.% and 12 wt.%), with the same melt flow index of 2.0 g/10 min. Samples were irradiated at doses ranging from 60 to 180 kGy. The impact of electron beam irradiation on the creep, frequency sweep, and stress–strain behaviors of the ethylene-vinyl acetate copolymers was evaluated using a dynamical mechanical analyzer (DMA). Crystallinity was measured using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). Creep compliance was quantitatively analyzed using four-parameter and six-parameter models. While crosslinking had minimal influence on the room-temperature properties, it significantly affected the behavior at 150 °C. With increasing irradiation dose, creep compliance decreased, while the shear modulus, viscosity, and shear stress at a strain of 0.03 increased, indicating enhanced resistance to deformation. Crosslink density also increased with irradiation dose. EVA 212 with a higher vinyl acetate content exhibited a higher resistance to creep and better high-temperature mechanical properties across all measurements. Full article

Fractured vuggy reservoirs exhibit intricate fracture networks, where large fractures impose significant shielding effects on smaller ones, posing formidable challenges for efficient exploitation. A systematic evaluation of foaming volume, drainage half-life, decay behavior, and viscosity under varying temperatures and salinities was conducted for conventional foam, polymer-enhanced foam, and gel foam. The results yield the following conclusions: Compared to conventional foam, polymer-enhanced foam exhibits markedly improved stability. In contrast, gel foam, cross-linked with chemical agents, maintains stability for over one week at elevated temperatures, albeit at the expense of reduced foaming capacity. The three-dimensional network structure formed post-gelation enables gel foam to retain a thicker liquid film, exhibiting exceptional foam stability. As salinity increases, the base liquid viscosity of conventional foam remains largely unaffected, whereas polymer foam shows marked viscosity reduction. Gel foam displays a non-monotonic viscosity response—initially increasing due to ionic cross-linking and subsequently declining from excessive charge screening. All three systems exhibit significant viscosity decreases under high-temperature conditions. Visualized plate fracture model experiments revealed distinct flow patterns and mobility control performance; narrow fractures exacerbate bubble coalescence under shear stress, leading to enlarged bubble sizes and diminished plugging efficiency. Among the three systems, gel foam exhibited superior mobility control characteristics, with uniform bubble size distribution and enhanced stability. Integrating the findings from the foam mobility control experiments in parallel fracture systems with the diversion outcomes of mobility control and flooding, distinct performance trends emerge. It can be seen that the stronger the foam stability, the stronger the mobility control ability, and the easier it is to start the shielding effect. Combined with the stability of different foam systems, understanding the mobility control ability of a foam system is the key to increasing the sweep coefficient of a complex fracture network and improve oil-washing efficiency. Full article

Rubber-modified asphalt (RMA) faces several challenges, including poor workability, difficult construction, and high energy consumption. The incorporation of renewable light oils offers a promising solution to address issues such as high viscosity and elevated carbon emissions in asphalt modified with a high dosage of rubber powder. The investigation of light oil and rubber powder composite-modified asphalt under low-temperature (160 °C) and short-term (30 min) shear processes is essential for understanding its rheological behavior and modification mechanism. This study explores composite-modified asphalt prepared with four types of light oils (fatty acids, aromatic oil, tall oil, and paraffin oil) at dosages of 10% and 15%, combined with 20% rubber powder. Conventional penetration and viscosity tests were carried out to assess the overall physical properties of the composite-modified asphalts, while rheological tests were conducted to examine their performance at high temperatures. Fourier transform infrared spectroscopy (FTIR) and fluorescence microscopy (FM) were employed to explore the interaction mechanisms that occurred between the light oils, rubber powder, and asphalt. The results suggest that the addition of various light oils leads to a reduction in the viscosity of rubber-modified asphalt, with the extent of reduction varying across different oils. Notably, 10% tall oil demonstrates the most significant reduction in viscosity while also facilitating the dissolution of rubber powder. The high-temperature PG-grade rubberized asphalt improved with the incorporation of light oils, with 5% tall oil yielding the highest PG grade of PG 82-34. FTIR analysis confirmed that light oils and rubber were physically blended in the asphalt, with the light components of the oils being absorbed by the asphalt. FM observations revealed that light oils promote the swelling of rubber particles, with the rubber particles fully swelling in tall oil. Considering the reduction in viscosity, the performance at both high and low temperatures, elasticity, and the extent of rubber particle swelling, tall oil is identified as the most effective material for preparing light oil–rubber composite-modified asphalt using the low-temperature, short-term shear process. Full article

This study investigates the potential of data-driven modeling to monitor and predict mechanical properties of extruded film using recyclates. The first step is to investigate whether a process parameter can indicate the input material quality of the material, which can vary significantly due to the use of recyclate. The die pressure was shown to be a key indicator due to its strong correlation with viscosity and material degradation. The second step is to explore the ability of machine learning models—Generalized Additive Models, Linear Regression, and Random Forest—to predict film tensile strength and modulus based on extrusion process and material parameters. The results demonstrate that including Melt Flow Rate and shear viscosity in addition to pressure and feedstock type (Virgin, PIR, and PCR) significantly improves model accuracy, with Generalized Additive Models achieving the highest R² of 85.7% for tensile strength prediction. Additionally, the observed variability between different recyclate streams highlights the need for a more detailed classification of recyclates to better predict and optimize the mechanical performance of the film. While data-driven approaches for predicting properties show promise, their effectiveness remains limited by data availability and feedstock variability. Expanding datasets and improving process stability will be critical to refining predictive models for industrial application. Full article

To investigate the lubrication mechanism of phytic acid (PA) solution, a “copper–PA solution–copper” confined model with varying concentrations was established. Molecular dynamics (MD) simulations were employed to model the behavior of compression and the confined shear process. By examining the variations in key parameters such as dynamic viscosity, compressibility, radial distribution function, relative concentration distribution, and velocity distribution of PA solutions under different normal loads or shear rates, we elucidated the lubrication mechanism of PA solutions at the molecular level. The results demonstrate that under standard loading conditions, higher PA concentrations facilitate the formation of denser hydrated layers with decreased compressibility compared to free water, thereby significantly enhancing the load-bearing capacity. The shear stress at the solution–copper interface exhibits a substantial increase as the shear rate rises. This phenomenon originates from shear-driven migration of PA to the copper interface, disrupting the hydration layers and weakening hydrogen bonds. Consequently, this reduction in PA–water interactions amplifies slip velocity differences, ultimately elevating interfacial shear stress. The load-bearing capacity of the PA solution and the interfacial shear stress between the PA and copper are critical factors that influence the lubrication mechanism at the PA/Cu interface. This study establishes a theoretical foundation for the design and application of PA solution as a water-based lubricant, which holds significant importance for advancing the development of green lubrication technology. Full article

Resorbable microparticles can be added to hydrogel-based biocompatible scaffolds to improve their mechanical characteristics and allow localised drug delivery, which will aid in tissue repair and regeneration. It is well-known that bioprinting is important for producing scaffolds personalised to patients by loading them with their own cells and printing them with specified shapes and dimensions. The question is how the addition of such particles affects the rheological responsiveness of the hydrogels (which is critical during the printing process) as well as mechanical parameters like the elastic modulus. This study tries to answer this question using a specific system: an alginate-gelatine hydrogel containing polyhydroxybutyrate-co-hydroxyvalerate (PHBV) microparticles. Scaffolds were made by bioprinting and moulding incorporating PHBV microspheres (7–12 μm in diameter) into alginate–gelatine inks (4.5 to 9.0% w/v). The microparticles (MP) were predominantly located within the polymeric matrix at concentrations up to 10 mg MP/mL ink. Higher particle concentrations disrupted their spatial distribution. Inks pre-crosslinked with 15 mM calcium and containingMPat concentrations ranging from 0 to 10 mg/mL demonstrated rheological characteristics appropriate for bioprinting, such as solid-like behaviour (G′ = 1060–1300 Pa, G″ = 720–930 Pa), yield stresses of 320–400 Pa, and pseudoplastic behaviour (static viscosities of 4000–5600 Pa·s and ~100 Pa·s at bioprinting shear rates). Furthermore, these inks allow high printing quality, assessed through scaffold dimensions, filament widths, and printability (Pr > 0.94). The modulus of elasticity in compression (E) of the scaffolds varied according to the content of MP and the manufacturing technique, with values resembling those of soft tissues (200–600 kPa) and exhibiting a maximum reinforcement effect with 3 mg MP/mL ink (bioprinted E = 273 ± 28 kPa; moulded E = 541 ± 66 kPa). Over the course of six days, the sample’s mass and shape remained stable during degradation in simulated body fluid (SBF). Thus, the alginate–gelatine hydrogel loaded with PHBV microspheres inks shows promise for targeted drug delivery in soft tissue bioengineering applications. Full article

This study investigates the atomization process in Respimat^® Soft Mist^TM Inhalers (SMIs) using a validated Volume of Fluid (VOF)-to-Discrete Phase Model (DPM) to simulate the transition from colliding liquid jets to aerosolized droplets. Key parameters, including colliding jet inlet velocity, surface tension, and liquid viscosity, were systematically varied to analyze their impact on the atomization, i.e., aerosolized droplet size distributions. The VOF-to-DPM simulation results indicate that higher jet inlet velocities enhance ligament fragmentation, producing finer and more uniform droplets while reducing total atomized droplet mass. The relationship between surface tension and atomization performance in colliding jet atomization is not monotonic. Reducing surface tension plays a complex dual role in the atomization process. On the one hand, lower surface tension enhances the likelihood of liquid jet breakup into a liquid sheet, leading to the formation of smaller ligaments under the same airflow conditions and shear forces. This increases the probability of generating more secondary droplets. On the other hand, reduced surface tension also destabilizes the liquid surface shape, decreasing the formation of fine, high-sphericity droplets in regimes where surface tension is a dominant force. Viscosity also influences atomization through complex mechanisms, i.e., lower viscosity reduces resistance to ligament breakup but promotes droplet interactions and coalescence, while higher viscosity suppresses ligament fragmentation, generating larger droplets and reducing atomization efficiency. The validated VOF-to-DPM framework provides critical insights for enhancing the performance and efficiency of inhalation therapies. Future work will incorporate nozzle geometry, jet impingement angles, and surfactant effects to better understand and optimize the atomization process in SMIs, focusing on achieving preferred droplet size distributions and emitted doses for enhanced drug delivery efficiency in human respiratory systems. Full article

This study systematically investigates the colloidal stability, rheological properties, and filtration behavior of palygorskite–montmorillonite mixed clays in both freshwater and seawater systems. By varying the mass content and dispersion medium (freshwater/seawater), we analyze the colloidal stability, zeta potential, flow curves, viscosity, shear-thinning behavior, thixotropy, and fluid loss of the dispersions. The results show that palygorskite exhibits good rheological performance in both freshwater and seawater, while montmorillonite performs better in freshwater but suffers a significant decline in seawater. However, palygorskite demonstrates high fluid loss, which is unfavorable for drilling fluid function. Mixed clays can mitigate the limitations of individual clays to some extent, but the specific performance depends on the clay mineral content and dispersion medium. In freshwater, a small amount of montmorillonite improves the viscosity and shear-thinning behavior of the dispersion, with optimal montmorillonite contents of 22% and 38%, respectively. The thixotropy and fluid loss reduction in the mixed clays are positively correlated with montmorillonite content. In seawater, the rheological performance inversely correlates with Mt content due to montmorillonite’s high sensitivity to electrolytes. The addition of Pal enhances the colloidal stability and rheological properties of the mixed clays in seawater. This work provides theoretical insights into the behavior of mixed clays in different media, offering valuable guidance for the design of seawater-based drilling fluids. Full article

Different processing conditions to produce emulsions can modify the dispersion of ingredients, visual aspect, and viscosity, influencing the final product’s effectiveness. In this study, a primary sunscreen emulsion was produced by the conventional stirring process and subsequently subjected separately to complementary processing methods. A Box-Behnken 2³ factorial design was applied to each complementary processing method: the High-Shear Method (CP-HS) and the High-Pressure Homogenization Method (CP-HPH). The present study aimed to investigate the influence of these complementary processes on particle size distribution (PSD), Zeta potential, pH, rheological properties, in vitro SPF, and photostability. In the CP-HS factorial design, the factors explored at three levels were stirring speed and stirring time, while in the CP-HPH design, the factors varied at three levels of pressure and the number of cycles through the high-pressure homogenizer. Results indicated that both complementary processing methods significantly influenced (p < 0.05) the physicochemical characteristics of the primary sunscreen emulsion, which was applied as the starting point. In CP-HS, the sample subjected to 15,000 rpm for 15 min exhibited the highest in vitro SPF (p < 0.05), with an average value of 42 at T0, while the primary sunscreen emulsion had an SPF of 30. In CP-HPH, a more pronounced reduction and uniformity in PSD among the studied methods were observed (p < 0.05), and the range of data was 0.20–0.34 μm. These results emphasize how different processing methods can influence the final characteristics of an emulsion and where suitable choices can significantly benefit the product. Full article

In this study, precise analytical formulas were obtained for dimensionless steady-state velocity and shear stress in modified Stokes flow scenarios involving fluids whose viscosity varies exponentially with pressure, with magnetic effects and gravitational acceleration also taken into account. Actually, these are the first exact solutions for such motions of fluids with exponential dependence of viscosity on pressure in which magnetic effects are taken into consideration. They are important for experimental researchers who want to know the transition moment of a motion to the steady state. In addition, the exact solutions can be used to test numerical methods that are developed to study more complex motion problems. For validation, different limiting cases were explored, and several well-known results from previous studies were recovered. The impact of the magnetic field on steady-state behavior and fluid flow was visually represented and thoroughly examined. The findings demonstrated that fluids flowed more slowly and attained steady-state conditions more quickly when influenced by a magnetic field. Full article

Background: Silibinin (SLB), a flavonoid derived from milk thistle, exhibits promising therapeutic properties but faces significant clinical limitations due to poor solubility and bioavailability. Objectives: This study focuses on the development and characterization of SLB-loaded nanoemulsions designed for mucosal delivery. Methods: Nanoemulsions were prepared using the spontaneous emulsification method, guided by pseudoternary phase diagrams to determine selected component ratios. Comprehensive characterization included particle size, polydispersity index (PDI), zeta potential, encapsulation efficiency, rheological properties, and surface tension. Mucoadhesive properties were evaluated using quartz crystal microbalance with dissipation (QCM-D) to quantify interactions with mucin layers. Results: The combination of Capryol 90, Tween 80, and Transcutol in selected proportions yielded nanoemulsions with excellent stability and solubilization capacity, enhancing the solubility of silibinin by 625 times compared to its intrinsic solubility in water. The ternary phase diagram indicated that achieving nanoemulsions with particle sizes between 100 and 300 nm required higher concentrations of surfactants (60%), relative to oil (20%) and water (20%), with formulations predominantly composed of Smix (surfactant and cosurfactant mixture in a 1:1 ratio). Rheological analysis revealed Newtonian behavior, characterized by constant viscosity across varying shear rates and a linear torque response, ensuring ease of application and mechanical stability. QCM-D analysis confirmed strong mucoadhesive interactions, with significant frequency and dissipation shifts, indicative of prolonged retention and enhanced mucosal drug delivery. Furthermore, contact angle measurements showed a marked reduction in surface tension upon interaction with mucin, with the SLB-loaded nanoemulsion demonstrating superior wettability and strong mucoadhesive potential. Conclusions: These findings underscore the suitability of SLB-loaded nanoemulsions as a robust platform for effective mucosal drug delivery, addressing solubility and bioavailability challenges while enabling prolonged retention and controlled therapeutic release. Full article

Three-dimensional bioprinting allows for the fabrication of structures mimicking tissue architecture. This study aimed to develop a gelatin-based bioink for a bioprinted simplified skin model. The bioink printability and chemical-physical properties were evaluated by varying the concentrations of gelatin (10, 15, and 20%) in a semi-crosslinked alginate-based bioink and calcium chloride (100, 150, and 200 mM) in post-printing crosslinking. For increasing the gelatin concentration, the gelatin-based formulations have a shear thinning behavior with increasing viscosity, and the filament bending angle increases, the spreading ratio value approaches 1, and the shape fidelity and the printing resolution improve. However, the formulation containing 20% of gelatin was not homogeneous, resulting also in poor printability properties. The morphology of the pores, degradation, and swelling depend on gelatin and CaCl₂ concentrations, but not in a significant way. The samples containing 15% of gelatin and crosslinked with 150 mM CaCl₂ have been selected for the bioprinting of a bilayer skin model containing human fibroblasts and keratinocytes. The model showed a homogeneous distribution of viable and proliferating cells over up to 14 days of in vitro culture. The gelatin-based bioink allowed for the 3D bioprinting of a simplified skin model, with potential applications in the bioactivity of pro-reparative molecules and drug evaluation. Full article

The presence of free muscovite in tailings can negatively affect the mechanical strength and rheological properties of cemented paste backfill, as has been observed for several cementitious materials. The aim of this study is to evaluate the influence of free muscovite content in tailings on the consistency and rheology of cemented paste backfill. For this purpose, cemented paste backfill mixtures were prepared from two different tailings. The mixtures were prepared at solids contents between 70% and 74% and with the addition of 5% GU (general use Portland cement)/slag binder. In addition, the influence of muscovite was studied by varying the muscovite content of the tailings from about 14% to 25%. Abrams cone slump tests and rheological analyses were carried out for each recipe. The results show a decrease in slump height and an increase in yield stress, Herschel–Bulkley flow index, and infinite shear rate Cross viscosity with increasing muscovite content for a given solids content. Therefore, water should be added to maintain the required flowability of cemented paste backfill, which increases the water/binder ratio and may affect the mechanical strength. A method is presented for determining the amount of binder to be incorporated to maintain the water/binder ratio of the original cemented paste backfill recipe. Full article