Search Results (458)

Electrokinetics has established itself as a central pillar in microfluidic research, offering a powerful, non-mechanical means to manipulate fluids and analytes. Mechanisms such as electroosmotic flow (EOF), electrophoresis (EP), and dielectrophoresis (DEP) re-main central to the field, once more layers of complexity emerge heterogeneous interfaces, viscoelastic liquids, or anisotropic droplets are introduced. Five research directions have become prominent. Field-driven manipulation of droplets and emulsions—most strikingly Janus droplets—demonstrates how asymmetric interfacial structures generate unconventional transport modes. Electrokinetic injection techniques follow as a second focus, because sharply defined sample plugs are essential for high-resolution separations and for maintaining analytical accuracy. Control of EOF is then framed as an integrated design challenge that involves tuning surface chemistry, engineering zeta potential, implementing nanoscale patterning, and navigating non-Newtonian flow behavior. Next, electrokinetic instabilities and electrically driven micromixing are examined through the lens of vortex-mediated perturbations that break diffusion limits in low-Reynolds-number flows. Finally, electrokinetic enrichment strategies—ranging from ion concentration polarization focusing to stacking-based preconcentration—demonstrate how trace analytes can be selectively accumulated to achieve detection sensitivity. Ultimately, electrokinetics is converging towards sophisticated integrated platforms and hybrid powering schemes, promising to expand microfluidic capabilities into previously inaccessible domains for analytical chemistry and diagnostics. Full article

The stimulated assembly/disassembly of particles is a technique allowing for precise spatial and temporal control over the resulting structures to be realized. The application of a photosensitive liquid crystal (LC) allows the use of a photo-initiated order–disorder transition for the ordering and redistribution of dispersed nanoparticles. The semiconductor quantum dots (QDs) among them are useful for the imaging of such redistribution through simple luminescent microscopy with excitation by laser radiation at a wavelength of 532 nm. Doping the LC matrix with azo-chromophore molecules allowed us to localize the light-driven phase transition of the LC from the organized to the isotropic phase inside the spot, illuminated by ultraviolet (UV) light through a slit. The phase transition leads to a redistribution of the QDs within the matrix, followed by QD-rich region formation. After the termination of UV illumination, the QDs were found to form droplets in the region where UV illumination resulted in a homogeneous distribution of the QDs. The translation of the sample through the UV-illuminated spot resulted in QD accumulation inside the isotropic phase at the borders of the isotropic phase. The results obtained provide a good agreement with the model calculations of nanoparticle diffusion at the LC phase–isotropic liquid interface. Full article

In the context of global energy demands, the efficient demulsification of highly stable heavy crude oil emulsions remains a critical challenge. This study systematically investigated the demulsification mechanisms of two demulsifiers (P1# and P2#) through multi-dimensional characterisation and performance evaluation. The results indicated that asphaltenes and resins can strengthen the oil–water interfacial film and stabilise the emulsion due to their unique structural properties. FTIR and ¹HNMR analyses showed that both demulsifiers contained polar groups and alkyl chains; however, P1# exhibited higher viscosity and lower surface tension, which favored its rapid adsorption at the interface. Demulsification tests at 60 °C demonstrated that P1# achieved superior efficiency (92.44% demulsification efficiency (DE) in 120 min versus 82.31% for P2#), attributable to its enhanced ability to displace asphaltene/resin at the oil-water interface. Turbiscan stability analysis and microscopic observations confirmed that P1#-treated emulsions underwent faster droplet coalescence and significant interfacial film disruption. Mechanistic studies indicated that the demulsifiers competitively adsorb at the interface, thereby weakening film cohesion through steric hindrance and charge redistribution. XRD and FTIR analyses suggested that interactions between the demulsifier and the asphaltene/resin increased interlayer spacing and reduced crystallinity. Zeta potential and interfacial tension measurements further highlighted P1#’s ability to neutralize negative charges (from −14.52 mV to +8.3 mV) and reduce the IFT (from 28.5 mN/m to 12.1 mN/m), thereby promoting droplet aggregation. This study helps elucidate the mechanism of emulsion phase transition induced by demulsifiers and provides theoretical support for improving the demulsification efficiency of crude oil emulsions. Full article

The structure–property relationship of chitin nanofibrils (NCh) with tailored lengths (L-, M-, S-NCh) and their efficacy in stabilizing Pickering emulsions were systematically investigated. The nanofibrils, produced via high-pressure homogenization and ultrasonication (20 or 60 min), were characterized by transmission electron microscopy (TEM). Emulsion stability was predominantly governed by nanofibril length and concentration, with S-NCh (shortest) exhibiting superior performance, as evidenced by its minimal creaming index, smallest droplet size (1.18 μm at 0.5%), and homogeneous microstructure observed by confocal laser scanning microscopy (CLSM). A critical stabilizer concentration of 0.05% was identified, below which instability occurred due to insufficient interfacial coverage. Rheological analysis confirmed shear-thinning behavior and solid-like viscoelasticity at high frequencies. CLSM microstructural observations directly confirmed nanofibril adsorption at the interface and the formation of a continuous network between droplets, elucidating the stabilization mechanism. These findings demonstrate that shorter chitin nanofibrils provide a marked improvement in emulsion stability, offering a superior biomass-derived alternative for the design of stabilizers in food and pharmaceutical applications. Full article

Whey protein is valued for its health and emulsifying benefits, yet its intrinsic instability limits its effectiveness as an emulsifier under food processing conditions. To address the need for physically stable emulsions, this study developed O/W Pickering emulsions stabilised by nanogel WPI (GWEs) and investigated their stability under common food processing conditions, including thermal treatment, pH adjustment, and cold storage. For comparison, emulsions stabilised by non-heated (NWEs) and heat-treated WPI (HWEs) were also prepared. The results showed that while the oil droplet size of GWEs (12.2 ± 1.16 µm) was comparable to NWEs (13.6 ± 0.26 µm), HWEs exhibited significantly larger droplets (18.0 ± 0.16 µm). GWEs demonstrated the highest protein adsorption at the oil–water interface (68.7%). TEM further revealed that whey nanogels achieved nearly full monolayer coverage of oil droplets. By contrast, only partial protein coverage and exposed interfaces were observed in NWEs and HWEs. Additionally, GWEs exhibited superior stability under food processing conditions, with minimal changes in emulsion capacity, droplet size, viscosity, and flow behaviour when subjected to heat (up to 90 °C), acidification (pH down to 3), and storage for up to 3 days, confirming the potential of nanogel WPI as an advanced stabiliser in emulsion-based formulations. Full article

This review explores the pervasive role of water in generating, storing, and mediating electric charge across natural and artificial systems. Far from being a passive medium, water actively participates in electrostatic and electrochemical processes through its intrinsic ionization, interfacial polarization, and charge separation mechanisms. The Maxwell–Wagner–Sillars (MWS) effect is presented as a unifying framework explaining charge accumulation at air–water, water–ice, and water–solid interfaces, forming dynamic “electric mosaics” across Earth’s environments. The authors integrate diverse phenomena—triboelectricity, hygroelectricity, hydrovoltaic effects, elastoelectricity, and electric-field-driven phase transitions—showing that ambient water continually shapes the planet’s electrical landscape. Electrostatic shielding by humid air and hydrated materials is described, as well as the spontaneous electrification of sliding or dripping water droplets, revealing new pathways for clean energy generation. In addition, the review highlights how electric fields and interfacial charges alter condensation, freezing, and chemical reactivity, underpinning discoveries such as microdroplet chemistry, “on-water” reactions, and spontaneous redox processes producing hydrogen and hydrogen peroxide. Altogether, the paper frames water as a universal electrochemical medium whose interfacial electric imprint influences atmospheric, geological, and biological phenomena while offering novel routes for sustainable technologies based on ambient charge dynamics and water-mediated electrification. Full article

The wheel–rail friction coefficient is a critical factor influencing train traction and braking performance. Low-adhesion conditions not only limit the enhancement of railway transport capacity but are also the primary cause of surface damage such as scratches, delamination, and flat spots. This study employs femtosecond laser technology to fabricate wavy groove textures on U75V rail surfaces, systematically investigating the effects of the wavy angle and texture area ratio on friction enhancement under various medium conditions. Findings indicate that parameter-optimized textured surfaces not only significantly increase the coefficient of friction but also exhibit superior wear resistance, vibration damping, and noise reduction properties. The optimally designed wavy textured surface achieves significant friction enhancement under water conditions. Among the tested configurations, the surface with parameters θ = 150°@η = 30% demonstrated the most pronounced friction enhancement, achieving a coefficient of friction as high as 0.57—a 42.5% increase compared to the non-textured surface (NTS). This enhancement is attributed to the unique hydrophilic and anisotropic characteristics of the textured surface, where droplets tend to spread perpendicular to the sliding direction, thereby hindering the formation of a continuous lubricating film as a third body. Analysis of friction vibration signals reveals that textured surfaces exhibit lower vibration signal amplitudes and richer frequency components. Furthermore, comparison of Stribeck curves under different lubrication regimes for the θ = 150°@η = 30% specimen and NTS indicated an overall upward shift in the curve for the textured sample. The amplitude, energy, and wear extent of the textured surface consistently decreased across boundary lubrication, hydrodynamic lubrication, and mixed lubrication regimes. These findings provide crucial theoretical insights and technical guidance for addressing low-adhesion issues at the wheel–rail interface, offering significant potential to enhance wheel–rail adhesion characteristics in engineering applications. Full article

Droplet-based microfluidics offers a promising approach for enhancing heat transfer in microchannels, which is critical for the thermal management of microsystems. This study presents a two-dimensional numerical investigation of flow and heat transfer characteristics of liquid–liquid two-phase droplet flow in a rectangular flow-focusing microchannel. The phase-field method was employed to capture the interface dynamics between the dispersed (water) and continuous (oil) phases. The effects of total velocity and droplet size on pressure drop and heat transfer performance are systematically analyzed. The results indicate that the heat transfer of two-phase droplet flow was significantly enhanced compared to single-phase oil flow, with its maximum heat transfer coefficient being approximately three times that of single-phase oil flow. The average heat transfer coefficient increases with total velocity and exhibits a non-monotonic dependence on droplet size. These findings provide valuable insights into the design and optimization of rectangular flow-focusing droplet-based microfluidic cooling systems. Full article

In natural gas gathering and transportation projects, efficient gas-liquid separation equipment is crucial to ensuring the stable operation of subsequent processes. Conventional separation units often have problems such as low efficiency, high energy consumption and poor resistance to load fluctuations when dealing with foam-containing gas-liquid mixtures. For this purpose, numerical simulation and structural optimization of multi-stage foam separation units were carried out in this study. Based on FLUENT software fluid analysis software, a three-dimensional, multi-physics coupled model incorporating cyclonic defoaming components and axial-flow separation tubes was developed. The volume of fluid (VOF) multiphase flow model was used to capture the dynamic characteristics of the gas-liquid interface, and the population balance model was used to simulate the coalescence and fragmentation of the foam. The results show that in the non-working fluid stage, the optimal operating pressure is 5.0–5.5 MPa, and the droplet concentration should be maintained below 50 × 10⁻⁵. The system performance during the working fluid stage is significantly influenced by foam size. The efficiency of millimeter-sized foams is stable above 88% in the 5.0–6.0 MPa range, while the efficiency of micrometer-sized foams is optimal in the 5.3–5.7 MPa range. It is recommended to control the foam proportion below 35% and add a pre-defoaming unit to improve overall performance. Full article

Low-salinity water flooding is a commonly used method to enhance oil recovery. At the microscopic scale, changes in pore structure and the distribution of remaining oil are critical to the effectiveness of water flooding. However, current research on the relationship between pore structure and remaining oil distribution is relatively limited. Therefore, this study employed micro-CT technology to analyze changes in pore structure and the distribution characteristics of remaining oil in sandstone cores during the water flooding process. Micron CT technology provides non-destructive, high-resolution three-dimensional imaging, clearly revealing the dynamic changes in the oil-water interface and remaining oil. The experiments included water saturation, oil saturation, and multi-stage water displacement processes in sandstone cores with different permeability values. The results show that the oil saturation in the rock core decreases during water flooding, and the morphology of remaining oil changes with increasing water flooding volume: cluster-like remaining oil decreases rapidly, while porous and membrane-like remaining oil gradually transforms, and columnar and droplet-like remaining oil increases under specific conditions. The study results indicate that at 1 PV flooding volume, the crude oil recovery rate reaches 57.56%; at 5 PV, the recovery rate increases to 64.00%; and at 100 PV, the recovery rate reaches 75.53%. This indicates that water flooding significantly improves recovery rates by enhancing wettability and capillary forces. Meanwhile, pore connectivity decreases, and particle migration becomes prominent, especially for particles smaller than 20 μm. These changes have significant impacts on remaining oil distribution and recovery rates. This study provides microscopic evidence for optimizing reservoir development strategies and holds important implications for enhancing recovery rates in mature oilfields. Full article

Smoothed particle hydrodynamics (SPHs) is a Lagrangian meshless method with distinct strengths in managing unstable and complex interface behaviors. This study develops an integrated multiphase SPH framework by merging multiple algorithms and techniques to enhance stability and accuracy. The multiphase model is validated by several benchmark examples, including square droplet deformation, single bubble rising, and two bubbles rising. The selection of numerical parameters for multiphase simulations is also discussed. The validated model is then applied to simulate oil–water–gas bubbly flows. Interface behaviors, such as coalescence, fragmentation, deformation, etc., are reproduced, which helps to take into account multiphysics interactions in industrial processes. The rising processes of many oil droplets for oil–water separation are first simulated, showing the advantages and stability of the SPH model in dealing with complex interface behaviors. To fully explore the potential of the model, the model is further extended to the field of wax removal. The melting process of the wax layer due to heat conduction is simulated by coupling the thermodynamic model and the phase change model. Interesting behaviors such as wax layer cracking, droplet detachment, and thermally driven flow instabilities are captured, providing insights into wax deposition mitigation strategies. This study provides an effective numerical model for bubbly flows in petroleum engineering and lays a research foundation for extending the application of the SPH method in other engineering fields, such as multiphase reactor design and environmental fluid dynamics. Full article

Structural heterogeneity is useful for improving the plasticity of metallic glasses (MGs) by blocking the propagation of shear bands (SBs). The introduction of a heterogeneous structure often introduces residual stresses, which significantly influences the deformation behaviors of MGs; however, the quantitative impact of residual/initial stresses on shear banding remains unclear. In this work, through finite element models, we demonstrate that residual/initial stresses can promote the initiation of SBs at the interfaces between droplet or particle reinforcements and the matrix in Binodal decomposed metallic glass composites (BDMGCs). These reinforcements do not effectively block the SBs when the fraction of particle reinforcement is very low. We demonstrate that a heterogeneous distribution of initial tensile stresses reduces the strength of BDMGCs, particularly in those containing a homogenous matrix. This profound understanding of the synergistic effects arising from a heterogeneous microstructure and initial stresses could effectively promote the design and optimization of MGs and their composites. Full article

This study applies circular and sustainable principles to the formulation of biopolymer-based materials using naturally occurring additives. To improve the affinity between the host matrix and additives such as metal oxides, the work involves adding stearic acid-modified zinc oxide (f-ZnO) and sonicated titanium dioxide (s-TiO₂) to a polylactic acid and bio-derived polyamide 11 (PLA/PA11 = 70/30 w/w biopolymer blend via melt mixing. To evaluate the impact of the functionalization and sonication on metal oxides (i.e., f-ZnO and s-TiO₂) introduced into the PLA/PA11 blend, composites containing unmodified ZnO and TiO₂ prepared under the same processing conditions were compared with the modified ones. All of the composites were characterised in terms of their solid-state properties, morphology, melt behaviour, and photo-oxidation resistance. The addition of both f-ZnO and s-TiO₂ appears to exert a plasticising effect on the rheological behaviour, in contrast to unmodified ZnO and TiO₂. The presence of stearic acid tails on ZnO has been estimated at approximately 4%, whereas sonication reduces the diameter of TiO₂ particles by half. In the solid state, both unmodified and modified particles can reinforce the biopolymer matrix, enhancing the Young′s (elastic) modulus. Calorimetry analysis suggests that unmodified and modified metal oxide particles do not influence the glass transition of the PLA phase but affect the melt temperatures of both biopolymeric phases by reducing macromolecular mobility. Morphology analysis shows that the presence of both f-ZnO and s-TiO₂ particles does not reduce the size of the PA11 droplets. The f-ZnO particles, which have long stearic tails and are more compatible with the less-polar phase (PLA), are probably located at the interface between the two biopolymeric phases or in the PLA phase. Furthermore, s-TiO₂ particles, like TiO₂, do not reduce the dimensions of PA11 droplets, suggesting that there is no preferential location of the particles. Due to the presence of both f-ZnO and s-TiO₂, an increase in the hydrophobicity of the PLA/PA11 blend has been detected, suggesting enhanced water resistance. The photo-oxidation resistance of the PLA/PA11 blend is significantly reduced by the presence of unmodified metal oxides and even more so by the presence of modified metal oxides. This suggests that metal oxides could be considered photo-sensitive degradant agents for biopolymer blends. Full article

In this study, the complexes (FG-P) based on fish gelatin (FG) and pectin (P) were prepared by a simple physical blending within a range of pectin concentrations (0–2%, w/v). The structure, interface, and emulsification properties of the obtained FG-P were analyzed. The binding between FG and pectin was dominated by electrostatic interaction and hydrogen bonding. Introducing pectin substantially increased the viscosity of FG-P. The water contact angle of FG-P gradually decreased with increasing pectin concentration. The highly interfacial viscosity and hydrophilicity of FG-P hindered the interfacial adsorption at the oil/water phase, thereby increasing the interfacial tension and phase angle. This was further manifested as an increase in the viscous modulus and a decrease in both the total modulus and elastic modulus. Despite the inhibition of interfacial adsorption, the unabsorbed FG-P was uniformly dispersed in the continuous phase to form a compact network structure, accompanied with improved rheological properties. Correspondingly, the emulsion precipitation phenomenon was effectively inhibited, and the stability of FG-P stabilized emulsions was improved with decreased droplet size. Full article

Flexible pressure sensors are essential for wearable electronics, human–machine interfaces, and soft robotics. However, conventional Polydimethylsiloxane (PDMS)-based sensors often suffer from limited conductivity, poor filler dispersion, and low structural integration with textile substrates. In this work, we present a robotic drop-coating approach for fabricating graphite–copper nanoparticle (G-CuNP)/PDMS composite pressure sensors with textile-integrated electrodes. By precisely controlling droplet deposition, a three-layer sandwiched structure was realized that ensures uniformity and scalability while avoiding the drawbacks of conventional full-line coating. The effects of filler loading and graphite nanoparticle (GNP) and copper nanoparticle (CuNP) ratios were systematically investigated, and the optimized sensor was obtained at 40 wt% total fillers with a graphite content of 55 wt%. The fabricated device exhibited high sensitivity in the low-pressure region, stable performance in the medium- and high-pressure ranges, and an exponential saturation fitting with R² = 0.998. The average hysteresis was 7.42%, with excellent cyclic stability over 1000 loading cycles. Furthermore, a hand-shaped sensor matrix composed of five distributed sensing units successfully distinguished grasping behaviors of lightweight and heavyweight objects, demonstrating multipoint force mapping capability. This study highlights the advantages of robotic drop-coating for scalable fabrication and provides a promising pathway toward low-cost, reliable, and wearable soft pressure sensors. Full article