Immiscible Interface Research Articles

Solvent mixing and ion partitioning effects in spontaneous charging and electrokinetic flow of immiscible liquid-liquid interface

Solvent mixing and ion partitioning effects in spontaneous charging and electrokinetic flow of immiscible liquid-liquid interface

Aqueous-Aqueous Triboelectric Nanogenerators Empowered Multifunctional Wound Healing System with Intensified Current Output for Accelerating Infected Wound Repair.

Triboelectric nanogenerators (TENGs) have emerged as promising devices for generating self-powered therapeutic electrical stimulation over multiple aspects of wound healing. However, the challenge of achieving full 100% contact in conventional TENGs presents a substantial hurdle in the quest for higher current output, which is crucial for further improving healing efficacy. Here, a novel multifunctional wound healing system is presented by integrating the aqueous-aqueous triboelectric nanogenerators (A-A TENGs) with a functionalized conductive hydrogel, aimed at advancing infected wound therapy. The A-A TENGs are founded on a principle of 100% contact interface and efficient post-contact separation of the immiscible interface within the aqueous two-phase system (ATPS), enhancing charge transfer and subsequently increasing current performance. Leveraging this intensified current output, this system demonstrates efficient therapeutic efficacies over infected wounds both in vitro and in vivo, including stimulating fibroblast migration and proliferation, boosting angiogenesis, enhancing collagen deposition, eradicating bacteria, and reducing inflammatory cells. Moreover, the conductive hydrogel ensures the uniformity and integrity of the electric field covering the wound site, and exhibits multiple synergistic therapeutic effects. With the capability to realize accelerated wound healing, the developed "A-A TENGs empowered multifunctional wound healing system" presenting an excellent prospect in clinical wound therapy.

Magnetic Nanoparticle-Based Microfluidic Platform for Automated Enrichment of High-Purity Extracellular Vesicles.

Extracellular vesicles (EVs) are available in various biological fluids and have highly heterogeneous sizes, origins, contents, and functions. Rapid enrichment of high-purity EVs remains crucial for enhancing research on EVs in tumors. In this work, we present a magnetic nanoparticle-based microfluidic platform (ExoCPR) for on-chip isolation, purification, and mild recovery of EVs from cell culture supernatant and plasma within 29 min. The ExoCPR chip integrates bubble-driven micromixers and immiscible filtration assisted by surface tension (IFAST) technology. The bubble-driven micromixer enhances the mixing between immunomagnetic beads and EVs, eliminating the need for manual pipetting or off-chip oscillatory incubation. The high-purity EVs were obtained after passing through the immiscible phase interface where hydrophilic or hydrophobic impurities nonspecifically bound to SIMI were removed. The ExoCPR chip had a capture efficiency of 75.8% and a release efficiency of 62.7% for model EVs. We also demonstrated the powerful performance of the ExoCPR in isolating EVs from biological samples (>90% purity). This chip was further employed in clinical plasma samples and showed that the number of GPC3-positive EVs isolated from hepatocellular carcinoma patients was significantly higher than that of healthy individuals. This ExoCPR chip may provide a promising tool for EV-based liquid biopsy and other fundamental research.

Traction–separation law for bridged cracks at immiscible polymers interface

A traction–separation law for bonds at cracks bridged zones at immiscible polymers interface is developed. It is assumed that bonds at the crack bridged zone between different polymers are formed by bundles of the polymer molecules–promoter of adhesion. It is taken into account that molecules of the polymer-promoter can form one-stitch and many-stitch bonds between polymers. Nonlinear deformation curves of bonds at the crack bridged zone were obtained on this basis. The model of different materials joint with bridged interface crack is used to simulate immiscible polymers adhesive bonding. The system of singular integral-differential equations is applied for evaluation of bonds traction for the polymers interface bridged crack. The analysis of the bond traction–separation law parameters influence on the numerical iterative solution convergence of the integral-differential equations system has been performed. Evaluations of the polymer joint fracture toughness were performed using the non-local two-parameter criterion for quasi-static growth of bridged cracks.

Lattice Boltzmann method for particulate multiphase flow system

This study proposes a numerical model for particulate three-phase flow in microchannels based on multiphase lattice Boltzmann method (LBM). The model combines the color-gradient method to track the immiscible fluid-fluid interface and the two-fluid model (TFM) to describe particle-particle and particle-fluid interactions, which can efficiently simulate transport and displacement processes involving large amounts of particles. A mixture-rheology TFM algorithm is proposed by introducing a mixture phase with rheology properties obtained from experiments instead of the conventional TFM particle phase with artificial viscosity models. Multi-relaxation-time (MRT) collision operator and GPU computing are adopted to enhance the numerical stability and efficiency. Various theoretical benchmarks for particle transport and two-phase flow are performed respectively to verify the accuracy of the proposed model. Exceptional consistency between results from particulate three-phase flow simulation and microfluidic experiments further confirms the reliability of our model, especially in capturing the inertial lagging and accumulation phenomena under multiphase and porous flow conditions. The proposed numerical framework will benefit our understanding of multiphase displacement with microgels in microchannels with complex geometries.

Theoretical analysis of the three-stage phase transition process of alkane droplet under supercritical conditions

With the development of heavy-duty diesel engines, the in-cylinder ambient conditions of the diesel engine are well above critical points of the main components of the diesel fuel. Therefore, significant changes arise in the phase transition process of the liquid fuels. However, the entire phase transition process of the liquid fuels in such supercritical environments is not well understood compared with that under subcritical conditions. In this work, A high-pressure transient droplet evaporation model was presented for the theoretical analysis of phase transition processes of the heptane/dodecane/hexadecane-nitrogen binary system under supercritical conditions. Analysis of the thermodynamic pseudo-trajectories reveals that the alkane droplets will undergo a three-stage phase transition process when the ambient condition is much higher than the critical point of alkanes, including classical two-phase mode, transitional two-phase mode, and supercritical single-phase mode. The evaporation dominates the phase transition process in the classical two-phase mode, and the transition from classical two-phase modes to transitional two-phase modes occurs when gas-liquid interfaces deviate from the global thermal equilibrium. In transitional two-phase modes, a gas-liquid interface still exists and separates the liquid phase and vapor phase, but with a questionable adoption of vapor-liquid equilibrium. The transition from the transitional two-phase mode to the supercritical single-phase mode occurs when the thermodynamic state of the binary mixture in the interface reaches the critical mixing state. We distinguished the phase states for the whole phase transition process according to the thermodynamic analysis of binary systems. Analogous to the immiscible interface in classical two-phase mode, a miscible boundary layer containing supercritical fluids exits between the liquid core and gas in the initial period of the supercritical single-phase mode. The pseudo-boiling phenomenon occurs in this boundary layer.

Flexible Electrohydrodynamic Fluid-Driven Valveless Water Pump via Immiscible Interface.

The conventional electrohydrodynamic (EHD) pump is limited to pumping functional and dielectric liquids, which restricts its applications in fields like microfluidics, food safety, and materials production. In this study, we present a flexible water pump driven by EHD fluid, achieved by integrating valveless elements into the fluidic channel. Our approach leverages the water-EHD interface to propel the immiscible aqueous liquid and reciprocate this process using the nozzle-diffuser system. All components of the water pump are digitally fabricated and assembled. The valveless parts are created using a laser cutting machine. Additionally, we develop a model for the EHD pump and nozzle-diffuser system to predict the generated flow rate, considering factors such as the asymmetrical performance of the EHD pump, pulse frequency, applied voltage, and structural parameters. Finally, we experimentally characterize the flow rates of both the EHD pump and water pump and apply the newly developed device to air bubble manipulation and droplet generation. This research broadens the range of specialized liquids pumped by EHD pumps to include other aqueous liquids or mixtures.

Interaction of inline bubbles with immiscible liquids interface

The present work investigates computationally the passage of single and two inline bubbles through liquid-liquid interface. Both the liquids are considered as Newtonian and the volume of fluid approach is used to track the interfaces between the three fluids. The effect of bubble diameter (D⁎), bubble gap (bg⁎) on rupture, retention and coalescence time has been studied. Jet formation and jet breakage is also investigated which depicts that the jet height is more for two inline bubbles in comparison to single bubble for same D⁎. The coalescence stage with different bubble gap (bg⁎) shows that bubbles after coalescence travel faster than that of single bubble rising through the interface. Inline bubbles with higher bg⁎ exhibit all surface phenomena (rupture, entrainment, jet formation) prior to coalescence. The velocity of the rear bubble is seen to be more than the front bubble for all bubble gaps.

Coalescence of immiscible sessile droplets on a partial wetting surface

Droplet coalescence is a common phenomenon and plays an important role in multidisciplinary applications. Previous studies mainly consider the coalescence of miscible liquids, even though the coalescence of immiscible droplets on a solid surface is a common process. In this study, we explore the coalescence of two immiscible droplets on a partial wetting surface experimentally and theoretically. We find that the coalescence process can be divided into three stages based on the time scales and force interactions involved, namely (I) the growth of a liquid bridge, (II) the oscillation of the coalescing sessile droplet and (III) the formation of a partially engulfed compound sessile droplet and the subsequent retraction. In stage I, the immiscible interface is found not to affect the scaling of the temporal evolution of the liquid bridge, which follows the same 2/3 power law as that of miscible droplets. In stage II, by developing a new capillary time scale considering both surface and interfacial tensions, we show that the interfacial tension between the two immiscible liquids functions as a non-negligible resistance to the oscillation which decreases the oscillation periods. In stage III, a modified Ohnesorge number is developed to characterize the visco-capillary and inertia-capillary time scales involved during the displacement of water by oil; a new model based on energy balance is proposed to analyse the maximum retraction velocity, highlighting that the viscous resistance is concentrated in a region close to the contact line.

Liquid Interfacial Coassembly of Plasmonic Arrays and Trace Hydrophobic Nanoplastics in Edible Oils for Robust Identification and Classification by Surface-Enhanced Raman Spectroscopy.

The ubiquity of micro-/nanoplastics poses a visible threat to the environment, aquatic organisms, and human beings and has become a global concern. Here, we proposed a liquid interface-based strategy using surface-enhanced Raman spectroscopy to coassemble nanoplastics and gold nanoparticles into a dense and homogeneous plasmonic array, thereby enabling the rapid and sensitive detection of trace nanoplastics. In addition, due to the uniqueness of the oil-water immiscible two-phase interface, we achieved ideal results for the detection of nanoplastics in a complex matrix (e.g., aqueous environment and edible oil) with a detection limit of μg/mL. With the aid of the principal component analysis algorithm, the differentiation and identification of multiple nanoplastic components (e.g., polystyrene, polyethylene, and polyethylene terephthalate) in aqueous environments and common hazards (e.g., Bap and Phe) in edible oil were achieved. Therefore, our self-assembled plasmonic arrays are expected to be used for monitoring environmental pollution and food safety.

Interaction mechanism between immiscible Fe-Mg element diffusion and crystal defect annihilation in the steel/Mg composite interface region

Crystal defect-induced elemental diffusion between immiscible metals is the key to achieve metallurgical bonding. However, the interaction between immiscible element diffusion and crystal defect annihilation is unclear. In this paper, in-situ heat treatment experiments were conducted at the steel/Mg composite interface by ambient atmosphere spherical aberration corrected transmission electron microscope. The immiscible element diffusion phenomenon and crystal defect annihilation phenomenon in the composite interface region were studied, and the interaction mechanism was revealed. The results show that during the heat treatment, the diffusion of Mg element to the steel side is obvious, while the diffusion of Fe element to the Mg side is not obvious, which is called “one-way selective diffusion effect”. The annihilation rate of steel crystal defects is much smaller than that of Mg. The stable crystal defects of steel in the interface region can provide a channel for Mg elements diffusion, while the faster annihilation rate of Mg crystal defects causes Fe elements to hardly diffuse into Mg. The Mg elements that have diffused into the steel side have a pinning effect on dislocations and grain boundary movement, which in turn increases the thermal stability of the steel crystal defects. This study provides theoretical guidance for promoting the element diffusion at the immiscible metals composite interface.

Ionosome single entity electrochemical detection at a micro water/alkylphosphonium ionic liquid interface

Ionic liquids (ILs) are composed of molecularly large organic ions that exist as supramolecular ion aggregates or contact ion pairs which contributes to their catalytic nature and control of metal nanoparticle growth. However, additions of small organic molecules may disrupt these aggregates. Herein, single entity electrochemistry (SEE) has been used to probe the formation of solvent microchannels that form in between IL and ion aggregates through the electrogeneration of ionosomes, i.e., water/ion-in-IL nanoclusters, at a micro water/IL (w|IL) immiscible interface. A concomitant increase in ionosome size was observed with increasing molecular solvent additions; however, diffusion NMR studies indicate that IL-ion aggregates do not shrink in size until a critical solvent level is achieved at ∼ 25% v/v solvent/IL indicating a ‘solvent tolerance’ limit. Thus, diffusion NMR and SEE paint two complementary pictures of the IL supramolecular system under solvent addition.

A streaming-potential-based microfluidic measurement of surface charge at immiscible liquid-liquid interface

Surface charging at immiscible liquid-liquid interface is essential to the emulsion stability, surfactant adsorption, and various engineering applications such as drug delivery and mineral flotation. However, droplet electrophoresis, as a widely-used electrokinetic method to measure the surface charge density, has various limitations in physical modeling and sample preparation. In this work, an alternative experimental method based on streaming potential setup is proposed. A Y-Y shaped microchannel was used to make a flat and stable liquid-liquid interface. The inner wall was coated with polymer to suppress the interference of the solid-liquid interfacial electrokinetics in the liquid-liquid one. The experimental setup was first verified by revisiting the aqueous solution-silicon surface charging, after which the surfactant-free decane-KCl solution interface charging was investigated. The negative surface charge at the decane-KCl solution interface is confirmed and found to increase when increasing the pH. This result is compatible with the probable charging mechanism that the acquired negative surface charge results from hydroxyl ion adsorption onto the interface. The proposed method enables the simplicity and flexibility for further side-by-side studies on the liquid-liquid interface charging mechanism and will inspire the quantitative macroscopic interfacial modeling for numerous scenarios, such as the droplet electrophoresis and interfacial electro-hydrodynamics.

Chlorine resistant polyamide desalination membrane prepared via organic-organic interfacial polymerization

Desalination of seawater, brackish water and urban sewage is an important way to solve the global water shortage. Polyamide (PA) membranes, including reverse osmosis (RO) membrane and nanofiltration (NF) membrane, are the primary technology for seawater desalination and clean water production. However, traditional thin-film composite PA (TFC-PA) membranes prepared from interfacial polymerization (IP) of amine monomers (either piperazine or m-phenylenediamine) in water and acyl chloride monomers in organic solvent are incapable of tolerating strong acid and chlorine environment. Here, we develop a new IP process, which takes place at the immiscible interface between dimethylacetamide (DMAc) and hexane (referred to as organic/organic IP), to prepare both chlorine-resistant and acid-resistant TFC-PA membranes. Compared to conventional water/oil IP process, the organic/organic IP process can adapt more kinds of amine monomers rather than just PIP, such as tetra (4-aminophenyl) methane (TMAP), tris (4-aminophenyl) amine (TAPA), and 4,4′,4''-(1,3,5-triazine-2,4,6-triyl) triphenylamine (TTA), which we studied in this work, thereby extending the PA molecular structure and enabling the membranes with greatly improved chemical stability. Among them, the TAPM-based TFC-PA membrane exhibits a NaCl rejection of 95.9% and no obvious NaCl rejection deterioration after soaking in a high concentration of NaClO (1000 ppm, pH 7) for more than 30 h, indicating excellent chlorine resistance. The TTA-based TFC-PA membrane shows a Na2SO4 rejection of 97% and remains unchanged after being exposed to a wide pH scan of 2–12. The Organic/organic IP provides a new and easy-to-operate platform for designing chlorine and acid resistant TFC-PA membranes, which will greatly improve their environmental stability as the most advanced desalination membrane at present.

Rapid automatic nucleic acid purification system based on gas-liquid immiscible phase.

The continuous expansion of nucleic acid detection applications has resulted in constant developments in rapid, low-consumption, and highly automated nucleic acid extraction methods. Nucleic acid extraction using magnetic beads across an immiscible phase interface offers significant simplification and parallelization potential. The gas-liquid immiscible phase valve eliminates the requirement for complicated cassettes and is suitable for automation applications. By analyzing the process of magnetic beads crossing the gas-liquid interface, we utilized a low magnetic field strength to drive large magnetic bead packages to cross the gas-liquid interface, providing a solution of high magnetic bead recovery rate for solid-phase extraction with a low-surfactant system based on gas-liquid immiscible phase valve. The recovery rate of magnetic beads was further improved to 90%-95% and the carryover of the reagents was below 1%. Consequently, a chip and an automatic system were developed to verify the applicability of this method for nucleic acid extraction. The Hepatitis B virus serum standard was used for the extraction test. The extraction of four samples was performed within 7 minutes, with nucleic acid recovery maintained above 80% and good purity. Thus, through analysis and experiments, a fast, highly automated, and low-consumption nucleic acid recovery method was proposed in this study.

Interfacial polymerization at unconventional interfaces: an emerging strategy to tailor thin-film composite membranes.

Interfacial polymerization is a well-known process to synthesize separation layers for thin film composite membranes at an immiscible organic liquid-aqueous liquid interface. The organic-aqueous interface determines the diffusion dynamics of monomers and the chemical environment for polymerization, exerting a critical influence on the formation of polymer thin films. This review summarizes recent advances in tailoring interfacial polymerization using interfaces beyond the conventional alkane-water interface to achieve high-performance separation films with designed structures. Diverse liquid-liquid interfaces are introduced for synthesizing separation films by adding co-solvents into the organic phase and/or the aqueous phase, respectively, or by replacing one of the liquid phases with other solvents. Innovative liquid-gel and liquid-gas interfaces are then summarized for the synthesis of polymer thin films for separation. Novel strategies to form reaction interfaces, such as spray-coating, are also presented and discussed. In addition, we discuss the details of how a physically or chemically patterned substrate affects interfacial polymerization. Finally, the potential of unconventional interfaces in interfacial polymerization is forecast with both challenges and opportunities.

An immiscible phase-separation electrolyte and interface ion transfer electrochemistry enable zinc/lithium hybrid batteries with a 3.5 V-class operating voltage

Zinc/lithium hybrid batteries with a phase-separation electrolyte achieve high average operating voltages of over 3 V.

Bridge evolution during the coalescence of immiscible droplets.

Droplet coalescence is a common phenomenon and plays an important role in many applications. When two liquid droplets are brought into contact, a liquid bridge forms and expands quickly. Different from miscible droplets, an extra immiscible interface exists throughout the coalescence of immiscible droplets and is expected to affect the evolution of the liquid bridge, which has not been investigated. We hypothesized that the liquid bridge of immiscible droplets exhibits a different growth dynamics. We experimentally study the coalescence dynamics of immiscible droplets. The evolution of the liquid bridge is measured and compared with miscible droplets. We also propose a theoretical model to analyze the effects of immiscibility. We find that immiscibility plays different roles in the viscous-dominated and inertia-dominated regimes. In the initial viscous-dominated regime, the coalescence of immiscible droplets follows the linear evolution of the bridge radius as that of miscible droplets. However, in the later inertia-dominated regime, the coalescence of immiscible droplets is slower than that of miscible droplets due to the water-oil interface. By developing a theoretical model based on the force balance, we show that this slower motion is due to the immiscible interface and the extra interfacial tension. In addition, a modified Ohnesorge number is proposed to characterize the transition from the viscous-dominated regime to the inertia-dominated regime.

Extraction-free techniques for sensitive detection of a petroleum marker on a paper-based platform

Fuel adulteration and cross-contamination lead to low-quality fuel products and loss of taxes. It is essential to develop methods of marking, identifying and monitoring tax classification of petroleum products in the market. In this work, a method for sensitive and fast detection of gasoline marker using paper-based platform and a smartphone camera detection are developed. A common dye, phenolphthalein (PhP), is used as a colorless dye marker in commercial gasoline. The color was developed by the interaction of PhP with NaOH on filter paper strips and evaluated by CMYK color systems. The newly developed counter-flowing technique, in which a gasoline sample containing PhP and NaOH solution are allowed to travel on a filter paper strip from the opposite end, gives the naked eye detection of PhP as low as 1 ppm with the limit of detection for a smartphone camera of 0.31 ppm. The high sensitivity is attributed to the preconcentration derived from accumulation of PhP at the immiscible liquid interface. The counter-flowing method can thus be a new facile analytical technique for enhancing chemical detection sensitivity.

In Situ Produced Nanoparticles at the Oil-Water Interface for Conformance Control and Enhanced Oil Recovery.

Nanoparticle-assisted enhanced oil recovery (Nano-EOR) has attracted intensive interest in the laboratory as a promising oil recovery technology. However, the nanoparticles' stability and long-distance delivery of nanoparticles (NPs) in large-scale reservoirs are two main challenges. In this work, we developed a novel concept of in situ synthesizing NPs at the oil-water interface inside the reservoir for EOR instead of injecting presynthesized NPs from outside. The pore-scale flooding experiments show that EOR efficiencies for tertiary flooding were 6.3% without reaction (Case 3), 14.6% for slow reaction (Case 1), and 25.4% for relatively quick reaction (Case 4). Examination of the EOR mechanism shows that in situ produced SiO2 NPs in microchannels could alter the substrate wettability toward neutral wetting. Moreover, the produced NPs tended to assemble on the immiscible oil-water interface, forming a barrier toward interface deformation. As the reaction continued, excessive surface-modified NPs could also diffuse into aqueous brine and accumulate as a soft gel in the flowing path swept by brine. Collectively, these processes induced a "shut-off" effect and diverted displacing fluids to unswept areas, which consequently increased the sweep efficiency and improved the oil recovery efficiency. Auxiliary bulk-scale experiments also showed that the reaction-induced nanoparticle synthesis and assembly at an immiscible interface reduced the interfacial tension and generated an elastic oil-water interface.