Emulsion Droplets Research Articles

The influence of microchannel structure on double emulsion droplets formation

Microfluidics for the preparation of double emulsion droplets for a wide range of applications in medicine, agronomy, and materials science. The requirements for droplet preparation vary in different fields, and these needs can be met by altering fluid parameters, microchannel geometries, and other means. Therefore, this paper explores the influence of microfluidic device geometry on double-emulsion droplet molding using a VOF approach. The influence of variations in the length between the inject tube of the inner phase and inlet of the collection tube, the outlet width, the angle between phases, and the outlet angle on the double-emulsion droplet formation distance as well as on the area and other parameters were emphasized. The results show that increasing the length between the inner phase injection tube and inlet of the collection tube helps to improve the stability of droplet formation; the change of the outlet width has less effect on droplet formation; and the change of the angle between the phases tends to lead to the shift of the droplet formation mode, which has a greater effect on droplet formation. This study can provide a reference for optimizing the microchannel structure.

Effects of oil-water interfacial properties on protein structuring and droplet deformation in high moisture meat analogues containing oil

Adding oil to high moisture meat analogues (HMMA) can increase juiciness, and can be achieved by incorporating emulsion droplets during extrusion. Since these droplets can coalesce when subjected to high shear, selecting appropriate emulsion stabilisers is important. For several commercial plant-protein emulsion stabilisers, it was investigated how oil-water interfacial mechanical properties affect droplet deformation and protein structuring in extrusion of HMMAs. Emulsions with 10 wt% or 15 wt% oil, stabilised by potato protein isolates (POPI-1 (Rich in patatin) and POPI-2 (rich in protease inhibitor)) and pea protein isolate PPI, were used to make extrudates with 5.7 wt% and 8.5 wt% oil, respectively. In 8.5 wt%-extrudates, POPI-2 had the most oil leakage from the cooling die, while PPI had the smallest amount despite having softer and more stretchable interfaces. Blade-cutting tests showed the highest maximum force for 8.5 wt%-extrudates with POPI-1, likely because POPI-1 formed the stiffest interfaces. Tensile stress testing showed the largest fracture strain in 8.5% wt%-extrudates with PPI, corresponding to its longer wedge length. Multiphoton excitation microscopy was used to visualise the extrudates protein structure and oil droplets. This showed that droplets near the surface of the extrudate were less deformed than droplets in the centre. There were only small differences between protein stabilisers regarding oil droplet deformation, indicating droplet deformation was dominated by deformation of the protein matrix. The O/W interfacial properties significantly affected oil leakage, cutting force, and tensile strength of extrudates. These results are important to consider when designing emulsions for HMMAs processed by extruders.

Influence of Emulsion Lipid Droplet Crystallinity on Postprandial Endotoxin Transporters and Atherogenic And Inflammatory Profiles in Healthy Men - A Randomized Double-Blind Crossover Acute Meal Study.

Consumption of high-fat meals is associated with increased endotoxemia, inflammation, and atherogenic profiles, with repeated postprandial responses suggested as contributors to chronically elevated risk factors. However, effects of lipid solid versus liquid state specifically have not been investigated. This exploratory randomized crossover study tests the impact of lipid crystallinity on plasma levels of endotoxin transporters (lipopolysaccharide [LPS] binding protein [LBP] and soluble cluster of differentiation 14 [sCD14]) and select proinflammatory and atherogenic markers (tumor necrosis factor-alpha [TNF-α], C-reactive protein [CRP], interleukin-1-beta [IL-1β], interferon-gamma [IFN-γ], interleukin-6 [IL-6], soluble intercellular adhesion molecule [sICAM], soluble vascular cell adhesion molecule [sVCAM], monocyte chemoattractant protein-1 [MCP-1/CCL2], plasminogen activator inhibitor-1 [PAI-1], and fibrinogen). Fasted healthy men (n = 14, 28 ± 5.5 years, 24.1 ± 2.6kgm-2) consumed two 50g palm stearin oil-in-water emulsions tempered to contain either liquid or crystalline lipid droplets at 37°C on separate occasions with blood sampling at 0, 2-, 4-, and 6-h post-meal. Timepoint data, area under the curve, and peak concentration values are compared. Overall, no treatment effects are seen (p > 0.05). There are significant effects of time, with values decreasing from baseline, for TNF-α, MCP-1/CCL2, PAI-1, and fibrinogen (p < 0.05). Responder analysis pointed to differential treatment effects associated with some participant baseline characteristics but, overall, palm-stearin emulsion droplet crystallinity does not acutely affect plasma endotoxin transporters nor select inflammatory and atherogenic markers.

Water-in-water emulsions stabilized by nano-chitin

A water-in-water (W/W) emulsion consists of microdroplets was formed by the spontaneous liquid–liquid separation by mixing polyacrylic acid and chitosan oligosaccharide in water, and these microdropletes were stabilized by nano-chitin, formed water-in-water Pickering emulsions. By taking the advantage of interfacial adsorption of nano-chitin, the W/W emulsion droplets composed of polyacrylic acid/chitosan oligosaccharide (COS/PAA) polyelectrolyte coacervate were successfully stabilized. Research results indicated that composite microspheres were formed by the nano-chitin stabilized COS/PAA emulsion, and the size of these composite microspheres was related to the concentration and morphology of the nano-chitin. As the concentration of nano-chitin increases, the size of the composite microspheres first increases and then decreases, gradually becoming more uniform; whereas a decrease in the length of nano-chitin will lead to an increase in the size of the composite microspheres. The formation of composite microspheres may be due to the electrostatic interactions between nano-chitin and the emulsion droplets. In addition, the composite microspheres exhibit the best release effect for berberine hydrochloride at a pH value of 3.

Fabrication of Spherical Colloidal Supraparticles via Membrane Emulsification.

Colloidal supraparticles are micrometer-scale assemblies of primary particles. These supraparticles have potential application in photonic materials, catalysis, gas adsorption, and drug delivery. Thus, the synthesis of colloidal supraparticles with a narrow size distribution and high yield has become essential. Here, we demonstrate membrane emulsification as a high-throughput approach for fabricating spherical supraparticles with a narrow size distribution and control over particle size and crystallinity. Spherical supraparticles with well-ordered surface structures are synthesized by generating emulsion droplets of an aqueous colloidal dispersion in fluorocarbon oil using a Shirasu porous glass membrane followed by the consolidation of particles through water removal within the emulsion. We systematically investigate process parameters, including the flow rate of the particle dispersion, the particle concentration, and the average pore diameter of the membrane, on the mean size and size distribution of the supraparticles, revealing key factors governing supraparticle properties and production throughput. A comparative evaluation with commonly employed methods highlights the advantage of membrane emulsification, which combines well-defined internal structure and controlled supraparticle sizes with comparably high yields on the order of tens of grams per day. Importantly, in contrast to widely used droplet-based microfluidics, membrane emulsification allows fabrication of supraparticles in nonfluorinated oil. Overall, membrane emulsification offers a simple yet versatile method for fabricating colloidal supraparticles with high quality and yield and may serve as a bridge between existing high-precision techniques, such as droplet-based microfluidics, and high-throughput processes with less control, such as spray-drying.

Synergistic effects of alkaline and heat treatments on structural and functional properties of mung bean protein isolate: improving physicochemical stability of plant‐based emulsions

SummaryPlant‐based meat alternatives often require fat replacers to mimic the texture of traditional products. This study aimed to develop plant‐based emulsion gels using mung bean protein isolate (MBPI) as a potential fat substitute. However, creating these gels via heat setting requires a high protein concentration, which demands modification of the MBPI structure to enhance emulsifying properties. This study investigated synergistic effects of alkaline treatment (0.3 or 3.5% Na2CO3) and heat treatments (40 or 70 °C) on the functional properties of MBPI at high protein levels, for potential application as a plant‐based emulsion. The combined treatments reduced the zeta potential of protein suspensions from −9 to −19 mV and altered the protein conformation to form smaller particles (from 426 to 166 μm) with increased β‐sheet content. These treatments improved dispersibility of 8% MBPI suspension (58 to 86%), emulsifying activity index (6.34–10.89 m2 g−1), and stability coefficient (43 to 96%). Notably, MBPI samples treated with 0.3% Na2CO3 at 40 and 70 °C exhibited excellent emulsifying properties, forming stable monolayers at the oil–water interface, likely due to the increased surface activity of MBPI. Increasing protein concentration to 11% facilitated heat‐set gel formation; however, addition of 3.5%‐Na2CO3 induced premature gelation, limiting its application in emulsions. At 0.3%‐Na2CO3, increasing the protein content from 8% to 11% and the oil content from 10% to 30% further reduced emulsion droplet size, especially for MBPI treated with 0.3% Na2CO3 at 70 °C (MB‐0.3%‐70 °C) from 5.10 to 2.61 μm, likely due to decreased coalescence. This treatment yielded superior MBPI‐stabilised emulsion gels with enhanced penetration, fluid retention, and stability by possibly reducing protein aggregation. These findings demonstrate the potential of MBPI modified by combined addition of 0.3% Na2CO3 and heat treatment, particularly MB‐0.3%‐70 °C, as a promising ingredient for producing plant‐based emulsions.

Rapid yet Controlled Synthesis of 2D Covalent Organic Framework Nanocapsules as High-Performance Photocatalytic Carriers.

Synthesis and assembly of two-dimensional (2D) polymeric materials present a tricky trade-off between the high reaction rate and precise morphology control. Here we report a nanoconfined synthesis of imine-based 2D covalent organic frameworks (COFs) at the interface of oil-in-water (O/W) emulsion droplets stabilized by cationic surfactants. Highly uniform nanocapsules (NCs) could be prepared without adding extra catalysts at room temperature in just 4.5 h at a yield of 86%. The NCs have tunable average diameters and shell thicknesses, depending on the monomer and surfactant types/concentrations. Their BET-specific surface areas are up to 139.0 m2/g, mainly contributedby narrowly-distributed mesopores at ~5.0 nm and micropores at 1.4 nm.The surfactant plays the role of a catalyst during the reaction and interestingly, it also regulates the formation of mesopores and their sizes. Both theoretical and experimental studies confirm that the reaction has been accelerated by two orders of magnitude at the microdroplet interface, compared to that without emulsification. The resulting NCs could be well dispersed in water, and they have been demonstrated to be highly efficient nanocatalystsin application of water-based hydrogen evolution.Such microdroplet interface-confined synthesis may facilitate the future development of 2D polymeric materials for more advanced applications.

Rapid yet Controlled Synthesis of 2D Covalent Organic Framework Nanocapsules as High‐Performance Photocatalytic Carriers

Synthesis and assembly of two‐dimensional (2D) polymeric materials present a tricky trade‐off between the high reaction rate and precise morphology control. Here we report a nanoconfined synthesis of imine‐based 2D covalent organic frameworks (COFs) at the interface of oil‐in‐water (O/W) emulsion droplets stabilized by cationic surfactants. Highly uniform nanocapsules (NCs) could be prepared without adding extra catalysts at room temperature in just 4.5 h at a yield of 86%. The NCs have tunable average diameters and shell thicknesses, depending on the monomer and surfactant types/concentrations. Their BET‐specific surface areas are up to 139.0 m2/g, mainly contributed by narrowly‐distributed mesopores at ~5.0 nm and micropores at 1.4 nm. The surfactant plays the role of a catalyst during the reaction and interestingly, it also regulates the formation of mesopores and their sizes. Both theoretical and experimental studies confirm that the reaction has been accelerated by two orders of magnitude at the microdroplet interface, compared to that without emulsification. The resulting NCs could be well dispersed in water, and they have been demonstrated to be highly efficient nanocatalysts in application of water‐based hydrogen evolution. Such microdroplet interface‐confined synthesis may facilitate the future development of 2D polymeric materials for more advanced applications.

Sphingomyelin-enriched milk phospholipids offer superior benefits in improving the physicochemical properties, microstructure, and surface characteristics of infant formula

Phospholipids from different sources have varying chemical compositions, but how they contribute to different properties of infant formula is unclear. In this study, four types of phospholipids, milk phospholipids (MPLs), soybean phospholipids (SBPLs), sunflower phospholipids (SFPLs), and egg yolk phospholipids (EYPLs), were added to infant formula to investigate their physicochemical properties, microstructure, and surface characteristics. MPLs uniquely offer high sphingomyelin and saturated fatty acid levels. The MPL-based emulsion had the smallest particle size (334.50 nm), lowest stability constant (0.30), and highest viscosity among all groups tested. Furthermore, the abundance of sphingomyelin in MPLs allowed for a denser interfacial film and the complete phospholipid-coated structure of lipid droplets in infant formula emulsion. This consequently improved the microstructure and fat encapsulation of the powder, leading to significantly lower surface fat content in the MPL group. Therefore, the proper selection of phospholipids is crucial for modulating the stability and surface characteristics of infant formula.

Bioinspired interlaced wetting surfaces for continuous on-demand emulsion separation

Maintaining high separation performance during continuous emulsion separation remains a challenge. Herein, based on biomimetic coupling ideas, hole array interlaced wetting surfaces (HAIWSs) and mastoid array interlaced wetting surfaces (MAIWSs) were prepared by laser processing, electroless silver deposition, thiol modification, and spraying for on-demand emulsion separation. When the separation is going on, randomly moving emulsion droplets are prone to being captured by holes or mastoids due to interlaced wettability. Under this unique interface behavior, the occurrence of filter cake and pore clogging is reduced, thus achieving both high efficiency (∼99.5 and ∼99.3 %). Meanwhile, the high flux can also be maintained (∼3212 and ∼3458 L m−2 h−1). Significantly better than surfaces without pores or mastoid structures. Further, the as-prepared surfaces also exhibit excellent recyclability. After 50 separation cycles, optimized HAIWS and MAIWS still maintained high efficiency (∼96.2 and ∼95.8 %) and high flux (∼3042 and ∼3164 L m−2 h−1), exceeding other surfaces without hole or mastoid structure. Notably, complex physical/chemical cleaning processes are avoided. Besides, even in harsh conditions, HAIWS and MAIWS still maintain excellent stability. The above strategy provides a novel mechanism for effective on-demand emulsion separation and is expected to encourage the creation of new-class separation devices for oily wastewater treatment in industry.

Self-Organization of Polymer-Tethered Gold Nanoparticles into Hybrid Polyhedral Clusters Confined in Soft Emulsion Droplets

Self-Organization of Polymer-Tethered Gold Nanoparticles into Hybrid Polyhedral Clusters Confined in Soft Emulsion Droplets

The application of optical tweezers in oil-in-water emulsions

Oil-in-water (O/W) emulsions are widely used in industrial production, food science, petrochemicals, and other fields. Quantitative measurement of the interaction between droplets is essential for the in-depth understanding of the stability mechanism of O/W emulsions. Optical tweezers are able to accurately and quantitatively measure the interaction forces between droplets in oil-in-water emulsion systems at the microscopic scale and offer numerous advantages. In this paper, the applications of optical tweezers in oil-in-water emulsion systems are reviewed. Optical tweezer can be used to control the droplet deformation and study the aggregation phenomenon of emulsion droplets. The most important application of optical tweezer for emulsion is to measure the interaction force between emulsion droplets. Some specific examples are given to illustrate the advantages and uniqueness of optical tweezers in measuring droplets interaction forces and the methods to improve the accuracy of interaction force measurement. We summarize the study progress of optical tweezers in measuring the interaction force between droplets in recent years and discuss the challenges and prospects of measuring the interaction force between droplets based on optical tweezers.

A novel route to 3D printable protein-based HIPEs developed with shiitake oil

Tuning protein-based Pickering high internal phase emulsions (HIPEs) into 3D printing inks is promising in the food fields. Currently, the correlation between the changes in oil phase composition and the regulation of protein-based HIPEs 3D printing performance is still unclear. In this study, spiking the shiitake oil (ranging from 0 to 60 %) into the soybean oil phase of HIPEs can enhance their rheological properties and induce the formation of 3D printable HIPEs. The rheological tests showed that the yield stress and viscosity of the HIPEs respectively increased from 81.8 ± 4.84 Pa to 309 ± 16.3 Pa and from 409 to 1.74 Pa.s to 1762–2.93 Pa.s with increasing the shiitake oil concentration (0 % to 60 %) in the oil phase. In this study, the spontaneous interaction between phenolic compounds in shiitake oil and interfacial casein promoted the aggregation of protein, which led to the formation of casein cross-linking network in emulsion droplets, thus realizing the self-supporting and printing fidelity required for 3D printing. These findings provide a new perspective for enhancing the 3D printing properties of protein-based HIPEs.

Evaporation of stable microemulsion droplets

Emulsion fuels have the potential to reduce both particulate matter and NOx emissions and can potentially improve the efficiency of combustion engines. However, their limited stability remains a critical barrier to practical use as an alternative fuel. In this study, we explore the evaporation behavior of thermodynamically stable water-in-oil microemulsions. The water-in-oil microemulsion droplets prepared from different types of oil were acoustically levitated and heated using a continuous laser at different irradiation intensities. We show that the evaporation characteristics of these microemulsions can be controlled by varying water-to-surfactant molar ratio (ω) and volume fraction of the dispersed phase (ϕ). The emulsion droplets undergo three distinct stages of evaporation, namely preheating, steady evaporation, and unsteady evaporation. During the steady evaporation phase, increasing ϕ reduces the evaporation rate for a fixed ω. It is observed that the evaporation of microemulsion is governed by the complex interplay between its constituents and their properties. We propose a parameter (η) denoting the volume fraction ratio between volatile and nonvolatile components, which indicates the cumulative influence of various factors affecting the evaporation process. The evaporation of microemulsions eventually leads to the formation of solid spherical shells, which may undergo buckling. The distinction in the morphology of these shells is explored in detail using scanning electron microscopy imaging.

Alleviation effect of lutein Pickering emulsion formed by casein-dextran conjugates through Maillard reaction against blue light retinal degeneration

With the increasing prevalence of electronic devices, awareness of the risks linked to blue light exposure has significantly heightened. Lutein, a powerful antioxidant, safeguards eye tissue by filtering blue light, while supplementation with docosahexaenoic acid (DHA) enhances retinal function. Adequate intake of these nutrients can help reduce the potential damage from prolonged blue light exposure. The protective effects of lutein and algal oil stabilized with Pickering emulsion were investigated using casein-dextran (CD) conjugates via Maillard reaction. Microstructural analysis revealed a three-dimensional network structure surrounding oil droplets formed by CD conjugates. With the increase of the oil phase ratio from 55 % to 80 %, the average size of Pickering emulsion droplets decreased. Pickering emulsion demonstrated higher viscoelasticity, excellent recovery, thixotropy, and good thermal stability as the oil phase ratio increased. The retention of lutein in CD-75 % Pickering emulsions showed significant improvement under various conditions. Simulated gastrointestinal digestion demonstrated that CD-75 % Pickering emulsions effectively enhanced the lutein bioaccessibility from 19.97 % to 48.99 %. In vivo experiments showed that lutein-loaded Pickering emulsion could effectively relieve blue light-induced retinal degeneration in mice. These findings suggested that Pickering emulsion can serve as a delivery system to protect lutein, offering a nutritional intervention to mitigate blue light-induced retinal degeneration.

Binary colloidal clusters with quantum dots for nanoscopic device applications

Colloidal clusters have garnered significant interest for their ability to elucidate nanoscopic phenomena in atomic arrangements and to enable the fabrication of complex nanostructures for advanced photonic and electronic applications. This study introduces a novel approach using binary colloidal clusters composed of semiconducting quantum dots and conductive gold-coated latex microspheres, fabricated via evaporation-driven self-assembly within emulsion droplets. This configuration not only demonstrates the binary colloidal clusters' capability for self-organization but also highlights the distinct regions formed by the smaller quantum dots, crucial for the electrical functionality of these nanoscopic devices. We have observed diode-like rectification behavior in these binary colloidal clusters, demonstrating their potential as active nanoscopic devices. Our findings present groundbreaking methodologies for integrating semiconductive and conductive materials in a colloidal form, offering a scalable and versatile platform for the development of next-generation devices in photonics and nanoelectronics.

Formation of double emulsion droplets in flow-focusing microchips: a numerical parametric study

Formation of double emulsion droplets in flow-focusing microchips: a numerical parametric study

Analysis of the motion and deformation of water-in-oil emulsion droplets under the action of an electric field

Molecular dynamics simulations are used to study the aggregation dynamics of water-in-oil emulsion droplets under an electric field, and to analyze the effects of electric field strength, type, droplet position, and ionic concentration on their kinematic properties. The best droplet aggregation is observed at E=0.03V/Å for DC field condition, and E=0.045V/Å - 80ps for rectangular AC field condition. The rectangular alternating current (AC) field is able to merge the droplets farther away from the center of mass, but the two fields are not able to merge when the angle between the center of mass of the droplets and the electric field force is ≥35.54°. For different ion concentrations, t40N < t20N < t60N < t0N in the DC field and t20N < t40N < t0N < t60N in the rectangular AC field, and for the same ion concentration, the rectangular AC field takes longer time to merge.

Effect of Acoustically Responsive Droplet-based Low-intensity Histotripsy on Canine Prostate

ObjectiveLow-intensity histotripsy (LIH) is a novel and safe technique for tissue ablation. This study aimed to explore the effects of LIH on canine prostate tissue and identify the degree of acute injury to the gland. MethodsWe constructed and evaluated two types of acoustically responsive droplet (ARD) emulsions using either perfluoropentane (PFP) with a lipid shell or perfluoromethyl-cyclopentane (PFMCP) with lauromacrogol (L) injection. Twenty beagles were assigned to four experimental groups: ultrasound (US) + PFP (n = 6), US + PFMCP-L (n = 6), PFMCP-L (n = 5) and PFP (n = 3). The ARDs were injected transcutaneously and transabdominally into normal canine prostates under US-guided imaging. Subsequently, focused therapeutic US was employed to induce acoustic droplet vaporization and bubble cloud cavitation. The mechanical damage to canine prostate tissue was evaluated using gross and histological examination. ResultsGross specimens showed that the injured area was dark brown. Hematoxylin and eosin-stained tissue sections of the damage zone showed significant cavity formation and interstitial edema. The total tissue damage scores in the US + PFP group were compared to those of the other three experimental groups. No statistically significant differences were observed in the extent of tissue damage and total scores among the US + PFMCP-L, PFMCP-L and PFP groups. ConclusionWe achieved significant mechanical tissue damage in the canine prostate using PFP ARD-based LIH that proved to be superior to that using PFMCP ARDs with LIH.

Fabrication and characterisation of whey–pea protein‐based emulsion gels induced by transglutaminase cross‐linking

Food industry has partially replaced animal proteins with plant‐derived alternatives, and effects of combining these two types on properties of food systems need to be elucidated. This study fabricated and characterised emulsion gels of mixed whey and pea protein, varying protein mass ratios from 100:0 to 0:100 and oil volumes from 30% to 45%, induced by transglutaminase cross‐linking. An increase in pea protein led to larger particle size and reduced surface charge in the solutions. Emulsion droplet size ranged from 0.60 to 15.17 μm, increasing with higher levels of pea protein and oil. Mixed protein gels exhibited significantly greater hardness compared to gels with individual proteins. Water‐holding capacity of pure whey protein emulsion gels exceeded 90%, while the value remained above 80% when pea protein was less than 50%. Partially replacing whey protein with pea protein may have potential applications in food products such as salad dressings and cheese.