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[Display omitted] Liquid-liquid phase separation at complex interfaces is a common phenomenon in biological systems and is also a fundamental basis to create synthetic materials in multicomponent mixtures. Understanding the liquid-liquid phase separation in well-defined macromolecular systems is anticipated to shed light on similar behaviors in cross-disciplinary areas. Here we study a series of immiscible polymers and reveal a generic phase diagram of liquid–liquid phase separation at double emulsion interfaces, which depicts the equilibrium structures by interfacial tension and polymer fraction. We further reveal that the interfacial tensions in various systems fall on a linear relationship with spreading coefficients. Based on this theoretical guideline, the liquid–liquid phase separation can be modulated by a low fraction of amphiphilic block copolymers, leading the double emulsion droplets configurable between compartments and anisotropic shapes. The solidified anisotropic microcapsules could provide unique orientation-sensitive optical properties and thermomechanical responses. The theoretical analysis and experimental protocol in this study yield a generalizable strategy to prepare multiphase double emulsions with controlled structures and desired properties. [ABSTRACT FROM AUTHOR]

[Display omitted] The unique role of the spatial distribution of crystallizable emulsifiers in regulating the structure and properties of double emulsions has been gradually recognized. Herein, we utilized crystallizable monoglycerides of different carbon chain length (GMS/GMP/GML) to "structuring" the intermediate oil phase of double emulsions during a two-stage emulsification process followed by a cooling treatment. A ternary eigenvector (I, M, E) based on the numerical processing of polarization images was invented to quantitatively characterize the distribution pattern of monoglycerides. Crystallization kinetics analysis and dissipative particle dynamic simulation were then employed to reveal the regulatory mechanism for the site-specific interface distribution behavior. Results suggested that the distribution pattern of monoglycerides could be pricesly tuned as the internal interface-, external interface- or oil-phase dominated one in double emulsions. The surface activity as well as crystallization rates of monoglycerides dominated the interfacial distribution kinetics, and the cooling gradient along the interface region further regulated their interfacial distribution potential. Specificly, shorter crystallization time (t 1/2) made GMP molecules rapidly solidified in oil phase, leading to the oil phase domninate crystallization (0, M, 0), whereas, slow crystallization rate rendered GML and GMS with sufficient time to diffuse to the interface, thus forming interfacial crystals ((I, 0, 0) and (0, 0, E)). The sensitivity of GML to cooling gradient along the interface region led to its preferential external interface distribution under cooling treatment. The presented study explored novel strategies that can be used in characterizing and manipulating the distribution pattern of crystallizable emulsifiers in multi-interface emulsion systems. [ABSTRACT FROM AUTHOR]

We report a simple and rapid route to produce double emulsion drops by utilizing phase separation of the confined fluid in micromolds and surface-tension-induced drop formation. Specifically, we use cross-shaped micromolds containing prepolymer solution that phase-separates into two compartments upon addition of wetting fluid with separation agent (SA). Subsequently, Laplace pressure-driven flow allows it to form double emulsion drops without use of any surfactants and complex formulations of fluids. The size of each compartment in the emulsion drops can be controlled by tuning composition of the prepolymer solution and separation agent, making the double emulsion drops with varying shell thicknesses. The phase separation creates two compartments with different polarity (i.e. water-soluble and water-insoluble), enabling encapsulation of both hydrophilic and/-or hydrophobic cargoes in desired compartments depending on their solubility. In addition, we produce poly(N -isopropylacrylamide) (pNIPAm) hydrogel microcapsules by solidifying middle phase in the double emulsion drops; thus, hydrophilic large cargo loaded priorly in the core can be encapsulated within hydrogel shells. Finally, by taking advantage of hydrophilic-hydrophobic phase transition behavior of pNIPAm, we achieve encapsulation of small cargo via post-loading approach; the encapsulated cargo can be released by tuning temperature. [ABSTRACT FROM AUTHOR]

In contrast to when polyglycerol polyricinoleate (PGPR) is used as lipophilic emulsifier, the used oil phase and phospholipid composition have a strong influence on the characteristics of water-in-oil (w/o) emulsions prepared using lecithin. These parameters are also expected to influence the characteristics of the corresponding water-in-oil-in-water (w/o/w) emulsions. Moreover, a hydrophilic emulsifier is typically added to the external water phase of w/o/w emulsions and is also expected to influence the characteristics of the w/o/w emulsions. Lecithin with a varying phospholipid composition was used to prepare w/o emulsions with medium chain triglyceride (MCT) oil as well as long chain triglyceride (LCT) oil. In case the w/o emulsion was stable, w/o/w emulsions were produced as well. Hereby, the w/o/w emulsions were prepared using different hydrophilic emulsifiers. Each of the lecithin samples could be used to produce a stable w/o emulsion in MCT-oil. In contrast, a stable w/o emulsion could only be produced in LCT-oil with phosphatidylcholine depleted lecithin. The storage stability of the w/o/w emulsions was also higher in case MCT-oil was used as compared to LCT-oil. Finally, a remarkable influence of the high-HLB emulsifier on the resulting enclosed water volume fraction in the w/o/w emulsions was observed. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of macromolecular assemblies in solution, such as Liquid-Liquid Phase Separation (LLPS), represents technologic and fundamental challenges in many fields. In cell biology, such dynamics are of great interest, because of their involvement in subcellular processes. In our study, we aimed to control the assembly of macromolecules in aqueous semi-permeable vesicles, that we named osmosomes, using microfluidics. We developed a microfluidic chip that allows for producting and trapping Giant Unilamellar Vesicles (GUVs) encapsulating macromolecules. This device also allows for modification of the composition of the inner phase and of the membranes of the trapped GUVs. The vesicles are produced from water-in-oil-in-water (w/o/w) double emulsions in less than 20 min after discarding the oil phase. They are highly monodisperse and their diameter can be modulated between 20 and 110 µm by tuning the flow rates of fluid phases. Their unilamellarity is proofed by two techniques: (1) fluorescence quenching experiments and (2) the insertion of the α-hemolysin membrane protein pore. We demonstrate that the internal pH of osmosomes can be tuned in less than 1 min by controlling solvent exchanges through the α-hemolysin pores. The detailed analysis of the exchange kinetics suggests that the microfluidic chip provides an efficient pore formation due to the physical trapping of vesicles and the constant flow rate. Finally, we show a proof of concept for macromolecular assembly within osmosomes by pH-triggered LLPS of wheat proteins within a few minutes. [ABSTRACT FROM AUTHOR]

This work focuses on fabrication of core-shell polyimide aerogel microparticles with and without a surfactant via oil-in-oil-in-oil (O/O/O) emulsion system aided by a simple microfluidic device. A double emulsion is formed through sequential, step-wise emulsification of co-flowing core and shell organic liquid streams in a simple microfluidic setup. The polyimide sol, introduced as the shell liquid, undergoes accelerated polymerization in a heated silicone oil bath to yield a porous polyimide shell around silicone oil core that eliminates the possibility of droplet coalescence or rupture. The core-shell gel microparticles are then isolated and supercritically dried to obtain core-shell aerogel microparticles. The diameter and shell thickness of hollow microparticles are studied as function of liquid flowrates in the microfluidic device and the viscosity of the shell liquid. [ABSTRACT FROM AUTHOR]

The use of colloidal particles (CPs) in the transport of drugs is developing rapidly thanks to its effectiveness and biosafety, especially in the treatment of various types of cancer. In this study Rose Bengal/PLGA CPs synthesized by double emulsion (W/O/W) and by electrostatic adsorption (layer-by-layer), were characterized and evaluated as potential breast cancer treatment. CPs were evaluated in terms of size, zeta potential, drug release kinetics and cell viability inhibition efficacy with the triple negative breast cancer cell line HCC70. The results showed that both types of CPs can be an excellent alternative to conventional cancer treatment by taking advantage of the enhanced permeation and retention (EPR) effect, manifested by solid tumors; however, the double emulsion CPs showed more suitable delivery times of up to 60% within two days, while layer-by-layer showed fast release of 50% in 90 min. Both types of CPs were capable to decrease cell viability, which encourage us to further testing in in vivo models to prove their efficacy and feasible use in the treatment of triple negative breast cancer. [ABSTRACT FROM AUTHOR]

The stability of vegetable oil-in-100 cS silicone oil-in-vegetable oil V/S/V emulsions to sedimentation and coalescence has been studied. The emulsions contained two types of silica particle of different surface silanol content, 70% and 20% SiOH, which prefer to stabilise 100 cS silicone oil-in-vegetable oil S/V and vegetable oil-in-100 cS silicone oil V/S emulsions respectively, in systems containing equal proportion of the oils. The emulsions were prepared in a two-step process and were characterised using the drop test and optical microscopy. The emulsions were completely stable to coalescence for over a month. However, they underwent sedimentation which decreases as the concentration of 70% SiOH silica particles stabilising the silicone oil globules increases. The gravity-induced sedimentation halted at a relatively high particle concentration (2 wt.%) and negligible amount of the vegetable oils was released even after a month. Their average droplet diameter also decreases as the concentration of 70% SiOH silica particles increases. Values of oil-oil-solid particle contact angles θ oo , measured on microscope glass slides composed of the particles, are in good agreement with the type of simple emulsions and hence double emulsions formed by the particles. [ABSTRACT FROM AUTHOR]

This paper reports synthesis of the first high internal phase emulsion (HIPE) system with double emulsion (DE) morphology (HIPE-DE). HIPE is a highly concentrated but highly stable emulsion system, which has a dispersed/internal phase fraction over 74 vol%. DE represents an emulsion system that hierarchically encapsulates two immiscible phases. The combination of HIPE and DE provides an efficient method for fabrication of complex structures. In this work, HIPE-DE having a water-in-oil-in-water (W/O/W) morphology has been prepared for the first time via a simple one-step emulsification method with poly(2-(diethylamino)ethyl methacrylate) (PDEA) microgel particles as Pickering stabilizer. An oil phase fraction up to 90 vol% was achieved by optimizing the microgel concentration in aqueous phase. The mechanism of the DE formation has been elucidated. It was found that while PDEA microgels stabilized the oil droplets in water, small amount protonated DEA monomers acted as surfactant and formed water-containing micelles inside the oil droplets. It was demonstrated that the W/O/W HIPE-DE could be precisely converted into porous polymer structures. With styrene as the oil phase in W/O/W HIPE-DE, porous polystyrene particles were obtained upon polymerization. With dissolved acrylamide as the aqueous phase and toluene as the continuous phase, porous polyacrylamide matrixes were prepared. Elevating temperature required for polymerization did not change the W/O/W HIPE-DE morphologies. This simple approach provides a versatile platform for synthesis of a variety of porous polymer systems. [ABSTRACT FROM AUTHOR]

Highlights: [•] A microfluidic method was developed to generate uniform zwitterionic hydrogel microparticles and shells. [•] Mesh size of the hydrogel network was characterized by the Peppas–Merrill equation and NMR cryoporometry. [•] Manipulation of the mesh property enabled fabrication of hydrogel microparticles with controlled permeability. [Copyright &y& Elsevier]

Highlights: [•] Differential scanning calorimetry allows characterization of multiple emulsions. [•] Drop breakup can be described by viscosity ratio of the emulsions. [•] Water release is correlated to double emulsion droplet sizes. [•] Coalescence between inner droplets influences release of water. [ABSTRACT FROM AUTHOR]

Abstract: A one-step double emulsification protocol using one surfactant was developed for oil-in-water-in-oil (O1/W/O2) double emulsions. Two n-alkane oils and three different surfactants were studied, with focus placed on a formulation containing mineral oil, glycerol monoleate (GMO) and deionized water. Phenomenologically, double emulsion formation and stability originate from the combined actions of phase inversion and interfacial charging of the oil/water interface during high shear homogenization. Based on the extent of double emulsion formation and stability, a critical emulsification zone dependent on the weight ratios of GMO to water was identified. Within this critical zone, enhanced O1/W/O2 emulsion formation occurred at higher pH and lower salt concentrations, demonstrating the key role of interfacial charging on double emulsification. Overall, this novel approach provides a novel platform for the development of double emulsions with simple compositions and processing requirements. [Copyright &y& Elsevier]

Abstract: Metal-ion retention properties of water-soluble amphiphilic polymers in presence of double emulsion were studied by diafiltration. Double emulsion systems, water-in-oil-in-water, with a pH gradient between external and internal aqueous phases were prepared. A poly(styrene-co-maleic anhydride) (PSAM) solution at pH 6.0 was added to the external aqueous phase of double emulsion and by application of pressure a divalent metal-ion stream was continuously added. Metal-ions used were Cu2+ and Cd2+ at the same pH of polymer solution. According to our results, metal-ion retention is mainly the result of polymer–metal interaction. Interaction between PSMA and reverse emulsion globules is strongly controlled by amount of metal-ions added in the external aqueous phase. In addition, as metal-ion concentration was increased, a negative effect on polymer retention capacity and promotion of flocculation phenomena were produced. [Copyright &y& Elsevier]

Abstract: We report the formation of giant vesicles and microcapsules having diameters of the order of 250μm obtained using the biocompatible and biodegradable amphiphilic block copolymer poly(ethylene glycol)-b-poly(γ-methyl ε-caprolactone). Using the solvent evaporation method with monodisperse water–oil–water double emulsion droplets, we found either preferentially giant vesicles or preferentially spherical microcapsules with thicker walls compared to the vesicle membrane. The morphology depends on the volume of the evaporating oil shell of the double emulsion droplets for a given concentration of the block copolymer. Accordingly, by using a microfluidic flow focusing device to form the double emulsion, it is possible to direct whether vesicles or microcapsules are preferentially formed, simply by adjusting the volume of the oil shell through the volumetric flow rates of the device. During the evaporation of the organic solvents from the oil shells, rough surface morphologies of the double emulsion droplets were observed as intermediate stages in their transformation to either vesicles or microcapsules. These intermediate stages are most likely related to a dewetting of the evaporating oil phase from the surface of the inner droplet, resulting in a spot-like dewetting pattern, or a phase separation of the oil phase into polymer-rich and polymer-poor domains. [ABSTRACT FROM AUTHOR]

Abstract: Water/oil (W1/O) emulsions containing fat crystals have been incorporated into an aqueous phase containing 1% na-caseinate as emulsifier to create stable water/oil/water (W1/O/W2) double emulsions. The W1/O primary emulsion was stabilised exclusively with monoglyceride and triglyceride crystal “shells”, and contained 30% W1 aqueous phase as well as KCl. The stability of the double emulsions was monitored over the course of 6weeks. It was found that, providing some salt or sugar were present in the W2 aqueous phase, emulsions retained their double structure – although coalescence between double emulsion globules occurred and creaming was observed. KCl encapsulated in the W1 phase of the primary emulsion was only slowly released to the W2 continuous aqueous phase: 20% within 6weeks. This release is due to the damage caused to the fat crystal shells during the secondary emulsification step used to create the double emulsion structure. [ABSTRACT FROM AUTHOR]

Abstract: The dielectric behavior of double emulsions with “core–shell droplet” morphology is investigated over a broad range of frequency. A new modified Pauly–Schwan model is proposed for the complex permittivity of double emulsions. The proposed model takes into consideration the morphology and packing limit of droplets. The dielectric behaviors of oil-in-water-in-oil (O/W/O) and water-in-oil-in-water (W/O/W) types of double emulsions, as predicted by the proposed model, are discussed. [Copyright &y& Elsevier]

Abstract: The dynamic viscoelastic behavior of multiple emulsions is investigated. A modified Palierne model is used to predict the storage and loss moduli of multiple emulsions. The multiple emulsions exhibit two relaxation domains due to relaxation of two different interfaces—internal and external. The internal interface is the interface between internal droplets and their suspending medium (primary emulsion continuous-phase). The external interface is the interface between multiple-emulsion droplets and their suspending medium (external continuous-phase). The factors affecting the dynamic viscoelastic behavior of multiple emulsions are discussed. [Copyright &y& Elsevier]

Abstract: New equations for the viscosity of concentrated double emulsions of core–shell droplets are developed using a differential scheme. The equations developed in the paper predict the relative viscosity () of double emulsions to be a function of five variables: (ratio of core drop radius to shell outer radius), (ratio of shell liquid viscosity to external continuous phase viscosity), (ratio of core liquid viscosity to shell liquid viscosity), (volume fraction of core–shell droplets in double emulsion), and (the maximum packing volume fraction of un-deformed core–shell droplets in double emulsion). Two sets of experimental data are obtained on the rheology of O/W/O (oil-in-water-in-oil) double emulsions. The data are compared with the predictions of the proposed equations. The proposed equations describe the experimental viscosity data of double emulsions reasonably well. [Copyright &y& Elsevier]

Abstract: Using a capillary video microscopy technique, the ion transport at liquid–liquid interfaces and through a surfactant-containing emulsion liquid membrane was visually studied by preparing a double emulsion globule within the confined space of a thin-walled, transparent, cylindrical microtube. NaCl and AgNO3 were selected as the model reactants and were prepared to form a NaCl/AgNO3 pair across the oil film. By observing and measuring the formed AgCl deposition, it was found that both Cl− and Ag+ could transport through a thick oil film and Ag+ was transported faster than Cl−. Interestingly, the ion transport was significantly retarded when the oil film became extremely thin (). The results suggested that the transport of ions mainly depends on the “reverse micelle transport” mechanism, in which reverse micelles with entrapped ions and water molecules can be formed in a thick oil film and their construction will get impeded if the oil film becomes extremely thin, leading to different ion transport rates in these two cases. The direction of ion transport depends on the direction of the osmotic pressure gradient across the oil film and the ion transport is independent of the oil film thickness in the investigated thick range. Ions with smaller Pauling radii are more easily entrapped into the formed reverse micelles and therefore will be transported faster through the oil film than bigger ions. Oil-soluble surfactants facilitate ion transport; however, too much surfactant in the oil film will slow down the ion migration. In addition, this study showed no support for the “molecular diffusion” mechanism of ion transport through oils. [Copyright &y& Elsevier]

Abstract: This study illustrates the entrapment of the dye molecule fluorescein sodium salt (FSS) by hydrogel nanoparticles, which are in turn confined inside a water-in-oil-in-water double-emulsion globule, and its subsequent release by the action of the competing agent hydrochloric acid (HCl). Thus, a “double carrier” concept is being introduced in which a nanoscale delivery vehicle is being transported by a microscale delivery vehicle in order to simultaneously take advantage of both systems. This may facilitate storage and handling while protecting the active substance and improving its action upon application. [Copyright &y& Elsevier]

Microchannel (MC) emulsification is a novel technique for preparing monodispersed emulsions. This study demonstrates preparing water-in-oil-in-water (W/O/W) emulsions using MC emulsification. The W/O/W emulsions were prepared by a two-step emulsification process employing MC emulsification as the second step. We investigated the behavior of internal water droplets penetrating the MCs. Using decane, ethyl oleate, and medium-chain triglyceride (MCT) as oil phases, we observed successful MC emulsification and prepared monodispersed oil droplets that contained small water droplets. MC emulsification was possible using triolein as the oil phase, but polydispersed oil droplets were formed from some of the channels. No leakage of the internal water phase was observed during the MC emulsification process. The internal water droplets penetrated the MC without disruption, even though the internal water droplets were larger than the resulting W/O/W emulsion droplets. The W/O/W emulsion entrapment yield was measured fluorometrically and found to be 91%. The mild action of droplet formation based on spontaneous transformation led to a high entrapment yield during MC emulsification. [Copyright &y& Elsevier]