Formation Of Multiple Emulsions Research Articles

Structuring gelatin methacryloyl - dextran hydrogels and microgels under shear.

Gelatin methacryloyl (GelMA) is a widely used semi-synthetic polymer for a variety of bioapplications. However, the development of versatile GelMA hydrogels requires tuning of their microstructure. Herein, we report the possibility of preparing hydrogels with various microstructures under shear from an aqueous two-phase system (ATPS) consisting of GelMA and dextran. The influence of an applied preshear on dextran/GelMA droplets and bicontinuous systems is investigated by rheology that allows the application of a constant shear and is immediately followed by in situ UV-curing of the GelMA-rich phase. The microstructure of the resulting hydrogels is examined by confocal laser scanning microscopy (CLSM). The results show that the GelMA string phase and GelMA hydrogels with aligned bands can be formed depending on the concentration of dextran and the applied preshear. The influence of the pH of the ATPS is investigated and demonstrates the formation of multiple emulsions upon decreasing the charge density of GelMA. The preshearing of multiple emulsions, following gelation, leads to the formation of porous GelMA microgels. The diversity of the formed structures highlights the application potential of preshearing ATPS in the development of functional soft materials.

Multiple emulsions: A new level-set based two-and-three dimensional simulation of multiphase immiscible flows for droplet formation

The present paper introduces a numerical approach based on the level-set framework to simulate multiphase flow in the context of multiple emulsion formation. The present technique, designed for the flow of n-phases, is applicable for the production of multiphase emulsions and also for the modeling of two and three-dimensional systems. This method is utilized to simulate the formation of single, double, and triple emulsions in a microfluidic cross-junction. The accuracy of the findings is confirmed by conducting an investigation of a single emulsion at home, as well as by referencing experimental and numerical literature on multiple emulsions. Until recently, the prospect of a shift in the double droplet formation regime at a constant capillary ratio between phases had not been taken into account. The present study yielded a flow regime mapping diagram that exhibits a transition in the double droplet formation regime under a constant capillary number ratio between the inner and middle phases. Using a morphological diagram, our method takes into consideration the effect of varying values of interfacial tension between the phases on the formation of double droplets. A comparison of two-dimensional and three-dimensional modeling strategies for double emulsion is also conducted, with the aim of clarifying the dissimilar results obtained from these two techniques.

Effect of nonionic surfactants on the synergistic interaction between asphaltene and resin: Emulsion phase inversion and stability

Interaction between surface active components in crude oils and nonionic surfactants plays an important role in phase inversion behavior of crude oil emulsion, while the interaction mechanism is not yet fully explored. Herein, the effects of nonionic surfactants on the synergistic interaction between asphaltene and resin, emulsion stability, and emulsion phase inversion were investigated. It is shown that the addition of Span 80 and Tween 80 promotes the reduction of phase inversion point of water in oil emulsion stabilized by asphaltene and resin, as well as increases the yield strain value of the emulsion. The addition of Tween 80 to the asphaltene and resin mixture reduces the inversion point from 70 % to 30 %. The decrease of phase inversion point is attributed to the difficulty in the formation of multiple emulsions after adding nonionic surfactants. The addition of nonionic surfactants can affect the hydrogen bonding between asphaltene and resin, thereby improving the emulsion stability. Span 80 coexists with asphaltene and resin at oil-water interface, reducing the Turbiscan Stability Index (TSI) of emulsion by 15 and improving the strength of the oil-water interface membrane. In comparison, Tween 80 with stronger hydrophilic ability dissolves asphaltene and resin into bulk phase, which leads to the oil-water interface occupied by a large amount of Tween 80. Its numerous EO groups result in the strong hydrogen bonding on the oil-water interface membrane, effectively increasing the strength of the oil-water interface membrane and reducing the TSI by 19. This work contributes to a better understanding of the phase inversion of crude oil emulsion and improves crude oil recovery.

Характеристика емульсій «вода в кам'яновугільній смолі», стабілізованих пилоподібною вугільною речовиною

CHARACTERIZATION OF "WATER IN COAL TAR" EMULSIONS STABILIZED WITH PULVERIZED COAL MATTER © L.P. Bannikov, PhD in Technjcal Sciences (State Enterprise "Ukrainian State Scientific Research Institute of Coal Chemistry (UKHIN), 7 Vesnina str., Kharkiv, 61023, Ukraine) Difficulties in dehydrating coal tar, especially those with a high degree of pyrolysis, are associated with the complex nature of numerous intermolecular interactions that provide high viscosity of the dispersion medium. On the other hand, emulsions are stabilized by dispersed particles insoluble in toluene and quinoline. However, the most distinctive feature is the stabilization of water droplets by the particles of the coke oven carry–over. First of all, the carry–over is related to the chamber loading process as well as the steam and hydro injection used. This leads to the absorption of the smallest dust particles by the condensing tar. The presence of functional groups in the coal substance gives hydrophilicity to the generally hydrophobic conventional coal molecule. In addition, the mineral part of coal also contributes to the diffusivity of the substance, which makes it surface active and capable of stabilizing emulsions. It has been shown that such particles are capable of forming stable multiple emulsions, which, as is known from the experience of oil dehydration, are very stable. The formation of emulsions was carried out on a mechanical stirrer, samples of crushed coking coal were used as emulsifiers, clay and sand were taken as a hydrophilic standard, and industrial soot was used as a hydrophobic standard. The maximum volume of the emulsion was obtained when "Zh" coal and "OS" coal were used as a powder emulsifier. The minimum volume of the emulsion was formed when hydrophilic components, such as sand and clay, were introduced into the system. The formation of multiple emulsions of the "tar in water/water in tar" type was noted. With an increase in the degree of hydrophobicity of powdered emulsifiers, the droplet size decreases, the interfacial surface increases, and the emulsion becomes more stable. The emulsifying ability of powders is explained by the formation of a structural and mechanical barrier. Keywords: coal tar, quinoline-insoluble substances, coal substance, stabilizers, hydrophilicity, hydrophobicity, multiple emulsions. Corresponding author: Bannikov Leonid P., e-mail: ukhinbannikov@gmail.com

Multiple Pickering emulsions fabricated by a single block copolymer amphiphile in one-step

The mixture of emulsifiers with opposite amphiphilicity was often necessary in generating multiple emulsions, whereas multiple emulsions might be generated by a single-component copolymer amphiphile. In this work, the emulsification of amphiphilic block copolymers poly (lauryl methacrylate)-b-poly (N-(2-methacryloylxyethyl) pyrrolidone) (PLMAm-b-PNMPn) in the water/dodecane systems was systematically studied by the confocal laser scanning microscopy and dynamic light scattering techniques. Interestingly, multiple emulsions instead of single emulsions were generated by employing single-component block copolymer amphiphiles PLMAm-b-PNMPn as emulsifiers under certain conditions. In specifically, the formation of multiple emulsions was highly depended on the molar ratio (rPNMP/PLMA = n/m) between the PNMP and PLMA segments regardless of the molecular weight of block copolymers. Through introducing an aggregation-induced emission amphiphile poly (N-(2-methacryloyloxyethyl) pyrrolidone)-b-poly (lauryl methacrylate-co-1-ethenyl-4-(1,2,2-triphenylethenyl) benzene) (PNMP35-b-P(LMA42-co-TPE16) into emulsifiers, the interfacial characters of multiple emulsions were also clarified. The complex emulsification of PLMAm-b-PNMPn was explained by a concordant manner based on the in-situ formed emulsifier mixture composed of PLMAm-b-PNMPn molecules and micelles, which were confirmed by the quantitative fluorescent analysis. It was found out that the preferred continuous phase of emulsions was mainly determined by the hydrophilicity of PLMAm-b-PNMPn molecules. However, the agglomeration of hydrophobic aggregates on the interfacial layer might inverse the amphiphilicity of mixed emulsifiers, and thereby resulting in the formation of multiple emulsions.

W/o/w multiple emulsions: A novel trend in functional ice cream preparations?

Ice cream is a popular product worldwide. Unfortunatelly, it contains a significant amount of fat. In this review, promising strategies for the use of w/o/w multiple emulsion structures in creams are assessed. W/o/w multiple emulsions (MEs) enable reduction the fat without losing the creamy taste and mouthfeel and also encapsulation of sensitive compounds. The encouraging application and formation of MEs in ice cream mixtures is supported by the use of natural food ingredients, such as fiber, which helps to stabilize the whole system and improves nutritional value. The future trends may be focused on the target stabilizations using Pickering paticles (PPs). The possible advantages, manufacture, evaluation methods, and predicted future prospects of MEs in ice creams are discussed.

Self-assembly in soft matter with multiple length scales

Spontaneous self-assembly in molecular systems is a fundamental route to both biological and engineered soft matter. Simple micellization, emulsion formation, and polymer mixing are well understood. However, the principles behind emergence of structures with competing length scales in soft matter systems remain unknown. Examples include droplet-inside-droplet assembly in many biomacromolecular systems undergoing liquid-liquid phase separation, analogous multiple emulsion formation in oil-surfactant-water formulations, and polymer core-shell particles with internal structure. We develop here a microscopic theoretical model based on effective interactions between the constituents of a soft matter system to explain self-organization both at single and multiple length scales. The model identifies how spatial ordering at multiple length scales emerges due to competing interactions between the system components, e.g., molecules of different sizes and different chemical properties. As an example of single and multiple length scale assembly, we map out a generic phase diagram for a solution with two solute species differing in their mutual and solvent interactions. We further connect the phase diagram to a molecular system via molecular simulations of a block-copolymer system that has a transition from regular single-core polymer particles to multicore aggregates that exhibit multiple structural length scales. The findings provide guidelines to understanding the length scales rising spontaneously in biological self-assembly but also open venues to the development and engineering of biomolecular and polymeric functional materials and pharmaceutical formulations.Received 20 January 2021Accepted 25 March 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.L022008Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasClassical statistical mechanicsClusteringPhase diagramsSelf-assemblyThermodynamicsCondensed Matter, Materials & Applied PhysicsStatistical PhysicsPolymers & Soft Matter

Multiple pickering high internal phase emulsions stabilized by modified diatomite particles via one-step emulsification process

Conventional approaches to generating double emulsions are cumbersome, complicated, and based on a two-step emulsification process using a combination of two distinctive surfactants. In this work, the surface properties of diatomite particles were successfully tailored by chemical modification with palmitoyl chloride. The properties of the resulting diatomite particles changed from the original hydrophilicity to hydrophobicity, leading to straightforward stabilization of oil-in-water-in-oil (O/W/O) Pickering double emulsions by a one-step emulsification process. Pickering double high internal phase emulsions (HIPEs) with an internal phase up to 80 vol% could be produced solely using the modified diatomite particles. The water-in-oil (W/O) droplet sizes of these HIPEs were much larger than the droplets of conventional nanoparticle-stabilized Pickering HIPEs. Furthermore, using the O/W/O Pickering double emulsions as templates, the porous polymer particles were fabricated. In addition, it was demonstrated that the wide particle size distribution of diatomite particles and modified heterogeneity were the reasons for the formation of multiple emulsions.

Fabrication of Novel Hierarchical Multicompartment Highly Stable Triple Emulsions for the Segregation and Protection of Multiple Cargos by Spatial Co-encapsulation

High-order multiple emulsions are of great interest in both fundamental research and industrial applications as vehicles for their encapsulation capability of actives. In this work, we report a hierarchically multicompartmental highly stable triple emulsion by emulsifying and assembling of natural Quillaja saponin. Water-in-oil-in-(oil-in-water) (W2/O2/(O1/W1)) triple emulsion indicates that the compartmented system consisted of surfaced saponin-coated nanodroplets (SNDs) and dispersed oil globules, which in turn contained smaller aqueous droplets. The effects of formulation parameters, including lipophilic emulsifier content, oil fraction, and SND concentration, on the formation of multiple emulsions were systematically investigated. The assembly into fibrillar network of SNDs at the outer oil-water interface effectively protected the triple emulsion droplets against flocculation and coalescence, and strongly prevented the osmotic-driven water diffusion between the internal water droplets and the external water phase, thus contributing to superior stability during 180 days storage. All of these characteristics make the multicompartmentalized emulsions suitable to co-encapsulate a hydrophilic bioactive (gardenia blue) and two hydrophobic bioactives (eapsanthin and curcumin) in a single emulsion droplet hierarchically for the segregation and protection of multiple cargos. This approach offers a promising route toward accessing the next generation of functional deliveries and encapsulation strategies.

Influence of particle concentration on multiple droplet formation in Pickering emulsions

HypothesisMultiphase droplets form when oil and water are mixed together at the ambivalent conditions that occur close to phase inversion. In this paper we propose a mechanism for the stabilisation of multiphase droplets by a single population of particles. ExperimentsWe investigated the microstructure of emulsions formed when dodecane and water are mixed in the presence of hydrophobic fumed silica nanoparticles. We identified the range of compositions, mixing times and rates where water-in-oil-in-water emulsions are stabilised in a single mixing step. To explore how the particle availability and mixing conditions lead to multiple emulsion formation we used light scattering and microscopy techniques to probe the size and morphology of the drops, and the particle coverage of the interfaces. FindingsOur key finding is that to stabilise multiphase drops there should be sufficient particles available to coat water drops that are entrained within coalescing oil droplets. The size of an entrained drop is determined by the volume of the rupturing film that forms between the oil drops. The particle coating prevents the entrained drop from escaping into the external aqueous phase. These results suggest a simple route for controlling the formation and stability of multiple emulsions for encapsulation applications.

Mixing Time, Inversion and Multiple Emulsion Formation in a Limonene and Water Pickering Emulsion.

It has previously been demonstrated that particle-stabilized emulsions comprised of limonene, water and fumed silica particles exhibit complex emulsification behavior as a function of composition and the duration of the emulsification step. Most notably the system can invert from being oil-continuous to being water-continuous under prolonged mixing. Here we investigate this phenomenon experimentally for the regime where water is the majority liquid. We prepare samples using a range of different emulsification times and we examine the final properties in bulk and via confocal microscopy. We use the images to quantitatively track the sizes of droplets and clusters of particles. We find that a dense emulsion of water droplets forms initially which is transformed, in time, into a water-in-oil-in-water multiple emulsion with concomitant changes in droplet and cluster sizes. In parallel we carry out rheological studies of water-in-limonene emulsions using different concentrations of fumed silica particles. We unite our observations to propose a mechanism for inversion based on the changes in flow properties and the availability of particles during emulsification.

Influencing factors of multiple emulsions formed by one-step emulsification

In this paper, the influence of the emulsifier structure, emulsifier solubility in oils, and oil polarity on the one-step formation of multiple emulsions was studied. The phase inversion process and the morphology of different types of multiple emulsions were investigated based on electrical conductivity measurements, microscopy, and pseudo-ternary phase diagrams. Emulsifiers with branched alkyl groups and polyethers, which were distributed on both sides of the main chain, or with amphiphilic diblock copolypeptides, can form multiple emulsions because of their strong hydrophilic properties. Hydrophobic emulsifiers with good solubility in oils were also conducive to the formation of one-step multiple emulsions. DC200 and Squalane worked well with the system, indicating that low-polarity oils were beneficial to the formation of one-step multiple emulsions. This study provides recommendations for future investigations and applications in food, pharmaceuticals, and cosmetics, including drug delivery and the encapsulation of hydrophilic active.

Influence of dispersion conditions on phase separation in liquid multiphase systems

The phase separation of liquid/liquid systems consisting of oil, water and amphiphilic molecules is a function of temperature and composition. The phase separation is fastest in liquid three phase systems, where the organic and aqueous excess phases are separated by a microemulsion middle phase. In this work, a detailed analysis of the relevant physical properties (density, rheology, interfacial tension) of the phases in combination with drop size distribution measurements and image analysis of the droplet interactions is performed using an endoscope measurement system. This methodology enables to directly quantify influencing effects of droplet size and droplet interactions on dispersion and phase separation processes. The duration and character of the separation process strongly depends on the droplet interactions (e.g. formation of multiple emulsions) of the dispersed phases.

Microfluidic Production of Multiple Emulsions

Microfluidic devices are promising tools for the production of monodispersed tuneable complex emulsions. This review highlights the advantages of microfluidics for the fabrication of emulsions and presents an overview of the microfluidic emulsification methods including two-step and single-step methods for the fabrication of high-order multiple emulsions (double, triple, quadruple and quintuple) and emulsions with multiple and/or multi-distinct inner cores. The microfluidic methods for the formation of multiple emulsion drops with ultra-thin middle phase, multi-compartment jets, and Janus and ternary drops composed of two or three distinct surface regions are also presented. Different configurations of microfluidic drop makers are covered, such as co-flow, T-junctions and flow focusing (both planar and three-dimensional (3D)). Furthermore, surface modifications of microfluidic channels and different modes of droplet generation are summarized. Non-confined microfluidic geometries used for buoyancy-driven drop generation and membrane integrated microfluidics are also discussed. The review includes parallelization and drop splitting strategies for scaling up microfluidic emulsification. The productivity of a single drop maker is typically <1 mL/h; thus, more than 1000 drop makers are needed to achieve commercially relevant droplet throughputs of >1 L/h, which requires combining drop makers into two-dimensional (2D) and 3D assemblies fed from a single set of inlet ports through a network of distribution and collection channels.

Effect of intermediate wettability nanoparticles on oil-water emulsion stability

Emulsions are ubiquitous in oil production operations and in general undesirable for various reasons. These include increased pressure losses leading to reduced oil productivity, pipeline and other equipment corrosion, as well as separation difficulties resulting in increased production costs. Surface active agents (also known as surfactants, like asphaltenes, resins, etc.) and solid particles (for example clays) are naturally present in crude oils. These components can act as stabilizers for oil and water emulsions. Therefore in order to mitigate the aforementioned problems related to emulsions, a better understanding of how emulsions are formed and stabilized is essential. This study focuses on nanoparticle stabilized emulsions and aims to contribute to a deeper understanding as it pertains to the effect of solid nanoparticles on the stability of oil and water emulsions.More specifically, the objective of this research is to investigate the separation kinetics of oil-water emulsions stabilized by spherical silica nanoparticles of intermediate wettability and its dependence on solid particle concentration, initial dispersion phase, water-cut, and shearing time. A novel, state-of-the-art, Portable Dispersion Characterization Rig (P-DCR) is used to run the experiments (as compared to the conventional bottle test method) and the relevant software for accurate data acquisition. All tests are conducted at ambient pressure and temperature conditions. Mineral oil and distilled water are used as the test fluids. The initial oil to water ratio in the batch separator is an important parameter. Therefore a broad range of water-cuts is tested. Starting with a 25% water-cut the experimental results indicate that in most cases no emulsion forms and complete phase separation takes place fast. However, when the water-cut increases to 50% and 75% a stable emulsion rag layer phase is always formed and full separation is not achieved within the experimental time frame. For the stirring times examined, faster separation takes place when the nanoparticles are initially dispersed in the oil phase. Using the specific type of nanoparticles, the formation of multiple emulsions (oil in water in oil, O/W/O) is observed. In general, as the nanoparticle concentration increases the rate of the separation process decreases. The size of the solid nanoparticles is also a critical factor and although not studied intentionally, it is inferred from the results that larger particles do not stabilize the formed emulsions as efficiently as smaller particles do.

New strategy of multiple emulsion formation based on the interactions between polymeric emulsifier and natural ingredients

Intensive studies have been conducted to determine biological activities of emulsions containing herbal extracts, but the effect of the extracts on technological characteristics of the emulsion system is poorly investigated. So the aim of our study was to determine the role of Rosmarinus officinalis L., Linum usitatissimum L., Avena sativa L. extracts and their interactions with polymeric emulsifier in the formation and stability of multiple emulsion. Herbal ingredient combinations were modified according to the experimental design matrix. The technological parameters of all the preparations were evaluated using centrifugation and conductivity tests, microscopic and viscometric analysis. A new approach to the formation of multiple emulsion has been taken by using an ethanolic rosemary extract in the presence of polymeric emulsifier. A direct, requiring no additional technological stages, emulsification process was established using herbal ingredients only. The different compositions revealed that all the plant extracts markedly affected rheological properties and stability of multiple emulsion. Weak herbal gels of linseed and oat groats were investigated and used as alternative additives to enhance stability of the emulsion. The prototype of potential w/o/w type drug delivery system was successfully created on the basis of natural ingredients using mixture design as an optimization tool.

Unique Dual Functions for Carbon Dots in Emulsion Preparations: Costabilization and Fluorescence Probing.

Recently, carbon dots (CDs) have drawn much attention as evidenced by their incorporation into many branches of science and engineering. Herein, a further unique application is elucidated: CDs that are synthesized by the hydrothermal treatment of gelatin for a dual functionality as expressed in costabilization of particle-based emulsions and their concomitant role as fluorescent probes. CDs either with or without gelatin matrixes induce the aggregation of Laponite particles. The introduction of CDs thus enhanced the stability of Laponite-stabilized emulsions and promoted the formation of multiple emulsions and emulsions with fine and uniform droplets when the CD-to-Laponite mass ratio was less than 45% and exceeded 60%, respectively. However, CDs without gelatin matrixes show slightly higher efficiency than CDs within gelatin matrixes for the costabilization of emulsions. CDs also costabilized emulsions with Laponite to allow the distribution of Laponite particles to be traced and the emulsion profiled under UV.

NMR studies of emulsion microstructure approaching the phase inversion point

Bench-top Nuclear Magnetic Resonance (NMR) pulsed field gradient (PFG) methods were used to measure the droplet size distributions (DSD) of various water-in-oil (w/o) emulsions as their water content was increased towards the phase inversion point (PIP). Such concentrated, opaque emulsions are not readily interrogated with alternative droplet sizing techniques. However, monitoring of the DSD as the PIP is approached is needed to help establish how different potential mechanisms, such as divergence of mean droplet size and/or the formation of multiple emulsions, are involved in the inversion process. Two separate NMR spectrometers were used and found to give consistent results for the emulsion DSDs and their evolution as the PIP was approached. An exponential increase in mean emulsion droplet size was observed for various crude oil emulsion samples prepared by sequential droplet phase (water) addition under shear as the PIP was approached, which is consistent with the mechanism of droplet coalescence exceeding droplet break-up. However, for w/o emulsions consisting of a pure hydrocarbon liquid stabilized by artificial surfactants, no change in mean droplet size was observed as the PIP was similarly approached. The NMR data were also analyzed for the presence of multiple emulsions – these were distinctly evident in several samples but were of the local w/o/w type.

Phase inversion pathways of emulsions stabilized by ethoxylated alkylamine surfactants

Composition changes are performed on an invert emulsion stabilized by ethoxylated alkylamine surfactants by adding acetic acid solutions. The addition of acetic acid induces a phase inversion that evolves through the following stages: W/O emulsion, O/W/O dual emulsion, bicontinuous state (studded with lamellar phase), random-shaped O/W emulsion, and normal O/W emulsion. The addition of excess acetic acid will always lead to the separation of pure oil. The speed and direction of the phase inversion can be influenced by the water/oil volume ratio; increasing this ratio facilitates the phase transition or causes it to switch to another direction with the W/O/W emulsion state as the destination. Three critical observations help to elucidate the mechanisms that control the phase inversion: increases in both the hydration radius and pliability of the surfactant layer, which result from the protonation and disorganization of rigid water structures at the interface; an increase in the effective volume fraction of the dispersed phase, which results from the formation of multiple emulsions; and a kinetic phase volume effect, which results in a kinetic phase separation and the nucleation of both oil and water domains.

Multiple emulsion formation from controllable drop pairs in microfluidics

A novel and reliable approach is developed for generating highly controlled multiple emulsions from controllable drop pairs in microfluidics. Drop pairs are accurately generated by drop-triggered drop formation and precise drop-pairing, and then one drop completely engulfs the other immiscible drop to form a multiple emulsion by adjusting their interfacial energies. This approach successfully avoids the complex sequential emulsifications and shows great stability and controllable flexibility. In addition, our strategy for drop-pairing is so reliable that it allows long-term operation without any misorder at all. Importantly, the proposed method of drop-pairing and multiple emulsion formation provides an innovative platform to precisely manipulate small volumes of fluids, which is of great value for exploiting novel microfluidics.