Multiple Emulsion Droplets Research Articles

Host-Guest Interaction Mediated Interfacial Co-Assembly of Cyclodextrin and Bottlebrush Surfactants for Precisely Tunable Photonic Supraballs.

Investigations of host-guest interactions at water-oil (w/o) interfaces are limited in single emulsion systems producing simple self-assembled objects with limited uses. Here, within hierarchically ordered water-in-oil-in-water (w/o/w) multiple emulsion droplets, interfacial self-assembly of (polynorbornene-graft-polystyrene)-block-(polynorbornene-graft-polyethylene glycol) (PNPS-b-PNPEG) bottlebrush block copolymers can be precisely controlled through host-guest interactions. α-Cyclodextrin (α-CD) in the aqueous phase can thread onto PEG side chains of the bottlebrush surfactants adsorbed at the w/o interface, leading to dehydration and collapsed chain conformation of the PEG block. Consequently, spherical curvature of the w/o internal droplets increases with the increased asymmetry of the bottlebrush molecules, producing photonic supraballs with precisely tailored structural parameters as well as photonic bandgaps. This work provides a simple but highly effective strategy for precise manipulation of complex emulsion systems applicable in a variety of applications, such as photonic pigments, cosmetic products, pesticides, artificial cells, etc.

Fabrication of monodisperse droplets and microcapsules using microfluidic chips: a review of methodologies and applications

Abstract Microfluidics has been applied in the preparation of monodisperse droplets and microcapsules due to its high encapsulation efficiency, its ability to create uniform particle sizes, and its capacity to control core–shell ratio and structure. To bring to the fore methodologies for the fabrication and application of monodisperse microcapsules using microfluidics, we present a review of the design, structure, materials, and surface modification techniques of various microfluidic chips. The review also covers fabrication methods, operating parameters and regulation methods of single and multiple monodisperse emulsion droplets fabricated from various microfluidic devices. Our findings show that particle size of monodisperse droplets depend mainly on microchannel characteristic size and flow rate, with particle size increasing with larger microchannel but decreasing with higher continuous phase flow rate. We additionally reviewed and compared various fabrication methods for monodisperse microcapsules, such as interfacial polymerization, free-radical polymerization, ionic cross-linking, and solvent evaporation. We further reviewed and examined the application of monodisperse microcapsules in biology applications, food engineering, composite materials development, and pharmaceutical industry. We found that high-throughput microfluidics for scale-up monodisperse microcapsule preparation towards uniform degradation and targeted release properties of monodisperse microcapsules would be key innovative direction for future applications.

Hierarchical Assemblies of Bottlebrush/Homopolymer Blends: Tailoring Phase Interfacial Curvature for Tunable Photonics†

Comprehensive SummaryOrganized spontaneous emulsification (OSE) produces ordered water‐in‐oil‐in‐water (W/O/W) multiple emulsion droplets stabilized by bottlebrush block copolymer (BBCP) surfactants, such as (polynorbornene‐g‐polystyrene)‐b‐(polynorbornene‐g‐polyethylene oxide) (PS‐b‐PEO), templating ordered porous particles with visible structural colors. Here, homopolymer polystyrenes (hPS) were used to swell the PS domain and thus to effectively increase the W/O interfacial curvature of the internal droplets. By variation of hPS concentration, pore diameter is largely tunable from 34 to over 210 nm, leading to tunable photonic bandgaps in the whole visible spectrum. The ratio (α) of molecular weight of hPS relative to that of the PS side chains of the BBCP can greatly influence their spatial distribution within the PS domain. For α ≤ 1, uniform solubilization of the hPS chains into the side chains of BBCP is achieved leading to a homogeneous porous structure. For α > 1, local solubilization of the hPS chains at interface of the internal droplets is disclosed at relatively low concentrations of hPS (≤ 42 wt%), resulting in a small change in pore diameter. For contrast, a rapid increase of the W/O interfacial curvature was observed upon further increase of the hPS content (> 42 wt%) through an evident influence on the OSE procedure.

Self-assembly and structures of nanoscale double emulsion droplets through coarse-grained molecular dynamics simulations.

Examples of self-assembled multiple emulsion droplets on the nanometre scale are very rare. In this work, we use coarse-grained (CG) molecular dynamics simulations to study the self-assembly of ternary mixtures consisting of water, n-heptane, and nonionic surfactant tetraethylene glycol monododecyl ether (C12E4). The water volume fractions studied are 1%, 3%, and 5%, respectively. Various nanoscale emulsions are obtained in a spontaneous process. When the water/surfactant volume ratio vm/s = 1.0/1.0, the obtained emulsion droplets are identified as oil-in-water-in-oil (O/W/O) double types, consisting of an oil core, an inner surfactant layer, a water layer, and an outer surfactant layer. The water molecules are distributed around the hydrophilic ends of the surfactants, while the hydrophobic ends of the surfactants wrap the oil cores and penetrate into the oil bulk. Hydrogen-bond interactions among water and the hydrophilic ends of the surfactants form cross-links that stabilize the double emulsion droplets. The sizes of all the oil cores inside the droplets are <6 nm in diameter, even with the highest water volume fraction of 5%. Both the concentration of free water molecules on the order of 10-6 mol/cm3 and the favourable energy change during emulsion formation indicate that the emulsion droplets are thermodynamically stable. In contrast, for vm/s = 1.0/5.5, no double emulsion but a simple water-in-oil emulsion was observed, with morphologies evolving from oblate to bicontinuous phases with an increase in the water volume fraction from 1% to 5%. Our coarse-grained molecular dynamics simulations provide valuable insight for the preparation of nanoscale double emulsions and the characterization of their structures.

Dielectrophoresis Response of Water-in-Oil-in-Water Double Emulsion Droplets with Singular or Dual Cores.

Microfluidic technologies have enabled generation of exquisite multiple emulsion droplets, which have been used in many fields, including single-cell assays, micro-sized chemical reactions, and material syntheses. Electrical controlling is an important technique for droplet manipulation in microfluidic systems, but the dielectrophoretic behaviors of multiple emulsion droplets in electrical fields are rarely studied. Here, we report on the dielectrophoresis response of double emulsion droplets in AC electric fields in microfluidic channel. A core-shell model is utilized for analyzing the polarization of droplet interfaces and the overall dielectrophoresis (DEP) force. The water-in-oil-in-water droplets, generated by glass capillary devices, experience negative DEP at low field frequency. At high frequency, however, the polarity of DEP is tunable by adjusting droplet shell thickness or core conductivity. Then, the behavior of droplets with two inner cores is investigated, where the droplets undergo rotation before being repelled or attracted by the strong field area. This work should benefit a wide range of applications that require manipulation of double emulsion droplets by electric fields.

Formation and stabilization of multiple water-in-water-in-water (W/W/W) emulsions

Multiple Water-in-Water-in-Water (W/W/W) emulsions were prepared, stabilized and characterized. The main objective was to find a simple and low-cost method for the preparation of W/W/W emulsions. The system composed of gelatin, maltodextrin and water was used, and two different methods were studied for producing multiple emulsions in this system. In the first method, maltodextrin-in-gelatin (M/G) emulsions with small droplet size were formed by pH-induced nucleation of maltodextrin droplets, and afterwards, maltodextrin-in-gelatin-in-maltodextrin (M/G/M) multiple emulsions were obtained by dispersing M/G droplets into maltodextrin solutions. The second method consisted in cooling down gelatin-in-maltodextrin (G/M) emulsions, leading to the spontaneous formation of inner maltodextrin droplets. The latter method allowed producing more homogenous M/G/M multiple emulsion droplets. The colloidal stability of such emulsions greatly improved with the addition of mucin particles, which is a glycoprotein that adsorbs on the G/M interface. Stable M/G/M multiple emulsions have been prepared and characterized by fluorescence optical microscopy, where contrast has been enhanced through covalently labelling the various components with fluorescent dyes. To our knowledge, this is the first report of a simple and cost-effective method for the production of multiple W/W/W emulsions, without using microfluidic techniques. Moreover, the present work also demonstrates that mucin microparticles can be effective stabilizers for protein-in-polysaccharide emulsions, and these dispersions can be easily prepared by phase transition methods.

Lipid Vesicle Preparation Using W/O/W Multiple Emulsions Via Solvent Evaporation: The Effect of Emulsifiers on the Entrapment Yield of Hydrophilic Materials

AbstractWe studied the effects of emulsifiers on the entrapment yields of a hydrophilic material, calcein, in lipid vesicles formed using the multiple emulsion method. The primary emulsion (W1/O) was prepared via sonication while the secondary emulsification that produced the W1/O/W2 multiple emulsions was achieved using the microchannel (MC) emulsification technique. The emulsifiers used in the continuous (W2) phase were Tween® 80, Pluronic® F68, and bovine serum albumin (BSA). Lipid vesicles formed via solvent evaporation of the multiple emulsion droplets had an average diameter of about 180 nm, similar to the size of the water droplets in the primary W1/O emulsions. The entrapment yields of calcein increased with decreasing concentrations of Tween® 80 but decreased with decreasing concentrations of Pluronic® F68 and BSA. The effects of type and concentration of emulsifier were considered in relation to three possible mechanisms: (i) destabilization/solubilization of lipid bilayers by emulsifiers, (ii) reversed‐micellar transport of W1 contents from internal to external water phases through the O phase, and (iii) release of inner water (W1) contents into the continuous (W2) phase via the instability of W1/O/W2 and leakage of W1 contents. Using the food grade emulsifier Tween® 80 at a low concentration of about 0.1 or 0.05 wt%, calcein as a model hydrophilic material could be efficiently entrapped (ca. 80%) in homogenously dispersed lipid vesicles.

Designable Polymeric Microparticles from Droplet Microfluidics for Controlled Drug Release

AbstractDrug delivery systems that can control drug release profile to ensure a high therapeutic efficacy and reduced side effects are highly desired in pharmaceutical and biomedical fields. Microparticles are the most commonly used drug delivery systems, because they can be easily administrated to patients, and be engineered with different structures and functions for keeping drug stability, delivering drugs to a desired location, and releasing drugs with a predetermined rate in a well‐controlled manner. Microfluidic techniques show great power for controllable generation of highly monodisperse multiple emulsion droplets with unprecedented structural diversity. Microfluidics‐templated emulsions allow elaborately design and controllable generation of highly uniform microparticles with well‐controlled sizes, shapes, compositions, and structures, and integrated functions for controlled drug release. This review highlights recent progress on controllable microfluidic fabrication of monodisperse emulsion templates and the resultant polymeric microparticles with well‐tailored structures and functions for flexible encapsulation and controlled release of drugs. Especially, a comprehensive overview of the recent biomedical applications of these microparticles with diverse release mechanisms is provided. Finally, perspectives on further advancing the microfluidic techniques for fabricating functional microparticles from lab scale to industrial scale are discussed.

Effect of asphaltene on the emulsions stabilized by graphene oxide: A potential application of graphene oxide in enhanced oil recovery

In this research, graphene oxide (GO) is used to prepare stable Pickering emulsions in chemical flooding for enhanced oil recovery (EOR). The effects of GO concentration (0–7 mg/mL), salinity of aqueous phase (0–10 wt%), and asphaltene concentration in organic phase (0–2 wt%) on the stability and morphology of the emulsions are examined. Moreover, the influence of these independent variables on the interfacial tension (IFT) between organic and aqueous phase is assessed through response surface methodology. The results show that the concentrations of GO and asphaltene have the most significant effect on the IFT; indeed, the IFT reduces with increasing both GO and asphaltene concentrations. Defining two quantitative indexes make it possible to compare the efficiency of emulsions formation (ESVI) and the stability of formed emulsions during time (ESTI) against creaming at different conditions. The maximum reported values for the ESTI and ESVI are 100% and 70%, respectively. In all conditions, the type of emulsions is oil-in-water (O/W) which is more suitable in EOR. However, water-in-oil emulsions (W/O) are observed at asphaltene concentrations higher than 1.5 wt%. For dominating this phenomenon, the water/oil ratio should be increased. At the presence of asphaltene and salinities higher than 1 wt%, some water-in-oil-in-water (W/O/W) multiple emulsion droplets are observed. The minimum of the reported average droplet size is 0.69 μm for GO concentration of 1 mg/mL and asphaltene concentration of 0.05 wt%. These results demonstrate the potential applications of graphene based functional materials for EOR.

Pore-Scale Transport Mechanisms and Macroscopic Displacement Effects of In-Situ Oil-in-Water Emulsions in Porous Media

Oil-in-water (O/W) emulsions are expected to be formed in the process of surfactant flooding for heavy oil reservoirs in order to strengthen the fluidity of heavy oil and enhance oil recovery. However, there is still a lack of detailed understanding of mechanisms and effects involved in the flow of O/W emulsions in porous media. In this study, a pore-scale transparent model packed with glass beads was first used to investigate the transport and retention mechanisms of in situ generated O/W emulsions. Then, a double-sandpack model with different permeabilities was used to further study the effect of in situ formed O/W emulsions on the improvement of sweep efficiency and oil recovery. The pore-scale visualization experiment presented an in situ emulsification process. The in situ formed O/W emulsions could absorb to the surface of pore-throats, and plug pore-throats through mechanisms of capture-plugging (by a single emulsion droplet) and superposition-plugging or annulus-plugging (by multiple emulsion droplets). The double-sandpack experiments proved that the in situ formed O/W emulsion droplets were beneficial for the mobility control in the high permeability sandpack and the oil recovery enhancement in the low permeability sandpack. The size distribution of the produced emulsions proved that larger pressures were capable to displace larger O/W emulsion droplets out of the pore-throat and reduce their retention volumes.

Synthesis and Characterization of Graphene Oxide–Polystyrene Composite Capsules with Aqueous Cargo via a Water–Oil–Water Multiple Emulsion Templating Route

Graphene oxide/polystyrene (GO/PS) nanocomposite capsules containing a two-compartment cargo have been successfully fabricated using a Pickering emulsion strategy. Highly purified GO sheets with typically micrometer-scale lateral dimensions and amphiphilic characteristics were prepared from the oxidation reaction of graphite with concomitant exfoliation of the graphite structure. These GO sheets were employed as a stabilizer for oil-in-water emulsions where the oil phase comprised toluene or olive oil. The stability and morphology of the emulsions were extensively studied as a function of different parameters including GO concentration, aqueous phase pH, ultrasonication time, effects of added electrolytes and stability to dilution. In selected conditions, the olive oil emulsions showed spontaneous formation of multiple w/o/w emulsions with high stability, whereas toluene formed simple o/w emulsions of lower overall stability. Olive oil emulsions were therefore used to prepare capsules templated from emulsion droplets by surrounding the oil phase with a GO/PS shell. The GO sheets, emulsions and composite capsules were characterized using a variety of physical and spectroscopic techniques in order to unravel the interactions responsible for capsule formation. The ability of the capsules to control the release of a model active agent in the form of a hydrophilic dye was explored, and release kinetics were monitored using UV-visible spectroscopy to obtain rate parameters. The composite capsules showed promising sustained release properties, with release rates 11× lower than the precursor GO-stabilized multiple emulsion droplets.

Surface modification of a glass microchannel for the formation of multiple emulsion droplets

We herein report a method for the preparation of a glass microchannel capable of forming multiple emulsion droplets (i.e., water-in-oil-in-water and oil-in-water-in-oil) by locally controlling the wettability of the glass microchannel. Production of multiple emulsion droplets using a glass microchannel requires partial control of its wettability using a method that consists of two steps: (1) hydrophobization of a whole glass microchannel by filling the microchannel with octadecyltrichlorosilane (OTS) solution, and (2) local hydrophilization of the OTS-treated glass microchannel by exposure to ultraviolet light through a mask. However, conditions for the preparation of OTS-SAMs for controlling microchannel wettability and subsequent multiple emulsion droplet formation have not yet been reported. In this study, we investigated the conditions required to form multiple emulsion droplets and demonstrated formation of multiple emulsion droplets using a treated glass microchannel with multiple junctions. The glass microchannel prepared according to this method was able to form various aqueous and organic droplets due to its resistance to swelling.

Stimuli-triggered Formation of Polymersomes from W/O/W Multiple Double Emulsion Droplets Containing Poly(styrene)-block-poly(N-isopropylacrylamide-co-spironaphthoxazine methacryloyl).

We report stimuli-triggered fabrication of polymersomes from water-in-oil-in-water (W/O/W) multiple double emulsion droplets and the dual-stimuli (temperature and UV) responsive behavior of corresponding polymersomes. The polymersome comprises Tween20, cholesterol, and poly(styrene)-block-poly(N-isopropylacrylamide-co-spironaphthoxazine methacryloyl), i.e., PS-b-P(NIPAAm-co-SPO), synthesized by stepwise reversible addition-fragmentation chain transfer (RAFT) polymerization. Amphiphilic PS-b-P(NIPAAm-co-SPO) copolymer forms micelles in water above the critical micelle concentration (CMC) of 0.7 g/L at 23 °C. The micelles show a temperature-driven aggregation among the micelles above 30.6 °C, confirmed by a decrease in UV-vis transmittance. The micelles also show a color change without colloidal instability under 365 nm UV at room temperature. PS-b-P(NIPAAm-co-SPO) plays not only a role of the polymeric surfactant in the preparation of W/O/W multiple double emulsions but also an important role in the stimuli-triggered transformation from multi- to single-core double emulsion droplets under heat and UV light irradiation. It was found that the morphological transformation of W/O/W multiple double emulsions by UV irradiation was much faster than temperature change. Dual-responsive polymersomes were simply prepared after solvent removal and they exhibit stable and reversible size and color variations under temperature and UV-visible changes, respectively.

Enhancement of aqueous stability of allyl isothiocyanate using nanoemulsions prepared by an emulsion inversion point method

Allyl isothiocyanate (AITC), an organosulfur compound in cruciferous vegetables, is a natural antimicrobial and potential chemopreventive agent. However, the instability of AITC in aqueous systems restrains its applications. In this study, oil-in-water AITC nanoemulsion was prepared by the emulsion inversion point (EIP) method, aiming at improving the aqueous stability of AITC. The optimal hydrophilic–lipophilic balance (HLBop) value of surfactants containing Tween 80 and Span 80 was established at 11.0–13.0, yielding nanodroplets with diameters of 137–215nm. The mechanism of droplet formation within the HLPop region was discussed in terms of the possible structure of adsorbed surfactant layers at the oil–water interface in multiple emulsion droplets. In a 6.5-month storage test, the droplet sizes and the count rates (intensity of scattered light) of nanoemulsions decreased only slightly by 4–13% (depending on surfactant-to-oil ratio), even in highly diluted status, indicating the desirable stability of the nanoemulsions. Moreover, the nanoemulsion demonstrated superior protection against AITC degradation (78% remaining after 60d at 30°C), compared with protein nanoparticles as well as non-encapsulated aqueous dispersion. This work shows for the first time that AITC can be formulated into nanoemulsions and thus obtains satisfactory aqueous solubility and chemical stability.

Production of food-grade multiple emulsions with high encapsulation yield using oscillating membrane emulsification

Food-grade water-in-oil-in-water (W/O/W) multiple emulsions with a volume median diameter of outer droplets of 50–210μm were produced by injecting a water-in-oil (W/O) emulsion at the flux of 30Lm−2h−1 through a 10-μm pore electroplated nickel membrane oscillating at 10–90Hz frequency and 0.1–5mm amplitude in 2wt% aqueous Tween® 20 (polyoxyethylene sorbitan monolaurate) solution. The oil phase in the primary W/O emulsion was 5wt% PGPR (polyglycerol polyricinoleate) dissolved in sunflower oil and the content of water phase in the W/O emulsion was 30vol%. The size of outer droplets was precisely controlled by the amplitude and frequency of membrane oscillation. Only 3–5% of the inner droplets with a mean diameter of 0.54μm were released into the outer aqueous phase during membrane emulsification. A sustained release of 200ppm copper (II) loaded in the inner aqueous phase was investigated over 7 days. 95% of Cu(II) initially present in the inner water phase was released in the first 2 days from 56-μm diameter multiple emulsion droplets and less than 15% of Cu(II) was released over the same interval from 122μm droplets. The release rate of Cu(II) decreased with increasing the size of outer droplets and followed non-zero-order kinetics with a release exponent of 0.3–0.5. The prepared multiple emulsions can be used for controlled release of hydrophilic actives in the pharmaceutical, food, and cosmetic industry.

Factors that Affect Pickering Emulsions Stabilized by Graphene Oxide

Stable Pickering emulsions were prepared using only graphene oxide (GO) as a stabilizer, and the effects of the type of oil, the sonication time, the GO concentration, the oil/water ratio, and the pH value on the stability, type, and morphology of these emulsions were investigated. In addition, the effects of salt and the extent of GO reduction on emulsion formation and stability were studied and discussed. The average droplet size decreased with sonication time and with GO concentration, and the emulsions tended to achieve good stability at intermediate oil/water ratios and at low pH values. In all solvents, the emulsions were of the oil-in-water type, but interestingly, some water-in-oil-in-water (w/o/w) multiple emulsion droplets were also observed with low GO concentrations, low pH values, high oil/water ratios, high salt concentrations, or moderately reduced GO in the benzyl chloride-water system. A Pickering emulsion stabilized by Ag/GO was also prepared, and its catalytic performance for the reduction of 4-nitrophenol was investigated. This research paves the way for the fabrication of graphene-based functional materials with novel nanostructures and microstructures.

Impact of osmotic pressure and gelling in the generation of highly stable single core water-in-oil-in-water (W/O/W) nano multiple emulsions of aspirin assisted by two-stage ultrasonic cavitational emulsification

The present investigation focuses in investigating the effect of osmotic pressure, gelling on the mean droplet diameter, polydispersity index, droplet size stability of the developed novel Aspirin containing water-in-oil-in-water (W/O/W) nano multiple emulsion. The aspirin-loaded nano multiple emulsion formulation was successfully generated using two-stage ultrasonic cavitational emulsification which had been reported in author's previous study. The osmotic behavior of ultrasonically prepared nano multiple emulsions were also examined with different glucose concentrations both in the inner and outer aqueous phases. In addition, introducing gelatin into the formulation also observed to play an important role in preventing the interdroplet coalescence via the formation of interfacial rigid film. Detailed studies were also made on the possible mechanisms of water migration under osmotic gradient which primarily caused by the permeation of glucose. Besides, the experimental results have shown that the interfacial tension between the two immiscible phases decreases with varying the composition of organic phase. Although the W/O/W emulsion prepared with the inner/outer glucose weight ratio of 1–0.5% (w/w) showed an excellent droplet stability, the formulation containing 0.5% (w/w) glucose in the inner aqueous phase appeared to be the most stable with minimum change in the mean droplet size upon one-week storage period. Based on the optimization, nano multiple emulsion droplets with the mean droplet diameter of around 400nm were produced using 1.25% (w/w) Span 80 and 0.5% Cremophore EL. Overall, our investigation makes a pathway in proving that the use of ultrasound cavitation is an efficient yet promising approach in the generation of stable and uniform nano multiple emulsions and could be used in the encapsulation of various active pharmaceutical ingredients in the near future.

Droplet Microfluidics for Fabrication of Non‐Spherical Particles

We describe new developments for controlled fabrication of monodisperse non-spherical particles using droplet microfluidics. The high degree of control afforded by microfluidic technologies enables generation of single and multiple emulsion droplets. We show that these droplets can be transformed to non-spherical particles through further simple, spontaneous processing steps, including arrested coalescence, asymmetric polymer solidification, polymerization in microfluidic flow, and evaporation-driven clustering. These versatile and scalable microfluidic approaches can be used for producing large quantities of non-spherical particles that are monodisperse in both size and shape; these have great potential for commercial applications.

On the viscoelastic behavior of multiple emulsions

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.

The development and characterisation of triglyceride-based ‘spontaneous’ multiple emulsions

The formation of multiple emulsion droplets from two oil systems (Labrafil M 1944 CS and Labrafac Lipophile WL 1349) via a one-step process involving minimal agitation in aqueous media has been investigated in terms of the multiple character of the droplets, the particle size distribution, the stability and the lipolysis profile in the presence of pancreatic lipase. It was noted that multiple emulsion droplets were formed from both oils in the presence and absence of Tween 80, with the stability and particle size of the droplets being dependent on the composition and choice of media. It was noted that optimum stability of up to several days was obtained using 10% Tween 80 for both oils, with two stages of the breakdown process being apparent, the relative propensities of which being dependent on the oil used. The particle size distribution in distilled water indicated the presence of two distinct size populations corresponding to multiple and single droplets. It was noted that droplet breakdown was greatly accelerated in simulated intestinal fluid and in high pH media, with evidence for liquid crystal structure formation apparent. Lipolysis studies indicated that pegylation and the presence of surfactant slowed the degradation process. The study has indicated that ‘spontaneous’ multiple emulsion formation is indeed possible, with a reasonable if not necessarily optimal stability profile being observed for these systems.