Emulsifying potency of new amino acid-type surfactant (II): stable water-in-oil (W/O) emulsions containing 85 wt% inner water phase

The ternary phase diagram for N-[3-lauryloxy-2-hydroxypropyl]-L-arginine L-glutamate (C12HEA-Glu), a new amino acid-type surfactant, /oleic acid (OA)/water system was established. The liquid crystal and gel complex formations between C12HEA-Glu and OA were applied to a preparation of water-in-oil (W/O) emulsions. Stable W/O emulsions containing liquid paraffin (LP) as the oil and a mixture of C12HEA-Glu and OA as the emulsifier were formed. The preparation of stable W/O emulsions containing 85 wt% water phase was also possible, in which water droplets would be polygonally transformed and closely packed, since the maximum percentage of inner phase is 74% assuming uniformly spherical droplets. Water droplets would be taken into the liquid crystalline phase (or the gel complex) and the immovable water droplets would stabilize the W/O emulsion system. The viscosity of emulsions abruptly increased above the 75 wt% water phase (dispersed phase). The stability of W/O emulsions with a lower weight ratio of OA to C12HEA-Glu and a higher ratio of water phase was greater. This unusual phenomenon may be related to the formation of a liquid crystalline phase between C12HEA-Glu and OA, and the stability of the liquid crystal at a lower ratio of oil (continuous phase). W/O and oil-in-water (O/W) emulsions containing LP were selectively prepared using a mixture of C12HEA-Glu and OA since the desirable hydrophile-lipophile balance (HLB) number for the emulsification was obtainable by mixing the two emulsifiers.     

Influence of composition on the encapsulation properties of P/O/W multiple emulsions for Vitamin C

Abstract

The aim of this work was to study the encapsulation properties of polyols-in-oil-in-water (P/O/W) multiple emulsions for Vitamin C (Vc). The influence of formulation factors, including the concentration of lipophilic emulsifier, hydrophilic emulsifier, salt and glycerol had been investigated. The results indicated that the encapsulation stability could be improved by increasing the lipophilic emulsifier concentration which could strengthen the interfacial film. In contrast, the excess of hydrophilic emulsifier destabilized the emulsion. The presence of glycerol in the outer aqueous phase accelerated the phase transfer, thus reduced the encapsulation rate. The addition of salt in inner polyols phase had little effect on encapsulation rate while markedly affected the morphology and stability of this system. P/O/W multiple emulsions showed better encapsulation stability than the W/O/W multiple emulsions as the former’s encapsulation rate could remain more than 75% after 2?weeks while the latter only remained less than 60%. Meanwhile, the P/O/W emulsions exhibited higher storage modulus (G’), bigger loss modulus (G’’) and broaden linear viscoelastic regions than W/O/W emulsions.     

Encapsulation and Prolonged Release Behaviour of W/O/W Type Multiple Emulsions

W/O/W type multiple emulsions were prepared by two step emulsification procedures using an oily lymphographic agent, lipiodol, as an inner oil phase and Pluronic F-68 as a hydrophilic emulsifier contained in the outer aqueous phase. Span 80, Pluronic L-64 and HCO-60 were used as emulsifiers incorporating them into the inner oil phase. The phase volume of the inner and outer aqueous phases and the yield of the w/o/w type multiple emulsions were studied. The dissolution behaviour of the w/o/w type multiple emulsions were determined by a dialysis method employing cellulose tubing. The effect of emulsifier type and the amount of HCO-60 on the stability and prolonged release behavior of the w/o/w type multiple emulsions with or without lecithin, was also examined. The results indicate the HCO-60 is a better emulsifier than Span 80 or Pluronic L-64. Its use improves the stability and the prolonged release behavior of w/o/w type multiple emulsions.     

部分析因法分析油包水型聚乙烯亚胺水溶液/石蜡乳液的稳定性

聚乙烯亚胺(PEI)及其乳状液被广泛用于酶固定化、基因治疗、污水处理等领域。 为提高PEI乳状液的稳定性,促进其应用,本文采用部分析因试验法考察了影响PEI水溶液/石蜡乳状液(W/O)稳定性的主因素和各因素间交互作用。 结果表明,乳化剂用量和PEI的水相质量分数是影响PEI水溶液/石蜡乳液稳定性的主因素。 PEI的水相质量分数和油/水体积比的交互作用最显著。 优化后,制备最稳定的PEI水溶液/石蜡乳状液(W/O)的条件是:m(Span-80):m(Tween-80)=6:1,PEI的水相质量分数为5%,乳化剂用量为0.07 g/mL,V(石蜡):V(PEI水溶液)=6:4,均质时间为3 min,转速为6000 r/min。 在优化条件下制备的PEI水溶液/石蜡乳状液在放置7 d后乳状液的外观无明显变化,这表明所制备的PEI水溶液/石蜡乳状液具有良好的稳定性。     

Three-dimensional molecular mapping of a multiple emulsion by means of CARS microscopy

Multiple emulsions consisting of water droplets dispersed in an oil phase containing emulsifier which is emulsified in an outer water phase (W/O/W) are of great interest in pharmacology for developing new drugs, in the nutrition sciences for designing functional food, and in biology as model systems for cell organelles such as liposomes. In the food industry multiple emulsions with high sugar content in the aqueous phase can be used for the production of sweets, because the high sugar content prevents deterioration. However, for these emulsions the refractive indexes of oil and aqueous phase are very similar. This seriously impedes the analysis of these emulsions, e.g., for process monitoring, because microscopic techniques based on transmission or reflection do not provide sufficient contrast. We have characterized the inner dispersed phase of concentrated W/O/W emulsions with the same refractive index of the three phases by micro Raman spectroscopy and investigated the composition and molecular distribution in water-oil-water emulsions by means of three-dimensional laser scanning CARS (coherent anti-Stokes Raman scattering) microscopy. CARS microscopy has been used to study water droplets dispersed in oil droplets at different Raman resonances to visualize different molecular species. Water droplets with a diameter of about 700 nm could clearly be visualized. The advantages of CARS microscopy for studying this particular system are emphasized by comparing this microscopic technique with conventional confocal reflection and transmission microscopies.     

Effects of compositions on the stability of polyols-in-oil-in-water (P/O/W) multiple emulsions

Polyols-in-oil-in-water (P/O/W) multiple emulsions were successfully prepared by using polyols as inner aqueous phase to avoid instabilities caused by water. The influence of polyols, oils and emulsifiers on the morphology and stability of P/O/W multiple emulsions were studied and the stability mechanisms of this new kind of multiple emulsions were also explored. Glycerol that has the worst solubility in oil phase contributed to the formation of stable inner droplets which agree with the Ostwald Ripening theory. Mineral oil worked well with the system proving that oils possessing similar solubility parameters with the hydrophobic group of emulsifiers benefited for system stability. Several typical surfactants had been investigated in this article, and it turned out that emulsifiers Cetyl PEG/PPG-10/1 Dimethicone and the block copolymer Poloxamer 407 were suitable for the P/O/W system. The stability of the system affected by different compositions was evaluated based on microscopic observation and rheological measurements. The novel multiple emulsions will provide enlightening recommendations for future investigations and applications in cosmetic, food and pharmaceuticals, including drug delivery and the encapsulation of hydrophilic actives and actives that are soluble in polyols.     

Phase transitions and microstructure of emulsion systems prepared with acylglycerols/zinc stearate emulsifier

The emulsification processes, during which acylglycerols/zinc stearate emulsifier, water, and oil phase formed ternary systems, such as water-in-oil (W/O) emulsions, oil-in-water (O/W) dispersions, and unstable oil-water mixtures, were investigated in order to characterize the progressive transformations of the dispersed systems. The type, structure, and phase transitions of the systems were found to be determined by temperature and water phase content. Crystallization of the emulsifier caused the destabilization and subsequent phase inversion of the emulsions studied, at a temperature of 60-61 degrees C. The observed destabilization was temporary and led, at lower temperature, to W/O emulsions, "O/W + O" systems, or O/W dispersions, depending on the water content. Simultaneous emulsification and cooling of 20-50 wt % water systems resulted in the formation of stable W/O emulsions that contained a number of large water droplets with dispersed oil globules inside them ("W/O + O/W/O"). In water-rich systems (60-80 wt % of water), crystallization of the emulsifier was found to influence the formation of crystalline vesicle structures that coexisted, in the external water phase, with globules of crystallized oil phase. Results of calorimetric, rheological, and light scattering experiments, for the O/W dispersions obtained, indicate the possible transition of a monostearoylglycerol-based alpha-crystalline gel phase to a coagel state, in these multicomponent systems.     

Influence of synthetic perfumes on stability of O/W emulsion in sodium dodecyl sulfate–n-dodecane–water ternary systems

Influence of synthetic perfumes having diverse chemical structures such as eugenol, linalool, benzyl acetate, α-ionone, α-hexylcinnamaldehyde, and d-limonene on stability of oil-in-water (O/W) emulsion composed of sodium dodecyl sulfate, n-dodecane, and water is investigated. Turbidity measurements of the O/W emulsion indicate that the emulsion is stabilized by adding the synthetic perfume, except for d-limonene, and that this tendency is remarkable in adding eugenol. The addition of the perfume, especially eugenol, shrinks oil droplets in the O/W emulsion, which inhibits coagulation and/or creaming of oil droplets. When adding eugenol, moreover, ζ-potential of oil droplets increases negatively, and viscosity of the external water phase of the emulsion rises drastically. The increment in ζ-potential and viscosity by the addition of eugenol also prevents oil droplets from coagulation and/or creaming and makes the O/W emulsion still more stable.     

Emulsion preparation using beta-cyclodextrin and its derivatives acting as an emulsifier

The preparation and formation mechanism of n-hexadecane/water emulsions using natural beta-cyclodextrin (beta-CD) and chemically modified beta-CDs (triacylated beta-cyclodextrins) as an emulsifier were investigated. The stable water/oil (W/O) emulsion was formed using tripropanoyl-beta-CD (TP-beta-CD). From observation using the contact angle (theta(ow)) of precipitates derived from CD, it was clarified that oil/water (O/W) emulsion at theta(ow)<90 degrees and (W/O) emulsion at theta(ow)>90 degrees are formed when the composition of each oil and water was mixed with natural beta-CD or triacylated beta-CDs.     

Freeze–thaw stability of water-in-oil emulsions

Factors influencing water-in-oil emulsion stability during freeze/thaw-cycling, namely interfacial crystallization vs. network crystallization and the sequence of crystallization events (i.e., dispersed vs. continuous phase or vice versa), are assessed. We show that destabilization is most apparent with a liquid-state emulsifier and a continuous oil phase that solidifies prior to the dispersed phase. Emulsions stable to F/T-cycling are obtained when the emulsifier crystallizes at the oil–water interface or in emulsions where the continuous phase crystallizes after the dispersed aqueous phase. The materials used are two food-grade oil-soluble emulsifiers – polyglycerol polyricinoleate (PGPR) and glycerol monostearin (GMS) and two continuous oil phases with differing crystallization temperatures – canola oil and coconut oil. Emulsion stability is assessed with pulsed field gradient NMR droplet size analysis, sedimentation, microscopy and differential scanning calorimetry. This study demonstrates the sequence of crystallization events and the physical state of the surfactant at the oil–water interface strongly impact the freeze–thaw stability of water-in-oil emulsions.     

Effect of Emulsifier Type on the Characterization of O/W Emulsions Using a Spectroscopy Technique

The droplet size distribution (DSD) of emulsions is the result of two competitive effects that take place during emulsification process, i.e., drop breakup and drop coalescence, and it is influenced by the formulation and composition variables, i.e., nature and amount of emulsifier, mixing characteristics, and emulsion preparation, all of which affect the emulsion stability. The aim of this study is to characterize oil-in-water (O/W) emulsions (droplet size and stability) in terms of surfactant concentration and surfactant composition (sodium dodecyl benzene sulphonate (SDBS)/Tween 80 mixture). Ultraviolet-visible (UV-vis) transmission spectroscopy has been applied to obtain droplet size and stability of the emulsions and the verification of emulsion stability with the relative cleared volume technique (time required for a certain amount of emulsion to separate as a cleared phase). It is demonstrated that the DSD of the emulsions is a function of the oil concentration and the surfactant composition with higher stability for emulsions prepared with higher SDBS ratio and lower relative cleared volume with the time. Results also show that smaller oil droplets are generated with increasing Tween 80 ratio and emulsifier concentration.     

Stabilization of Water‐Soluble Antioxidant in Water‐in‐Oil‐in‐Water Double Emulsions

Abstract

In this study, we are introducing a method that can effectively stabilize antioxidants in water‐in‐oil‐in‐water (W/O/W) double emulsions. Preliminarily, stable W/O/W double emulsions were produced by manipulating the characteristics of internal aqueous phase via two‐stage emulsification, resulting consequently in the formation of fine internal water droplets in the dispersed oil droplets. From conductivity measurements that can determine the elution amount of internal aqueous phase, it was confirmed that the double emulsion stability could be improved by treating the internal aqueous phase with a hydroxypropyl‐beta‐cyclodextrin. In this study, kojic acid, 5‐hydroxy‐2‐(hydroxymethyl)‐4‐pyrone was selected as a model antioxidant. The stabilization of kojic acid was attempted by locating it in the internal water droplets of the stable W/O/W double emulsions. The stability of kojic acid in the double emulsion system could be maintained at 90% for 10 weeks at high temperature. We believe that these stable W/O/W double emulsions could be used meaningfully as a carrier for many unstable antioxidants.     

影响环氧树脂E-44相反转乳化的因素

研究了乳化剂的HLB值、乳化剂浓度、乳化温度、搅拌强度对环氧树脂E-44相反转乳化中临界含水量Rf值与乳状液稳定性的影响,探讨了环氧树脂E-44相反转机理。实验结果表明环氧树脂E-44从W/O向O/W相反转的发生与乳化剂的HLB值与浓度、乳化温度、搅拌强度等因素都有关,其Rf值随着乳化条件的不同是动态变化的。     

The effects of emulsifier type,phase ratio,and homogenization methods on stability of the double emulsion

The double emulsion technology has a potential effect on the development of diversity and quality of functional foods by means of decreasing oil or salt concentration, encapsulating and controlling release of valuable components. In this study, it was aimed to formulate stable double emulsions to be used in food systems. W1/O ratios of primary emulsions, stabilized by polyglycerol polyricinoleate (PGPR), were designed as 2:8 and 4:6, and (W1/O)/W2 ratios of the double emulsions were used as 2:8 and 4:6. W/O/W phase ratios, homogenization methods applied to primary emulsion (high-speed homogenization, ultrasonic homogenization), and emulsifier types used in W2 phase [sodium caseinate (SC), xanthan gum, lecithin-whey protein concentrate] were used as independent variables. Particle size and distributions, stability, encapsulation efficiency (EE), rheological properties, long-term stability, and morphological properties of the double emulsions were investigated.

The double emulsions prepared with SC and (W1/O)/W2 ratio of 4:6, were found to have the higher stability values, higher apparent viscosity, and lower particle size. High-speed homogenization applied to primary emulsion reduced particle size of the double emulsion and increased apparent viscosity, but did not affect stability and EE of the double emulsions, significantly.     

Phase Transitions in Emulsions Formed by Aqueous Emulsifier and its Action on Improving Mobility in Oil Recovery

Transition from oil-in-water (O/W) emulsions to water-in-oil (W/O) emulsions and its action on enhanced oil recovery was investigated by viscosity, morphology, and simulated flooding experiments. This transition can be realized by increasing the volume ratio of oil to water or decreasing the emulsifier concentration. At a mass concentration of 0.3 wt%, the self-developed emulsifier FJ-1 mainly forms O/W emulsions at a volume ratio (oil to water) of 1:1. The emulsions behave as O/W emulsions with a low viscosity when the volume ratio of oil to water is below 2:1. Above 2:1, increasing volume ratio leads to the O/W emulsions transferring into W/O emulsions with high viscosity. For example, at a volume fraction of 4:1, the viscosity of W/O emulsions reaches 229.1 mPa · s, and separated water can hardly be detected. Transition from O/W emulsions to W/O emulsions with high viscosity can also be realized by decreasing the concentration of emulsifier to 0.05 wt% or lower at a volume ratio of 1:1. These may be the critical factors leading to transition from O/W emulsions to W/O emulsions at core conditions. Simulated flooding experiments show that emulsifier fluids can act as an in situ mobility improver and make an improvement of oil recovery even by 20.4%. The results indicate that the water-in-crude-oil emulsions possess great potential in enhancing oil recovery.     

High internal phase emulsions: catastrophic phase inversion, stability, and triggered destabilization

We have investigated the formation, drop sizes, and stability of emulsions prepared by hand shaking in a closed vessel in which the emulsion is in contact with a single type of surface during its formation. The emulsions undergo catastrophic phase inversion from oil-in-water (o/w) to water-in-oil (w/o) as the oil volume fraction is increased. We find that the oil volume fraction required for catastrophic inversion exhibits a linear correlation with the oil-water-solid surface contact angle. W/o high internal phase emulsions (HIPEs) prepared in this way contain water drops of diameters in the range 10-100 μm; emulsion drop size depends on the surfactant concentration and method of preparation. W/o HIPEs with large water drops show water separation but w/o HIPEs with small water drops are stable with respect to water separation for more than 100 days. The destabilization of the w/o HIPEs can be triggered by either evaporation of the oil continuous phase or by contact the emulsion with a solid surface of the "wrong" wettability.     

KETAMINE-IN OIL-IN-WATER MULTIPLE EMULSION FOR PROLONGED DRUG RELEASE

A preparation of Ketamine [2-(Chlorophenyl)-2-(methylamino) cyclohexanone, C₁₃H₁₆ClNO, anesthetic agent] in oil in water multiple emulsion for prolonged drug release was formulated and evaluated. Ketamine, the cyclohexylamine, is used as a short-acting anaesthetic in humans and in some animal species [1]. Ketamine is poorly bound to plasma proteins and has a half-life of approximately 4 hours following intravenous injection [2]. Ketamine leaves the blood very rapidly to be distributed into the tissues with a high lipid solubility [2]. The recommended dosage of intravenous Ketamine is 2.5-20mg/kg [3]. The LD50 injected intraperitoneally in mice and rats is 100 times the intravenous and 30 times the intramuscular dose used in humans.

The objective of this study was to test the concept that a multiple emulsion could be formulated which has high porosity and lower viscosity at 37°C consistent with its intended use for sustained drug release and to prolong the half-life of the anesthesia. The results showed that the Ketamine (100mg/ml in inner phase) released 8.2% at 10 minutes, 67.0% at 30 minutes, and 95.5% at 60 minutes from the Ketamine/O/W multiple emulsion in a well-controlled manner.     

Temperature-induced phase separation in pseudoternary mixtures of Triton X-100–butanol–kerosene–water

The transparent Winsor IV domain in the phase diagram of the mixtures of emulsifier (Triton X-100 and butanol), oil (kerosene), and water is found to be 34% of the total phase diagram in presence of emulsifier with surfactant:cosurfactant::1:1, and is water dominant. Increase in cosurfactant/surfactant ratio inverts the Winsor IV domain to become oil rich. The plot of conductance of the microemulsions prepared by substituting water by brine against water content depicts the existence of three distinct phases like oil-in-water, bicontinuous, and water-in-oil microemulsion in the phase diagram. The phase contrast micrographs of the mixtures of different compositions in these three different phases reveal the existence of microdroplets of oil dispersed in water and water dispersed in oil. Further, the dynamic light scattering studies of these solutions reveal an inhomogeneity in the size distribution of the droplets. A temperature-induced clouding in the microemulsion domain leading to phase separation has been observed. Additives like glucose, sucrose, and sodium chloride decrease the cloud point (CP), while addition of ammonium thiocyanate increases it. A quantitative relationship of the clouding temperature with the composition of the microemulsion has been established. With increase in oil and emulsifier, the cloud point of the microemulsion increases. The separated phases after the clouding have been used for preconcentration of water-soluble metal ions as well as oil-soluble dyes. The turbid systems on heating led to separation into three isotropic phases which are found to be stable at ambient temperature. The stability of these phases is ascribed to the formation of stable microemulsions by mass transfer from one phase to other.     

A novel preparation method for microspheres by glycerol modified solid‐in‐oil‐in‐water multi‐emulsion

Biodegradable material poly(D, L ‐lactic‐co‐glycolic) acid (PLGA) plays an important role in drug‐sustained release systems. Here, we describe a glycerol modified solid‐in‐oil‐in‐water (m‐S/O/W) emulsion method for PLGA microspheres, in order to encapsulate proteins in PLGA by utilizing dextran glassy particles to protect the proteins from denaturing, unfolding, and aggregation during preparation and new external water phase to prevent the inner dextran glassy particles from leaking into the external water phase. External water phase containing 20, 40, 60, 80% glycerol showed that proteins released faster and more completely with increased glycerol content. According to their varied release profiles, microspheres of different formulations could be used to encapsulate vaccines or for delivering proteins over long‐term. Copyright © 2009 John Wiley & Sons, Ltd.     

Study on thermal induced phase inversion of concentratedO/W emulsions stabilized by various tween emulsifiers

Summary Thermal induced phase inversion of concentrated oil-in-water emulsions stabilized by various fatty acid polyoxyethylene esters of sorbitan (Tween 21, Tween 61, Tween 65, Tween 80 and Tween 81) has been studied. Phase inversion temperature (PIT) was determined by differential thermal analysis and the changes in internal structure of emulsions caused by heating were followed microscopically. The PITS obtained were dependent on the kind of Tween. When the emulsions were stabilized by Tween 65, the PIT also depended on whether the emulsifier was dissolved in water or in oil phase or in the both. Microscopic examination of the emulsions during heating showed that the appearance of water droplets within the oil drops, i.e. the development of a multiphase (W/O/W) emulsion structure precedes phase inversion.

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Zusammenfassung Die thermische Phaseninversion konzentrierter Öl-in-Wasser-Emulsionen (durch verschiedene Emulgatoren des Tween-Typs stabilisiert) wurde untersucht und die Phasen-inversionstemperatur durch Differentialthermoanalyse bestimmt.Die Phaseninversionstemperatur hängt von der Tweenart ab. Mit Tween 65 ist die Phaseninversionstemperatur auch davon abhängig, ob der Emulgator in Wasser, in Öl oder in beiden Phasen gelöst wird. Mikroskopische Untersuchungen haben gezeigt, daß Wassertröpfchen innerhalb der Öltropfen entstehen, d. h., daß die Entwicklung einer mehrphasigen Wasser-Ö1-Wasser-Struktur der Phaseninversion vorangeht.

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With 5 figures