Study of Liquid‐Crystalline Phase Changes during Evaporation in Vegetable Oil Emulsions

During evaporation, the rate between volatile and nonvolatile components in an emulsion changes. In this study, emulsions of marigold and canola oil were made according to a phase diagram, simulating the decreasing water amount that happens when the water evaporates from an emulsion. In addition, two basic emulsions were submitted to evaporation and then to microscopic analysis to compare the results of both tests. It was observed that when the water rate decreases, the liquid‐crystalline phase changes its organization, reaching a proportion that it is not hydrated anymore, having a solid aspect. Moreover, these emulsions submitted to evaporation remained to show lamellar phase even when there was no water in the formulation. This is interesting to understand the behavior of an emulsion after it is applied under the skin.     

Release of Mandelic Acid from O/W Emulsions with Lamellar Phases

The aim of this work was to prepare and to characterize stable O/W emulsions containing liquid crystals as vehicles of mandelic acid. Influence of some components on the behavior of the systems has been also studied. Particularly, the release of mandelic acid was compared from different formulations showing that the lamellar phases prolonged the active release and consequently they might reduce its irritation potential on the skin. Results of evaporation test suggested that lamellar phases contributed to increase the moisturizing action of these emulsions by limiting their water loss.     

Factors Affecting the Droplet Size of Water‐in‐Oil Emulsions (W/O) and the Oil Globule Size in Water‐in‐Oil‐in‐Water Emulsions (W/O/W)

Multiple emulsions of the W₁/O/W₂ type are promising tools for encapsulating bioactive ingredients in the inner aqueous droplets. It is necessary, however, to control the factors influencing their encapsulation efficiency. One important factor is the particle size because it determines the surface area available for mass transport. Because of the coexistence of water and oil droplets in multiple emulsions, there are numerous factors that have an impact on particle size, for example, oil phase composition, interfacial properties, and viscosity of the phases. The purpose of this study was to systematically investigate the effect of these factors on particle sizes in multiple emulsions.     

Viscosity Variation During Evaporation of a Vegetable Oil Emulsion Stabilized by Tween 80R

The viscosity during evaporation was determined for emulsions in the system water, vegetable oil, a commercial surfactant, Tween 80^R, and the results related to the phases of the emulsion according to the phase diagram. The correlation between the viscosity and the fraction of liquid crystal in the emulsion was pronounced for the emulsions with the oil as the dispersed phase. For the emulsions with oil as the major phase, the effect was significantly less.     

纳米粒子稳定乳液及其在纳米结构合成中的应用*

本文在介绍常规乳状液、微乳液和固体稳定乳液的基础上,着重综述了纳米粒子稳定乳液的特点及其在纳米结构合成中的应用进展,并对目前该研究领域亟待解决的问题进行了分析。纳米粒子稳定乳液具有独特的油、水、固三相环境和水油、水固、油固三个相界面,分散相液滴尺寸可以在微米、亚微米乃至纳米尺度调节,因而可以作为合成组成、结构和性能极为丰富多样的纳米结构的介质。纳米粒子对乳液稳定作用的机理,以及纳米粒子稳定乳液中化学反应的特殊规律还有待深入研究。本文在介绍固体稳定乳液的基础上,着重综述了纳米粒子稳定乳液的特点及其在纳米结构合成中的应用进展,并对目前该研究领域亟待解决的问题进行了分析。纳米粒子稳定乳液具有独特的油、水、固三相环境和水油、水固、油固三个相界面,分散相液滴尺寸可以在微米、亚微米乃至纳米尺度调节,因而可以作为合成组成、结构和性能极为丰富多样的纳米结构的介质。纳米粒子对乳液稳定作用的机理,以及纳米粒子稳定乳液中化学反应的特殊规律还有待深入研究。     

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.     

Composition Ripening in Mixed Water-in-Oil Emulsions Stabilized with Solid Particles

Water and oil transport in emulsified systems is far from being elucidated. Calorimetric analysis has proved to be an appropriate technique to study composition ripening in mixed water in oil emulsions. In this article, the role of the stabilizing agent is studied and particular attention is given to emulsions stabilized solely with solid particles. Mixed emulsions are prepared by mixing two simple water-in-oil (W/O) emulsions, one with pure water droplets and one with droplets containing an aqueous urea solution. At different time intervals, a sample is introduced in a calorimeter cell and submitted to successive cooling and heating cycles. During the cooling phase, the aqueous internal phase solidifies at a temperature which depends on its composition. Just after the mixed emulsion was prepared, the calorimetric experiment identified two solidification peaks, one corresponding to pure water droplets, and the other one to urea solutions. After a long enough stabilization time, just one peak was observed, showing that the systems evolved toward one type of droplets characterized by a unique composition, due to water transfer between the two aqueous phases. The effect of emulsion stabilizing agent (particles or nonionic emulsifier) on the kinetics of water transfer was investigated.     

Water‐in‐Crude Oil Emulsions in the Burgan Oilfield: Effects of Oil Aromaticity,Resins to Asphaltenes Content (R/(R+A)), and Water pH

Asphaltenes and resins separated from emulsion samples collected from Burgan oil field were used with heptane‐toluene mixtures as model oil to study the effect of oil aromaticity, resin content, and pH of the aqueous phase on the stability of water in model emulsions. It was confirmed that, as long as the asphaltenes are completely solubilized, increasing aromaticity leads to less stable emulsions. A consistent correlation between emulsion stability and relative resin mass content (R/(R+A)) was observed for all three of the field samples. There was a sharp decrease in stability when the R/(R+A) value exceeded 0.75. Emulsion stability was enhanced at high pH and possibly at very low pH (<2).     

Study on preparation and formation mechanism of n-alkanol/water emulsion using alpha-cyclodextrin

Surfactants are usually used for the preparation of emulsions; however, some have an adverse effect on the human body such as skin irritation, hemolysis, and protein denaturation, etc. In this study, we examined the preparation and formation mechanism of n-alkanol/water emulsions using alpha-cyclodextrin (alpha-CD) as an emulsifier. Emulsions were prepared by mixing oil and water phases for 4 min at 2500 rpm using a vortex mixer. The mechanism of emulsification was investigated with some physico-chemical techniques. From phase diagrams of n-alkanol/alpha-CD/water systems, the emulsion phase extended as the chain length of n-alkanols and the amount of alpha-CD added increased. Furthermore, the emulsion was not formed in the region where the n-alkanol/alpha-CD complex didn't precipitate; however, the emulsion was formed in the region where the complex precipitated. In addition, it was clear that the emulsions have a yield stress value and correspond to the Maxwell model from rheological measurement. Our experiments clearly showed that the stable emulsions are formed because the precipitated complexes form a dense film at the oil-water interface and prevent aggregation among dispersed phases. Furthermore, it is suggested that the creation of a three-dimensional network structure formed by precipitated complexes in the continuous phase contributes to the stabilization of the emulsion. Thus, we concluded that the n-alkanol/water emulsions using alpha-cyclodextrin were a kind of the Pickering emulsion.     

Microemulsification of triglyceride sebum and the role of interfacial structure on bicontinuous phase behavior

A unique triblock surfactant is reported that allows for the efficient microemulsification of triglycerides. Unlike the results of all previous efforts, these triglyceride microemulsions can be formed without the use of cosurfactants or dilution with co-oils and follow the classical patterns of surfactant phase behavior exhibited by mixtures of water, alkane oils, and nonionic oligoethylene glycol surfactants, i.e., progression from oil/water emulsions to one-phase microemulsions to water/oil emulsions with increasing temperature. Lamellar phases that usually dominate the aqueous phase behavior of surfactant/triglyceride mixtures are suppressed, allowing for the formation of single-phase microemulsions containing equal amounts of triglyceride and water. These isotropic and low-viscous fluids are particularly useful for cleansing and delivery of functional ingredients in skin care products. The effects of mixing a variety of typical skin care ingredients and components of sebum (skin oil) were also explored. Fatty acids significantly reduce the average microemulsion temperature, while other ingredients and oils, which do not partition at the oil/water interface, have less impact on the phase behavior. In all cases, one-phase microemulsions containing equal amounts of oil and water can be formed even at high additive concentrations. Indeed, partial replacement oftriglyceride with any of the additives examined consistently reduced the amount of surfactant necessary to form single-phase microemulsions. However, the greatest boost in surfactant efficiency was found with the addition of medium molecular weight amphiphilic block copolymers.     

After‐Rinsing Hair Growth Promotions of Hinokitiol‐Containing Vesicles and Emulsions

Two kinds of topical dosage forms of hinokitiol (HKL), namely vesicles and oil‐in‐water (O/W) emulsions, were prepared. Behenyl trimethylammonium chloride (BTMAC) and fatty acids were used as bilayer‐forming materials of the vesicles, and oils were employed as oil phases of the emulsions. The substantivity of HKL in the preparations was evaluated in vitro using hairless mouse skins. After applying the preparations onto the skin and rinsing it, the amount of HKL left on the skin was determined using high performance liquid chromatography (HPLC). It was higher when HKL was encapsulated in cationic vesicles rather than in nonionic vehicles, emulsions. An ionic interaction between the cationic vehicle and negatively charged skin is likely to account for the high substantivity. Among the emulsion preparations, an emulsion having octyl salicylate as oil phase exhibited the highest substantivity of HKL. This is probably because that the oil is a good solvent for HKL and it is skin‐retentive. In vivo hair growth‐promotion effect of each dosage form was investigated, where the sample application onto the clipped backs of female mice (C57BL6) and the subsequent rinsing of the backs were done once a day for 30 days. Only HKL in the cationic vesicles had hair growth promotion effect, possibly due to the significant substantivity.     

壬基酚聚氧乙烯醚在油相中的CMCo及相关问题研究

对壬基酚聚氧乙烯醚在油相中的临界胶束浓度(CMC_o)及与之相关的问题进行了研究,并获得了部分CMC_o值.对CMC_o与表面活性剂自身结构的关系进行分析和数学处理后,发现CMC_o与活性物质自身结构间仍为对数关系.同时在对某些具体体系的界面张力随表面活性剂不同而发生的变化进行了详细分析,发现CMC_w和CMC_o是评价表面活性剂性能的有效工具.     

Evaporation rates of water from concentrated oil-in-water emulsions

We have investigated the rate of water evaporation from concentrated oil-in-water (o/w) emulsions containing an involatile oil. Evaporation of the water continuous phase causes compression of the emulsion with progressive distortion of the oil drops and thinning of the water films separating them. Theoretically, the vapor pressure of water is sensitive to the interdroplet interactions, which are a function of the film thickness. Three main possible situations are considered. First, under conditions when the evaporation rate is controlled by mass transfer across the stagnant vapor phase, model calculations show that evaporation can, in principle, be slowed by repulsive interdroplet interactions. However, significant retardation requires very strong repulsive forces acting over large separations for typical emulsion drop sizes. Second, water evaporation may be limited by diffusion in the network of water films within the emulsion. In this situation, water loss by evaporation from the emulsion surface leads to a gradient in the water concentration (and in the water film thickness). Third, compression of the drops may lead to coalescence of the emulsion drops and the formation of a macroscopic oil film at the emulsion surface, which serves to prevent further water evaporation. Water mass-loss curves have been measured for silicone o/w emulsions stabilized by the anionic surfactant SDS as a function of the water content, the thickness of the stagnant vapor-phase layer, and the concentration of electrolyte in the aqueous phase, and the results are discussed in terms of the three possible scenarios just described. In systems with added salt, water evaporation virtually ceases before all the water present is lost, probably as a result of oil-drop coalescence resulting in the formation of a water-impermeable oil film at the emulsion surface.     

Quantitative determination of alpha-tocopherol distribution in a tributyrin/Brij 30/water model food emulsion

Until recently, determining the distribution of antioxidants, AOs, between the oil, interfacial and aqueous regions of opaque emulsions has not worked well because the concentrations of AOs in interfacial regions cannot be determined separately from their concentrations in the oil and water phases. However, our novel kinetic method based on the reaction between an arenediazonium ion and vitamin E, or alpha-tocopherol, provides the first good estimates for the two partition constants that describe alpha-tocopherol distribution between the oil/interfacial and water/interfacial regions of tributyrin/Brij 30/water emulsions without physical isolation of any phase. The reaction is monitored by a new derivatization method based on trapping unreacted arenediazonium ion as an azo dye and confirmed by linear sweep voltammetry, LSV. The results by both derivatization and LSV methods are in good agreement and show that alpha-tocopherol distributes strongly in favor of the interfacial region when the oil is tributyrin, e.g., ca. 90% when the surfactant volume fraction is Phi I=0.01. The second-order rate constant for reaction in the interfacial region is also obtained from the results. Our kinetic method provides a robust approach for determining antioxidant distributions in emulsions and should help develop a quantitative interpretation of antioxidant efficiency in emulsions.     

An Experimental Study on the Viscosity of Water-in-Oil Emulsions

Water-in-oil (W/O) emulsions are very common in the petroleum industry, and their viscosities are the principle parameters for the operation design. Typical correlations composed by one or two factors cannot always fit the apparent viscosity of W/O emulsions very well, especially when applied to the crude oil/water emulsions. The viscosities of W/O emulsions, which were made from three kinds of crude oil, were measured by Anton Paar MCR302 viscometer at atmospheric pressure with different temperatures as well as shear rates. The experiment results indicate that W/O emulsion would exhibit Newtonian characteristic when water content is no higher than 0.2 and non-Newtonian characteristic otherwise. According to the experimental data, a modified correlation based on the Broughton–Squires model and Ronningsen model was introduced to predict the viscosity of W/O emulsions, and the comparison results showed that the new modified correlation has better accuracy than the original models.     

W/O/W多重乳液中水传递的控制

建立了简化的W/O/W(水/油/水)多重乳液乳珠模型——统计平均半径模型, 预测出当W/O/W多重乳液内水相水滴之间以及内外水相之间均达到水传递平衡时的内外水相中盐的浓度, 从而实现对水传递的控制, 以维持W/O/W多重乳液的稳定. 按理论预测制备出了不同稳定态的W/O/W多重乳液, 利用差分扫描量热仪(DSC)检测了多重乳液中水的传递过程, 确定体系在实验状态下的稳定程度, 实验结果与理论预测基本吻合.     

Effect of oil phase transition on freeze/thaw-induced demulsification of water-in-oil emulsions

Recently, there has been an increasing interest in the breakage of water-in-oil (W/O) emulsions by the freeze/thaw method. Most of the previous works focused on the phase transition of the water droplet phase. This paper emphasizes the effect of continuous oil phase transition. A series of oils with different freezing points were used as oil phases to produce model emulsions, which were then frozen and thawed. The emulsion whose oil phase froze before the water droplet phase did (OFBW) on cooling was readily demulsified with a dewatering ratio as high as over 80%, but the emulsion whose oil phase did not freeze when the water droplet phase did (NOFBW) was relatively hard to break. The difference in demulsification performance between them resulted from the distinction between their demulsification mechanisms via the analyses of the emulsion stability, emulsion crystallization/melting behaviors, oil phase physical properties, and wettability of the frozen oil phase, etc. For the OFBW emulsion, the first-frozen oil phase was ruptured by the volume expansion of the subsequently frozen droplet phase, and meanwhile, some liquid droplet phase was drawn into the fine gaps/crevices of the frozen oil phase to bridge droplets, which were considered to be essential to the emulsion breakage, whereas for the NOFBW emulsion, the demulsification was attributed to the collision mechanism proposed in our previous work. The findings may provide some criteria for selecting a proper oil phase in the emulsion liquid membrane (ELM) process and then offer an alternative approach to recycle the oil phase for continuous operation. This work may also be useful for emulsion stability against temperature cycling.     

Magnetically Recoverable Efficient Demulsifier for Water‐in‐Oil Emulsions

A magnetically recoverable and efficient demulsifier is shown to demulsify surfactant‐stable water‐in‐oil emulsions rapidly. Ferroferric oxide (Fe₃O₄) particles are firstly coated by amorphous silicon dioxide (SiO₂), and further functionalized with a commercial dodecyltrimethoxysilane solution (KH‐1231). Owing to their paramagnetic properties, the demulsifier particles can be easily recovered with a magnet. Upon addition of demulsifier to emulsions and subsequent sonification, the supernatant becomes completely transparent and no droplets are observed in the micrographs. It was also demonstrated that this demulsifier is effective for emulsions prepared with a variety of oils. Moreover, magnetically recovered demulsifier can be recycled after simple treatment without any decline of efficiency. This work presents a feasible approach for demulsifying water‐in‐oil emulsions, and has potential value in industry.     

FLOW PROPERTIES OF WEATHERED CRUDE OILS AND THEIR EMULSIONS

The present paper proposes the emulsification of weathered crude oils in water as a competitive and cost effective method for reducing their viscosities. Weathered crude oil samples were collected from major Kuwaiti oil lakes. Emulsion preparation involved using, either a nonionic surfactant or alkali, as well as both alkali and fatty acid. The obtained emulsions were characterized by measuring the droplet size distribution of the dispersed phase using optical microscopy. Emulsion stability was also examined in terms of the system breakdown. The rheological properties were measured using a concentric cylinder rotary rheometer. The emulsion rheological behavior has been studied as a function of composition, temperature, and shear rate. A constitutive model was developed to characterize the pseudoplastic behavior of the crude oil and the emulsion systems. The model fitted well the experimental results with a correlation coefficient higher than 95%. Associated with the pseudoplastic behavior, viscoelastic behavior has been observed with emulsions and some oils at high shear rates.

The results of this investigation indicated that the examined weathered crude oils can be transported through pipelines as emulsions of up to 80 vol.% oil concentrations. The proposed method of treatment with NaOH and oleic acid offers several advantages over the surfactant treatment. It exhibited comparable rheological behavior at lower cost and less mixing energy. It also provided higher emulsion stability, which favors oil transportation for longer distances.     

RELEASE OF VOLATILES FROM CUBIC PHASES: MONITORING BY GAS SENSORS

Structured fluids such as emulsions and liquid crystalline mesophases can be used to control aroma release

This study shows that the use of a gas sensor array coupled with pattern recognition analysis can be particularly useful in studying volatile profiles

A mixture of 8 carefully selected volatile, hydrophilic and hydrophobic compounds was entrapped in 4 different matrices: water, lipids (sunflower oil, unsaturated monoglycerides), emulsion (20% wt water) and cubic phases (20 and 3% wt water)

A clear discrimination between the release pattern of the different matrices has been measured by the sensor array system. It has been shown that the cubic phase release patterns is not only controlled by its composition but also depended strongly on ihe lipid/water interfacial area

The combined use of structured fluids (structure-release relationship) and sensor arrays allows to control and to distinguish the release patterns of volatile.