Application of the fractional factorial design in multiple W/O/W emulsions

In presented research, multiple W/O/W emulsions were developed by using experimental design method. A 24-1 fractional factorial design was performed by varying the following input parameters: primary polymeric emulsifier (PEG 30-dipolyhydroxystearate) concentration (0.8% and 2.4%), secondary polymeric emulsifier (Poloxamer 407) concentration (0.8% and 1.2%), electrolyte magnesium sulfate heptahydrate (0.08% and 0.4%) and electrolyte sodium chloride (0.08% and 0.4%). Multiple emulsions were prepared by a two-step emulsification process. Obtained emulsions were characterized with rheological measurements, conductivity and centrifugation tests. Factorial analysis revealed that the concentration of the primary emulsifier was the predominant factor influencing the phase separation, conductivity and maximal apparent viscosity. Additionally, electrolyte magnesium sulfate heptahydrate was more efficient in stabilizing these systems, compared to sodium chloride. The applied fractional factorial design method enabled determination of the optimal concentrations of the primary and secondary emulsifier, as well as the concentration of electrolytes, in order to obtain W/O/W emulsions with desired maximal apparent viscosities, low values of conductivity and without phase separation after centrifugation.     

Emulsification properties of chitosan

 The chitosans use as an emulsifier in food emulsions was explored. The properties of chitosan (air/solution surface activity, electrical conductivity, HLB) were studied. The obtained emulsions were stable multiple w/o/w emulsions, whose characteristics were explained on the basis of the emulsifier structure and solution properties. The reaction with an anionic surfactant, sodium dodecylsulfate, was also studied, giving a water-insoluble complex at a given surfactant/chitosan ratio. Received: 24 March 1998 Accepted: 13 July 1998     

反相乳液共聚合制备两性丙烯酰胺共聚物的研究

采用Span80-Tween80复合乳化剂和AIBA引发剂,进行丙烯酸钠(NaAA)/丙烯酰胺(AM)/丙烯酰氧基乙基三甲基氯化铵(DAC)反相乳液共聚合.研究了聚合温度、引发剂用量、单体浓度、共聚单体中DAC和AM含量、乳化剂用量及其HLB值、水/油比和水相pH值等聚合反应工艺条件或参数对聚合反应单体转化率和聚合物特性粘度的影响,聚合物特性粘度随引发剂用量和单体浓度的增大而增大的实验结果证实了该两性丙烯酰胺共聚物反相乳液制备过程中凝胶效应的存在.傅立叶红外光谱组成分析表明了两性丙烯酰胺共聚物的成功合成,扫描电镜观测乳胶粒粒径范围在0.6~8.0μm.     

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.     

Preparation of waterborne dispersions of epoxy resin by the phase-inversion emulsification technique. 1. Experimental study on the phase-inversion process

 Waterborne dispersions of bisphenol A epoxy resin were prepared by the so-called phase-inversion emulsification technique. The electrical properties, rheological behavior and morphological evolution during the phase inversion process were characterized systematically. It was shown that both emulsifier concentration and emulsification temperature play great roles in controlling the phase inversion process as well as the structural features of the waterborne particles. A high emulsifier concentration, i.e. 10.90 wt% and a low emulsification temperature, i.e. 73 °C, facilitate complete phase inversion, in which all water droplets in the system are simultaneously transformed into the continuous phase at the phase-inversion point (PIP). In this case, sub-micron-sized, discrete waterborne particles were formed. In contrast, a complex water-in-oil-in-water structure was achieved by incomplete phase inversion at a low emulsifier concentration, i.e. 2.33 wt%, and a high temperature of 80 °C. The morphological evolution observed by scanning electron microscopy revealed that not all the water droplets in the system were converted into the continuous phase at the PIP and that some small water drops were trapped within the waterborne structure. Received: 15 March 2000/Accepted: 16 May 2000     

Effect of calcium salts and surfactant concentration on the stability of water-in-oil (w/o) emulsions prepared with polyglycerol polyricinoleate

The objective of this work was to obtain water-in-oil (w/o) emulsions with polyglycerol polyricinoleate (PGPR) as emulsifier and to study the effect of the addition of calcium in the dispersed aqueous phase on the stability of these systems. Emulsions were formulated with 0.2, 0.5 and 1.0% w/w PGPR and 10% w/w water containing calcium chloride at varied concentrations or other salts (calcium lactate or carbonate; sodium, magnesium or potassium chloride). The stability of these systems was studied with a vertical scan analyzer during 15 days; coalescence and sedimentation were observed as simultaneous destabilization processes. The increase of PGPR concentration and/or calcium chloride content gave more stable emulsions. The stabilizing effect of calcium salt was attributed to the diminution of the water droplets size, the decrease of the attractive force between water droplets and the increase of the adsorption density of the emulsifier. The viscoelastic parameters of the interfacial film were decreased with increasing calcium and PGPR concentrations. Calcium chloride produced a higher increase of stability than calcium salts with lower dissociation degree. The presence of any assayed salt in the aqueous phase also allowed the stabilization of w/o emulsions with higher water contents.     

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.     

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     

Impact of Tween 60 on physicochemical properties and stability of Pistacia lentiscus fruit oil-in-water emulsion at a semi-low temperature

This study shows the effects of the Tween 60 emulsifier at different concentrations on the aqueous emulsion containing 5% of Pistacia lentiscus fruit oil. The rheological behavior and the droplet size distribution of cosmetic oil-in-water emulsions were investigated. This investigation was carried out by analyzing the shear flow and dynamic oscillatory followed by microscopic analysis and physical stability study for 24?hours and 4 months. During the period of 4 months, the emulsions were stored in a refrigerator at a semi-low temperature 12?°C. The physical stability test showed that the sample not emulsified yielded a creaming process after a short aging time. Flow curves of emulsions prepared with TW 60 exhibited a non-linear relationship between the shear stress σ and shear rate γ ?, which implies that the Herschel–Bulkley rheological model was the appropriate model for the shear flow. The increase of emulsifier quantities leading to an increase in the internal structure coherence, whereas the excess quantity affects the structure. Therefore, the optimal quantity proposed was 3.47%. Furthermore, the storage time at a semi-low temperature performed the stability and maintain the structure of emulsions.     

Analysis of an Emulsification Process Using Fractional Experimental Design

ABSTRACT

Soy oil-in-water emulsions (30% oil) with soy lecithin as emulsifier (4%) were prepared using a stirred vessel under batch conditions. The effects of 7 process variables (impeller-to-tank diameter ratio, temperature, agitation speed, mode of cooling and also pre-emulsification mixing rate, pre-emulsification mixing time and resting time before emulsification) were studied according to a fractional factorial design 2^7?3. The droplet size distributions of the emulsions were measured and the kinetics of destabilization were monitored during 3 months. In the experimental domain, the mixing rate was found to be the most significant variable affecting both the size distribution and the stability. It was followed by the temperature, and the impeller-to-tank ratio depending on the Sauter mean diameter or the half-life time of the emulsions. Interaction of the temperature with the agitation speed and with the impeller-to-tank diameter ratio was also observed.     

Premix Membrane Emulsification: Preparation and Stability of Medium-Chain Triglyceride Emulsions with Droplet Sizes below 100 nm

Premix membrane emulsification is a promising method for the production of colloidal oil-in-water emulsions as drug carrier systems for intravenous administration. The present study investigated the possibility of preparing medium-chain triglyceride emulsions with a mean particle size below 100 nm and a narrow particle size distribution using sucrose laurate as an emulsifier. To manufacture the emulsions, a coarse pre-emulsion was repeatedly extruded through alumina membranes (Anodisc^™) of 200 nm, 100 nm and 20 nm nominal pore size. When Anodisc^™ membranes with 20 nm pore size were employed, nanoemulsions with z-average diameters of about 50 nm to 90 nm and polydispersity indices smaller than 0.08 could be obtained. Particle growth due to Ostwald ripening was observed over 18 weeks of storage. The Ostwald ripening rate linearly depended on the emulsifier concentration and the concentration of free emulsifier, indicating that micelles in the aqueous phase accelerated the Ostwald ripening process. Long-term stability of the nanoemulsions could be achieved by using a minimised emulsifier concentration or by osmotic stabilisation with soybean oil added in a mass ratio of 1:1 to the lipid phase.     

乳化剂对丙烯酰胺反相乳液共聚合的影响

丙烯酰亚胺乙酯基三甲基氯化铵;乳化剂;乳化剂对丙烯酰胺反相乳液共聚合的影响     

Sandwich structures at oil-water interfaces under alkaline conditions

Equilibrium liquid crystal (LC) layer on an interface between crude oils and water was observed at high pH. This layer is composed mainly of sodium naphthenates produced in situ at the water/oil interface. Transient LC layer was also evolved at the interface of aqueous phase of sodium hydroxide solutions and oleic phase of naphthenic acid (NA) solutions as result of a chemical reaction between NaOH and NA. This chemical reaction causes transport process resulting in a disturbance of the interface. Optical observation of this interface disturbance reviled that the interface covered with LC shows considerably lower flexibility as compared to LC free interface. The LC layer eventually dissolves in the water phase at low oil-to-water ratio, while at high oil-to-water ratio it can form an equilibrium phase, which spreads spontaneously at the oil-water interface.     

St-BA copolymer emulsions prepared by using novel cationic maleic dialkyl polymerizable emulsifier

A novel polymerizable cationic dialkyl maleic emulsifier with 12 carbon atomic hydrophobic chain lengths (R = C₁₂H₂₅) as well as a similar conventional cationic emulsifier, cetyltrimethyl ammonium bromide (CTAB) as comparison, were investigated in batch emulsion copolymerization of styrene and butyl acrylate. A series of emulsion samples have been prepared with two kinds of emulsifiers, and their properties have been characterized and compared. Compared with the emulsions prepared by using cationic CTAB emulsifier, the emulsions prepared by using maleic emulsifier have larger particle size, higher surface tension, generally more stable on certain electrolytes and less water absorption ratio as 34.87% after 30 days vs. 50.65% for the emulsion containing CTAB emulsifier. Whereas, the maleic emulsifier itself has lower CMC and surface tension compared with cationic CTAB emulsifier.     

A dynamic light scattering study of the influence of the phospholipid concentration in a model perfluorocarbon emulsion

Perfluorohexyl iodide in water emulsions stabilised by phospholipids were prepared by microfluidisation. Photon correlation spectroscopy revealed that the particle size distributions of these emulsions were bimodal. Centrifugation experiments indicated that the larger mode was caused by the emulsion droplets, whereas the smaller mode was due to phospholipid vesicles formed from the excess amount of phospholipid emulsifier. Comparing the particle size distributions of perfluorocarbon emulsions containing different amounts of phospholipids, it could be concluded that emulsions with a phospholipid/fluorocarbon ratio of 2% at the most were emulsifier limited, whereas those with a ratio of at least 5% were energy input limited.     

Performance of a rotating membrane emulsifier for production of coarse droplets

A versatile and high capacity membrane emulsification system which utilises a rotating membrane for the precision manufacture of oil-in-water (o/w) emulsions is investigated. The o/w emulsions produced used a low viscosity paraffin wax as the dispersed phase, Tween 20 or sodium dodecyl sulphate (SDS) as the emulsifier and carbomer as the stabiliser, respectively. The ability to generate coarse monodisperse emulsions was demonstrated with droplets of average diameter 80–570 μm and coefficient of variation ranging from 9.8% to 33.6%. The effects of key process parameters on the droplet size and distribution are discussed, including requirements for future developments of the membrane.     

Phase transitions in O/W lauryl acrylate emulsions during phase inversion,studied by light microscopy and cryo-TEM

Phase changes during the preparation of nano-emulsions containing polymerizable monomer as the oil phase, by the phase inversion temperature technique (PIT), were investigated using light microscopy, cryo-TEM and viscosity measurements. The nano-emulsions were prepared using a poly(oxyethylene) nonionic surfactant and a polymerizable acrylic monomer (lauryl acrylate) as the oil phase. Inversion of the emulsion, followed by rapid cooling, resulted in emulsions having an average droplet size as low as 25 nm. Cryo-TEM was used to observe the structures that are present above and below the phase transition temperature, and gave, for the first time, visual indication of the presence of a microemulsion and a locally ordered structure in the process. At high surfactant concentrations, the inversion–cooling process yields emulsions with unique structures, in which the oil phase is present as worm-like structures.     

Highly Concentrated Emulsions: Physicochemical Principles of Formulation

This review deals with the preparation, stability, rheology and different applications of highly concentrated emulsions. These emulsions, which are known as high internal phase ratio emulsions (HIPRE), gel-emulsions, biliquid foams, etc., containing over 90% internal phase by volume, have a swollen micellar (L₁ or L₂) solution of nonionic or ionic surfactants as a continuous phase. These emulsions have the structure of biliquid foams and behave as gels since they present viscoelastic and plastic properties. The functional macroscopic properties of gel-emulsions are dependent on the structural parameters of the microemulsion continuous phase as well as of the interfacial properties (interfacial tension, bending modules, spontaneous curvature) of surfactant monolayers. The depletion interaction between emulsion droplets due to the non-compensated osmotic pressure of micelles is revealed as a main factor, along with surface forces, which determine the aggregative stability and the rheological properties of these emulsions. The effect of electrolyte and surfactant concentration, temperature, as well as other physicochemical parameters on the fiocculation threshold, stability, and yielding properties of highly concentrated emulsions is explained by the effect of these parameters on the critical micelle concentration (CMC) and the aggregation number of surfactants, and, consequently, on the depletion interaction. The thermodynamic theory of adhesion of fluid droplets in micellar solution and the suggested model of elasticity of gel-emulsions permit to explain the effect of mentioned physicochemical parameters on the elasticity modulus, the plastic strength and the linear deformation of these emulsions. A novel mechanism for the spontaneous formation of gel-emulsions by the phase inversion temperature (PIT) route is suggested, allows the selection of ternary systems able to yield these emulsions, and explains how the droplet size can be controlled during the PIT process. An original model for liquid film rupture is also suggested, and allows the prediction of the effect of structural parameters of micellar solutions and the interfacial properties of surfactant monolayers on the stability of gel-emulsions.     

含氟丙烯酸酯三元共聚物乳液的研究

以丙烯酸全氟烷基酯 (ZonylTM)、甲基丙烯酸甲酯 (MMA)、丙烯酸丁酯 (BA)为原料 ,在阴离子乳化体系中制备了含氟丙烯酸三元共聚物乳液 .研究了聚合反应动力学、转化率的各种影响因素 ,得出了聚合速率方程 ,并得出反应的表观活化能 (Ea)为 5 0 75 8kJ mol.考察了乳液的稀释稳定性、贮存稳定性、离心稳定性、耐热、耐寒稳定性 ,及乳胶膜的吸水性和耐溶剂性 .并用Wilhelmy方法测定了乳胶膜与水的接触角 ,结果表明乳胶膜对水的抗浸润力大大提高     

Rapid Evaluation of Water-in-Oil (w/o) Emulsion Stability by Turbidity Ratio Measurements

In this Note, we investigated the turbidity ratio method for the evaluation of water-in-oil emulsion stability. The slope of turbidity ratio of water-in-oil emulsions with time was taken as an index of stability; the higher the slope, the less stable the system. Various factors affecting the stability of emulsion such as HLB of emulsifier, amount of emulsifiers, and water were tested using this technique. The results of the turbidity ratio technique for the evaluation of emulsion stability were well consistent with those obtained by the measurement of phase separation when incubated for 30 days at room temperature. Copyright 2000 Academic Press.