Microemulsion In Equilibrium Research Articles

Effect of polymer addition on the phase behavior of oil-water-surfactant systems of Winsor III type.

Ternary oil-water-surfactant systems can give rise to an O/W microemulsion in equilibrium with excess oil, a W/O microemulsion in equilibrium with excess water, or a bicontinuous microemulsion in equilibrium with excess oil and water. This type of phase behavior has been known for a long time and the three systems are often referred to as Winsor I, Winsor II and Winsor III, respectively after the British scientist P. A. Winsor who pioneered the area. The Winsor systems are technically important and well understood today. It was later found that addition of a polymer to the oil-water-surfactant system can influence the phase behavior considerably. While a hydrophilic polymer will be incorporated in the water phase and a hydrophobic polymer in the oil phase, an amphiphilic polymer with the right hydrophilic-lipophilic balance may expand the middle phase microemulsion in a Winsor III system. Expansion of the middle phase of such a system will lead to a reduction of the oil/microemulsion and the microemulsion/water interfacial tensions. This can be practically important, and the effect is currently of considerable interest for so-called surfactant flooding for enhanced oil recovery (EOR). Boosting the middle phase of the Winsor III system by addition of a polymer to the surfactant system is still not an established procedure and not so well understood from a scientific point of view. In this review we summarize the work done in the field and we demonstrate that the role of the polymer is intimately linked to its interactions with the three other components in the system: the oil, the water, and the surfactant(s).

글리시돌을 원료로 한 비이온 계면활성제 합성에 관한 연구

글리시돌과 라우릭산으로부터 PGLE와 PGLE3 비이온 계면활성제를 합성하였으며, 합성한 계면활성제들의 구조를 <TEX>$^1H$</TEX> 및 <TEX>$^{13}C$</TEX> NMR 분석을 통하여 확인하였다. PGLE와 PGLE3 비이온 계면활성제의 CMC는 각각 <TEX>$3.59{\times}10^{-2}$</TEX> mol/L, <TEX>$8.80{\times}10^{-1}$</TEX> mol/L이며, CMC에서의 표면장력 값은 각각 26.09 mN/m과 28.68 mN/m이었다. 동적 표면장력 측정 결과에 의하면 PGLE와 PGLE3 비이온 계면활성제 모두, 공기와 수용액의 계면이 계면활성제 단분자에 의하여 비교적 짧은 시간 내에 포화되었으며, 1 wt% PGLE와 PGLE3 계면활성제 시스템들의 접촉각은 각각 <TEX>$25.5^{\circ}$</TEX>와 <TEX>$9.5^{\circ}$</TEX> 나타내었다. 비극성 오일 n-decane과 1 wt% 계면활성제 수용액 사이의 계면장력은 시간에 따라 감소하며, PGLE와 PGLE3 시스템 모두 20분 이내에 평형에 도달하였고, 평형에서의 계면장력 값은 각각 0.42 mN/m와 0.53 mN/m를 나타내었다. PGLE 비이온 계면활성제가 PGLE3 비이온 계면활성제에 비하여 거품 안정성이 큼을 확인하였으며, 이러한 거품 안정성 측정 결과는 표면장력 측정 결과와도 일치하였다. 계면활성제, 물, 비극성 탄화수소 오일로 이루어진 3성분 시스템에 보조계면활성제를 첨가하여 <TEX>$25{\sim}60^{\circ}C$</TEX>의 온도에서 상평형 실험을 수행한 결과, lower phase 마이크로에멀젼 혹은 oil in water 마이크로에멀젼이 excess oil 상과 평형을 이루는 2상 영역만이 관찰되었다. The PGLE and PGLE3 nonionic surfactants were synthesized from the reaction between glycidol and lauryl acid and their structures were confirmed by <TEX>$^1H$</TEX> and <TEX>$^{13}C$</TEX> NMR analysis. The CMCs of PGLE and PGLE3 surfactants were found to be <TEX>$3.59{\times}10^{-2}$</TEX> mol/L and <TEX>$8.80{\times}10^{-2}$</TEX> mol/L respectively and the surface tensions at their CMC conditions were 26.09 mN/m and 28.68 mN/m respectively. Dynamic surface tension measurement has shown that the adsorption rate of surfactant molecules at the interface between air and surfactant solution was found to be relatively fast in both surfactant systems, presumably due to high mobility of surfactant molecules. The contact angles of PGLE and PGLE3 nonionic surfactants were <TEX>$25.5^{\circ}$</TEX> and <TEX>$9.5^{\circ}$</TEX> respectively. Dynamic interfacial tension measurement showed that both surfactant systems reached equilibrium in 20 minutes and the interfacial tensions at equilibrium condition in both systems were 0.42 mN/m and 0.53 mN/m respectively. The PGLE surfactant system has indicated higher foam stability than the PGLE3 surfactant system, which is consistent with surface tension measurement. The phase behavior experiments performed at <TEX>$25{\sim}60^{\circ}C$</TEX> in systems containing nonionic surfactant, water, n-hydrocarbon oil and cosurfactant showed a lower phase or oil in water microemulsion in equilibrium with excess oil phase at all conditions investigated during this study.

Classification of Fragrances and Fragrance Mixtures Based on Interfacial Solubilization

AbstractIn the present study, the influence of perfumes on the interfacial curvature of microemulsions is investigated. The hydrophilic‐lipophilic deviation (HLD) concept was applied to nonionic Winsor I type systems (O/W microemulsions in equilibrium with an oil excess phase) containing a mixture of oils with isopropyl myristate as supporting oil and a variety of liquid solutes as co‐oil for which an Equivalent Alkane Carbon Number of the mixture (EACNmix) was defined. Temperature was used as a formulation variable and the phase inversion temperature change, provoked by the solubilization of different solutes, was determined. The hydrodynamic radius of the droplet and the interfacial solubilization of fragrances were measured subsequently and correlated to the EACNmix. In a first step, selected perfumery raw materials (PRMs) were used as solutes and were studied separately. It was demonstrated that the PRMs can be classified in interfacial solubility according to their chemical functionalities and they follow the order alcohols &gt; aldehydes &gt; terpenes &gt; aromatics &gt; alkanes. Solutes that lead to low EACNmix values (&lt;6) have preferential interfacial solubility and provoke strong curvature changes, whereas those leading to higher EACN values (&gt;6) typically do not change the curvature significantly. The HLD method was also applied to complex fragrances and it was demonstrated that they can be considered as single, non‐polar entities, and studied as such instead of investigating each raw material included in the composition separately. Determination of the dimensionless number EACNmix offers the possibility of classifying perfumes in an environment similar to surfactant formulations of typical consumer products and to predict the interaction with the surfactant base according to the rules established on the basis of the individual raw materials.

Influence of nanoparticle addition to Winsor surfactant microemulsion systems

The influence of adding negatively charged silica nanoparticles to multiphase Winsor microemulsion systems of cationic surfactant/alcohol cosurfactant is reported. It is found that the particles do not change the salt-induced progression of Winsor systems to any great extent, even when added at the same concentration as the surfactant. We find that all of the particles transfer from water where they originate to oil at all salt concentrations, although the distribution of surfactant between phases is unaffected. It is ascertained that alcohol addition renders particles more hydrophobic promoting this transfer. Emulsions prepared from the equilibrium microemulsion and excess phase(s) invert from oil-in-water to water-in-oil with increasing salt concentration, such that the continuous phase is the one containing the surfactant aggregates. Their stability to coalescence is extremely low, due to mainly the ultralow tensions at the oil–water interface. Particle addition does not alter the emulsion stability, implying that they are not adsorbed to drop interfaces.

Formation of 10−100 nm Size-Controlled Emulsions through a Sub-PIT Cycle

We have re-examined the phase inversion temperature (PIT) emulsification process. This is a low-energy method that uses a physicochemical drive to produce very fine oil/water emulsions in the absence of high shear flows. We used the polyoxyethylene 8 cetyl ether (C(16)E(8))/hexadecane/water system, which has a PIT of 76.2 degrees C. We find that successful emulsification depends on two conditions. First, the mixture must be stirred at low speed throughout the whole process: this makes it possible to produce emulsions at surfactant concentrations that are too low to form an equilibrium microemulsion. Second, the stirred mixtures must be heated above a threshold called the clearing boundary (CB) and then quenched to lower temperatures. The clearing boundary is determined experimentally by a minimum in the turbidity of the stirred mixture, which results from solubilization of all the oil into swollen micelles. This matches the emulsification failure boundary, and it is expressed mathematically by the condition R*C(0) = 1, where R* is the radius that results from the oil/surfactant composition for monodisperse spheres and C(0) is the spontaneous spherical curvature of the surfactant. Thus, we show that such cycles do not need to cross the PIT. In fact, sub-PIT cycles and cross-PIT cycles give exactly the same result. These conditions lead to emulsions that have a narrow size distribution and a mean diameter controlled by the oil/surfactant ratio. The typical range of those diameters is 20-100 nm. Moreover, these emulsions have an excellent metastability, in contrast with emulsions made with shorter oil and surfactant molecules.

Multi-phase equilibrium microemulsions and synthesis of hierarchically structured calcium carbonate through microemulsion-based routes

Middle-phase microemulsions (MPMs) in two systems of a cationic surfactant, tetradecyltrimethylammonium bromide (TTABr)/ n-butanol/iso-octane/Na 2CO 3 or CaCl 2 and an anionic surfactant, sodium dodecyl sulfate (SDS)/ n-butanol/iso-octane/Na 2CO 3 or CaCl 2, were used to synthesize nanostructured calcium carbonates. MPMs provide a simple and versatile reaction media, i.e., upper-phase W/O, BC, and O/W structured equilibrium microemulsions to be used for synthesizing hierarchically structured CaCO 3 at the nanometer scale. On the basis of the investigations on the phase behavior of the MPMs, hierarchically structured calcium carbonates with dendrites, ellipsoids, square-schistose cubes, and spheres were synthesized through the MPM-based routes.

Multi-phase equilibrium microemulsions-based routes to synthesize nanoscale BaWO 4 spheres, cylinders and rods

This article presents the multi-phase equilibrium microemulsions-based routes to synthesize BaWO 4 nanospheres, nanocylinders and nanorods. Unlike reverse micelles or single-phase W/O microemulsions, middle-phase microemulsions equilibrated with residual water or residual oil phase, having the properties of facile, mild and effective, are easily prepared by any traditional surfactants under the existence of cosurfactants. Our investigations demonstrated that the middle-phase microemulsions instantaneously provide a simple and versatile reaction media, i.e., upper-phase W/O and bicontinuous (B.C.) structured equilibrium microemulsions could be used to generate nanoscale inorganic materials with different morphologies, such as BaWO 4.

Clean-up of Oily Wastewater by Froth Flotation: Effect of Microemulsion Formation III: Use of Anionic/Nonionic Surfactant Mixtures and Effect of Relative Volumes of Dissimilar Phases

ABSTRACTFroth flotation, a surfactant-based separation process, can be used to remove emulsified oil from water. In previous work, the maximum removal of ortho-dichlorobenzene from water using froth flotation was achieved when a Winsor Type III microemulsion was formed. However, the exact relationship between the equilibrium microemulsion characteristics and the froth flotation operation is still not clear. In the Winsor Type III microemulsion, three phases are present: an excess water phase containing little surfactant or oil, an excess oil phase containing little water or surfactant, and a middle phase containing almost all of the surfactant and large volume fractions of both oil and water (even equal volumes of oil and water). The Winsor Type III microemulsion also corresponds to a minimum in interfacial tension between liquid phases at equilibrium. In order to elucidate which aspect of the microemulsion is responsible for flotation of oil, flotation experiments were performed with three different combinations of phases: water and middle phases (w-m); water and oil phases (w-o); and water, middle, and oil phases (w-m-o). Since it was deduced that most oil being recovered when in the Winsor Type III microemulsion region is in the excess oil phase (not the middle phase), the reason why the Winsor Type III microemulsion results in excellent oil removal in flotation operation is probably the ultralow interfacial tensions present, and the formation of the middle phase is incidental.

A nucleophilic substitution reaction performed in different types of self-assembly structures.

A nucleophilic substitution reaction between 4-tert-butylbenzyl bromide and potassium iodide has been performed in oil-in-water microemulsions based on various C12Em surfactants, i.e., dodecyl ethoxylate with m number of oxyethylene units. The reaction kinetics was compared with the kinetics of reactions performed in other self-assembly structures based on very similar surfactants and in homogeneous liquids. The reaction was fastest in the micellar system, intermediate in rate in the microemulsions, and most sluggish in the liquid crystalline phase. Reaction in a Winsor I system, i.e., a two-phase system comprising an oil-in-water microemulsion in equilibrium with excess oil, was equally fast as reaction in a one-phase microemulsion. The reactions in microemulsion were surprisingly fast compared to reaction in homogeneous, protic liquids such as methanol and ethanol. The rate was independent of the microstructure of the microemulsion; however, the rate was very dependent on the type of surfactant used. When the C12Em surfactant was replaced by a sugar-based surfactant, octyl glucoside, the reaction was much more sluggish. The high reactivity in microemulsions based on C12Em surfactants is belived to be due to a favorable microenvironment in the reaction zone. The reaction is likely to occur within the surfactant palisade layer, where the water activity is relatively low and where the attacking species, the iodide ion, is poorly hydrated and, hence, more nucleophlic than in a protic solvent such as water or methanol. Sugar surfactants become more hydrated than alcohol ethoxylates and the lower reactivity in the microemulsion based on the sugar surfactant is probably due to a higher water activity in the reaction zone.

Molecular Transport in a Nonequilibrium Droplet Microemulsion System

In this paper, we consider the problem of oil molecular transport between nonequilibrium microemulsion oil droplets in water. In particular, we have investigated the kinetics of solubilization of big oil drops by smaller microemulsion droplets transforming a bimodal size distribution into an equilibrium microemulsion with a unimodal size distribution. The process involves the diffusion of oil monomers across the aqueous solvent. Solubilization experiments are presented on a well-characterized nonionic microemulsion system, where interfacial area and dispersed volume are conserved and where the excess oil chemical potential is dominated by interfacial curvature energy. An analysis of the experiments shows that the solubilization kinetics depend significantly on the concentrations and sizes of big and small droplets. We formulate a quantitative model for the solubilization kinetics where the effects of size and concentrations are treated within the framework of a cell model. A quantitative agreement between model and experiment is obtained, and the analysis also shows that the majority of oil monomers are captured by small droplets already in the vicinity of the big drop surface when the concentration of small droplets is high.

Phase Inversion Temperatures of Macro- and Microemulsions

There exists a parallelism between emulsions and the corresponding microemulsions. In this framework and on the basis of the Gibbs adsorption equation, an explanation is provided for the experimental observation that the phase inversion temperature of a macroemulsion almost coincides with the phase inversion temperature of the corresponding middle phase microemulsion in equilibrium with the two excess phases.

Activation of human plasma cholestryl ester transfer protein by human apolipoprotein A-IV

Function of apolipoprotein (apo) A-IV was studied for its role in cholesteryl ester transfer protein (CETP; lipid transfer protein, LTP) reaction between lipid microemulsions having the diameter of low density lipoprotein, being compared to apoA-I. CETP hardly catalyzed lipid transfer without apolipoproteins. ApoA-IV bound to the surface of the microemulsion in equilibrium with a similar affinity to that of other helical apolipoproteins, and activated the transfer reaction by CETP of cholesteryl ester, triacylgycerol and phosphatidylcholine between the emulsions. The rate of the transfer reaction of cholestery ester and triacylglycerol was directly proportional to the amount of the bound apoA-IV to the surface of the emulsion. For phosphatidylcholine, activation was less effective until 40% of total binding capacity of lipid emulsion was occupied by the apolipoprotein. Cholesteryl ester was highly preferred by CETP over triacylglycerol when equal amount of these lipids was present in the core of the apoA-IV-activated emulsion, resulting in almost no triacylglycerol transfer. However, when the emulsion has the core exclusively of triacylglycerol, triacylglycerol was transferrd by CETP with the rate in the same order as that of cholesteryl ester transfer. These findings were all comparable to the results with apoA-I, and also consistent with our previous observation for other amphiphilic helical apolipoproteins such as apoA-Ii, E and C-III.

Structure of Microemulsions Studied by NMR

AbstractWe discuss the application of NMR to investigate microemulsion structure. There are mainly two important NMR experiments; relaxation and self‐diffusion studies. Of these two, self‐diffusion studies have been found to be particularly informative in that it is the only technique which can demonstrate bicontinuity in equilibrium microemulsions. Self‐diffusion coefficients of water, oil and surfactant can be obtained in the same experiment. For droplet microemulsions, the self‐diffusion coefficients of the surfactant and enclosed solvent correspond to the droplet diffusion coefficient, which in turn depends on its hydrodynamic radius and on interactions. The self‐diffusion coefficient of the continuous solvent is slightly reduced due to obstruction effects, which depends on the droplet shape. For bicontinuous structures, the solvent diffusion on both sides of the surfactant film as well as the surfactant diffusion within the film is monitored. In particular the diffusion of the two solvents depends on how the surfactant film curves. NMR relaxation is found to be useful in the studies of droplet microemulsions. It is very sensitive to the droplet size while at the same time being insensitive to interactions. The latter allows for reliable size information even at higher droplet concentrations.

Emulsion type below and above the CMC in AOT microemulsion systems

In systems containing the pure anionic surfactant AOT (sodium bis-2-ethylhexyl sulphosuccinate), heptane and aqueous sodium chloride, the effect of surfactant concentration on emulsion type with respect to salt concentration has been studied by conductivity measurement. At high enough AOT concentrations, inversion of emulsions, prepared from equilibrium microemulsions and their excess phases, from oil-in-water (o/w) to water-in-oil (w/o) emulsions occurs close to salt concentrations around which three phases appear in equilibrium systems. At low salt concentrations, where aggregates (once formed) are o/w microemulsions, emulsions are o/w both below and above the CMC of the aqueous phase. At high salt concentrations, where aggregates (once formed) are w/o microemulsions, inversion of emulsions (from o/w to w/o) occurs with increasing surfactant concentration, at concentrations approximately five times the CMC. The results are discussed in relation to Bancroft's rule and to the distribution of both monomeric and aggregated surfactant.

Phase behavior and physicochemical properties of sodium octyl sulfate/n-decane/1-hexanol/aqueous aluminum chloride middle-phase microemulsion

The phase behavior and physicochemical properties of sodium octyl sulfate/n-decane/1-hexanol/aqueous AlCl[sub 3] middle-phase microemulsion have been studied as a function of salinity to develop an experimental investigation for better understanding of the microstructure of a middle-phase microemulsion. The system exhibits a Winsor-type phase transition (Winsor I [leftrightarrow] Winsor III [leftrightarrow] Winsor II) with increasing salinity. Over an appreciable salinity (from 0.50% to 9.2%), the formation of Winsor III, composed of a middle-phase microemulsion in equilibrium with the excess water and oil phases, was observed. It has been observed that as the salinity is increased, the phase volume of the middle-phase microemulsion undergoes a drastic decrease at a specific brine concentration (3.8%). Furthermore, the physicochemical properties such as water content, electrical conductivity, diffusion coefficient, and solubilization of 1-hexanol in the AlCl[sub 3] middle-phase microemulsion all show abrupt changes at this salinity. The drastic change in the phase volume and physicochemical properties at the specific salinity of 3.8% may be attributed to a phase inversion of the AlCl[sub 3] middle-phase microemulsion from oil-rich to water-rich continuous phase with increasing AlCl[sub 3] concentration, which is quite a different behavior from that observed for monovalent and divalent salt systems. Specifically, it may be assumedmore » that a fluctuating structure of bicontinuous type and a liquid crystal structure overcome the droplet structure in the phase equilibrium at a certain salinity during the increase in the trivalent salt concentration. 25 refs., 10 figs.« less

Effect of microemulsified surfactant in destabilising water-in-oil emulsions containing C 12E 4

We have investigated microemulsion formation and emulsion stability in oil—water mixtures containing the non-ionic surfactant n-dodecyltetraoxyethylene glycol ether (C 12E 4). The oil component was either pure n-heptane or mixtures of heptane with a medium chainlength triglyceride (MCT). Equilibrium microemulsion droplet sizes, critical microemulsion concentrations (c.μ.c.) and post-c.μ.c. oil—water interfacial tensions are reported for water-in-oil (w/o) microemulsions present in equilibrium with excess water (Winsor II systems). The major effect of incorporation of MCT in these systems is to increase the c.μ.c. in the oil phase. Homogenisation of the two-phase Winsor II systems produces w/o macroemulsions in which the continuous oil phase is itself a w/o microemulsion. At surfactant concentrations higher than the c.μ.c., the main emulsion breakdown process is water drop sedimentation with concomitant oil phase separation. Maximum emulsion stability is found to occur at a surfactant concentration equal to the c.μ.c. for all the different systems. The rate of oil phase separation is accelerated by increasing the concentration of microemulsion droplets in the continuous phase of the emulsion. The accelerating effect was similar for different microemulsion droplet sizes. The experimental observations were found to be reasonably consistent with a depletion flocculation interaction of the emulsion drops.

Incorporation of hydrocarbons into surfactant monolayers

Alkane incorporation into close-packed surfactant monolayers at oil-water interfaces can greatly influence the surface concentration of surfactant, depending on the chain length of the alkane. Such incorporation into monolayers stabilising microemulsion droplets in Winsor systems (microemulsions in equilibrium with excess of the dispersed phase) can cause an inversion of the microemulsion type from oil-in-water to water-in-oil or vice versa. Closely related to this are the effects which solubilised hydrocarbon can have on the cloud points of aqueous solutions of nonionic surfactants. It is difficult to measure quantitatively the extent of hydrocarbon incorporation into surfactant monolayers at oil-water interfaces, but we have determined the extent of uptake of a range of alkanes into monolayers of various surfactants at the air-water surface. In this paper we consider close-packed monolayers at both planar and curved (microemulsion droplet) interfaces, and the effects which incorporation of hydrocarbons into the monolayers has on system behaviour. The extent to which mixed alkane+surfactant monolayers resemble monolayers at oil/water interfaces is explored, and for one system we show how alkane incorporation into films at A/W surfaces directly mirrors microemulsion behaviour in the same system.

Spherical shape instability induced changes in the structure of microemulsions

The dispersed phase of a microemulsion in equilibrium with the excess dispersed phase is in the form of spherical globules. A change in the structure of the microemulsion near the transition from two to three phases is predicted on the basis of thermodynamic considerations. This change occurs because the spherical interface of the globules becomes unstable to perturbations. Because this instability is a result of the condition of equilibrium itself, there is a similarity (but not identity) to the behavior near a critical point. The spherical interface can also become unstable to perturbations in some single-phase microemulsions, although it is stable in microemulsions that coexist with the excess dispersed phase. Thermodynamic considerations also indicate that at the transition from two to three phases, the curvature of the spherical globules must be zero. This result is extended to the entire middle-phase microemulsion as the condition of zero mean-time or space-average curvature. Such a condition can be satisfied in the neighborhood of the transition points from two to three phases and again from three to two phases via the oscillations of the globular interface; in the central region of the middle phase, where the volume fraction of oilΦ∼0.5, this condition is likely to be satisfied via the oscillations of the interface of a bicontinuous sponge.

Equilibrium Extraction and Concentration of Multivalent Metal Ion Solutions by Using Winsor II Microemulsions

Abstract Experimental results on the selective extraction and concentration of bivalent copper into the aqueous core of a water-in-oil microemulsion in equilibrium with an aqueous phase are presented. We have developed an electrostatic model which describes this phenomenosn as a preferential substitutin of the conthe counterions of the surfactant by the introduced bivalent cations. We have assumed that the adsorption of counterions onto the charged surface of the reverse micelle can be modeled by the Stern double layer model. Comparisons of the theoretical predictions against the experimental results are encouraging. The positive features of the model and its limitations are discussed.

An application of the Poisson-Boltzmann equation inside a spherical cavity: Calculus of the equilibrium radius of reverse micelles in the presence of a saline solution

The equilibrium radius of reverse micelles for a microemulsion in equilibrium with a saline water solution is calculated by calculating the Gibbs energy change relative to the uptake of water and to the exchange of ions between the two phases. A major role is played by electrostatic effects. In order to take these effect into consideration, the Poisson-Boltzmann equation relative to the inside of the micelle has been considered. The solution is found in the form of a convergent series. The electroneutrality, the mass balance of the species and the thermodynamic equilibrium allow the problem to be resolved unambiguously. Once the potential profile inside the micelle is known, the electrostatic energy and entropy can easily be calculated. The entropic terms corresponding to ideal mixing of the species inside the micelle and in the bulk water solution, and to mixing of the micelles are also considered. The Gibbs energy is varied as a function of the radius and an equilibrium radius is found that corresponds to the minimum value of the Gibbs energy. The calculated values show good agreement with the experimental ones deduced from the water content of the microemulsion.