Phase Behavior Of Microemulsions Research Articles

Water/Chlorocarbon Winsor I ⇔ III ⇔ II Microemulsion Phase Behavior with Alkyl Glucamide Surfactants

The investigation of the microemulsification of chlorocarbons that contaminate aquifers is addressed in this study. The surfactants employed are alkyl glucamidesglucamine coupled with either n-heptanoic, n-nonanoic, or n-dodecanoic acids as well as the Guerbet version of the dodecanoic acid. The chlorinated hydrocarbons studied include tetrachloroethylene (PCE), carbon tetrachloride, 1,1,1-trichloroethane (TCA), trichloroethylene (TCE), 1,2-dichlorobenzene (DCB), 1,2-dichloroethane (DCE), chloroform, methylene chloride, and 1,1,2,2-tetrachloroethane. It was possible to generate classical Winsor I ⇔ III ⇔ II phase behavior with nearly all of the above chlorocarbons.

Phase behaviour and physicochemical properties of microemulsions with a non-ionic surfactant (IGEPAL)

The non-ionic surfactant pentaethylenglycol-4-octylphenyl ether (igepal CA-520) represents a good industrial alternative to the long-tail members of the CiEj family. In this paper, the phase behaviour of the microemulsion system igepal CA-520/n-decane/brine is studied in detail. An isotropic phase was found, as well as liquid crystalline and cream-like structures, depending on composition and temperature. Such structures can either form single-phase homogeneous mixtures, or coexist with other structures when phase separation takes place. Below surfactant concentration of about 20%, more complicated phase equilibria develop as temperature changes. The presence of different additives shifts the temperature ranges where the different phases exist, while keeping the general shape of the phase diagram, which agrees with the general rules for non-ionic surfactants. Complementary rheology experiments reveal a change from non-Newtonian to Newtonian behaviour during the phase transition from a lamellar phase to the isotropic microemulsion. A structure of water droplets associated in clusters can be proposed from SANS and electrical conductivity.

Phase Behavior of Ionic Microemulsions

AbstractNon‐polar oils and water can form thermodynamically stable quasi‐homogeneous (colloidal) mixtures (called microemulsions) in the presence of relatively large amounts (several %) of ionic surfactants. If the surfactant contains a single hydrocarbon chain (e.g. Sodium Dodecyl Sulphate) the presence of a non‐ionic cosurfactant (e.g. hexanol) and electrolyte (concentration of the order 0.1 M) is essential. With a double chain surfactant (e.g. Aerosol OT) the cosurfactant can be missed. At increasing concentrations of electrolyte and/or cosurfactant the nature of the microemulsion changes from droplets of oil in water via a presumably bicontinuous pattern to droplets of water in oil. It should be obvious that thermodynamic stability requires the interfacial tension between water and oil to be low (order of 0.01‐0.1 mN m−1) so that the dispersion entropy can offset the interfacial free energy. At these low interfacial tensions the influence of curvature on the interfacial tensions becomes important. It turns out that a given amount of surfactant (and co‐surfactant) can only disperse a limited amount of oil in water or of water in oil or of water and oil into one another and therefore a microemulsion may be in equilibrium with non colloidal oil and/or water phases. In the bicontinuous microemulsion oil and water may have a geometrically irregular interface or they may form lamellae of more or less constant thickness or other structures, such as a “molten cubic phase”. These equilibria lead to very interesting, but rather complicated phase diagrams. It will be discussed by what mechanisms the various components of the mixture influence the interfacial tension and promote the stability of the microemulsion and how this depends on the chemical nature of the components.

The Effect of Temperature on the Adsorption of Dodecane onto Nonionic and Ionic Surfactant Monolayers at the Air‐Water Surface

AbstractWe have measured the adsorption isotherms for dodecane adsorption at the solution‐vapour surface for surfactant monolayer covered aqueous surfactant solutions at concentrations in excess of their critical micelle concentration (cmc) values. The temperature dependence of the adsorption have been determined for both a nonionic surfactant (H(CH2)12(OCH2CH2)5OH, abbreviated to C12E5) and an ionic surfactant (n‐dodecyltrimethyl‐ammonium bromide, abbreviated to DoTAB). For the nonionic surfactant, dodecane adsorption decreases with increasing temperature at low surface concentration of the oil whereas it increases at high surface concentrations. With the ionic surfactant DoTAB, the temperature effect shows a similar crossover in behaviour but the changes in adsorption are opposite in direction to those seen for the nonionic surfactant. The adsorption data are correlated to the effects of temperature on the microemulsion phase behaviour of ionic and nonionic surfactants and discussed in relation to the microstructures of the mixed oil/surfactant films as determined by neutron reflection methods.

Nonionic Microemulsions

AbstractWe review and summarize the features of nonionic microemulsion phase behavior. Particular emphasis is given to the behavior of mixtures of oil, water or other polar materials with nonionic surfactants from the family of n‐alkyl polyglycol ethers, usually denoted as CiEj. The patterns of phase behavior are reviewed and the roles of various additives such as electrolytes and alcohols are discussed.

Microemulsions in Supercritical Hydrochlorofluorocarbons

We report the properties of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) microemulsions formed in supercritical hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons, and flourocarbons. The fluids used in this study include compounds that are of low toxicity and flammability and that are expected to remain environmentally acceptable well into the next century (e.g., 1,1,1, 2-tetrafluoroethane (R134a) and chlorodifluoromethane (R22)). We show that it is possible to form a water-in-oil type of microemulsion in a low molecular weight HCFC (R22). In addition to these HCFCs, We also review the ability to form microemulsions in 14 other fluids (ethane, propene, propane, n-butane, n-pentane, n-haxane, isobutane, isooctane, difluoromethane, trifluoromethane, hexafluoroethane, sulfur haxafluoride, xenon, and carbon dioxide) at conditions just above or below the critical point (0.75 < T/T{sub c} <1.1) of the solvent. We report extensively the phase behavior of AOT and didodecyldimethylammonium bromide microemulsions formed in a supercritical HCFC, R22. We show that microemulsions in HCFCs are practical alternatives to other fluids, such as supercritical carbon dioxide. 56 refs., 7 figs., 1 tab.

FORMATION AND PHASE BEHAVIOR OF WATER-IN-DIESEL OIL MICROEMULSION WITH SODIUM OLEATE AND CETYLTRIMETHYLAMMONIUM BROMIDE

ABSTRACT The phase behavior and solubilization of multiphase microemulsions in mixed anionic-calionic surfactant systems were studied for fixed ratios of water to diesel oil and surfactant to alcohol. In the mixed surfactants (sodium oleate + cctyltrimcthylammonium bromide) /diesel oil/ alcohol/water systems, microcmulsion and birefringent phases are formed by adjusting the surfactant ratio e and the cationic weight fraction δ The bicontmuous—→birefringent→o/w microcmulsion transition takes place with dilution for i-pentanol-containing systems. The birefringent region shrinks rapidly with increasing alcohol and/or CTAB weight fractions in total surfactant concentration. The normal solution→w/o microemulsion transition for n-hcxanol systems and only w/o microemulsion for n-octanol systems were observed along the dilution with diesel oil and water. And microemulsion domain enlarges with increasing ∊ for three alcohol systems. The optimum surfactant concentration γ increases and the corresponding optimum δ d...

Preparing Microemulsions with Alkyl Monoglucosides and the Role of n-Alkanols

With this paper, we continue the series of our studies on the applicability of biological amphiphiles for emulsifying mineral oils. In the first part, we show that the effect of n-alkanols on the phase behavior of microemulsions results from the position of the plait points in the isothermal phase tetrahedra of quaternary water-oil-amphiphile-alkanol mixtures. In the second part, we demonstrate the dependence of the effect of propanol, in particular, on the carbon number of the oil in mixtures with alkyl poly(glycol ethers) as amphiphiles and, correspondingly, supplement our recently published recipe for preparing microemulsions with aromatic oils and lecithins. In the last part, we study the applicability of alkyl monoglucosides C i G 1 for preparing microemulsions, resulting in a recipe of how to choose the carbon number of the alkanol for emulsifying alkanes and aromatic oils with C i G 1 Alkyl monoglucosides turn out to be efficient emulsifiers, with the one-phase microemulsions being rather insensitive to temperature and salt concentration.

Statistical morphology of random interfaces in microemulsions

We introduce a phenomenological lattice model of interacting surfaces to relate the phase behavior of microemulsions with the random geometry and topology of microstructures formed by the self-assembling surfactants. The model rests upon an effective Hamiltonian whose morphological character is manifest. In contrast to earlier membrane models, we focus attention on energy parameters favoring multiply connected microstructures. By employing mean-field and related approximations supported by Monte Carlo simulations, we study phase diagrams, liquid structure factors, and macroscopic surface tensions to demonstrate that the model reflects prominent features of microemulsions.

Phase Behavior and Microstructure of Nonaqueous Microemulsions. 2

The microstructure of nonaqueous microemulsions formed with propylene glycol, glycerol, three different alkanes, and pentaethylene glycol mono-n-dodecyl ether (C{sub 12}E{sub 6}) is probed with NMR self-diffusion measurements and small angle neutron scattering (SANS). At low oil concentrations, both NMR self-diffusion and SANS results can be modeled in terms of a microstructure of ellipsoidal oil-rich droplets with only excluded volume interactions. These droplet structures percolate to an oil-continuous structure as the volume fraction of oil in the microemulsions increases. Percolation thresholds measured as a function of alkane chain length are interpreted in terms of the phase behavior of the microemulsion and the strength of droplet interactions. 41 refs., 6 figs., 3 tabs.

Equilibrium and dynamic behavior for systems containing nonionic surfactants, n-hexadecane, triolein and oleyl alcohol

Phase behavior and electrical conductivity experiments were carried out for systems containing water, nonionic surfactants, triolein, n-hexadecane and oleyl alcohol. In systems where the amount of triolein was equal to or greater than the amount of n-hexadecane, the surfactant appeared successively in the lamellar liquid crystalline phase L α, the sponge phase D′, a bicontinuous microemulsion D and an oil-rich microemulsion O m as the system was made more lipophilic. The temperatures of the various phase transitions decreased with increasing hydrocarbon content. In one system five phases were found to coexist simultaneously: L α, D′, D, and excess water and oil. Conductivity measurements indicated no major change in microstructure of either D′ or D phases when the n-hexadecane-to-triolein ratio was changed from zero to one. In systems where the amount of hydrocarbon was much greater than the amount of triolein, the usual microemulsion phase behavior was seen with continuous variation of oil and water solubilization over a wide range. Videomicroscopy contacting experiments were consistent with the phase behavior results in that the D′ phase was observed as one intermediate phase when drops rich in triolein were injected into aqueous surfactant solutions but not when the drops were mainly hydrocarbon. In the latter case, microemulsions were seen which inverted continuously until the surfactant concentration in the drops became high enough that the lamellar phase formed.

Microemulsifying fluorinated oils with mixtures of fluorinated and hydrogenated surfactants

Microemulsions containing fluorinated oils are, in general, prepared by mixing water, the perfluorinated oil, and a fluorinated surfactant which may be either ionic or non-ionic. In this paper we describe our study of the phase behavior of three dilterent fluorinated oils in mixtures with water and n-fluoroalkyl polyglycol ether. Furthermore, our experiments show that replacing fluorinated surfactants by mixtures of fluorinated and hydrogenated surfactants (up to a 25% weight ratio of hydrogenated to fluorinated surfactant) leads to microemulsion formation with a variety of fluorinated oils. The ratio of the two types of surfactant and the chain length of the added hydrogenated surfactant are ideal parameters with which either to increase the efficiency of the amphiphile blend or to control the temperature of microemulsion formation. The experimental results point to general rules governing the phase behavior of microemulsions of fluorinated oils and mixtures of hydrogenated and fluorinated surfactants.

Properties of surfactant monolayers in relation to microemulsion phase behaviour

The relationship between the properties of surfactant monolayers at oil-water interfaces and the phase behaviour in bulk of mixtures of oil + water + surfactant is discussed. Such monolayer properties include the spontaneous curvature, c o the interfacial tension, I γ, the elasticity K (or rigidity) associated with the mean curvature, and the elasticity K associated with the Gaussian curvature. The model system chosen for investigation is the anionic surfactant AOT + aqueous NaCl + n-alkane at 20°C. In such systems, inversion of microemulsion type from oil-in-water (o/w) to water-in-oil (w/o) is possible with increasing electrolyte concentration. The tension, γ, passes through an ultralow minimum value at conditions corresponding to the formation of three phases. Using small angle neutron scattering, we have determined the structure of surfactant-rich third phases (c o ~ 0) formed with the different alkanes. Lamellar phases consisting of surfactant monolayers separated alternately by oil and water appear with short alkanes, whereas L 3 and bicontinuous phases form in systems containing longer alkanes. The bending elasticity K has been measured for planar monolayers at the oil-water interface by ellipsometry. K is independent of salt concentration but depends markedly on alkane chain length N, falling from ~ 1 k BT for N < 11 to ~0.1 k BT for N = 14. This is discussed in terms of the differing extents of oil penetration into the surfactant chains. Higher rigidities favouring lamellar phases and lower rigidities favouring bicontinuous microemulsions are in line with the theoretical predictions of de Gennes and Taupin. Estimates of the constant K have been obtained in droplet microemulsions (w/o) from a knowledge of their size, K and γ. The sign of the constant is in agreement with the geometry of the phases formed in three phase systems. Finally, the ideas and concepts developed in the oil-water systems described above are used to explain the wetting behaviour by alkanes of AOT monolayers at the air-water surface.

Surface chemistry and microemulsion formation in systems containing dialkylphthalate esters as oils

The surface chemical behaviour of phthalate esters in oil–water mixtures, both in the presence and absence of a conventional surfactant, has been investigated. We have estimated the surface activity of phthalate esters and the extent to which this type of moderately polar oil can be coadsorbed into concentrated monolayers of conventional surfactants at the oil/water interface. In the absence of surfactant, phthalate oils are adsorbed from dilute solution in heptane at the heptane/water interface, exhibiting a surface activity typical of non-aromatic diesters and similar to that of alcohols. However, the surface chemical and microemulsion phase behaviour in mixtures of phthalate oils and aqueous NaCl solutions in the presence of the anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) indicates a low extent of penetration of the phthalate oils into AOT monolayers. This is interesting since the phthalates have similar surface activities (from hydrocarbon oils) to alcohols which are very effective cosurfactants capable of strong coadsorption into surfactant monolayers. The main effects of substituting phthalate oils for alkanes in mixtures of oil–AOT–aqueous NaCl are (i) to increase the critical aggregate concentration of surfactant in the oil phase, (ii) to increase the NaCl concentration required for microemulsion phase inversion and (iii) to increase the magnitude of the minimum interfacial tension obtained by varying the salt concentration. It is concluded that phthalate oils do not act as strongly adsorbed cosurfactants in AOT–water–oil systems and the extent of phthalate oil penetration of AOT monolayers is less than for alkanes.

Phase behavior of dense three-component ionic microemulsions and electrical conductivity in the lamellar phase.

An extended phase diagram for an ionic microemulsion system made of water, n-decane, and the ionic surfactant sodium-di-2 ethyl-hexyl sulfosuccinate is deduced from a very extensive set of electrical-conductivity and neutron-scattering measurements. This diagram shows high-temperature phase transitions that explain some original features previously not reported. Furthermore we propose a phenomenological model based on the solution of a Poisson-Boltzmann equation which accounts well for electrical conductivity data we obtain in the lamellar phase.

Structure and Phase Behavior of Lecithin-Based Microemulsions: A Study of the Chain Length Dependence

We present a study of the structure and phase behavior of phospholipid-based water-in-oil microemulsions. The considerable influence of solvent (isooctane and cyclohexane) and cosolvent (short chain alcohol) structures and surfactant chain length on the phase behavior is shown, and an investigation of the aggregate size and structure by means of dynamic and static light scattering is reported. Synthetic short chain lecithin requires the use of a cosolvent and forms classical droplet-type microemulsion particles, whereby the droplet radius is largely determined by the water-to-surfactant molar ratio. Soybean lecithin as an example of a naturally occurring long-chain lecithin mixture requires no cosolvent, and we observe a water-induced transition from small spherical reverse micelles to giant flexible cylindrical particles.

Relationship between microemulsion phase behavior and macroemulsion type in systems containing nonionic surfactant

Relationship between microemulsion phase behavior and macroemulsion type in systems containing nonionic surfactant

Optimization of a surfactant flooding process by core-flood experiments

As a part of the preparation for a surfactant flooding pilot in a North Sea oil reservoir, several hundred core flood experiments have been performed. This paper summarizes the experience obtained from these core floods. The experiments were carried out at temperature of 90°C, using seawater as the brine, and a modified reservoir crude as the oil phase. The purpose of these experiments was to define the surfactant slug design for obtaining a maximum oil recovery per unit surfactant. The core-flood experiments involved variation of critical parameters like surfactant concentration, slug size and microemulsion phase behavior. The core floods are compared not only by the optimum defined as the maximum in the volumetric oil recovery per volume of surfactant injected, but also by several other requirements like: early oil breakthrough, high fractional flow of oil, low pressure buildup and low surfactant retention.

Effect of alcohols on the phase behavior of microemulsions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffect of alcohols on the phase behavior of microemulsionsM. Kahlweit, R. Strey, and G. BusseCite this: J. Phys. Chem. 1991, 95, 13, 5344–5352Publication Date (Print):June 1, 1991Publication History Published online1 May 2002Published inissue 1 June 1991https://doi.org/10.1021/j100166a077RIGHTS & PERMISSIONSArticle Views459Altmetric-Citations120LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts

Phase behavior of AOT microemulsions in compressible liquids

The phase behavior of bis(2-ethylhexyl) sodium sulfosuccinate (AOT)-alkane-brine systems is described over a wide range of pressure, temperature, and salinity for alkanes from ethane to dodecane. The partitioning of AOT between the oil, middle, and brine phases is reported for propane in order to determine the natural curvature. This is important for understanding separation processes with water-in-oil microemulsions. For the lighter, more compressible alkanes, the pressure effect on the hydrophilicity of the surfactant is much larger and in the opposite direction as for the heavier, less compressible ones. In propane at constant temperature and salinity, water-in-oil (w/o) microemulsions have been converted to middle phase microemulsions and then to oil-in-water (o/w) microemulsions by decreasing the pressure. These phase inversions are described in terms of the immiscibilities in the binary systems, and the molecular interactions at the surfactant interface. Although temperature and salinity are used commonly to manipulate interactions primarily on the water side of the interface, these results show it is possible to control interactions on the oil side by adjusting the pressure. The well-established trends in the phase behavior and size of microemulsion drops for dodecane through hexane are not observed for the lighter alkanes. For butane through ethane, amore » new unusual behavior is identified and attributed to a significant decrease in the strength of the attractive interactions between the surfactant tails and the alkane.« less