Middle-phase Microemulsion Research Articles

Changes in morphology of three-phase emulsions with temperature in ternary amphiphile/oil/water systems

The morphologies of the three phases (aqueous or bottom phase B, middle-phase microemulsion M , and oleic or top phase T) of the ternary 2-butoxyethanol/ n-decane/water system were examined at various temperatures and water-to-oil ratios (WORs). There are various hypotheses regarding the effect of temperature on three-phase emulsion morphology. One states that three-phase emulsions should always be M-continuous, irrespective of temperature and the WOR. Another states that three-phase emulsions should be B-continuous at temperatures lower than the phase inversion temperature (PIT) and T-continuous at temperatures higher than the PIT and that the inversion line separating the B-continuous and T-continuous region is horizontal in the three-phase body of the fish diagram. However, measurements recorded in the current study indicated that the inversion line dividing the three-phase body of the ‘fish’ diagram is almost vertical, thereby completely contradicting those previous hypotheses. Moreover, the three-phase emulsion morphologies obtained are found to depend on the WOR. In the region right to the inversion line, the morphology remains M-continuous, irrespective of the WOR, yet in the region left to the inversion line, the morphology is M-continuous at a WOR <1, T-continuous or B-continuous at a WOR ≈ 1, and B-continuous at a WOR >1 Accordingly, the current results are proposed as a new model for the morphology of three-phase emulsions in the fish diagram.

Effect of Hydrophobically Modified Polymer on Salt-Induced Structural Transition in Microemulsions

The phase boundaries of the middle-phase microemulsion for NaCl/SDS/H2O/1-heptane/1-pentanol systems in the absence of polymer and in the presence of unmodified poly(acrylamide) (PAM) and hydrophobically modified poly(acrylamide) (HMPAM) have been determined at varying salt concentrations. These three middle-phase microemulsions (with HMPAM, with PAM, and without polymer) were studied using interfacial tension measurement, steady-state fluorescence, and time-resolved fluorescence quenching. Compared to the polymer-free system and the system with PAM, the addition of HMPAM significantly enlarges the range of the salt concentrations for the formation of the middle-phase microemulison and causes both the excess oil and aqueous phases to increase in volume at the expense of the middle-phase microemulsion. For the middle-phase microemulsion with HMPAM, the interfacial tensions of the microemulsion phase with the excess oil phase and with the excess aqueous phase are all ultralow and exhibit higher values than those with PAM and without polymer. At the same salt concentration, the apparent surfactant aggregation number in the middle-phase microemulsion with HMPAM has the smallest value among these three systems. All results indicate that the strong interaction of surfactant with hydrophobically modified polymer has a large effect on the formation and properties of the middle-phase microemulsion.

Self-assembly in linker-modified microemulsions

Linker molecules are added to microemulsion systems to enhance the interaction between the surfactant and oil (lipophilic linkers) or water (hydrophilic linkers) phases. Previous results suggest that when lipophilic and hydrophilic linkers are combined they behave as a self-assembled surfactant at the oil/water interface. In this work we investigate this self-assembly phenomenon as a function of surfactant, linker and electrolyte concentration. We find that middle phase microemulsion appears at a specific concentration higher than the critical micelle concentration (CMC), which we denote as the critical middle phase microemulsion concentration (CμC). When the lipophilic linker dodecanol is added in equimolar ratio to the hydrophilic linker sodium mono- and dimethyl naphthalene sulfonate (SMDNS), the middle phase microemulsion did not appear until the surfactant sodium dihexyl sulfosuccinate (SDHS) concentration was larger than the CμC of the SDHS-alone system. Dodecanol is shown to segregate near the surfactant tails following a Langmuir-type adsorption process. This segregation is not affected by the electrolyte concentration but is significantly reduced when the surfactant (SDHS) concentration approaches the CμC. The data suggest that the self-assembly between hydrophilic and lipophilic linkers to form middle phase microemulsions is only possible if a minimum amount of surfactant is present.

Microstructure of Alkyl Glucoside Microemulsions: Control of Curvature by Interfacial Composition

The phase behavior of water/n-octane/n-octyl-β-d-glucopyranoside (C8G1)/1-octanol (C8E0) permits formulating temperature-insensitive microemulsions spanning the whole water−oil composition range. The types of microstructures formed along the trajectory of the middle-phase microemulsion are examined by NMR diffusometry, yielding the respective diffusion coefficients of all the components. The diffusion experiments provide clear evidence of the transition from oil-in-water to water-in-oil microemulsions via bicontinuous structures in a remarkably large range around phase inversion. Small-angle neutron scattering (SANS) along the same path confirm the picture. Furthermore, SANS curves on the absolute scale permit extracting the specific internal interface in the microemulsion as it passes through phase inversion. When the composition of the internal interface is known, the mean area per surfactant molecule is determined. It is found that as the interfacial film becomes increasingly rich in C8E0, that is, the...

Preparation of Nano-TiO2 from a Crude Solution Containing Ti(IV)–Fe(II) and H2SO4 with Extraction and Hydrolysis

The extractions of TBP (or TOPO)–kerosene/a crude solution containing Ti(IV), Fe(II), and H2SO4 were studied for the separation of Ti/Fe. Nano-TiO2 powder, about 20 nm, was prepared by hydrolysis of the middle phase microemulsion loading Ti(IV) obtained in TBP extraction system. By hydrolyzing the colloidal liquid aphrons (CLA) made by the extracted organic solution loading Ti(IV) in TOPO extraction system as the inner phase, a porous spherical TiO2 was obtained. The contents of Fe in both products were less than 100 ppm.

Coalescence and Solubilization Kinetics in Linker-Modified Microemulsions and Related Systems

Previously, we reported on formulating microemulsions with combined linker molecules. These linker molecules enhance the interaction of the dynamic surfactant membrane with water, in the case of hydrophilic linkers, or oil, in the case of lipophilic linkers, thereby yielding microemulsions with desirable properties. In this paper we evaluate the coalescence and solubilization kinetics of trichloroethylene emulsions and microemulsions using sodium dihexyl sulfosuccinate and different linker formulations. Sodium mono- and dimethylnaphthalenesulfonate (SMDNS) was used as the hydrophilic linker, and dodecanol was used as the lipophilic linker. The interfacial properties (interfacial thickness/tension/rigidity) of these linker-based microemulsions were also studied. The turbidity curves of optimum middle phase microemulsions are fitted with a second-order kinetic equation, with the coalescence activation energy being a function of the interfacial rigidity of the systems. It was found that the addition of lipop...

Emulsion stability in sucrose monoalkanoate system with addition of cosurfactants

The hydrophile-lipophile property of the sucrose monododecanoate changes from hydrophilic to lipophilic by adding an alcohol as a cosurfactant. With the addition of a short-alkyl-chain alcohol (pentanol, hexanol), the surfactant forms the middle-phase microemulsion whereas a lamellar liquid crystal (Lα) appears with a medium- or long-chain alcohol (heptanol, octanol, decanol) at the balanced state in water/ SE/ cosurfactant/ decane system. The effect of changing oil was also studied in the presence of a middle-chain cosurfactant (heptanol). A short-chain aromatic oil (m-xylene) forms middle-phase microemulsion whereas a longer aliphatic one (hexadecane) forms lamellar liquid crystalline phase in a dilute region when the HLB of surfactant is balanced in a given system. O/W emulsions become stable on the hydrophilic-surfactant-rich side whereas W/O emulsions are stable on the cosurfactant-rich side. Emulsions are very unstable in the three-phase regions. However, when the lamellar phase is produced, emulsions become stable at the balanced state because water and oil are incorporated in Lα phase in the longer cosurfactant systems such as water/ SE/ octanol/ decane and water/ SE/ decanol/ decane.

Formation of Two-Phase Multiple Emulsions by Inclusion of Continuous Phase into Dispersed Phase

The formation of multiple emulsions, M/O/M, has been observed for conjugate middle-phase microemulsion (M) and top or oleic (O) phase formed by the system 2-butoxyethanol/n-decane/water at a temperature (35.0 °C) about midway between the critical endpoint temperatures (i.e., lowest and highest temperatures at which top, middle, and bottom phases can coexist) of this system. The M/O/M morphology was discovered by measuring the electrical conductivities of steady-state emulsions and confirmed by photomicrography; it was formed by the top and middle phases of the top−middle−bottom tie triangle, as well as by conjugate phases of other tie lines between the top−middle limiting tie line and the microemulsion−oleic phase critical point. The volume fractions of microemulsion in the cores of the multiple emulsions were calculated from the conductivity measurements. They decreased with increasing volume fraction of oleic phase in the system. Inversion of O/M emulsions to the M/O emulsion occurred at still smaller volume fractions of microemulsion in the system, after the volume fraction of microemulsion in the cores apparently had decreased to zero. It is suggested that the line of phase compositions at which the core volume apparently goes to zero may terminate at the microemulsion−oleic phase critical point, where the hysteresis lines for O/M → M/O, and M/O → O/M inversions also terminate. No evidence was found for decreases of volume fraction of continuous oleic phase with decreasing volume fraction of oleic phase in the system or for the hypothetical morphology change M/O/M → M/O, caused by “disappearance” of continuous M phase. This appears to be the first observation of the formation of multiple emulsions by microemulsion and oleic phases at a temperature between the two critical-endpoint temperatures. Also, we have observed that the emulsion inversion path was quite different from that in previous studies. In these studies inversion took place through the morphology change of O/W to W/O/W to W/O. However, in our study the inversion took place through the change of M/O/M to O/M to M/O. That is, multiple emulsions M/O/M were formed first by inclusion of M phase into O-phase drops. Then the M/O/M emulsions inverted to O/M emulsions at which the volume fraction of M-phase droplets in the core became zero. From this point on O/M morphology was maintained with increasing O-phase fraction up to the emulsion inversion point, and then inversion to M/O took place.

Electrochemistry in Middle Phase Microemulsion Composed of Saline and Toluene with Sodium Dodecylsulfate and n-Butanol

Abstract A “middle phase” microemulsion, which bicontinuously composed of saline and toluene microphases, with sodium dodecylsulfate (SDS) and n-butanol was electrochemically characterized. When electrochemistry was performed in the “middle phase” microemulsion, reversible redox peaks of the Fe(CN)6 ion in the micro water phase and the ferrocene in the micro toluene phase could be observed simultaneously, although the electrolyte was present only in the water phase.

Phase-behavior-based surfactant–contaminant separation of middle phase microemulsions

This research studied separation of contaminants solubilized in middle phase microemulsions by shifting the contaminant-rich microemulsions from Winsor type III to type I systems. Precipitation-based exchange of polyvalent cations (Al3+ and Ca2+) with equivalent amounts of a monovalent cation (Na+) broke the middle phase microemulsions. Most of the contaminants solubilized in the middle phase microemulsion separated as free phase contaminant due to the much lower solubilization capacity of the resulting type I system. The phase transitions between Winsor type III and type I systems were reversible with the precipitation and re-dissolution of the polyvalent cations, allowing subsequent reuse of the surfactant solution. The phase transitions brought about by deprotonation/protonation of oleic acid, an organic additive used to promote formation of middle phase microemulsions, were also studied. The neutral form of oleic acid was more effective than its dissociated anion for promoting the formation of middle phase microemulsions, but oleic acid in the middle phase microemulsions could not be deprotonated by adding aqueous OH−. On the other hand, the oleate anion could be protonated even when it was in middle phase microemulsions because of its relative distribution in the systems. While exchange of surfactant counterions could separate contaminant solubilized in middle phase microemulsions, transformation of oleic acid in middle phase microemulsion systems did not produce the desired result.

Formation of Microemulsions with Gemini-Type Surfactant.

Disodium N,N’-dilauroylethylenediamine-N,N’-disuccinate (gemini surfactant, GS) and sodium N-lauroyl-N-methylamine succinate (monomeric surfactant, MS) form middle-phase microemulsions at an optimum mixing ratio with glycerol mono(2-ethylhexyl)ether (MEH) as a cosurfactant in the presence of NaCl. The solubilization capacity of microemulsion in the GS system is about twice as much as that of microemulsion in the MS system. This difference in solubilization capacity may be attributed to tight packing of GS molecules at a micro water-oil interface inside the microemulsion. With decreasing the salt content in water, the three-phase region consisting of excess water, oil phases and a middle-phase microemulsion shrinks and finally disappears, perhaps, at a tricritical point, at which three phases become simultaneously identical. The temperature dependence on the phase behavior of the microemulsions is also reported.

Formation of Microemulsions in Aqueous NaCl/Sodium (3-Dodecanoyloxy-2-Hydroxy-Propyl) Succinate/Glycerol Mono(2-Ethylhexyl) Ether/Oil Systems

ABSTRACT Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) forms microemulsions by mixing with cosurfactants such as glycerol mono(2-ethylhexyl) ether (MEH), although the combination with ordinary cosurfactant such as hexanol does not form a microemulsion of large solubilization. The middle-phase microemulsion coexists with excess water and oil (octane) phases at an optimum-mixing fraction of SLGMS and MEH in the presence of salt. The monomeric solubility of MEH in oil is low and MEH is mainly combined with SLGMS at an oil—water interface inside microemulsions. With decreasing salinity, the three-phase body shrinks and eventually disappears. The three-phase body may be terminated at a tricritical point, at which three phases simultaneously coexist. The effect of type of oil on the solubilization capacity of the microemulsions is also discussed.

Thermodynamics of carbohydrate surfactant containing systems

The skillful combination of carbohydrate surfactant–water–oily component–cosurfactant is successful in obtaining microemulsion states for the solubilization of comparable amounts of materials as dissimilar as oil and water into a single, thermodynamically stable, liquid phase. This paper focused on theoretical study of the phase behavior of the corresponding binary and ternary subsystems and the quaternary system. The phase equilibrium calculations based on the Koningsveld–Kleintjens model. Applying the Koningsveld–Kleintjens model the essential features of phase behavior, including two- and three-phase equilibria, in the ternary system can be calculated. The calculation results are in good quantitative agreement with the experimental observations. Not unexpectedly, it turned out to be impossible to model the quaternary systems, and with these theoretical frameworks it was even impossible to form the correct three-phase equilibria, especially the microemulsion phase. The quantitatively correct composition of the middle phase microemulsion cannot be modeled, whereas the composition of excess water-rich and of the oil-rich phase can be predicted. Taking into account the partially ordering of the system by a special entropy contribution or the screening of the enthalpy repulsion between water and oil do not lead to an improvement of the modeling results.

Alcohol‐free diphenyl oxide disulfonate middle‐phase microemulsion systems

AbstractDiphenyl oxide disulfonate (DPDS) surfactants were successfully used to formulate Winsor Type III middlephase microemulsion systems with tetrachloroethylene (PCE) and decane. To our knowledge this is the first time that monochain DPDS surfactant phenyloxide monohexadecyl disulfonate surfactant (C16MADS) and commercially available DOWFAX 8390 were found to form middle‐phase microemulsion systems with oils. Hydrophobic dioctyl sodium sulfosuccinate (Aerosol OT) was also used as a cosurfactant to lower the systems' hydropholic‐liphophilic balance. Two organic acids (hydrophobic octanoic acid and hydrophilic l‐tartaric acid) were used in place of the alcohol to formulate middle‐phase microemulsion. The middle‐phase microemulsion systems dramatically increased organic solubility when compared to micellar DPDS surfactant systems. Winsor Type I systems near the Type I–III boundary produced “super” solubilization for hydrophobic oils. Findings from this study enable us to improve DPDS solubilization enhancement of hydrophobic compounds.

Supersolubilization in Chlorinated Hydrocarbon Microemulsions: Solubilization Enhancement by Lipophilic and Hydrophilic Linkers

In this paper, the effect of linker molecules on the solubilization capacity of an anionic surfactant system (sodium dihexyl sulfosuccinate) is studied. N-Alkyl alcohols are used as lipophilic linkers in middle-phase microemulsions of trichloroethylene, tetrachloroethylene, and hexane. The lipophilic linker effect increases the solubilization capacity of the anionic surfactant system. The solubilization parameter for both hydrocarbons and chlorinated hydrocarbon oil increases as a function of alcohol concentration. As the alkyl chain length of the alcohol linker molecule increases, the solubilization capacity increases. Moreover, the longer chain alcohol is more effective at linking oil molecules for hexane than for chlorinated hydrocarbon oils, indicating that the linker effect is more effective for higher equivilant alkane carbon number (EACN) oils. Sodium mono- and dimethylnaphthalenesulfonate is proposed as a hydrophilic linker to enhance the solubilization of lower EACN oils. The combination of lipophilic and hydrophilic linkers synergistically enhances the solubilization capacity of chlorinated hydrocarbon microemulsions.

Formulating Microemulsion Systems for a Weathered Jet Fuel Waste Using Surfactant/Cosurfactant Mixtures

This paper identifies surfactant systems capable of forming middle phase microemulsions with a weathered jet fuel at Hill AFB, Utah. A series of batch studies was conducted to characterize the hydrophobicity of this light nonaqueous phase liquid (LNAPL) and to evaluate microemulsion systems for this LNAPL. The contaminant was found to be more hydrophobic than ordinary jet fuel, thus requiring cosurfactant and electrolyte addition to formulate middle phase microemulsions. Successful salinity (NaCl) and hardness (CaCl2) scans were conducted with one anionic surfactant, Aerosol OT (AOT), and three different cosurfactant systems—one alcohol (isobutanol), one hydrotrope (sodium mono- and dimethyl naphthalene sulfonate or SMDNS), and two nonionic surfactants [POE[20] sorbitan monostearate or T-MAZ 60 and POE[20] sorbitan monooleate or T-MAZ 80]. Of the five systems which successfully microemulsified the LNAPL (versus 10 others evaluated), one was selected for implementation in a subsequent field demonstration.

Application of Cryo-Transmission Electronic Microscopy in Sodium Dodecylsutfonate Middle Phase Microemulsion

The middle phase microemulsion of Sodium Dodecylsulfonate / 2-Phenyloxyethanol / heptane / Brine was studied at optimal salinity. The fact that structure nonhomogeneity develops upon standing was revealed by cryo-TEM, polarizing microscopy and small angle X-ray diffraction. The structural complexity in this middle phase microemulsion is demonstrated and the cause of structure transformation from spherical micelles to thread-like ones, then to vesicles and to lamellar phase was analyzed using a concentration gradient of surfactant and cosurfactant in the middle phase microemulsion. This experiment also shows the advantages of this new cryo-TEM method.

Structure Study of Liquid Crystal in Sodium Dodecylsulfonate Middle Phase Microemulsion

Structure Study of Liquid Crystal in Sodium Dodecylsulfonate Middle Phase Microemulsion

Study of Middle Phase Microemulsion Formed by Petroleum Sulfonate

Study of Middle Phase Microemulsion Formed by Petroleum Sulfonate

Structure Properties for SDS/ n-C4H9OH/ H20 Microemulsion

The structure properties of isotropic solution are studied with the electrochemical methods for SDS/ n-C4H 9OH/H 20 system. The measurements of the conductivity show that the isotropic range in the phase diagram is composed of three areas with different structures: OAV structure connecting with water corner, bicontinuous structure in the middle area and W/ O structure connecting with n-C 4H 9OH corner. This result has been proved by the measurements of eletrochemical diffusion coefficient. The middle phase microemulsion shows bicontinuous structure. The solubilization fraction of n-C 4H 9OH in SDS micelle is about 0.98.