Winsor Type Research Articles

Formation of Single-Phase Microemulsions in Toluene/Water/Nonionic Surfactant Systems

Mixtures of toluene and water from 5 to 50% oil fraction and 5 to 25% surfactant by weight were studied. Winsor Type IV microemulsions were formed in numerous cases. Review of partial ternary phase diagrams for these systems indicated the area of single-phase microemulsion with toluene could be maximized at an hydrophilic-lipophilic balance (HLB) of approximately 14.5. Select single-phase samples were further analyzed by surface tension and dynamic light scattering techniques, which allowed a detailed characterization of the solution equilibrium thermodynamics and size stability. Particle sizes averaged approximately 5 nm and were nearly constant over a wide variety of conditions and for 6-18 months. When benzyl alcohol was used instead of toluene, the optimum HLB for the formation of single-phase systems was found to have a lower limit of 17. Particle sizes in these systems were <30 nm but showed greater variability. The decrease in particle size as surfactant concentration increased was determined to be associated with changes in ethlyene oxide chain conformation. The increase in particle size due to swelling with increased oil concentration was used to determine the surfactant surface area in the oil phase. A detailed comparison of alkylamine ethoxylate to octyl- and nonylphenol ethoxylate surfactants in terms of micelle thermodynamics, size, and stability indicate that the alkylamine-based surfactants are potential candidates for the replacement of nonylphenol-based surfactants in some systems with a more polar oil phase like benzyl alcohol.

Study and Modeling of Iron Hydroxide Nanoparticle Uptake by AOT (w/o) Microemulsions

Control over nanoparticle size is a key factor which labels a given preparation technique successful. When organic reactions are mediated by ultradispersed catalysts, the concentration of the colloidal nanoparticle catalysts and their stability become key factors as well. In this study, variables affecting iron hydroxide nanoparticle size, stability, and maximum possible colloidal concentration in AOT/water/isooctane microemulsions were investigated. Iron hydroxide was prepared in single microemulsions by first solubilizing iron chloride powder in the water pools, followed by addition of aqueous NaOH. Upon addition of NaOH, Fe(OH)3 nanoparticles stabilized in the water pools formed in addition to bulk precipitate of Fe(OH)3. The time-invariant concentration of the stabilized Fe(OH)3 is defined as the nanoparticle uptake, and it corresponds to the maximum possible concentration of the colloidal nanoparticles. The effect of the following variables on the nanoparticle uptake and size distribution was investigated: mixing time; surfactant concentration; water to surfactant mole ratio; and the initial concentration of the precursor salt. At 300 rpm of mixing a constant uptake of iron hydroxide nanoparticles was achieved in about 2 h and further mixing had limited effect on the nanoparticle uptake and particle size. An optimum R was found for which a maximum nanoparticle uptake was obtained. Nanoparticle uptake increased linearly with the surfactant concentration and displayed a power function with the initial concentrations of the precursor salt. The surface area/g of the nanoparticles was much higher than literature values, however, following a trend opposite to that of the nanoparticle uptake. The surface area/unit volume of the microemulsion, on the other hand, followed the same trend as the nanoparticle uptake. The particle size increased as R and/or the surfactant concentration increased. A mathematical model based on correlations for water uptake by Winsor type II microemulsions accurately accounted for the effect of the aforementioned variables on the nanoparticle uptake.

Studies on the middle-phase microemulsion of lauric-N-methylglucamide

The middle-phase behavior and the solubilization power of the lauric-N-methylglucamide/alcohol/alkane/water quaternary system are studied. A series of phase inversions of Winsor Type I (2) → III (3) → II ( $$\overline 2 $$ ) emulsions are observed from the fishlike phase diagram. The compositions of the hydrophilic-lipophilic balanced interfacial layer in the middle of the middle-phase are calculated by the HLB plane equation. The effects of different alkanes, alcohols, and the concentration of an NaCl solution on the phase behavior and solubilization power are investigated, which indicates that alkanes with short hydrocarbon chains and alcohols with long alkyl chains have large solubilization power. The concentration of NaCl solution has a small influence on the solubilization power, whereas, the larger the NaCl concentration, the smaller the weight fraction of alcohol needed to balance the hydrophilic-lipophilic layer.

Structural transformations in a water-n-octane + chloroform-sodium dodecyl sulfate-n-pentanol microemulsion

Conductivity, viscosity, and water and oil solubilization are measured, and the parameter of hydrophilic-lipophilic balance is calculated for stable water-n-octane + chloroform-n-pentanol-sodium dodecyl sulfate microemulsions (Winsor Type IV system) at a water content of 2.5–56 vol %. Domains of the most probable existence of globular and bicontinuous structures and the boundaries of the transitions between the following states of the system are determined: reverse micelles containing solubilized water, a water-in-oil microemulsion, a microemulsion with a continuous structure, an oil-in-water microemulsion, and normal micelles containing solubilized oil. Peculiarities of the bicontinuous structure of the microemulsions and the relation between parameter R of the Winsor theory and the parameter of the hydrophilic-lipophilic balance of microemulsion, which the authors have determined, are discussed.

Studies on the Middle‐phase Microemulsion of Lauric‐N‐methylglucamide

AbstractThe phase behaviour of the middle‐phase microemulsion for the quaternary system lauric‐N‐methylglucamide (MEGA‐12)/n‐butanol/alkane/water has been studied with Winsor type, δ‐γ fishlike and novel ε‐β fishlike phase diagrams. A series of phase inversions Winsor I ($\underline {2}$)→III (3)→II ($\overline {2}$) were observed for the three kinds of phase diagrams. The phase types, the phase volumes and the range of alcohol concentrations from the beginning to the end of the middle‐phase microemulsion were obtained from Winsor phase diagram. From δ‐γ fishlike phase diagram, the physicochemical parameters, such as the mass fraction of n‐butanol in the hydrophile‐lipophile balanced interfacial layer, AS, the coordinates of the start and end points of the middle‐phase microemulsion, and the solubilities of MEGA‐12 and n‐butanol in alkane phase were calculated. The novel ε‐β fishlike phase diagram was also presented. From this kind of diagram, the above experimental phenomena were observed and the physicochemical parameters were calculated precisely. The novel fishlike phase diagram has advantages over the Winsor and δ‐γ fishlike phase diagrams in the evaluation of the solubilization power of the microemulsion and calculation of the related physicochemical parameters.

Enhanced triolein removal using microemulsions formulated with mixed surfactants

AbstractIn previous work, a microemulsion‐based formulation approach yielded excellent laundry detergency with hydrophobic oily soils hexadecane and motor oil. In this work, the same approach is used in detergency of triolein, which is a model triglyceride, some of the most difficult oils to be removed from fabric. The linker concept was applied in formulation of the microemulsion system. Three different surfactants were used: (i) dihexyl sulfosuccinate, an ionic surfactant with a moderate hydrophile‐lipophile balance (HLB); (ii) secondary alcohol ethoxylate, a lipophilic nonionic surfactant with a very low HLB; and (iii) alkyl diphenyl oxide disulfonate (ADPODS), a hydrophilic anionic surfactant with a very high HLB. The phase behavior and interfacial tension (IFT) of the surfactant systems were determined with different concentrations of ADPODS. The results indicate that as the HLB of the system increases, a higher salinity is required to shift the phase transition from Winsor Type I to Type III to Type II. The three formulations at different salinities were used in detergency experiments to remove triolein from polyester/cotton sample fabric. The results showed that there were two peaks of maximum detergency in the range of salinity from 0.1% to 10% NaCl. The higher the hydrophilicity of the system, the higher the salinity required for maximum detergency. The results of the dynamic IFT and the detergency performance from two rinsing methods lead to the hypothesis that one of these maxima in detergency results from a spreading or wetting effect. The other maximum in detergency is believed to be related to ultralow IFT associated with oil/water middle‐phase microemulsion formation. Triolein removal exceeding 80% was attained, validating the microemulsion approach to detergency.

Microemulsion phase behavior of anionic‐cationic surfactant mixtures: Effect of tail branching

AbstractThis research evaluated middle‐phase microemulsion formation by varying the mole ratio of anionic and cationic surfactants in mixtures with four different oils (trichloroethylene, n‐hexane, limonene, and n‐hexadecane). Mixtures of a double‐tailed anionic surfactant (sodium dihexyl sulfosuccinate, SDHS) and an unbalanced‐tail (i.e., doubletailed with tails of different length) cationic surfactant (benzethonium chloride, BCl) were able to form microemulsions without alcohol addition. The amount of NaCl required to form the middle‐phase microemulsion decreased dramatically as an equimolar anionic‐cationic surfactant mixture was approached. Although the mixture of anionic and cationic surfactants demonstrated a higher critical microemulsion concentration (cμc) compared to the anionic surfactant alone, the Winsor Type IV single‐phase microemulsion started at lower surfactant concentrations for the anionic‐cationic mixture than for the anionic surfactant alone. Under optimum middlephase microemulsion conditions, mixed anionic‐cationic surfactant systems solubilized more oil than the anionic surfactant alone. Pretreatment detergency studies were conducted to test the capacity of these mixed surfactant systems to remove oil form fabrics. It was found that anionic‐rich mixed surfactant formulations yielded the largest oil removal, followed by cationic‐rich systems.

Analytical solutions for surfactant‐enhanced remediation of nonaqueous phase liquids

Benchmark compositional solutions are presented for the remediation of aquifers contaminated with nonaqueous phase liquids (NAPLs) by injection of surfactant‐water mixtures. The method of characteristics (MOC) is used to find one‐dimensional analytical solutions to the Riemann problem where three partially miscible phases are flowing in a Winsor type III microemulsion. In partially miscible flow, two or three phases form when the components (constituents) are mixed in some but not all proportions. Three relative permeability models are examined, and MOC solutions are found. Fine‐grid numerical simulations match the MOC results. The composition routes and contaminant recoveries can differ significantly depending on the relative permeability model used. The results for each model are optimized to determine the minimum surfactant volume required for complete contaminant recovery. Unlike two‐phase partially miscible flow, the presence of three flowing phases makes it impossible to reach miscibility between the injected and resident fluids, regardless of surfactant concentration.

Ethylbenzene Removal by Froth Flotation Under Conditions of Middle‐Phase Microemulsion Formation I: Interfacial Tension, Foamability, and Foam Stability

The objective of this study was to investigate the relationship of the froth flotation performance in removal of emulsified ethylbenzene in water with microemulsion formation and with foam formation characteristics. The surfactant used was dihexyl sulfosuccinate (Aerosol MA or AMA) which can form microemulsions with ethylbenzene. The systems studied were designed to form Winsor Type III microemulsions with ethylbenzene, which generally correspond to ultra‐low interfacial tensions between oil and water phases. By varying the surfactant concentration, NaCl concentration, and oil‐to‐water ratio, it was found that the lowest interfacial tension was obtained at 1 wt% AMA and 3 wt% NaCl, while the interfacial tension was not substantially influenced by the oil‐to‐water ratio. The highest oil removal was achieved in froth flotation with 0.3 wt% AMA and 3 wt% NaCl. No separation was experienced when the NaCl concentration exceeded 4 wt% due to the poor foamability of the froth formed under these conditions. Therefore, these results demonstrate that both interfacial tension and foam characteristics influence the efficiency of oil removal in the froth flotation process.

Microemulsion formation and detergency with oily soils: III. Performance and mechanisms

AbstractThe objective of this study was to investigate the correlation between oily soil removal efficiency and low oil‐water interfacial tension (IFT) generated by microemulsion formation. A mixture of sodium dioctyl sulfosuccinate, alkyl diphenyl oxide disulfonate, and sorbitan monooleate was selected as a detergent formulation to evaluate detergency performance for two highly hydrophobic oils: hexadecane and motor oil. The maximum detergency corresponds to formation of a Winsor Type III microemulsion as well as to the supersolubilization region, which is a Winsor Type I microemulsion close to the Winsor Type III region. In addition, the oil removal in the rinse step is almost as high as that in the wash step for both regions. We propose the following mechanism to explain these results: During the wash step, the contact angle of the oil on the fabric surface is progressively increased, resulting in the detachment of the oil droplets. However, owing to the very low IFT, the spreading effect is dominant, thereby causing incomplete oil removal. During the subsequent rinse step, the IFT increases, passing through a composition at which the rollup mechanism causes additional oil removal. These results demonstrate that microemulsion formation and the resulting IFT reduction are important mechanisms in oily soil detergency.

Preferential solubilization of dodecanol from dodecanol–limonene binary oil mixture in sodium dihexyl sulfosuccinate microemulsions: Effect on optimum salinity and oil solubilization capacity

Solubilization of dodecanol–limonene binary oil mixtures has been studied in saturated Winsor type I and III sodium dihexyl sulfosuccinate microemulsions. The systems showed different oil solubilization behavior below and above dodecanol volume fraction 0.2. Below 0.2 dodecanol volume fraction regular Winsor type microemulsions formed. The oil solubilization was characterized in this concentration range by the optimum salinity and the maximum characteristic length. Dodecanol showed Langmuirian-type surface excess adsorption at the vicinity of the surfactant layer. Variation of the optimum salinity and middle phase characteristic length with increasing dodecanol concentration could be linked to changes in the dodecanol surface excess. These relationships were used to develop new mathematical models for the optimum salinity and characteristic length as a function of oil phase composition. Both models yield excellent agreement with the data. Above dodecanol volume fraction 0.2 regular Winsor type III microemulsions are not formed. Therefore our new models are not applicable in this concentration range.

Clean-up of Oily Wastewater by Froth Flotation: Effect of Microemulsion Formation II: Use of Anionic/Nonionic Surfactant Mixtures

ABSTRACTFroth flotation can be an effective method to remove emulsified oil from wastewater. In this series of studies, the relationship between surfactant phase behavior (the type of microemulsion that is formed between the oil and water) and efficiency of the flotation of ortho-dichlorobenzene is being investigated. The phase behavior is related to surfactant composition and salinity in this work. Use of anionic/nonionic surfactant mixtures here permit examination of a wide range of conditions compared to the use of only anionic surfactants. Optimum oil flotation corresponds to a Winsor Type III microemulsion, which also corresponds to minimum interfacial tensions between oil and water and to maximum solubilization of water and of oil into a surfactant-rich microemulsion phase. In this work, high selectivity for oil compared to water in the overhead froth was demonstrated, a necessary criterion for an effective separation.

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 two-state model for selective solubilization of benzene-limonene mixtures in sodium dihexyl sulfosuccinate microemulsions.

When surfactants are used to solubilize oil, the oil to be solubilized is often a mixture of components with differing properties, for example, solubilization of drug molecules in microemulsion formulations, remediation of organic polluted aquifers using surfactants, and so forth. Previous research has demonstrated that selective solubilization of one organic component over the other may occur if the organic components are dissimilar. In this research, we investigated selective solubilization from benzene-limonene mixtures in Winsor type I and III microemulsion systems containing water, sodium di-n-hexyl sulfosuccinate, and NaCl. The effect of the oil phase composition and the electrolyte concentration on the selectivity was studied. It was found that the selectivity toward benzene was highest at low electrolyte and benzene concentrations, decreasing as the electrolyte or benzene concentration increased. The results are discussed on the basis of the two-state solubilization theory and by correlating the curvature of the surfactant film in the microemulsion with changes of the electrolyte concentration and the oil phase composition. A simple mathematical model is developed for the selectivity, which combines the two-state solubilization theory and the net-average curvature model of microemulsion solubilization to yield close agreement with the experimental data.

Apparent Equilibration Time Required for Surfactant−Oil−Water Systems to Emulsify into the Morphology Imposed by the Formulation. Part 2: Effect of sec-Butanol Concentration and Initial Location

Winsor type I equilibrated surfactant-oil-water (SOW) systems produce o/w emulsions upon stirring. However, if the surfactant is initially dissolved in the oil phase, the attained type after inmediate emulsification is usually w/o. If the SOW system is partially equilibrated, it could result in a normal o/w emulsion, as if it were fully equilibrated. The minimum contact time for that to happen, the so-called apparent equilibration time tAPE, was previously shown (Langmuir 2002, 18, 607) to strongly depend on formulation, surfactant molecular weight, and oil viscosity. The present report shows that it depends on alcohol concentration and location in the unequilibrated system.

Microemulsion formation and detergency with oily soils: II. Detergency formulation and performance

AbstractIn part I of this series (J. Surfact. Deterg. 6, 191–203, 2003), the mixed surfactant system of sodium dioctyl sulfosuccinate (AOT), alkyl diphenyl oxide disulfonate (ADPODS) and sorbitan monooleate (Span 80) was shown to form Winsor type I and type III microemulsions with hexadecane and motor oil. In addition, high solubilization and low interfacial tension were obtained between the oils and surfactant solutions both in the supersolubilization region (Winsor type I system close to type III system) and at optimal conditions in a type III system. In the present study, this mixed surfactant system was applied to remove oily soil from fabric (a polyester/cotton blend), and detergency results were correlated to phase behavior. Dynamic interfacial tensions were also measured between the oils and washing solutions. In the supersolubilization and in the middle‐phase regions (type III), much better detergency performance was found for both hexadecane and motor oil removal than that with a commercial liquid detergent product. In addition, the detergency performance of our system at low temperature (25°C) was close to that obtained at high temperature (55°C), consistent with the temperature robustness of the microemulsion phase behavior of this system.

STUDY ON THE THIOPHOSPHINIC EXTRACTANTS. I. THE BASIC PROPERTIES OF THE EXTRACTANTS AND THE PHASE BEHAVIOR IN THEIR SAPONIFIED SYSTEMS1*

ABSTRACT Commercial extractants Cyanex 302 and Cyanex 301 have been purified, and their sodium salts prepared. The basic physic-chemical parameters, such as solubility and pKa values in water of the acids, cmc of the salts, have been reported. The phase behaviors during saponification of purified extractants by NaOH have been measured. The system of monothiophosphinic extractant is similar to that of purified Cyanex 272 except when the middle phase of the former appears at lower neutralization fraction and the volume of the third phase is bigger. But there is no third phase formed in dithiophosphinic acid extractant system and it always maintains the equilibrium of bottom phase microemulsion with the excessive oil phase (Winsor type I). The pseudo-ternary phase diagrams of unpurified Cyanex 302 (or Cyanex 301)-n-C6H14-NaOH (2.4 mol/L) are compared with Cyanex 272 system. There are some differences in all of 3L, 2L, L and D regions. The pseudo-ternary phase diagrams of purified sodium salt NaA-n-C5H11OH-kerosene (80%, w/w)-H2O system for different extractants have also been drawn. The mono-phase microemulsion (w/o) area increases with the increasing of sulfur atom in extractants, indicating that the replacement of oxygen atom by sulfur makes sodium salt more hydrophilic. This study is supported by the National Natural Science Foundation of China (29971020) and the Natural Science Foundation of Shandong Province (L2000B01).

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.

Apparent Equilibration Time Required for a Surfactant−Oil−Water System to Emulsify into the Morphology Imposed by the Formulation

This paper deals with surfactant−oil−water (SOW) system whose formulation corresponds to a Winsor type I phase behavior at equilibrium. When the surfactant is initially dissolved in the oil phase and the system is immediately stirred, the usual emulsion morphology is the anomalous W/O type, which is not the expected one for a Winsor type I formulation. However, if the SOW system is left to rest and to partially equilibrate during some time, it could result in a normal O/W emulsion upon stirring, as if it were fully equilibrated for several days. The minimum rest time required to produce the normal emulsion morphology is called the apparent equilibration time tAPE. It is shown that tAPE strongly depends on formulation and decreases as formulation approaches the boundary between Winsor I and Winsor III phase behavior. In some instances tAPE is essentially zero, as if equilibration had taken place instantly. The apparent equilibration time tAPE is found to depend on the surfactant molecular weight and on the oil viscosity.

EVALUATION OF REMEDIATION PERFORMANCE AND COST FOR FIELD-SCALE SINGLE-PHASE MICROEMULSION (SPME) FLUSHING

Pump-and-treat strategies employed to contain contaminant plumes have been demonstrated to be inefficient, and often ineffective, for remediation of aquifers contaminated by nonaqueous phase liquids (NAPLs). This has prompted the development of alternative technologies to provide enhanced remediation of NAPL source zones. The results reported here are from a solubilization study wherein the objective was to achieve high NAPL remediation efficiencies using a low concentration of chemical additives in the flushing solution. A surfactant/alcohol mixture was used to generate a Winsor Type I system, where the NAPL was solubilized and transported as a single-phase microemulsion (SPME). For the SPME process, only 5.5 wt% of the flushing solution comprised chemical additives. The costs associated with this project are discussed and approaches aimed at reducing costs are suggested.