Middle-phase Microemulsion Research Articles

Phase Behavior and Physicochemical Properties of (Sodium Dodecyl Sulfate + Brine + Propan-1-ol + Heptane) Microemulsions

Experimental investigations have been made on the phase behavior of the (sodium dodecyl sulfate + brine + propan-1-ol + heptane) microemulsion system and its stability under reservoir conditions for its use in enhanced oil recovery (EOR). An increase in salinity is found to decrease the single-phase microemulsion region as salt interacts with surfactant to reduce its activity. As salinity changes from a low to high value, a phase transition takes place from Winsor I to Winsor II via Winsor III. The temperature also induces a phase transition for low- and high-salinity microemulsion systems. With an increase in temperature, the phase transition takes place from Winsor I to Winsor III for low salinity and Winsor II to Winsor III for high salinity microemulsion systems. The solubilization parameter of oil increases with an increase in salinity, whereas that of water decreases and at optimal salinity both are same. With increasing salinity, interfacial tension (IFT) between oil and microemulsion decreases, whereas that of water and microemulsion increases. At optimal salinity, both IFT values are the same. The optimal salinity increases with increasing temperature. Interestingly the conductivity of the middle-phase microemulsion system showed maxima around optimal salinity.

Synergetic effect of cationic surfactive ionic liquid C 12mimBr and anionic surfactant SDBS on the phase behavior and solubilization of microemulsions

Synergistic effect of the surfactant mixture of ionic liquid 1-dodecyl-3-methylimidazolium bromide (C 12mimBr) and sodium dodecyl benzene sulfonate (SDBS) on the phase behavior and the solubilization ability of the microemulsion systems was studied with ɛ– β fishlike phase diagrams. The middle-phase microemulsion appears at the range of the mole ratios of C 12mimBr to SDBS 0–0.1 and 0.7–1.0. The solubilization ability (SP*) of the mixed surfactant based microemulsion systems increased markedly compared to the pure C 12mimBr or SDBS-based microemulsion systems. The mixture of C 12mimBr and SDBS also shows preferable synergism in the solubility of the alcohol and the composition of the interfacial layer. The effects of alcohols, alkanes and NaCl concentrations on the ɛ– β fishlike phase diagrams of C 12mimBr/SDBS (molar ratio = 8:2)/alcohol/alkane/brine microemulsion systems were also investigated.

Formulating Middle Phase Microemulsions Using Extended Anionic Surfactant Combined with Cationic Hydrotrope

The phase behavior of systems containing sodium alkyl polypropylene oxide sulfate with equimolar ratio of polypropylene oxide ammonium chloride was determined as a function of salt concentration and alkane carbon number at ambient temperature. Visual inspection as well as cross polarizers were used to detect anisotropy. Solubilization ratios for oil and brine in the middle phases were measured and used to calculate the interfacial tension (IFT) between the microemulsion and oil or brine. The fish diagram is presented showing a minimum amount of 0.20 wt% surfactant needed to form the middle phase. Swelling increases with decreasing the alkane carbon number of the oil. Ultra low IFT values were predicted for the systems investigated.

Interfacial tension and the behavior of microemulsions and macroemulsions of water and carbon dioxide with a branched hydrocarbon nonionic surfactant

Measurements of interfacial tensions for 2-ethyl-hexanol-(propylene oxide)∼ 4.5–(ethylene oxide)∼ 8 (2EH-PO 4.5-EO 8) at the planar water–CO 2 interface and the surfactant distribution coefficient are utilized to explain microemulsion and macroemulsion phase behavior from 24 to 60 °C and 6.9 to 27.6 MPa. A CO 2 captive bubble technique has been developed to measure the interfacial tension γ at a known surfactant concentration in the aqueous phase, with rapid equilibration at the water–CO 2 interface. The surface pressure ( γ o − γ) decreases modestly with density at constant temperature as CO 2 solvates the surfactant tails more effectively, but changes little with temperature at constant density. The area per surfactant at the CO 2–water interface determined from the Gibbs adsorption equation decreases from 250 A 2/molecule at 24 °C and 6.9 MPa, to 200 A 2/molecule at 27.6 MPa. It was approximately twofold larger than that at the water–air interface, given the much smaller γ o driving force for surfactant adsorption. For systems with added NaCl, γ decreases with salinity at low CO 2 densities as the surfactant partitions from water towards the W–C interface. At high densities, salt drives the surfactant from the W–C interface to CO 2 and raises γ. Compared with most hydrocarbon surfactants, this dual tail surfactant is unusually CO 2-philic in that it partitions primarily into the CO 2 phase versus the water phase at CO 2 densities above 0.8 g/ml, and produces γ values below 1 mN/m. With this small γ, a middle phase microemulsion and a C/W microemulsion were formed at low temperatures and high CO 2 densities, whereas macroemulsions were formed at other conditions.

Phase Diagrams and Solubilization of Chlorocarbons in Chlorocarbon/Water/Anionic Surfactant/Alcohol Microemulsion Systems

The solubilization abilities of various chlorocarbons were investigated in a middle phase microemulsion system anionic surfactant sodium dodecyl sulfate (SDS) or sodium dodecyl sulfonate (AS)/n-butanol/chlorocarbon/brine with a ϵ-β fishlike phase diagram. The composition of the balanced interfacial layer of the microemulsion and some other parameters are calculated. The result shows that surfactant little dissolves in water and chlorocarbon phases, while alcohol mainly dissolves in water and oil phases besides in the interfacial layer. The order of the solubilization ability is dichloromethane (CH2Cl2) ∼ carbon tetrachloride (CCl4) > tetrachloroethylene (PCE) > o-dichloro-benzene. The solubility of the alcohol decreases with the increase in NaCl concentrations, which should be compensated by the increase in the amount of alcohol as cosolvent (Cs), so as to maintain the balanced interfacial layer. Salinity has little effect on the partition of surfactant between phases.

Phase Behavior of Microemulsions Prepared from Surfactant-like Ionic Liquids

Abstract The phase behavior and the influencing factors of middle phase microemulsions prepared from surfactant-like ionic liquid 1-alkyl-3-methylimidazolium bromide (C12mimBr, C14mimBr and C16mimBr) were studied systematically with Winsor-type phase diagrams. The minimum alcohol content needed to form the middle phase microemulsion, the alcohol width (the range of the alcohol concentrations from forming to disappearing of the middle-phase microemulsion) and the percent volume of the optimal middle phase at the midpoint of the middle phase region were obtained from the phase diagrams. It was found that with the increase in the carbon chain length of CnmimBr molecules, the minimum alcohol content and the alcohol width decrease, and the solubilization ability (the percent volume of the middle phase microemulsion) increases. With the increase in CnmimBr content, the minimum alcohol content increases, and the alcohol width increases at first and then decreases, and the solubilization ability of the microemulsion systems increases. The minimum alcohol content, the alcohol width and the solubilization ability are also influenced by alcohols, oils and brine. The minimum alcohol content and the alcohol width decrease, and the solubilization ability increases, with the increase in the carbon chain length of the alcohols, the decrease in the carbon chain length of the oils, and the increase in NaCl contents.

Phase diagrams and chemical physical properties of dodecyl sulfobetain/alcohol/oil/water microemulsion system

The HLB plane equation was deduced according to the mass balance relation in microemulsion systems for the first time. The δ-γ fishlike phase diagram was plotted and the composition of the interfacial layer was calculated for dodecyl sulfobetain/alcohol/oil/water microemulsion system. The solubilities of dodecyl sulfobetian and alcohol and the solubilization capacity for the middle-phase microemulsion were examined. The effects of different alcohols, oils, and aqueous solution composition (NaCl content and pH values) on the phase behavior and the related parameters were also investigated. The phase behavior for dodecyl sulfobetain-based microemulsion system was compared with corresponding phase behavior for lauric-N-methylglucamide-based and sodium dodecyl sulfatebased systems.

Ionic Liquid Tunes Microemulsion Curvature

Middle-phase microemulsions formed from cationic dioctadecyldimethylammonium chloride (DODMAC), anionic sodium dodecylsulfate (SDS), n-butanol, and n-heptane were studied. An ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), was employed as the electrolyte in the aqueous media instead of inorganic salts usually used in microemulsion formulation. Studies have been carried out as a function of the concentrations of [bmim][BF4], n-butanol, total surfactant (cDODMAC+SDS), and temperature on the phase behavior and the ultralow interfacial tensions in which the anionic component is present in excess in the catanionic film. Ultralow interfacial tension measurements confirmed the formation of middle-phase microemulsions and the necessary conditions for stabilizing middle-phase microemulsions. Electrical conductivity, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) experiments were also performed, indicating that the typical heptane domain size has an average radius of 360 A and the ionic liquid induces softening of the charged catanionic film. Most interestingly, the IL concentration (cIL) is shown to act as an effective interfacial curvature-control parameter, representing a new approach to tuning the formulation of microemulsions and emulsions. The results expand the potential uses of ILs but also point to the design of new ILs that may achieve superefficient control over interfacial and self-assembly systems.

Diesel Oil Removal by Froth Flotation Under Low Interfacial Tension Conditions I: Foam Characteristics, and Equilibration Time

Froth flotation is a surfactant‐based separation process which is suitable for treating dilute wastewaters. To achieve high performance for the froth flotation operation, the combination of an ultra‐low interfacial tension (IFT) between excess oil and excess water phases, high foam production rates, and high stability of the foam produced, must be attained. To obtain the ultra‐low interfacial tensions, a Winsor Type III or middle phase microemulsion has to be formed. In this study, branched alcohol propoxylate sulfate sodium salt with 14–15 carbon number and 4 PO groups (Alfoterra 145–4PO) was used to form microemulsions with diesel oil. From the results of this work, an increase in surfactant concentration decreased the IFT, and increased foam stability. To obtain the minimum IFT in the region of a Winsor Type III microemulsion, the addition of 5 wt.% NaCl was needed. However, this optimum salinity does not result in effective froth flotation due to poor foam characteristics. The results indicate that both the IFT and the foam characteristics should be optimized to achieve high efficiency of oil removal in a froth flotation operation. Unlike the previously‐studied ethylbenzene system, agitation of the solution before introduction into the flotation column yielded the lowest diesel oil removal efficiency because of the poor foam characteristics compared to either unagitated systems or systems allowed to equilibrate for one month.

Microemulsion Formation and Detergency with Oily Soil: IV. Effect of Rinse Cycle Design

AbstractThe objective of this work was to apply a microemulsion‐based formulation for the removal of motor oil in laundry detergency at low salinity. To produce the desired phase behavior, three surfactants were used: alkyl diphenyl oxide disulfonate (ADPODS), sodium dioctyl sulfosuccinate (AOT) and sorbitan monooleate (Span 80). The mixed surfactant system of 1.5% ADPODS, 5% AOT and 5% Span 80 (13 parts ADPODS, 43.5 parts AOT, and 43.5 parts Span 80 of the total actives) was found to form a middle phase microemulsion (Type III) at a relatively low salinity of 2.83% NaCl. When this formulation was diluted, detergency performance increased with increasing total surfactant concentration and leveled off above about 0.1% total actives on the three types of fabrics studied (pure cotton, 65/35 polyester/cotton blend, and pure polyester). Detergency was found to improve with increasing hydrophilicity of the fabric with cotton being cleanest after washing and polyester the most difficult to clean. To achieve a specified oil removal, less rinse water can be used if a higher number of lower‐volume rinses are employed. An interesting characteristic of microemulsion‐based formulations is that a substantial fraction of oil removal occurs during the rinse cycle. In this work, this removal is shown to be due to the low oil/water interfacial tension during initial rinsing and is therefore strongly correlated to residual surfactant concentration in the rinse steps. As a result, the number of rinses and the volume of water per rinse can profoundly affect detergency in these systems.

Phase behavior studies of quaternary systems containing N-lauroyl- N-methylglucamide/alcohol/alkane/water

The three-phase behavior of quaternary systems comprising N-lauroyl- N-methylglucamide (MEGA-12)/alcohol/alkane/water has been studied using ε – β fishlike phase diagrams. From the ε – β fishlike phase diagrams a series of phase inversions Winsor I ( 2) → III (3) → II ( 2 ¯ ) were observed, and the hydrophilic–lipophilic balanced (HLB) plane equation for the quaternary system was deduced. Some physicochemical parameters, such as the mass fraction of alcohol in the HLB interfacial layer, A S , the coordinates of the start ( β B , ε B ) and end points ( β E , ε E ) of the middle-phase microemulsion, the mass fractions of MEGA-12 and alcohol in the total system ( C S and C A ), and the solubilities of MEGA-12 and alcohol in oil phase ( S O and A O ), were calculated. The effects of different alcohols, alkanes, and NaCl concentrations in the aqueous phase on the phase behavior and solubilization capacity were investigated, which indicates that alcohol with longer and alkane with shorter hydrocarbon chains have a larger solubilization capacity. NaCl concentration has little influence on the phase behavior.

Middle-phase microemulsion induced by brine in region of low cationic gemini surfactant content

The middle-phase microemulsion (Winsor III) induced by salt in the low surfactant + cosurfactant (S + A) region of n-butanol/ n-octane/water/alkanediyl-α,ω(dimethydodecyl-ammonium bromide) (12-3-12) system was investigated by salinity scan. It is shown that the original water-in-oil single phase cannot form Winsor III even when the NaCl aqueous solution added reaches saturation. However, the original coexisting multi-phase and oil-in-water single phase can form Winsor III easily in a wide concentration range of salt, which is favorable to the application of Winsor III. The super low salinity for the initial formation of Winsor III ( S 1) attributes to the special structure of geminis. The water content, salinity, and temperature have great effect on the volume fraction of Winsor III and the temperature induces different phase transition from Winsor II to Winsor III. The condition for the formation of stable Winsor III was obtained by the interfacial tension (IFT) measurements. The multi-phase microemulsion was also studied by fluorescence, and the information, which was used to determine the microstructure of single-phase microemulsion. The results agree well with that obtained from the conductivity measurement carried out in our previous work.

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.

Studies on the phase behavior of the microemulsions formed by sodium dodecyl sulfonate, sodium dodecyl sulfate and sodium dodecyl benzene sulfonate with a novel fishlike phase diagram

The middle-phase behavior for the quaternary system of sodium dodecyl sulfonate (AS) (sodium dodecyl sulfate, SDS; sodium dodecyl benzene sulfonate, SDBS)/alcohol/oil/water has been studied with a novel ɛ– β fishlike phase diagram at 40 °C. The composition of the hydrophile–lipophile balanced interfacial layer was determined. The coordinates of the start point B and the end point E of the middle-phase microemulsion, and the solubilities of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium dodecyl benzene sulfonate and alcohol in the oil phase were calculated. The solubilization power of the middle-phase microemulsion was investigated. The effects of different alcohols, oils and inorganic salts on both the phase behavior and the composition of the interfacial layer were also investigated. The shorter the carbon chain lengths of the oils and the longer the carbon chain lengths of the alcohols, the higher the solubilization of the microemulsions. The inorganic salt (NaCl) facilitates the microemulsion inversion Winsor I → III → II.

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.

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.

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.

Alternative or Simultaneous Electrochemical Access with Micro Water/Oil Phases in a Middle Phase Microemulsion Based on the Hydrophilic/Lipophilic Balance on Electrode Surfaces

Abstract The electrochemical contact with the micro aqueous phase and the micro organic solvent phase in the “middle phase” microemulsion, in which the water phase and the oil phase bicontinuously coexist on a microscopic scale, was alternatively or simultaneously achieved by controlling the hydrophilicity and lipophilicity on electrode surfaces.

Modeling solubilization of oil mixtures in anionic microemulsions: II. Mixtures of polar and non-polar oils

Polar/amphiphilic oils, called lipophilic linkers, are sometimes added to oil–water–ionic surfactant microemulsions in order to increase the solubilization of hydrophobic oils. The solubilization increase has been well documented for a number of systems. However, mathematical models to calculate the solubilization increase have been proposed only for optimum microemulsions (i.e., middle phase microemulsions solubilizing equal volumes of oil and water). In this paper we propose a model, which predicts solubilization enhancement for non-optimum microemulsion systems as well. The model is an extension of the net-average curvature model of microemulsion. The net-average curvature model is combined with a surface activity model to account for the increased palisade layer solubilization due to the presence of the polar/amphiphilic oil component. New non-linear mixing rules are also incorporated to account for the optimum salinity and the characteristic length variation of the anionic surfactant microemulsion as a function of the lipophilic linker concentration. The model predicts the effect of the lipophilic linker and the electrolyte concentration on the oil solubilization in accordance with the experimental results.

Removal of non-ionic organic pollutants from water via liquid–liquid extraction

The removal of model pollutants bromocresol green (BG) and phenol from water is demonstrated via two liquid–liquid extraction methods. Both methods exploit selective interactions established by the pollutant molecule with a surfactant, oil, or alcohol, and are variants of the more general Winsor systems where the phases are in contact along an extremely large interfacial area. In the first method the surfactant and the co-surfactant move from a predominantly oil-in-water microemulsion (Winsor I), to a middle phase microemulsion (Winsor III), and finally to a water-in-oil microemulsion (Winsor II), as the physicochemical conditions of salinity, temperature or hydrophilic–lipophilic balance of the surfactant system are varied. This method achieves better than 99% removal of the pollutant BG from water. It is argued that the removal is produced upon increasing the salinity of the system because the interaction of BG with a medium chain-length alcohol drives it to move along with the alcohol to another phase. The second method, which is scalable to industrial levels, uses a spontaneously produced water-in-oil microemulsion with large interfacial area that appears after bringing in contact water and a pre-formed Winsor II or Winsor III microemulsion system containing different surfactants and oils. The method is applied to the removal of phenol from water, and it is found that systems with polar oils such as ethyl butyrate or with cationic surfactants such as stearyl trimethylammonium chloride are more efficient in removing phenol than systems with normal alkanes or anionic surfactants. It is also shown that a microemulsion formed using a polar oil performs better than using only the polar oil as the extraction solvent. Finally, the efficiency of the second liquid–liquid extraction method can be increased from 69% in a single-stage process to 83% in a two-stage process, using the same total amount of extraction solvent.