Effect of Interfacial Alcohol Concentrations on Oil Solubilization by Sodium Dodecyl Sulfate Micelles

Alcohol partitioning and its effect on oil solubilization in Winsor Type I microemulsion systems was investigated. The microemulsion systems consisted of sodium dodecyl sulfate (SDS), pentanol, isopropanol (IPA), and dodecane, with either deionized water or an aqueous solution of 50 mM CaCl(2). Alcohol partitioning between aqueous, oil, and interfacial phases of the microemulsion was described using a pseudophase model in which the alcohol was assumed to self-associate in the oil phase. Partitioning in these miroemulsions was consistent with pentanol self-association in the oil phase. IPA did not self-associate but co-associated with pentanol in the oil phase. IPA concentrations as high as 20 g/kg of water had no effect on pentanol partitioning. The partition coefficient for pentanol between aqueous and interfacial phases was about 220 on a mole fraction basis. However, pentanol saturated the interfacial phase at a mole ratio of 3 : 1 pentanol to SDS. Addition of pentanol beyond that sufficient to saturate the interface resulted in large amounts of pentanol partitioning into the oil, reaching concentrations in excess of 25 g dL(-1) of oil phase. Dodecane solubilization increased linearly with pentanol mole fraction in the interface up to the 3 : 1 pentanol-to-SDS saturation level. The fact that dodecane solubilization was unaffected by pentanol at concentrations beyond those necessary for interfacial saturation suggests that pentanol behaves as a cosurfactant and not a cosolvent in these microemulsion systems. Copyright 2000 Academic Press.     

The effect of structural variation of alcohols on water solubilization in nonionic microemulsions 2. Branched alcohols as solubilization modifiers: results and interpretation

In this second part of a paper dealing with the effect of branched alcohols on solubilization, an attempt has been made to provide explanations of experimental data related mostly to the system Brij 97/branched alcohol + dodecane = 1:1 (by weight)/water at 27+/-0.2 degrees C. Applying the Hou-Shah mechanism it was shown that for many C4-C6 branched alcohol isomers having one methyl branch, solubilization behavior is readily interpreted by assuming control of the critical radius, R(c). Two parameters, both included in the definition of the branching factor, F(b) (which was treated in the first part of the paper), were also used to analyze solubilization data. The first, l(i), is defined as the distance from the free end of the alcohol molecule to the methyl branch. The second, d, is virtually N(A), the chain length of the alcohol. When l(i)>3, the solubilization becomes dominated by the natural radius of curvature, R0. Also, we have suggested that for R(c)-control, solubilization will be enhanced in direct proportion to the distance d-l(i), whereas for R0-control, solubilization will increase with decreasing d-l(i). The validity of our assumptions was demonstrated in many cases. Some examples of the more complicated case of double branching (two methyl groups along the alcohol chain) were also analyzed.     

Effect of Pentanol Partitioning on Solubilization of Tetrachloroethylene and Gasoline by Sodium Dodecyl Sulfate Micelles

The effect of interfacial pentanol concentrations on solubilization of tetrachloroethylene (PCE) and gasoline by sodium dodecyl sulfate (SDS) micelles was compared to that for dodecane solubilization, which had been measured in a previous study. The solubilization of PCE and gasoline reached their maximum values at a 1 : 3 SDS-to-pentanol molar ratio in the interface. As pentanol concentrations increased beyond that necessary for interfacial saturation, solubilization of PCE and gasoline decreased. This behavior was similar to that observed when dodecane was the oil phase. Electrical conductivity of aqueous SDS/pentanol solutions followed a trend similar to that for oil solubilization, reaching a maximum value at a 1 : 3 molar ratio of SDS to pentanol in the interface. The results of this and previous studies suggest that pentanol partitioning in SDS micelles can be described by a simple two-region model: Region I is the interface between the water-continuous phase and oil and Region II is the micelle inner core. When the mole fraction of pentanol in the interface is less than 0.75, pentanol partitions strongly into Region I, where it acts as a cosurfactant along with SDS and enhances oil solubilization. Above 0.75 mole fraction in the interface, pentanol partitions strongly into Region II, where it acts as a polar oil and competes with other oils for solubilization. Copyright 2001 Academic Press.     

Sub-zero temperature behavior of water in non-ionic microemulsions

Sub-zero temperature DSC measurements were conducted to evaluate the behavior of water in non-ionic microemulsions. Two surfactant systems were studied. The first, based on ethoxylated fatty alcohol, octaethylene glycol monon-dodecylether [hereafter referred to as C₁₂(EO)₈] and also containing water, pentanol and dodecane at a fixed weight ratio of 1:1. The second system, based on oligomeric ethoxylated siloxanes, water and dodecanol as oil phase. In both systems it was found that in up to 30 wt.% of the total water content, all water molecules solubilize in the amphiphilic phase and are bound to the ethylene oxide (hereafter referred to as EO) head-groups. No free water exists in the surfactant aggregates’ core. Up to three molecules of water are bound to each EO group. In the first system, the behavior changes significantly upon adding more water. The added pentanol allows further swelling and the water penetrates into the amphiphile structures and forms a reservoir of free water. Structures are deformed and grow from elongated channels (up to 15–20 wt.% water), via illdefined (one-dimensional growth) local lamellar structures (up to ca. 60 wt.% water) to spherical normal, O/W micelles (at ≥85 wt.% water). In contrast, the oligomeric systems, due to geometrical restrictions of the amphiphiles and the nature of their curvature that prevents inversion, cannot further solubilize water in the surfactant aggregates’ core, causing phase separation to occur. Part of the results presented in this paper were included in S. E.’s doctoral thesis in Applied Chemistry at The Hebrew University of Jerusalem, Israel.     

Solubilization of triglycerides in liquid crystals of nonionic surfactant

The solubilization of triglycerides [1,2,3-tributanoylglycerol (TBG) and 1,2,3-trihexanoylglycerol (THG)] in water/octa(oxyethylene) dodecyl ether (C(12)EO(8)) systems has been investigated. Oil-induced changes in the structure of liquid crystals in water/C(12)EO(8) system have been studied by optical observation and small-angle X-ray scattering (SAXS) measurements. In the water/C(12)EO(8)/oil systems, solubilization of THG and TBG induces a transition between H(1) (hexagonal) and L(alpha) (lamellar) liquid crystals at high C(12)EO(8) concentrations, whereas at low surfactant concentrations a H(1)-I(1) (discontinuous micellar cubic phase) transition occurs. This anomalous behavior is attributed to the partitioning of solubilized oil in the micelles. At low surfactant concentrations THG is mainly solubilized into the hydrophobic cores of the surfactant micelles, indicating high swelling or low penetration tendency, resulting in a steep increase in the radius of the aggregates (r(H)), thereby inducing a rod-sphere transition. At high surfactant concentrations, THG is not mainly solubilized into the core but distributed between the palisade layer and the core of the aggregates. The TBG is considerably solubilized into the surfactant palisade layer, indicating a high penetration tendency, resulting in an increase in the effective cross-sectional area per surfactant molecule, a(s). The thermal stability of the I(1) phase increases with the solubilization of THG into the aggregate cores. The percentage deviation of the experimental interlayer spacings (P(d)) from complete swelling was also evaluated for different triglycerides in the H(1) and L(alpha) phases or different surfactant concentrations. It is found that the penetration tendency of triglycerides could be used as a tuning parameter for I(1) phase formation depending on the surfactant concentration and the molecular weight of the oil.     

Microemulsion structure in the lenticular monophasic areas of brine/SDS/pentanol/dodecane or hexane systems: electrochemical and fluorescent studies

The properties of pseudo-ternary systems involving brine, sodium dodecylsulfate (SDS), pentanol and dodecane or hexane have been investigated. When the hydrocarbon is dodecane, the microemulsion system includes in addition to the main monophasic area a small lens inserted in an oil-rich zone. With hexane, the microemulsion domain splits into two parts, one of which consists of a narrow scythe-blade shaped area which spreads from the water top up to compositions very rich in hydrocarbon. The properties of these uncommon microemulsions were compared with those of microemulsions belonging to the main monophasic area in order to gain additional understanding of their structure. Results of experiments including electrical conductivity and viscosity measurements, electrochemical and fluorescent probe studies lead to the following conclusions: Microemulsions of the small lens of the brine/SDS/pentanol/dodecane system exhibit properties which are reminiscent of structures with at once water and oil countinuous phases. Microemulsions of the lenticular area of the brine/SDS/pentanol/ hexane system seem to undergo the same structural transitions as microemulsions of systems which present a single monophasic area: water-continuous, bicontinuous and oilcontinuous structures.     

Effect of Adding an Amphiphilic Solubilization Improver, Sucrose Distearate, on the Solubilization Capacity of Nonionic Microemulsions

We have studied the effect of adding sucrose distearate (2C(18)SE) on the solubilization capacity of microemulsions formed in the water/C(12)EO(6)/n-decane system. Upon addition of 2C(18)SE to the binary water/C(12)EO(6) system, a lamellar liquid crystal region developed. This suggests that the rigidity of the surfactant layer is strengthened. The solubilization of water and n-decane in the bicontinuous microemulsions increases about three times upon replacing 10% C(12)EO(6) with 2C(18)SE; besides, the HLB temperature is not greatly affected by 2C(18)SE. On the other hand, sucrose monostearate (C(18)SE) does not have such a function. The effect of added 2C(18)SE on the solubilization capacity of the discrete droplet-type o/w or w/o microemulsions was also studied. The efficiency of the solubilization-improving effect is reduced when the system is far from the HLB temperature. Copyright 2001 Academic Press.     

Solubilization in alkanes by alcohols as reverse hydrotropes or "lipotropes"

Hydrotropes in aqueous systems do not aggregate in micelles, inhibit presence of mesophases and allow significant and progressive solubilization of "insoluble" molecules in water. It was shown that n-alcohols in alkanes develop the same properties, including the power-law for maximum solubilization of "hydrophilic" molecules. The aim of this paper is to highlight properties of reverse hydrotropes or "lipotropes" by taking n-alcohol/alkane mixtures as model systems. So as to establish a clear parallel between lipotropes and hydrotropes the same methodology used to characterize hydrotropes was applied to these systems. The solubilization of solutes insoluble in alkane, i.e. water and a hydrophilic dye in dodecane, enabled by the addition of n-alcohols ( n = 2, 3, 4 and 7) was studied. In parallel, the nonmicellar aggregation state of butan-1-ol and heptan-1-ol in dodecane was investigated by small-angle X-ray scattering. By applying the Porod's treatment the specific area of the H-bond network formed by heptan-1-ol and the area occupied by hydroxyl group in this network were determined as a function of concentration. A correlation between the aggregation of alcohols in dodecane and the solubilization was made. The disrupting of concentrated mesophases by a lipotrope was illustrated by studying the effect of adding n-alcohols to water/oil/extractant ternary systems used in liquid/liquid extraction. Under some conditions the organic phase splits up into two phases: an extractant mesophase and nearly pure oil. The amount of n-alcohols required to make the extractant mesophase disappear was determined for water/alkane/malonamide extractant systems. The influence of the chain length of the n-alcohol on the efficiency as lipotrope was also experimentally studied. The trend obtained was similar to the one observed with the solubilization experiments.     

Effects of Mixed Anionic-Cationic Surfactants and Alcohol on Solubilization of Water-in-oil Microemulsions

The solubilization of water in w/o microemulsions formed with mixed-surfactants containing one anionic and one cationic surfactant and alcohol was studied as a function of alkyl chain length of oil (C6 to C16), mixed-surfactant (sodium dodecyl sulfate, SDS, and cetyltrimethylammonium bromide, CTAB, or cetylpyridinium bromide CPB), and alcohol (1-butanol, 1-pentanol, 1-hexanol). The results show that the solubilization of water in microemulsion systems increases significantly with the mixed-surfactants due to the synergistic effect resulting from the strong Coulombic interactions between cationic and anionic surfactants and the solubilizing efficiency increases as the chain length or concentration of alcohol increases. With increasing the oil chain length the solubilization for water increases, decreases, and has the chain length compatibility effect when the systems contain 1-hexanol, 1-butanol, 1-pentanol, respectively. The total solubilizing capacity increases as the surfactant concentration (keep the ratio of SDS to butanol constant) increases.     

Dielectric and Calorimetric Characteristics of Bound and Free Water in Surfactant-Based Systems

The hydration behavior of the system polyoxyethylene (10) oleylalcohol [C_18:1 (EO)₁₀ or Brij 97]/water/dodecane/butanol (model system B) was investigated along a dilution line for which the respective weight ratio of dodecane:butanol:Brij 97 is 3:3:4. Two experimental methods were applied: time domain dielectric spectroscopy (TDDS) and sub-zero temperature differential scanning calorimetry (SZT-DSC). Two types of bound water (with melting peaks at -25 and -11°C) were detected by SZT-DSC (using the endothermic mode), whereas TDDS revealed only one such type. Nevertheless, roughly the same total amount of bound water was estimated from these two techniques. The average number of bound water molecules per ethylene oxide (EO) group, N_W/EO is 2.3 (TDDS data) or 2.5 (SZT-DSC data) in good agreement with the observation that 1–2 water layers are formed in the hydration of ethoxylated surfactants. We have also shown that butanol is involved in the formation of the bound water that melts at -25°C. We suggest that butanol molecules occupy binding sites within the second hydration shell, thereby reducing the expected total bound water content.     

Microemulsions studies: Correlation between viscosity,electrical conductivity and electrochemical and fluorescent probe measurements

Microemulsion systems involving brine and dodecane, and stabilized by sodium dodecylsulfate and both pentanol and heptanol have been investigated. Results of various experiments including conductivity and viscosity measurements, electrochemical diffusion coefficients and fluorescent probe studies have been gathered and compared in order to gain additional understanding of the microemulsion structure. The diffusion coefficients of hydrophilic hydroquinone and hydrophobic ferrocene obtained from the Levich equation at the rotating disc electrode, vary as the self-diffusion coefficients of water and dodecane, respectively; the results are consistent with those obtained by other workers from tracer or NMR self-diffusion studies. The fluorescence analysis of the polarity sensed by pyrene and the microviscosity felt by dipyrenylpropane suggests that the progressive addition of pentanol and dodecane to SDS micelles leads to solubilizate the probes more in the droplet interior where they experience a more hydrophobic environment. The systematic study of the two microemulsion systems provides insight into the microscopic properties of the oil domains in which the fluorescent probes are assumed to be located. In the system stabilized by n-heptanol as cosurfactant, the microviscosity sensed by P(CH₂)₃P is shown to be much lower than the bulk viscosity of the microemulsion. All the results evidence the well-known structural transitions: water continuous, bicontinuous and oil continuous in the single monophasic area of the brine/ SDS/n-pentanol/dodecane system; premicellar aggregates and water swollen micelles in the W/O area of the brine/SDS/n-heptanol/dodecane system.     

Effect of temperature and salt on the phase behavior of nonionic and mixed nonionic-ionic microemulsions with fish-tail diagrams

The phase behavior of Brij-56/1-butanol/n-heptane/water is investigated at 30 degrees C with alpha [weight fraction of oil in (oil+water)]=0.5, wherein a 2-->3-->2 phase transition occurs with increasing W1 (weight fraction of 1-butanol in total amphiphile) at low X (weight fraction of both the amphiphiles in the mixture) and a 2-->1-->2 phase transition occurs at higher X. Addition of an ionic surfactant, sodium dodecylbenzene sulfonate, destroys the three-phase body and decreases the solubilization capacity of the system at different delta (weight fraction of ionic surfactant in total surfactant). A three-phase body appears at alpha=0.25, but not at alpha=0.75 for the single system. No three-phase body appears with the mixed system at either alpha value. Increased temperature increases the solubilization capacity of the Brij-56 system; on the other hand, a negligible effect of temperature on the Brij-56/SDBS mixed system has been observed. Addition of salt (NaCl) produces a three-phase body for both single and mixed systems and increases their solubilization capacities. The monomeric solubility of 1-butanol in oil (S1) and at the interface (S1s) has been calculated using the equation hydrophile-lipophile balance plane for both singles- and mixed-surfactant systems. These parameters have been utilized to explain the increase in solubilization capacity of these systems in the presence of NaCl.     

Thermodynamic properties of alcohols in a micellar phase. Binding constants and partial molar volumes of pentanol in sodium dodecylsulfate micelles at 15, 25, and 35°C

Densities of the ternary system water-sodium dodecylsulfate (NaDS)-pentanol and of the binary systems butanol-octane and pentanol-octane were measured at 15, 25, and 35 °C. The apparent molar volume of pentanol in the ternary system was analyzed using a mass-action model for the alcohol distribution in micellar solutions. The partial molar volume of alcohol bound to the micelles and the ratio between the binding constant and the aggregation number of the surfactant are calculated. The partial molar volume binding constant, is discussed in terms of solubilization sites of the alcohol in the micelles whereas the binding constant is compared with that derived from the Nernstian partition constant previously obtained calorimetrically. From the binding constant and Poisson statistics the distribution function of the number of alcohol molecules per micelle, as a function of the concentration of alcohol and of surfactant, are calculated. The derived distribution functions show that a large amount of alcohol can be solubilized in the micelles so that alcoholic mixed micelles can be predicted when the concentration of pentanol is greater than that of NaDS.     

Glycerol effects on the formation and rheology of cubic phase and related gel emulsion

We have investigated the effects of glycerol on the formation and rheological behavior of cubic phase (I(1)) and related O/I(1) gel emulsion in a water/C(12)EO(8)/dodecane system at 25 degrees C. The phase behavior of the water/C(12)EO(8)/dodecane system was studied by optical observation and structures of different liquid crystalline phases were identified by small-angle X-ray scattering (SAXS) techniques. Addition of dodecane (2 wt%) to aqueous solutions of C(12)EO(8) in a concentrated region (40 wt%) leads to the formation of the I(1) phase (which was absent without the addition of oil). The I(1) phase solubilized some amount of oil and at higher oil concentrations the I(1)+O phase was formed, allowing the preparation of O/I(1) gel emulsion. Rheological measurements have shown that the complex viscosity, |eta( *)|, of the I(1) phase is tremendously high ( approximately 10(7) Pas) and it increases with increasing oil concentration, attains a maximum value near the phase boundary, and then decreases drastically in the I(1)+O region. The increasing |eta( *)| or decreasing tandelta(G(')/G(')) can be ascribed with the interactions among the neighboring micelles. The decreasing trend of the |eta( *)| in the I(1)+O region is simply due to the low volume fraction of the I(1) phase. It has been shown that glycerol decreases the viscosity of the I(1) phase and related gel emulsion, which is due to the I(1)-hexagonal phase (H(1)) microstructural transition. Digital images show the physical appearance of the emulsion, which depends on the glycerol concentration changes from translucent to transparent.     

Solubilization of butanol/pentanol/hexanol in dodecylpyridinium chloride

The specific conductivities of dodecylpyridinium chloride have been determinated in water-butanol/pentanol/hexanol solutions in the temperature range of 10 to 35°C, and butanol, pentanol and hexanol concentrations up to 0.05 mol kg^–1. From these data the temperature dependence of the critical micelle concentration, (cmc), was determined. The molar fraction of alcohol in the micelle was estimated using the theory suggested by Motomura et al. for surfactant binary mixtures. The standard Gibbs free energy of solubilization of alcohols in the micelles was worked out using the phase separation model.     

Study of nano-emulsion formation by dilution of microemulsions

The influence of different dilution procedures on the properties of oil-in-water (O/W) nano-emulsions obtained by dilution of oil-in-water (O/W) and water-in-oil (W/O) microemulsions has been studied. The system water/SDS/cosurfactant/dodecane with either hexanol or pentanol as cosurfactant was chosen as model system. The dilution procedures consisted of adding water (or microemulsion) stepwise or at once over a microemulsion (or water). Starting emulsification from O/W microemulsions, nano-emulsions with droplet diameters of 20 nm are obtained, independently on the microemulsion composition and the dilution procedure used. In contrast, starting emulsification from W/O microemulsions, nano-emulsions are only obtained if the emulsification conditions allow reaching the equilibrium in an O/W microemulsion domain during the process. These conditions are achieved by stepwise addition of water over W/O microemulsions with O/S ratios at which a direct microemulsion domain is crossed during emulsification. The nature of the alcohol used as cosurfactant has been found to play a key role on the properties of the nano-emulsions obtained: nano-emulsions in the system using hexanol as cosurfactant are smaller in size, lower in polydispersity, and have a higher stability than those with pentanol.     

Studies on the middle-phase microemulsion of lauric-<Emphasis Type="Italic">N</Emphasis>-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 ( ) 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. The text was submitted by the authors in English.     

CTAB/CnH2n+1OH/H2O体系的热力学和电化学性质

微乳液通常由表面活性剂、助表面活性剂、油和水等四组分自发生成,注意到表面活性剂、助表面活性剂和水三组分体系与上述四组分体系在相行为及其物理化学性质上具有相似性,为方便起见,人们通常以此三组分体系为对象,研究四组分体系微乳液的有关性质,并亦将其称为微乳液[1].另一方面,助表面活性剂一般为具有中等碳链长度的直链饱和一元醇,但实验已经发现,即使是像乙醇这样的短链醇,也能以相当数量存在于胶束栅栏中形成膜相[2],或存在于两亲双层中形成层状液晶[3].本文以热力学方法与无探针循环伏安法研究了直链饱和一元醇对ＣＴＡＢ/醇(Ｃ2Ｈ…     

Hexagonal phase based gel-emulsion (O/H1 gel-emulsion): formation and rheology

The formation, stability, and rheological behavior of a hexagonal phase based gel-emulsion (O/H1 gel-emulsion) have been studied in water/C12EO8/hydrocarbon oil systems. A partial phase behavior study indicates that the oil nature has no effect on the phase sequences in the ternary phase diagram of water/C12EO8/oil systems but the domain size of the phases or the oil solubilization capacity considerably changes with oil nature. Excess oil is in equilibrium with the hexagonal phase (H1) in the ternary phase diagram in the H1+O region. The O/H1 gel-emulsion was prepared (formation) and kept at 25 degrees C to check stability. It has been found that the formation and stability of the O/H1 gel-emulsion depends on the oil nature. After 2 min observation (formation), the results show that short chain linear hydrocarbon oils (heptane, octane) are more apt to form a O/H1 gel-emulsion compared to long chain linear hydrocarbon oils (tetradecane, hexadecane), though the stability is not good enough in either system, that is, oil separates within 24 h. Nevertheless, the formation and stability of the O/H1 gel-emulsion is appreciably increased in squalane and liquid paraffin. It is surmised that the high transition temperature of the H1+O phase and the presence of a bicontinuous cubic phase (V1) might hamper the formation of a gel-emulsion. It has been pointed out that the solubilization of oil in the H1 phase could be related to emulsion stability. On the other hand, the oil nature has little or no effect on the formation and stability of a cubic phase based gel-emulsion (O/I1 gel-emulsion). From rheological measurements, it has found that the rheogram of the O/H1 gel-emulsion indicates gel-type structure and shows shear thinning behavior similar to the case of the O/I1 gel-emulsion. Rheological data infer that the O/I1 gel-emulsion is more viscous than the O/H1 gel-emulsion at room temperature but the O/H1 gel-emulsion shows consistency at elevated temperature.     

Design of low-toxic and temperature-sensitive anionic microemulsions using short propyleneglycol alkyl ethers as cosurfactants

The phase behavior of anionic microemulsions composed of water, sodium dodecyl sulfate (SDS), dodecane, and short propyleneglycol monoalkyl ethers (C(n)()PO(m)(); n = 3, m = 1 and n = 4, m = 2, 3) is studied. From the pseudoternary phase diagrams, it is inferred that C(n)()PO(m)() compounds have cosurfactant behaviors comparable to those of 1-butanol and 1-pentanol, which are the most efficient and widely used cosurfactants. In contrast to these alcohols, the C(n)()PO(m)() cosurfactants induce high temperature dependences in the SDS microemulsion systems. Furthermore, SDS/C(n)()PO(m)() microemulsions can be formed with small SDS concentrations (SDS/C(4)PO(3) mass ratio of 1/6.26). These have a low toxicity in contrast to systems containing genotoxic short ethyleneglycol ethers (C(n)()EO(m)()) as the cosurfactant. The strong temperature dependence can be favorable in the recovery of reaction products when the microemulsion is used either as a reaction medium or in extraction processes.