Formation of Cubic-Phase Microemulsions with Anionic and Cationic Surfactants at Equal Amounts of Oil and Water

The formation and microstructure of cubic phases were investigated in anionic and cationic surfactant-containing systems at 25 degrees C. In the system sodium dodecyl sulfate(SDS)-dodecyltrimethylammonium bromide(DTAB)-water, mixing of two surfactants shows the phase transition hexagonal phase (H(1))-->surfactant precipitate, accompanied by an obvious decrease in the cross-sectional area per surfactant in the rod micelles of the hexagonal liquid crystal. In the mixed systems brine(A)-dodecane(B)-SDS(C)-DTAB(D)-hexanol(E), the isotropic discontinuous cubic phase is formed from the H(1) phase at a low cationic surfactant weight fraction, Y=D/(C+D), and from the lamellar phase at high Y upon dilution with equal amounts of oil and brine, respectively. The minimum surfactant concentration to form the cubic phase decreases with increases both in cationic surfactant weight fraction Y from 0 to 0.30 and in hexanol weight fraction, W(1)=E/(C+D+E), accordingly. The maximum solubilization for oil of the cubic phase reaches 43 wt% at 14 wt% of mixed surfactants and alcohol. Copyright 2000 Academic Press.     

Chiral microemulsion electrokinetic chromatography: Effect of cosurfactant identity on enantioselectivity, methylene selectivity, resolution, and other chromatographic figures of merit

The effect of cosurfactant identity on microemulsion size, elution range, retention factor, enantioselectivity, methylene selectivity, efficiency, and resolution in chiral microemulsion formulations was examined. The chiral surfactant dodecoxycarbonylvaline was used in conjunction with the cosurfactants 1-butanol, 1-pentanol, 2-pentanol, 1-hexanol, 2-hexanol, cyclopentanol, and cyclohexanol. The millimolar concentration of cosurfactant was held constant regardless of identity. Ethyl acetate was incorporated as the microemulsion oil core and the buffer utilized was 50 mM phosphate at a pH of 7.0. In general, secondary alcohols improved enantioselectivities and primary alcohols had the opposite effect, with the exception of the 1-butanol. The trends observed varied slightly depending on analyte. Of the six chiral analytes tested, cyclopentanol provided the best enantioselectivity for three, 1-butanol for two compounds, and 2-pentanol for one analyte. The lowest enantioselectivities were achieved with 1-pentanol or 1-hexanol for all compounds. Methylene selectivity was found to decrease with reductions in alcohol chain length. Among equal carbon number alcohols, methylene selectivity was lower for secondary alcohols. Efficiency and resolution values varied with different cosurfactants and depended on analyte identity.     

P507(K)-醇-正庚烷-水微乳液界面含醇量变化及对体系结构的影响

Ｐ５０７（Ｋ）－醇－正庚烷－水微乳液界面含醇量变化及对体系结构的影响沈兴海,高宏成（北京大学技术物理系,北京,１００８７１）关键词微乳液,２－乙基己基－２－乙基己基膦酸钾,饱和溶水量醇的性质与含量通过影响微乳液界面性质而影响其结构,而Ｗ／Ｏ型微乳液中...     

Experimental and theoretical investigation of the micellar-assisted solubilization of ibuprofen in aqueous media

Surfactants can be used to increase the solubility of poorly soluble drugs in water and to increase drug bioavailability. In this article, the aqueous solubilization of the nonsteroidal, antiinflammatory drug ibuprofen is studied experimentally and theoretically in micellar solutions of anionic (sodium dodecyl sulfate, SDS), cationic (dodecyltrimethylammonium bromide, DTAB), and nonionic (dodecyl octa(ethylene oxide), C12E8) surfactants possessing the same hydrocarbon "tail" length but differing in their hydrophilic headgroups. We find that, for these three surfactants, the aqueous solubility of ibuprofen increases linearly with increasing surfactant concentration. In particular, we observed a 16-fold increase in the solubility of ibuprofen relative to that in the aqueous buffer upon the addition of 80 mM DTAB and 80 mM C12E8 but only a 5.5-fold solubility increase upon the addition of 80 mM SDS. The highest value of the molar solubilization capacity (chi) was obtained for DTAB (chi = 0.97), followed by C12E8 (chi = 0.72) and finally by SDS (chi = 0.23). A recently developed computer simulation/molecular-thermodynamic modeling approach was extended to predict theoretically the solubilization behavior of the three ibuprofen/surfactant mixtures considered. In this modeling approach, molecular-dynamics (MD) simulations were used to identify which portions of ibuprofen are exposed to water (hydrated) in a micellar environment by simulating a single ibuprofen molecule at an oil/water interface (modeling the micelle core/water interface). On the basis of this input, molecular-thermodynamic modeling was then implemented to predict (i) the micellar composition as a function of surfactant concentration, (ii) the aqueous solubility of ibuprofen as a function of surfactant concentration, and (iii) the molar solubilization capacity (chi). Our theoretical results on the solubility of ibuprofen in aqueous SDS and C12E8 surfactant solutions are in good agreement with the experimental data. The ibuprofen solubility in aqueous DTAB solutions was somewhat overpredicted because of challenges associated with accurately modeling the strong electrostatic interactions between the anionic ibuprofen and the cationic DTAB. Our results indicate that computer simulations of ibuprofen at a flat oil/water interface can be used to obtain accurate information about the hydrated and the unhydrated portions of ibuprofen in a micellar environment. This information can then be used as input to a molecular-thermodynamic model of self-assembly to successfully predict the aqueous solubilization behavior of ibuprofen in the three surfactant systems studied.     

Microemulsion electrokinetic chromatography for the analysis of green tea catechins: effect of the cosurfactant on the separation selectivity

Microemulsion electrokinetic chromatography (MEEKC) was applied to the separation of six catechins and caffeine, the major constituents of the green tea. The developed methods involved the use of sodium dodecyl sulfate (SDS) as surfactant, n-heptane as organic solvent and an alcohol as cosurfactant. The separations were performed under acidic conditions (pH 2.5 phosphate buffer, 50 mM) to ensure good stability of the catechins, with reversed polarity (anodic outlet). The effect of the alcohol nature on the MEEKC selectivity was evaluated; nine alcohols were used as cosurfactant: 1-butanol, tert-butanol, 1-pentanol, 2-pentanol, 3-pentanol, cyclopentanol, 1-hexanol, 2-hexanol, and cyclohexanol. The migration order of (+)-catechin (C), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-gallocatechin (GC), (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG), caffeine and theophylline was significantly affected by the alcohol used as cosurfactant. Using nine microemulsions, four different selectivities were achieved: A (cyclohexanol); B (2-pentanol, 3-pentanol, 1-hexanol, 2-hexanol); C (1-butanol, 1-pentanol, cyclopentanol); D (tert-butanol). MEEKC methods, based on 2-hexanol and cyclohexanol as cosurfactant were validated and successfully applied to the analysis of catechins and caffeine in commercial green tea products.     

Catanionic surfactants: microemulsion formation and solubilization

We review and summarize the three-phase behavior and solubilization of microemulsions with catanionic surfactants. Particular emphasis is placed to the three-phase behavior of mixtures of oil, water and alcohol with mixed surfactants containing one anionic and one cationic surfactant. The effect of salt and catanionic surfactant on the HLB composition and solubilizing capacity of surfactants to form microemulsions is discussed.     

Enzymatic esterification and phase behavior in ionic microemulsions with different alcohols

The esterification of hexanoic acid and 1-pentanol catalyzed by the lipase fromChromobacterium viscosum was studied at 298.2 K using different Winsor systems as reaction medium. The microemulsion systems consisted of brine and alkane stabilized by the anionic surfactant sodium dodecylsulphate and a short-chained alcohol. The alcohol acts both as a reactant and as a part of the reaction medium. Therefore, it is of great fundamental interest to know the phase behavior of the used microemulsion systems. Partial phase diagrams were determined and the efficiency of different alcohols on the transition from a Winsor I system to a Winsor III or a Winsor IV system with bicontinuous structure and further to a Winsor II system was investigated. The investigated alcohols were 2-methyl-1-propanol, 1-butanol, 2-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, and 1-hexanol. The aqueous medium consisted of 0.5 m NaCl(aq) or a phosphate buffer (pH=7) and the organic medium of octane or 2,2,4-trimethyl pentane. A long alkyl chain of the alcohol or a branching far from the hydroxyl group gives a more efficient cosurfactant and a transition from Winsor I to Winsor III or Winsor IV at lower alcohol contents. In the Winsor III system the yield of 1-pentyl hexanoate is twice as high as the yield in the bicontinuous Winsor IV system.     

Excess volumes of the binary mixtures of trichloroethylene withn-alcohols at 30 and 40°C

Volumes of mixing binary systems formed by trichloroethylene with n-alcohols (1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, and 1-octanol) were measured as a function of composition at 30 and 40°C, by dilatometric measurements. All the systems show a change of sign for V ^E from negative to positive as the mole fraction trichloroethylene increases at both temperatures The positive value of the excess volumes increase as carbon chain length increases. The results are explained in terms of depolymerization of hydrogen bonded alcohol aggregates and weak hydrogen-bonding interaction of the type Cl-H–O between unlike molecules.     

Influence of sodium sulfate or sodium sulfite on the solubilization of benzylalcohol in cationic micellar solutions

The enthalpy of benzylalcohol (BzOH) solution has been determined as a function of alcohol concentration in aqueous trimethyltetradecylammonium bromide (TTAB) solutions in the presence of sodium sulfite or sodium sulfate up to high salt concentration. The electrolytes studied do not seem to induce TTAB sphere-torod transition at least up to 0.6 mol/kg of salt. Comparison with the enthalpic behavior of BzOH in sodium dodecylsulfate solutions and with that of 1-pentanol in both cationic and anionic micellar solutions suggests that the solubilization of BzOH in TTAB solutions is specifically favored by intramolecular interactions between alcohol molecules within the cationic micelles. The replacement of the bromide counterions by the sulfite or sulfate ions has been studied using potentiometry with an ionselective electrode in the case of trimethylhexadecylammonium bromide (CTAB). No difference could be detected between the effects of either divalent anions on the rate of change of the bromide ion-condensation with the salt/surfactant concentration ratioR. The degree of counter-ion condensation on micellar surface depends not only on theR values, but also on the total surfactant concentration.     

Application of Polyglycerol Diisostearate Ethoxylates in Microemulsion

Effect of surfactants [polyglycerol diisostearate ethoxylates (PGDIS-E31, PGDIS-E36 and PGDIS-E40) and Tween-80], alcohols (1,2-propandiol, ethanol, 1-propanol, 1-butanol, 2-butanol and 1-pentanol), oils [isopropyl palmitate (IPP), isooctyl palmitate (IOP), dioctyl carbonate (DOC), and dioctyl hexanediate (DOH)], temperature and sodium chloride on the microemulsion formation of the surfactant/alcohol/oil/water system has been investigated by the pseudo-ternary phase diagrams. The capacities of the four surfactants in the microemulsion formation of the surfactant/alcohol/IPP/water system at surfactant/alcohol of 2:1 are in the order of PGDIS-E31 > PGDIS-E36 > Tween-80 > PGDIS-E40, whatever alcohol (ethanol, 1-propanol, and 1-butanol) is used. PGDIS-E31 and 1-butanol exhibit best synergism in the microemulsion formation. In addition, the volume, structure and polarity of oil all influence the microemulsion formation. At the optimum weight ratio 2:1 of PGDIS-E31/1-butanol, the microemulsion region of the PGDIS-E31/1-butanol/IPP/water system is the largest among the studied systems. The microemulsion system of PGDIS-E31/1-butanol/IPP/water is not sensitive to lower temperature such as 40°C. It is also not sensitive to sodium chloride when the concentration of sodium chloride is in the range of 0 to 1.0%.     

Effect of alcohols on the micellar properties in aqueous solution of alkyltrimethylammonium bromides

The effect ofn-butanol,n-propanol, andn-hexanol on the critical micelle concentration (CMC) and degree of ionisation of the micelles of dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromides in aqueous solution has been determined by conductimetric techniques. Increase of the molality of added alcohol over the concentration ranges examined (up to 0.3 mol kg^–1 butanol, 0.07 mol kg^–1 pentanol and 0.025 mol kg^–1 hexanol) caused a progressive decrease of CMC and increase of the degree of ionisation for each surfactant-alcohol system. At a constant molality of added alcohol the degree of ionisation increased with a) an increase of the chain length of the surfactant for each alcohol and b) an increase of the chain length of the alcohol for each surfactant. The distribution of each alcohol between the aqueous and micellar phases and the free energy of solubilization were determined from the change of CMC with molality of added alcohol.     

Alcohol modifiers in MEKC with SDS as surfactant. Study on the influence of the alcohol chain length (C1?C12)

The influence of alcohol modifiers with different chain length on the migration time window in micellar electrokinetic chromatography (MEKC) has been studied. Highly polar alcohols like methanol and 1-propanol are typical aqueous phase modifiers. Higher alcohols like 1-butanol, 1-pentanol and 1-hexanol influence the micellar structure and are considered as micellar phase modifiers. The effect of long chain alcohols is small because of their low applicable concentrations.     

Spectroscopic investigations in molecularly organized solvent media. Part 3. Examination of the nitromethane selective quenching rule in aqueous anionic + cationic and anionic + nonionic mixed surfactant solutions

Applicability of the nitromethane selective quenching rule for discriminating between alternant versus nonalternant polycyclic aromatic hydrocarbons (PAHs) is examined for 20 representative PAH solutes dissolved in micellar sodium dodecylsulfate (SDS) + cetyltrimethylammonium bromide (CTAB), SDS + dodecyltrimethylammonium bromide (DTAB), SDS + Brij-35, and SDS + sodium octanoate (SO) mixed surfactant solvent media. Experimental results show that nitromethane quenched fluorescence of all 8 alternant PAHs studied in the four different solvent systems. Unexpected quenching behavior was observed, however, in the case of nonalternant PAHs. Nitromethane quenched fluorescence emission of nonalternant PAHs dissolved in the SDS + SO solvent media, which is contrary to the selective quenching rule. In the case of the mixed anionic + cationic surfactant solvent media, nitromethane quenching selectivity was restored at concentration ratios of approximately 4?:?1 (anionic:cationic) or less.     

The phase behavior of microemulsion systems containing kerosene

The phase behavior of microemulsion systems containing an anionic surfactant (SDS) as well as a nonionic surfactant (Triton X-100) along with cosurfactant (1-pentanol) and using kerosene as an oil phase is reported. The unusual features observed are explained.     

A Study of the Solubilization of Polar Oily Materials by Alkyl Polyglucoside and Sodium Dodecyl Sulfate in Mixed Surfactant System

The effects of different alkyl chains of nonionic surfactants and solubilized polar oily material on the solubilizing capacity of binary anionic‐nonionic mixed surfactant systems were studied. This system includes surface tension measurements to determine the critical micelle concentration. Results were analyzed using regular solution theory to obtain the mixed micelle and the interaction parameter β, in order to evaluate the type of interactions of surfactants in the mixed micelle. Solubilizing capacity has been investigated by measuring the optical density of solubilized polar oily materials like octanol, decanol, and dodecanol. The solubilizing phenomenon exhibited by mixed surfactants systems showed better results than that of the individual surfactant system. The amount of solubilization in mixed surfactant increases with increase in carbon chain length of alkyl polyglucoside.     

Depletion flocculation of latex dispersion in ionic micellar systems

The flocculation behavior of anionic and cationic latex dispersions induced by addition of ionic surfactants with different polarities (SDS and cetyltrimethylammonium bromide (CTAB)) have been evaluated by rheological measurements. It was found that in identical polar surfactant systems with particle surfaces of SDS + anionic lattices and CTAB + cationic lattices, a weak and reversible flocculation has been observed in a limited concentration region of surfactant, which was analyzed as a repletion flocculation induced by the volume-restriction effect of the surfactant micelles. On the other hand, in oppositely charged surfactant systems (SDS + cationic lattices and CTAB + anionic lattices), the particles were flocculated strongly in a low surfactant concentration region, which will be based on the charge neutralization and hydrophobic effects from the adsorbed surfactant molecules. After the particles stabilized by the electrostatic repulsion of adsorbed surfactant layers, the system viscosity shows a weak maximum again in a limited concentration region. This weak maximum was influenced by the shear rate and has a complete reversible character, which means that this weak flocculation will be due to the depletion effect from the free micelles after saturated adsorption.     

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.     

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.     

Effect of 1-hexanol on the phase behavior of SDS/CTAB/NaBr/H2O system

Abstract

The influence of 1-hexanol on the phase behavior of sodium dodecyl sulfate (SDS)/cetyltrimethyl ammonium bromide (CTAB)/NaBr/H₂O system has been systematically investigated in this paper. The results showed 1-hexanol effectively dissolved the precipitate formed by the CTAB and SDS surfactants, while liquid crystal (LC) and aqueous two phase system (ATPS) were formed in a wider range. When the molar ratio of 1-hexanol to surfactant is higher than 1, the precipitation in the system disappeared completely and was transformed into ATPS and LC, indicating that alcohol inserted at least evenly between every two surfactant molecules and hence effectively weakened the electrostatic interaction between the anionic and cationic surfactants and limited the formation of precipitation. Polarizing microscope (POM) with crossed polarizers was employed to investigate the textures of liquid crystals. It was shown that the existence of lamellar LC was confirmed by “Maltese crosses” textures. Additionally, we showed that the thermal stability of LC was promising. The ATPS and LC regions remained stable and changed slightly when the temperature was increased from 40 to 70?°C. The results indicated that ATPS and LC of the system were quiet resistant to temperature with the addition of 1-hexanol.     

Synergistic effect of mixed anionic and cationic surfactant systems on the interfacial tension of crude oil-water and enhanced oil recovery

Surfactant based enhanced oil recovery (EOR) is an interesting area of research for several petroleum researchers. In the present work, individual and mixed systems of anionic and cationic surfactants consisting of sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (CTAB) in different molar ratios were tested for their synergistic effect on the crude oil-water interfacial tension (IFT) and enhanced oil recovery performance. The combination of these two surfactant systems showed a higher surface activity as compared to individual surfactants. The effect of mixed surfactant systems on the IFT and critical micellar concentration (CMC) is strongly depends on molar ratios of the two surfactant. Much lower CMC values were observed in case of mixed surfactant systems prepared at different molar ratios as compared to individual surfactant systems. The lowest CMC value was found when the molar concentration of SDS was higher than the CTAB. When the individual and mixed surfacant systems were tested for EOR performance through flooding experiments, higher ultimate oil recovery was obtained from mixed surfactant flooding compared to individual surfactants. Combination of SDS and CTAB or probably other anionic-cationic surfactants show synergism with substantial ability to reduce crude oil water IFT and can be a promising EOR method.