Effect of Ethylene Oxide Group in the Anionic–Nonionic Mixed Surfactant System on Microemulsion Phase Behavior

The phase behavior of microemulsions stabilized by a binary anionic–nonionic surfactant mixture of sodium dihexyl sulfosuccinate (SDHS) and C12-14 alcohol ethoxylate (C_{12 − 14}E_j) that contains an ethylene oxide (E_j) group number, j, of either 1, 5, or 9 was investigated for oil remediation. The oil–water interfacial tension (IFT) and optimal salinity of the microemulsion systems with different equivalent alkane carbon numbers (EACN) were examined. The anionic–nonionic surfactant ratio was found to play a pivotal role in the phase transition, IFT, and optimal salinity. The minimum IFT of mixed SDHS − C_{12 − 14}E_j systems were about three times lower than those of neat SDHS systems. A hydrophilic–lipophilic deviation (HLD) empirical model for the mixed anionic–nonionic surfactant system with the characteristic parameter was proposed, as represented in the excess free energy term . The results suggested that the mixed system of SDHS − C_{12 − 14}E₁ was more lipophilic, while SDHS − C_{12 − 14}E₉ was more hydrophilic than the ideal mixture (no excess free energy during the microemulsion formation), and the SDHS − C_{12 − 14}E₅ system was close to the ideal mixture. The findings from this work provide an understanding of how to formulate mixed anionic–nonionic microemulsion systems using the HLD model for oils that possess a wide range of EACN.     

Water solubilization in microemulsions containing amines as cosurfactant

Water-in-oil microemulsions were produced by mixing different combinations of the cationic surfactants cetyltrimethylammonium bromide and cetylpyridinium chloride,n-alkanes (C₅–C₇) and benzene as oils,n-alkylamines (C₆ and C₈) and cyclohexylamine as cosurfactants with water. The influence of chainlength of the alkanes and amines on water solubilization behavior of these systems has been investigated. The solubilization of water in a particular microemulsion is governed by the partitioning of amines among oil, water and interfacial phases, depending on the chainlength and nature of oil and amine, and their interaction with the surfactant. The molar ratio of amine to surfactant at the droplet interface increased with the length of the oil chain. The free energy changes accompanying cosurfactant adsorption at the interface have also been computed.     

非离子表面活性剂在油溶液中的流变性质

反胶团是形成Ｗ／Ｏ乳液或微乳液的基础。通过对若干表面活性剂和油二元系溶液粘滞系数的实际测量,发现不同的表面活性剂与油的组合,其粘滞系数性质有不同的表现。从这个结果可以确定反胶团粒子出现与否,而反胶团粒子的出现能够提供了一个简单的方法,来判断某未知油能否被乳化成Ｗ／Ｏ型乳液或微乳液。     

Investigation of the properties of decaoxyethylene <Emphasis Type="Italic">n</Emphasis>-dodecyl ether,C<Subscript>12</Subscript>E<Subscript>10</Subscript>, in the aqueous sugar-rich region

Interfacial, thermodynamic, and morphological properties of decaoxyethylene n-dodecylether [CH₃ (CH₂)₁₁(OCH₂CH₂)₁₀OH](C₁₂E₁₀) in aqueous solution were analyzed by tensiometric, viscometric, proton nuclear magnetic resonance (NMR), and small-angle neutron scattering (SANS) techniques. Dynamic and structural aspects at different temperatures in the absence and presence of sugars at different concentrations were measured. Critical micelle concentrations (CMC) were determined by surface tension measurements in the presence of ribose, glucose, and sucrose. The heat capacity (ΔC _p.m.), transfer enthalpy (ΔH _m.tr.), transfer heat capacities (ΔC _p.m.tr.), micellization constant (K _m ), Setchenow constant (K _S ^N ), and partition coefficient (q) were determined and discussed as an extension of the usual thermodynamic quantities of micellization and adsorption at the air-water interface. An enthalpy-entropy compensation effect was observed with an isostructural temperature (T _c ) of about 310 K for both micellization and interfacial adsorption. SANS measurements were taken to elucidate structural information, viz., aggregation number (N _agg), shape, size, and number density (N _m ) on C₁₂E₁₀ micelles in D₂O at different concentrations of sugars (0.05, 0.02, 0.3, and 0.5 M) and temperatures (30, 45, and 60°C). Intrinsic viscosity gave the hydrated micellar volume (V _h ), volume of the hydrocarbon core (V _c ), and volume of the palisade layer of the oxyethylene (OE) unit (V _OE). SANS, as well as rheological data, supported the formation of nonspherical micelles with or without sugars. By SANS, we also observed that at the studied temperature intervals, oblate ellipsoid micelles changed into prolate ellipsoids and the number density of micelles decreased with an increase in temperature both in the presence and in the absence of sugars and also on increasing the concentration of sugars. Proton NMR showed a change in chemical shift of the OE group of micelles above the CMC. We also studied the phase separation of C₁₂E₁₀ by sugars in cloud point measurements.     

Nanofiltration membranes prepared by direct microemulsion copolymerization using poly(ethylene oxide) macromonomer as a polymerizable surfactant

A novel polymer membrane with nanosized pore structures has been prepared from the direct copolymerization of acrylonitrile (AN) with a polymerizable nonionic surfactant in water‐in‐oil (w/o) or bicontinuous microemulsions. This polymerizable surfactant is ω‐methoxy poly(ethylene oxide)₄₀ undecyl‐α‐methacrylate macromonomer [CH₃O (CH₂CH₂O)₄₀ (CH₂)₁₁ OCO(CH₃)CCH₂, abbreviated: C₁‐PEO‐C₁₁‐MA‐40]. Besides PEO macromonomer, AN, and crosslinker ethyleneglycol dimethacrylate, the microemulsion system contained varying amount of water that formed w/o microemulsions having water droplet structures and bicontinuous microemulsions consisting of interconnected water channel. The polymerized membranes prepared in this study have pore radii ranging from 0.38 to 2.4 nm as evaluated by PEG filtration. The pore size appears to vary linearly with water content in precursor microemulsions. But a sharp change in the gradient of the linear relationship is observed around 25 wt % water content. Membranes made from bicontinuous (>25 wt % water) microemulsion polymerization have a larger and interconnected (open‐cell) nanostructures. In contrast, much smaller closed‐cell (disinterconnected) nanostructures were obtained from w/o (<25 wt % water) microemulsion polymerization and the membrane exhibited a permselectivity toward water in pervaporation separation of high ethanol (>50 wt %) aqueous solutions. The separation factor (α) for 95% ethanol aqueous solution by the membrane derived from the microemulsion containing 10 wt % water is about 20. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2785–2794, 2000     

Gemini表面活性剂微乳液相行为的影响因素研究

研究了Gemini表面活性剂微乳液的界面相行为,考察了中间联接基团长度、表面活性剂和助表面活性剂的配比、醇链长和烷烃链长对相图的影响。结果表明：短链联接基团较易形成单相微乳液,表面活性剂用量较少且有较高的含水量;随着烷烃链长增加,形成O/W区域所需表面活性剂含量增加,且区域面积在逐渐减小;醇链长改变时,沿着油-（S＋A）轴都能形成W/O型微乳液。     

Effects of the Polypropylene Oxide Number on the Surface Properties of a Type of Extended Surfactant

The surface properties of 5 extended surfactant C_12–14P _mE₂S solutions in pure water and 0.1 M NaCl were investigated through surface tension and electrical conductivity measurements. The surface properties measured include the critical micelle concentration (CMC), critical surface tension (γ_cmc), maximum surface excess concentration (Γ_max), minimum area occupied per surfactant molecule (A_min), and efficiency in surface tension reduction (pC₂₀). The CMC values of the 5 surfactants decreased with increasing polypropylene oxide number (PON) and were higher than those obtained in 0.1 M NaCl. The Γ_max values showed a downward trend whereas the A_min values exhibited an upward trend with increasing PON without NaCl. The Γ_max values were higher and the A_min values were lower than those obtained without 0.1 M NaCl. The CMC values increased at elevated temperatures. The CMC values of C_12–14P₃E₂S, C_12–14P₅E₂S, and C_12–14P₈E₂S were similar but were markedly lower than those of C_12–14E₂S at different temperatures. When PON was less than 12, the log CMC value decreased linearly with increasing PON in the absence of salt, and the relationship between pC₂₀ and PON was linear. But in the presence of 0.1 M NaCl, the log CMC value decreased exponentially with increasing PON.     

Evaluation of mixed micellar interactions of CnBCl and SDBS mixtures using dissociated Margules model and influence of different salts

The conductivity measurement has been used to determine the first and second CMC's (CMC₁ and CMC₂) of alkyldimethylbenzylammonium chloride (C_nBCl; n = 12, 14 and 16) as well as gemini surfactant trimethylene-1,2-bis-(dodecyldimethylammonium bromide) (12-2-12) with sodium dodecylbenzenesulphonate (SDBS) in aqueous solutions using Rubingh's the regular theory approximation as well as the dissociated Margules Model. The use of Margules model allows us to calculate activity coefficients of the constituents and hence provides better values of micellar parameters for asymmetric mixed systems as compared to the regular solution theory. The CMC₁ values for C_nBCl/SDBS mixtures were seen to be lower than those predicted from their ideal mixtures suggesting synergistic interactions although the synergism increases with chain length (n) of the cationic surfactant. Both CMC₁ and CMC₂ experience a decrease with rising values of n. The addition of salts including NaCl, KCl, NaBr, Na₃PO₄, and Na₂SO₄ in mixtures of C₁₆BCl and SDBS suggests that salt counterions have a considerable impact on CMC₁ when either surfactant is in excess. Zeta potential (ζ) measurements provide more evidence in favor of these observations. The thermodynamic features of micellization have also been scrutinized using isothermal titration calorimetry (ITC).     

Hydroformylation with rhodium phosphine-modified catalyst in a microemulsion: comparison of organic and aqueous systems for styrene, cyclohexene and 1,4-diacetoxy-2-butene

Use of microemulsion as a reaction media in the hydroformylation of different alkenes, namely styrene, cyclohexene and 1,2-diacetoxy-2-butene have been studied using alkylpolygylcol ether-type nonionic surfactant in the presence of phosphine-modified rhodium catalyst. The combination of the experiments under comparable homogeneous and biphasic conditions were performed in order to make direct comparison of microemulsion with classical systems. Thus, the experiments were also carried out using catalysts such as unmodified rhodium carbonyl H Rh(CO)₄ and H Rh(CO)(PPh₃)₃ in homogeneous system, Rh–TPPTS complex in two-phase system and in association with co-solvent.     

Aggregation of unsaturated long-chain fatty alcohols in nonaqueous systems

Aggregation and related phenomena in nonaqueous binary and ternary solutions containing unsaturated long-chain fatty alcohol amphiphiles have been studied. Six C₁₈ fatty alcohols were studied—oleyl alcohol (9Z-octadecen-1-ol), elaidyl alcohol (9E-octadecen-1-ol), linoleyl alcohol (9Z, 12Z-octadecadien-1-ol), elaidolinoleyl alcohol (9E, 12E-octadecadien-1-ol), linolenyl alcohol (9Z, 12Z, 15Z-octadecatrien-1-ol) and elaidolinolenyl alcohol (9E, 12E, 15E-octadecatrien-1-ol). Equivalent conductivity and photon correlation spectroscopy confirmed that unsaturated long-chain fatty alcohols form large and polydisperse aggregates in methanol. Critical micelle concentration (CMC) results showed that the degree of unsaturation and configuration of the double bonds in the fatty alcohol significantly influences aggregation. Aggregation of oleyl alcohol in a series of straight and branched medium-chainlength (C₃-C₈) alkanol solvents was studied. For shorter-chained alkanols (C₁-C₄), decreasing solvent dielectric constant decreases the CMC; however, for longer-chained alkanols (C₄-C₈), no significant effects occurred on the CMC. The effect of solubilized soybean oil on the viscosity of long-chain fatty alcohol/methanol solutions was also analyzed. Relative viscosity results were consistent with those expected for microemulsions. Although preliminary in nature, these results generally support the notion that soybean oil is solubilized by incorporation into large soybean oil-in-fatty alcohol aggregates in methanol solvent, resembling a nonaqueous detergentless microemulsion. Presented at the 67th Colloid and Surface Science Symposium, Toronto, Canada, June 20–23, 1993.     

Synthesis and Surface Properties of Anionic Gemini Surfactants having N-acylamide and Carboxylate Groups

A straightforward synthetic strategy to an anionic gemini surfactant having both N-acylamide and carboxylate groups in a molecule has been demonstrated. The surface properties of the anionic gemini surfactant, such as CMC (critical micelle concentration), C₂₀ (the concentration required to reduce the surface tension of the solvent by 20 mN/m), γ _CMC (the surface tension at the CMC), ∏ _CMC (the surface pressure at the CMC), Γ _max (the maximum surface excess concentration at the air/aqueous solution interface), A _min (the minimum area per surfactant molecule at the air/water interface), and the CMC/C₂₀ ratio (a measure of the tendency to form micelles relative to adsorbtion at the air/water interface), have been studied. The influence of the different concentrations of NaCl on the surface properties of the gemini surfactant has been discussed. The results have shown that the CMC values decreased with an increase in the concentration of NaCl indicating that the Na⁺ preferentially adsorbs onto the surface of the charged aggregate and facilitates the aggregate growth by suppressing the main impediment of electrostatic repulsion among head groups. Additionally, the values of Γ _max are always higher in salt solutions as compared to those in pure water due to their salting out effect. The larger pC₂₀ value indicates that the surfactant adsorbs more efficiently at the air/water interface and reduces surface tension more efficiently. In addition, the geminis in water show little or no break in their specific conductance versus surfactant molar concentration plots. This is attributable to protonation of the carboxylate group and strong Na⁺ release during micellization.     

含非离子表面活性剂吐温-80的微乳液结构研究

采用非离子表面活性剂吐温-80,以石油醚为油相,正丁醇为助表面活性剂来制备微乳液。用稀释法测定并计算了Tween-80/石油醚/正丁醇/水体系O/W型微乳的结构参数。测量微乳液体系在15~30℃温度范围内的pH及电导,考察温度对微乳液体系的影响。向微乳液体系中加入PVP,测量体系的电导和接触角,考察水溶性高分子对微乳液体系的影响。结果表明微乳液体系的电导随温度的上升而变大,相同温度时,加入PVP会使体系的电导变大,接触角变小。     

Rhodium catalyzed hydroformylation of 1-octene in microemulsion: comparison with various catalytic systems

In this work, we describe how addition of alkylpolyglycol ether type nonionic surfactant affects the hydroformylation of 1-octene in the presence of phosphine modified rhodium catalyst. Influence of different process parameters such as ligand excess and amount of surfactant on the reaction rate and selectivity were discussed. Direct comparison of microemulsion systems with classic processes was achieved by performing the reactions under comparable homogeneous and biphasic conditions. Thus, the experiments were carried out using catalysts such as unmodified rhodium carbonyl HRh(CO)₄ and HRh(CO)(PPh₃)₃ in homogeneous system, Rh–TPPTS complex in two-phase system and in association with co-solvent.     

Alanine-based surfactants: Synthesis and some surface properties

A homologous series of anionic surfactants, namely, sodium-N-(alkyloxycarbonyl) alanine (where alkyl=octyl-, dodecyl-, hexadecyl-, and octadecyl-) were synthesized having the formula: R-OCO-CH₂NH-CH₂-CH₂-COONa. Surface properties of their solutions, including surface tension, critical micelle concentration, effectiveness, maximum surface excess, and minimum surface area, were investigated for different concentrations at 25°C. The effects of these surfactants on the solubilization of a polar and a nonpolar solute were studied. Standard free energies of micellization and adsorption were calculated for the prepared surfactants in aqueous solution.     

Hydrolysis and biodegradation studies of surface-active esters

Base-catalyzed hydrolysis, biodegradation, and enzyme-catalyzed hydrolysis of a series of four monoesters of tetra(ethylene glycol) have been investigated. The surfactants varied in substitution on the α-carbon of the acyl chain, from no substitution, to 2-methyl, to 2-ethyl, and on to 2,2-dimethyl. All surfactants were based on C₈-acids except the methyl-substituted, which was based on a C₇-acid. The hydrolysis was investigated using ¹H nuclear magnetic resonance. The surfactants showed a pronounced difference in stability with respect to type of substitution in the vicinity of the ester bond. In alka-line hydrolysis the most significant difference in reactivity lay between the surfactant with an ethyl group and the surfactant with a methyl group in the α-position of the acyl chain. However, in the biodegradation studies these surfactants broke down at almost exactly the same rate as the nonsubstituted surfactant. In the biodegradation test, the disubstituted surfactant deviated considerably. Two lipases, from Mucor miehei (MML) and Candida antarctica B (CALB), were used in the enzyme-catalyzed hydrolysis. The surfactant with no substitution was found to hydrolyze much faster than the other surfactants, and the hydrolytic activity of MML, but not CALB, increased in the presence of surfactant micelles.     

Nanosized TiO2 synthesis by EbCDAB microemulsion

BACKGROUND: Microemulsion is the easiest and cleanest of the popular methods of synthesizing nanomaterial. This work investigated the possibility of forming a single‐phase microemulsion using ethanediyl‐α,β‐bis (cetyldimethylammonium bromide), termed EbCDAB, in a n‐hexanol/water system, and looked for the best scale of microemulsion to synthesize TiO₂ to give the best cleaning of organic pollution. RESULTS: Results confirm that EbCDAB, n‐hexanol and water form a microemulsion system, and this system is an effective way to synthesize nanoparticles of TiO₂. Photo catalysis experiments showed sample E_6?3 to be the best catalyst, and it decomposed 82% of Methyl Orange (10 mg L^?1) in 60 min under UV‐light irradiation. E_6?3 had 1.4 times higher activity than the commercial P25. Analyses using transmission electron microscopy (TEM), X‐ray diffraction (XRD), thermographic differential scanning calorimetry (TG‐DSC) and Fourier transform infrared microscopy (FT‐IR), showed that particles of E_6?3 were of size around 11 nm and of anatase phase. CONCLUSION: The best microemulsion was found to have weight ratio n‐hexanol:EbCDAB:water of 6:3:1. At this ratio, TiO₂ nanoparticles were easily produced. Copyright © 2010 Society of Chemical Industry     

Formulation of ultralow interfacial tension systems using extended surfactants

Inspired by the concept of lipophilic and hydrophilic linkers, extended surfactants have been proposed as highly desirable candidates for the formulation of microemulsions with high solubilization capacity and ultralow interfacial tension (IFT), especially for triglyceride oils. The defining characteristic of an extended surfactant is the presence of one or more intermediate-polarity groups between the hydrophilic head and the hydrophobic tail. Currently only limited information exists on extended surfactants; such knowledge is especially relevant for cleaning and separation applications where the cost of the surfactant and environmental regulations prohibit the use of concentrated surfactant solutions. In this work, we examine surfactant formulations for a wide range of oils using dilute solutions of the extended surfactant classes sodium alkyl polypropyleneoxide sulfate (R-(PO) _x −SO₄Na), and sodium alkyl polypropyleneoxide-polyethyleneoxide sulfate (R-(PO) _y -(EO) _z −SO₄Na). The IFT of these systems was measured as a function of electrolyte and surfactant concentration for polar and nonpolar oils. The results show that these extended surfactant systems have low critical micelle concentrations (CMC) and critical microemulsion concentrations (CμC) compared with other surfactants. We also found that the unique structure of these extended surfactants allows them to achieve ultralow IFT with a wide range of oils, including highly hydrophobic oils (e.g., hexadecane), triolein, and vegetable oils, using only ppm levels of these extended surfactants. It was also found that the introduction of additional PO and EO groups in the extended surfactant yielded lower IFT and lower optimum salinity, both of which are desirable in most formulations. Based on the optimum formulation conditions, it was found that the triolein sample used in these experiments behaved as a very polar oil, and all other vegetable oils displayed very hydrophobic behavior. This unexpected triolein behavior is suspected to be due to uncharacterized impurities in the triolein sample, and will be further evaluated in future research.     

Effects of Surfactant Headgroups on Oil-in-Water Emulsion Droplet Formation: An Experimental and Simulation Study

Nonpolar oils such as kerosene and diesel oil are common collectors in coal flotation. Surfactants are usually added to the pulp to emulsify the oil collectors. The present study used dodecane as the oil collector and anionic sodium dodecyl sulfonate (SDS) and nonionic tetraethylene glycol monododecyl ether (C₁₂EO) with different headgroups and identical chain alkyls to investigate the effect of the surfactant headgroups on oil-in-water emulsion droplet formation. The morphology and stability of dodecane emulsions were determined experimentally. Density functional theory (DFT) and molecular dynamics (MD) simulations were used to explain the microscopic mechanism. The results of DFT indicated a larger interaction between SDS and the water molecules than that between C₁₂EO and water molecules. The results obtained by MD suggested that the SDS headgroup exhibited a loose arrangement and a relatively large gap size, thereby weakening the interaction between SDS and water molecules at the dodecane/water interface. In contrast, the headgroups of C₁₂EO were bent and interwoven with others to form a tight reticulation at the interface. According to the simulation results, the ability of the surfactant to form dodecane-in-water emulsion droplets depends on the arrangement of the surfactants at the oil–water interface rather than on the interaction strength between the headgroups of the surfactants and water molecules. The presented microscopic mechanism of the surfactant headgroup formation of oil-in-water emulsion droplets offers surfactant selection and design references.     

Lauryl alcohol and amine oxide as foam stabilizers in the presence of hardness and oily soil

The effects of two potential foam boosters, n-dodecanol (or lauryl alcohol: LA) and tetradecyldimethylamine oxide (C₁₄DMAO), were investigated for two situations in which foam made from a 0.01 wt% solution of a common alkylethoxy sulfate surfactant was highly unstable in the presence of oil drops consisting of an n-hexadecane/oleic acid mixture. In one case in which dissolved CaCl₂ was present at alkaline pH, insoluble calcium oleate particles formed in situ and facilitated foam breakage. In the other, a much higher concentration of calcium was present at neutral pH, and drops of a microemulsion phase formed but no calcium oleate. In both cases, 0.005 wt% LA reduced the entry coefficient, E, of the oil to the air-water surface sufficiently to prevent drop entry and stabilized the foam. In contrast, 0.005 wt% C₁₄DMAO caused smaller reductions in E and was ineffective as a foam booster. LA was more effective because it was able to form a more compact monolayer with the surfactant than C₁₄DMAO at the air-water surface, which led to lower surface tensions and hence lower values of E.     

Microemulsion Extraction of Monascus Pigments from Nonionic Surfactant using High Polarity of Diethyl Ether as Excess Oil Phase

Stripping of organic compound from nonionic surfactant micelle aqueous solution is indispensable for many industrial processes. In this paper, a relatively high polarity diethyl ether was screened for forming Winsor I microemulsion, which was used for stripping of organic compound from nonionic surfactant. Setting up extractive fermentation of Monascus pigments in Triton X-100 aqueous solution as a model, cloud point extraction of Monascus pigments from fermentation broth, and back-extraction of Monascus pigments from the coacervate phase of cloud point system by Winsor I microemulsion were conducted. Monascus pigments were successfully separated from nonionic surfactant into the excess diethyl ether phase.