SOLUBILIZATION IN MIXED REVERSE MICELLAR SYSTEMS OF AOT/NONIONIC SURFACTANTS/n-HEPTANE

Solubilization of water and aqueous NaCl solutions in mixed reverse micellar systems of anionic surfactant AOT and nonionic surfactants in n-heptane was studied. It was found that the maximum solubilization capacity of water was higher in the presence of certain concentrations of NaCl electrolyte, and these concentrations increased with the increase of nonionic surfactant content and their EO chain length. Soluibilization capacity was enhanced by mixing AOT with nonionic surfactants. The observed phenomena were interpreted in terms of the stability of the interfacial film of reverse micellar microdroplet and the packing parameter of the surfactant that formed mixed reverse micelles.     

非离子表面活性剂的雾点研究-电解质的影响

研究了１－１型钠盐对五种非 离子表面活性剂水溶液雾点的影响，有九种钠盐使雾点下降，下降的依次是ＩＯ＾－３＞ＯＨ＾－＞Ｆ＾－＞ＣＨ３ＣＯＯ＾－＞ＢｒＯ＾－３＜＞Ｃｌ＾－＞Ｂｒ＾＿＞ＣｌＯ３＾－≥ＮＯ＾－３；有三种钠盐使雾点升高，升高的效率依次是ＣＮＳ＾－＞ＣｌＯ＾－＞Ｉ＾－。     

Micropartioning and solubilization enhancement of 1,2-bis(bis(4-chlorophenyl) methyl)diselane in mixed micelles of binary and ternary cationic-nonionic surfactant mixtures

The aqueous solubilization of the organoselenium compound viz., 1,2-bis(bis(4-chlorophenyl)methyl)diselane [(ClC(6)H(4))(2)CHSe](2) has been investigated experimentally in micellar solutions of two cationic (hexadecyltrimethylammonium bromide, CTAB, hexadecyltrimethylammonium chloride, CTAC) and one nonionic (polyoxyethylene(20)mono-n-hexadecyl ether, Brij 58) surfactants possessing the same hydrocarbon "tail" length and in their single as well as equimolar binary and ternary mixed states. Solubilization capacity determined with spectrophotometry and tensiometry has been quantified in terms of molar solubilization ratio and micelle-water partition coefficient. FTIR, UV-vis, fluorescence and zeta potential measurements have been utilized to ascertain the interaction of organochalcogen compound with surfactants. Equimolar cationic-nonionic surfactant combinations show better solubilization capacity than pure cationics or nonionics, whereas equimolar cationic-cationic-nonionic ternary surfactant systems exhibit intermediate solubilization efficiency between their single and binary counterparts. Locus of solubilization of [(ClC(6)H(4))(2)CHSe](2) in different micellar solutions was probed by UV-visible spectroscopy. The investigation has presented precious information for the preference of mixed surfactants for solubilizing water-insoluble compounds. Indeed the solubilization aptitude of these surfactants is not merely related to molar capacity. The results furnish adequate support to justify comprehensive exploration of the surfactant properties that influence solubilization.     

Intermicellar material exchange in reverse micelles formed by ionic AOT and nonionic Igepal surfactants studied by means of pulse radiolysis. Influence of the temperature

The recombination of thiocyanate anion radicals, (SCN) ₂ ⁻ , formed pulse radiolytically within the water pools of reverse micelles stabilized with anionic AOT and nonionic Igepal surfactants, was proved as an indicator reaction to study intermicellar exchange. It was found that the exchange process is slower inIgepal than in AOT reverse micelles with the same water to surfactant ratio. The apparent activation enthalpy and entropy of the exchange process were determined in different alkanes. For the AOT and Igepal reverse micelles the activation parameters increase with the droplet size, but for the AOT systems they do not significantly change with the increase of droplet concentration. For non-percolated systems the activation parameters for Igepal reverse micelles approach those for AOT reverse micelles. This result supports existing suggestions that the mechanism of intermicellar exchange does not differ in principle between reverse micelles stabilized with ionic and nonionic surfactants.     

Igepal CO系列表面活性剂溶致液晶的结构特性

对壬基酚聚氧乙烯醚（IgepalCO）系列表面活性剂,生成何种溶致液晶与其EO基团数n有关,而在何浓度范围内生成溶致液晶则与生成溶致液晶的最低水含量及最大水增溶量有关．EO基团数n小于10时,生成层状液晶,n大于10时则生成六角状液晶,层状液晶两亲双层内,水与表面活性剂的最低摩尔比rmin和最高摩尔比rmax随EO基团数n增加分别是非线型增加与线型增加,在IgepalCO520（n＝5）中加入IgepalCO710（n＝10．5）,对层状液晶的生成无显著影响,在IgepalCO710中加入IgepalCO520,则对六角状液晶的生成产生显著影响,出现了六角状液晶向层状液晶的转变。     

Physicochemical properties of mixed surfacant systems: sodium dodecyl benzene sulfonate with triton X 100

The physicochemical properties of a mixed surfactant system were studied under various conditions. The surfactants were anionic sodium dodecyl benzene sulfonate and nonionic Triton X 100. Variation of specific conductivity with concentration was used to determine the critical micelle concentration of anionic as well as the mixed surfactants. Iodine solubilization method was used to determine the CMC of the nonionic surfactant. The interaction parameter between the surfactant molecules were calculated. The wetting, foaming and detergent properties of mixed surfactant systems were studied. The variation of contact angle of the solution with teflon surface as a function of surfactant concentration was found to be a reasonably good method to determine the critical micelle concentration. Viscosity and cloud points were also determined. All these quantities are discussed. Received: 14 January 1998 Accepted: 11 June 1998     

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

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

Experimental study on methane solubilization by organic surfactant aggregates

Seeking to enhance coal mine safety, an experimental study of a kind of water-based explosion suppression medium for the absorption of mine gas was carried out. Using methane as the model gas, solubilizing experiments with different concentrations of anionic and nonionic surfactants were carried out using headspace gas chromatography for surfactants consisting of sodium fatty alcohol polyoxyethylene ether carboxylate (AEC), fatty acid methyl ester sulfonate (MES), fatty methyl ester ethoxylate (FMEE), hexyl d-glucoside (APG06), octyl beta-d-glucopyranoside (APG08) and n-decyl glucoside (APG10). By selecting individual surfactants, the study investigated the methane solubilization performance of water mist with binary anionic–nonionic surfactants. Furthermore, the release of methane in solution was also examined. The results show that the apparent solubility of methane in solution is linearly and positively correlated with the surfactant concentration. The methane solubilization is significantly improved by the addition of anionic–nonionic surfactants. The optimal solubilizing ratio of the anionic–nonionic surfactant varies with the solution compositions. For a fixed ratio, surfactant compositions exhibit the most distinct synergistic effect and the best performance for methane solubilization. The release of methane from mixed micelles composed of the compound solution is superior to that of a single surfactant. Through the analysis of the solubilization effect and the stability of different absorbents, it is concluded that the anionic–nonionic surfactant system shows much better capability than the other selected surfactants.     

Electrophoretic separations in poly(dimethylsiloxane) microchips using mixtures of ionic,nonionic and zwitterionic surfactants

The use of surfactant mixtures to affect both EOF and separation selectivity in electrophoresis with PDMS substrates is reported, and capacitively coupled contactless conductivity detection is introduced for EOF measurement on PDMS microchips. First, the EOF was measured for two nonionic surfactants (Tween 20 and Triton X‐100), mixed ionic/nonionic surfactant systems (SDS/Tween 20 and SDS/Triton X‐100), and finally for the first time, mixed zwitterionic/nonionic surfactant systems (TDAPS/Tween 20 and TDAPS/Triton X‐100). EOF for the nonionic surfactants decreased with increasing surfactant concentration. The addition of SDS or TDAPS to a nonionic surfactant increased EOF. After establishing the EOF behavior, the separation of model catecholamines was explored to show the impact on separations. Similar analyte resolution with greater peak heights was achieved with mixed surfactant systems containing Tween 20 and TDAPS relative to the single surfactant system. Finally, the detection of catecholamine release from PC12 cells by stimulation with 80 mM K⁺ was performed to demonstrate the usefulness of mixed surfactant systems to provide resolution of biological compounds in complex samples.     

电解质水溶液在丙酸十二铵-四氯化碳溶液中的增溶

表面活性剂在非极性溶剂中形成的反胶束在催化反应、光化学、蛋白质苹取分离等方面有着广泛的应用问．这些应用与反胶束的性质有着密切的关系，而增溶水后的反胶束其形状和大小都会发生很大的变化．增溶不同水量的反胶束的微极性、酸碱性、微勤度等已有不少文献报导［2－5］．一些不溶于非极性溶剂而溶于水的物质可以溶解在非极性溶剂中的反胶束核心水团中，这个现象被称为二次增溶．其中，电解质的二次增溶对于研究配体转换反应。酶催化反应问及改变反胶束内部的微环境有着十分重要的作用，Aebi和Weibush回首先研究了有水存在时N。CI在A…     

Surfactant media for constant-current coulometry. Application for the determination of antioxidants in pharmaceuticals

Effect of surfactant presence on electrochemical generation of titrants has been evaluated and discussed for the first time. Cationic (1-dodecylpyridinium and cetylpyridinium bromide), anionic (sodium dodecyl sulfate) and nonionic (Triton X100 and Brij^® 35) surfactants as well as nonionic high molecular weight polymer (PEG 4000) do not react with the electrogenerated bromine, iodine and hexacyanoferrate(III) ions. The electrogenerated chlorine chemically interact with Triton X100 and Brij^® 35. The allowable range of surfactants concentrations providing 100% current yield has been found. Chain-breaking low molecular weight antioxidants (ascorbic acid, rutin, α-tocopherol and retinol) were determined by reaction with the electrogenerated titrants in surfactant media. Nonionic and cationic surfactants can be used for the determination of antioxidants by reaction with the electrogenerated halogens. On contrary, cationic surfactants gives significantly overstated results of antioxidants determination with electrogenerated hexacyanoferrate(III) ions. The use of surfactants in coulometry of α-tocopherol and retinol provides their solubilization and allows to perform titration in water media. Simple, express and reliable coulometric approach for determination of α-tocopherol, rutin and ascorbic acid in pharmaceuticals using surfactant media has been developed. The relative standard deviation of the measurements does not exceed of 5%.     

Phase behavior of water/oil/nonionic surfactants with normal distribution of the poly(ethylene oxide) chain length

The phase behavior of systems consisting of water/n-hexane/polyethoxylated nonionic surfactants with a normal distribution of ethylene oxide (EO) chain length has been investigated. The surfactants used were octylphenol ethoxylated with eight EO units and nonylphenol ethoxylated with seven and ten EO units. The oil/water weight ratio was keep constant at 1, whereas the amount of surfactant and the temperature were variables. The pseudobinary phase diagrams were used to find out the triphasic bodies on the temperature scale, the tricritical points and the effect of electrolyte on them. The presence of electrolyte and the increase in surfactant hydrophobicity promote the phase inversion.     

Water dynamics--the effects of ions and nanoconfinement

Hydrogen bond dynamics of water in highly concentrated NaBr salt solutions and reverse micelles are studied using ultrafast 2D-IR vibrational echo spectroscopy and polarization-selective IR pump-probe experiments performed on the OD hydroxyl stretch of dilute HOD in H(2)O. The vibrational echo experiments measure spectral diffusion, and the pump-probe experiments measure orientational relaxation. Both experimental observables are directly related to the structural dynamics of water's hydrogen bond network. The measurements performed on NaBr solutions as a function of concentration show that the hydrogen bond dynamics slow as the NaBr concentration increases. The most pronounced change is in the longest time scale dynamics which are related to the global rearrangement of the hydrogen bond structure. Complete hydrogen bond network randomization slows by a factor of approximately 3 in approximately 6 M NaBr solution compared to that in bulk water. The hydrogen bond dynamics of water in nanoscopically confined environments are studied by encapsulating water molecules in ionic head group (AOT) and nonionic head group (Igepal CO 520) reverse micelles. Water dynamics in the nanopools of AOT reverse micelles are studied as a function of size by observing orientational relaxation. Orientational relaxation dynamics deviate significantly from bulk water when the size of the reverse micelles is smaller than several nm and become nonexponential and slower as the size of the reverse micelles decreases. In the smallest reverse micelles, orientational relaxation (hydrogen bond structural randomization) is almost 20 times slower than that in bulk water. To determine if the changes in dynamics from bulk water are caused by the influence of the ionic head groups of AOT or the nanoconfinement, the water dynamics in 4 nm nanopools in AOT reverse micelles (ionic) and Igepal reverse micelles (nonionic) are compared. It is found that the water orientational relaxation in the 4 nm diameter nanopools of the two types of reverse micelles is almost identical, which indicates that confinement by an interface to form a nanoscopic water pool is a primary factor governing the dynamics of nanoscopic water rather than the presence of charged groups at the interface.     

The importance of lipophobicity in surfactants: methods for measuring lipophobicity and its effect on the properties of two types of nonionic surfactant

In researching the properties of surfactants, lipophobicity is an important consideration. Increasing surfactant lipophobicity corresponds to a decrease in the saturation concentration of a singly dispersed surfactant in oil, i.e., a decrease in the critical micelle concentration in oil (CMC(oil)). This, in turn, is the crucial property in discussing the efficiency of a surfactant. Lipophobicity is influenced by the structure and length of the hydrophilic moiety of the surfactant. Surfactants that consist of OH or CO groups are effective for use in both aliphatic and aromatic hydrocarbon-rich systems because they are highly lipophobic and of a compact size and function independent of temperature. These characteristics are also reflected in their phase behavior. Phase diagrams illustrate the following properties: temperature independence; strong absorption at the water-oil interface and efficient action even with a very small amount of surfactant with a low CMC; high solubilization of water and oil into an aggregated surfactant solution phase. Through phase diagrams, the CMC(oil) of R10EO8 was obtained and the result used to compare the many different characteristics of the more typical oxyethylene nonionic surfactants with the new polyglyceryl nonionic surfactants.     

Microstructure of un-neutralized hydrophobically modified alkali-soluble emulsion latex in different surfactant solutions

At low pH conditions and in the presence of anionic, cationic, and nonionic surfactants, hydrophobically modified alkali-soluble emulsions (HASE) exhibit pronounced interaction that results in the solubilization of the latex. The interaction between HASE latex and surfactant was studied using various techniques, such as light transmittance, isothermal titration calorimetry, laser light scattering, and electrophoresis. For anionic surfactant, noncooperative hydrophobic binding dominates the interaction at concentrations lower than the critical aggregation concentration (CAC) (C < CAC). However, cooperative hydrophobic binding controls the formation of mixed micelles at high surfactant concentrations (C > or = CAC), where the cloudy solution becomes clear. For cross-linked HASE latex, anionic surfactant binds only noncooperatively to the latex and causes it to swell. For cationic surfactant, electrostatic interaction occurs at very low surfactant concentrations, resulting in phase separation. With further increase in surfactant concentration, noncooperative hydrophobic and cooperative hydrophobic interactions dominate the binding at low and high surfactant concentrations, respectively. For anionic and cationic surfactant systems, the CAC is lower than the critical micelle concentration (CMC) of surfactants in water. In addition, counterion condensation plays an important role during the binding interaction between HASE latex and ionic surfactants. In the case of nonionic surfactants, free surfactant micelles are formed in solution due to their relatively low CMC values, and HASE latexes are directly solubilized into the micellar core of nonionic surfactants.     

混合表面活性剂在非极性溶剂中的聚集行为

表面活性剂在非极性溶剂中的聚集行为比在水溶液中复杂得多. 水溶液中表面活性剂有一明确的临界胶束浓度(CMC),而在非极性溶剂中至今对CM C概念仍有怀疑^[1], 但已有多种手段如染料增溶法、水增溶法、光散射法、荧光偏振、紫外和核磁共振谱等证实并测定了非极性溶剂中 CMC 的存在^[1～5]. 表面活性剂在非极性溶剂中以非离子化状态存在, 其缔合主要靠两亲分子之间的偶极-偶极以及离子对相互作用, 那么在一种表面活性剂溶液中加入另一种表面活性剂, 即表面活性剂的复配, 必然对其聚集行为产生重大影响, 但迄今为止, 尚未见关于混合表面活性剂在非极性溶剂中聚集行为的报道. 本文采用碘光谱法和水增溶法测定了阴离子表面活性剂AOT 和非离子表面活性剂 Brij30 混合后在正庚烷中形成反胶束的 CMC, 以期考察表面活性剂的复配对其聚集行为的影响。     

Adsorption of nonionic mixtures at the air-water interface: effects of temperature and electrolyte

Specular neutron reflection has been used to investigate the effects of temperature and added electrolyte on the adsorption of nonionic surfactants and nonionic surfactant mixtures at the air-water interface. For the alkyl poly-oxyethylene oxide nonionic surfactants, C(n)EO(m), the adsorption at the air-water interface is independent of temperature for surfactants with shorter ethylene oxide groups, whereas there is an increasing tendency for increased adsorption with temperature for surfactants with longer ethylene oxide groups. The addition of "salting in" (sodium thiocyanate, NaSCN) and "salting out" (sodium chloride, NaCl, sodium sulphate, Na2SO4) electrolyte results in reduced and enhanced adsorption, respectively, for C12EO8, whereas both types of electrolyte result in enhanced adsorption for C12EO12. The addition of electrolyte does not substantially alter the temperature dependence of the adsorption of the pure monolayers. For the nonionic mixtures of C12EO3/C12EO8 increasing temperature results in a surface richer in the least surface-active component, C12EO8. For the same nonionic mixture, the addition of "salting in" and "salting out" electrolyte results in an reduced and increased adsorption, respectively. The addition of "salting in" electrolyte results in a surface more rich in C12EO3, whereas for the addition of both "salting in" and "salting out" electrolyte the surface composition is essentially unaltered.     

Thermodynamic characterization of 3-[(3-cholamidopropyl)-dimethylammonium]-1-propanesulfonate (CHAPS) micellization using isothermal titration calorimetry: temperature, salt, and pH dependence

A systematic investigation of the micellization process of a biocompatible zwitterionic surfactant 3-[(3-cholamidopropyl)-dimethylammonium]-1-propanesulfonate (CHAPS) has been carried out by isothermal titration calorimetry (ITC) at temperatures between 278.15 K and 328.15 K in water, aqueous NaCl (0.1, 0.5, and 1 M), and buffer solutions (pH = 3.0, 6.8, and 7.8). The effect of different cations and anions on the micellization of CHAPS surfactant has been also examined in LiCl, CsCl, NaBr, and NaI solutions at 308.15 K. It turned out that the critical micelle concentration, cmc, is only slightly shifted toward lower values in salt solutions, whereas in buffer media it remains similar to its value in water. From the results obtained, it could be assumed that CHAPS behaves as a weakly charged cationic surfactant in salt solutions and as a nonionic surfactant in water and buffer medium. Conventional surfactants alike, CHAPS micellization is endothermic at low and exothermic at high temperatures, but the estimated enthalpy of micellization, ΔHM0, is considerably lower in comparison with that obtained for ionic surfactants in water and NaCl solutions. The standard Gibbs free energy, ΔGM0, and entropy, ΔSM0, of micellization were estimated by fitting the model equation based on the mass action model to the experimental data. The aggregation numbers of CHAPS surfactant around cmc, obtained by the fitting procedure also, are considerably low (nagg ≈ 5 ± 1). Furthermore, some predictions about the hydration of the micelle interior based on the correlation between heat capacity change, Δcp,M0, and changes in solvent-accessible surface upon micelle formation were made. CHAPS molecules are believed to stay in contact with water upon aggregation, which is somehow similar to the micellization process of short alkyl chain cationic surfactants.     

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.     

Spectroscopic studies of 2-(2-bromo-ethyl)-6-nitro-benzo[de]isoquinolene-1,3-dione in water/alkanol mixed solvents and nonionic micelle of Igepal CO series

Spectroscopic studies of newly synthesized bioactive compound 2-(2-bromo-ethyl)-6-nitro-benzo[de]isoquinolene-1,3-dione (BNBIO) have been carried out in polar aprotic solvent, viz. acetonitrile, tetrahydrofuran, 1,4-dioxan, ethylene glycol, dimethyl formamide, and polar protic solvent, viz. methanol, ethanol, propanol, water. Variation in absorbance of BNBIO in water-methanol, water-ethanol and water-propanol mixtures at their different compositions have been observed. Absorption behaviour of the dye has been studied in poly(oxyethylene) nonylphenol surfactants Igepal CO 630, Igepal CO 720 and Igepal CO 890 containing same hydrophobic tail and different numbers of poly(oxyethylene) groups. Experimental results of the BNBIO nonionic micelles have been explained in terms of 1:1 electron donor-acceptor (EDA) complexation and the complexation equilibrium becomes suppressed with increasing number of poly(oxyethylene) residue on the Igepal surfactant. Variation in binding constant of dye-micelle complexation has been rationalized considering a competitive equilibrium process between the BNBIO-water interactions.