Micelle–monomer equilibria in solutions of ionic surfactants and in ionic–nonionic mixtures: A generalized phase separation model

On the basis of a detailed physicochemical model, a complete system of equations is formulated that describes the equilibrium between micelles and monomers in solutions of ionic surfactants and their mixtures with nonionic surfactants. The equations of the system express mass balances, chemical and mechanical equilibria. Each nonionic surfactant is characterized by a single thermodynamic parameter — its micellization constant. Each ionic surfactant is characterized by three parameters, including the Stern constant that quantifies the counterion binding. In the case of mixed micelles, each pair of surfactants is characterized with an interaction parameter, β, in terms of the regular solution theory. The comparison of the model with experimental data for surfactant binary mixtures shows that β is constant — independent of the micelle composition and electrolyte concentration. The solution of the system of equations gives the concentrations of all monomeric species, the micelle composition, ionization degree, surface potential and mean area per head group. Upon additional assumptions for the micelle shape, the mean aggregation number can be also estimated. The model gives quantitative theoretical interpretation of the dependence of the critical micellization concentration (CMC) of ionic surfactants on the ionic strength; of the CMC of mixed surfactant solutions, and of the electrolytic conductivity of micellar solutions. It turns out, that in the absence of added salt the conductivity is completely dominated by the contribution of the small ions: monomers and counterions. The theoretical predictions are in good agreement with experimental data.     

Surface adsorption and micelle formation of aqueous solutions of polyethyleneglycol and sugar surfactants

The surface tension of aqueous solutions of tetraethyleneglycol octyl ether (C8E4) and octyl-β-d-maltopyranoside (OM) mixture was measured as a function of the total molality of surfactants and the composition of OM under atmospheric pressure at 298.15 K by drop volume technique. The results of surface tension measurements were analyzed by originally developed thermodynamic equations, then phase diagrams of adsorption and micelle formation were constructed. From the analysis of the surface tension data, it was found that the C8E4 and OM molecules interact attractively in the adsorbed film and the excess Gibbs energy of adsorption can be compared with those observed in typical cationic–nonionic surfactant systems; nevertheless, they are mixed almost ideally in the mixed micelle. Judging from a negative excess surface area calculated by differentiating the excess Gibbs energy by the surface tension, we concluded that the attraction between C8E4 and OM molecules is a short-range one originated in the hydrogen bonding between them which favors the planar configuration.     

Markov chain model for the critical micelle concentration of surfactant mixtures

An extension of the Markov chain model (MC) for micellization is proposed, which allows the distribution of the surfactants between the monomer solution and the micelles in a mixed surfactant system to be predicted. The dependence of the critical micelle concentration (cmc) on the composition of the solution is investigated. The equilibrium thermodynamic relation between cmc and micelle composition is discussed. The case of ternary mixtures is analyzed, and theoretical triangular diagram is constructed according to MC. Available experimental data for binary and ternary mixtures agree well with the new MC theory. The dependence of MC parameters on the structure of the surfactants is discussed. Comparison of MC with the simple mixture (“regular solution”) model is presented. The parameters of the MC theory are related to the interaction parameter β _SM of the simple mixture model.     

Miscibility of sodium dodecyl sulfate and sodium decyl sulfate in the adsorbed film and micelle

The interfacial tension of the aqueous solution of sodium dodecyl sulfate (SDS) and sodium decyl sulfate (SDeS) mixture against hexane was measured as a function of the total molality and composition of the surfactant mixture at 298.15 K under atmospheric pressure. The compositions of adsorbed film and micelle were evaluated numerically by applying the thermodynamic relations to the experimental results. These results were shown in the form of the phase diagrams of adsorption and micelle formation and compared with those of the aqueous solution of sodium perfluorooctanoate (SPFO) and SDeS mixture. It was found that the diagrams of SDS and SDeS system have swollen cigar shapes and are quite different from those of SPFO and SDeS system which show non-ideal mixing both in the adsorbed film and micelle. This finding was attributed to the fact that the interaction between fluorocarbon and hydrocarbon chains is weaker than that between hydrocarbon chains.     

离子液体型表面活性剂C12mimBr与普通表面活性剂混合性质的研究

研究了离子液体型表面活性剂C12mimBr与阳离子表面活性剂Gemini 12-3-12, DTAB及阴离子表面活性剂SDS复配体系的性质, 并分别采用Rubingh-Margules模型和Rubingh-正规溶液模型计算了临界胶束浓度和混合胶团组成. 研究发现, 两表面活性剂分子结构的匹配性及带电头基之间的相互作用是影响混合溶液性质的主要因素. 对于分子结构差别较大的C12mimBr与Gemini 12-3-12的混合, 其行为远远偏离理想混合性质; 对疏水链长相同仅亲水头基不同的C12mimBr与DTAB则接近于理想混合; 而对C12mimBr＋SDS的复配体系, 正、负电荷间强烈的相互吸引使得混合体系大大偏离理想行为. 计算发现, 两种理论模型得到的混合胶团组成基本一致, 但Rubingh-Margules模型预测的临界胶束浓度比Rubingh-正规溶液模型要好     

Mixed micelle formation in aqueous solutions of nonyl-N-methylglucamine with sodium perfluorooctanoate at different pressures

For the mixed system of nonyl-N-methylglucamine (MEGA9) with sodium perfluorooctanoate (SPFO), the critical micelle concentrations (CMC) at atmosphreic pressure and 30°C were determined from measurement of surface tension, and those at high pressures were determined by the electroconductivity method at mole fractions of MEGA9 up to 0.6. All of MEGA9-SPFO mixed systems have been found to have a surface activity much greater than the respective pure systems, i.e., a synergism of surface activity caused by mixing MEGA9 and SPFO. The mixing reduces the pressure dependence of the CMC. This suggests that this combination is useful when it is desirable for a surfactant solution to be independent of pressure. The composition of the mixed micellar phase has been estimated by applying the Motomura equation. The Gibbs energy of the mixed micelle formation has also been calculated as a function of mole fraction of a surfactant in the surfactant mixture.To whom correspondence should be addressed.     

Interaction between biosurfactant surfactin and cationic surfactant cetyl trimethyl ammonium bromide in mixed micelle

An anionic/cationic mixed surfactant aqueous system of surfactin and cetyl trimethyl ammonium bromide (CTAB) at different molar ratios was studied by surface tension and fluorescence methods (pH 8.0). Various parameters that included critical micelle concentration (cmc), micellar composition (X ₁), and interaction parameter (β ^m) as well as thermodynamic properties of mixed micelles were determined. The β ^m was found to be negative and the mixed system was found to have much lower cmc than pure surfactant systems. There exits synergism between anionic surfactin and cationic CTAB surfactants. The degree of participation of surfactin in the formation of mixed micelle changes with mixing ratio of the two surfactants. The results of aggregation number, fluorescence anisotropy, and viscosity indicate that more packed and larger aggregates were formed from mixed surfactants than unmixed, and the mixed system may be able to form vesicle spontaneously at high molar fraction of surfactin.     

CnNCl和SDS在水溶液中的相互作用

CnNCl和SDS在水溶液中的相互作用;滴定式微量热法; 烷氧基羟丙基三甲基氯化铵; 十二烷基硫酸钠;胶束;疏水作用     

Miscibility of sodium chloride and decyl methyl sulfoxide in the adsorbed film and micelle

The surface tension of aqueous solutions of a sodium chloride (NaCl)-decyl methyl sulfoxide (DeMS) mixture was measured as a function of the total molality of the mixture and the mole fraction of DeMS in the mixture at 298.15 K under atmospheric pressure. The total surface density of the mixture and the mole fraction of DeMS in the adsorbed film and micelle were numerically evaluated by applying the thermodynamic treatment of surfactant mixture to the NaCl-DeMS mixture. Miscibility of NaCl and DeMS in the adsorbed film and micelle was clarified by use of the phase diagram of adsorption and micelle formation. Positive adsorption of NaCl was observed in the presence of DeMS and attributed to attractive interaction between the polar head group of DeMS molecule and Na+ or Cl- ions in the adsorbed film and micelle. The results were compared with those of NaCl-octyl methyl sulfoxide and NaCl-decyldimethylphosphine oxide mixtures to elucidate the structure effect of nonionic surfactant on the miscibility.     

Triton X-100/CTAB在乙二醇/水混合溶剂中的热力学性质和胶团化行为

利用表面张力法, 研究了非离子表面活性剂Triton X-100和离子表面活性剂十六烷基三甲基溴化铵(CTAB)混合体系在混合极性溶剂乙二醇/水(乙二醇的体积分数分别为5%、10%和20%)中的热力学性质和胶团化行为. 结果表明, 混合体系在乙二醇水溶液中存在协同效应, 临界胶束浓度随乙二醇含量的增加而增大. 利用Rubingh和Maeda模型计算了混合物中各组分在胶团相中的组成、相互作用参数以及自由能的贡献. 在实验研究的乙二醇浓度范围内, 发现该非离子/离子混合体系在离子组分摩尔分数约为0.3时, 协同效应最强.     

Volume behavior of mixed micelles of dodecyltrimethylammonium chloride and bromide

Densities of aqueous solutions of mixtures of dodecyltrimethylammonium chloride (DTAC) and dodecyltrimethylammonium bromide (DTAB) have been measured as a function of total molality at constant composition and the apparent molar volumes of the mixtures were derived from the density data. The partial molar volumes of monomeric surfactant mixtures, the molar volumes of mixed micelles, and the volumes of formation of mixed micelles were evaluated and are compared with those for decyltrimethylammonium bromide (DeTAB) and DTAB mixtures. The partial molar volumes of monomeric surfactant mixtures and the molar volumes of mixed micelles are observed to depend linearly on the monomer and micelle compositions, respectively. Although the volume of formation of mixed micelles of the DeTAB-DTAB mixture depends on the micellar composition, that of the DTAC-DTAB mixture is observed to be almost independent of the micellar composition. This suggests that the volumes of the counter ions in the micellar solutions are almost equal to those in the monomeric solutions.     

Thoughts on the ideal behavior of mixed micelles and the appropriate application of regular solution theory (RST)

Solutions of mixed surfactants are often considered as solvent mixtures. Usually, mixed micellar aggregates are considered as a homogeneous mixture of solvents dispersed in a solution. But the transposition of the usual thermodynamic models of solvent mixtures to mixed micelles is not always so obvious. We discussed this point in this paper by considering several cases of surfactant mixtures. A major problem is to define the molar fraction of each surfactant in the aggregate especially when a charged surfactant is employed in the mixture, because possible dissociation of the components of the mixture must be considered in the bulk as well in the micelle. This definition is crucial especially for the characterization of the ideal behavior which is usually described by the Clint relation, as well as for the application of regular solution theory (RST) which is the most frequently applied model for interpreting the behavior of surfactant mixtures. We show in this paper how the definition of the molar fraction can change the equations and the interpretations.     

混合胶束中Gemini阳离子表面活性剂14-s-14与常规表面活性剂的协同作用:连接臂及反离子效应(英文)

The mixed micelle formation of binary cationic 14-s-14 gemini with conventional single chain surfactants was studied by conductivity measurements.The critical micelle concentration(cmc) and the degree of counterion binding values(g) of the binary systems were determined.The results were analyzed by applying regular solution theory(RST) to calculate micellar compositions(X),activity coefficients(f1,f2),and the interaction parameters(β).The synergistic interactions of all the investigated cationic gemini+conventional surfactant combinations were found to be dependent upon the length of hydrophobic spacer of the gemini surfactant.The excess Gibbs free energy of mixing was evaluated,and it indicated relatively more stable mixed micelles for the binary combinations.     

Micellisation behaviour of mixtures of sodium dodecylsulphate and sodium lauroylsarcosinate in water

The critical micelle concentrations of binary mixtures of sodium dodecylsulphate (SDS) and sodium lauroylsarcosinate (SLAS) have been determined in water by conductivity measurements at different mole fractions for each of the components. The critical micelle concentrations were slightly lower than that predicted from ideal mixing theory indicating positive synergistic interactions in mixed micelle formation. The results of the mixed systems were analysed using the Regular Solution Theory and the approach based on the Gibbs–Duhem equation which allowed for the determination of the composition of the mixed micelle, the activity coefficients and the pair-wise molecular interaction parameter β. The β values were all negative at all mole fractions investigated, showing a slight deviation from ideality, with an average value of –0.27. The excess free energy of the mixed systems was also calculated and the values were all negative for the mixed systems studied, an indication that the mixed micelles are thermodynamically stable relative to the individual component. This thermodynamic parameter also exhibits symmetrical behaviour with respect to micellar composition suggestive of a regular solution behaviour of the mixed surfactant system.     

A simple rule for describing the composition dependence of the aggregation number of mixed micelles

The mean aggregation numbers of mixed micelles composed of hydrocarbon surfactants (nonionic/nonionic and ionic/nonionic surfactants) have been determined by the intensity light-scattering method, in order to compare them with the values calculated by using the equations derived. The equations have been derived for representative micellar shapes (disk-like, rod-like, and spherical shapes) by making the assumptions that (i) the surface area of the hydrocarbon core of a mixed micelle is built up by independent contributions from each surfactant monomer, and (ii) the dimension of the hydrocarbon core is determined by the number of carbon atoms of a surfactant. The closest agreement of the observed aggregation numbers with the calculated ones has been obtained for the mixed micelle of an oblate ellipsoidal shape as a geometrical model for a disk-like micelle. This suggests that an oblate ellipsoidal shape may be more probable for a micelle formed at a moderate range of surfactant concentration than a prolate ellipsoidal (a rod-like) and a spherical shape if the assumptions (i) and (ii) hold. The equations presented here are useful, since they make it possible to calculate an accurate aggregation number of the mixed micelle of any composition from the aggregation numbers of the pure micelles of the components and the number of carbon atoms of component surfactants as long as there is no highly specific interaction between different surfactant components.     

Activity Coefficients of Aqueous Mixed Ionic Surfactant Solutions from Osmometry

Osmotic techniques for measuring thermodynamic activities, such as isopiestic equilibration, are well established for multicomponent solutions, especially mixed salt solutions. Surprisingly, these techniques have not yet been applied to mixed ionic surfactants, despite the numerous practical applications of these systems and the importance of the Gibbs free energy for micelle stability. In this study, mass-action equations are developed for the osmotic coefficients of solutions of ionic surfactant CA + ionic surfactant CB, with common counterion C. Extended Debye–Hückel equations are used for the ionic activity coefficients. The equilibrium constants for mixed micelle formation are evaluated by Gibbs–Duhem integration of critical micelle concentrations. Fitting the derived equations to the osmotic coefficients of aqueous sodium decanoate + sodium dodecylsulfate solutions measured by freezing-point osmometry is used to evaluate the activities of the total surfactant components. Very large departures from ideal solution behavior are indicated, including stoichiometric surfactant activity coefficients and micelle activity coefficients that drop below 0.05 and 10^?8, respectively, relative to unity for ideal solutions. Osmometry offers many interesting and unexplored possibilities for studies of mixed surfactant thermodynamics.     

Volumetric behavior and micelle formation of aqueous surfactant mixtures

A thermodynamic treatment of the volumetric behavior of surfactant mixtures in water have been developed on the basis of the thermodynamic treatment of mixed micelle by Motomura et al. Densities of aqueous solutions of mixtures of decyltrimethylammonium bromide (DeTAB) and dodecyltrimethylammonium bromide (DTAB) have been measured as a function of total molality at constant compositions. The apparent molar volumes of the mixtures have been derived from the density data and the mean partial molar volume of monomeric surfactant mixture V _t ^w , the molar volume of mixed micelle V^M/N _t ^M , the voluem of formation of mixed micelle _W ^M V, and the composition of surfactant in the mixed micelle have been evaluated. The V _t ^W , V^M/N _t ^M , and _W ^M V have been observed to depend on the composition. The linear dependence of V _t ^W and V^M/N _t ^M on the composition indicates that the mixing of DeTAB and DTAB is ideal both in the monomeric and micellar states. This has been confirmed further by the shape of the critical micelle concentration vs. composition curves.     

以混合中性-阳离子表面活性剂为模板合成MCM-48

本文首次将中性和阳离子表面活性剂混和(S^0S^+)形成胶束后,共同作为模板剂合成了立方相中孔分子筛,经此途径得到的中孔分子筛材料既具有MCM-48的立方结构,又能体现出更好的热稳定性。混合不同性质的表面活性剂作为模板剂,将是一种制备不同性能的中孔分子筛的有效易行的途径。     

Adsorption and micelle formation of alkylammonium chloride-alkyltrimethylammonium chloride mixtures

The surface tension of the aqueous solutions of binary cationic surfactant mixtures of (1) dodecylammnonium chloride (DAC)-tetradecyltrimethylammonium chloride (TTAC), (2) decylammonium chloride (DeAC)-dodecyltrimethylammonium chloride (DTAC), and (3) DAC-DTAC was measured as a function of the total molality and composition of surfactants at 298.15 K. The compositions of surfactants in the adsorbed film and micelle were evaluated and the phase diagram of adsorption and that of micelle formation were constructed. Furthermore the excess Gibbs energies of adsorption and micelle formation were calculated to estimate the deviation from the corresponding ideal mixing. It was found that the surface and micelle are enriched in trimethylammonium salts in (1) and (2), while in ammonium salt in (3) compared to the bulk solution. On the other hand, the micelle is enriched in trimethylammonium salts compared to the surface at the critical micelle concentration (CMC) in all the systems. The miscibility of the surfactants was clarified from the standpoints of the structure of the head group and of the matching between the size of polar head group of surfactants and the difference in hydrocarbon chain length.