MICELLE FORMATION IN MIXTURES OF ANIONIC AND NONIONIC SURFACTANTS

The critical micelle concentration of mixtures of anionic and nonionic surfactants was measured. The anionic surfactants were alkylbenzene sulfonates and the nonionic surfactants were polyoxyethylene nonylphenols and a polyoxy-ethylene alcohol. The effect of added electrolyte, the number of ethylene oxide units in the polyethoxylate, and the anionic alkyl chain length were studied. All systems showed substantial negative deviations (lower CMC) from ideal solution theory. The results can be represented by regular solution theory. Charge separation appears to be the source of the nonideality. This considers the reduction of electrostatic repulsion between the ionic surfactant head groups in the mixed micelle, due to the insertion of nonionic hydrophilic groups between these charged groups, to be the cause of enhanced micelle formation. The physical basis of regular solution theory was shown to be consistent with the charge separation effect.     

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     

Solution properties of mixed surfactant systems (IV)

Electric properties of mixed anionic-nonionic surfactant systems in aqueous solutions above the CMC have been studied in terms of pNa values, electrical conductivities, and dielectric constants; these systems are sodium 3, 6, 9-trioxaicosanoate (ECL) — alkyl polyoxyethylene ethers (C_mPOE; m=12, 14, 16, and 18). The degree of ionic dissociation of mixed micelle increases with increasing the number of carbon atoms of the alkyl group in the nonionic surfactant. The electrical conductivity increases with increasing the alkyl chain length in the nonionic surfactant, in spite of the increase of the activation energy for conduction. The size of mixed micelles also increases with increasing alkyl chain length. This may be attributed to the fact that the mixed micelle is formed more easily by a nonionic surfactant including long alkyl chains than for one having shorter alkyl chains.     

Pseudo-homogeneous micelle extraction of ion-associates formed between tetrabutylammonium ion and some aromatic sulfonate ions into nonionic surfactant micelle studied through the mobility measurements in capillary zone electrophoresis

Ion-association extraction of some aromatic sulfonate ions including alkylbenzene sulfonates with tetrabutylammonium ion (TBA+) into nonionic surfactant micelle has been investigated through the changes in the electrophoretic mobility. Nonionic surfactants of Brij 35 and Brij 58 were used as micelle substrates to which the ion-associates formed could distribute. The electrophoretic mobility of the aromatic sulfonate ions was measured by capillary zone electrophoresis in the presence of TBA+ and/or the nonionic surfactant to determine ion-association constants (K(ass)), binding constants of the anions to the nonionic surfactant micelle (K(B)), and binding constants of the ion-associates to the nonionic surfactant micelle (K(B,IA)). Nonlinear phenomena induced with the alkyl chain moiety were observed on K(ass) and K(B) by its linear structure and the mixed micelle formation, respectively. Larger K(B) values were obtained with Brij 58 as micelle matrix than with Brij 35, while the differences in K(B,IA) were small between Brij 58 and Brij 35.     

Fading phenomena of azo oil dye in anionic-nonionic surfactant solutions II. Effects of alkyl and/or oxyethylene groups in nonionic surfactant on the fading rate

The effects of alkyl and/or oxyethylene groups in a nonionic surfactant on the fading phenomena of 4-phenylazo-1-naphthol (4-OH), which occur in aqueous solutions of anionic-nonionic surfactant systems, are described; these systems are sodium dodecyl sulfate (SDS) — alkyl poly(oxyethylene) ethers (C_mPOE_n, m=12,14,16, and 18 at n=20; n=10, 20, 30, and 40 at m=16). The fading phenomenon is observed when 4-OH is added to the anionic-nonionic mixed surfactant solutions at a molar ratio of 11. A singlet oxygen, which is caused by the hydrophilic-hydrophilic interaction between two surfactants, is thought to attack the tautomer of 4-OH. The fading rate of 4-OH accelerates with increasing alkyl chain length or with decreasing oxyethylene chain length in the nonionic surfactant molecule. The effect on the fading behavior of 4-OH would be larger for a system which can easily form a mixed micelle than for a system in which two kinds of micelles coexist.     

Comparing Decyl-beta-maltoside and Octaethyleneglycol Mono n-Decyl Ether in Mixed Micelles with Dodecyl Benzenesulfonate

In this study the mixed micelle behavior of an alkyl polyglycoside is compared to a surfactant of polyoxyethylene type, by means of surface tension measurements. The two nonionic surfactants are compared in mixed micelle systems together with an anionic surfactant. The surfactant mixtures are: decyl-beta-maltoside (C(10)M) with dodecyl benzenesulfonate (C(12)BS) and octaethyleneglycol mono n-decyl ether (C(10)EO(8)) with C(12)BS. The mixture of C(10)M and C(10)EO(8) is also studied. Critical micelle concentration (CMC) and the concentration at which the surface tension reduction is 20 mNm(-1) (C(20)) are determined at different mixing ratios of the surfactant mixtures. By applying the nonideal mixed micelle theory, interaction parameters at CMC (beta(CMC)) and C(20) (beta(C20)) are calculated for the surfactant mixtures. The results show that the C(10)M-C(12)BS mixture has a beta(CMC) parameter of -2.1, whereas the beta(CMC) parameter for the C(10)EO(8)-C(12)BS mixture is -3.3, indicating a weaker net attractive interaction between C(10)M and C(12)BS than between C(10)EO(8) and C(12)BS. This is attributed to a small negative and positive charge of the respective nonionic surfactants. This is supported by a slightly negative beta(CMC) parameter obtained for the surfactant mixture C(10)M-C(10)EO(8), indicating a small net attractive interaction between the two nonionic surfactants. Copyright 2000 Academic Press.     

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。     

Interfacial and Thermodynamic Properties of Anionic‐Nonionic Mixed Surfactant System: Influence of Hydrophobic Chain Length of the Nonionic Surfactant

The influence of hydrophobic chain length in nonionic surfactants on interfacial and thermodynamics properties of a binary anionic‐nonionic mixed surfactant was investigated. In this study, nonionic surfactants lauric‐monoethanolamide (C₁₂ MEA) and myrisitic‐monoethanolamide (C₁₄ MEA) were mixed with an anionic surfactant, α‐olefin sulfonate (AOS). The critical micelle concentration (cmc), maximum surface excess (Γ_max), and minimum area per molecule (A_min) were obtained from surface tension isotherms at various temperatures. The thermodynamic parameters of micellization and adsorption were also computed. Micellar aggregation number (N_agg), micropolarity, and binding constant (K_sv) of pure and mixed surfactant system was calculated by fluorescence measurements. Rubingh's method was applied to calculate interaction parameters for the mixed surfactant systems.     

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.     

Variegated micelle surfaces: correlating the microstructure of mixed surfactant micelles with bulk solution properties

Electron paramagnetic resonance, viscosity, and small-angle neutron scattering (SANS) measurements have been used to study the interaction of mixed anionic/nonionic surfactant micelles with the polyampholytic protein gelatin. Sodium dodecyl sulfate (SDS) and the nonionic surfactant dodecylmalono-bis-N-methylglucamide (C12BNMG) were chosen as "interacting" and "noninteracting" surfactants, respectively; SDS micelles bind strongly to gelatin but C12BNMG micelles do not. Further, the two surfactants interact synergistically in the absence of the gelatin. The effects of total surfactant concentration and surfactant mole fraction have been investigated. Previous work (Griffiths et al. Langmuir 2000, 16 (26), 9983-9990) has shown that above a critical solution mole fraction, mixed micelles bind to gelatin. This critical mole fraction corresponds to a micelle surface that has no displaceable water (Griffiths et al. J. Phys. Chem. B 2001, 105 (31), 7465). On binding of the mixed micelle, the bulk solution viscosity increases, with the viscosity-surfactant concentration behavior being strongly dependent on the solution surfactant mole fraction. The viscosity at a stoichiometry of approximately one micelle per gelatin molecule observed in SDS-rich mixtures scales with the surface area of the micelle occupied by the interacting surfactant, SDS. Below the critical solution mole fraction, there is no significant increase in viscosity with increasing surfactant concentration. Further, the SANS behavior of the gelatin/mixed surfactant systems below the critical micelle mole fraction can be described as a simple summation of those arising from the separate gelatin and binary mixed surfactant micelles. By contrast, for systems above the critical micelle mole fraction, the SANS data cannot be described by such a simple approach. No signature from any unperturbed gelatin could be detected in the gelatin/mixed surfactant system. The gelatin scattering is very similar in form to the surfactant scattering, confirming the widely accepted picture that the polymer "wraps" around the micelle surface. The gelatin scattering in the presence of deuterated surfactants is insensitive to the micelle composition provided the composition is above the critical value, suggesting that the viscosity enhancement observed arises from the number and strength of the micelle-polymer contact points rather than the gelatin conformation per se.     

Mixed micelle formation and solubilization behavior toward polycyclic aromatic hydrocarbons of binary and ternary cationic-nonionic surfactant mixtures

Water solubility enhancements of polycyclic aromatic hydrocarbons (PAHs), viz., naphthalene, anthracene and pyrene, by micellar solutions at 25 degrees C using two series of surfactants, each involving two cationic and one nonionic surfactant in their single as well as equimolar binary and ternary mixed states, were measured and compared. The first series was composed of three surfactants, benzylhexadecyldimethylammonium chloride (C16BzCl), hexadecyltrimethylammonium bromide (C16Br), and polyoxyethylene(20)mono-n-hexadecyl ether (Brij-58) with a 16-carbon (C16) hydrophobic chain; the second series consisted of dodecyltrimethylammonium bromide (C12Br), dodecylethyldimethylammonium bromide (C12EBr), and polyoxyethylene(4)mono-n-dodecyl ether (Brij-30) with a 12-carbon (C12) chain. Solubilization capacity has been quantified in terms of the molar solubilization ratio, the micelle-water partition coefficient, the first stepwise association constant between solubilizate monomer and vacant micelle, and the average number of solubilizate molecules per micelle, determined employing spectrophoto-, tensio-, and flourimetric techniques. Cationic surfactants exhibited lesser solubilization capacity than nonionics in each series of surfactants with higher efficiency in the C16 series compared to the C12 series. Increase in hydrophobicity of head groups of cationics by incorporation of ethyl or benzyl groups enhanced their solubilization capacity. The mixing effect of surfactants on mixed micelle formation and solubilization efficiency has been discussed in light of the regular solution approximation (RSA). Cationic-nonionic binary combinations showed better solubilization capacity than pure cationics, nonionics, or cationic-cationic mixtures, which, in general, showed increase with increased hydrophobicity of PAHs. Equimolar cationic-cationic-nonionic ternary surfactant systems showed lower solubilization efficiency than their binary cationic-nonionic counterparts but higher than cationic-cationic ones. In addition, use of RSA has been extended, with fair success, to predict partition coefficients of ternary surfactant systems using data of binary surfactants systems. Mixed surfactants may improve the performance of surfactant-enhanced remediation of soils and sediments by decreasing the applied surfactant level and thus remediation cost.     

Study of mixtures of n-dodecyl-beta-D-maltoside with anionic, cationic, and nonionic surfactant in aqueous solutions using surface tension and fluorescence techniques

Surfactants of practical interest are invariably mixtures of different types. In this study, mixtures of sugar-based n-dodecyl-beta-D-maltoside with cationic dodecyltrimethylammonium bromide, anionic sodium dodecylsulfate, and nonionic pentaethyleneglycol monododecyl ether in solution, with and without supporting electrolyte, have been studied using surface tension and fluorescence spectroscopic techniques. Interaction parameters and mole fraction of components in mixed micelles were calculated using regular solution theory. The magnitude of interactions between n-dodecyl-beta-D-maltoside and other surfactants followed the order anionic/nonionic > cationic/nonionic > nonionic/nonionic mixtures. Since all surfactants have the same hydrophobic groups, strengths of interactions are attributed to the structures of hydrophilic headgroups. Electrolyte reduced synergism between n-dodecyl-beta-D-maltoside and ionic surfactant due to charge neutralization. Industrial sugar-based surfactant, dodecyl polyglucoside, yielded results similar to that with dodecyl maltoside, implying that tested commercial alkyl polyglucosides are similar to the pure laboratory samples in synergistic interactions with other surfactants. Fluorescence study not only supported the cmc results using tensiometry, but showed that interfaces of all the above mixed micelle/solution interfaces are mildly hydrophobic. Based on these results, an attempt is made to discover the nature of interactions to be a combination of intermolecular potential energies and free energy due to packing of surfactant molecules in micelles.     

Mixed micelle behavior of Pluronic L64 and Triton X-100 with conventional and dimeric cationic surfactants

The mixed micellar properties of a triblock copolymer, Pluronic L64, (EO)13(PO)30(EO)13, and a nonionic surfactant, Triton X-100, in aqueous solution with conventional alkyl ammonium bromides and their dimeric homologues were investigated with the help of fluorescence and cloud point measurements. The composition of mixed micelles and the interaction parameter, beta, evaluated from the critical micelle concentration (cmc) data for different mixtures using Rubingh's and Motomura's theories are discussed. It has been observed that the mixed micelle formation between monomeric/dimeric alkyl ammonium bromides and L64 was due to synergistic interactions which increase with the increase in hydrophobicity of the cationic component. On the other hand, synergistic mixing was observed in the mixed micelles of Triton X-100 and monomeric cationic surfactants, the magnitude of which decreases slightly with the increase in hydrophobicity of the cationic component. Antagonistic interactions were observed in the case of Triton X-100 and dimeric cationic surfactants.     

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.     

Solubilization and Transfer Free Energy of Some Organic Compounds from Bulk Aqueous Phase to Micelle of a New Type of Surfactant

A new type of surfactant, 3‐alkoxyl‐2‐hydroxylpropyltrimethyl ammonium bromide (C_nH_2n+1OCH₂CH(OH)CH₂N(CH₃)₃ ⁺Br^?, abbreviated as R_nTAB, n=8, 12, 14, 16) was synthesized. The solubilization of n‐pentanol, n‐hexanol, n‐heptanol, benzyl alcohol, n‐hexane, benzene, toluene, heptane, and carbon tetrachloride in aqueous solutions of R_nTAB, sodium dodecyl sulfonic(R₁₂SO₃N_a), and in the mixed solution of R₁₆TAB/R₁₂SO₃N_a have been studied by the microtitration method. The experimental results show that the solubilized amounts of the organic compounds increase with the growing of the hydrocarbon chain of R_nTAB, and the solubilizing ability of the binary system is lower for polar substances than for a mono‐surfactant aqueous solution. “V” isothermal curves of the solubilized amount of polar substances have been observed, and the minimum solubilized amount is at the molar ratio 1∶1 of R₁₆TAB/R₁₂SO₃N_a. However, the solubilizing ability of mixed surfactants for non polar substances is higher than that for a mono‐surfactant solution, the solubilizing isotherm curves present a “saddle” shape, and the maximum solubilized amount is at the molar ratio 1∶1 of R₁₆TAB/R₁₂SO₃N_a too. The length of hydrophobic chains of surfactant and the polarity of the organic compound affect the transfer free energy from aqueous to micelle phase. The longer the hydrophobic chain of R_nTAB and the lower the polarity of the organic compound, the more easily will the compound transfer from aqueous phase to micelle phase.     

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.     

Cloud point variation of amphiphilic drug promethazine hydrochloride with added surfactants

In this paper we report clouding phenomenon occurring in an amphiphilic phenothiazine drug promethazine hydrochloride (PMT) in presence of surfactants. Cationic and nonionic surfactants increase the CP of 75 mM PMT solutions (prepared in 10 mM sodium phosphate buffer). These surfactants form mixed micelles with PMT. Anionic surfactants also form mixed micelles with the drug but the CP behavior is different by showing a peaked behavior. At low concentrations, anionic surfactants hinder micelle formation by forming ion-pairs whereas the usual CP decreasing effect at higher concentrations is due to mixed micellization. The CP behavior of 75 mM PMT+50 mM TBAB+surfactant systems is also explored which is found similar to PMT+surfactant systems with the difference only in magnitude of the clouding temperature.     

混合反胶束的电导与微结构研究

反胶束是两亲分子在非极性溶剂中形成的一种有序组合体，在医药、化工、采油、胶束催化及酶催化等领域中有重要应用．与胶束溶液相比，人们对反胶束的形成与结构的了解至今仍不充分．特别是对于由混合表面活性剂形成的反胶束的研究几乎无人涉及．本文采用动态光散射、电导及荧光光谱等手段对阴离子表面活性剂AOT与非离子表面活性剂形成的混合反胶束进行了研究，旨在探讨利用表面活性剂的复配来调节和控制反胶束的结构和性能．亚实验部分二异辛基磺化琉璃酸钠（AOT，Sigma公司）；Brij30为含4个氧乙烯基（EO基）的十二碳醇（AcrosOrgani…     

Electrophoretic behaviour and viscosities of metal oxides in mixed surfactant systems

 The electrokinetic behavior and viscosity of anatase and alumina in mixed-surfactant solutions were investigated. Sodium dodecylsulfate and nonionic polyoxyethylene ethers were investigated as model surfactants. Pure nonionic surfactants adsorbed on anatase and coated the particles, so that the zeta potential was nearly zero near the critical micelle concentration of surfactant. At higher surfactant concentrations, an increase in the zeta potentials was observed, suggesting a change in the microstructure of the adsorbed layer. Addition of nonionic surfactant to positively charged anatase and alumina with some preadsorbed sodium dodecylsulfate reversed the surface charge of the oxide to negative, indicating enhanced coadsorption of the anionic surfactant. At higher concentrations of the nonionic surfactant, the charge reversed back to positive. Nonionic surfactants did not reverse the surface charge of these oxides in the absence of the anionic surfactant. Coenhanced adsorption of nonionic and anionic surfactants was used to stabilize alumina at the isoelectric point, where neither surfactant adsorbed appreciably on its own. These results suggest a dramatic change in conformation of the surfactant chains in mixed systems. Further explanation and justification of the proposed changes in adsorbed surfactant conformation require spectroscopic evidence. Received: 12 March 1997 Accepted: 22 July 1997