Aggregation Numbers Of Mixed Micelles Research Articles

Amphiphilic copolymers and surface active ionic liquid systems in aqueous media – Surface active and aggregation characteristics

The surface active and micellar behavior of a di- and tri-block copolymer of EB and EBE, where E is oxyethylene and B is oxybutylene moieties and surface active ionic liquids (SAILs) namely 4-dodecyl-4-methylmorpholinium chloride, [C12mmor][Cl] and 1-dodecyl-1-methylpyrrolidinium chloride, [C12mpyrr][Cl]) is studied in aqueous media by surface tension, steady-state florescence and particle size measurements. The critical micelle concentration (CMC), surface active parameters (adsorption efficiency, surface excess, surface tension reduction, minimum area per molecule at air/water interface, etc.), average translation diffusion coefficient, size parameters and aggregation numbers are calculated. The effect of both SAILS and also copolymers as additives on the surface active and micellar behavior of one another is studied. The shape and size parameters of the micelles of the pure copolymer or SAILs are determined from translational diffusion coefficients at infinite dilution. The mixed micelles of copolymer–SAIL systems are treated in terms of spheres and it is observed that their hydrodynamic radii decreased with the increase in the proportion of SAIL. The aggregation number of mixed micelles as determined from steady state florescence quenching method initially increased, reached a peak value and decreased drastically at high SAIL mole fractions. It is rationalized that the SAILs in general facilitate the dissolution of copolymer micelles but the mixed micelles predominantly consist of SAIL molecules or micelles over most of the mole fraction range. Regular solution theory formulations are tested on copolymer–SAIL mixture solutions and micellar mole fraction, interaction parameter (β) and activity coefficients (f1, f2) are calculated. The values of β ranged from −3.3 to −5.9 suggesting synergistic interactions between the two amphiphiles.

Synergism in mixtures of n-octyl-β-d-thioglucoside and different n-alkyltrimethylammonium bromides: effect of the alkyl chain length

Mixtures of n-octyl-β-d-thioglucoside with three different n-alkyltrimethylammonium bromides (n = 12 (DTAB), 14 (TTAB), and 16 (CTAB)) have been studied by using fluorescence spectroscopic techniques. The critical micelle concentration values of pure and mixed systems were determined by the pyrene 1:3 ratio method. The experimental results were treated by using thermodynamic mixing approaches based on the pseudophase separation model. It was found that all the mixed systems show a negative deviation from ideal behavior, more pronounced as the larger the alkyl tail of the co-surfactant. It was also observed that the three mixed systems fulfill the conditions of synergism, this behavior being also dependent on the alkyl chain length. By using the static quenching method, the mean micellar aggregation numbers of mixed micelles were obtained. In all the cases, it was observed that the aggregation number is initially reduced with the participation of the cationic surfactant, remaining almost constant and close to the aggregation number of the pure cationic micelles. The local viscosity of pure and mixed micelles was examined by the photophysical response of the hydrophobic probe coumarin 6 solubilized in the micellar medium. It was found that the participation of the ionic component induces the formation of a less ordered structure than that of pure nonionic micelles. This effect being less pronounced as the chain hydrocarbon length of the co-surfactant increases.

Interaction and Stability of Mixed Micelle and Monolayer of Nonionic and Cationic Surfactant Mixtures

Interaction and stability of binary mixtures of cationic surfactants hexadecyltrimethylammonium bromide (HTAB) or hexadecylpyridinium bromide (HPyBr) with nonionic surfactant decanoyl-N-methyl-glucamide (Mega-10) have been studied at different mole fraction of cationic surfactants by using interfacial tension measurements and fluorescence probe techniques. From interfacial tension measurements, the critical micellar concentration and various interfacial thermodynamic parameters have been evaluated. The experimental cmc's were analyzed with the pseudophase separation model, the regular solution theory, and the Maeda's approach. These approaches allowed us to determine the interaction parameter and composition in the mixed state. By using the static quenching method, the mean micellar aggregation numbers of pure and mixed micelles of HTAB + Mega-10 were obtained. It has been observed that the aggregation number of mixed micelles deviates negatively from the ideal behavior. The micropolarity of the micelle was monitored with pyrene fluorescence intensity ratio and found to be increase with the increase of ionic content. The polarization of fluorescence probe Rhodamine B was monitored at different mole fraction of cationic surfactants.

Interactions in binary mixed systems involving a sugar-based surfactant and different n-alkyltrimethylammonium bromides

In this paper, mixtures of sugar-based decanoyl- N-methylglucamide with three different n-alkyltrimethylammonium bromides ( n = 12 (DTAB), 14 (TTAB), and 16 (CTAB)) have been studied using conductance and fluorescence spectroscopic techniques. The critical micelle concentration values of pure and mixed systems were determined by both the conductance and the pyrene 1:3 ratio methods. The experimental results were interpreted using thermodynamic mixing approaches based on the pseudophase separation model. These analyses allowed us to determine the interaction parameters and the composition of the mixed micelles through the whole composition range. Since all the ionic surfactants used in this study have the same headgroup, the differences observed between the three mixed systems were attributed to the lengths of their hydrocarbon chains. It was established that, besides interactions of electrostatic character, additional short-range interactions must be considered. By using the static quenching method, the mean micellar aggregation numbers of mixed micelles were obtained. In the cases of the mixed systems with DTAB and TTAB it was observed that the aggregation number is initially reduced with the participation of the ionic component, remaining almost constant and close to the aggregation number of the pure ionic micelle. However, in the systems involving CTAB it is observed that the size of micelles initially increases and then decreases slightly for mixtures with a high content of the ionic component. The hydrophobic index pyrene 1:3 ratio was used to examine possible changes in the micellar micropolarity; however, no definitive conclusions could be derived from these experiments. In order to study the evolution of the local viscosity of the mixed micelles upon addition of the ionic surfactant, fluorescence polarization measurements were carried out with two different probes, fluorescein and coumarin 6. It was found that the participation of the ionic component in the mixed micelle induces the formation of less ordered structure than that of pure nonionic micelles. An attempt was made to correlate these effects with the interaction parameters obtained from the theoretical mixing model and, consequently, with the alkyl chain length of the ionic components.

Stability, Interaction, Size, and Microenvironmental Properties of Mixed Micelles of Decanoyl-N-methylglucamide and Sodium Dodecyl Sulfate

The mixed micellization between the nonionic surfactant decanoyl-N-methylglucamide (MEGA-10) and the common sodium dodecyl sulfate (SDS) in aqueous solutions of 0.1 M NaCl was investigated by the fluorescence probe method. The critical micelle concentrations were determined by the pyrene 1:3 ratio method. The experimental data are discussed in light of two mixing thermodynamic models within the framework of the pseudophase separation model, including the conventional regular solution theory and a recent treatment proposed by Maeda (J. Phys. Chem. B 2004, 108, 6043). This last approach provides a more appropriate description of the mixed system, particularly in two aspects: the nature of the interactions responsible for the stability of the mixed micelle and the behavior of the excess free energy per monomer of the system. By using the static quenching method, the mean micellar aggregation numbers of mixed micelles in the whole range of compositions were obtained. It was found that the micellar aggregation number initially increases with the content of the ionic component, then remains roughly constant, and, finally, decreases slightly for high content of this component. This behavior was analyzed taking into account the effects produced by the presence of the charged headgroups of sodium dodecyl sulfate, as this component increases its participation in the mixed micelle. The micropolarity of the mixed micelles was studied by the pyrene 1:3 ratio index. It was observed that the increasing participation of the ionic component induces the formation of micelles with a more dehydrated structure. Data of micellar microviscosity were obtained by using different methods, including fluorescence intensity measurements of Auramine O and steady-state fluorescence anisotropy of rhodamine B and diphenylbutadiene. The results obtained from these experiments are in good agreement and suggest the formation of mixed micelles with a less ordered structure as the content of SDS increases.

Influence of Tetraethoxylated Nonylphenol on the Properties of Dodecaethoxylated Nonylphenol Micelles in Aqueous Medium

Properties of the mixed micelles of tetraethoxylated nonylphenol and dodecaethoxylated nonylphenol (NP12) in water are studied by spectrophotometry, dynamic and static light scattering methods. Data on the composition, aggregation numbers (N), sizes (Rh), and hydration (nOE) of mixed and individual micelles of NP12 are obtained. Two NP12 concentration regions are disclosed where mixed micelles of various compositions but with the close values of N, Rh, and nOE are present. It is established that the sizes and aggregation numbers of mixed micelles are noticeably larger than those of individual micelles. Features of the mixing of two studied surfactants in a micellar state are analyzed in terms of the theory of phase separation.

Properties of Binary Mixed Micelles of α, ω-Ditetraethylene Glycol Dodecyl Ether and Bile Salts

Determination was made of surface tension, polarity of intramicelles, mean aggregation number, hydrodynamic radius and 1H-NMR of binary mixed micelles of bile salts, such as sodium glycochenodeoxycholate (NaGCDC) and sodium glycoursodeoxycholate (NaGUDC) and nonionic surfactants, such as α, ω-ditetraethylene glycol dodecyl ether (C122E4) and octaethylene glycol mono-n-decyl ether (C10E8) for the following four systems; (1) NaGCDC-C122E4 system, (2) NaGCDC-C10E8 system, (3) NaGUDC-C122E4 system and (4) NaGUDC-C10E8 system.Micellar composition for each system was noted to change from nonion-rich to bile salt-rich with mole fraction of a bile salt and the microenvironment of intramicelles for C10E8 systems became more hydrophobic compared to C122E4 systems. Mean aggregation number of mixed micelles for C10E8 systems abruptly decreased with increase in mole fraction of bile salts in the range of the low mole fraction, while for C122E4 systems, was essentially constant. From the results of 1H-NMR, NaGUDC molecular orientation in mixed micelles differed from that of a NaGCDC molecule. Schematic models of the mixed micelles were established based on the present results.

Behaviors of sodium glycochenodeoxycholate and sodium glycoursodeoxycholate in binary mixed micelles of bile salt and nonionic surfactant

The behavior of sodium glycochenodeoxycholate (NaGCDC) and sodium glycoursodeoxycholate (NaGUDC) in binary mixed micelles consisting of bile salt and octaoxyethylene glycol mono n-decyl ether (C 10E 8) has been studied on the basis of micellar compositions, polarities of the interior of intramicelles, mean aggregation numbers and 1H NMR measurements. Micellar compositions for both NaGCDCC 10E 8 and NaGUDCC 10E 8 systems showed a tendency to change from C 10E 8-rich micelles to bile-salt-rich micelles with an increase on the mole fraction of bile salts from the results of both theoretical calculations using the critical micelle concentration and the micellar polarity. The microenvironment of intramicelles for the NaGCDCC 10E 8 system was found to be more hydrophobic than that for the NaGUDCC 10E 8 system. Mean aggregation numbers of mixed micelles for both systems decreased abruptly with an increase in the mole fraction of bile salts in the range of low mole fraction, but those for NaGCDC were larger than those for NaGUDC. Furthermore, from the results of 1H NMR measurements, the motions of the methyl group protons in the 18 position of the molecular structure of NaGCDC were slightly restricted with an increase in the mole fraction of NaGCDC. In contrast, the methyl group protons in the 18 and 19 positions of the molecular structure of NaGUDC became freer with an increase in the mole fraction of NaGUDC.

Mixed micellar properties of octyl-β-d-glucoside and lithium perfluorooctane sulfonate

Abstract Mixed micellar properties of octyl-β- d -glucoside (AG8) and lithium perfluoroonate sulfonate in aqueous solution have been studied. The mixture CMC values are lower than data for ideal mixing, indicating that a favorable interaction in the mixed micelles arises, having the interaction parameter −1.85. The aggregation number of mixed micelles increases gradually until the mole fraction of AG8=0.8 and the increases sharply. A similar change is observed for the micellar radius. Thus, the micellar properties of mixed micelles are markedly affected by incorporation of the fluorocarbon surfactant.

Behaviors of Sodium Taurocholate and Sodium Taurodeoxycholate in Binary Mixed Micelles of Bile Salt and Nonionic Surfactant

Behavior of sodium taurocholate (NaTC) and sodium deoxycholate (NaTDC) in binary mixed micelles consisting of bile salt and octaethylene glycol mono-n-decyl ether (C10E8) has been studied on the basis of micellar compositions, polarities of interior of intramicelles, mean aggregation numbers, and 1H-NMR measurements, respectively. Micellar compositions for both the NaTC−C10E8 system and NaTDC−C10E8 system tended to change from C10E8-rich micelles to bile-salt-rich micelles with the mole fraction of bile salts from the results of both theoretical calculations using critical micellar concentration (cmc) and the micellar polarity, and also a microenvironment of intramicelles for the NaTDC−C10E8 system was more hydrophobic than that for the NaTC−C10E8 system. Mean aggregation numbers of mixed micelles for both systems abruptly decreased with the increase of mole fraction of bile salts in the range of the low mole fraction, but mean aggregation numbers for the NaTDC−C10E8 system were larger than those for NaTC−C10E8 system. Furthermore, from the results of 1H-NMR measurements, the methyl group protons at the 18, 19, and 21 positions in NaTC molecules were found to have a slight freedom with an increase of mole fraction of NaTC, but those of NaTDC were found to be restricted with an increase of mole fraction of NaTDC.

Micellar properties and solubilization of cholesterol in aqueous binary mixed solutions consisting of sodium cholate and non-ionic surfactant

The micellar properties and behavior of cholesterol solubilization in aqueous binary mixed solutions of sodium cholate (NaC) and octaoxyethylene glycol mono n-decyl ether (C 10E 8) were studied by examination of the composition of the mixed micelles, polarities of the micelle interior, mean aggregation number and saturated amounts of the solubilized cholesterol in the mixed solutions. The mole fraction of NaC in the mixed micelles near the CMC was found to be less than that in aqueous mixed solution. The hydrophobicity of the interior of the mixed micelles increased with the mole fraction of NaC in the mixed solution, and the mean aggregation number abruptly decreased in the range of the low mole fraction of NaC. The saturated amount of the solubilized cholesterol in the mixed solution depends on the mean aggregation number of mixed micelles. The cholesterol solubilization behavior, studied by thermodynamic analysis, was similar to the variation of the hydrophobicity of the mixed micelles.

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.

Study on the aggregation number of mixed micelles in aqueous binary mixtures of the bile salts and nonionic surfactant

The mixed micellar behavior of sodium cholate, NaC, and octa-oxyethylene glycol n-decyl ether, C 10E 8, has been studied from the viewpoints of the aggregation number and the polarity of the interior of the micelle. The polarity of the interior of the mixed micelle obtained from I 1 I 3 and the lifetime of pyrene fluorescence shows that the solubilization site of pyrene varies with the molar fraction. This fact is considered to be caused by the differences in the chemical structure and the hydrophobic nature between NaC and C 10E 8. Concentration dependencies are seen for the aggregation number and I 1 I 3 . These dependencies indicate that the size and composition in the mixed micelles vary with the total concentration of surfactants, and that the initial micelles formed near the CMC contain higher molar fractions of C 10E 8 than do analytical molar fractions. Furthermore, theoretical calculations using regular solution theory and excess thermodynamic quantities have been performed with the values of CMCs. The calculated values of the molar fraction in the micelle were lower than those of the analytical molar fraction; however, there was a large difference between the values of the two methods. The experimental results agreed best with ones obtained from the excess thermodynamic quantities.