Mass,size and shape of micelles formed in aqueous solutions of ethoxylated nonyl-phenols

The study was extended to analysis of mass, size and conformation of micelles formed in aqueous solutions of ethoxylated nonyl phenols. The results obtained by ultracentrifugal technique between 293 and 323 K have proved that the slightly ethoxylated nonyl phenols form micelles with high molecular mass and larger size at constant temperature, while the increasing length of the ethylene oxide chain favours formation of micelles of smaller molecular mass and size. The transformation of conformation from oblate to spherical shapes ensues with increasing temperature at constant ethoxy number or with ethoxylation at constant temperature. The second virial coefficient decreases with increasing temperature and decreasing ethoxy number. In accordance with the earlier conclucions, the change of the second virial coefficient relates to enhanced variation of monomer solubility, stabilization of micelle structure and increased deviation from ideal behaviour of a given micellar system.Symbols a major axis of micelle, Å - a _m attractivity factor, cm³ erg molecule² - b minor axis of micelle, Å - c concentration, g dm^–3 - c _b equilibrium concentration at the bottom of the cell, g dm^–3 - c _m equilibrium concentration at the meniscus of the cell, g dm^–3 - c _o initial concentration in the cell, g dm^–3 - c _M critical micellization concentration, mol dm^–3 - e eccentricity - f _IS Isihara-constant - f/f _o frictional ratio of micelle - amount of water in micelle per ethoxy group, mol H₂O/mol EO - n aggregation number, monomer micelle^–1 - n _EO number of ethoxy groups - r distance of Schlieren peak from the axis, cm - r _b distance of cell bottom from the axis, cm - r _m distance of cell meniscus from the axis, cm - R _h equivalent hydrodynamic radius of micelle, Å - s _t sedimentation coefficient, s - reduced sedimentation coefficient, s - reduced limiting sedimentation coefficient, s - ¯v _t volume of micelle, cm³ micelle^–1 - partial specific volume of solute, cm³g^–1 - partial specific volume of solute reduced to 293 K, cm³ g^–1 - B _a, B_e constants, cm³ mol g^–2 - B ₂ second virial coefficient, cm³ mol g^–2 - M _m ^a mass average apparent molecular mass of micelle, g mol^–1 - M _m mass average molecular mass of micelle corrected withB ₂, g mol^–1 - M _m ^cM mass average molecular mass of micelle belonging toc _M, g mol^–1 - M ¹ mass average molecular mass of monomer, gmol^–1 - N _A the Avogadro's number, molecule mol^–1 - R universal gas constant, erg mol^–1 K^–1 - T temperature, K - _t ^o dynamic viscosity of solvent atT temperature, g cm^–1 s^–1 - dynamic viscosity of solvent at 293 K, g cm^–1 s^–1 - _t density of solution atT temperature, g cm^–3 - _t ^o density of solvent atT temperature, g cm^–3 - density of solvent at 293 K, g cm^–3 - angular velocity, rad s^–1 - time, s     

Solubilization of oleyl alcohol by pure and mixtures of surfactants

The solubilization behavior of oleyl alcohol by pure and mixtures of surfactants systems have been studied in terms of the maximum additive concentration (MAC), the solubilizing power, and the particle sizes of micelles with or without oleyl alcohol. The surfactants used are amphoteric (N,N-dimethyl-N-lauroyl lysine, DMLL; N,N,N-trimethyl-N-lauroyl lysine, TMLL; N,N-dimethyl-N-(carboxymethyl)-lauryl ammonium, DMCL), anionic (sodium dodecyl sulfate, SDS) and nonionic (alkyl polyoxyethylene ethers).The maximum additive concentration of oleyl alcohol by pure surfactants is larger by nonionic surfactants than by others.For a nonionic surfactant system mixed with DMLL, the mixing effect of surfactant on the increase in the MAC is not recognized. While, for DMLL mixed with SDS, the MAC becomes larger than that by pure surfactants. This may be attributed to the fact that the large micellar size will result in increasing the maximum additive concentration.     

Micelle aggregation numbers from colligative properties

An equilibrium model has been developed to derive micelle aggregation numbers n from colligative properties of surfactant solutions, with special regard to freezing point depression. The introduction of a mass action approach in the solute activity equation allows to get aggregation numbers close to those obtained from light scattering. The model can be applied with small formal changes to ionic and nonionic surfactants.     

Steric repulsion of polyoxyethylene groups for emulsion stability

Rapid coalescence was studied on liquid paraffin emulsion stabilized with a series of poly(oxyethylene) dodecyl ethers [C₁₂H₂₅ (EO),n=1, 2, 3, 4, 5, 6, 7, 8] and of poly(oxyethylene) nonylphenyl ethers [C₉H₁₉(EO) _n ,n=2, 4, 5, 6, 12]. The turbidity of emulsion was measured as a function of the solution pHs at constant ionic strength of 0.1 mol dm^–3.As a result, it was found that the emulsions (which were formed with C₁₂H₂₅(EO) _n surfactants having less than four oxyethylene groups, or with C₉H₁₉ (EO) _n surfactants having less than six oxyethylene groups) brought about rapid coalescence in the bulk pH between 2.03.5, which corresponded to the zero point of charges for the emulsions of the present systems. According to the Tadros treatment for emulsion flocculation, the total flocculation potennual was estimated as a function of the distance relative to the number of oxyethelene groups in the surfactants. The critical coalescence energy was obtained as –343 ×10^–19 J for the C₁₂H₂₅(EO) _n surfactants and –2.14×10^–19) J for the C₉H₁₉ (EO) _n surfactants. Furthermore, the formation of a hole for coalescence was estimated under the simple assumption that the coalescence was caused only by the energy dissipation.     

Investigations of a series of nonionic surfactants of sugar-lipid hybrids by light scattering and electron microscopy

Sugar-lipid hybrids of the type C_nC_m were prepared by coupling an alkane chain (C_n) with a maltooligosaccharide (G_m) over an amide linkage. Coupling was performed with maltobionolactone (G₂) and n-alkylamine chains C_n withn=8,10,12,14,16, i.e. variation of the hydrophobic part of the molecule, and with hexadecylamine (C₁₆) and different maltooligosaccharides (G_m, m=2,3,4,6). The solution properties of the various products were studied by means of static and dynamic light scattering (LS) and by electron-microscopy (EM).The results may be summarized as follows: If the alkane chain is shorter thann=14, small spherical micelles with a radius of about 3 nm are observed. In time these micelles aggregate further to form increasingly larger spherical clusters which eventually precipitate. Long rod-like micelles form whenn 14. Contour length and chain stiffness were determined by applying theories of semiflexible chains. A qualitative confirmation of the light scattering results, i.e., micelle size and shape, was obtained from electron microscopy.     

Binding of calcium ions to micelles — a metallochromic indicator study

The complex formation of Ca⁺⁺ with murexide was investigated spectrophotometrically. In the presence of surfactants, such measurements can be used to determine the extent of binding of Ca⁺⁺ to the micelles. Experiments with secondary alkane sulphonate showed that there is competition between Na⁺ and Ca⁺⁺ for the micelles. Below the critical micelle concentration, no binding was observed.Dedicated to Prof. Dr. Wolfgang Hilger on the occasion of his 60th birthday.     

Small angle neutron scattering studies on micellar systems part 1. Ammonium octanoate,ammonium decanoate and ammonium perfluoroocatanoate

Small angle neutron scattering has been used to examine the size and shape of micelles of ammonium octanoate, ammonium decanoate and ammonium perfluoro-octanoate. Ammonium octanoate was found to form micelles with a micellar weight of 1640 and ammonium decanoate with a micellar weight of 12,576; both materials appeared to form spherical micelles. Ammonium perfluoro-octanoate formed micelles with a micellar weight of 17,610. Evidence from the scattering experiments suggested that the micelles were cylindrical and a model for the micelle is proposed.     

Estimation of the critical micelle concentrations and the aggregation numbers of sodium alkyl sulfates by capillary-type isotachophoresis

The analytical procedure for the separation and quantification of bulk and micellar phases for sodium alkyl sulfates has been investigated by a capillary-type isotachophoresis using a potential gradient detector. Monomer solutions were distinguished from micellar solutions at pH 5.5–6.0; hydrochloric acid — L-Histidine mixture was used as the leading electrolyte and 2-(N-Morpholino) ethanesulfonic acid as the terminating electrolyte.The potential unit value (PU value) due to the monomer solutions was larger than that due to the micellar solutions. The zone length due to monomer solutions increased with increasing concentration of surfactant until a given concentration (CMC); beyond this point the values became constant. On the other hand, the zone length due to micellar solutions increased from this point. We report an applicability of capillary-type isotachophoresis to determination of the CMC's and aggregation number for various sodium alkyl sulfates.     

On the observation of micellar structures by dielectric spectroscopy

Many cationic surfactants form, in the presence of certain organic acids, large supramolecular micellar structures in water. The dielectric response of one such system (cetyl trimethyl ammonium bromide-salicylic acid, CTMAS) has been studied as a function of frequency, concentration and temperature. The results are compared with dynamic mechanical data on the same system, which has been published in the literature.The dielectric response shows that the micelles form a rigid, open network structure, which does not impede ionic transport in the bulk liquid. However, the response also shows the presence of a frequency dispersive barrier capacitance. From the variation of the properties of this capacitance with CTMAS concentration and applied voltage over a range of frequencies, it is deduced that the barrier originates in an ordered micelle structure at each electrode.     

Hemimicelle shape and size

Based on the assumption of spherical hemimicelle with a hydrophobic core of diameter of maximum hydrocarbon chain length of surfactant, the aggregation numbers of hemimicelles have been calculated for several values ofn, the carbon atoms of surfactant alkyl chain. The results are in reasonable good agreement with the hemimicelle aggregation number from experimental data for several corresponding systems. The other possibilities of the hemimicelle shape which allow to incorporate a larger number of hydrocarbon chains in a hemimicelle have also been discussed.On leave from Department of Chemistry, Peking University, Beijing, China     

The salt-induced sphere-rod transition of micelles of dodecylpyridinium iodide in aqueous NaI solutions

Static light scattering has been measured on aqueous NaI solutions of dodecylpyridinium iodide (DPI) over NaI concentrations from 0 to 0.05 M. Reduced intensity of scattered light increases with increasing DPI concentration above the critical micelle concentration. The Debye plot is generally a curve with an initially positive slope and with a weakly convex, upward curvature, when the NaI concentration ranges from 0 to 0.005 M. The molecular weight of the spherical micelle of DPI is 28400 in water, and it increases slightly with increasing NaI concentration. The initial slope decreases with increasing NaI concentration and changes from positive to negative across 0.007 M NaI, which is the threshold for the sphere-rod transition and where the micelle has a molecular weight of 34400. At NaI concentrations from 0.01 to 0.05 M, the Debye plot is a curve with an initially negative slope and with a convex, downward curvature. The magnitudes of slope and curvature are larger, and the rodlike micelles of DPI have larger molecular weight and stronger mutual interaction, as the NaI concentration increases. The linear double logarithmic relationship between molecular weight and ionic strength holds for spherical and rodlike micelles, respectively.     

Stability of spherical and rod-like micelles of ionic surfactants,in relation to their counterion binding and modes of hydration

Aqueous salt solutions of ionic surfactants in both spherical and rod-like micelles have been treated on the basis of a statistical thermodynamic theory, and the double logarithmic relationship between micelle molecular weight and ionic strength is derived for each micelle. Counterion binding on both micelles are assumed to occur specifically, and their degrees of dissociation are related to the slopes of the linear double logarithmic relations. It is found from the relationship observed for typical surfactants that the effective charge of spherical micelles is 29±4. The degree of dissociation of rod-like micelles of these surfactants is primarily determined by the counterion species, yielding values 0.8 for Na⁺, 0.4–0.6 for Cl^– and 0.2–0.3 for Br^–. Hydrophilic hydration of both micelles can be evaluated from the intercepts of the linear relations. Hydrophilic hydration acts repulsively in spherical micelles, while it is attractive or much less repulsive in rod-like micelles.     

Miscibility of dodecyltrimethylammonium bromide and dodecyltrimethylammonium chloride in surface-adsorbed film and micelle

Surface tension of aqueous solutions of mixtures of dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) has been measured and analyzed by using thermodynamic relations. The adsorbed film has been found to contain more DTAB molecules than the solution. The shape formed by the curves of the total molality at constant surface tension against the solution and surface compositions indicates the ideal mixing of the DTAB and DTAC molecules in the adsorbed film. Micellar composition has been estimated at the critical micelle concentration (CMC). The micelles have been found to be richer in DTAB than the solution, but poorer in DTAB than the adsorbed film at the CMC. The DTAB and DTAC molecules have been shown to mix ideally in the micelles. From the comparison with the results on the system of decylammonium bromide and decylammonium chloride, it has been concluded that, on the mixing of surfactants differing only in counter ions, the adsorbed film is influenced more significantly by the ionic head group of the surfactant than the micelle.     

Small angle X-ray scattering study of an extremely elongated micelle system of CTAB-p-toluidine solution

Whenp-toluidine is added to an aqueous solution of CTAB, a remarkable increase of viscosity is accompanied by a spectacular elasticity. We detected the existence of extremely elongated rod-like micelles in electron micrographs. SAXS measurements indicate a closely packed array of cylindrical rod-like micelles, brought about when solutions flow through a thin capillary. A scattering maximum ofd=160 Å almost corresponds to the distance between the nearest neighbours of the cylindrical rod-like micelles. This value agrees with the diameter measured on electron micrographs. The second broad peak (d=75 Å) is assigned to a subsidiary maximum of the shape function of the cylinder with infinite length.     

On the shape of giant micelles in aqueous solutions of cetyltrimetylammoniumbromide (CTAB)

Low-temperature electron microscopy was used to image fracture faces of shock-frozen aqueous solutions containing the very large micelles of CTAB existing in the presence of N-methyl-N,N-diphenylamine (MDPA) and 9-anthracene carboxylic acid (9-AC) as solubilizates. When MDPA is present, large globular micelles are formed which have total aggregation numbers of the order of 10⁵ and are seen to be clusters of smaller disc-like structures containing some thousand CTAB-units. Thread-like features are visualized in solutions containing 9-AC which is known to induce the formation of micellar rods.     

Micelle structure in isotropic aqueous colloids of a poly(oxyethylene) amphiphile C12E8

Micelle structure in aqueous colloids in the isotropic liquid phase (L₁) of a nonionic amphipile (n-dodecyl octa(oxyethylene glycol) monoether (C₁₂E₈) has been investigated as a function of concentration and temperature using light scattering (LS), viscometry, NMR, and small-angle X-ray scattering (SAXS).The spherical micelles, having a radius of 28–31 Å, remain in a wide concentration range from very dilute to ca. 42 wt %. The micelle size increases sligthly with increasing temperature in the range of 25–60 °C. In the concentrated colloids, the spherical micelles are likely to be arranged in a certain ordered structure. Even at such a high concentration as 30 wt %, the isotropic colloid shows Newtonian flow. This suggests that interaction between micelles in the ordered structure is very weak and the structure is very fragile. Moreover, coexistence of the isotropic phase and the ordered structure in L₁ phase is discussed.     

The effect of carrier solution on the particle size distribution of inorganic colloids measured by steric field-flow fractionation

The number average and the weight average particle diameters for suspended inorganic colloids found by the new technique of steric field-flow fractionation may be successfully used provided that the most suitable carrier solution is selected, in order to minimize the coagulation and adhesion phenomena.In the present work polydisperse, irregular colloidal particles of FePO₄·2H₂O (strengite) were studied. The average particle diameters were found to vary with the electrolyte concentration in the suspending medium. A strong variation of the number and weight average particle diameters was also observed with the quantity of the surfactant added to aquatic medium in order to increase colloidal stability. The influence of the electrokinetic charge of the FePO₄·2H₂O particles in relation to the surface charge of the material of the column employed, on the particle size measured was investigated. The proper carrier solution for minimizing coagulation and adhesion phenomena in the FePO₄·2H₂O colloidal particles was found to contain either 1.5% (v/v) detergent FL-70 and 0.1 MKNO₃ or 0.5% (v/v) detergent FL-70 and 0.033 MNa₂SO₄.     

Narrow size distribution polystyrene latexes prepared in the presence of amphoteric sulfobetaine surfactants

Polystyrene latexes with a narrow size distribution (Dw/Dn < 1.05) were prepared with a large range of particle sizes (from 40 to 800 nm) in the presence of various amphoteric sulfobetaine surfactants. The influence of the nature of the surfactant and of the ionic strength, the pH and solid content were studied. The results are discussed and compared with those obtained using sodium dodecyl sulfate or in the absence of surfactants.     

Properties of aqueous solution of sodium glycocholate and a nonionic surfactant,and their mixtures

The micellar properties of aqueous binary mixed solutions of sodium glycocholate, NaGC, and octa-oxyethylene glycol mono-n-decyl ether, C₁₀E₈, have been studied on the basis of surface tensions, the mean aggregation number and the polarity of the interior of the micelles. The mean aggregation number, measured by steady state quenching method, decreased with the increase of the mole fraction of NaGC in the mixed system. The polarity of the interior, estimated by the ratio of first and third vibronic peak in a monomeric pyrene fluorescence emission spectrum, suggested that the hydrophobicity of intramicelles increased with the increase of the mole fraction of NaGC in the mixed system. These are considered to be caused by the differences in the chemical structure and the hydrophobic nature between NaGC and C₁₀E₈. The mean aggregation number and the polarity of the interior for each micelle near the CMC in lower total concentration of surfactants showed the tendency approaching those of pure micelle of the nonionic surfactant. This suggests that the ratio of NaGC in the initial micelles in the range of lower total concentration near the CMC is lower than that of the corresponding prepared mole fraction in the mixed system. This lower value was confirmed also from theoretical calculation of the ratio of NaGC at the CMC in the mixed micelle by regular solution treatment of Rubingh in the solution.     

Evaluation of solute distribution coefficients in solubilized systems

A theoretical treatment is proposed for the determination of the distribution characteristics of a solubilizate between micellar and aqueous phases from the variation of the critical micelle concentration (CMC) with the molar ratio of components in the system. The theory has been tested by determining the distribution coefficient and free energy of solubilization of n-butanol in the n-butanol/sodium dodecyl sulphate/water system from CMC values determined by conductimetric techniques.