Surfactants In Mixed Micelles Research Articles

A study of the interaction of dodecyl sulfobetaine with cationic and anionic surfactant in mixed micelles and monolayers at the air/water interface

The miscibility and interactions between components in mixed adsorbed films and micelles containing zwitterionic (dodecyl sulfobetaine—DSB) and cationic (dodecyltrimethylammonium bromide) or anionic (sodium dodecyl sulfonate) surfactant, respectively, have been investigated. The molecular interactions have been quantified by the values of the excess free energy of adsorption ( Δ G S , Exc ) and micelle formation ( Δ G M , Exc ). The obtained results indicate nonideal behavior of the investigated mixtures since the values of Δ G S , Exc and Δ G M , Exc are negative. Moreover, it has been found that DSB interact more strongly with anionic surfactant as compared to cationic surfactant owing to different structure of mixed monolayers and micelles.

A small-angle neutron scattering study of biologically relevant mixed surfactant micelles comprising 1,2-diheptanoyl-sn-phosphatidylcholine and sodium dodecyl sulfate or dodecyltrimethylammonium bromide.

Small-angle neutron scattering (SANS) has been employed to characterize mixed micelles comprising the surfactants 1,2-diheptanoyl--phosphatidylcholine (DHPC)/sodium dodecyl sulfate (SDS) and 1,2-diheptanoyl--phosphatidylcholine (DHPC)/dodecyltrimethylammonium bromide (DTAB) using the classical model of a micelle consisting of a hydrocarbon core surrounded by a polar shell. Various constraints are applied to the data fitting, specifically the volume of the hydrocarbon core using the aggregation number determined from time-resolved fluorescence quenching (TRFQ) and the degree of micelle hydration as determined from an electron paramagnetic resonance (EPR) experiment. The morphologies of the DHPC/SDS and DHPC/DTAB mixed micelles are largely invariant with composition-as might be expected given the similarity in the tail volumes of the respective surfactants, and the observed behaviour of the aggregation number-with a radius comparable to the fully extended length of a dodecyl chain, the longer of the two hydrophobic moieties. The shell thickness is also largely invariant with composition, indicating that the phosphatidylcholine headgroup lies flat at the interface. For both cases, the degree of counter-ion dissociation extracted from the fitting of the SANS data increases significantly on addition of DHPC, in a manner very similar to that observed for related binary surfactant mixtures, provided there is only a small change in micelle aggregation number (micelle curvature). The coincidence of the degrees of counter-ion dissociation for these quite different systems suggests a common underlying behaviour in which the nonionic species merely dilutes the surface charge associated with the ionic headgroups.

Novel fluorescent probe as aggregation predictor and micro-polarity reporter for micelles and mixed micelles

Aggregational behaviour of micelles sodium dodecyl sulphate (SDS and Triton X-100, TX-100 both in pure and mixed form) and micelle like aggregates such as polymer–surfactant system [polymer poly(vinyl pyrrolidone), PVP]–SDS have been studied by using fluorescence characteristics of a newly synthesized probe. The critical micelle concentration (CMC) values determined at various surfactant compositions are lower than the ideal values indicating a synergistic effect. The value of the interaction parameter for the surfactant mixture has been determined which agrees well with the value calculated according to molecular thermodynamic theory. The total aggregation number of surfactant in mixed micelle shows a drastic variation in the SDS mole fraction range 0 ≤ α 1 ≤ 0.3 and beyond the range it remains practically constant. Molar-based partition coefficients for the dye between the micellar and aqueous phase have been determined and a non-linear variation is obtained for the mixed micellar system. Variations of micro-polarity in the mixed micellar region have been investigated as a function of surfactant composition and results have been explained in terms of a suitable realistic model.

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 Micelles of Polyethylene Glycol (23) Lauryl Ether with Ionic Surfactants Studied by Proton 1D and 2D NMR

1H NMR chemical shift, spin–lattice relaxation time, spin–spin relaxation time, self-diffusion coefficient, and two-dimensional nuclear Overhauser enhancement (2D NOESY) measurements have been used to study the nonionic–ionic surfactant mixed micelles. Cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as the ionic surfactants and polyethylene glycol (23) lauryl ether (Brij-35) as the nonionic surfactant. The two systems are both with varying molar ratios of CTAB/Brij-35 (C/B) and SDS/Brij-35 (S/B) ranging from 0.5 to 2, respectively, at a constant concentration of 6 mM for Brij-35 in aqueous solutions. Results give information about the relative arrangement of the surfactant molecules in the mixed micelles. In the former system, the trimethyl groups attached to the polar heads of the CTAB molecules are located between the first oxy-ethylene groups next to the hydrophobic chains of Brij-35 molecules. These oxy-ethylene groups gradually move outward from the hydrophobic core of the mixed micelle with an increase in C/B in the mixed solution. In contrast to the case of the CTAB/Triton X-100 system, the long flexible hydrophilic poly oxy-ethylene chains, which are in the exterior part of the mixed micelles, remain coiled, but looser, surrounding the hydrophobic core. There is almost no variation in conformation of the hydrophilic chains of Brij-35 molecules in the mixed micelles of the SDS/Brij-35 system as the S/B increases. The hydrophobic chains of both CTAB and SDS are co-aggregated with Brij-35, respectively, in their mixed micellar cores.

Adsorption and Micelle Formation of Mixed Surfactant Systems in Water. I. A Combination of Top-heavy Type Anionic Surfactants.

The micellization and adsorbed film formation for an aqueous binary mixed system of anionic top-heavy type surfactants: sodium salt of α-sulfonatomyristic acid isopropyl ester (α-SMy·iPr) and sodium 1-oxo-1 [4-(tridecafluorohexyl) phenyl]-2-hexanesulfonate (FC6-HC4), were studied by means of surface tension measurement (drop volume method). The surface tension (γ) was precisely measured for the solutions of the respective single and eleven mixed systems at 30.00 ± 0.03°C in order to determine critical micellization concentrations (CMC) and surface excesses (Γ) as a function of net mole fraction of FC6-HC4 (XFC6-HC4). The effect of added NaCl on CMC was examined for each single system to determine the degree of counterion binding (βi) from the Corrin-Harkins plot. Using the data of CMC and βi, we estimated the micellar composition (YFC6-HC4), activity coecients (fi) of the two surfactants in mixed micelles, and the interaction parameter (ω0), the calculation of which was made on the basis of our own theoretical equations taking into account of mutual counterion effect in binary ionic surfactant mixtures. From the CMC-YFC6-HC4 curve, markedly positive and slightly negative deviations from ideal mixing micelle formation were found, i.e. the positive deviation at the range of 0 < XFC6-HC4 < ca. 0.3 and the slightly negative deviation at the range of ca. 0.3 < XFC6-HC4 < 1. On the other hand, the composition of adsorbed film (ZFC6-HC4) was also estimated as a function of XFC6-HC4 using the surface tension data from below CMCs. In addition, Γ was determined as functions of XFC6-HC4 and ZFC6-HC4 and the partial molecular area (PMA) was evaluated from the plot of mean molecular surface area (Am) vs. ZFC6-HC4. All the data obtained showed without exception that an addition of 10 to 20% α-SMy·iPr to FC6-HC4 results in a marked enhancement of surface activity and micelle formation ability, accompanying a favorable packing in two-dimensional or three dimensional structuring by the two top-heavy type surfactants, and that the two or three dimensional structures are thermodynamically more stable due to higher FC6-HC4 content.

Adsorptive partitioning of an organic compound onto polyelectrolyte-immobilized micelles on porous glass and sand.

Halting the spread of organic contaminants in subsurface aquifers is a critical environmental problem. We describe a novel "permeable reactive barrier" that results when organophile-solubilizing properties are conferred on siliceous materials by treating them with a cationic polymer and oppositely charged mixed surfactant micelles. Controlled pore glass, quartz sand, and sea sand were treated with poly(diallyldimethylammonium chloride) and with mixed micelles of Triton X-100 and sodium dodecyl sulfate, either sequentially or simultaneously, following different treatment procedures. A model organophilic compound, Orange OT, was adsorbed and retained under aqueous agitation on the siliceous treated surfaces but not on untreated surfaces or those treated with micelle only. The aspect of the treatment procedure producing the most significant effect on Orange OT solubilization was the ionic strength. The retention of Orange OT in a layer of polyelectrolyte-micelle-treated sand under flow, within a column of untreated sand, demonstrates the possibility of using similar processes as a permeable reactive barrier to trap organic pollutants.

New approach for the studies of physicochemical parameters of interaction of Triton X-100 with cationic surfactants

The interaction of cationic surfactants (alkyltrimethylammonium bromide) with Triton X-100 ( p-(1,1,3,3-tetramethylbutyl) poly (oxyethylene)) as nonionic surfactant has been investigated using potentiometeric and surface tension techniques. New methods have been used to evaluate the values of physicochemical parameters, concentration of free monomer of ionic and nonionic surfactants, degree of dissociation of ionic surfactant and the mole fraction of surfactants in mixed micelles. The comparison between these new techniques and previous methods indicates noticeable difference between the values of calculated synergetic parameters. The comparison between the values of cmc that have been measured by above two techniques, indicates a synergistic effect for C 18TAB (octadecyltrimethylammonium bromide) with Triton X-100 whereas a cosurfactant effect has been observed between C 12TAB (dodecyltrimethylammonium bromide), C 14TAB (tetradecyltrimethylammonium bromide), C 16TAB (hexadecyltrimethylammonium bromide), and Triton X-100.

Dodecyltrimethylammonium bromide-disodium dodecanephosphonate mixed micelles

The aqueous catanionic system dodecyltrimethylammonium bromide (DTAB)–disodiumdodecanephosphonate (DSDP) was studied by potentiometry, conductivity, surface tension, spectrometry and dye solubilization. No precipitation of neutral salts was found in the entire range of compositions studied. Up to four transitions were detected. The first transition, at about 0.001 mol dm−3, was probably related to a state change in the adsorption monolayer at the air/water interface. The second, at about 0.0065 mol dm−3, was probably related to the formation of ion pairs. The third transition was the critical micelle concentration which was analyzed with the pseudophase separation model and regular solution theory. The interaction between DTAB and DSDP molecules in micelles was weaker than in other cationic–anionic surfactant mixed micelles. Large, probably rodlike, micelles formed at the fourth transition at higher surfactant concentration. No vesicles or lamellar liquid crystals were detected. The adsorbed monolayer at the air/water interface was also studied by means of regular solution theory. It was much richer in DTAB than the micelles and the intermicellar solution. The interaction between DTAB and DSDP molecules at the air/water interface was very low. The results were explained on the basis of steric factors.

Interaction of Unimolecular Micelles of Hydrophobically-Modified Polyelectrolytes with Nonionic/Ionic Mixed Surfactant Micelles

Interactions of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate and N-dodecylmethacrylamide (DodMAm) with n-dodecyl hexaethylene glycol monoether (C12E6) with and without added n-hexadecyltrimethylammonium chloride (CTAC) in 0.2 M NaCl aqueous solutions were investigated by fluorescence and light-scattering techniques. The polymers with the DodMAm contents (fDod) ranging from 10 to 50 mol % were singly labeled with pyrene (1 mol %) or doubly labeled with pyrene (1 mol %) and naphthalene (4 mol %). These polymers form unimolecular micelles (unimer micelles) owing to intramolecular self-association of polymer-bound dodecyl groups, the compactness of the unimer micelle depending on fDod. The unimer micelles of the polymers with fDod ≥ 30 mol % have a particularly compact nanostructure where polymer chains are highly collapsed. In the presence of C12E6/CTAC mixed micelles, the polymer with fDod = 10 mol % abruptly undergoes bulk phase separation as the mole fraction of CTAC (Y) in the mixed micelle is increased to a certain critical level (Yp) (i.e., Yp ≈ 0.15). With an increase in fDod, the bulk phase separation becomes significantly less abrupt, accompanying a marked increase in Yp. For the polymers with fDod ≥ 40 mol %, no such bulk phase separation was observed in a region of 0 ≤ Y ≤ 0.6. Intrapolymer nonradiative energy transfer indicates that the unimer micelles of the polymers with fDod ≥ 30 mol % are unfolded by interactions with C12E6. The formation of soluble polymer−micelle complexes was manifested by an increase in the hydrodynamic radius (Rh) upon addition of C12E6 to polymer solutions. The Rh for the unimer micelle with fDod = 50 mol % increased from 8.2 to 15.8 nm by the addition of 5.0 mM of C12E6 at a polymer concentration of 1.5 g/L. The Rh at Y = 0 further increased to 21.5 nm as CTAC was added to Y = 0.07, indicating an interplay of hydrophobic and electrostatic interactions in the complexation between the unimer micelle and C12E6/CTAC mixed micelles.

Interfacial and Thermodynamic Properties of SDBS−C12E10 Mixed Micelles in Aqueous Media: Effect of Additives

The interfacial and thermodynamic properties of SDBS/C12E10 mixed system in aqueous solution in the presence of additives, i.e., poly(ethylene glycol) 400, sucrose, and urea have been investigated. The critical micelle concentrations (cmc) were determined by both surface tension and conductivity measurements. The maximum surface excess (Γmax) and minimum area per molecule (Amin) were determined from surface tension data. The thermodynamic parameters of micellization and adsorption were computed and discussed. The enthalpy−entropy compensation effect was observed in all the cosolvent systems. The partition coefficient of these hydrophilic additives between the micelle and the solvent was found to be zero. The transfer quantities, which are sensitive to the solvent structure, were also computed. The interaction parameters between the surfactant molecules both in the presence and absence of additives were evaluated by Rubingh's approach. Micellar aggregation number (Nagg) for the mixed system in the presence and absence of additives were determined by fluorescence measurements. 1H NMR was also used to study the behavior of surfactants in mixed micelles.

Mixtures of Nonionic and Ionic Surfactants: Determination of Mixed Micelle Composition Using Cross-Differentiation Relations

Cross-differentiation relations are used in thermodynamics to describe the behavior of cationic and nonionic surfactants in mixed micelles. This study uses dodecyltrimethylammonium bromide (DTABr) as cationic surfactant and dodecylpoly(oxyethylene glycol ether)23, or BRIJ 35, as nonionic surfactant. One of these cross-differentiation relations allows us to connect the nonionic surfactant activity with that of the cationic surfactant by following the variations of DTABr molality with BRIJ 35 molality, at constant DTABr chemical potential. This was possible with a reliable DTA+-selective electrode. We show that this approach gives access to the activity of nonionic species in solution and into the micelle from potentiometric measurements.

A new method for the determination of the dehydration coefficient of ethylene oxide groups of non-ionic surfactants in mixed micelles

A new method for determining the temperature dehydration coefficient of the ethylene oxide groups of non-ionic surfactant molecules in mixed micelles is proposed. The method is based on using experimental data on micellar structure, aggregation number, size and electrical charge, obtained from scattering experiments and the theory of mixed micelle formation. The range of the dehydration coefficient for ethylene oxide groups of Triton X-100 was determined to be 0.001–0.002 K −1.

THE EFFECT OF MIXED MICELLES OF SURFACTANTS ON THE ALKALINE HYDROLYSIS OF DIMETHYLFORMAMIDE

ABSTRACT The alkaline hydrolysis of dimethylformamide has been studied at 40°C In mixed micelles of surfactants (CTAB—Brij35, SD6 — Brij35, CTAB — BHMI, SDS —BHMI, Brtj35—BHMI) and functional molecule 1—benzyl—2—hydroxymethylimidazole (BHMI) solutions with analog thermogram method of thermokinetics. The kinetic parameters km In micellar pseudophase, rate constant ke in functional molecular solution, and the association constant of reactant with micelle Ki, with functional molecule K, have been calculated from kinetic equations of mixed micellar catalysis in the case of [S]>[M]. The results indicate that all the researched systems exhibit catalytic effect on the reaction. Polarity and local concentration effect were employed to explain these phenomena. A mechanism of catalysis of BHMI and mixed micelles of a surfactant and BHMI was proposed.

Kinetic treatment of the reaction of m-chloroperbenzoic acid and iodide in mixed anionic/non-ionic micelles

Catalysis and inhibition of the title reaction in mixed micelles of Brij-35 and SDS is described. The kinetics are treated using a combined multiple micellar pseudophase model and transition state pseudoequilibrium constant approach that was previously used for the catalysis and inhibition of the reaction of peracids and iodide in non-ionic and anionic micelles, respectively (D. M. Davies, N. D. Gillitt and P. M. Paradis, J. Chem. Soc., Perkin Trans. 2, 1996, 659). In the present mixed micellar system the following factors are taken into account: (i) the mole ratio of the surfactants in the mixed micelle, which is the relevant quantity for the micellar kinetics and is different from the stoichiometric mole ratio of the surfactants; (ii) non-ideal mixing of the surfactants, which also influences the composition of the mixed micelle; (iii) the ideal behaviour of the apparent molar volume of micellized surfactant in mixed micelles; and (iv) deviations from ideality of the partitioning of reactants and transition state between mixed micelles and the bulk aqueous phase. Logarithms of micellar association constants of the reactants and transition state in the two surfactants have been obtained, together with parameters closely related to the excess Gibbs function associated with the deviations from ideality described by (iv). The relationship between the parameters that describe non-ideal mixing of the surfactants in (ii) and the deviations from ideality in (iv) is discussed.

Surfactant—surfactant interactions in their binary mixtures in the mixed solvent 1,4-dioxane + H 2O

Surface tension and viscosity measurements have been carried out for two surfactant binary mixtures, namely, sodium dodecyl sulphate (SDS) + Triton X-100 and dodecyltrimethylammonium bromide (DTAB) + Triton X-100, each in 1,4-dioxane + H 2O at 303.15 and 313.15 K. From the mixed critical micelle concentration (values obtained from surface tension data), the interaction parameter β has been calculated using the regular solution treatment of Rubingh for mixed surfactant micelles; β values have been rationalized in terms of the intermolecular interactions between unlike surfactant molecules in the mixed solvent. The magnitude of surfactant—surfactant interactions within the mixed micelles in 1,4-dioxane + water is lower than that in pure water. Further, interaction between anionic—non-ionic surfactants was found to be stronger than in cationic—non-ionic surfactant.

Counterion effect on the immiscibility of fluorocarbon and hydrocarbon surfactants in mixed micelles

Counterion effect on the immiscibility of fluorocarbon and hydrocarbon surfactants in mixed micelles

Interactions between betaine-type zwitterionic and anionic surfactants in mixed micelles

The interaction between zwitterionic and anionic mixed surfactants has been investigated by means of surface tension, static and dynamic light-scattering, {sup 1}H NMR spectroscopy, rheological measurement, and probing methods. These systems are N-alkyl-N,N-dimethylbetaine (C{sub 12},DNB; C{sub 14}, TNB) and sodium dodecyl sulfate (SDS) in the presence of 0.01 mol dm{sup {minus}3} NaCl. These systems show a composition dependency in micellar properties. When the molar fraction of DNB and TNB is about 0.6, the cmc values of these systems exhibit minima, whereas the solubilized amount of water-insoluble dye, viscosity, and NMR line widths show maxima. Furthermore, the size of a micelle is found to increase at the same fraction. The viscosity displays a Newtonian flow at all compositions for the DNB-SDS system, while a strong shear dependence is observed at a certain composition for the TNB-SDS system where a sphere-rod transition would occur in micellar shape due to the formation of intramolecular complexes by the electrostatic interaction of oppositely charged head groups between TNB and SDS.

The efficiency of solubilization in mixed micelles of nonionic and anionic surfactants

The dependency of water-isoluble and slightly soluble dyes on the composition of nonionic hydrocarbon-anionic hydrocarbon and of nonionic hydrocarbon-amionic fluorocarbon surfactants in micelles has been studied through the solubilization characteristics of these dyes. Yellow OB as a water-insoluble dye and azobenzene as a slightly water-soluble dye were used. According to the regular solution theory, the composition of surfactants in mixed micelles and their concentrations were calculated from the critical micelle concentration of the mixed surfactant systems. The ideal solubilized amounts for mixed micelles were also calculated from solubilizing power, and compositions of mixed micelles with different concentrations. From the comparisons of ideal and observed solubilized amounts, the following results were obtained. (1) The efficiency of solubilization decreased when two surfactants were mixed. The extent of the efficiency depends on the kinds of mixed surfactant systems and dyes, and the efficiency of solubilization has a minimum at 0.2–0.4 molar fraction of nonionic surfactant in the mixed micelles. (2) The efficiency of solubilization decreased with an increase in the difference of the solubilizing power between two surfactants in the mixed systems.

The Application of Mixed Surfactant Micelles in Wool Textile Finishing

Anti‐shrinkage procedures based on the deposition of Hercosett on untreated wool fibres combined with either the use of an amphoteric surfactant or mixed micelles of amphoteric/anionic surfactants are described. Specific molar ratios of the surfactants were found to promote good stability of the bath, giving area felting shrinkage values of the treated fabrics less than 10%.