In this research, the micellar behavior of a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB) and an nonionic surfactant, polysorbate 20 (Polyoxyethylene (20) sorbitan monolaurate) in different alcohol solutions media was investigated over the temperature range 293.15–313.15 K. The interaction between two surfactants in binary systems can be determined by calculating the values of their β parameters. The critical micelle concentrations (CMC) of the micelles were determined from the surface tension, the conductivity at different temperatures. The CMC behavior of CTAB and polysorbate 20 was analyzed in terms of the effect of temperature and the increase in the alcohol carbon chain. Changes in the critical micelle concentration of mixed surfactant systems of different alcohol solutions were measured. The CMC decreased sharply as the hydrocarbon chain length of the alcohols becomes larger. This shows that the more hydrophobic alcohols are, the more marked a decrease in CMC is observed.

A proposed method of determining the composition of mixed micelles in equilibrium with monomer of known composition is described. The systems were sodium dodecyl sulfate-polyoxyethylene 23 lauryl ether (Brij 35) in water and in 0.1 M sodium chloride solution at 25°C. This technique applies the Gibbs-Duhem equation to the mixed micelle, which is treated as a pseudophase. This proposed methodology, which needs only critical micelle concentration data as a function of monomer composition, is applied to an anionic/nonionic surfactant pair. The calculated monomer-micelle equilibrium is found to be very similar to the much-used regular solution for nonideal systems.Paper no. S1066 in JSD 3, 77-80 (January 2000).KEY WORDS: Anionic/nonionic surfactant, critical micelle concentration, interaction parameter, mixed micelle, regular solution theory, surface tension.Micelles composed of mixtures of surfactants with different structures (mixed micelles) are of great theoretical and industrial interest (1-4). There is increasing interest in understanding the structure and properties of mixed micelles, while the surfactants used in practical applications are rarely pure. Different techniques have been used to collect structural information on mixed micelle formation, and to obtain their critical micelle concentration (CMC) (5-8). CMC have been determined as a function of surface tension, density, conductivity, and pH for pure surfactant and mixed surfactants (9-11).Micelles formed from a solution of mixed surfactants generally have a different surfactant composition than a monomer (12). In modeling the equilibrium between monomer and these mixed micelles, the micelle is often considered as a pseudophase (a thermodynamic phase in equilibrium with the monomer).Micelles composed of mixtures of surfactants of similar structure are nearly ideal; i.e., ideal solution theory describes the thermodynamics of mixing in the micelle when it is considered as a pseudophase (13,14). However, mixed micelles containing ionic and nonionic or anionic and cationic surfactants show negative deviations from ideality (15,16). On the other hand, mixed micelles composed of mixtures of fluorocarbon and hydrocarbon surfactants exhibit positive deviations from ideality (17). There has been a great deal of recent effort to model and understand these mixed surfactants. Rubingh (15) successfully explained this nonideal behavior by using the phase separation model of micellization and regular solution approximation. An equation was derived that describes the interaction between the two surfactants. Rosen and Shinoda (13) also derived equations for synergism in surface-tension reduction efficiency, mixed micelle formation, and surface tension reduction effectiveness in aqueous solution of mixed surfactants based on nonideal solution theory.A new method for calculating the composition of mixed micelles in equilibrium with monomer of known composition has been proposed by Nguyen et al. (12). This method applies the Gibbs-Duhem equation to the mixed micelle, which...

Mixed surfactant solutions consisting of cationic/ nonionic surfactants were prepared in different compositions of the components in aqueous solution in order to determine the surface properties. The critical micelle concentration (CMC) of aqueous solutions of the individual surfactants cetyl trimethyl ammonium bromide (CTAB) and polysorbate nonionics, and their mixtures are determined at different proportions. The results show that there is synergistic behavior in mixtures at higher mole fraction of nonionic surfactant. The effect of the alkyl chain on the CMC is also determined.

The behavior of mixed cationic/anionic and cationic/nonionic surfactants solutions have been studied by viscosimetry. The systems studied were sodium dodecyl sulfate (SDS)/cetyltrimethylammonium bromide (CTAB) and CTAB/Brij (polyoxyethylene lauryl ether, n = 10 and 23) in aqueous and sodium chloride solutions. The relative viscosity of single nonionic surfactant solutions is larger than that of SDS or CTAB solutions. It increases with the number of ethylene oxide groups. In the mixed systems, viscosity deviates from ideal behavior. The deviation results from electrostatic interactions. The surfactant mixture composition affects the self-assembled microstructure and rheology. A new mixed system that forms clear micellar solution above CMC was detected. In CTAB/Brij systems, the experimental data also deviate from ideal behavior due to mixed micelle formation and electroviscous effect. This effect is less pronounced than that of SDS/CTAB system and could be suppressed by adding an electrolyte (NaCl). ş 1 The text was submitted by the authors in English.

The micellar properties of the cationic Gemini surfactant ethanediyl-1,2-bis(dimethyldodecyl ammonium bromide), C12H25 · (CH3)2N+–(CH2)2–N+(CH3)2C12H25 · 2Br− (12-2-12), with short chain alcohols have been studied by conductivity and surface tension measurements within the temperature range 293.15 K–313.15 K and alcohol percentage. The critical micelle concentration (CMC) of 12-2-12 solution, degree of ionization (α) and standard Gibbs free energy of micellization (ΔG°m), standard enthalpy of micellization (ΔH°m) were calculated from conductivity and surface tension data. The experimental data show that the CMC values of cationic Gemini surfactants increased with addition of methanol, ethanol and n-propanol. The thermodynamic parameters (ΔG°m), (ΔH°m) and (ΔS°m) of micellization of 12-2-12 in alcohol were also calculated from the temperature dependence of the CMC values. CMC, (α), (ΔH°m) and (ΔS°m) increased linearly with increasing temperature. In the mixture of dimeric cationic surfactant (12-2-12) and alcohol solutions, the CMC values showed a slight increase with increasing alcohol concentration. CMC, maximum surface excess concentration at the solution/air interface, Γmax, minimum area per surfactant molecule, Amin, and the surface pressure at CMC, ¶CMC, values calculated from the surface tension measurements and thermodynamic parameters have been evaluated at same temperatures.

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