Nagamune Nishikido

An interrelationship between heat of micelle formation and critical micelle concentration

A discussion whether or not the contribution of water must be introduced into a thermodynamic equation of micellization was made on the basis of a phase separation model. As a result, an enthalpy change on micelle formation at very low CMC can be fairly approximated by the conventional expression, ΔHm = − nRT2(∂ ln CMC/∂T)p. The contributions of hydrophilic and hydrophobic groups to the enthalpy change were investigated for the case of four kinds of sodium alkyl sulfates with different chain lengths from C8 to C14 over the temperature range from 10 to 55°C. It was found that the hydrophilic part has a major contribution at lower temperatures but at higher temperatures it gives a minor contribution, and that the hydrophilic part of ΔHm is always positive having a minimum around 40°C, while the hydrophobic part is always negative and decreases monotonically with temperature. Furthermore, the water around the hydrophilic head group was found to have a great effect on the CMC; when a parameter due to the water is selected properly, the degree of dissociation of micelle and other electrochemical properties at the micellar surface can be calculated to be the reasonable values.

Mixed micelles of polyoxyethylene-type nonionic and anionic surfactants in aqueous solutions

Abstract Critical micelle concentrations (CMC) and the solubilization toward dyestuff yellow OB in aqueous solutions of mixed polyoxyethylene-type nonionic and anionic surfactants at 30°C were measured. As for the CMC, the stabilization of the mixed micelles relating to polyoxyethylene chains was suggested by application of the pseudo-phase-separation model. Concerning solubilization, the same measurements were also performed for various other surfactant mixed systems, and we defined the solubilizing power of the mixed surfactant solution and the ratio of this quantity to that in the additivity law. Solubilization in the system of mixed polyoxyethylene-type nonionic and anionic surfactants showed a specific behavior as compared with the other systems. From the CMC and solubilization studies, we proposed the model concerning the mixed micelles of polyoxyethylene-type nonionic and anionic surfactants. In the model, polyoxyethylene chains in the mixed micelle have an attracting interaction with anionic head groups, and the interaction is enhanced by the formation of a hydrocarbon core. This status is different from that in free polyethylene glycol and surfactant systems.

The critical micelle concentration of multicomponent mixtures of metal alkyl sulfates in aqueous solutions. II

Abstract The critical micelle concentration (CMC) was determined in aqueous solution at 47°C for two-component mixtures and multicomponent mixtures, i.e., sodium dodecyl sulfate-sodium tetradecyl sulfate, copper dodecyl sulfate-copper tetradecyl sulfate, sodium tetradecyl sulfate-copper dodecyl sulfate, sodium dodecyl sulfate-potassium dodecyl sulfate-sodium tetradecyl sulfate, potassium dodecyl sulfate-sodium tetradecyl sulfate-copper dodecyl sulfate, and sodium dodecyl sulfate-potassium dodecyl sulfate-sodium tetradecyl sulfatecopper dodecyl sulfate systems. The observed CMC of the sodium tetradecyl sulfate-copper dodecyl sulfate mixture showed a minimum near 0.25 in mole fraction unit of copper dodecyl sulfate. The CMC of other two-component mixtures did monotonously decrease with an increase in the amount of the component with lower CMC value. The variation of CMC with the composition could be explained by an equation in which a charge density of the micellar surface and an effective coefficient of an electrostatic contribution to micellization were modified. Agreement was obtained between experimental and theoretical values for all systems.

The critical micelle concentration of ionic-nonionic detergent mixtures in aqueous solutions. III

Abstract Critical micelle concentrations (CMC) have been theoretically calculated for mixed micelles between ionic and nonionic detergents, i.e., sodium dodecyl sulfate-octaoxyethylene dodecyl ether, sodium dodecyl sulfate-tetraoxyethylene octyl ether, sodium dodecyl sulfate-dodecaoxyethylene octyl ether, sodium pentadecyl sulfate-hexaoxyethylene decyl ether, and sodium dodecyl sulfate-hexaoxyethylene octyl ether systems in aqueous solution and sodium dodecyl sulfate-octaoxyethylene dodecyl ether, sodium decyl sulfate-dodecaoxyethylene octyl ether, and sodium dodecyl sulfate-sodium decyl sulfate systems in electrolyte solution. The CMC of all of the above mixtures showed the vat form with variation of the composition, except the first and the last, which gave a monotonously decreasing CMC with an increase of the amount of the component with lower CMC value. The CMC from the theoretical calculation was in fair agreement with the experimental results. The variation of CMC with composition could be explained by the assumption that the state of the mixed micelle is a linear combination of the state of pure ionic detergent and that of one ionic detergent molecule surrounded by infinite number of nonionic detergent molecules. All CMC values were obtained from the table and figures of the paper by Lange (4).