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An interrelationship between heat of micelle formation and critical micelle concentration

1975; Elsevier BV; Volume: 50; Issue: 2 Linguagem: Inglês

10.1016/0021-9797(75)90228-3

1095-7103

Yoshikiyo Moroi, Nagamune Nishikido, Hiromoto Uehara, Ryôhei Matuura,

Thermodynamic properties of mixtures

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.