Conductance stopped-flow study on the micellar equilibria of ionic surfactants

Abstract

Rapid ionic equilibria of solutions of cationic and anionic surfactants were studied by the concentration-jump method with the use of the conductance stopped-flow technique. The slow relaxation times ( ⊺ 2 ) assigned to the micellization-dissolution process were obtained from the traces of the conductance changes in a much wider concentration range than in the previous methods. The ⊺ 2 of sodium dodecyl sulphate (SLS) observed coincided fairly well with those obtained from the temperature-jump technique by Folger et al . (1974) and by Aniansson et at . (1976), when comparison was possible. In a wide concentration range above c. m. c. ⊺ 2 -1 of SLS sharply decreased with increasing concentration, increased with temperature, and decreased with addition of foreign salts. The ⊺ 2 -1 of sodium tetradecyl sulphate (STS) and sodium hexadecyl sulphate (SCS) showed similar trends. The magnitudes of the ⊺ 2 -1 were in the order SLS > STS > SCS. The ⊺ 2 -1 of hexadecyl trimethylammonium bromide solution, which was much smaller than those of the anionic micelles studied, also showed similar dependence on concentration (above c. m. c.) and temperature.

Fundamentals of Colloid and Surface Chemistry

“…2.17, A). 48 Micellization reaction corresponds to the interface formation, and so many studies on micellization are helpful for understanding the mechanism of colloidal organization. Depending on the relative distribution of the hydrophilic and hydrophobic groups, various modes of assembling and orientation take place to reduce Gibbs free energy in the total system as much as possible.…”