Absorption and Emission Studies of Solubilization in Micelles: Part 2.—Determination of Aggregation Numbers and Solubilisate Diffusion in Cationic Micelles

Abstract

Excimer formation of pyrene is studied as a function of temperature in decyl-, dodecyl-, tetradecyl- and hexadecyl-trimethylammonium bromide (C10–C16TAB) micelles. The distribution of the solubilisate in the micelles is discussed and concluded to be Pn=nn/(1 +n)1 +n, where Pn is the fraction of micelles containing n pyrene molecules, and n is the average number of solubilised molecules per micelle. The activation energy of the micellar microviscosity is 37.0 kJ mol–1 for C10- and C12–TAB and 34.0 ± 3.0 kJ mol–1 for C14- and C16-TAB. The average density per unit chain-length is shown to be the same for C10- and C12-TAB, this value being greater than the constant value measured for C14- and C16-TAB. Aggregation numbers are reported for the four surfactants, and these show that the longer the hydrocarbon chain the less is the temperature variation.