Roles of Counterion Binding in the Micelle Formation of Ionic Surfactants in Water

Abstract

In order to evaluate the role and the degree of counterion binding in the micelle formation of different ionic surfactants in water, the following recent studies on the counterion effects are overviewed. (i) Studies on solubility and micellization of cationic surfactants with perfluorocarboxylates as counterions and (ii) temperature studies on dodecylammonium alkanesulfonates as a function of carbon atom number in the hydrophobic counterions. Next, (iii) the mixing effects of dodecylammonium surfactants having different hydrophobic counterions, are examined for the binary mixed systems such as (A) perfluorocarboxylate vs. alkanesulfate ions and (B) perfluoroacetate vs. perfluoropropionate ions. Then, (iv) studies of the micelle properties of α, ω-type amphipiles having different types of counter-ions such as (A) α, ω-alkanediammonium bis (dodecyl sulfate) differing in alkane chain length and (B) the various surfactants consisting of α, ω-type surfactant ions and the same type counterions are introduced, and from these studies, the combination effect of the charge separations of both the surfactant ion and the counterion on the micelle properties is clarified.Further, regarding the determination methods of critical micellization concentration (CMC) and degree of counterion binding (β), or degree of electrical dissociation of micelles (α), the results and discussion of the temperature study on α-sulfonatomyristic acid methyl (or ethyl) ester micelles by electroconductivity measurements are described. In advance of the above contents, first, theoretical aspects of micelle formation of ionic surfactants are briefly outlined.