Measurement of the critical micelle concentration of ionic-nonionic mixed micelles by the first derivative absorption spectrum method.

Abstract

In anionic-nonionic and cationic-nonionic mixed surfactant systems, when two surfactants below their individual critical micelle concentrations (cmc) were mixed, the formation of mixed micelles was confirmed and the cmc values were measured by the first derivative absorption spectrum (FDAS) method, the solubilization method (with Sudan Red dye) and the surface tension method (Wilhelmy plate method). From plots of the mole fraction normalized with respect to cmc (=[[sodium dodecyl sulface (SDS)]/cmcSDS]/[[SDS]/cmcSDS+[hyptaethylene glycol dodecyl ether (HED)]/cmcHED] where [SDS] (or [HED]) is the concentration of SDS (or HED), and cmcSDS (or cmcHED) is the cmc of SDS (or HED)) on the abscissa against the sum of concentraions corresponding to the cmc (=[SDS]*HED/cmcSDS+[HED]*SDS/cmcHED where [SDS]*HED (or [HED]*SDS) is the concentration of SDS (or HED) in the cmc of mixed micelles of SDS-HED binary systems) on the ordinate, obtained by the FDAS method and the surface tension method, the boundary line between the regions forming mixed micelles and the regions of monomer was obtained. The results obtained are compared and the usefulness of the methods is discussed.