Measurement of the critical micelle concentration of nonionic-nonionic mixed surfactant systems by the first derivative absorption spectrum method and the region of cooperative micelles.

Abstract

In nonionic-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). The region corresponding to mixed micelle formation was obtained from plots of the sum of the concentrations corresponding to the cmc (=[OED]*PED/cmcOED+[PED]*OED/cmcPED : [OED]*PED (or [PED]*OED) is the concentration of OED (or PED) in the cmc for mixed micelle formation of OED-PED binary systems, and cmcOED (or cmcPED) is the cmc of OED (or PED)) on the ordinate against the mole fraction normalized with respect to cmc (=[[OED]/cmcOED/[[OED]/cmcOED+[PED]/cmcPED] : [OED] (or [PED]) is the concentration of OED (or PED)) on the abscissa by the FDAS method.In the region of cooperative micelles which was a part of the region forming mixed micelles, it was found that the longer the ethylene glycol chain length of the nonionic-nonionic mixed surfactants, the wider was the region of cooperative micelles. The order of the width was 0.78mM OED-0.43mM PED>0.43mM OED-0.43mM PED>0.78mM OED-0.43mM TED=0.43mM PED-0.43mM TED>0.43mM OED-0.43mM TED mixed surfactant systems. In ionic-nonionic mixed surfactant systems, the cmc values of the mixed micelles were under the influence of the nonionic surfactant. But in nonionic-nonionic mixed surfactant systems, the cmc values of the mixed surfactant systems were under the influence of both nonionic surfactans. (Abbreviations used are : OED, PED and TED=octa-, penta- and triethylene glycol dodecyl ether.)