MIXED MICELLIZATION OF DIMERIC (GEMINI) SURFACTANTS AND CONVENTIONAL SURFACTANTS - I - MIXTURES OF AN ANIONIC DIMERIC SURFACTANT AND OF THENONIONIC SURFACTANTS C12E5 AND C12E8

The mixed micellization between the anionic dimeric surfactant Dim1 (d isodium 1,11-didecyl-3,6,9-trioxaundecane 1,11-disulfate) and the two nonionic surfactants C12E5 and C12E8 (penta-and octaoxyethylene monodo decyl ethers, respectively) has been investigated. The cmc of the mixt ures has been measured by fluorescence probing, using the fluorescent probe pyrene. Its variation with composition revealed synergism in mic elle formation. The micelle aggregation (N) numbers have been measured using time-resolved fluorescence quenching at a total surfactant conc entration of about 70 mM and at 25, 40, and 55 degrees C. The differen ces in total aggregation number of the mixed micelles in the two syste ms reflect (i) the higher aggregation number of C12E5 micelles with re spect to C12E8 and Dim1 micelles; (ii) the higher cloud temperature of C12E8 with respect to C12E5; and (iii) the opposite temperature depen dences of N for Dim1 and nonionic surfactants micelles. The results sh ow nonideal mixing behavior with a shallow minimum in the variation of the mixed micelle aggregation number with the mixture composition at a Dim1 mole fraction around 0.5. (C) 1998 Academic Press.