Turbidimetric and Nephelometric Studies on Aggrregation of Cationic-Anionic Surfactants$^\dag$

The aggregation between cationic and anionic surfactants was studied by turbidimetric and nephelometric methods with emphasis on facile analysis of the surfactants and understanding of the mixed micellization. The turbidimetric titration of sodium dodecylsulfate (SDS) with cetyltrimethylammonium bromide (CTAB) or cetylpyridinium bromide (CPB) showed maximum turbidity at equimolar composition in the SDS concentration range of 0.1-0.9 mM. The nephelometric titration of the same systems extended the limit of analysis to 0.001 mM. The sodium salts of decylsulfate and sulfonate gave similar maxima, but not at equimolar composition. The coexistence of equimolar aggregates and mixed micelles were shown over broad composition range. The aggregation and mixed micellization of the anionic/cationic surfactants mixtures depended sensitively on the hydrophobic character of the surfactants.