Mixed micellar aggregates of cationic and nonionic surfactants with short hydrophobic tails. An intradiffusion study

Abstract

The ternary system water–pentaethyleneglycol monooctyl ether (C₈E₅)–octyltrimethyl ammonium bromide (C₈TAB) has been studied at 25 °C. Accurate c.m.c. values have been determined through spectrofluorimetric measurements, by using DL-tryptophan as a molecular probe. The surfactant intradiffusion coefficients have been measured through the PGSE-NMR technique. Experimental data show the formation of mixed micelles. The compositions of the aqueous and micellar pseudo-phase have been computed over the whole micellar composition range; they indicate that C₈E₅ has a larger tendency to form aggregates than C₈TAB. The aggregation number and the Gibbs energy of mixed micelle formation are calculated and interpreted in terms of interactions among the surfactants in the micellar aggregates. The experimental results have been compared with those predicted by the regular solution model finding reasonable agreement.