Mixed Micellar Aggregates of Anionic and Nonionic Surfactants with Short Hydrophobic Tails. A PGSE-NMR Study

Abstract

Intradiffusion coeffs. for the ternary system heavy water-sodium hexanesulfonate (C6SNa)-pentaethylene glycol monohexyl ether (C6E5), in both the premicellar and micellar compn. ranges, were measured by the PGSE-NMR technique at 25°C. Exptl. data show the formation of mixed micelles and allow the detn. of the cmc. In the premicellar compn. range the monomer-monomer interactions are analyzed. The compns. of the aq. and micellar pseudophase have been computed in the whole micellar compn. range; they indicate that C6E5 has a larger tendency to form aggregates than C6SNa. The aggregation no. and the free energy of micellization are calcd. and interpreted in terms of interactions among the tensides in the micellar aggregates. The exptl. results have been interpreted in terms of a regular soln. model, and the interaction parameter β is computed. β Increases by increasing the no. of micellar aggregates in the system; this effect can be interpreted in terms of intermicellar interactions

Mixed Micellar Aggregates of Nonionic and Anionic Surfactants with Short Hydrophobic Tails: A Microcalorimetric Study

“…The A S E dependence on m S can be interpreted as due to a smooth increase of the interactions between the C 6 E 5 monomers in the presence of C 6 SNa. This is in agreement with the results of intradiffusion measurements made on the same system by some of us (6).…”

“…We focused our attention on short tail surfactants having cmc values at concentrations high enough to allow experimental investigation also in the premicellar composition range. At the same time C 6 E 5 and C 6 SNa show all the characteristics of a typical surfactant (7,8). The investigations on the water-C 6 E 5 -C 6 SNa system showed the formation of mixed micellar aggregates, to which both surfactants participate.…”

“…Figure 4 collects the apparent molar relative enthalpies of C 6 E 5 at various C 6 SNa compositions. The curves obtained with a C 6 SNa molality lower than 0.58 mol kg −1 show a large slope change in the composition range where micelles appear.…”

“…The investigations on the water-C 6 E 5 -C 6 SNa system showed the formation of mixed micellar aggregates, to which both surfactants participate. The intradiffusion coefficients allowed computation of the partitioning of the two surfactants between the aqueous environment and the micelles (6); the data were interpreted in terms of the regular solution theory proposed by Holland and Rubingh (9) that assumes an ideal mixing entropy of the surfactants into the micelles.…”

“…In the past some of us studied the ternary system waterpentaethylene glycol monohexylether (C 6 E 5 )-sodium hexyl sulfonate (C 6 SNa) measuring mutual and intradiffusion coefficients through the interferometric Gouy technique (5) and the NMR-PGSE method (6). We focused our attention on short tail surfactants having cmc values at concentrations high enough to allow experimental investigation also in the premicellar composition range.…”