Small angle neutron scattering measurements of aggregation behaviour of mixed micelles of conventional surfactants with triblock polymer L64

Abstract

Small angle neutron scattering (SANS) technique has been used to study the aggregation behaviour of binary mixtures of cationic surfactants such as hexadecyltrimethylammoniumbromide (HTAB), tetradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DTAB) and nonionic surfactant (Triton X-100) with triblock polymer L64. The interactions between surfactants and triblock polymers have been explained on the basis of parameters like aggregation number, charge fraction and axial ratio. The SANS analysis indicated that the shape of micelles of cationic surfactants (HTAB, TTAB and DTAB), mixed micelles of these surfactants with triblock polymer (L64) and pure Triton X-100 is prolate ellipsoidal. For pure cationic surfactants DTAB to HTAB, there is an increase in aggregation number and decrease in charge fraction, which indicates that, the micelle grow in size with increase in the number of carbon atoms in hydrophobic tail. In case of mixture of cationic surfactant with triblock polymer (L64), the mixed micelles appear to grow in size with increase in the concentration of triblock polymer. But the shape of mixed micelle is determined largely by cationic surfactant even at very high concentration of triblock polymer and the shape of mixed micelle is prolate ellipsoidal. On the other hand, the mixed micellization of nonionic surfactant (Triton X-100) with triblock polymer (L64) are completely dominated by concentration of triblock polymer. The micellar size decreases with the increase in the concentration of triblock polymer L64. The shape of mixed micelle is spherical, same as in case of pure triblock polymer.