Small-angle neutron scattering study of the effect of n -alkanols on interacting micelles

Small-angle neutron scattering cross-section distributions of sodium dodecyl sulphate (SDS) and dodecyl trimethyl ammonium bromide (DTAB), each 0·3 M in D₂O were obtained in the absence and presence of 0·1 M 1-pentanol, 1-hexanol, and 1-octanol at 25°C. The Hayter-Penfold type analysis was adopted. An ellipsoidal model with semiminor axis (a=16·5 ?) and semimajor axes (b=40·7 ? and 29·8 ?) for pure SDS and DTAB micelles has produced best fits. On increasing alkanol chain lengths an increase inb values was found. Micellar parameters like effective radius (R), (a, b), fraction of counterions per micelle, and intermicellar distances were obtained. Surfactant aggregation number, additive aggregation number intermicellar interaction potentials and values of Debye screening length were obtained for SDS and DTAB in the presence of alkanols. Implications of partitioning effect, surfactant ionicity and intermicellar potentials on the microstructures are rationalised.