Effect of the addition of n-alkylamines on the growth of sodium decyl sulfate micelles

Abstract

The effect of the addition of n-alkylamines [CH₃(CH₂)_mNH₂; m= 5, 6, or 7] on the growth of sodium dodecyl sulfate (SDS) micelles has been studied by small-angle neutron scattering (SANS) and viscosity measurements at 30 °C. The viscosities of SDS (0.3 mol l^–1 in D₂O) solutions show a distinct rise at a certain amine concentration (X_C) which depends on the chain length of the amine. This has been attributed to a change in micellar shape. To corroborate our viscosity results, SANS experiments were carried out on 0.3 mol l^–1 SDS–amine micellar systems. SANS distribution showed a well defined peak for 0.3 mol l^–1 SDS which shifts towards low Q-values on addition of different amines. The SANS spectra were analysed using the Hayter–Penfold model and shape and size parameters were computed. The results are interpreted in the light of micellar growth caused by the addition of amines. The micelles are shown to be ellipsoidal with the length of the semi-major axis depending on the chain length of the amine.