Spectral and hydrodynamic studies on p-toluidine induced growth in cationic micelle.

The effect of p-toluidine (PTD) on the growth of cationic surfactant micelles in aqueous solutions was examined by viscosity, UV-visible spectroscopy, dynamic light scattering (DLS), (1)H NMR and nuclear Overhauser effect spectroscopy (NOESY). Viscosity and scattering results are used to follow the growth of the aggregates and examine the structural transitions that occur. The reduction of electrostatic repulsions between the surfactant headgroups in combination with the hydrophobicity of the additive caused micellar growth and viscoelasticity at high PTD concentration; the micellar growth was found to be more pronounced in the presence of salt. (1)H NMR chemical shift changes reflect the interaction of PTD molecules with surfactant micelles while 2D NOESY experiments reveal that PTD molecules insert themselves in micelles such that its -CH(3) group is in contact with the core region and the benzene ring resides near the palisade layer of micelle.