Formation and Growth of Micelles in Dilute Aqueous CTAB Solutions in the Presence of NaNO3 and NaClO3

Self-assembly of cetyltrimethylammonium bromide (CTAB) in aqueous solution, in the presence of two inorganic salts viz, NaNO3 and NaClO3 was investigated by steady-state fluorescence, electrical conductance, surface tension, viscosity, dynamic light scattering (DLS) and cryogenic transmission microscopy (cryo-TEM). The counterions located at short enough distances to CTA(+) micellar surface experience a very strong electrostatic attraction and thus become condensed. This counterion condensation plays a significant role in deciding the effective charge on the micelle, their screening interaction and structural transition of the micelles. In the present work, the probable mechanism of the salts' action in aqueous solution of CTAB is explained. The critical micelle concentration (CMC), area per molecule (a<<(2)), micelle hydrodynamic diameter (D (h) ), and aggregation number (N (agg)) of CTAB micelles in the absence and presence of the salts are reported. The addition of both salts followed the lyotropic series and showed a remarkable decrease in CMC. A detailed investigation of the structural transitions from spherical to rod or even to entangled wormlike structures is presented from cryoTEM.