Small-Angle Neutron Scattering Studies of Mixed Cetyl Trimethylammonium Bromide−Butyl Benzene Sulfonate Solutions

The effect of hydrotropes, sodium salts of butyl benzene sulfonate (Na-BBS), viz., n- butyl benzene sulfonate (Na-nBBS), iso- butyl benzene sulfonate (Na-iBBS), and tert- butyl benzene sulfonate (Na-tBBS), on microstructures of cetyl trimethylammonium bromide (CTAB) in aqueous solutions has been studied using small-angle neutron scattering (SANS) and viscosity changes. The viscosity of CTAB solutions increased with the addition of the hydrotropes, but differently with different isomers. This behavior is attributed to the structural differences in the hydrotropes. The SANS studies indicated the growth of the CTAB micelles on the addition of the hydrotropes while the micellar shape changed from sphere to ellipsoid depending upon the structure of the hydrotrope. Na-nBBS showed the highest aggregation number and a lower fractional charge on the micelles as compared to the sterically hindered Na-tBBS, at the same concentration.