Change in the aggregational character of the cationic surfactant cetyl trimethyl ammonium bromide in the presence of o- and p-nitrophenolates

The effect of the addition of sodium salts of p-nitrophenol and o-nitrophenol on the structural transition of aqueous micellar solutions of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) was studied by viscosity, H-1 nuclear magnetic resonance, and dynamic light scattering measurements. The rapid increase in the relative viscosity of CTAB solutions on the addition of sodium salts of o-nitrophenol and p-nitrophenol was due to the transition in micellar shape from spheres to rods. Dynamic light scattering studies indicated a decrease in the diffusion coefficient of the micelles with the addition of p-nitrophenol. The adsorption and orientation of the salts on the micellar surface and subsequent growth of the micelles was studied by nuclear magnetic resonance.