WATER-IN-OIL MICROEMULSIONS FORMED BY AMMONIUM AND TETRAPROPYLAMMONIUM SALTS OF AEROSOL OT

The effects of replacing the Na+ counterion of Aerosol OT for ammonium (NH4+) and tetrapropyl-ammonium [(C3H7)4N+] on the properties of the L2 phase in cyclohexane are described. The results from electrical conductivity and small-angle neutron scattering (SANS) experiments at low volume fraction (phi almost-equal-to 0.025-0.075) indicate that the type of counterion has an important effect on the aggregate structure. For NH4+ (ionic hydrated radius r(h) = 1.5 angstrom), spherical micelles are formed and behavior similar to that of the usual Na+ salt (r(h) = 1.8 angstrom) is observed. With (C3H7)4N+ (r(h) = 3.9 angstrom) cylinders are present at w < 10.0, while at higher w spheres are preferred.