MICROSTRUCTURE OF THE CTAB-BUTANOL-OCTANE-WATER MICROEMULSION SYSTEM - EFFECT OF DISSOLVED SALTS

We present a microstructural study of a new water-in-oil microemulsion composed of cetyltrimethylammonium bromide (CTAB), butanol, octane and an aqueous phase. The system solubilizes relatively large proportions of metal salt solutions such as Y(NO3)3 and Cu(NO3)2. The properties studied include electrical conductivity, viscosity and effective hydrodynamic diameter (from dynamic light scattering). The non-monotonic dependence of the hydrodynamic diameter on the aqueous phase fraction has been explained by a simple equipartition model with variable surfactant aggregation number. The presence of Cu2, ions in very small water-in-oil droplets (<5 nm) is found to lead to the formation of a [CuBr3]- complex, but the complex is destroyed with an increase in the size of the droplets.