Characterization of reverse microemulsion formed with functionalized surfactants based on ferrycianide ions

Abstract

Schulman's titration (ST) and dynamic light scattering (DLS) were employed to obtain structural parameters of the reverse microemulsions formed by the functionalized surfactants cetyltrimethylammonium ferricyanide (CTAFeIII) and didodecyldimethylammonium ferricyanide (DDAFeIII). From the ST, the amount of surfactant and cosurfactant per droplet can be calculated, and if the droplets are spherical, it is possible to determine the droplet radius taking into account geometrical parameters. DLS measures the collective diffusion coefficient of the droplets, and then by means of the Stoke-Einstein equation, the droplets radius can be calculated. When the amount of water in the microemulsions is lower than 15 wt%, both techniques yield similar droplet radii, regardless of the functionalized surfactant used, which indicates that the microemulsions contain spherical droplets in this range of water concentration. When the amount of water reaches 20 wt% the radii obtained by DLS are larger than the one deduced from ST, suggesting that at this water concentration, the droplets are not spherical. These results are useful to understand the behavior of bulky functionalized surfactants and their possibility to be applied in the synthesis of nanoparticles based on ferricyanide ions.