The study on magnetite particles coated with bilayer surfactants

Magnetite particles were prepared by co-precipitation, then sodium oleic (SO) and sodium dodecyl benzene sulfonate (SDBS) were applied as inner and outer surfactants, respectively. IR and TG were used to study the surface adsorption of SO and SDBS on magnetite particles. The experimental results demonstrated that SO molecules were linked to the magnetite particles through chemical bond and SDBS coated on the surface of magnetite particles covered with SO by means of Van der Waals attraction. Furthermore, based on the adsorption isotherms of surfactants on the magnetite particles and the dependence of Zeta potential of particles on the surfactants concentrations, the adsorption mechanisms of these two surfactants on the magnetite particles were studied. The isotherm adsorption model for SO on magnetite particles showed excellent correlation to Langmuir type and the adsorption equation was Γ=0.162c1+0.303c (25 °C), while that for SDBS on magnetite particles coated with SO showed excellent consistence with Freundlich type and the adsorption equation was Γ = 0.32c0.475 (25 °C). In addition, the results demonstrated that both SO and SDBS formed monolayer adsorption on the surface of magnetite particles.