Synthesis and Characterization of Bilayer Ferrofluids

The role of sodium dodecyle sulfate (SDS) adsorption as the second layer surfactant in a double layer surfactant ferrofluid is investigated. Preparation of the solid phase is based on the growth of the magnetic oxide by dehydration of a salt solution of FeCl₂ and FeCl₃ in an identical molar ratio. Particle size was determined through the magnetic measurements by VSM to be about 8-10 nm and by STEM to be about 12 nm. The data show that in a certain thermal interval, a local maximum appears in the magnetic oxide concentration which is a function of the stirring time and the SDS concentration. Increasing temperature causes surface oxidation which decreases the magnetization, similar to the behavior of monolayer ferrofluids. In addition, in the double layer systems, the intersolubility of the layers varies. This has a profound effect on the saturation magnetization.