Maria Stjerndahl

Superparamagnetic Fe3O4/SiO2 Nanocomposites: Enabling the Tuning of Both the Iron Oxide Load and the Size of the Nanoparticles

Using a water-in-oil microemulsion system, silica nanoparticles containing superparamagnetic iron oxide (SPIO) crystals have been prepared and characterized. With this method, the loading of iron oxide crystals, the thickness of the silica shells, and the overall particle sizes are tunable. Moving from low to high water concentration, within the microemulsion region, resulted in a gradual shift from larger particles, ca. 100 nm and fully loaded with SPIOs, to smaller particles, ca. 30 nm containing only one or a few SPIOs. By varying the amount of silica precursor, the thickness of the silica shell was altered. Field dependent magnetization measurements showed the magnetic properties of the SPIOs were preserved after the synthesis.

Surfactants Containing Hydrolyzable Bonds

There is a growing demand for hydrolyzable surfactants, i.e., surfactants that break down ina controlled way by changing the pH. Environmental concern is the main driving force behind currentinterest in these surfactants, but they are also of interest in applications where surfactants are neededin one stage but later undesirable at another stage of a process. This chapter summarizes the fieldof hydrolyzable surfactants with an emphasis on their more recent development. Surfactants that break downeither on the acid or on the alkaline side are described. It is shown that the susceptibility to hydrolysisfor many surfactants depends on whether or not the surfactant is in the form of micelles or as free unimersin solution. It is shown that whereas nonionic ester surfactants are more stable above the CMC (micellarretardation), cationic ester surfactants break down more readily when aggregated than when present as unimers(micellar catalysis).