We prepared Fe3O4 magnetic nanoparticles having diameters of approximately 12 nm by chemical coprecipitation, which were coated with three different fatty acid surfactants: oleic acid, lauric acid, and myristic acid. From x-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy measurements we confirmed that Fe3O4 is the only phase present in the samples. The zero field cooled magnetization curves for the nanoparticles exhibit broad peaks, consistent with superparamagnetic blocking for the polydisperse samples, and a saturation magnetization smaller than that for bulk Fe3O4. Although there are minimal differences in the magnetic properties of the nanoparticles having different surfactants, we find significant changes in the hydrodynamic response depending on chain length. Hyperthermia measurements show considerably larger response for oleic acid-coated samples, while magneto-optical studies indicate that these samples have slower dynamics of aggregation under the influence of a dc field. These results suggest that the magnetohydrodynamic response of ferrofluids can be controlled by judiciously selecting appropriate surfactants.

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Use of force in the care of patients with severe anorexia nervosa is controversial but can be justified when the disorder becomes lifethreatening. This commentary examines the role of force in compassionate care of an adolescent patient hospitalized with extreme anorexia nervosa and suggests strategies for reaching consensus, minimizing harm, and maximizing the chance of a therapeutic outcome when forced intervention is a compassionate thing to do.To claim one AMA PRA Category 1 Credit TM for the CME activity associated with this article, you must do the following: (1) read this article in its entirety, (2) answer at least 80 percent of the quiz questions correctly, and (3) complete an evaluation. The quiz, evaluation, and form for claiming AMA PRA Category 1 Credit TM are available through the AMA Ed Hub TM .