In the Laboratory
Preparation and Properties of an Aqueous Ferrofluid
Patricia Berger† Department of Chemistry, Southern Oregon University, Ashland, OR 97520 Nicholas B. Adelman, Katie J. Beckman, Dean J. Campbell,†† and Arthur B. Ellis* Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706; *firstname.lastname@example.org George C. Lisensky Department of Chemistry, Beloit College, Beloit, WI 53511
Introduction Imagine the production and applications of a liquid that can be controlled by a magnetic field. Creating a strongly magnetic liquid is not as easy as melting a strongly magnetic solid, since magnetic solids lose much of their magnetism above what is known as the Curie temperature, as thermal energy overwhelms the tendency of their electrons to align in magnetic domains (regions of similarly oriented electron spins). The Curie temperature is well below the melting point for known magnetic materials (1–3). Ferrofluids, which are colloidal suspensions of magnetic material in a liquid medium, are an example of a liquid that responds to an external magnetic field. The coupling of liquid and magnetic behavior means that the liquid’s location may be manipulated by an applied magnetic field. Ferrofluids were first developed and classified in the 1960s by Stephen Pappell at NASA as a method for controlling fluids in space (4). NASA initially used them as rotating shaft seals in satellites, and they now serve the same purpose in a wide variety of machines, ranging from centrifuges to computer hard disk drives (1, 2). They are incorporated into the voice coil gap of loudspeakers for damping undesired vibrations and for cooling. Ferrofluids have also been used in the separation of metals from ores by taking advantage of a density change that appears in the fluid under application of a magnetic field. One South African company has even been utilizing ferrofluids to separate diamonds from beach sand (5). In medicine, a ferrofluidic actuator has...