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(Why aren't there any) MAGNETIC LIQUIDS

Strong magnetic effects in materials derive from the ordering of the spins on electrons. Gases and liquids by their very nature are disordered materials and hence strong magnetic effects are not observed. However it is possible to create a magnetic liquid by the dispersion of nanoparticles or larger entities into the liquid so long as a truly stable colloidal dispersion is produced. Having made such a liquid, the preparation of which will be described, one is then in the position of being able to apply an additional force to the liquid phase of matter. This results in many remarkable effects such as the surface instability shown in the image. It is also possible to position remotely the liquid creating vacuum seals and to provide a heat conduction mechanism in electrical systems such as loudspeakers. The additional force can cause dense objects to float in a less dense liquid and other applications are limited by the imagination of the reader. Other colloids using larger particles at higher concentrations can also be created which are semi-stable. Such materials exhibit significant changes in rheology in the presence of a magnetic field and have applications in dampers and slip clutches etc. In this lecture the underlying physics of these applications will be described and demonstrations of a number of effects presented.