Ferrofluid 

Spikes of ferrofluid

Have you ever seen a magnetic liquid?  Ferrofluids have the fluid properties of liquids and the magnetic properties of a solid.  Ferrofluid contains tiny nanoparticles (~10 nm in diameter) of a magnetic solid called magnetite (Fe3O4) that are coated in a surfactant (like a soap) and suspended in a liquid (like an oil or water).  One huge advantage of this material is that the location of the fluid can be precisely controlled with a magnetic field and, by changing the strength of the field, the fluid can be forced to flow in the desired direction.  

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