Ferrofluid

On first inspection ferrofluid could easily be mistaken for petrol, given its dark colour and oily consistency. However, when placed in a magnetic field, its surface suddenly bristles with spikes, which follow a magnet around in an entrancing ballet, and its viscosity surges, thickening the fluid in an instant. Ferrofluid is a dispersion of dense magnetic particles of iron oxide, each one no bigger than a few nanometers, stabilized in a carrier liquid by an emulsifier. The dual nature of this material – both a collection of tiny solid magnets and a flowy, goopy liquid – is responsible for its unusual behaviour, and the emergence of these rippling, intricate surface patterns. 

Ferrofluid was developed in collaboration with NASA in the 1960s to address the issue of moving fuels around in space: ferrofluid was added to rocket fuel to allow it to be drawn towards a fuel pump using magnets in the absence of gravity. Today ferrofluid has a strong following of artists who use its unusual properties to generate unique shapes in their work. Anecdotally, it is thought to have possible applications in loudspeakers to damp vibrations, as a seal in hard disk drives to stop dust getting in, and even in biomedical applications for drug delivery. 

Researchers at UCL have explored the use of ferrofluid to create 4D printed magnetically-actuated chainmail fabrics for wearable assistive devices. These nylon chainmails doped with ferrofluid drape downwards until a magnetic field is applied, and then they stiffen like a muscle. The idea behind these magnetically-functionalised materials is that they can be used to create mobility aids that can be worn comfortably against the skin like a fabric until support is needed.