The rise of ferrofluids

Rocket scientists at Nasa were working day and night. It was 1963 and they were testing hundreds of different combustion chamber designs and injectors for liquid hydrogen engines, trying to iron out problems with combustion stability that could thwart efforts to put astronauts on the moon. Solomon ‘Steve’ Papell, a mechanical engineer, was working on a problem particular to liquid propellants. Back then, it wasn’t clear how liquid fuel sloshing about in zero gravity could be guided to the combustion chamber when the engine needed to be restarted. Papell attempted to solve the problem by adding magnetic dust to rocket fuel, proposing that the fuel could be drawn to the chamber using a strong magnet.

Papell’s approach worked but it never took off, so to speak. His solution meant adding ground-up iron oxide particles to the fuel and that didn’t sit well with the rocket scientists as it changed the efficiency of their rockets. Papell did receive a 1965 patent for his magnetic fluid, which turned out to have some intriguing properties – and not just in zero gravity.

Outside a magnetic field, a so-called ‘ferrofluid’ behaves as you might expect any liquid to behave, but if a container of it is held next to a strong magnet, its surface appears to become solid, with jagged spikes pointing along the magnetic field lines. All this weirdness makes ferrofluids well-suited to showy science demonstrations and art installations, even if they didn’t make it as rocket fuels. However, the last decade has seen scientific interest in ferrofluids rising again, with emerging uses in biomedicine, liquid robotics, plastic recycling and environmental remediation.