Ferrofluid & microplastic

Hi, some of my students saw [this](https://www.designboom.com/technology/google-science-fair-winner-fionn-ferreira-cork-microplastics-08-01-2019/) article about using ferrofluid to extract microplastic from water (hopefully that elevates this post above “anecdotal evidence?”) and they want to use a NASA balloon in the TechRise program to see whether the technique could remove them from the air too.

In the article it’s claimed that the nonpolarity of the oil and plastic causes the attraction. But that immediately leads one to question: why does the oil need to have iron oxides in it? Because the guy in the video showed that oil alone wouldn’t work.

All I can come up with are half-baked ideas about the plastic acquiring an electrostatic charge in the air and the moving charge then being attracted to the magnetite, or an even worse conjecture about dipole moments in long plastic polymers somehow interacting with the ions of the iron oxide salts.

But the former seems lame because even if the oxides are magnetized the Lorentz force would be awfully weak, and it seems unlikely that plastic could retain a charge underwater anyway. The latter seems no good because dipoles get weak fast.

Thank you in advance for any insights.