An air–liquid interface is important in many biological
and industrial applications, where the manipulation of liquids on
the air–liquid interface can have a significant impact. However,
current manipulation techniques on the interface are mostly limited
to transportation and trapping. Here, we report a magnetic liquid
shaping method that can squeeze, rotate, and shape nonmagnetic liquids
on an air–ferrofluid interface with programmable deformation.
We can control the aspect ratio of the ellipse and generate repeatable
quasi-static shapes of a hexadecane oil droplet. We can rotate droplets
and stir liquids into spiral-like structures. We can also shape phase-changing
liquids and fabricate shape-programmed thin films at the air–ferrofluid
interface. The proposed method may potentially open up new possibilities
for film fabrication, tissue engineering, and biological experiments
that can be carried out at an air–liquid interface.