Fast Responsive and Controllable Liquid Transport on a Magnetic Fluid/Nanoarray Composite Interface

Controllable
liquid transport on surface is expected to occur by
manipulating the gradient of surface tension/Laplace pressure and
external stimuli, which has been intensively studied on solid or liquid
interface. However, it still faces challenges of slow response rate,
and uncontrollable transport speed and direction. Here, we demonstrate
fast responsive and controllable liquid transport on a smart magnetic
fluid/nanoarray interface, i.e., a composite interface, via modulation of an external magnetic field. The wettability
of the composite interface to water instantaneously responds to gradient
magnetic field due to the magnetically driven composite interface
gradient roughness transition that takes place within a millisecond,
which is at least 1 order of magnitude faster than that of other responsive
surfaces. A water droplet can follow the motion of the gradient composite
interface structure as it responds to the gradient magnetic field
motion. Moreover, the water droplet transport direction can be controlled
by modulating the motion direction of the gradient magnetic field.
The composite interface can be used as a pump for the transport of
immiscible liquids and other objects in the microchannel, which suggests
a way to design smart interface materials and microfluidic devices.