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.