Tunable Adhesive Superhydrophobic Surfaces for Superparamagnetic Microdroplets

Inspired by the gecko's ability to reversibly stick and unstick to a variety of solid surfaces during locomotion, a new superhydrophobic iron surface that has a tunable adhesive force with the superparamagnetic microdroplet as a function of the magnetic field was fabricated by a simple and inexpensive method. The as-prepared surface is low adhesive, and a superparamagnetic microdroplet can roll easily on the surface. After the surface is magnetized, it becomes highly adhesive, which can pin a superparamagnetic microdroplet. Further demagnetizing the surface that has been magnetized, a superparamagnetic microdroplet can roll on the surface again, indicating that the surface returns to its initial low adhesive state. Reversible transition between the high adhesive pinning state and low adhesive rolling state can be achieved by simply magnetizing and demagnetizing the surface alternately. The tunable effect maybe attribute to the cooperation of the soft ferromagnetic property of iron plate and the microstructure on the surface. Such intelligent surface could potentially be used in a wide range of applications such as biochemical separation, no-loss transport of microdroplet, and in situ detection.