Figure 4

Analysis of the wetting properties of the magnetically responsive pillar arrays.

(a) Contact angles of DI water on various magnetically responsive pillar arrays with different numbers of coating-curing processes when no magnetic field is applied to the sample. (b) Contact angles of DI water on various magnetically responsive pillar arrays with different numbers of coating-curing processes when the pillar arrays are fully flattened on the substrate by an applied magnetic field. (c) Roll-off angles of DI water on various magnetically responsive pillar arrays for different numbers of coating-curing processes and magnetic field application. The symbol “(c)” on the x-axis of the graphs in (a–c) represents CNP coated samples. (d) Schematic illustration of active droplet manipulation on the magnetically actuating hierarchical pillar array. When the pillars are bent by a magnetic force, a local difference in the potential energy (“PE”) is generated in the array. Furthermore, actuation of the pillars provides a driving force (kinetic energy, “KE”) for the droplet to move along the direction of the pillars. As a result, the droplet moves towards the location of the bent pillars.