From Cassie state to Gecko state: A facile hydrothermal process for the fabrication of superhydrophobic surfaces with controlled sliding angles on zinc substrates

Superhydrophobic surfaces with controlled sliding angles (SAs) on zinc substrates have been fabricated via a simple hydrothermal process as well as the subsequent modification of stearic acid. We regulate the hydrothermal process by changing the concentration ratio of H2O2/NaOH and temperature to tune the surface morphologies. After being modified with stearic acid, the as-prepared surfaces show an analogous superhydrophobicity but tunable water adhesion that ranges from extremely low to medium and very high, on which the SAs change from 8 ± 1° to 12 ± 1°, 54 ± 3° and 90° (the water droplet is firmly pinned on the superhydrophobic surface even when the surface is titled vertically or reversed totally). Based on the different SAs (also reflected by different adhesive forces) of the as-prepared superhydrophobic surfaces, we have achieved the selective transportation of droplets with different volumes. In addition, we also demonstrated a process of selective transportation of droplets with different volumes for the application in qualitative detection of sodium hydroxide, which would be promising in selective transportation with quantitative volume and many other important fields.