Reversible Mobility Switching and Programmable Liquid Drop Transport on Air-Permeable Superhydrophobic Surfaces

Superhydrophobic surfaces enable liquid drop mobility with minimal friction but inherently lack control due to their extremely low adhesion. Here, we report a simple, accessible approach for programmable drop manipulation on an air-permeable superhydrophobic substrate using pressure modulation. We use a substrate which is commercially available, in our case, a rough hydrophobic sintered porous PTFE sheet. Its surface is rendered superhydrophobic via manual wet sanding, eliminating the need for micropatterning or chemical treatment. Air injection (positive pressure difference across the sheet) reduces solid-liquid contact, forming an air cushion that induces drop depinning and levitation, similarly with the Leidenfrost effect. Conversely, air suction (negative pressure) enhances adhesion, which increases contact angle hysteresis and roll-off angles and can immobilize drops even on inclined surfaces. Switching between suction and injection enables reversible switching between pinned and mobile states in real time. We demonstrate stepwise motion of drops on inclined surfaces by tuning the duration of positive pressure pulses. On horizontal substrates, directional transport is achieved by synchronizing pressure pulses with horizontal substrate oscillations, enabling motion without gravitational bias. This low-cost, programmable method enables robust and reversible switching of drop mobility, holding promise for applications in open-surface microfluidics, lab-on-chip devices, and adaptive liquid handling systems.