This paper describes the fabrication and characterization of a prototype wettability switching soft skin device that dynamically switches its surface morphology between flat and rough states. The device, which consists of a 1-μm-thick polydimethylsiloxane (PDMS) deformable diaphragm on a PDMS substrate with a micro-bump arrays, was successfully formed with a high fabrication yield by a novel method of device releasing from a dummy substrate. In buffered hydrofluoric acid (BHF) solution, a sacrificial layer of a novolak-resin-based resist was able to be rapidly released from the OH-terminated SiO2 surface of the dummy substrate, probably due to the breaking of hydrogen bonds at the interface. The wettability of the fabricated device was reversibly switched using micro-diaphragm deformation by varying the inner pressure. When a droplet was placed on the surface in the rough state, a large contact angle of approximately 140° was obtained, close to the Cassie mode with air in the concave-deformed PDMS micro-diaphragms, which indicated a high surface hydrophobicity. During cyclic switching between the rough and flat states after second switching, the contact angle reversibly changed between 106° and 120°, in good agreement with the Wenzel mode, where the micro-diaphragm surfaces were fully wet. Additionally, we observed that the droplet did not move even on the tilted device.
PDMS Soft Skin Device with Deformable Micro-Diaphragm Array Fabricated with Rapid Substrate-Releasing Process