Dynamic wettability switching by surface roughness effect

This paper presents a novel wettability (i.e., contact angle) switching mechanism for micro-droplet transportation by surface roughness effect. A roughness switchable device, with a thin polydimethylsiloxane (PDMS) membrane bonded on the top of a rough PDMS substrate, was fabricated and tested. It was found that the surface wettability can be dynamically switched from medium hydrophobic to super hydrophobic states by deflecting the membrane with a pneumatic method. The reported mechanism is the first demonstration of wettability switching by roughness modification. This technology enables a microscale liquid droplet transport mechanism by surface tension without using thermal effect or electrical potential.