Self-propelled liquid motion on micro/nanoscale ratchet surfaces in the film-boiling regime

Keywords:
self-propulsion, ratchet, Leidenfrost, film-boiling, fluid motion

Abstract:
In this study, we examined the feasibility of using this driving mechanism in micro- and nanofluidic devices. Saw-tooth gratings of various sizes down to sub-micrometer period were fabricated using micro- and nanoscale machining tools (Figure 1) and the motion of water drops on those surfaces in the Leidenfrost regime was systematically studied (Figure 2). Surprisingly, a dramatic increase in the maximum velocity was observed as the period of the saw-tooth grating decreases, even reaching ~40 cm/s for the ratchet period of 833 nm (Figure 3). This result clearly indicates that a nanoscale asymmetric potential enhances the propulsion of liquid motion dramatically and thus this self-propulsion mechanism with a nanoscale potential can be a powerful candidate to drive micro- and nanofluidic devices without any external power. At higher temperature ranges, the size of the ratchets does not affect the liquid velocity any more, maintaining a constant value (a few cm/s). In addition, we will show results of the parametric studies on the influence of the wettability, droplet sizes, and different fluids on the fluid motion on micro- and nanoscale saw-tooth gratings.

Nanotech 2008 Conference Program Abstract