Movies

	The Moving Droplet (QuickTime, 1.1 MB) Real-time side view of water droplets placed by pipette on a heated brass surface (TR = 460 °C) machined into a ratchet-like (sawtooth) geometry (s = 1.5 mm, d = 0.3 mm), demonstrating the immediate acceleration of the droplets. A coin (diameter 2.4 cm) is included as length scale reference. Credit: Mike Taormina
	Slow Motion (QuickTime, 696 kb) High-speed video of a R134a droplet on a brass ratchet (s = 1.5 mm, d = 0.3 mm) at room temperature (side view). Filmed at 500 fps, replayed at 30 fps. Credit: Amanda Stout, Corey Dow-Hygelund, and Benji Aleman
	Downhill Start, Turns Around (QuickTime, 708 kb) High-speed video of a nitrogen droplet (Tb = - 196 ºC ) on a horizontally leveled brass ratchet at room temperature (s = 1.5 mm) in side view. The droplet moves initially to the left due to inertia, but stops and turns around under the action of the ratchet. Filmed at 500 fps, replayed at 30 fps. Credit: Amanda Stout, Corey Dow-Hygelund, and Benji Aleman.
	Droplet in a Channel (QuickTime, 1.1 MB) Top-view of a horizontally leveled brass channel (3 mm wide and 8 mm deep, T ~ 400 ºC) . The sidewalls have ratchet-like topology. A slug of water of 12 mm length (spanning about eight ratchet periods) moves rapidly to the right. Filmed and replayed at 30 fps. Credit: Benji Aleman and Mike Taormina.
	Uphill Slow-motion (QuickTime, 5.1 MB) High-speed video of a R134a droplet climbing against an incline on a ratchet (s = 1.5 mm). At the end of the ratchet, the droplet continues to move due to inertia, but slows due to gravity. Filmed at 1000 fps, replayed at 60 fps. Credit: Amanda Stout, Corey Dow-Hygelund, Benji Aleman, and Zeb Schweickert.
	Droplet and Glitter (QuickTime, 1.9 MB) Nitrogen droplet on a room-temperature, brass ratchet (s = 1.5 mm). Pieces of glitter (CB-123 Glitter, Creative Beginnings, Morro Bay, CA) visualize vapor flow. Some glitter pieces are incorporated into the droplet. Filmed at 2000 fps, replayed at 30 fps. Credit: Amanda Stout, Corey Dow-Hygelund, Benji Aleman, and Zeb Schweickert.
	Droplet Jumps Up a Step (QuickTime, 896 kb) Nitrogen droplet (r ~ 1.5 mm) with initial velocity to the right accelerates upon interaction with the edge of a piece of electrical tape (VWR Scientific Tape) attached onto a room-temperature, brass surface. A vapor bubble forming inside the droplet indicates a nucleate boiling event. Credit: Amanda Stout, Corey Dow-Hygelund, Benji Aleman, and Zeb Schweickert.
	About (.mpg, 39 MB) Undergraduate Mike Taormina explains movement of droplets on a ratchet surface. Credit: Christine Gramer
	Incline (.mpg, 23 MB) Water droplets travel up an inclined heated brass ratchet surface. Credit: Christine Gramer and Mike Taormina.
	Inertia (.mpg, 46 MB) Water droplets travelling downhill will stop and turn around after they move onto a heated ratchet surface. Credit: Christine Gramer and Mike Taormina.
	Channel (.mpg, 48 MB) Water droplets in a channel with ratchet faces will travel uphill. Credit: Christine Gramer and Mike Taormina.

Imaging methods
High-speed movies were obtained using a Phantom 5.0 high-speed video camera (Vision Research, Wayne, New Jersey), a Nikon 35 - 70 mm, ø 58 mm macro zoom lens, and a Nikon PK13 27.5 mm spacer. Diffuse, indirect lighting was used.

Video-rate movies (Supplementary Videos 2 and 4) were acquired using a Canon GL2 video camera (30 fps) with 4.2 - 84 mm, ø 58 mm zoom lens.

R134a droplets were formed using the nozzle of a can of dusting gas (Techspray, Amarillo, Texas) held upside down (spray visible in Movies S3 and S6 originates from the can's nozzle).

Nitrogen droplets were formed using a stainless steel tube (outer ø 1.6 mm, inner ø 0.7 mm) that was inserted horizontally into the wall of a 500 ml polyethylene wash bottle that was filled with liquid nitrogen and thermally insulated using a neoprene stubby holder. As described in Fig. 2 in Ref. [1], the tube was bent at right angles, and the downward pointing tube end was blocked by solder. Liquid nitrogen emerged from a ø0.5 mm hole drilled near the bend and formed droplets of r ~ 1 mm at the tube end. To avoid ice crystals forming in the nitrogen, a lid with a vent hole was placed on the wash bottle.