Ink-jet printers, flat-panel displays and biochips all require the precise placement of microscopic amounts of fluids, but getting fluids to go where you want takes a lot more than just asking nicely. Researchers at Philips Research Laboratories in Eindhoven, the Netherlands, have come up with a promising approach. Their “electrocapillary” system, which uses no moving parts, shuttles fluid quickly through tubes as narrow as 350 micrometers wide-roughly three times the width of a human hair.
The tubes are actually filled with two fluids, which repel each other: one fluid is electrically conductive while the other is insulating. The wall of the tube also repels the fluids, but it’s lined with electrodes. When the electrodes are charged, the walls exert less force on the conducting fluid, which is squeezed up the tube by the greater force exerted by the insulating fluid. The fluid moves at several centimeters per second, which is about a hundred times faster than the speeds other electrical techniques deliver. A Philips group led by Menno Prins has demonstrated a network of thousands of such electrocapillaries, which they say could have applications in optical switching.