Surface tension: floater clustering in a standing wave.

How do waves affect the distribution of small particles that float on water? Here we show that drifting small particles concentrate in either the nodes or antinodes of a standing wave, depending on whether they are hydrophilic or hydrophobic, as a result of a surface-tension effect that violates Archimedes' law of buoyancy. This clustering on waves may find practical application in particle separation and provides insight into the patchy distribution on water of, for example, plastic litter or oil slicks.