Surfactant driven propulsion

A small autonomous boat powered by a volatile surfactant has been developed by scientists in Finland and Israel. The surfactant modifies the surface tension of the liquid it floats on to create a surface tension gradient that propels the boat forward.

Propulsion induced by a surface tension gradient is known as Marangoni propulsion. It’s used in nature by small creatures such as Microvelia (small aquatic insects) to give a burst of speed to escape predators. In man-made devices, the Marangoni effect has been used to power small ‘camphor boats’ and ‘soap boats’; however, these systems normally offer only short term propulsion or require the boat to be confined to specific channels.  More...

http://www.rsc.org/chemistryworld/2012/06/surfactant-driven-propulsion