Autonomous and directional flow of water and transport of particles across a subliming dynamic crystal surface.

Chemical and morphological traits of natural substrates that can propel and transport fluids over their surfaces have long provided inspiration for the engineering of artificial materials that can harvest and collect water from aerial humidity. Here we report that the gradual widening of parallel microchannels on a surface of a slowly subliming hexachlorobenzene crystal can promote the autonomous and bidirectional transduction of condensed aerial water. Driven by topology changes on the surface of the crystal and water exchange with the gas phase, droplets of condensed water migrate over the crystal. These droplets are also able to transport silver particles and other particulate matter, such as dust. The velocity of the particles was shown to be dependent on both the sublimation rate of the crystal and the relative humidity of its environment. This example of a sublimation-powered water flow demonstrates that topological surface changes accompanying crystal phase transitions can be harnessed to transport liquid and solid matter over surfaces.