Ratchet-like topological structures for the control of microdrops

The concepts of 'force-free' motion can be applied to liquid microdrops confined in asymmetrically structured geometries to set them into motion. We illustrate this idea with several experiments in which fluctuations in the drop shape and wetting properties are triggered by different physical means either by acting transversally to the motion with an on/off electric field, or along this motion with a low-frequency electric field of zero mean value or by vibrating the substrate. These findings can find natural applications in the field of integrated analysis systems.