Low-dissipation capillary switches at small scales

A system of two coupled capillary surfaces is made to switch between its stable states via mechanical and electrochemical disturbances. The bistable switch is experimentally demonstrated using water droplets, where the mechanical activation or “toggle” is achieved by a momentary air-pressure change. Requirements for capillary switches to avoid viscous dissipation are described and strategies for utilizing capillary switches for transporting other liquids or solids are discussed. Addressability of individual switches is achieved using electrochemical activation via a redox surfactant, where surface tension of one element of the switch is changed relative to the other.