Controlled Trapping and Release of Droplets through Dynamically Reconfigurable Surfaces

Most previous publications attempt to control the trapping and release of liquid droplets on a surface through tuning the surface energy of the substrate, for example, by photoisomerization. In this work, the energy barrier between the trapped and released state is raised or lowered by controlling the droplet contact area. This is achieved by designing a dynamically reconfigurable surface where an external stimulus is used to change the surface topography. The system consists of two microstructured components, one being ridges separated by microtrenches and the other a perforated membrane. They are aligned in such a way that the ridges can be raised or lowered through the perforations with the help of a piezo drive. This way the topography changes from surfaces consisting of hills to one consisting of holes - and back again. This dynamic surface reconfiguration changes the contact area such that drops resting or rolling on them become captured or released on demand. Dynamic changes in the free energy of a water droplet resting on a surface are achieved by changing the contact area between droplet and surface. To this end, dynamically reconfigurable surfaces are described where ridges are raised and lowered through a perforated membrane using a piezo drive, thus changing the surface topography and allowing on-demand capture and release of the drop. image