Metamaterial Architectures for Programmable Droplet Motion

This grant supports fundamental research for controlling the motion of liquid droplets on solid surfaces. The problem of droplet control is relevant for numerous industrial applications, from self-drying surfaces and heat transfer via droplet condensation to water harvesting and biomedical analysis. Therefore, research in this direction can lead to discoveries with vast societal impact. Most strategies for droplet motion control involve doctoring, either chemically or mechanically, the surface that is in direct contact with the fluid, thus altering irreversibly its default properties. This project promotes a different paradigm that exploits the interaction between moving droplets and vibrating surfaces. The project idea revolves around the use of emerging notions of engineering metamaterials to design surfaces with spatially programmable vibrational response that allows to alter the available landscape of droplet motion on demand. In addition, the ability to couple metamaterials with fluidic motion will be exploited to design intuitive demonstration devices that allow visualizing, with the naked eye, complex elastic wave phenomena, making them ideal for scientific outreach and for teaching advanced engineering concepts. The technical objective of the project is to design vibrating metamaterials for programming the locomotion of liquid droplets on solid surfaces. Specifically, this research aims to realize control strategies that allow deep manipulation of the fluid motion when the vibrating state is on, while preserving the default system conditions in the off configuration. With resonant metamaterials, it is possible to modulate the vibrational response available in different regions of a surface. Through a proper interplay of structural design and excitation tuning, one can selectively program the onset of droplet depinning in select regions, thus spatially engineering the available landscape of droplet motion according to a virtually endless array of spatial patterns. Such design flexibility can be leveraged to program a variety of complex logic scenarios for droplet motion, such as clustering and segregation based on droplet size. The investigation is supported by a series of table-top experiments via laser vibrometry and high-speed imaging. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.