Ultrasound-Enabled Spatial Multi-Droplet Manipulation on Slippery Surfaces

Controllable droplet manipulation plays a crucial role
in microfluidics,
biomedicine, and energy harvesting. Despite significant advances,
synchronously controlling multiple droplets on a monolayer surface
or spatially dislocated surfaces remains challenging. Here, a droplet
ultrasonic bowl (DUB) is developed to enable the multi-droplet manipulation
on a spatial slippery liquid-infused surface. By leveraging multiple
twin-trap ultrasonic fields and dynamically modulating their quantity
and positions, the DUB achieves programmable manipulation of single
and multiple droplets on a monolayer surface such as single droplet
precise movement, synchronous position exchange of two droplets, and
simultaneous transport of three droplets. Furthermore, the spatial
reach of the twin trap allows for the synchronized manipulation of
multiple droplets on double-layer surfaces as well as steady control
of pendant droplets. These capabilities demonstrate the applications
in intelligent droplet circuits, spatial chemical reactions, and obstacle
avoidance, offering a promising strategy for contactless droplet manipulation.