Heterogeneous Integration of Magneto-Responsive Shape Memory Polymers with Superhydrophobic Black Silicon for Programmable Droplet Manipulation Platform

Reconfigurable droplet manipulation remains challenging because most active platforms require continuously applied external stimuli to maintain their functional geometries, limiting the energy efficiency, operational stability, and structural tunability. Here, we introduce reconfigurable heterostructures that involve magneto-responsive shape memory polymer ridges and superhydrophobic black silicon strips to construct a programmable droplet manipulation platform. Once deformed under magnetic and thermal stimuli, the heterostructures are programmed to form a superhydrophobic ratchet surface semi-permanently, which may be further reprogrammable. This ratchet-shaped platform can induce a Laplace pressure gradient in droplets dispensed on top of it, enabling programmable droplet propulsion. A magneto-mechanical model is developed to guide the controlled programming of the ratchet surface geometries. Through sequential programming enabled by thermally assisted magneto-mechanical deformation, the heterostructures were shaped into diverse ratchet geometries. These programmed geometries enabled diverse droplet manipulation modes such as large-area unidirectional transport, trapping, and merging. Moreover, this semi-permanent, shape-fixable platform allows for investigating the interaction between Laplace pressure gradient and gravitation regarding the droplet motion. Lastly, experimental results reveal impact-type-dependent jump-off behaviors in terms of small droplet impact dynamics. These results and findings propose an extension of using shape memory polymer-based heterostructures to create a tunable, yet semi-permanent shape-fixable droplet manipulation platform.