Programmable Droplet Manipulation and Wetting with Soft Magnetic Carpets

The ability to regulate interfacial and wetting properties is highly demanded in anti-icing, anti-biofouling, medical and energy applications. Recent work on liquid-infused systems achieved switching wetting properties, that allow to turn between slip and pin states. However, patterning the wetting of surfaces in a dynamic fashion still remains a challenge. In this work, we use programmable wetting to activate and propel droplets over large distances. We achieve this with liquid-infused soft magnetic carpets (SMC) that consists of pillars that are responsive to external magnetic stimuli. Liquid infused SMCs which are sticky for a water droplet become slippery upon application of a magnetic field. Application of a patterned magnetic field results a patterned wetting on the SMC. A travelling magnetic field wave translates the patterned wetting on the substrate, which allows droplet manipulation. The droplet speed increases with an increased contact angle or with the droplet size, which offers a potential method to sort and separate droplets with respect to their contact angle or size. Furthermore, programmable control of the droplet allows us conducting reactions by combining droplets loaded with reagents. Such ability of small-scale reactions on SMCs has the potential to be used for automated analytical testing, diagnostics and screening with a potential to reduce the chemical waste.