In situ reversible control between sliding and pinning for diverse liquids under ultra-low voltage

Thermally responsive paraffin-infused slippery surfaces have demonstrated intriguing performance in manipulating the behaviors of versatile droplets. However, present methods have been limited to ex situ rigid heat sources with a high voltage of 220 V or certain specific photothermal materials, which greatly hinders its practical applications. To solve this problem, an intelligent droplet motion control actuator (DMCA) composed of paraffin wax, hydrophobic micropillar-arrayed ZnO film, and a flexible transparent silver nanowire heater (SNWH) is reported in this work. Due to the good portability of DMCA, in situ switchable wettability for several liquid droplets with different surface tensions can be achieved by simply loading and unloading Joule heat at an ultra-low voltage (12 V). The relationship among sliding velocity and droplet volume and inclined angles was quantitatively investigated. By virtue of the flexible and mechanical endurance, this smart DMCA is dramatically functional for droplet motion manipulation (e.g., reversible control between sliding and pinning) on complex 3D surfaces. Significantly, an impressive self-healing ability within 22 s is also demonstrated through the in situ application of Joule heat on the scratched DMCA, which renders its practical usability in various harsh conditions. This work provides insights for designing intelligent, flexible, and portable actuators dealing with the challenges of smart temperature-responsive surfaces.