Ultralow-Voltage-Driven Smart Control of Diverse Drop’s Anisotropic Sliding by in Situ Switching Joule Heat on Paraffin-Infused Microgrooved Slippery Surface

Stimuli-responsive anisotropic slippery surfaces (ASSs) have demonstrated intriguing performance in manipulating the behaviors of some liquids. However, most present methods have been limited to conductive droplets, certain specific conductive platforms, and higher manipulation temperature that greatly hinder its practical applications. Here, an electric-responsive paraffin-infused ASS (ER-PIASS) composed of paraffin, microgrooved PDMS, and flexible embedded silver nanowire heater is reported. Owing to the fast electric-response of ER-PIASS, smart control between anisotropic sliding and pinning for diverse liquids can be realized by remotely loading and discharging electric-stimuli. The underlying mechanism is that the generated Joule heat melts the solidified paraffin to slide a pinning droplet once an electric-trigger is loaded due to the formation of a slippery air/liquid/liquid/solid system. Once the voltage is discharged, the liquefied paraffin would rapidly solidify to stick to a slipping droplet because of the recovery of a frictional air/liquid/solid system. Additionally, the effect of the groove’s height (h), spacing between two adjacent grooves (d), and thickness of the paraffin layer on the anisotropic degree was quantitatively studied and an optimized value of 75° is thus harvested. Through tuning the recipe of the hybrid lubricant, the responsive voltage and temperature for ER-PIASS can be dramatically decreased to ultralow figures of 2.0 V and 34.2 °C. By taking advantage of this ultralow-voltage-driven biocompatible ER-PIASS, we enable the anisotropic smart control of cell culture medium and yeast droplets for their directional coalesce, growth, and fission. We believe that such stimuli-responsive surfaces will be promising candidates for manipulating droplets’ directional sliding behavior and further bloom the studies of flexible microfluidics devices.