Reversible Electrowetting on Superhydrophobic Silicon Nanowires

This paper reports for the first time on the reversible electrowetting of liquid droplets in air and oil environments on superhydrophobic silicon nanowires (SiNWs). The silicon nanowires were grown on Si/SiO2 substrates using the vapor−liquid−solid (VLS) mechanism, electrically insulated using 300 nm SiO2, and hydrophobized by coating with a fluoropolymer C4F8. The resulting surfaces displayed liquid contact angle (θ) around 160° for a saline solution (100 mM KCl) in air with almost no hysteresis. Electrowetting induced a maximum reversible decrease of the contact angle of 23° at 150 VTRMS in air.