Directional droplet transport behavior on gradient wettability wedge track with extreme wettability contrast

Abstract

To enhance transport capacity of open-surfaces, a gradient wettability wedge track laid on superhydrophobic background (wedge track No. 2) was fabricated by using masking tape and alkaline-assisted oxidation. The effects of gradient wettability and extreme wettability contrast are emphasized and investigated. The maximum instant velocity of a 10 μL droplet on track No. 2 is ∼ 883.53 mm/s with final transport displacement x = 46.79 mm, which was 64.15 % faster and 11.67 % farther than that on a superhydrophilic wedge track (wedge track No. 1) respectively. Oscillation happens at the wide end of wedge tracks when kinetic energy remains. Oscillation time on wedge track No. 2 is longer, which means gradient wettability can provide an extra driving force. This novel wedge track highlights the necessity of both gradient wettability and extreme wettability contrast and will have broad prospects in directional transport on open-surfaces, biological research, energy conversion and microfluidic mixers.