Tunability of the Adhesion of Water Drops on a Superhydrophobic Paper Surface via Selective Plasma Etching

We report the fabrication of a sticky superhydrophobic paper surface with extremely high contact angle hysteresis: advancing contact angle similar to 150 degrees (superhydrophobic) and receding contact angle similar to 10 degrees (superhydrophilic). In addition, we report the controlled tunability of the contact angle hysteresis from 149.8 +/- 5.8 degrees to 3.5 +/- 1.1 degrees, while maintaining superhydrophobicity, as defined through an advancing contact angle above 150 degrees. The hysteresis was tuned through the controlled fabrication of nano-scale features on the paper fibers via selective plasma etching. The variations in contact angle hysteresis are attributed to a transition of the liquid-surface interaction from a Wenzel state to a Cassie state on the nano-scale, while maintaining a Cassie state on the micro-scale. Superhydrophobic cellulosic surfaces with tunable stickiness or adhesion have potential applications in the control of aqueous drop mobility and the transfer of drops on inexpensive, renewable substrates. (C) Koninklijke Brill NV, Leiden, 2009