Tunable wettability and rewritable wettability gradient from superhydrophilicity to superhydrophobicity.

A simple method for the fabrication of tunable surfaces with wettability that can be manipulated rapidly and reversibly from superhydrophilicity to superhydrophobicity is reported. A polyelectrolyte multilayer (PEM) was deposited on a rough substrate, and via ion exchange of the counterion in the PEM, the water contact angle of the surface was switched between <5 degrees and 164 degrees. By controlling the ion-exchange kinetics, on the same surface, completely erasable, rewritable gradient wettability from superhydrophilicity to superhydrophobicity was conveniently achieved.