Superhydrophobic to superhydrophilic wetting transition with programmable ion-pairing interaction

The fabrication of a smart surface with a wettability that can be reversibly programmed between superhydrophobicity and supersydrophilicity by selection of the proper counterion was reported. The gold micro/nanotextured substrate was characterized with field-emission scanning electron microscopy (FESEM) and confocal laser scanning microscopy (CLSM). The magnified image shows that the gold microstructure is composed of various of proturberances with diameter of approximately 50 nm. The water contact angle (CA) of the smooth surface is 35°∓1°, which results from the coordination of QA ⁺ and Cl^- as the counterion. The results also show that the switching between the superhydrophobic and superhydrophilic wetting states can be achieved by proper ion-pairing exchange on the textured surface with the QA⁺-bearing PMETAC brushes.