Achieving reversible superhydrophobic-superhydrophilic switching of lignocellulosic paper surface with modified Nano-TiO2 coating

Environmentally friendly flexible materials with functionalities such as reversibly tunable wettability have become much sought after because of their great potential for biological, chemical and electronic applications. We prepared a flexible superhydrophobic material by coating the hydrophobic nano-TiO2 particles on lignocellulosic paper. The coated paper surfaces exhibited a reversible switching between superhydrophobicity and superhydrophilicity through UV irradiation and heating, respectively. After the UV irradiation treatment for about 100 min, the wettability of the coated paper is switched from superhydrophobicity to superhydrophilicity. After the coated paper with superhydrophilicity is heated for 25 h, the water contact angle (WCA) recovers to the original superhydrophobic state. Compared to the literatures, the switching time between two kinds of superwettability is significantly reduced. SEM images and XPS spectra indicate that the change in chemical composition of the coated paper surface is responsible for the reversible switching of wettability. The coated paper developed in this study is an attractive smart material with reversibly switchable wettability which has significant potential application in many fields which require tunable wettability.